ford v6 and v8 spec. doc. for simulation
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CRANFIELD UNIVERSITY
MATTHIEU GRIFFON
THE DEVELOPMENT OF SPECIFICATION DOCUMENT FOR SIMULATION OF FORD V6 AND V8 MACHINING LINES
SCHOOL OF INDUSTRIAL AND MANUFACTURING SCIENCE
MSC THESIS
CRANFIELD UNIVERSITY
SCHOOL OF INDUSTRIAL AND MANUFACTURING SCIENCE
MSC THESIS
ACADEMIC YEAR 2005 – 2006
MATTHIEU GRIFFON
THE DEVELOPMENT OF SPECIFICATION DOCUMENT FOR SIMULATION OF FORD V6 AND V8 MACHINING LINES
SUPERVISOR: DR BENNY TJAHJONO
<SEPTEMBER 2006>
This Thesis is submitted in partial fulfilment of the requirements for the Degree of Master of Science
© Cranfield University 2006. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.
ABSTRACT
Ford Motor Company is a worldwide group specialised in the car industry. The globalisation and the customer satisfaction increase the competition. To face this competition Ford has to continuously improve their manufacturing facilities all around the world. Since the 80s, Ford has applied simulation tools to support them in this mission.
Ford is well established in the UK, the Dunton Technical Centre and Dagenham plant are the largest car centres in the UK. At Dagenham, Ford provides V6 and V8 diesel engines. This requires three machining lines to produce essential component for these engines. Ford wants to improve the simulation tools for these machining lines.
The first requirement is to develop some specification of the machining lines for the simulation purpose. The aim of this thesis is to help Ford improve the simulation for the V6 and V8 machining lines through the development of the Specification Document.
The development of this document required three main stages: the real system analysis, the validation of the findings by Ford specialist, and the setting of the document. The fourth stage is the first utilisation of the document to compare the real system with the simulation models. This analysis revealed that the simulation is closed to the real system but rooms of improvement have been identified.
This document proposes a standard approach to specify the real system for simulation purpose and addresses specialist and non-specialist of the simulation. It is an opportunity to improve the simulation tool and it promotes simulation utilisation bringing it more accessible. However the developed document is the first attempt and improvement could be identified using it. Recommended works are presented to progress in the development of this document. Finally this document is a chance to help the continuous improvement of the simulation tools at Ford.
ACKNOWLEDGEMENTS
First of all I would like to thank the main Ford sponsor John Ladbrook. I thank Phill Dewson for the shared work then colleagues and family who supported me to review this thesis. Finally I thank my supervisor Dr Benny Tjahjono for his substantial help.
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Thesis Content
1 Introduction ..................................................................................................1 1.1 Overview of the Industrial Problem .......................................................1 1.2 Summary of Thesis Aim, Objectives .....................................................1 1.3 Thesis Structure ....................................................................................2
2 Industrial Context and Problem Statement...................................................4 2.1 Ford Motor Company ............................................................................4
2.1.1 The Main Products and Markets Pressures ...................................4 2.1.2 The Manufacturing Facilities ..........................................................4
2.2 Simulation at Ford .................................................................................5 2.2.1 FIRST ............................................................................................6 2.2.2 Simulation Issues...........................................................................7
2.3 Summary of Industrial Context and the Problem Statement ...............12 3 Literature Review .......................................................................................13
3.1 System Specifications .........................................................................13 3.2 Data/logic Collection and Communication...........................................14 3.3 Simulation Validation...........................................................................17 3.4 Simulation Document ..........................................................................18
3.4.1 Documentation Content ...............................................................18 3.4.2 Documentation Support ...............................................................21
3.5 Elements Logic ...................................................................................22 3.6 Summary of this Chapter ....................................................................23
4 Research Programme ................................................................................26 4.1 Problems Identification........................................................................26 4.2 Aim and Objectives .............................................................................26 4.3 Methodology .......................................................................................27
5 Stage 1: Understand and Represent the Logic of the Machining Lines......29 5.1 Dagenham Lion V6 and V8 Machining lines .......................................29 5.2 Logic Representation ..........................................................................31
5.2.1 Real Equipment List.....................................................................31 5.2.2 Flow diagram ...............................................................................33 5.2.3 Represent the Logic Diagram ......................................................33 5.2.4 Flow Diagram Example................................................................35
5.3 Common Flow Diagram Establishment ...............................................37 5.3.1 Common Diagram Construction...................................................38 5.3.2 Equipment Interactions ................................................................43 5.3.3 Equipment Hierarchy ...................................................................45
5.4 Issues..................................................................................................47 5.5 Summary of the Logic Understanding Stage.......................................47
6 Stage 2: Validate the Logic and its Representation....................................48 6.1 Validation of Logic by Ford Specialist .................................................48
6.1.1 Control Engineering .....................................................................48 6.1.2 Simulation Engineering ................................................................51
6.2 Selection of the level of logic...............................................................53 6.2.1 Logic: Level 1 and Level 2 ...........................................................53 6.2.2 Logic: Level 0...............................................................................53
6.3 Selection of Boundaries ......................................................................54
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6.4 Finalisation of the Representation.......................................................55 7 Stage 3: Specification Document Development .........................................56
7.1 General Introduction of the Specification Document ...........................56 7.1.1 Assumptions ................................................................................57 7.1.2 Flow Diagram...............................................................................57 7.1.3 Standard Approach ......................................................................58
7.2 Example of Turntable-Elevator-Lowerator...........................................58 7.2.1 Element Definition........................................................................58 7.2.2 Real System Logic Interpretation .................................................60
7.3 Specification Document Framework....................................................61 7.3.1 Actual Specification Document Framework .................................61 7.3.2 Specification Document Framework Idea ....................................61
7.4 Summary of the Specification Document ............................................63 7.4.1 Summary of Work ........................................................................63 7.4.2 Difficulties Encountered ...............................................................63 7.4.3 Limitations of the Specification Document ...................................64
8 Stage 4: Identify Gaps between the Machining Lines and Simulation........65 8.1 Identified Gaps and Similarities for each Element...............................65 8.2 Special Cases .....................................................................................66 8.3 Summary of Identifying Gaps between the Machining Lines and Simulation......................................................................................................68
9 Key Findings and Discussion .....................................................................70 9.1 Key Findings and Work Review ..........................................................70
9.1.1 Problem Analysis .........................................................................70 9.1.2 Research .....................................................................................70 9.1.3 Understand and Represent the Logic of the Machining Lines......71 9.1.4 Validate the Logic and its Representation....................................72 9.1.5 Specification Documentation Development .................................73 9.1.6 Simulation ....................................................................................74 9.1.7 Identify Gaps between the Machining Lines and Simulation........74
9.2 Discussion...........................................................................................75 9.2.1 Different Interpretation .................................................................75 9.2.2 Gaps between Real System and Simulation Logic ......................77 9.2.3 Non-specialist User......................................................................79 9.2.4 Specification Document Benefits Summary .................................80
9.3 Specification Document Limits ............................................................81 9.4 Specification Document Summary Analysis........................................82
10 Conclusions................................................................................................83 10.1 Summary of Key Findings ...................................................................83
10.1.1 Understand and Represent the Logic of the Machining Lines......83 10.1.2 Validate the Logic and its Representation....................................83 10.1.3 Development of the Specification Document ...............................84 10.1.4 Identify gaps between the machining lines and simulation ..........84
10.2 Benefits ...............................................................................................84 10.3 Limitations...........................................................................................85 10.4 Recommended Future Work ...............................................................85
References ........................................................................................................87 Appendix ...........................................................................................................89
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Appendix A ....................................................................................................89 Appendix B ....................................................................................................92 Appendix C ..................................................................................................102 Appendix D ..................................................................................................104
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List of Figures
Figure 1: Ford Simulation Tools ......................................................................... 6 Figure 2: Simulation Gaps Reduction................................................................. 8 Figure 3: Raw Simulation Process ..................................................................... 8 Figure 4: Simulation Support .............................................................................. 9 Figure 5: Simulation Users ............................................................................... 10 Figure 6: Real System Interpretation Issue ...................................................... 11 Figure 7: Typical Stage of a Simulation Project................................................ 14 Figure 8: 7 Steps of the Law Process............................................................... 16 Figure 9: Nordgren Simulation Stages ............................................................. 19 Figure 10: Simulation Project Requirement and Real System Specifications... 21 Figure 11: Flow Chart Basics ........................................................................... 22 Figure 12: Specification Documentation Scope................................................ 24 Figure 13: V8 and V6 Machined Components.................................................. 29 Figure 14: Platen .............................................................................................. 30 Figure 15: Lion Head machining Line............................................................... 31 Figure 16: Microsoft Visio Flow Diagram Elements .......................................... 33 Figure 17: Turntable Diagram........................................................................... 36 Figure 18: Turntable with Signals ..................................................................... 44 Figure 19: Equipment Hierarchy....................................................................... 46 Figure 20: Control vs. Simulation Logic View Point .......................................... 50 Figure 21: Element Description ........................................................................ 51 Figure 22: Turntable Boundaries ...................................................................... 52 Figure 23: Level of Logic .................................................................................. 53 Figure 24: Simulation Element Boundaries ...................................................... 54 Figure 25: Real Element “Spontaneous” Boundaries ....................................... 54 Figure 26: Simulation Boundaries .................................................................... 55 Figure 27: Element and Flow Diagram Colour Coding ..................................... 57 Figure 28: Turntable Elevator Lowerator Drawings .......................................... 59 Figure 29: Specification Document Framework Idea........................................ 62 Figure 30: CNC Cell of the Head (Left) and CNC Cell of the Crankshaft (Right)
Machining lines ......................................................................................... 66 Figure 31: Diagram Drafts (First and Second).................................................. 71 Figure 32: Diagram Drafts (First, Second and Final) ........................................ 73 Figure 33: Different Interpretation Gaps ........................................................... 76 Figure 34: Gaps Reduction............................................................................... 78 Figure 35: Future Trend of the Simulation Utilisation ....................................... 79 Figure 36: SWOT Analysis ............................................................................... 82
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List of Tables
Table 1: Nordgren Data Collection ................................................................... 20 Table 2: Nordgren Documentation ................................................................... 20 Table 3: Objectives and Methods Summary..................................................... 28 Table 4: Diagram Structure Advantages & Disadvantages .............................. 34 Table 5: Turntable Example ............................................................................. 38 Table 6: First Draft Diagram for Common Element (Turntable) ........................ 40 Table 7: First Draft Diagram for Common Element (Turntable 1) Level 2 ........ 41 Table 8: First Draft Diagram for Common Element (Turntable 2) Level 2 ........ 42 Table 9: Flow Diagram for Turntable- Elevator- Lowerator............................... 60 Table 10: Real System and Simulation Logic ................................................... 65 Table 11: Real System and Simulation Logic Gap Observation for Gantry ...... 67 Table 12: Gap and Similarities Summary ......................................................... 68
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Glossary
FIRST Fast Interactive Replacement Simulation Tool FAST Ford Assembly Simulation Tools WITNESS Simulation software developed by Lanner Group Crankshaft Component of an engine Cylinder Block Component of an engine Cylinder Head Component of an engine Machining lines
Production lines which machine engine components
Specification Document
The document which compiles the specification of the real production system for the simulation purpose.
Piece of equipment
Component of the line such as machine, conveyor or turntable.
Introduction
1
1 INTRODUCTION
This first chapter presents briefly the industrial problem, the aim and the objectives of the thesis and an overview of the thesis structure.
1.1 Overview of the Industrial Problem
Ford Motor Company is a global car manufacturer; Ford manufactures cars and car components such as engines. Globalisation and customer level satisfaction increase the competition in the car industry. Consequently Ford knows market pressures and in order to stay competitive has to improve continuously its manufacturing facilities. The Ford Power Train department is in charge of the manufacturing facilities management. Since the 80s, Power Train engineers have applied simulation tool to support them in this mission.
Ford is well established in the UK, Dunton Technical Centre is the largest research centre in the UK, Dagenham factory is the biggest car manufacturing centre in the UK. Dagenham plant has several activities such as the V6 and V8 components machining lines. These components are essential to assemble V6 and V8 diesel engines; these engines are used by more than 3 brands. Production of these components requires three different machining lines.
For many years, Ford has applied simulation tools to continuously improve their manufacturing facilities. Simulation is a key tool to support decision making.
1.2 Summary of Thesis Aim, Objectives
Ford needs to improve the simulation tool for the Lion machining lines. Ford has identified room of improvement and wants to develop a research to explore the opportunities. The first requirement of Ford is the development of the specification of the V6 and V8 machining lines for the simulation purpose.
According to this context, the aim of this thesis is to help Ford improve the simulation model for the Lion Machining lines through the development of a Specification Document. This document is the specification of the real system (Lion machining lines) for the simulation.
After the problem has been identified, it appears that the body of the Specification Document will be based on the real system logic communication. The Specification Document has to communicate the logic of the different component of the machining lines. The logic describes what happens in the real lines, what the current scenario is for each component.
Introduction
2
In order to achieve the Specification Document development, the following objectives are identified:
1. Understand and represent the logic of the Machining lines
2. Validate the logic and its representation
3. Develop the Specification Documentation
4. Identify gaps between the machining lines and simulation models
These four stages are presented in this thesis; each stage corresponds to one chapter.
1.3 Thesis Structure
The structure of the Thesis is decomposed in ten chapters:
Following this chapter, chapter 2 presents the industrial context and the problem statement. A deep analysis of the problem is presented in this chapter.
Chapter 3 presents the literature review. Having identified and analysed the industrial problem, a literature review needs to be done to find out the issues of the related problem. This research enables to have a specialised point of view on the problem.
Chapter 4 presents the aim of the thesis, its objectives and the deliverable. The methodology is proposed including four stages.
The four following chapters are related to each stage of the development:
Chapter 5 is the real system analysis. The stage 1 allows having a deep understanding of the machining lines logic. Another important part of this stage is to obtain the first attempt of the logic representation. This stage enables to identify issues which need validations from Ford specialists.
Chapter 6 is the logic validation. The stage 2 is focused on two main points. First, the logic of the real system must be validated by specialists. Secondly, the representation of the validated logic needs to be approved. This stage finalises the approach to represent the logic of the three machining lines.
Chapter 7 is the development of the Specification Document. This third stage presents the development of the deliverable for Ford. The deliverable itself is not directly included but remarks and analysis on the development of this document are presented.
Introduction
3
Chapter 8 is the first utilisation of the Specification Document. Comparing this document with the simulation logic, gaps and similarities between real system and simulation logic are identified and analysed. This is the value added for Ford since this stage reports the possible improvement for the simulation models. This is directly related with the aim of the thesis which is to help Ford improve the simulation. The gaps and similarities are documented and include in the deliverable for Ford.
The four stages are presented in the four precedent chapters, analysis of the findings is proposed.
Chapter 9 presents the key findings of the Thesis. Going through the four stages, findings are presented and commented. This Chapter discusses the work realised in the thesis. The benefits and the limits are presented and commented.
Finally Chapter 10 concludes the thesis. This chapter gives an overview of the work realised and summarises the findings. The benefits and the limits of the results are summarised, the last section proposes future work.
Industrial Context and Problem Statement
4
2 INDUSTRIAL CONTEXT AND PROBLEM STATEMENT
This first chapter sets out the industrial context and the industrial problem. It goes through a large picture until a focus problem which is the subject of this Thesis. The purpose is to present why Ford sponsors this thesis. This helps understand the subject and its impact.
2.1 Ford Motor Company
Ford Motor Company was created in 1903 by Henry Ford and eleven associates. Today, Ford Motor Company is one of the largest automotive corporations and counts a range of brand such as: Ford, Lincoln, Mercury, Jaguar, Land Rover, Aston Martin, Mazda and Volvo.
The Ford manufacturing techniques revolutionised industry world and are still considered as an essential reference today. Ford was the pioneer of the mass production line firstly implemented in Highland Park plant (Michigan, US) in 1913.
2.1.1 The Main Products and Market Pressures
Ford is a car manufacturer and more specially engines manufacturer such as V8 and V6 engines. Ford Motor Company has counted a total vehicle sale of 6,818,000 units in 2005, Ford (2006).
Automotive market encounters more and more pressure. Globalisation has introduced low wage countries in the competition. The customer level of satisfaction also contributes to raise the competition. For these reasons, Ford must be more and more efficient to design, develop and build cars and car components (e.g. engines). To face this challenge Ford concentrates on the manufacturing issues. Ford engineers organise facilities and production lines in the most efficient way. Actually, an efficient production system contributes to compete efficiently. The production systems impact directly on costs, quality and delivery which are the basics to satisfy the customer demand.
2.1.2 The Manufacturing Facilities
Ford has 44 manufactures around the world and is well established in the UK. Ford is implemented in Dunton (European Engineering Research Centre) and in Dagenham (Manufacturing facility).
Dunton Technical Centre (Essex) is the largest automotive research and development centre in the UK. Dunton is in charge to organise the Ford facilities in Europe and counts 3,000 employees.
Industrial Context and Problem Statement
5
Dagenham manufacturing site is located in Essex UK; this plant is the biggest Ford plant in the UK. Since 1931, Dagenham has produced ranges of cars and car equipments, today Dagenham provides diesel engines. Several facilities support this production such as assembly lines and machining lines. Machining lines provide engines components: cylinder block, cylinder head, camshaft and crankshaft. Assembly lines supply Puma engines (4 cylinders in lines engine), Lion engines (6 or 8 cylinders in V engine) and others.
The Power Train engineers working at Dunton are responsible of Dagenham plant. In order to organise, develop and improve these facilities and the forty-three other manufactures around the world, Ford applied for the simulation tools.
2.2 Simulation at Ford
In manufacturing, simulation is a tool which could support decision making and plan production system behaviour. Simulation is a computer based tool and according to Robinson (1994) simulation has many benefits such as:
• “Risk reduction • Faster plant changes • Capital cost reduction”
Ford has to face the competitiveness of the automobile market, applying the simulation tools Ford reinforce the effectiveness of the manufacturing facilities management. The aim of the simulation is to answer to the “what if” question. Simulation supports the continuous improvement of the facilities.
Since the mid 1980s, Ford has applied computer simulation tools to design and operate manufacturing facilities (Ladbrook and Januszack, 2001). The first simulation package used at Ford was SEEWHY, a simulation package offering visual interaction. Nowadays, Ford uses WITNESS which was developed from SEEWHY (Gilman and Watremez, 1986). Considerable improvements have been performed by Ford engineers in term of simulation since the 1980s. WITNESS is provided by Lanner Group.
Power Train Operation engineers at Ford are responsible for the planning and the establishment of the forty-four manufactures facilities around the world (Ladbrook and Januszack, 2001). Simulation has supported this department to make decisions on this mission.
WITNESS is a powerful software package which helps the Ford Engineer predict, discuss and develop manufacturing facilities (Ladbrook and Januszack, 2001). This tool helps:
Industrial Context and Problem Statement
6
• Predict the manufacturing performance • Identify the impact of adjusting or changing parameters in the
manufacture • Understand the manufacture capacities • Support the decision making for investments or modifications
However, the complexity of certain simulation model makes that only simulation specialists can use it. For this reason, Ford engineers had developed an Excel interface called FIRST.
2.2.1 FIRST
Ford had internally developed simulation tools to ease the simulation model building and utilisation. In the case of the engine machining lines simulation, Ford has developed FIRST (Fast Interactive Replacement Simulation Tool). FIRST is an interface which is supported by Excel/Visual Basic language and had been developed in 2000 (Ladbrook and Januszack, 2001). The spreadsheet enables the users to build a simulation model, make modifications, run the simulation and collect the results. This spreadsheet is linked with WITNESS via the Visual Basic support. FIRST was created by Ford simulation expert and a Lanner Consultant (Lanner is the provider of WITNESS). Typically, the user builds the model via FIRST, launches the simulation that runs on WITNESS and collects the results through FIRST. Basically no specific knowledge in simulation programming is required to use this tool. Figure 1 gives a picture of the simulation tools.
Figure 1: Ford Simulation Tools
FIRST interface Excel + Visual basic support
Simulation software WITNESS package
Users Simulation engineers, specialists
and non specialists
Users Simulation engineers
Simulation software WITNESS package
In the past Today
Direct contact user WITNESS
No direct contact user WITNESS
Industrial Context and Problem Statement
7
FIRST enables non specialist to use the simulation tools to model complex systems (Ladbrook and Winnell 2004). It was the first purpose to create such interface. Improvements and guideline have been created to help FIRST users since the original version was created.
The simulation models are built around what Ford engineers call elements. A dozen of elements are used; via FIRST the user can modify many parameters of these elements and organise them in order to build the model. These elements are some part of equipment of the machining lines such as conveyor, turntable, manual or machining operation, etc. In simulation language these elements are called entities; an entity is defined as a component of the system (Carrie, 1988).
2.2.2 Simulation Issues
Ford simulation specialists have identified some gaps between the actual simulation model of the machining lines and the real system. As simulation is a key tool for Ford, these gaps must be understood, identified and documented. According to simulation experts, the real logic philosophy of the elements is not represented by the simulation.
Simulation Gaps
As explained above the gaps between simulation and reality are the initial drivers to sponsor the research of this thesis. Ford wants to reduce the gaps noticed by the engineers. Specialists speak in term of “gap between the real world engineering understanding and the simulation”.
Gaps are the differences between the real system and the simulation. Gaps reduce dramatically the simulation efficiency and decrease the level of confidence of simulation user. That is the reason why Ford wants to develop a support to understand the real system. This support will help the simulation user to localise and reduce gaps between the model and the real system as shows Figure 2.
Industrial Context and Problem Statement
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Figure 2: Simulation Gaps Reduction
Ford Simulation Process
The process of building a simulation model is briefly presented here by Figure 3.
Figure 3: Simulation Process
Four main stages are presented, the first three stages are realised by the simulation builder (Collect data/information, build and validate the simulation model). The last one is the utilisation of the simulation; it is done by the simulation user. Two main roles are presented here: builder and user. These two roles could be played by the same person.
The builder follows a process to collect data and information. Figure 4 presents the different sources available for the model builder.
Validate the simulation model
Build the simulation model
Collect data and
informations
Apply simulation model to predict, organise, and improve the system
(use simulation)
FIRST and FAST interface s Excel + Visual basic support
Simulation software WITNESS package
Users Simulation engineers, specialists
and non-specialists
Real system Ford manufactures
Real system understanding
support
Current Ford methods
Gaps
Makes the real system closer to the builder
Gaps
Industrial Context and Problem Statement
9
Figure 4: Simulation Support
Few explanations are required to understand this figure:
• Layout of the production line: this is the “map” of the production line (the real system).
• Operation standard is the list of the time necessary to realise each step of the process. This is called the cycle time.
• Quality data are from the Ford quality department who collects the average time of breakdown, time between two failures and time required to fix the problem. These data are required for each operation.
Figure 4 presents where information is collected. In blue appears the source of information and in green appears the information nature. This shows clearly that nothing is really dedicated to the logic explanation. Actually, the layout is supposed to give enough information to understand the logic (what the real system behaviour is). Interviews with simulation model builders confirm that visits must be done on the plant to examine the system running and understand it. This revealed that a support to explain the logic is useful.
Ford Simulation Builders and Users
As presented above, builders who build the model and users who use the simulation model to predict the system behaviour have a link with the simulation. Three categories of people are noticed:
• Specialists
Today, few simulation specialists have the knowledge about the real logic of the system and the simulation logic. The document developed in this thesis could be viewed as knowledge management. One opportunity is to sustain the actual simulation specialist knowledge and/or enable specialists to delegate simulation utilisation for certain project.
Layout of the production line
Operation standard
Distance
Sequence
Logic
Cycle Time
Quality data
Breakdown time
Mean time between failures
Other data
Simulation user
Industrial Context and Problem Statement
10
• Non-specialists
Ford attempts to improve the simulation utilisation by developing friendly interface for non-specialists. However, if the understanding of the real system is a barrier to use simulation, the number of user will not be as large as Ford expected. To avoid the real system logic understanding limiting the number of user, Ford wants to develop a support to ease this understanding. Such support could optimise the utilisation of the Ford simulation tools.
Figure 5 illustrates the possible extension of simulation users through a right real system understanding support. It is also notable that the support will help the “actual users”.
Figure 5: Simulation Users
• Current/future users
Today different people use simulation at Ford; their point of view of the real system and the simulation are different. Simulation is a conceptual approach to model the reality, interpretation is required to build a model. Problem of different interpretations of the system rises to build the model. Basically when two people see a machine running, they could interpret the machine behaviour (machine logic) differently. From that, if they want to model it, two simulation models could be built. This does not necessary means that one is right and the other wrong, but it highlights that from one observation different interpretations are possible. As today at Ford no support to understand the system logic exists, the problem of interpretations is present. The risk is to increase the perceived gaps between the existing simulation models and the real system. This could dramatically affect the simulation model credibility, so the level of confidence of the users for the simulation is also affected.
Implementing some specification for the real system is the best way to reduce the risk of different interpretation.
Ford Simulation and Process non-specialists
Ford Simulation non-specialists
Ford Simulation specialists
FAST&FIRST interfaces
Real system understanding support
Actual users
Future users
Industrial Context and Problem Statement
11
Figure 6 presents the possible gaps between the different interpretations. The system specification (support for understanding the real system) trends to reduce the gaps, supporting the real system understanding. In the case presented in Figure 6, gaps between the interpretations of builder and the user make the user does not believe the simulation, this affect the simulation credibility.
Figure 6: Real System Interpretation Issue
To summarise, Ford wants this thesis project to develop a support for understanding the real system and give specifications for the simulation. The
Real System
Model Builder
Model User
Gaps
Observations
Interpretations
Observations
Interpretations
Real System
Specification Document
Model Builder
Model User
Gaps
Observations
Interpretations
Observations
Interpretations
Without System Specification
Specification reduce the
gaps of interpretation
With System Specification
Industrial Context and Problem Statement
12
purpose of this support is to reduce the gaps between the simulation model and the real system and to broaden the simulation user. The support is also the best way to reduce the risk of different interpretations of the real system. Such support will increase the credibility of the simulation model. The main objectives are to improve the simulation and to promote the simulation tools.
2.3 Summary of the Problem Statement
Ford is a large company and one of the oldest car manufacturers in the world. Since 1903, Ford has provided cars and produced car components, such as engines. However the global market pressures are increasing the competition. This enforces Ford to continually improve manufacturing performances. Actually Ford has many plants around the world and improvements on manufacturing facilities help Ford stay competitive.
Since the 1980s, Ford has applied simulation to support the manufacturing facilities improvements. Simulation is complex and required programming specialists. For this reason, Ford has developed “easy-to-use” interfaces using Excel spreadsheet to develop and run simulation models. However, Ford engineers have to face issues about the simulation.
First of all, Ford simulation experts noticed gaps between simulation and the real system. Developing a support to understand the real manufacturing system will help them identify precisely gaps and reduce it. Actually gaps in simulation could dramatically reduce the simulation model credibility and so reduce the simulation efficiency as a decision making tool. This is the starting point of the thesis: development of a document which specifies the real logic for simulation.
Secondly, interpretation of the real system behaviour is necessary to build the simulation model. However different interpretations are possible. To reduce the risk of gaps between interpretations a specification document is required. Actually the interpretation gaps affect the simulation credibility.
Finally, addressing the simulation to non-specialist, Ford wants to develop documentation to help non-specialists understand the real manufacturing system (real system logic). The real system logic explanation is called the Specification Document.
Literature Review
13
3 LITERATURE REVIEW
After identifying the problem three questions must be answered: how the manufacturing system specification should be presented how the real system logic should be explained and what the content of the Specification Document is. To answer these questions and in order to have an overview about how simulation specialists use to deal with these issues, a literature review has been done. This chapter presents the findings of the literature review.
3.1 System Specifications
Ford engineers want to develop a Specification Documentation which standardises the way to explain to the model builder and user how the real system works.
The real system is the manufacturing operations; according to the Chambers Dictionary a system is defined as “anything formed of parts placed together or adjusted into a regular and connected whole”. Parts are some components of the system and there are some links between parts. The nature of the links and interaction between parts are seen as the logic by Ford engineers.
According to the Chambers Dictionary, the specification is “a detailed description of the requirement”. The requirement is a key in the development of any product since it is the origin of the whole work (Kirner and Abib, 1997). In the case of the simulation, the requirements of the real system are the explanation of the logic of the component of the system, it includes: the element logic and the logic of the interaction between them. Understanding of the real system is vital for the simulation model builder as Chung (2003) and Robinson (1994) said “Garbage in, garbage out”.
A manual has been developed to use the interface FIRST, but the builder needs to understand the system that he wants to model. However, for a complex system like the machining line, nobody usually knows the whole process and the logic of the system (Law, 2005). The basic question is how the builder could collect information? Interviews with manufacturer engineers, process engineers, and control engineers seem to be high time consuming. For this reason, Ford simulation engineers want to standardise the way to communicate the logic of systems. Ford looks for a systematic way to express the real system logic.
Standardise such type of document presents many advantages:
• Reduce the model building time, speeding up the real system understanding
• Increase the confidence of the simulation providing proof of real logic • Broaden the simulation user bringing the simulation tool more accessible
Literature Review
14
3.2 Data/logic Collection and Communication
Papers propose some processes where logic and data collection are generally done in the same stage. Experts usually do not make the difference between the logic and the data. However, data is quantity, value or name and logic is the behaviour of the system, the story of what happens on the lines for the component.
Robinson (1994) presents a process to build a simulation model; the process is compared to a project. Figure 7 presents the main stages of this project. Formal document to clarify the project is recommended but no formal document is available on site to collect data and represent the real system logic. Robinson proposes to use “layout diagrams with flows and logic identified” but specifies that each builder uses a different method to represent the real system. The importance of data collection and logic understanding are underlined since they impact on the final model: “garbage in garbage out”.
Figure 7: Typical Stage of a Simulation Project, Ro binson (1994)
Problem Definition
Model Building and Testing
Experimentation
Project Completion and Implementation
Structure the Model
Build the Model: � Coding � Documenting � Verifying
Project Completion and Implementation
Identify the Problem and set the Objectives
Define Experimental Factors and Reports
Collect and Analyse Data
Determine the Scope and the Level of the Model
Provide a Project Specification
Literature Review
15
The stage “Structure Model” calls the data collected during the “Problem Definition”. These data are required to build the model in the stage “Building Model and Testing”. Data are classified in several types:
• Quantitative (E.g. cycle time, arrival rates) • Logic rules (“control of flows, scheduling strategy and work allocation”) • Physical layout
The Ford engineers are quite confident about the used system for quantitative and physical layout data. However, Ford engineers want to develop a systematic way to collect and presents the “logic rules data”.
Carson (2005) proposes an overview of a typical simulation project and points out the importance of the model input like data and logic. A classic team is presented to collect information. The team involves people directly link with the real system “staff, plant and line manager” and simulation modeller. Unfortunately, no formal documents are available on site to communicate information about logic. Carson (2005) makes reference to an “Assumption Document” or “Function Specification Document” to set the assumption made. Carson recommends writing this document in the language of the “real system” avoiding jargon of modelling language as the document is used by all team members. However non standard format for this document is presented.
In the Ford case, the logic specification will be used by simulation specialists and non-specialists. For that reason, it seems important to follow the previous recommendation to remain understandable for each future user. The language of the documentation should not be a specialist simulation language but current language.
Law (2005) also proposes a typical process to apply for simulation tool. Seven steps are described in the process, as Figure 8 shows.
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Figure 8: 7 Steps of the Process, Law (2005)
Information and data collection is also presented as a critical step. How data are collected is presented; Law (2005) points out how difficult it is and recommends conducting interviews to collect real system information. Many interviews are necessary with “Subject-Master Experts”. These experts as processes specialists know the logic of the operations. Law does not propose a standard document to collect and organise the information. However, the nature of data required to build the model is listed:
• “Collect information on the system layout and operating procedures. • Collect data to specify model parameters and probability distributions
(e.g., for the time to failure and the time to repair of a machine). • Document the model assumptions, algorithms, and data summaries in a
written conceptual model.”
These recommendations are quite similar to Robinson’s (1994). “Operating procedures” and “model parameters” are linked with the “logic rules” proposed by Robinson. However, how information should be expressed is not described.
A common idea appears through the previous papers. Defining the objective and the scope of the simulation model is a key element before starting any work about the data collection. This provides information about the level of detail on the data that the builder needs. In the other hand, Robinson (1994) shows that data collection can affect “the project specification” since the data available can
Design, Conduct and Analyse Experiments
Document and Present the Simulations Results
Formulate the Problem
Collect Information/Data and Construct the Conceptual
Model
Program the Model
Yes
Yes
Is the Conceptual Model Valid?
Is the Programmed Model Valid?
No
No
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influence “the project specification”. For that reason, Robinson (1994) recommends in a typical simulation project to collect data before doing “the project specifications”.
The literature confirms the importance of the “data collection” during the model building. It confirms the necessity of the Specification Document development.
3.3 Simulation Validation
In the Ford case, the documentation is developed after the simulation model (models are already created). The first utilisation of the documentation will be to validate the current model. Papers on simulation validation present different approaches and processes; it appears that real system logic it also key at this stage.
Chung (2003) specifies the difference between verification and validation. The verification of the model is progressively done during the model building process and ensures “that the simulation model has all the necessary components”. After verifying the simulation, the validation is “the process of insuring that the model represents reality”. Chung notices that even “experienced practitioners” know some confusion between these two different stages. In the Ford case it is clear that the Specification Document is a validation tool.
Brade (2000) deals with Model Verification, Validation and Accreditation (VV&A). Levels of validity of a model are presented as a model is not valid or no-valid. One of the parameter which influences the degree of validity is the “available information about the real system”. How the system is known and how information is communicated both influence the performance of the simulation.
Brade (2000) presents a process to VV&A. It appears that intermediate experiments are performed during the model development. Brade (2000) makes references to documentation which describes how the model was built. The process to build a simulation is quite similar to the previous one, and the available information is dependent on parameters, by the fact that:
• “The real system does not exist. • The real system is under development and only partially exists. • The real system is not exportable or simply too complex.”
Brade (2000) highlights the current lack of information of the real system. From this paper, two mains things appear. First, the Specification Document will be used in phase of validation of the models. Secondly a model is never 100% validated (simulation does not represent the exact system behaviour some simplification are done), this means some gaps will be always present.
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3.4 Simulation Document
As saw above, documentation is a large issue in simulation; document what and how is an important question. Papers deal with these points.
3.4.1 Documentation Content
Gass (1984) deals with the document issue in the simulation “life cycle”. An overview of a typical simulation “life cycle” is presented and a description of the content of the documentation for each stage is provided. The stages of the “life cycle” are:
• Embryonic: “Needs description” • Feasibility: “Feasibility study” • Formulation: “Model formulation description” • Data: “Data requirement description” • Design: “Design specification” • Software development: “Software description” • Validation: “Validation description” • Training education: “Training plan” • Installation: “Installation plan” • Implementation: “Implementation plan” • Maintenance and up date: “Maintenance plan” • Evaluation and review: “Evaluation plan” • Documentation and dissemination: “Documentation plan”
In the Ford case, the issue is focus on the data collection and the communication of the data to the model builder. Only the stage “Data requirement description” is directly linked to the subject. “Data requirement description” has to be detailed. “This report describes the detailed data needs as required by the model; data sources; the process for obtaining the data; experiments, data collections and surveys to be performed; organizational and individual responsibilities for obtaining, updating and processing the data; numerical and forecasting techniques to be used for parameter estimation; data validation procedures; acceptable data ranges, data input procedures to the computer model, etc. This is an operational document that is maintained throughout the model life cycle.” This document is focused on the acquisition and evaluation of the data. Unfortunately, the logical data are not noticed directly, quantitative data and qualitative data are not differentiated.
The principal risk to develop such documentation is to increase dramatically the volume of the documentation. This does not mean that these documents must not be written, but the developer of the documentation must take care about keeping the documents accessible: not too heavy and not too specialised (Keep
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it Simple and Short). Of course the documentation complexity must be balanced with the level of the complexity of the simulation model.
Nordgren (1995) breaks down a typical simulation project. A large part of the project is the “data collection and assumption documentation”. Actually as Figure 9 shows this stage represents 40% a simulation project. It is notable that this stage is the most important.
Model buiding, 35%
Output analysis, 10%
Model objectives and flowcharting,
5%
Model experiments, 10%
Data collection and assumption documentation,
40%
Figure 9: Simulation Stages, Nordgren (1995)
Nordgren (1995) recommends and explains in detail the steps of the “data collection and assumption documentation”. The manufacturing facilities must be fully understood by the model builder by visiting manufacture or reading design documentation if the system does not exist yet. In other words, “the engineer must have a complete understanding of the operational characteristics of the system”.
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Table 1 describes the proposed way to collect data.
Table 1: Data Collection, Nordgren (1995)
Nordgren Steps Data Collection “List system components” During the manufacture tours and visits, all
components must be listed: machine, storage location, platens, tools location, parts, etc.
“System resources” Resources must also be listed conveyors, operation operators, maintenance staff and all resources that support the production
“Make note of operational characteristics”
“As each system element is reviewed, make notes of the operational characteristics. Are there any special processing logic, how does the machine interact with other elements of the system.”
“Make a list of system terminology and acronyms”
The name of the operation, parts and elements must be similar in the simulation and in the real system; this will ease the simulation understanding and will avoid misunderstood.
The content of the documentation after collecting data is presented in Table 2.
Table 2: Documentation, Nordgren (1995)
Nordgren Steps Data Documentation “List system components” The documentation is a list of all component of the
real system; “any operating characteristics” must be included.
“List system resources” The document must list all system resources in detail “List system terminology and acronyms”
The document must explain all system terminology in detail
“Draw and label system layout”
This is a visual support in the documentation
Nordgren (1995) is relevant since it describes the data collection and the organisation of the document, but no format for this documentation is recommended. For the logic viewpoint the step “make note of the operational characteristics” is the key step to collect data (“Are there any special processing logic, how does the machine interact with other elements of the system”?) Nordgren refers to the logic as the “operational characteristics” and proposes to present it on the first part of the documentation: “List system components”.
Nordgren (1995) proposes also “assumptions document data”, this document informs the builder about the data, the assumption and includes more general subject like “goal and objective of the simulation”, “issues investigated” or “key performance measures”. This document is the “most important item of the
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project” according to Nordgren. This document must include the list of the elements, the related data, and assumption made for each element.
The Specification Document content is critical since it is related to the scope of the project. In the Ford case, the work is limited to the logic communication; in other hand it appears in literature that the logic explanation is related with general issues of the whole simulation project.
Specification Documentation is the characteristic of the real system and its behaviour. It includes the characteristics of the components and the logic rules which link each component. The Specification Documentation is included in the Simulation Project Requirement which describes the requirement of the simulation model and defines the needs, the scope and the objectives of the simulation project. Figure 10 draws the boundaries between the Simulation project requirement and the Specification Document.
Figure 10: Simulation Project Requirement and Real System Specifications
3.4.2 Documentation Support
Oscarson and Moris (2002) compare a manufacturing simulation model to a product and demonstrate the importance of standard documentation to illustrate a complex simulation model. As a model is used, re-used and up-dated the explication of how it works and how it has been developed reduces the time consumed for new users. Standard documentation also increases the confidence in the model since the users know how it has been developed. In the Ford case it seems clear that the presence of a standard document to communicate the real elements logic will speed up the model building. This document could reduce the data collection time, and it could enable a better understanding of how model the reality.
Oscarson and Moris (2002) evaluate and discuss different “notations” (language: IDEF0, UML) to support a standard document. “Documentation
Simulation Project Requirement
Specification Document
Scope of the Thesis
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deals with storage of experience and with communicating or making this experience accessible to others”, this underline the importance of the standard selection. The conclusion is that non specific language is recommended for the documentation since it depends of the simulation model complexity and of the personal understanding.
3.5 Elements Logic
As describe above the approach of Ford simulation is based on “elements”. This part present what literature currently proposes to explain the system logic of what it is called the “elements” logic and interaction.
Chung (2003) recommends using a “high-level flow chart” because it “helps the practitioner obtain a fundamental understanding of the system logic”. Such diagram enables to understand visually how “components and events interact”.
Figure 11: Flow Chart Basics
Figure 11 presents the basics of the flow chart that Chung proposes. Four basic components are presented: the oval for the start/end, the parallelogram to illustrate the input/output, the rectangle for the process and the diamond for the decision.
It appears that this tool is suitable to communicate a simple process or the basic of a complex process. It is difficult to explain every details of the process.
Start/stop
Input/output
Decision
Process
Yes
No
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3.6 Summary of this Chapter
During this first research, Winter Simulation Conferences were a great source of information. These conferences propose a large range of issues directly connected with simulation and the majority of paper are available via internet.
This literature review enables to have a specialised viewpoint and to:
• Measure the importance of real system logic understanding at the building stage and validation stage
• View some recommended content for such documentation • View some recommended simple support (flow diagram)
Related to the subject, the literature of Winter Simulation Conference generally speaks to the model building in term of methodology. No papers give a real example of how the system logic representation to the model builder is addressed.
An interesting point is in which “language” expresses the document, in one hand Carson (2005) recommends to use the real system language avoiding programming and simulation jargon. But on the other hand, the purpose is to describe the elements logic and the element is a simulation concept that Excel interface uses. The documentation should be a translator or an intermediary between process engineering and simulation engineering and obviously they do not use the same language.
From this literature review, it appears that the “specification” in the simulation is broad. The volume of the document could be increased dramatically if each recommended section would appear. The initial Ford requirement is to be developed a documentation focused on the machining lines logic. Figure 12 illustrates the scope and issues of this documentation.
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Figure 12: Specification Documentation Scope
At the top, in the shop floor section, Line 1 and 2 represent different plants or steps of the process where each operation or component has its own logic. It is the process engineering viewpoint, because each component is design for a specific application. Translation is an issue of the thesis. Simulation engineering uses the “simulation language” when the real components are grouped in elements. Several components are represented by one element, so the element logic description should be enough flexible to enable several applications.
Simulation Engineering Element 1
Logic Element 2
Logic
Shop floors: Real System
Process Engineering
Line 1
Operation 11
Operation 12 Conveyer 11
Line 2
Operation 21
Operation 22 Conveyer 21
Logic Operation
11
Logic Conveyer
11
Logic Operation
12
Logic Operation
21
Logic Conveyer
21
Logic Operation
22
Common logic
Common logic Translation
FIRST and FAST Interface s Excel + Visual basic support
Simulation Software WITNESS Package
Specification Documentation Other source of
information/data…
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Figure 12 illustrates the scope of the Specification Document. The aim of the documentation is to translate and communicate the real logic. The idea is to go from the shop floor language to the simulation language. To go from real system component logic to the element logic which is the simulation language.
It appears that the Verification, Validation and Accreditation of a complex model are time consuming. The development of Specification Document will support the model building and reduce the VV&A process.
It emerges also that developing a Specification Document is fully justified. The Specification Document could have some great advantages at several step of a simulation process:
• Understanding of the real system elements • Communicate from process to simulation model builder • Build the simulation: ease the model building • Verification, Validation and Accreditation: increase the credibility of the
model • Standardise the way of communication the real system logic • Limit the different interpretations of the real system logic
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26
4 RESEARCH PROGRAMME
This chapter sets the problem identification and presents the aim, objectives and methodology of the thesis.
4.1 Problems Identification
The automobile market pressures enforce Ford to stay competitive; one way to compete is to continuously improvement of the manufacturing facilities. To support Ford engineers in this mission, Ford has applied simulation tools for many years. Ford has developed strong tools for modelling the manufacturing facilities.
Ford knows some gaps between their simulation models and the real system in the factories. Today Ford does not have any support to understand the real system logic. Different interpretations of the real system logic are possible and simulation models know a lack of credibility. Furthermore Ford attempts to extend the simulation user but few documents are available to help new users. These three points affect simulation utilisation for the V8 and V6 engine machining lines.
4.2 Aim and Objectives
According to the problem above, the aim of the thesis is to help Ford improve the simulation model for the V6 and V8 machining lines through a Specification Document development.
In order to achieve this, the following objectives are identified:
1. Understand and represent the logic of the machining lines
2. Validate the logic and its representation
3. Develop the Specification Documentation
4. Identify gaps between the machining lines and simulation models
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4.3 Methodology
In order to be familiarised with the issues and gain a specialised point of view, research in literature has been done. This literature review confirms that the development of the Specification Document has not been done so far and required a thesis research.
Stage 1: Understand real system logic
This purpose of the first stage is to understand and represent the real system logic for the machining lines.
In order to achieve this first objective, visits and interviews are performed. The machining lines logic must be fully understood and then its representation can be done. Through several visits to Dagenham and interviews with the Ford engineers, the logic of the real system is understood and represented with the selected way to express it.
The output of this stage is the representation of the logic for the machining lines.
Stage 2: Validate logic and its representation
Having obtained a representation of the logic, a validation stage is required. The purpose is to validate the logic itself and its representation.
In order to validate the logic and its representation, reviews with control and simulation experts are done. The control and the simulation engineering viewpoint are confronted through the output of the first stage.
The deliverable is the validated logic and validated logic representation for the machining lines.
Stage 3: Develop the Specification Document
After validating the logic and its representation, this stage pays attention to the development of the Specification Document.
The development of the Specification Document is based on analysis of several lines (3 Machining lines). The validation of this document through three cases makes it stronger. To develop the document, logic representations are compiled and organised.
The deliverable is the Specification Document itself.
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Stage 4: Identify gaps between the machining lines and simulation models
Here it is the value added of the thesis, gaps and similarities between simulation and real system are fully documented.
This stage is done in cooperation with a Ford simulation expert. This is the first utilisation of the Specification Document. The document is compared with the simulation logic.
The results of this stage are also included in the final deliverable for Ford.
Table 3 summarises the stages their purposes, the methods followed and the deliverables of each stage.
Table 3: Objectives and Methods Summary
Stages Purpose Methods Deliverable Understand real system logic
Understand and represent the real system logic
Factory visits and interviews applying the selected way to represent logic
Representation of the logic of the machining lines
Validate logic and its representation
Validate the logic of the real system and its representation
Logic review with control engineering point of view and simulation engineering point of view
Validated representation of real system and finalised representation
Develop the Specification Document
Develop the Specification Document
Compile the finalised logic representation and organise the document
Specification Document
Identify gaps between the machining lines and simulation
Quantify the credibility of the simulation model
Compare the real logic with the simulation model
Documented gaps and similarities between simulation and real system
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5 STAGE 1: UNDERSTAND AND REPRESENT THE LOGIC OF THE MACHINING LINES
The first stage of the thesis is to understand the real system logic. In order to deal with this objective, several visits at Dagenham plant of the engine machining line, interviews with process engineers and operators had been done. This stage attempts to develop the logic representation.
It is important to notice that at this stage the simulation is not taken in account. This stage deals only with the logic of the real system; this enables to picture the machining lines logic. The logic representation (the way to explain the logic) is not finalised at the stage, this is part of the next stage which is the validation.
Different steps were necessary to obtain a picture of the real system; the steps match the recommendation of the literature review:
• Lion machining lines tours • Identify the equipments and apply the selected way to explain the logic
for every piece of equipment (flow diagram) • Establish the flow diagrams for all pieces of equipment with a common
approach: common vocabulary and diagram structure • Analyse the issues which need validation from specialists
Each of these items is presented in this chapter. Details, explanation and analysis are here provided.
5.1 Dagenham Lion V6 and V8 Machining lines
In Dagenham plant Ford machines Lion engine components, Figure 13 presents pictures of these components.
• Cylinder Block for the V6 engine • Cylinder Head left and right for the V6 and V8 engine • Crankshaft for the V6 engine
Figure 13: V8 and V6 Machined Components
Crankshaft Cylinder Block
Cylinder Head
×2
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These components are some key part for an engine. Cylinder block, cylinder head for and crankshaft required thee different machining lines.
For Lion head machining line the process is a succession of around 20 operations. There are 4 main types of operation: machining (e.g. milling, drilling), assembly (e.g. insertion of guides), washing and testing (e.g. visual inspection). The inputs are cylinder heads roughly machined and the outputs are cylinder heads ready to be assembled with other components to make a V8 or V6 engine. V6 or V8 cylinder head left and right are machined. During the major part of the process cylinder heads are transported on some platens. Other machining lines have some platens; Figure 14 presents a cylinder block on its platen.
Figure 14: Platen
One line is a complete system; this system is composed into sub-systems: zones. Zones are composed of pieces of equipments (e.g. machines, conveyors). It is comparable to a zoom: zooming in enables to go from the system (line) then sub-system (zone) and finally piece of equipment. All lines have the same principal: inputs are work pieces roughly machined and outputs are work pieces ready to be assembled. Machining lines are sequences of operations.
Figure 15 presents the simplified layout of the line. Line (system), zone (sub-systems) and pieces of equipment are shown.
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Figure 15: Lion Head machining Line
5.2 Logic Representation
The section presents the approach followed to obtain the logic of the machining lines.
5.2.1 Real Equipment List
Here, it is presented the list of the different component identified on the Lion machining lines:
• Conveyor Multi Part A Conveyor Multi Part transports horizontally part, this conveyor could contain 2 or more parts. Longer is this conveyor more part it can contain. • Conveyor Single Part A Conveyor Single Part is similar but contains just one part. • Turntable A Turntable changes the direction of a part; the orientation of the part could be also changed. Usually a Turntable is at a corner of the line.
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• Divert A Divert changes the route of parts. The direction of a part, the orientation of the part could be also changed. Usually a Divert is present for an intersection of several conveyors. • Swing Gate A Swing Gate is a Divert that can be manually opened to go through the line. To open it, a button is pressed and the Divert opens.
• Lowerator A Lowerator transports part vertically; it generally enables to go from conveyor to a lower conveyor. • Elevator An Elevator transports part vertically; it generally enables to go from conveyor to a higher conveyor.
• Lowerator Turntable A Lowerator Turntable transports part vertically, it also changes the direction of a part and the orientation of the part could be also changed. It generally enables to go from conveyor to a lower conveyor at a corner of the line.
• Elevator Turntable An Elevator Turntable transports part vertically, it also changes the direction of a part and the orientation of the part could be also changed. It generally enables to go from conveyor to a higher conveyor at a corner of the line. • Orientator An Orientator is located generally at the corner of conveyor. It changes the direction and the orientation of the part. • Machine A machine realises an operation on the part, this could be a lot of different kind of operations: automated or semi-automated or manual operation. • CNC (Computer Numerical Control) Machine CNC machine are fully automated machine could be milling, drilling, surfacing part.
• Transfer Machine Transfer machine has the particularity to unload one when it can load one part: a part leaves the machine when another part enters in the machine. There is always a part in this machine.
• Gantry Gantry transports part in high level. Generally Gantry distributes part to the CNC machine(s).
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This list gives an overview of the equipment used in the machining lines. Having identified all the pieces of equipment, the next stage is the represent their logic applying the flow diagram.
5.2.2 Flow diagram
As viewed in the literature review and validated by Ford, the flow diagram is the selected tools to illustrate the real logic of the system. The basic elements of the flow diagram are used. In order to have a homogenous viewpoint the Microsoft Visio 2003 standard has been selected.
Process Decision Data
Yes
NoStart postision
Figure 16: Microsoft Visio Flow Diagram Elements
Starting Position: All pieces of equipment have a starting position. They return on the position cyclically. Start position is the initial statement of the piece of equipment.
Process: Processes are some actions. Process can be action which does not take time as “activate stopper”. An activated stopper blocks a part in a conveyor until the action “deactivate stopper” is done. Process can be action which takes time. This process is completed processes, in action like “rotate turntable” it is considered the action is started, carried out and finished.
Decision: Many questions are asked in cycle, this means the system asks questions until obtaining the answer which will unblock the piece of equipment. It obtains the right condition before going further in the flow diagram (go to the next process or decision).
Data: Data could be produced and/or received. Decision point could call data to go further.
5.2.3 Represent the Logic Diagram
To develop the flow diagram of the machining lines logic several issues were taken in account.
Piece of Equipment Boundaries:
The definition of a piece of equipment is not so obvious with an approach of logic representation. Set the boundary is not simple and has a great influence
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34
on the logic. A piece of equipment is composed by sensors (e.g. photo electric, mechanic), motors (e.g. electrical motors), and mechanical support (e.g. chains or rails). The interaction of these different components makes the logic. The challenge comes from the fact that sensors produce signals, these signals are sent to the control system, and different pieces of equipment use these signals. Sensors are at the boundaries of piece of equipment since one sensor can be used by two or more pieces of equipment.
One typical example was to define properly what a piece of conveyor is. The set of the boundaries is critical since it influences the logic representation and so the diagrams. It has been chosen to have intuitive boundaries.
Logic Structure:
Specific structure vs. common structure is also an issue to set the diagrams. Specific structure is that each piece of equipment is represented using a different diagram structure. Basically the sequence of decision points is different for each piece of equipment. Common structure is that every piece of equipment will have the same diagram structure; the sequence of the decision point is similar for all pieces of equipment.
Table 4 presents advantages and disadvantages of specific and common structure.
Table 4: Diagram Structure Advantages & Disadvantag es
Specific Structure Advantages Disadvantages
Clearer to understand for one specific piece of equipment
Not flexible, when two pieces of equipment are linked the vocabulary can change
Shorter, the diagram is less large and each step is useful
Could rise many configuration and increase the amount of vocabulary
Practical approach and vocabulary closer to piece of equipment
Do not standardise the approach
Common Structure Advantages Disadvantages
Same vocabulary and structure for each piece of equipment
Larger diagram and could contain useless information for some piece of equipments
Standardise the approach More theory approach and less practical Limit the amount of vocabulary More difficult to represent special piece of
equipment
From this analisis the common structure has been selected. A common structure with a common vocabulary provides standard approach; this is closer to the Ford requirement.
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Level of Logic:
The level of logic is a complex issue; this affects the amount of information and the level of detail. The approach “deeper is better” can provide complex diagrams which are difficult to follow. The risk is to increase the volume of the documentation. The first question to ask is how deep does the simulation model have to be? This depends of each simulation project as presented in the literature review. In the present case the Specification Document should be used for each project, it means that the level of logic stay critical and should be review during the validation stage. At this stage, the approach followed is “deeper is better”.
Active and Passive Actions:
Active actions are actions that the piece of equipment has to launch to do a process. For instance, to load a part some pieces of equipment do several actions. In other hand, other pieces of equipment do nothing for loading a part. For example a conveyor has always its transportation system running. This means that conveyor does not need to launch any action for loading. The loading action of a conveyor is passive. How the passive actions should appear on the diagrams.
Future User:
The future user should be the simulation user, but as presented before Ford attempts to increase the number of user. This means that a broad range of people could use the Specification Document in the future. People from different background and different skills will use it. A particular attention should be paid to keep the flow diagrams as accessible as possible.
5.2.4 Flow Diagram Example
For all the piece of equipment listed above flow diagram were built. These diagrams are a first draft. The development of these diagrams enables to have a first understanding of the piece of equipment logic.
It is important to notice that the first draft required several attempts. Since the beginning common vocabulary and structure was a target. For instance the Turntable flow diagram had many versions. Actually the development of diagrams of other pieces of equipment brought some modifications to the Turntable diagram. Figure 17 presents the flow diagram of a Turntable. In these diagrams, piece of equipment is called element.
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Figure 17: Turntable Diagram
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37
Such diagrams were developed for the following pieces of equipment (a part of them are presented in Appendix A):
• Conveyor Multi Part • Conveyor single part • Turntable • Divert • Lowerator • Elevator • Lowerator Turntable • Elevator Turntable • Orientator • Machine CNC (Computer Numerical Control) • Machine transfer • Manual operation • Gantry
These pieces of equipment were principally studied from visits of the Lion cylinder head machining Line. The flow diagrams provided are the first draft and required validation through analysis of their relevance for the other machining lines. Some of these pieces of equipment are also present in the other machining Line, common logic should be established by providing common flow diagram.
5.3 Common Flow Diagram Establishment
The common flow diagram establishment is an important part of this Chapter. This enables to standardise the approach used to build and to structure the diagram. Common means common approach, structure and vocabulary for different pieces of equipment. Some of these pieces of equipment are present in the three machining lines; this second diagram is validated for all lines.
It is important to notice that a piece of equipment could look different from one line to another but have the same logic. However the opposite is possible, a piece of equipment could look similar but have different logic.
Here is presented the list of the selected piece of equipment for this second flow diagram draft, 9 equipments were selected:
• Conveyor Multi Part • Conveyor Single Part • Turntable • Elevator • Lowerator • Operation Auto/Man/Test • Operation Transfer
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• Divert • Orientator
Based on this list, the next stage is to establish the diagrams. A basic approach was selected to set the vocabulary and the processes. For all these pieces of equipment diagrams were already done but without systematic vocabulary and diagram structure. This means that the logic was understood, but the way to express was confuse and non homogeneous.
5.3.1 Common Diagram Construction
This part presents the approach follows to provide the second flow diagram draft. This part presents the approach and the provided results on one specific piece of equipment: Turntable.
Followed Approach
Having selected the list of piece of equipment, the establishment of the vocabulary and the structure is done. This is based on a basic approach which consists to have a good picture of what the Turntable is, what it does and what the difference and similarities between Turntables are. For each of these pieces of equipment the following table was used:
Table 5: Turntable Example
Turntable Components Actions Processes
1 stopper Activated or deactivated Hold or release part Conveyor Stat or stop conveyor Load and unload part Rotation motor Start or stop motor Rotate in unload and load
position Sensor Send signals No process
Differences between Turntables
• With or without stopper • Conveyor runs forward and backward
Common Vocabulary
• Subject: – Part – Position
• Processes: – Load / Unload – Rotate
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Components make actions which enable to realise the processes. The processes make the piece of equipment realise its function. The sequence of the processes makes the piece of equipment logic.
• Components are the parts which compose the Turntable. All the components are not listed but just components which play a direct role to complete the processes of the Turntable.
• Actions are the behaviour of the components, what the components do to as actions. Actions must be done to make a process.
• Processes are the breakdown of the function of the Turntable. Several processes are necessary to realise the function of the Turntable.
The list of component, actions and process enable to have a good picture of the piece of equipment and to compare similarities and the differences from one to another the. For a Turntable difference were highlighted.
Using this table and the understanding of the logic (first flow diagram draft) second flow diagram draft was built. These diagrams are an interpretation of the real logic. This interpretation is common for all Turntables present on the three machining lines.
Diagram Construction
After having a good picture of the Turntable characteristics and behaviour, the flow diagram was built. It is important to highlight that diagrams were built one by one. This means that the approach described above was followed for one piece of equipment, the diagram was built then another piece of equipment was studied. This enable to work by iteration, the construction of the diagram of one piece of equipment could influence the structure and the vocabulary of the others.
As presented above within a common piece of equipment similarities and differences are present. To deal with the issue what is common/ what is different? Two level of logic were set. One level presents what is done (load and unload) and the second level (deeper logic) explains how is done (how part is loaded and unloaded).
Table 6 represents the level 1 of logic; it is the common logic for all Turntables.
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Table 6: First Draft Diagram for Common Element (Tu rntable)
Flow Diagram for Turntable (Level 1) Diagram Description
1. Starting position is a key element it defines the initial statement of the equipment. Spontaneously, it was selected as start when the Turntable is reset and part is arriving. Consequently, the flow of the diagram is closer to the flow of the part. 2. Here this is a decision point; it is considered that the Turntable knows when a part is arriving. If no part is arriving, the flow stays in the loop until a part is arriving. When a part arrives the Turntable launches the loading action. 3. Load one part, this is typically a process. How it is loaded is not describe at the level of logic. “One part” is specified since it is important to know how many parts enter into the Turntable. 4. Rotate is the basic function of the Turntable; this process enables to achieve the principal function of this piece of equipment.
5. Before unloading a part the Turntable must check if the next position is available. Next position available means that the next position is free and the next piece of equipment idle.
6. How this unloading process is done is not describe at the level of logic. “One part” is specified since it is important to know how many parts are unloaded.
7. Rotate is the basic function of the Turntable; this process enables to return to the initial position. If the Turntable is not at its initial position it cannot receive a new part.
Differences appear when more details are provided. When the diagram answers to the question how a process (load or unload) is performed, the level 2 of logic is necessary. Table 7 presents a level 2 of logic for the Turntable. The level 1 is still valid but in level 2, it is explained how the processes are done.
1
2
3
4
5
6
7
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Table 7: First Draft Diagram for Common Element (Tu rntable 1) Level 2
Flow Diagram for Turntable (Level 2) Diagram Description
1, 2, 3 explain how the process load is done. 1. Start conveyor enables to load the part (conveyor could be rollers, chains). This means the conveyor starts running.
2. P0 is the position in the Turntable where the part is loaded. Here the equipment checks if the part is properly loaded.
3. When the part is properly loaded the conveyor is stopped. This means the conveyor stops running. 4, 5, 6, 7 and 8 explain how the process unload is done.
4. Here start conveyor enables to unload the part (conveyor could be rollers, chains). This means the conveyor starts running.
5. Stopper is naturally activated, this hold the part. To release one part (unload) this Turntable needs to have conveyor running and to deactivated the stopper.
6. This decision point checks if the part is properly unloaded. In this case the Turntable can launch the reset.
7. To reset, the stopper should be activated since it is naturally activated
8. The conveyor is stopped since to reset the conveyor should be stopped.
1
2
3
4
5
6
7
8
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In this case, level 2 just concerns the loading and unloading actions because it is at these points that differences were highlighted. To load and unload all Turntables do not use the same principal. Table 8 presents another Turntable type.
Table 8: First Draft Diagram for Common Element (Tu rntable 2) Level 2
Flow Diagram for Turntable (Level 2) Diagram Description
1, 2, 3 explain how the process load is done. 1. Start conveyor enables to load the part (conveyor could be rollers, chains). This means the conveyor starts running. The conveyor is stated forward.
2. P0 is the position in the Turntable where the part is loaded. Here the equipment checks if the part is properly loaded.
3. When the part is properly loaded the conveyor is stopped. This means the conveyor stops running.
4, 5, and 6 explain how the process unload is done. 4. Here start conveyor enables to unload the part (conveyor could be rollers, chains). This means the conveyor starts running. The conveyor is started backward (the change the orientation of the part). 5. This decision point checks if the part is properly unloaded. In this case the Turntable can launch the reset.
6. The conveyor is stopped since to reset the conveyor should be stopped. In this Turntable no stopper is used.
Comparing the two different Turntables presented previously, the main processes are similar, but how perform some of them could be different. Level 1 of logic is called the parent and level 2 is called the child. From one parent several children are possible.
1
2
3
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6
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Summary
From one piece equipment to another, vocabulary and the structure used are as common as possible. Actually to ease the diagram understanding vocabulary and structure of diagram are keys. It is much easier to follow when these two points are quite similar from one piece of equipment as Turntable to another as an Operation. So the set of the vocabulary form this Turntable is coherent with the other pieces of equipment. Actually the key is to set what conceptual approach is the best to build the diagram. This approach is not fixed yet and needs some validations; this validations part of the work of the next chapter.
The development of the 9 pieces of equipment diagrams applied a standard approach. Actually many approaches are possible to build diagram. If two people explain the same thing through a diagram, the logic could be the same but the diagrams different. In the case of Specification Document, how build the diagram and what approach to follow must be included. This should guide the diagram builder who wants to add new pieces of equipment in the Specification Document.
5.3.2 Equipment Interactions
Set interaction between equipments is not simple. What is interaction? Interaction is which pieces of equipment interfere, what information they exchange and how this drives their logic.
To represent the interaction with a Conveyor and a Turntable; is it better to have one diagram or two diagrams (one for the conveyor and one the Turntable)? How join these diagrams? These issues were difficult to solve. To keep simple diagram, it has been chosen to represent some signals. These signals are represented at the level 1 of logic and illustrate the external information exchanges. Figure 18 presents the signal exchange for the Turntable.
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Turntable
Next element
Comments
Flow
Position: P0, Next and
Previous Previous element
Studied element
Conveyor
Stopper
Movement
Rotation
Flow
Turntable
Conveyor
Stopper
Next
Position
Part Orientation
Top view
Figure 18: Turntable with Signals
To generate the signals two new processes were added: “Set Part Leaving” and “Set P0 Available”. These two processes enable to generate tow signals: “Part Release” and “P0 Available”.
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Signals presentation:
• Part Arrival is an external signal which enables to answer the question “Is Part Arriving?” This signal is from the previous piece of equipment.
• Position Availability is the signal which enables to answer the question “Is Next Position Available?” This signal is from the next piece of equipment.
• Part Release is a message sends to the next piece of equipment; it is to match with Part Arrival.
• P0 Available is send to the previous piece of equipment; it is to match with Position Availability.
The solution of applying signal makes changes in all the diagrams. This solution was the simplest found to solve the problem of interaction. Here again, it is an intermediate solution, validation is required to finalise the diagrams.
Remark: the diagrams of other piece of equipment are on the Appendix B.
5.3.3 Equipment Hierarchy
Figure 19 presents the first draft of the hierarchy. Two main families were identified: transporters which transport part and operations which operate part.
The transporters are decomposed in three stages:
• First stage represents the type of transportation: horizontal movement, vertical movement and rotation movement.
• Second stage represents the piece of equipment at the level 1 of logic (the list is the same than the list presented at this section)
• The third stage represents the level 2 of logic (how processes are performed). The differences are presented as activated/deactivated (a stopper need to be activated and deactivated for performing one process) or start/stop (a conveyor needs to be started or stopped for performing one process)
The operations are decomposed in two stages:
• The first one distinguishes between Auto/Manual/Test Operations and the Transfer Operation.
• The second one represents the level 2 of logic. The differences are also highlighted with the same principal than for the transporters.
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Figure 19: Equipment Hierarchy
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5.4 Issues
During the establishment of these diagrams many issues were noticed, all these issues need validation::
• Start position affect the structure of the diagram, this position should be wherever
• Equipment boundaries is essential
• Conveyer multi part is difficult to represent
• Structure, vocabulary and level of logic required validation
• Different view point different interpretations (control vs. simulation)
• Stay easy to understand, this point is difficult.
• Interaction solution is not finalised
5.5 Summary of the Logic Understanding Stage
This chapter was focused on the real logic understanding and its explanation. All pieces of equipment identified in the first section were understood and explained through a first application of flow diagrams. Then a standard approach was followed and enabled to establish a second flow diagram draft. This approach enables to set levels of logic and hierarchies for the pieces of equipment. The work realised of the chapter allowed raising a number of issues which are briefly described above.
In order to validate the results and to deal with the current issues, validation is required. The validation stage is presented in the next chapter.
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6 STAGE 2: VALIDATE THE LOGIC AND ITS REPRESENTATION
The previous stage enables to obtain the logic explanation. On this chapter the validation is done. The diagrams are modified, update and organised according to this validation.
The validation stage is done through interviews conducted with control engineers, production engineers and simulation specialists. The deliverable is the validated logic and the validated representation.
6.1 Validation of Logic by Ford Specialist
The logic validation was in part performed through several interviews with Ford specialists. Both engineering view point control and simulation were explored.
6.1.1 Control Engineering
In order to validate the logic understanding and its explanation different presentations were performed. Having developed the 9 flow diagrams (level 1 and level 2 of logic), interview with a Ford control engineer was done. This meeting was useful to validate the logic and have a good flavour of the control engineering role in the system logic.
The control engineering is the management of all the signals which drive every process of piece of equipment. As example, every signal necessary to drive the action of a stopper are from the control system. The control system is the deepest logic which drives every piece of equipment.
Control System
The control system indicates what equipment is doing (at what step of its process it is). At each process a messages are produced, before starting and after complete the process messages are sent. A process does not start if the previous one is not finished. In the case of breakdown, a diagnostic message is displayed on the Human Machine Interface (HMI) which is a screen where staff visualise the state of the piece of equipment.
All messages are signals provided by sensors. Sensors send signals to the PLC (Programmable Logic Controller). Basically when a process is finished (e.g. rotation finished for a Turntable) a sensor sends a signal to its PLC. The PLC of another piece of equipment shares this signal and so knows the state of the previous equipment. Simply each piece of equipment has its own PLC and PLCs communicate together (share signals).
Different configurations for PLC are possible:
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• One to One (PLC): one piece of equipment exchanges information with one piece of equipment.
• Many to One (PLC): several pieces of equipment exchange information with one piece of equipment.
• One to Many (PLC): one piece of equipment exchanges information with several pieces of equipment.
Example of the Stopper
A stopper is component of Conveyor or Turntable. Its characteristic is to hold a part. The PLC representation (Ladder diagrams) for this stopper is detailed and contains a lot of information. However this enables to represent each situation where a stopper is used. The Ladder diagrams stay available for a stopper in a Conveyor and a Turntable although these are two different configurations. These Ladder diagrams understanding are difficult and required some trainings and practices but represent the deepest logic of the piece of equipment.
Summary and Analysis
Here was briefly presented the real logic representation through the control engineering tools (Ladder diagrams). These diagrams are complex and required special skill to be understood. The deepest level of logic is presented using Ladder diagrams; it reveals that it is impossible to present simply such diagrams for non-specialists.
Comparing the control system with the simulation viewpoint gaps appears: control system presents the logic of the system “as is”. The simulation interprets the logic using much less details. Finally simulation is a conceptual interpretation about the system logic and does not required the deepest level of logic.
Simulation interpretation is necessary to build a model, two reasons promote this interpretation. First it is impossible to exactly represent the exact system and particularly complex systems such as machining or assembly line. Secondly it is useless to represent the exact system (every component of the line). It could be high time consuming for a low value added.
Figure 20 represents the different viewpoints. Two axes are used; the first one is called the level of logic, and goes from the conceptual logic (simulation interpretation of the real logic) to the real logic (the logic of the real system). The second axis is called the level of tangibility, it goes from the real system which is 100% tangible (real machine and components) to the simulation model which is virtual (computer based calculations).
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Figure 20: Control vs. Simulation Logic View Point
Figure 20 enables to picture the actual situation:
1. Real system and control engineering (deepest logic)
The real system is 100% tangible and has the real logic. This system is driven by the control system through PLC, this is still the real logic but less tangible since signal are not tangible. Then Control System Logic explanation support: Ladder diagrams, this is a support based on software so it is less tangible but it refers to the real logic.
2. Simulation model and simulation engineering (logic interpretation)
The WITNESS model is simulation and a virtual way to represent the reality so it is not tangible; this is based on an interpretation of the reality. The simulation model is driven by the codes. These codes are written on WITNESS and Visual Basic, this is still an interpretation of the logic. Then the simulation tool FIRST is based on interpretation of the reality but more tangible since the real system characteristics (length of conveyor, cycle time to machine) are required.
Real System
Control System PLC
Control System Logic explanation support: Ladder Diagrams for every components
Logic Explanation: Flow diagrams of piece of
equipment logic
Specification Document
Conceptual Simulation Tools:
First interface and Witness code
Level of Logic
Conceptual Logic
Real Logic
What Level of Logic?
Code/Structure of the interfaces and Witness
Witness Model
Real
System
S
imulation
Model
Level of Tangibility
How
Level of Tangibility?
1
2 3
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3. Specification Document (specification logic)
Adjust the level of logic and tangibility of the Specification Documents are critical issues. The stage of validation is basically done to adjust and fix these two issues.
As presented above the level of logic and the tangibility of the system specification are not yet fixed. Now the real system is well know and fully understood. The deepest level of logic has been viewed. The next step is to explore the simulation model to understand its logic.
6.1.2 Simulation Engineering
From the previous part, it appears clearly the Specification Document is the link between the control engineering (deepest level of logic) and the simulation engineering (interpretation of the real logic). To increase the simulation understanding interviews and works were done with Ford simulation specialist.
Simulation Logic
Simulation is based on what is called an element, as presented in the first chapter an element is an entities (Carrie, 1988). Several elements are used; the main principal is that an element is composed by a Pre-stop, an Operation and a Buffer.
Figure 21: Element Description
The Pre-stop is a part of the equipment which can hold a part; the Operation is the body of the element since it does the main action on the part. This could be machining, assembling, rotate, elevate, etc. Then the conveyor is where the operation unloads part. This conveyor has a capacity define by its length. A longer conveyor could contain more part than a short one. This conveyor could contain 1 or more part and is called a Buffer.
Operation Conveyor: Buffer Pre-stop
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Several elements were reviewed; their logic is presented in Appendix C:
• Operation (manual, auto, semi-auto, test) • Bend – Step
• Turntable – Elevator – Lowerator
• Divert
• Transfer Operation
• CNC Cell
Summary and Analysis
The main issue is that boundaries are different that the “spontaneous” boundaries used to study the pieces of equipment. The pieces of equipment observed on the lines are grouped to constitute an element. To clarify the vocabulary it will be called real element.
For example, the real element Turntable is constituted by a Pre-stop, a Turntable and a Buffer.
Figure 22: Turntable Boundaries
The simulation boundaries simplify the real system analysis.
The level of logic is another important point; simulation is time orientated. All processes which do not take time are not relevant. From the presentation of the first draft diagram different remarks were noticed. Every flow diagram process must represent an activity which takes time. For example “set equipment idle” or “set position idle” does not take time. For this reason all this type of step was withdraw for all diagrams.
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6.2 Selection of the level of logic
As discuss before, the level of logic is a key criterion. The level of logic is the amount of detail given in the logic explanation. After understanding the real logic, two levels of logic were set. The level 1 describes what processes are and level 2 describes how processes are done.
6.2.1 Logic: Level 1 and Level 2
As simulation is a time based approach, it has been decided to keep the level 1 of logic. The level 2 explains how processes are done and does not spend time. Furthermore simulation does not require the amount of details presented in the level 2. Finally, the level 2 explanation could increase dramatically the amount of information in the specification. However, it is important to highlight that this level of logic has been explored. This gives more credibility to the diagrams so more credibility to the specification.
6.2.2 Logic: Level 0
From the simulation model analysis, it appears that another level of logic should be proposed in the specification. To understand this need, Figure 23 presents the chronology of the logic representation.
Going from the real system to the simulation the logic has been analysed:
1. Visits of the real system (machining lines) enable to understand the real system and level 1 & 2 of logic were set to represent the real element logic.
2. Control engineering point of view has validated the logic. 3. After having a better idea of the simulation approach another level of
logic should be set: level 0. This level must to be closer to the simulation approach.
4. Level 0 of logic enable to compare “like with like”.
Figure 23: Level of Logic
Real System
Simulation model
Control System Logic
Level 2 Logic: How
Level 1 Logic: What
Level 0 Logic
Sim
ulat
ion
Logi
c Comparison is possible (Like with Like)
2 3
1
4
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6.3 Selection of Boundaries
The element boundary is an important issue. Boundaries are the limits of what is internal and external for an element. The boundary of an element will affect its logic and can dramatically affect the interactions between elements. This makes the establishment of the element boundaries key for the Specification Document.
As presented above simulation element applies boundaries which are not “spontaneous”, i.e. an element boundary used in the simulation is not intuitively recognisable from observation of the real system. Figure 24 presents the boundaries used in the simulation approach.
Figure 24: Simulation Element Boundaries
Operation can be different for each element: Turntable, Elevator, or Orientation.
There are several justifications for using the simulation approach.
Real system analysis is simpler
Figure 25: Real Element “Spontaneous” Boundaries
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Figure 25 shows a section of Lion machining Line; the “Spontaneous” boundaries give 5 pieces of equipment.
Pre-stop
Figure 26: Simulation Boundaries
Figure 26 shows the same section of the Line using the simulation boundaries, the result is the identification of 2 elements. For the same section changing the boundaries of the element reduces notably the numbers of element, this makes the real system analysis simpler.
The interaction between elements is much simpler
As presented in the previous chapter interaction between elements is a complex issue. With the simulation boundaries no real interaction are required other than simple logic rules. The number of elements has been reduced therefore the number of interaction has also been reduced.
The comparison of the simulation and real system logic is more direct
Applying simulation boundaries makes the comparison of the real system is easier as the elements are compared like with like.
6.4 Finalisation of the Representation
The finalisation of the representation of the logic takes in account all the work realised so far. The principal is to use the understanding of the real system presented in chapter 5 and to apply the validated approach presented in this chapter. Basically, this means that at this stage, the real system is understood and its logic is validated. Secondly the approach (level of logic and boundaries) is validated and matches with the real system and the simulation. The representation of the logic is finalised and the next step requires reviewing diagrams and compiling them to develop the Specification Document.
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7 STAGE 3: SPECIFICATION DOCUMENT DEVELOPMENT
This chapter presents the development of the Specification Document. The Specification Document is the main deliverable for Ford. This Document has been provided and present to the Ford sponsor.
7.1 General Introduction of the Specification Document
This section presents few items that should be understood to follow the Specification Document. These items are presented at the beginning of the Specification Document.
The document is divided in 6 main chapters. The structure of the document is presented below.
The introduction defines the aim and the objectives of the document. Definitions are provided to clarify the terminology.
The second part provides the “Logic Analysis Approach”. Here assumptions are given and the approach is described explaining the general simulation approach (level of logic and elements boundaries). The list of all real system elements is provided and the flow diagram technique is introduced.
The third part is the “Real System and Simulation Logic”. In this part real system logic is presented for every element. This is the body of this document. Here is also included the comparison of the real system and the simulation logic. Gaps and similarities between the machining lines and the simulation are documented (more detail about this are given in the next chapter).
The fourth part is the “General Cases and Specific Observations”. This part presents the general issues like breakdown and changeover. Specific observations are also provided.
A fifth part proposed a summary a gaps identified (work realised in the next stage, stage 4).
Finally the conclusion gives a summary of the document, difficulties encountered and the limits of the document.
The document is included in Appendix D. The next section present the keys part of the Specification Document.
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7.1.1 Assumptions
The assumptions are an important point. The following assumptions where made when assembling the Specification Document:
1. When a scenario was observed on a real element or group of elements, it is assumed that this is the regular scenario. This scenario can be applied systematically to those elements.
2. Observations of the logic of an element are applied to elements of the same type. Validation of the logic for every element of the same type is assumed not to be necessary as the elements look and behave the same. It is not physically possible within the time constraints to observe every element in every situation. Basically to validate the logic of a Turntable, all Turntables of the three machining lines were not been studied.
3. Information from Ford employees who know the lines was necessary as not all scenarios were directly observed. Interviews were necessary to bridge this lake. The information was validated, however it is assumed that the information given is correct and represents the real system.
7.1.2 Flow Diagram
The flow diagram is the selected tools to illustrate the real logic of the system. The basic components of the flow diagram are used. In order to have a homogenous view point the Microsoft Visio 2003 standard has been selected. More details about the flow diagram are provided in chapter 5.
To help the understanding of the diagrams a colour coding is used. Figure 27 illustrates the colour code. The Element Body could be an Elevator, Lowerator or Operation etc.
Figure 27: Element and Flow Diagram Colour Coding
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7.1.3 Standard Approach
To build the diagram the standard approach is describe in the Specification Document. The approach is based on the simulation requirement, two main points are keys: the level of logic and the element boundaries.
The level of logic is defined by the processes which takes time. This is the simplest way to define the required level logic, more details about the selection of this level is given in chapter 6. The boundaries used are the simulation boundaries this enables to compare “apple with apple”, more details about the boundary issue is given in chapter 6.
7.2 Example of Turntable-Elevator-Lowerator
This section presents the Turntable-Elevator-Lowerator example in his last version. This is the version used in the Specification Document. Systematically for each element of the real system these steps were followed.
7.2.1 Element Definition
Turntable, Elevator and Lowerator are three different real elements. There are also combinations of Elevator Turntable and Lowerator Turntable. All are considered as automation.
A Turntable changes the direction of a part; the orientation of the part could be also changed. Usually a Turntable is at a corner of the line.
An Elevator transports part vertically; it enables a part to go from one conveyor to a higher conveyor.
A Lowerator transports part vertically; it enables a part to go from one conveyor to a lower conveyor.
A Lowerator Turntable transports part vertically, it also changes the direction of a part and the orientation of the part could be also changed. It enables a part to go from one conveyor to a lower conveyor at a corner of the line.
An Elevator Turntable transports part vertically, it also changes the direction of a part and the orientation of the part could be also changed. It enables a part to go from one conveyor to a higher conveyor at a corner of the line.
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Figure 28: Turntable Elevator Lowerator Drawings
This sketch presents a simple drawing of these elements. In green is the element itself, in yellow is where parts arrive (Pre-stop) and the Buffer is in blue. The capacity of the Buffer depends on each situation. The diagrams have the same colour code. The logic of these elements has the same structure.
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7.2.2 Real System Logic Interpretation
Table 9: Flow Diagram for Turntable- Elevator- Lowe rator
Flow Diagram for Turntable- Elevator - Lowerator Diagram Description
1. Starting position is select when the element is reset and ready to load part.
2. If no part is at the Pre-stop the flow will stay in the loop until a part arrives at the Pre-stop. When a part is at the Pre-stop the element goes to next process. 3. Load one part is a process. How it is loaded is not describe at the level of logic. How is loaded could be different for a Turntable or for an elevator. 4. Operate could be:
• Rotate (for Turntable) • Elevate (for Elevator) • Lower (for Lowerator) • Elevate and Rotate (for Elevator Turntable) • Lower and Rotate (for Lowerator Turntable)
5. This is the second decision point. Before unloading a part the element checks if there is a space in the Buffer. If there is no space the flow will stay in the loop until there is a space. When there is a space the element goes to next process. 6. Unload one part is a process. How it is unloaded is not describe at this level of logic. How it unloads could be different for a Turntable or for an elevator.
7. Reset could be:
• Rotate back (for Turntable) • Lower (for Elevator) • Elevate (for Lowerator) • Elevate and Rotate back (for Elevator Turntable) • Lower and Rotate back (for Lowerator Turntable)
Comments Nature of Buffer
The Buffer of these elements is generally a multi or single part forward conveyor.
Breakdowns A Breakdown of this section will not affect the pieces of automation in its Zone.
1
2
3
4
5
6
7
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7.3 Specification Document Framework
This section presents the actual framework of the Specification Document and gives an idea about what it could be in the future.
7.3.1 Actual Specification Document Framework
The support of the Specification Document was considered as an important part of the thesis at the beginning of the work. Going further in the work it appears that the development of the logic explanation and its validation was more important. Actually this development required more time than expected and was much more important for the value added of the work. It appears that is better to have a strong content with a simple framework than a medium content with a friendlier framework. Considering this point the orientation of the work changed and it was decided to pay more attention to the content than the support of the content (its framework).
According to this remark, a simple framework was selected; the Specification Documentation is only developed through Microsoft Word.
7.3.2 Specification Document Framework Idea
The framework of the Specification Document is in Word format which occupies a lot of pages. A more user friendly solution is obtainable using other frameworks such as an interactive Web based or PDF document with hyperlinks, videos and pictures. Figure 29 presents a suggestion for the future Specification Document framework.
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Figure 29: Specification Document Framework Idea
Using hyperlink the user can reach quicker the information. Two kind of interfaces could be used one based on a simple lay out (similar to the lay out presented at the beginning of chapter 6). This enables to localise the different elements on the machining lines. The other one could simply be the list of all the elements, the element could be sorted in two families: Automation, Operations. General issues like Change Over or Breakdown could be included.
• Automation o Turntable o Elevator o Lowerator
• Operation o Manual Operation o Automatic Operation o Transfer Operation o CNC Cell
• General Logic Issues o Changeover o Breakdown
Diagram + its explanation
Animation
Drawing
Data Base
Simplified Lay Out List of All Elements
Two Kinds of Interface
Flow Diagram for Turntable- Elevator - Lowerator Diagram Description
1. Starting position is select when the element is reset and ready to load part.
2. If no part is at the Pre-stop the flow will stay in the loop until a part arrives at the Pre-stop. When a part is at the Pre-stop the element goes to next process.
3. Load one part is a process. How it is loaded is not describe at the level of logic. How is loaded could be different for a turntable or for an elevator. 4. Operate could be:
• Rotate (for Turntable) • Elevate (for Elevator) • Lower (for Lowerator) • Elevate and Rotate (for Elevator Turntable) • Lower and Rotate (for Lowerator Turntable)
5. This is the second decision point. Before unloading a part the element checks if there is a space in the Buffer. If there is no space the flow will stay in the loop until there is a space. When there is a space the element goes to next process. 6. Unload one part is a process. How it is unloaded is not describe at this level of logic. How it unloads could be different for a turntable or for an elevator.
7. Reset could be:
• Rotate back (for Turntable) • Lower (for Elevator) • Elevate (for Lowerator) • Elevate and Rotate back (for Elevator Turntable) • Lower and Rotate back (for Lowerator Turntable)
Comments Nature of Buffer
The Buffer of these elements is generally a multi or single part forward conveyor.
Breakdowns A Breakdown of this section will not affect the pieces of automation in its Zone.
1
2
3
4
5
6
7
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Using these interfaces the user could click on links and have access through a database to the logic explanation (diagrams + its explanation) and draws. Simple animations for each element could be also presented. The standard approach to obtain these diagrams and simulation issues should also be included in an introduction.
Develop such support is time consuming and the real value added must be evaluated before investing in such work. Develop the framework of the Specification Document means that the content of the documentation is fixed and fully satisfies the Ford simulation specialist. May be further work should be done on this issue before developing a user friendly interface.
7.4 Summary of the Specification Document
A summary of the development of the Specification Document is presented in this section.
7.4.1 Summary of Work
The aim of the Specification Document is to support the understanding of the behaviour of the real systems components, in order to represent them accurately in a simulation model.
The Specification is decomposed in several sections:
One Section is dedicated to present the standard approach to develop the element logic explanation. This includes the presentation of the relevant level of logic and the elements boundaries. The level of logic presented was not the deepest level that was possible to represent. The level chosen is deep enough to match the real system element logic with the logic of the simulation elements.
In a second Section each elemental component of the real system were studied using the selected boundaries and level of logic. When observing some apparently dissimilar elements (such as Turntable/Elevator) the logic was analysed to find a common pattern. 12 elements were studied and presented.
In third Section general issues relating to Ancillary Logic was presented such as Breakdown or Changeover. Special cases for Machining lines have been presented. Some elements have special logic in special situation; in this section this special logic is presented.
7.4.2 Difficulties Encountered
During the development of the Specification Document the following difficulties and problems where encountered and solved:
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• Define a common vocabulary that relates to the simulation model and the real system. As presented before the vocabulary used was an issue at this stage of the work the vocabulary was fixed and defined in a glossary included in the Specification Document.
• The identification of a common structure of the flow diagrams was an issue because what was observed in reality differed from case to case. The actions performed in reality by an element can differ but the underlying logic principles remain constant. The difficulty arises when translating these differences into common patterns of logic flow.
• It is less difficult to explain what occurs in the real life orally, a textual transcription is so possible. However the length of the descriptions would make them indigestible. The diagrams are produced to reduce the text and make the explanation friendlier. The sketches with colour coding assist in conveying this message.
These three important difficulties were overcome. This have enabled the information contained in the Specification Document to be communicated as simply as possible without damaging the message.
7.4.3 Limitations of the Specification Document
This document is the first attempt of the specification of the Lion machining lines. There are therefore some intern weaknesses and possible improvements:
• The framework of this document is in Word format which occupies a lot of pages. A more user friendly solution is obtainable using other frameworks.
• It is possible that there are logic components missing from this specification as a limited number of lines were observed. When people in the future use this document there may be gaps in the logic specified due to lack of total immersion in the real system.
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8 STAGE 4: IDENTIFY GAPS BETWEEN THE MACHINING LINES AND SIMULATION
The objective of this chapter is to compare the real system with the simulation logic. Here the value added is not only to identify gaps between the real system and the simulation logic but also to identify the similarities. Actually this could also be viewed as a validation of the simulation logic.
As the documented gaps and similarities between the simulation and the real system logic were parts of the deliverable for Ford. This gaps analysis is included in the Specification Document.
8.1 Identified Gaps and Similarities for each Element
For each element the real and simulation logic have been confronted. A table was used to have a quicker picture. Table 10 presents the analysis for the element presented in the chapter 7: Turntable-Elevator-Lowerator.
Table 10: Real System and Simulation Logic
Simulation logic Gaps In the simulation these elements are modelled with the same logic. The difference is only on the Cycle Time.
No gap
In the simulation model the element could load and unload part at the same moment.
In the reality this is not possible the Element needs resetting. This gap is small since the reset action does not take a significant amount of time.
The typical scenario of this element is to load a part, rotate, elevate or lower and if there is a space in its buffer to unload the part. After unloading a part the element return to its initial position. This logic is represented by the simulation. However the time required resetting is not directly represented in the simulation. The simulation uses the Cycle Time to model this reset time. Actually the reset time is included in the Cycle Time. The simulation element can unload and load at the same moment which is in reality impossible. This means that there is a little delay between load part and unload part actions. This is not represented in the simulation. However the delay is not significant for the simulation since it is few seconds.
Such analyses were done for each of the 12 elements presented in the Specification Document. It enables to identify what is similar what is different and quantify the difference.
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8.2 Special Cases
The CNC Cell was the more critical element to study. The CNC Cell is a group of machine(s) and automation including CNC Machine, Pre-stop, Buffer and Gantry. Two main types of cells have been identify, one for the cylinder head machining line and one for the crankshaft machining line.
Figure 30: CNC Cell of the Head (Left) and CNC Cell of the Crankshaft (Right) Machining
lines
These Cells are modelled as a Transfer Machine, different gaps were identified. Table 11 presents the analysis.
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Table 11: Real System and Simulation Logic Gap Obse rvation for Gantry
Simulation logic Gaps In the simulation Gantry with its Pre-stop, Buffer and Operation(s) is represented like a Transfer Operation. This means that the logic loads & unloads a part at the same time when a part is at the Pre-stop and a Space is at the Buffer.
The Crank Gantries could load when the Buffer is full. This gap makes that 1 or 2 parts enter into the element in the reality and not in the simulation.
The head Gantry follow the logic without gap.
A Transfer Operation CNC Machine always has parts inside except during a manual intervention
No gap
Loading and unloading is done at the same moment.
For the Head Gantry this is right as there is a part at the Pre-stop when the Gantry unloads to its Buffer. If there is no part at the Pre-stop the Gantry will unload without loading a new part.
For the Crank Gantry, the load and unload Buffer positions are at opposite ends of the Cell. This means that the gantry loading and unloading actions are carried out with a significant time delay between them. Between the Pre-Stop and Buffer positions there could be several machines which will increase the delay.
Breakdowns Head Gantry supports the CNC cell and several machines are in parallel doing the same operations. If one machine breaks down all Cells will not be blocked but the flow will be reduced. The throughput time for the same number of parts through the CNC Cell will increase.
Crank Gantry supports the CNC Cell; several CNC Machines are one after the other. This means that if one of them breaks down the whole cell will be blocked.
In Both cases if the gantry breaks the CNC Cell will be blocked.
Whatever component breaks down, all other component of the Cell will complete their operation Cycle Times.
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8.3 Summary of Identifying Gaps between the Machining Lines and Simulation
The comparison of the real system and the simulation logic was not just to identify gaps but also to identify the similarities. This enables to picture what are the strength and the weakness of the simulation.
All the gaps were not always significant for the simulation. As mention in the literature review a simulation model is never 100% representative of the reality (Brade, 2000). The work presented in this section is included in the deliverable for Ford. Analysis about these gaps must be done by simulation specialist at Ford to evaluate if simulation requires modification or not. Actually, it could appear that some gaps necessitate developing complex logic in the simulation model and so requiring modification of the FIRST interface. The amount of work necessary to bridge gaps must be balanced with the real value added for the simulation. Such decision required simulation specialist expertise and cannot been presented here.
The next table gives an overview of the 12 real elements logic compared with the 5 simulation elements used to model it.
Table 12: Gap and Similarities Summary
Real Element
GapTurntable Elevator
LoweratorDivert Operation
Transfer Operation
Orientator OK
Elevator OK
Elevator Turntable
OK
Turntable OK
Lowerator Turntable
OK
Lowerator OK
Swing GateAdd
Frequency Event
DivertCheck
Scenario Cycle Time
Manual Operation
OK
Machine Operation
OK
CNC Cell
Crank Gantry (Load if
Buffer Full)Transfer Machine
Washing Machine
Simulation Element
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Comparing like with like (same level of logic and same boundaries), 8 real elements are modelled with the right logic in the simulation model and 4 elements have some differences.
This enables to conclude that the simulation model represents the reality closely for the majority of the elements. However, there are a number of elements where greater attention should be paid when modelling. This is the case for the Swing gate, the Divert, the CNC Cell and the Transfer machine. More details are provided on these cases in their respective sections in the Specification Document.
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9 KEY FINDINGS AND DISCUSSION
The methodology has been followed, the precedent chapters described and analysed the work realised at each stage of the work. This chapter summarises the keys findings for the problem statement, the literature review and the 4 stages of the work. This chapter also discusses and analyses the benefits of this thesis.
9.1 Key Findings and Work Review
For each of the steps of the work, this part presents the key findings and review the work realised.
9.1.1 Problem Analysis
As presented in Chapter 2, Ford has developed powerful interface (FIRST) which eases and speeds up the simulation utilisation for the facilities management of the Lion machining lines.
The development of this interface is based on interpretation of logic of the real system (V8/V6 machining lines). However different interpretation of the real system is possible, this affects the credibility of the simulation models and the level of confidence that certain simulation user has. Actually users could have another interpretation of the real system.
Ford simulation experts noticed gaps between simulation and the real system. The logic of the simulation model could not match the real system logic. These gaps also affect the simulation credibility.
Addressing the simulation to non-specialist, Ford has to develop tools to help them understand the real system logic and the simulation.
These three main points are the source of the requirement to sponsor the thesis research. To deal with these issues, the initial requirement of Ford was to develop a documentation which presents the specification of the real system for the simulation utilisation.
9.1.2 Research
Research on the literature has been done at the beginning of the Thesis and has been maintained update. This literature review enables to:
• Quantify the importance of real system logic understanding at the building stage and validation stage
• View some recommended content for such documentation • View some recommended simple support
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This research and the problem analysis enable to identify the aim and the objectives of the Thesis. The aim of the thesis is to help Ford improve the simulation model for the V6 and V8 machining lines through a Specification Document development. In order to achieve this, the following objectives are identified:
1. Understand and represent the logic of the machining lines
2. Validate the logic and its representation
3. Develop the Specification Documentation
4. Identify gaps between the machining lines and simulation models
9.1.3 Understand and Represent the Logic of the Mac hining Lines
The real system understanding and analysis was longest part of the work. Many visits to Dagenham were necessary.
Having identifying all pieces of equipment; a first draft of flow diagrams were provided for each of them. This first draft is based only on the observation done on the cylinder head machining line. Then a standard approach was followed to establish a second draft. This approach enables to set levels of logic and hierarchies the pieces of equipment. This approach was common for the 12 pieces of equipment identified. The work realised at this stage allow raising a number of issues which required validation. The second draft is based on the observation done on all the Machining lines. Figure 31 summarises the diagram drafts and their inputs.
Figure 31: Diagram Drafts (First and Second)
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The methodology proposed at the chapter 4 was followed. However, the development of two diagram drafts required time and may be the second draft approach should have been followed since beginning of this stage. Actually this approach was more systematic and efficient to obtain homogenous diagrams. In other hand it is not possible to build diagrams without knowing well the real system that is why the first draft was necessary. Nevertheless the first draft was too much polished and this was not necessary. This stage was the longest and required more attention.
9.1.4 Validate the Logic and its Representation
The logic validation was done by interviews with control system specialist and simulation specialist. This enabled to present the results obtained so far and to compare with the deepest logic (control system) and the simulation logic. This stage was a key stage to finalise the approach to build the final diagrams.
Three main findings were provided:
• The diagrams represented the reality.
• The simulation is time based and pays attention to processes which spend time. The level of logic required by the simulation was presented in the diagrams.
• The simulation element boundaries are special. It is not “spontaneous” boundaries. Using these boundaries simplify dramatically the real system analysis and solve the problem of the interaction between of the pieces of equipment.
At this stage the real system was understood and its logic was validated. Secondly the approach (level of logic and boundaries) to represent the logic was validated. It is important to highlight that a deep level of logic had been understood, and then has been adjust to match the simulation expectation. Figure 32 summarises the diagram drafts and their inputs.
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Cylinder Block
Machining
Lines
Crankshaft
Machining
Lines
Cylinder Head
Machining
Lines
First Diagram
Draft
Second Diagram
Draft
Final Diagram
Draft
Cylinder Block
Machining
Lines
Real system Analysis Validation
Input Input
Simulation
Boundaries
Simulation
Level of Logic
Figure 32: Diagram Drafts (First, Second and Final)
The stage matches with the methodology set at the chapter 4. Here again the diagram obtained from the stage before were polished. This does not really bring a real value added, it was an extra work. The time necessary to polish it should have been used to go further in the work. On the other hand this polishing enables to raise issues and force to have a deeper understanding of the real system logic. Actually the validation stage enables to notice that the logic understanding was deeper that the simulation needs. This is strength since the real system was fully understood but it is a weakness since the spent time could have been used to develop more other stages.
9.1.5 Specification Documentation Development
This stage was to develop the deliverable for Ford. This stage summarises the Specification Document structure, the assumption made, the difficulties and the limits of the Specification Document. Examples of the real logic explanation (diagrams, explanations and drawings) are included.
The main finding is the development of the document itself. This document is focused and detailed. An important issue that needed to be overcome was to stay simple. This document needs a lot of explanations and it was difficult to stay simple without damaging the message. Secondly the volume of the document is important as today the framework of the document is based on Microsoft Word.
During the thesis, the attention paid to the framework of the Specification Document decreased. It appeared that it was more relevant to develop a strong content with a simple framework than a medium content with friendlier interface. Considering this and the time restriction, it was chosen to focus on the content
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and used a simple framework. A proposition of a framework based on web or PDF is presented at this stage. A proper framework could solve the problem of the Specification Documentation volume.
Furthermore, the deliverable is a first attempt of the Specification Document. Future user could identify some lack or other items that should been included. Further work could be required after several utilisation of the document. Develop a nice framework is less important than finalised the document itself.
From the review of the stage 1 and 2, it appears that time could have been saved. The saved times could have been used to review more the Specification Document with specialists. This could have enabled to finalise more the deliverable. However this was not really included in the thesis scope and the main sponsor was fully satisfied.
9.1.6 Simulation
From interviews with Ford employees, it appeared that few people really understand the simulation model assumption. Typically for a piece of equipment the simulation boundaries need to be explained. Today no paper explains these boundaries and all other simulation assumptions.
FIRST is a simple tool, a web based manual is available to use it; however nothing about the assumption is available. Some of section of the Specification Document will be really useful at the point.
9.1.7 Identify Gaps between the Machining Lines and Simulation
In the initial subject, only gaps were mentioned, these gaps which generated the basic need to sponsor this thesis. However the precedent findings presented that the simulation has a lack of credibility. Gaps were presented and documented in this stage but the similarities were also presented. Actually that is the similarities between the real system and the simulation logic that give more credit to the simulation not the gaps.
This point makes that the initial approach was more pessimistic since the research were done to find the gaps and not the similarities. It appears retrospectively that this approach was good since it forced to go deeper into the logic understanding. The logic understanding has been done deeper than the simulation required. Finally this reinforced the credit of the logic so the credit of the simulation on the similarities.
The main finding of comparing the real system to the simulation logic was that the simulation model represented the reality closely for the majority of the pieces of equipment. However there were a number of elements where greater attention should have been paid. This is the case for 4 pieces of equipment.
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Local gaps were identified for these 4 pieces of equipment. What the impact of these gaps in is the simulation model will depend of the Lines. Actually one piece of equipment is more used in one line than another (e.g. Gantries are more used in the crankshaft than in the cylinder block machining line). The global impacts of local gaps could be different from one line to another. The analysis of the global gaps is not included in the scope of the thesis. The stage is the utilisation of the deliverable by Ford simulation specialist.
Here again, the potential saved time from the stage 1 and 2 could have been used to compare deeper the Specification Document with the simulation model. However this comparison would require more time spent with specialist and according to their availability it is not possible to insure that this comparison could have been done.
9.2 Discussion
The main benefits of the Specification Document are based on its future utilisation. These benefits are linked with the identified problems. This Document has also some limits which are directly linked with its development.
9.2.1 Different Interpretation
The Specification Document defines the simulation approach. It gives the level of logic expected for the simulation and the boundaries of the pieces of equipment. Following the simulation approach the derivative of interpretation are reduced. Actually this approach was followed to represent the logic of 12 pieces of equipment and no real possible derivatives were highlighted.
The Specification Document does not reduce the derivative to zero. However the Specification familiarises user with the simulation approach and guides the user understand the real system logic.
Figure 33 represents the issue presented above. Before simulation user interpreted the real system through their own observations and their experiences. Using the Specification they will interpret the real system through a common point of view. This does not mean that real system observation is not necessary but it means that the approach to watch the real system is similar. This will reduce the possible variation of interpretations. Users will look the same system with the same approach.
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Specification
Document
Interpretation 1 Interpretation 2 Interpretation 3 Interpretation n
Real System
Logic of the Lion
Machining Lines
Interpretation 1 Interpretation 2 Interpretation 3 Interpretation n
Real System
Logic of the Lion
Machining Lines
Interpretation Gaps Interpretation Gaps Interpretation Gaps
Interpretation Gaps
Reduced
Interpretation Gaps
Reduced
Interpretation Gaps
Reduced
One Approach Stadardised
Without Specification Document
With Specification Document
Figure 33: Different Interpretation Gaps
Interpretation of the real system is necessary in the simulation, if simulation users have a common interpretation of the real system the comparison of the real system and the simulation logic will be easier as users compare “apple with apple”. The reduction of interpretation gaps gives to user the benefits to understand better the simulation model and to identify the similarities and the gaps between the reality and simulation model logic. This is the first step to give more credibility to the simulation model since is the similarities which give more credit to the simulation model.
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Same interpretation supports people to identify the same similarities and the same gaps. The advantage is that people will understand better similarities/gaps of the model. They will have a stronger confidence on some points and a better idea of the rooms of improvement for the simulation models.
9.2.2 Gaps between Real System and Simulation Logic
From the Specification Document rooms of improvement are identified. Gaps reduction makes the simulation closer to the reality. Gaps between real system and simulation logic have been identified locally for certain pieces of equipment; the impact of these local gaps on complete model has not been done. This requires simulation specialist expertise. Simulation specialists using the Specification Document can improvement the simulation as they have local identified gaps. This answer to the first aim which is to help Ford to improve the simulation models for the lion machining lines.
Figure 34 gives an overview of the gaps reduction and is decomposed in 3 parts:
• Before: Simulation specialists had identified gaps; these gaps were based by the comparison of their own interpretation compared to the simulation models. Nothing was really documented and general gaps were highlighted.
• Thesis Work: Applying a standardised approach the Specification has been produced during this thesis. Gaps and similarities have been identified and documented. The Specification Document reduces the variation possible of the interpretation since people look in same things with a common approach. This is a value added of the work realised during the thesis. Users see the same local gaps and similarities.
• Future Utilisation: Using the first attempt of the Specification Document, simulation specialists could estimate the influence of local gaps in the global simulation model. According their decision of bridging the gaps or not (balance value added and amount of work) the simulation can be improved reducing certain of gaps. Having feedbacks on the Specification Document, this document could be improved (more details, more research, and review of the scope). This is basically the room of improvement for the Specification Document it self. Here two points are clear: simulation as the potential to be improved and the Specification Document as well. As they are link feedbacks are necessary to apply continuous improvement on both.
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Gaps
Gaps
Gaps
Figure 34: Gaps Reduction
From this discussion two points are noticed:
• Simulation as the potential to be improved applying the Specification Document
• Using the feedbacks of its utilisation, the Specification Document can be improved as well. As simulation and Specification Document are linked; feedbacks are necessary and give the opportunity to apply continuous improvement on both.
This thesis enables to establish a first attempt to provide a Specification Document of the real system for the simulation utilisation. In the future the document needs to be updated and improved to enable cyclic simulation improvement. The work realised on the Thesis enables to generate the opportunities of continuous improvement of the simulation tools at Ford. This will required more work on the simulation tools and on the document itself.
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9.2.3 Non-specialist User
The future utilisation of the Specification Document can change the simulation approach. As Ford simulation specialists want to broaden the number of users of the simulation to non-specialists. Today, only the web based manual helps users use FIRST. The utilisation of the Specification Document is an opportunity to help them understand the real system and the simulation approach. Figure 35 pictures the benefits of implementing the Specification Documentation.
The simulation utilisation required amount of information from number of sources. In the actual trend, information is found in the documentation (Layout, Operation Standard, Quality Data), through visits of the lines and discussions with simulation specialists. The future trend can use the Specification Document. The benefit is the increase the documentation to support the simulation utilisation. In parallel, it reduces the number of visit of the lines and discussion with simulation experts.
Figure 35: Future Trend of the Simulation Utilisati on
Furthermore, this also sustains the simulation knowledge at Ford. Actually, the Specification Document groups the knowledge of the real system required for simulation. Today few people at Ford have this knowledge. The Specification Document could also be considered as a knowledge management tool.
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9.2.4 Specification Document Benefits Summary
The main benefit of Specification Document developed during the thesis is to picture what are the gaps and the similarities between the real system and the simulation logic. Secondly the Specification Document reduces the possible variation of the interpretation of the real system logic since it proposes a common approach. Its utilisation has the potentials to:
• Improve the simulation model itself reducing the identified gaps
• Improve the simulation utilisation. Actually, the Specification Document reduces the interpretations gaps and supports the understanding of user of the real system; therefore this document promotes the simulation utilisation.
It is notable that the Document has been developed on one specific example based on the analysis of Lion machining lines in Dagenham. However the document is applicable for all the factories of Ford. Actually, the standardised approach matches with the Ford simulation tool and with all real systems. Based on this work, Ford could expend the Specification Document for many lines.
Relating to the benefits described in this section, the Specification Document could be used by different people at different stage of the simulation utilisation.
• Model Construction
Specification Document supports the model building as a documentation to understand quicker the real system and the simulation approach. For instance people do not necessary need to visit the plant to see how work a Turntable since it is described in the document. Furthermore, people do not necessary need to ask to simulation specialists what the element approach, element boundaries and level of logic required are. Finally, using the Specification Document if two people build a model, the models are similar since the Specification Document specifies what real element corresponds to what simulation element.
• Model Validation
Specification Document is a validation tool. Using the Specification Document, Ford engineers can validate the model. Actually, the similarities and the gaps are documented for the elements and Ford specialists can evaluate the impact on the global models. In the future, Ford has the opportunities to develop this document and cyclically review the simulation models which is a chance to contribute to the continuous improvement of the simulation.
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• Model Utilisation
Specification Document reduces the risk of the variation of the interpretation of the real logic. During the model utilisation, user has a better understanding of the simulation approach. The user has a better confidence on the model since the specification Document pictures what the logic of the real system is and what the logic of the simulation is.
9.3 Specification Document Limits
Different limits were noticed during the work:
• As presented above the content of the Specification Document is not fixed yet. Many utilisations with several users need must be done, then feedbacks must be organised to finalise the content of the Specification Document.
• The Specification Document could have a “moving content” as improvement is link with the simulation improvement; if the simulation is improved the Specification Document needs to be improved. The Specification Document will have to be updated.
• Today due to the time restriction and the fact that the content is not finalised the framework is really simple. This does not make the Specification Document friendly to use.
• Today, the Specification Document is specialised. More introductions should be necessary to make it more accessible, but this will increase its volume.
The development of the Specification in the future could bring two risks:
• A dramatic expansion of the volume of the documentation.
• Requirement of a large amount of work to finalised the content, develop a framework and unable to have an updatable document.
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9.4 Specification Document Summary Analysis
To summarise this part, a Specification Document analysis is done through the SWOT analysis (Strength, Weakness, Opportunities and Threats). This tool is used to simply analyse a situation. The SWOT presents the summary of the chapter.
Figure 36: SWOT Analysis
SWOT for the Specification Document Strength Weakness
The Document gives a view of the simulation gaps and similarities with the reality.
The Document supports the simulation improvement.
The Document promotes the simulation utilisation improvement.
Content not fixed yet, needs feedbacks from several utilisations with several users.
Need to be updated.
Simple framework makes it unfriendly.
Specialised content.
Opportunities Threats Develop a continuous improvement process for the simulation tools.
Broaden the simulation users.
Knowledge management tool.
Increase dramatically the volume of the documentation.
Large amount of work to finalised the content, develop a framework and unable to have an updatable document.
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10 CONCLUSIONS
This last chapter is the conclusion of the thesis; three main sections are presented: the summary of the key findings, the limitations and the recommended future work.
10.1 Summary of Key Findings
The aim of the thesis was to help Ford improve the simulation model for the V6 and V8 machining lines through a Specification Document development.
To deal with this subject four objectives were set and decomposed the work into four stages:
1. Understand and represent the logic of the machining lines
2. Validate the logic and its representation
3. Develop the Specification Documentation
4. Identify gaps between the machining lines and simulation
A literature review enabled to identify some contents of the Specification Document and to select the logic representation support. This review revealed that Specification Document is new and required a thesis to be developed.
10.1.1 Understand and Represent the Logic of the Ma chining Lines
This stage enabled to identify 12 pieces of equipment used in the machining lines. Each piece of equipment was studied separately. The logic was understood for all of them and the flow diagram was selected to represent their logic. Two flow diagram drafts were done, the first one from the observation on cylinder head machining line and the second one from the observation of all the machining lines. The second draft applies a standard approach to built diagram and is based on two levels of logic (level of detail of the diagrams). A hierarchy was provided and shown families of piece of equipment. The work realised at this stage allowed raising number of issues which required validation.
10.1.2 Validate the Logic and its Representation
The logic validation was done by interviews with control system and simulation specialists. Three main findings were provided:
• All the pieces of equipment logic were valid.
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• The right level of logic had been set and this level was fully represented in the second draft of diagram.
• The boundaries of the piece of equipment in the simulation were not spontaneous and required explanation. Apply this boundaries dramatically simplified the logic explanation.
At the stage the real system was understood and its logic is validated.
10.1.3 Development of the Specification Document
This stage was the development of the deliverable itself. As this document is specialised, it required a lot of explanations and it was difficult to stay simple without damaging the message. The Specification Document is the compilation of diagrams which represents the machining line logic. The volume of the document is important since today the framework of the document is based on Microsoft Word.
10.1.4 Identify gaps between the machining lines an d simulation
The main finding was that the simulation model represents the reality closely for the majority of the pieces of equipment. However there are a number of elements where greater attention should be paid. This is the case for 4 pieces of equipment.
10.2 Benefits
The main benefit of Specification Document is that it presents what the gaps and the similarities are between the real system and the simulation logic. Furthermore, the Specification Document reduces the variation of the interpretation of the real system logic since it is a guide to interpret the real logic.
Using this document Ford can:
• Improve the simulation model itself reducing identified gaps.
• Improve the simulation utilisation. Actually, the Specification Document reduces the interpretation variations and supports the understanding for the user of the real system; therefore this document promotes the simulation utilisation.
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10.3 Limitations
The limitations of the work are the limitation of the Specification Document itself. Actually this document is a first attempt and potential improvements could be identified by using it.
This first attempt needs to be used by different simulation specialists, their feedbacks is necessary the finalised the content of the Specification Document. However, this stage was not included in the scope of the thesis.
During the thesis, more attention was focused on a strong content. Therefore the Specification Document has a simple framework today. This makes it less friendly to use.
10.4 Recommended Future Work
As mentioned in the limitations the work realised during the thesis is a first attempt for developing a Specification Document. Therefore, there are some intern weaknesses and possible improvements which required further work.
As mentioned, the content should be reviewed after several utilisations of the Specification Document. Utilisations could raise the review of the scope of the document. Today the document is focused on the real system logic. From the literature review, other content had been highlighted such as aim and objectives of the simulation project. Furthermore, more details of the simulation model itself could be added. Actually, from interviews with Ford employee, it appeared that few people have a good overview of the simulation assumptions. The recommended future work is to collect feedbacks after a time of the Specification Documentation implementation, then organise these feedbacks, and review the document scope and the content with Ford simulation specialist.
The second room of improvement is to develop the framework of the Specification Document. It is logical that after having fixed the content of the Specification Document, the final framework should be developed. This framework should be enough flexible to unable to keep update the Specification Document. This framework should match the Specification Document scope. Today, this document is focused on the specification of the real system for the simulation. As mentioned above, the trend is to increase the number of simulation user. This document should give an introduction to the simulation for non initiated people and the framework should take this in account.
Ford has developed powerful interface (FIRST) this means that simulation user does not need to have as much documentation as the literature review proposed. Actually the literature review proposed a large amount of documentation for building a model from scratch without an easy-to-use interface. Therefore, the documentation that authors proposed should be
Conclusion
86
focused on addressing the requirement for simulation specialist people. From the work realised at Ford, it appears that the interfaces have a weakness in the lake of documentation on their development, their logic and the assumption made. This should be documented. The Specification Document developed here is a chance to review the simulation at Ford. Tomorrow, if Ford wants to develop this, they should redefine what the aim of this document is. If Ford want to broaden the simulation users, they should integrate more details about the simulation interface and fully documented the related issues. To have the specification documentation in line with standard commented in literature, Ford should review the scope and invest to develop the Document. Findings from the thesis would recommend developing a document which broadens the simulation users.
Developing this work Ford could have the opportunity to expand the number of user of simulation and to set a standard approach to continuously improve their simulation model. However, the amount of work necessary to develop the Specification Document must be balanced with the benefits for the simulation. Finally, the Specification Document will be a chance to contribute to the continuous improvement of the manufacturing facilities at Ford.
References
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REFERENCES Andrew R. Gilman Renee M. Watremez Istel, (1986) “A tutorial on SEE WHY and WITNESS” 1986, Winter Simulation Conferences, pp. 3-4 Brade D. (2000) “Enhancing modelling and simulation accreditation by structuring verification and validation results” 2000, Winter Simulation Conference, pp. 2-7 Carrie A. (1988) “Simulation of Manufacturing Systems” 1988, John Wiley & Sons, pp. 6-7 Carson J. (2005) “Introduction to modelling and simulation” 2005, Winter Simulation Conference, pp. 5-6 Chung C. 2003 “Simulation modelling hand book: a practical approach” 2003, Industrial and Manufacturing Engineering Series, series editor Hamid R. Parsaei CRC, pp. 20-22 Gass S. (1984) “Computer Model Documentation” 1984, Interfaces, vol. 14, no. 3, pp.84 Kirner T. and Adid J. (1997) “Inspection of software requirements specification (SRS) documents: a pilot study” 1997, SIGDOC Snowbird Utah USA, pp. 9 Ladbrook, J. and Januszczak, A (2001) “Fords PowerTrain Operations – Changing the Simulation Environment.” UKSIM 2001, Conference of the United Kingdom Simulation Society pp.81-87 Ladbrook J. and Winnel A. (2004) “Collaborative Component-based simulation: Supporting the Design of Engine Assembly Line” 2004, Winter Simulation Conference, pp. 2-9 Law A. (2005) “Simulation Modelling and Analysis” 2005, Mcgraw-Hill, pp. 10-11
References
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Nordgren, W.B. (1995) "Steps for proper simulation project management", 1995, Winter Simulation Conference, pp. 68. Oscarsson J. and Urenda Moris M. (2002) “Documentation of discrete event simulation models for manufacturing system life cycle simulation” 2002, Winter Simulation Conference, pp. 7-9 Robinson S. (1994) “Successful simulation: a practical approach to simulation projects” 1994, Mc Graw-Hill Book Company, pp. 6-7, pp 29-35 The Chambers Dictionary 1990, Chambers Harrap Publisher
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APPENDIX
Appendix A This appendix presents a part of the first draft diagram for the machining lines.
Appendix
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Appendix
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Appendix B
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Appendix B This appendix present the first draft of the common piece of equipment diagrams. All diagrams are not represented.
Appendix B
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97
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Appendix C
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Appendix C This presents the simulation logic for several elements.
Operation:
The logic of the simulation of this element is:
1. Initially the operation is idle 2. If there is a part at the pre-stop operation pulls it (load it) 3. Then the operation “operates” 4. If there is a space in the buffer (conveyor is not full) operation pushes
part to the buffer (unload part to the buffer) 5. The element return to its initial position
Remark: the buffer is passive in this approach. It does not need to make any action.
Bend – Step:
The logic of the simulation of this element is:
1. Initially the Bend-Step is idle (in loading position and ready to load a new part)
2. If there is a space in the buffer (conveyor is not full)? Yes, goes further else wait
3. If there is a part at the pre-stop, Bend-Step pulls it (load it) 4. Then the Bend-Step pushes part to the buffer 5. The element return to its initial position
Remark: the buffer is passive in this approach. It does not need to make any action.
Turntable – Elevator – Lowerator:
The logic of the simulation of this element is:
1. Initially the Turntable – Elevator – Lowerator is idle 2. If there is a part at the pre-stop, Turntable – Elevator – Lowerator pulls it
(load it) 3. If there is a space in the buffer (conveyor is not full)? Yes, goes further
else wait 4. Then the Turntable – Elevator – Lowerator pushes part to the buffer 5. The element return to its initial position
Appendix C
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Remark: the buffer is passive in this approach. It does not need to make any action.
Divert: (this element change the route of a part, typically it could convey straight a part or change it route rejecting it)
The logic of the simulation of this element is:
1. Initially the Divert is idle 2. If there is a part at the pre-stop, Divert pulls it (load it) 3. If part is ok, goes further else reject it. 4. If there is a space in the buffer (conveyor is not full)? Yes, goes further
else wait 5. Then the Divert pushes part to the buffer 6. The element return to its initial position
Transfer Operation:
The logic of the simulation of this element is:
1. Initially the Operation is idle 2. Is part at the pre-stop? Yes, goes further else waits. 3. If there is a space in the buffer (conveyor is not full) operation pulls part
which is at the pre-stop (load it) and pushes another part to the buffer 4. Then the operation “operates” 5. The element return to its initial position
CNC Cell:
CNC cell are composed by a gantry, operation(s) and buffer. CNC cells as modelled as Transfer Operation.
Appendix D
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Appendix D This appendix is the deliverable submitted at Ford.
Lion Machining Lines Specification
Including Comparison with the Respective Simulation Models
Written and Compiled by:
Matthieu Griffon Cranfield University
In conjunction with: John Ladbrook
Ford Motor Company UK
Appendix D
I
Specification Document Contents
1 Introduction.................................................................................................. 1 1.1 Aim....................................................................................................... 1 1.2 Objectives ............................................................................................ 1 1.3 Real Element List and Definitions......................................................... 1
1.3.1 Real Element Definition................................................................. 2 1.4 Key Term Definitions ............................................................................ 3
2 Logic Analysis Approach ............................................................................. 4 2.1 Assumption .......................................................................................... 4 2.2 General Simulation Approach .............................................................. 4
2.2.1 Focus of the Simulation................................................................. 4 2.2.2 Logic Level .................................................................................... 5
2.3 Element Boundaries ............................................................................. 5 2.3.1 Simulation Boundaries .................................................................. 5 2.3.2 Updated Element List .................................................................... 8
2.4 Flow Diagram Definition ....................................................................... 9 3 Real System and Simulation Logic ............................................................ 10
3.1 Gap Section Conveyor ....................................................................... 10 3.1.1 Real System Logic Interpretation ................................................ 11 3.1.2 Gaps between Simulation Logic and Reality ............................... 11
3.2 Turntable-Elevator-Lowerator............................................................. 12 3.2.1 Real System Logic Interpretation ................................................ 13 3.2.2 Gaps between Simulation Logic and Reality ............................... 14
3.3 Divert.................................................................................................. 14 3.3.1 Real System Logic Interpretation ................................................ 15 3.3.2 Gaps between Simulation Logic and Reality ............................... 20
3.4 Swing Gate......................................................................................... 20 3.5 Manual & Auto Operation ................................................................... 20
3.5.1 Real System Logic Interpretation ................................................ 21 3.5.2 Gaps between Simulation Logic and Reality ............................... 21
3.6 Transfer Machine ............................................................................... 22 3.6.1 Real System Logic Interpretation ................................................ 23 3.6.2 Gaps between Simulation Logic and Reality ............................... 24
3.7 Gantry ................................................................................................ 24 3.7.1 Real System Logic Interpretation ................................................ 24 3.7.2 Gantry Logic Summary ............................................................... 34 3.7.3 Gaps between Simulation Logic and Reality ............................... 35
4 General Cases and Specific Observations ................................................ 36 4.1 General Logic Issues.......................................................................... 36
4.1.1 Breakdowns ................................................................................ 36 4.1.2 Antenna....................................................................................... 36 4.1.3 Frequency Event ......................................................................... 36
4.2 Specific Issues from Machining Line Analysis.................................... 37 4.2.1 Changeover................................................................................. 37 4.2.2 Zones .......................................................................................... 37 4.2.3 Washing Machine........................................................................ 37 4.2.4 Crankshaft Buffer ........................................................................ 37 4.2.5 Specific Crank Gantry - OP140 in Head...................................... 38
Appendix D
II
4.2.6 Elevator 2 Parts........................................................................... 39 4.2.7 Turntable – Elevator - Lowerator Reset ...................................... 39 4.2.8 Orientator Could Have Two Different Logic Patterns .................. 39 4.2.9 Crankshaft Gantry Special Logic: OP100.................................... 39 4.2.10 Crankshaft Gantry Special Logic: OP200.................................... 40
5 Summary of the Gaps................................................................................ 41 6 Conclusion................................................................................................. 42
6.1 Summary of Work............................................................................... 42 6.2 Difficulties Encountered...................................................................... 42 6.3 Limits of the Specification Document ................................................. 42
Appendix D
III
List of Figures
Figure 1: Simulation Element Boundaries .................................................................. 5 Figure 2: Real Element “Spontaneous” Boundaries ................................................... 6 Figure 3: Simulation Boundaries................................................................................. 6 Figure 4: Simplified Element List ................................................................................ 8 Figure 5: Microsoft Visio flow Diagram Components .................................................. 9 Figure 6: Element and Flow Diagram Colour Coding ................................................. 9 Figure 7: Diagram of Orientator .................................................................................10 Figure 8: Turntable Elevator Lowerator Drawings .....................................................12 Figure 9: Divert Drawings ..........................................................................................14 Figure 10: Diagram of Divert Variations.....................................................................15 Figure 11: Manual & Auto Operation Drawing ...........................................................20 Figure 12: Transfer Operation Drawing .....................................................................22 Figure 13: Transfer Operation ...................................................................................23 Figure 14: Cylinder Head Gantry Drawing.................................................................24 Figure 15: Crankshaft Gantry ....................................................................................29 Figure 16: Operation 140 Drawing.............................................................................38 Figure 17: Special Elevator Drawing .........................................................................39 Figure 18: Diagram of Crankshaft Gantry Special Logic OP100................................40 Figure 19: Diagram of Crankshaft Gantry Special Logic OP200................................40
Appendix D
IV
List of Tables
Table 1: Real System Elements ................................................................................. 2 Table 2: Vocabulary Definitions .................................................................................. 3 Table 3: Road Section Conveyor...............................................................................11 Table 4: Simulation and Reality Gap Analysis for Gap Conveyor..............................11 Table 5: Flow Diagram for Turntable-Elevator-Lowerator ..........................................13 Table 6: Real System and Simulation Logic Gap Observation for Turntable,
Lowerator and Elevator ......................................................................................14 Table 7: Divert General Logic ....................................................................................16 Table 8: Divert Scenario 1: Inject Part Logic..............................................................17 Table 9: Divert Scenario 2: Part Goes Straight..........................................................18 Table 10: Divert Scenario 3: Reject Part ...................................................................19 Table 11: Real System and Simulation Logic Gap Observation for Divert.................20 Table 12: Manual & Auto Operation ..........................................................................21 Table 13: Real System and Simulation Logic Gap Observation for Manual & Auto
Operation............................................................................................................21 Table 14: Real System and Simulation Logic Gap Observation for Transfer Machine
...........................................................................................................................24 Table 15: Real System Logic for Gantry: Inject Scenario ..........................................25 Table 16: Real System Logic for Gantry: Through Flow Scenario .............................26 Table 17: Real System Logic for Gantry: Reject Scenario part 1...............................27 Table 18: Real System Logic for Gantry: Reject Scenario (Part 2)............................28 Table 19: Real System Logic for Gantry (Crankshaft): Injected Scenario..................30 Table 20: Real System Logic for Gantry (Crankshaft): Through Flow Scenario ........31 Table 21: Real System Logic for Gantry (Crankshaft): Reject Scenario (Part 1) .......32 Table 22: Real System Logic for Gantry (Crankshaft): Reject Scenario (Part 2) .......33 Table 23: Comparison of Gantry Logic between Machining Lines.............................34 Table 24: Real System and Simulation Logic Gap Observation for Gantry ...............35 Table 25: Gap and Similarities Summary ..................................................................41
Appendix D: Introduction
1
1 INTRODUCTION
This document presents a specification of the real system logic for the Lion Machining and Assembly Lines. The specification of the logic is how the machines and pieces of automation work in the real systems.
To build a simulation model an interpretation of the real system logic is necessary. A comparison of the real logic and the simulation interpretation is also presented.
1.1 Aim
The aim of this document is to allow a reader to understand the behaviour of components of the real systems in order to represent them accurately in a simulation model.
1.2 Objectives
To achieve this aim several steps have been followed:
• Defined an approach to specify the real systems • Break down the real system into elemental components • Diagram and explain the logic for each element • Compare key real system elements with logic with the simulation logic • Present general issues related to real ancillary logic and simulated
logic • Present specific issues for Assembly and Machining Line Logic and
simulated Logic
1.3 Real Element List and Definitions
In this section the Real system elements are defined and a glossary of terms is presented to be used throughout this document.
Appendix D: Introduction
2
1.3.1 Real Element Definition
Table 1 presents the real elements, for each a brief description is provided.
Brief Description
Forward ConveyorA section of conveyor that transports a part towards the end of the line.
Forward & Reverse Conveyor
A section of conveyor that transports a part towards the end or start of the line.
Road section ConveyorA section of conveyor where a part cannot stop to allow vehicles to cross the line.
Walk Over ConveyorA section of conveyor where a part cannot stop to allow people to cross the line.
Bend Conveyor A section of conveyor that changes the direction of the line.
TurntableA section of conveyor that actively accepts a part and changes its direction onto a set section of conveyor.
DivertA section of conveyor that actively accepts a part and changes its direction dependant on an input.
Spur ConveyorPlaten insertion or extraction using a straight conveyor attached to a Dirert.
OrientatorA section of conveyor that changes the orientation of a part relative to the conveyor.
ElevatorA Section of conveyor that raises a part from the starting conveyor level.
LoweratorA Section of conveyor that lowers a part from the starting conveyor level.
Elevator + TurntableA Section of conveyor that raises a part from the starting conveyor level and changes its direction onto a set section of conveyor
Lowerator + TurntableA Section of conveyor that lowers a part from the starting conveyor level and changes its direction onto a set section of conveyor
Forward ConveyorA section of conveyor that transports multiple parts towards the end of a conveyor.
Swing GateA section of conveyor that actively accepts a part and changes its direction dependant on an input.
Manual An operation carried out by a person on a stationary part.Continuously Moving Line An operation carried out by a person on a continuously moving platen.Kitting Loop An operation carried out by a person on multiple platens.
Cold TestAn operation that requires fixtures and fittings applied to the platen before an automated cold test sequence is performed.
Hot TestAn operation that requires fixtures and fittings applied to the platen before an automated hot test sequence is performed.
Robot An operation carried out on a stationary platen by a robot.Machine An operation carried out on a stationary platen by a Machine.
CNC Machining CellA group of CNC Machines including the overhead transportation system to load and unload parts.
Transfer Machine A multiple operation carried out on multiple platens at the same time.
Aut
omat
ion
Ope
ratio
n
Automatic
Semi Automatic
Manual
Real System Terminology
Single Part
Multipart
Table 1: Real System Elements
Appendix D: Introduction
3
1.4 Key Term Definitions
The table below lists and describes briefly the terms used in this document. The aim of this list is to prevent any miscommunication through the document.
Reading of this list prior to use of the document is recommended.
Term DescriptionAntenna RFID Read/Right Sensor.
AutomationAutomation is the generic family name for a piece of equipment that is only used in the transportation of the platen around the system.
Bend Used at the end of a section of line to change the direction of the platen.
Boundary A conceptual limit of an element of the real or simulated system.
Breakdown When a process does not complete due to a failure in the real system.
BufferA length of conveyor that can hold a number of parts, determined by the length before the next pre-stop or element.
ChangeoverThe process required to change an element prior to a change in derivative.
Check Buffer Space in the Gantry Buffer allocated for manually checking parts.CML Continuously Moving Line.Conveyor A piece of automation that transports platen through system.Conveyor Forward Conveyor transports part towards end of line.Conveyor Reverse Conveyor transports part towards beginning of line.Cycle An interval during which a recurring sequence of events occurs.
Cycle Time (CT)The time taken to complete a recurring sequence of events from a fixed starting and ending viewpoint.
Derivative A variation in the part from the generic base. Dog Tooth Component of a CML that hooks onto the platen.
ElementA piece of equipment or simulation module that is repeated throughout the real or simulated system that interacts with others to make a complete system.
Flow The movement of parts through the system.Index time The time platen is held in a pitch.Inject The process occurs to insert a part onto the main line.
InteractionThe exchange of information and/or parts between elements of the real or simulated system.
Load Load Action could be release pre-stop and in some cases start conveyor.
Logic The sequence of events that take place.
Operation (OP)The part in the operation is physically changed. Material could be removed in the case of the machining line. Components could be added in the case of the assembly line.
Marker Operation A small operation where part codes are inscribed on components
PartThis is a part in the system and has operations performed on it, such as: Cylinder Block, Cylinder head, Kitting Boxes, Pistons, Crankshaft or Camshaft.
Pitch A length of conveyor that can hold one part for an operation
PlatenThe part is mounted on a platen and transported through the real system on it.
Pre-StopStop on a conveyor before a component of an element of the real system that carries out a process on a part.
ProcessThe activity that occurs in the flow diagrams to changes or maintains the a part or an element in a busy state or changes from busy to idle.
Reject A process occurs to take a part from the line.Reset An element is set back to it's initial conditions.
SpaceA unoccupied section of conveyor that has the capacity for one or more parts.
Stop Device on element that stops the platen.Travel Time time for platen to move completely through one pitch.Wait The current state of the element is held.x Parts Number of parts is dependant on element under consideration.
Table 2: Vocabulary Definitions
Appendix D: Logic Analysis Approach
4
2 LOGIC ANALYSIS APPROACH
To describe the logic of the real system elements listed, it is necessary to present the simulation background.
Two main issues that dramatically impact on the representation of the real system element are:
• Depth of Logic • Element Boundaries
2.1 Assumption
The following assumptions where made when compiling this document:
1. When a scenario is observed on an element or group of elements, it is assumed that this sis a normal occurrence and can be applied systematically to those elements.
2. Observations of the logic of an element are applied to elements of the same type. Validation of the logic with every element of the same type is assumed not to be necessary as the elements look and behave the same. It is not physically possible within the time constraints to observe every element in every situation.
3. Input from Ford employees who know the lines was necessary as not all scenarios where directly observed. The input was validated, however it is assumed that the information given is correct and represents the real system.
2.2 General Simulation Approach
The simulation approach is specific and may require explanation to be understood. Roughly simulation models enable the observation and experimentation on the flow of parts in the real system. How parts travel through the Assembly and Machining Lines can be examined using simulation models.
2.2.1 Focus of the Simulation
Basically simulation looks for how parts travel from one operation to another, the travel time and the operation time. Simulation is time orientated and requires in information on the route followed by the parts.
In the case of Lion Assembly and Machining Lines, the simulation model needs to know:
• The part flow • Travel time between operations • Loading scenario for an operation • Unloading scenario for an operation • Operating Time
Appendix D: Logic Analysis Approach
5
• The impacts of ancillaries (e.g. Breakdowns and Changeover etc)
The logic of the complete system is composed of all scenarios, the part flow and the impact of ancillaries. A step in the logic takes a time equal a transportation time, operation time or time of an ancillary.
2.2.2 Logic Level
The level of the logic is the depth of the explanation of the real system behaviour. Simulation pays attention to events which spend time since these will impact the parts’ flow. The level of logic required for the simulation is a level where processes which takes time are described. This can be presented in following Turntable example:
Turntable Example
The Turntable loading process requires two steps:
• Start Conveyor • Open Pre-stop
These two actions do not spend a significant time from a simulation point of view. These two actions describe the necessary step to realise the process of loading part into Turntable. Simulation does not take into account this level of logic detail where a process is broken down into its sub-processes. This is because these sub-processes do not always take time.
2.3 Element Boundaries
The element boundary is a very important issue. Boundaries are the limits of what is internal and external for an element. The boundary of an element will affect its logic and can dramatically affect the interactions between elements. This makes the establishment of the element boundaries key for the specification of the real system.
2.3.1 Simulation Boundaries
Simulation element applies boundaries which are not “Spontaneous”, i.e. an element boundary used in the simulation is not intuitively recognisable from observation of the real system. In the simulation interpretation every real element is considered as an operation that takes a Cycle Time.
Figure 1: Simulation Element Boundaries
Appendix D: Logic Analysis Approach
6
The Buffer size of an element can be Zero if the elements are back to back. This also means the there can be no Pre-stop as the elements internal stop can act as the Pre-stop. This means that when a cycle finishes the part is transferred to the next operation directly if it is free.
There are several justifications for using this approach, some of which are presented in below:
Real system analysis is simpler
Op 250
Pi PviPvPiv
Piii
Pvii
Op 260
Pii
Observed Element
Boundaries
OperationConveyor
Single Part
Divert
Conveyor Multi
Part
Walkover
Conveyor
Conveyor
Single PartOperation
Conveyor
Single Part
Figure 2: Real Element “Spontaneous” Boundaries
Figure 2 shows a section of Lion Assembly Line, the “Spontaneous” boundaries give 8 elements.
Piii
Figure 3: Simulation Boundaries
Figure 3 shows the same section of Assembly Line using the simulation boundaries, the result is the identification of 4 elements. For the same section changing the boundaries of the element reduce notably the numbers of element, this makes the real system analysis simpler.
Appendix D: Logic Analysis Approach
7
The interaction between elements is much simpler
From studies, the interaction between elements is a complex issue, with the previous boundaries. With the simulation boundaries no real interaction are required other than simple logic rules. The number of elements has been reduced and hence the number of interaction has also been reduced.
The comparison of the simulation and real system logic is more direct
Applying simulation boundaries makes the comparison of the real system is easier as the elements are compared like with like.
Appendix D: Logic Analysis Approach
8
2.3.2 Updated Element List
The number of elements has been reduced; Figure 4 shows the Simulation elements and the Real System logic elements that have been grouped together for simulation purposes.
Figure 4: Simplified Element List
Appendix D: Logic Analysis Approach
9
2.4 Flow Diagram Definition
The flow diagram is the selected tools to illustrate the real logic of the system. The basic components of the flow diagram are used. In order to have a homogenous view point the Microsoft Visio 2003 standard has been selected.
Process Decision
Yes
NoStart postision
Figure 5: Microsoft Visio flow Diagram Components
Starting Position: All elements have a starting position. They return to this state cyclically. Start position is the initial statement of an element.
Process: Processes are actions. As describe above, processes spend time to be performed. These processes are completed processes, in action like “rotate turntable” it is considered the action is started, carried out and finished.
Decision: Decisions ask questions. Many questions are asked in cycle, this means the system asks questions until obtaining the answer which will unblock the element. It obtains the right condition before going further in the flow diagram (go to the next process or decision).
To help the understanding of the diagrams a colour coding is used. Figure 6 illustrates the colour code. The Element Body could be an Elevator, Lowerator or Operation etc.
Pre-stop
Figure 6: Element and Flow Diagram Colour Coding
Appendix D: Real System and Simulation Logic
10
Flow
Orientator
Element
Boundary
3 REAL SYSTEM AND SIMULATION LOGIC
In this section of the specification the logic analysed from the real systems is presented in flow diagrams. The results from the analysis show that there are common logic patterns that allow the real system elements to be grouped together.
3.1 Gap Section Conveyor
Gap section logic incorporates a piece of conveyor that cannot hold a part and is used for transportation purposes only. The real system elements that fall into this category are:
Orientator
Figure 7: Diagram of Orientator
Appendix D: Real System and Simulation Logic
11
3.1.1 Real System Logic Interpretation Flow Diagram for Gap Conveyor Logic
Diagram Step Description
1. Starting position is select when the element is reset and ready to load part from the Pre-stop.
2. To advance to the next stage of the element a part must be present at the Pre-stop. If not the Gap Section will wait.
3. To advance to the next stage of the Gap Section process there must be space at the exit Buffer as the conveyor section of the Gap does not hold a part. The Pre-stop will not release until this is true.
4. The part is transported across the Gap to the next vacant position of the Buffer.
Comments Nature of Buffer
The Buffer of these elements is a multi or single part forward conveyor.
Breakdown A Breakdown of a gap will not affect the pieces of automation in its Zone.
Specific comment An Orientator rotates the platen in relation to the conveyor. An Orientator can also change its direction.
Table 3: Road Section Conveyor
3.1.2 Gaps between Simulation Logic and Reality Simulation logic Gaps
The simulation approach to modelling these elements allows the representation to be Simple and accurate.
The simulation logic matches the real life accurately.
Table 4: Simulation and Reality Gap Analysis for Ga p Conveyor
1
2
3
4
Appendix D: Real System and Simulation Logic
12
3.2 Turntable-Elevator-Lowerator
Turntable, Elevator and Lowerator are three different real elements. There are also combinations of Elevator Turntable and Lowerator Turntable.
A Turntable changes the direction of a part; the orientation of the part could be also changed. Usually a turntable is at a corner of the line.
An Elevator transports part vertically; it enables a part to go from one conveyor to a higher conveyor.
A Lowerator transports part vertically; it enables a part to go from one conveyor to a lower conveyor.
A Lowerator Turntable transports part vertically, it also changes the direction of a part and the orientation of the part could be also changed. It enables a part to go from one conveyor to a lower conveyor at a corner of the line.
An Elevator Turntable transports part vertically, it also changes the direction of a part and the orientation of the part could be also changed. It enables a part to go from one conveyor to a higher conveyor at a corner of the line.
The logic of these elements have the same structure, the next flow diagram illustrate this logic.
Pre-stop
Pre-stop
Pre-stop
Figure 8: Turntable Elevator Lowerator Drawings
This sketch presents a simple drawing of these elements. In green is the element itself, in yellow is where parts arrive (Pre-stop) and in the Buffer is in blue. The capacity of the Buffer depends on each situation. The diagram has the same colour code.
Appendix D: Real System and Simulation Logic
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3.2.1 Real System Logic Interpretation Flow Diagram for Turntable- Elevator - Lowerator
Diagram Description 1. Starting position is select when the element is reset and ready to load part.
2. If no part is at the Pre-stop the flow will stay in the loop until a part arrives at the Pre-stop. When a part is at the Pre-stop the element goes to next process.
3. Load one part is a process. How it is loaded is not describe at the level of logic. How is loaded could be different for a turntable or for an elevator.
4. Operate could be:
• Rotate (for Turntable) • Elevate (for Elevator) • Lower (for Lowerator) • Elevate and Rotate (for Elevator Turntable) • Lower and Rotate (for Lowerator Turntable)
5. This is the second decision point. Before unloading a part the element checks if there is a space in the Buffer. If there is no space the flow will stay in the loop until there is a space. When there is a space the element goes to next process.
6. Unload one part is a process. How it is unloaded is not describe at this level of logic. How it unloads could be different for a turntable or for an elevator.
7. Reset could be:
• Rotate back (for Turntable) • Lower (for Elevator) • Elevate (for Lowerator) • Elevate and Rotate back (for Elevator Turntable) • Lower and Rotate back (for Lowerator Turntable)
Comments Nature of Buffer
The Buffer of these elements is generally a multi or single part forward conveyor.
Breakdowns A Breakdown of this section will not affect the pieces of automation in its Zone.
Table 5: Flow Diagram for Turntable-Elevator-Lowera tor
1
2
3
4
5
6
7
Appendix D: Real System and Simulation Logic
14
3.2.2 Gaps between Simulation Logic and Reality Simulation logic Gaps
In the simulation these elements are modelled with the same logic. The difference is only on the Cycle Time.
No gap
In the simulation model the element could load and unload part at the same moment.
In the reality this is not possible the Element needs resetting. This gap is very small since the reset action does not take a significant amount of time.
Table 6: Real System and Simulation Logic Gap Obser vation for Turntable, Lowerator and Elevator
3.3 Divert
A Divert can change the route of parts. The direction of a part, the orientation of the part could be also changed. The direction and/or orientation is dependant on an input signal from the control or quality system. Usually a Divert is present for an intersection of several conveyors.
Figure 9: Divert Drawings
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15
There have been different types of Divert identified. At the junction more conveyors could be present as shown below:
Figure 10: Diagram of Divert Variations
The logic of these Diverts and of the Divert presented above could be represented by a common global logic.
3.3.1 Real System Logic Interpretation
The common logic is first presented and an example of the scenarios that are possible.
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16
Flow Diagram for Divert Diagram Description
1. Starting position is selected when the Divert is reset and ready to load part from the Pre-stop. Several Pre-stop could be present. The reset position depends of each Divert (each situation). 2. The Divert prioritises one Pre-stop or could work as “first come first served”, here again it depends of each situation.
3. According to which Pre-stop the part is at, the Divert could rotate to this Pre-stop. If it is at the Pre-stop of the reset position the Divert does not need to rotate.
4. The Divert loads one part from the selected Pre-stop.
5. The unload position depends on the nature of the part (rejected or injected) or which Pre-stop the part is from. Again this depends of each situation. The Rotation could be different or some times unnecessary to “go” to the unload position.
6. Before unloading a part the Divert checks if there is a space in the selected Buffer. If there is no space the flow will stay in the loop until there is a space. When there is a space the Divert goes to next process.
7. Once the Divert is in the right position to unload, it unloads one part.
8. The Divert rotates to its initial position. This rotation will depend on the situation. It will depend in which position the Diverts was to unload comparing it to the initial position. It could happen that no rotation is required.
Comments
Nature of Buffer The Buffer of the Divert is generally a multi or single part forward or reverse conveyor.
Breakdowns A Breakdown of a Divert will not affect the pieces of automation in its Zone.
Specific comment The external input to know if the part must be rejected or not comes from the control system. To know if a part has to be injected that also the control system which provide the information.
Table 7: Divert General Logic
1
2
3
4
5
6
7
8
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17
The following Logic describes the logic of the Divert when considering the Rejection or Injection of a part from the Spur Buffer.
Flow Diagram for Divert Scenario 1: Inject Part Diagram Description
1. Starting position is selected when the Divert is reset and ready to load part from the Pre-stop. 2. The Divert prioritises the injection of a part into the line.
3. To inject a part, the Divert needs to rotate to the Spur Buffer.
4. The Divert loads one part from the Spur Buffer.
5. The Divert rotates to the initial position which is turned to unload one part to the Buffer.
6. This is the second decision point. Before unloading a part the Divert checks if there is a space in the Buffer. If there is no space the flow will stay in the loop until there is a space. When there is a space the element goes to next process.
7. The Divert unloads one part to the Buffer.
Table 8: Divert Scenario 1: Inject Part Logic
1
2
3
4
5
6
7
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18
Flow Diagram for Divert Scenario 2: Part Goes Strai ght Diagram Description
1. Starting position is selected when the Divert is reset and ready to load a part from the Pre-stop. 2. The Divert prioritises the injection of a part into the line.
3. If no part is at the Pre-stop the flow returns to the start. If a part is at the Pre-stop the Divert goes to next process.
4. The Divert loads one part from the Pre-stop.
5. This decision needs an external input to know the state of the part. In this scenario the part does not need to be rejected.
6. Before unloading a part the Divert checks if there is a space in the Buffer. If there is no space the flow will stay in the loop until there is a space. When there is a space the Divert goes to next process.
7. The Divert unloads one part to the Buffer.
Table 9: Divert Scenario 2: Part Goes Straight
1
2
3
4
5
6
7
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19
Flow Diagram for Divert Scenario 3: Reject Part Diagram Description
1. Starting position is selected when the Divert is reset and ready to load a part from the Pre-stop. 2. The Divert prioritises the injection of a part into the line.
3. If no part is at the Pre-stop the flow returns to the start. If a part is at the Pre-stop the Divert goes to next process.
4. The Divert loads one part from the Pre-stop.
5. This decision needs an external input to know the state of the part. In this scenario the part needs to be rejected.
6. The Divert rotates to the Spur Buffer.
7. Before unloading a part the Divert checks if there is a space in the Spur Buffer. If there is no space the flow will stay in the loop until there is a space. When there is a space the element goes to next process.
8. The Divert unloads one part to the Spur Buffer.
9. The Divert rotates to its initial position.
Table 10: Divert Scenario 3: Reject Part
1
2
3
4
5
6
7
8
9
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3.3.2 Gaps between Simulation Logic and Reality Simulation logic Gaps
In the simulation a Divert is modelled with the same logic. The difference is only on the Cycle Time. Different Cycle Times are used for the different scenario.
Load and unload part take the same time but the number of rotations make the Cycle Time different. If rotations are necessary to turn to the loading and the unloading area the Cycle Time will be longer.
No gap, but different types of Divert exist on the lines. The rotations are different in each situation so the Cycle Times are different. Diverts follow one logic but with different Cycle Time.
In the simulation model the element could load and unload part at the same moment.
In the reality this is not possible the Element need to reset. This gap is very small since the reset action does not take a significant amount of time.
Table 11: Real System and Simulation Logic Gap Obse rvation for Divert
3.4 Swing Gate
A Swing Gate is a Divert that can be manually opened to go through the Machining Line. To open it a button is pressed and the Divert opens. A Swing Gate can reject and inject parts. A Swing Gate can be opened when a part is inside.
3.5 Manual & Auto Operation
An operation that involves a man and tools can be called a manual operation. The operator has work content that must be finished within a pre-defined time. If the operator goes over this pre-defined time then they push a button to release it. If it doesn’t release then a repair or some other process is required in order to pass the part as good quality. If there are any problems that occur in an operation (manual, semi or automatic) the quality system is written to via an Antenna. If a manual operation finishes before the designated time the part will not release until the end of the cycle. An Automatic operation carries out all the above part flow functions automatically.
Figure 11: Manual & Auto Operation Drawing
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21
3.5.1 Real System Logic Interpretation Flow Diagram for Manual and Auto Operation
Diagram Description 1. Starting position is select when the element is reset and ready to load part from the Pre-stop.
2. If no part is at the Pre-stop the flow stays in the loop. If a part is at the Pre-stop the Operation goes to next process.
3. The Operation loads one part
4. The Operation “operates”.
5. Before unloading a part the element checks if there is space in the Buffer. If there is no space the flow will stay in the loop until there is a space. When there is space the element goes to next process.
6. The Operation unloads one part.
Comments
Nature of Buffer The Buffer of the Operation is generally a multi or single part forward conveyor.
Breakdowns In case of Breakdown for on step of the Operation all the Operation stops.
Specific comment In case of Manual Operation, a button must be pressed manual to finish the Operation
Table 12: Manual & Auto Operation
3.5.2 Gaps between Simulation Logic and Reality
Table 13: Real System and Simulation Logic Gap Obse rvation for Manual & Auto Operation
Simulation logic Gaps The simulation approach to modelling these elements allows the representation to be Simple and accurate.
The simulation logic matches the real life accurately.
1
2
3
4
5
6
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3.6 Transfer Machine
Transfer machine has the characteristic to unload parts when it loads parts. Loading and unloading are done as the same moment. There are always parts in this machine. Transfer Operation can contain several parts. The Transfer Operation can have several steps.
Transfer Operation can have several Sub-operations; the Pres-stop is located at the first Sub-operation and the Buffer at the last Sub-operation. Between Sub-operations buffer are possible but they are include as the Transfer Operation capacity.
Pre-stop
Figure 12: Transfer Operation Drawing
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23
3.6.1 Real System Logic Interpretation Flow Diagram for Transfer Operation
Diagram Description 1. Starting position is select when the Transfer Operation is reset and ready to load part from the Pre-stop.
2. If no part is at the Pre-stop the flow stays into the loop. If a part is at the Pre-stop the Transfer Operation goes to next process.
3. Before unloading a part the Transfer Operation checks if there is space in the Buffer. If there is no space the flow will stay in the loop until there is a space. When there is space the Transfer Operation goes to next process.
4. The Transfer Operation loads and unloads parts at the same time.
5. The Transfer Operation “operates”, several steps could be included in the operation.
Comments
Nature of Buffer The Buffer of the Transfer Operation is generally a multi or single part forward conveyor.
Breakdowns In case of Breakdown for one step or one Sub-operation of the Transfer Operation all the Transfer Operation is blocked, but other steps or Sub-operation finish there cycle.
Changeover Changeover requires stopping the machine. The time required could be different from one operation to another.
Specific comment Generally, parts are loaded / unloaded one by one but it could be two by two or more.
The operation could contain more than one part.
The Transfer Operation could be manually emptied by an operator.
Figure 13: Transfer Operation
1
2
3
4
5
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3.6.2 Gaps between Simulation Logic and Reality Simulation logic Gaps
In the simulation Transfer Operation loads & unloads at the same time.
Washing Station could unload without loading in special case.
Table 14: Real System and Simulation Logic Gap Obse rvation for Transfer Machine
3.7 Gantry
The Gantry is a component of a CNC cell including CNC Machine, Pre-stop and Buffer (Figure 17). Two main types of cells have been identify, one for the Cylinder Head Machining Line and one for the Crankshaft Machining Line.
3.7.1 Real System Logic Interpretation
The Gantries of the Cylinder Head Machining Line have the same logic. They have 2 arms and distribute part one by one to several CNC Machines. The CNC Machines are doing the same Operation in parallel. The two arms are dependant and fix to each other.
Gantry
Buffer
Pre-stop
Flow
Flow
CNC
Machine
CNC
Machine
Check Box
Boundaries
Top View
Figure 14: Cylinder Head Gantry Drawing
Appendix D: Real System and Simulation Logic
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Flow Diagram for Gantry: Inject Scenario Diagram Description
1. Starting position is selected when the Gantry is reset and ready to load a part from the Pre-stop. The Gantry is above the Pre-stop.
2. The Gantry prioritises the injection of a part into the line.
3. If a part has to be injected, the Gantry goes to the Check Box.
4. The Gantry unloads parts from the CNC Machine. One arm takes a part from the CNC Machine.
5. Gantry goes to the Buffer.
6. The Gantry unloads a part to the Buffer. One arm puts a part into the Buffer. The Gantry is at its initial position above the Pre-stop and the Buffer.
Table 15: Real System Logic for Gantry: Inject Scen ario
1
2 3
4
5
6
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Flow Diagram for Gantry: Through Flow Scenario Diagram Description
1. Starting position is select when the Gantry is reset and ready to load part from the Pre-stop. The Gantry is above the Pre-stop. 2. The Gantry prioritises the injection of a part into the line.
3. If no part is at the Pre-stop the flow stays in the loop. If a part is at the Pre-stop the Gantry goes to next process.
4. Before unloading a part the Gantry checks if there is space in the Buffer. If there is no space the flow will stay in the loop until there is a space. When there is a space the element goes to next process. 5. Here Gantry controls that a machine is idle before load part. A Gantry could distribute parts to several CNC Machines. The CNC Machine calls the Gantry a few seconds before completing the operation. The Gantry prioritises the calls: first call first served. 6. The Gantry loads one Part from the Pre-stop. 7. As the principal is “first call first served”, the Gantry goes to the calling CNC Machine.
8. The Gantry unloads a part from the CNC Machine. One arm takes a part from the CNC Machine.
9. The Gantry loads a part to the CNC Machine. The other arm puts part into the CNC Machine. 10. The Gantry could reject a part. In this scenario the part does not need to be rejected. 11. If the part does not need to be rejected, the Gantry goes to the Buffer.
12. The Gantry unloads a part to the Buffer. One arm puts part into the Buffer. The Gantry is at its initial position above the Pre-stop and the Buffer.
Table 16: Real System Logic for Gantry: Through Flo w Scenario
1
2
3
4
5
6
7
8
9
10
11
12
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Flow Diagram for Gantry: Reject Scenario Diagram Description
1. Starting position is select when the Gantry is reset and ready to load part from the Pre-stop. The Gantry is above the Pre-stop. 2. The Gantry prioritises the injection of a part into the line.
3. If no part is at the Pre-stop the flow stays into the loop. If a part is at the Pre-stop the Gantry goes to next process.
4. Before unloading a part the Gantry checks if there is space in the Buffer. If there is no space the flow will stay in the loop until there is a space. When there is space the Gantry goes to next process.
5. Here Gantry controls that a machine is idle before load part. A Gantry could distribute parts to several CNC Machines. The CNC Machine calls the Gantry a few seconds before completing the operation. The Gantry prioritises the calls: first call first served. 6. The Gantry Load one Part from the Pre-stop. 7. As the principal is “first call first served”, the Gantry goes to the served CNC Machine.
8. The Gantry unloads a part from the CNC Machine. One arm takes a part from the CNC Machine.
9. The Gantry loads part to the CNC Machine. The Other arm puts part into the CNC Machine. 10. The Gantry could reject a part. In this scenario the part needs to be rejected. The Gantry rejects part for the quality checks. 11. If the part needs to be rejected, Gantry goes to the Check Box. 12. The Gantry checks if there is space in the Check Box. 13. The Gantry unloads a part to the Check Box. One arm puts part into the Check Box.
14. The Gantry return to the initial position above the Pre-stop and the Buffer.
Table 17: Real System Logic for Gantry: Reject Scen ario part 1
1
2
3
4
5
6
7
8
9
10
11
12
13
14
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Comments
Nature of Buffer
The Buffer of the Gantry is generally a multi or single part forward conveyor.
When the Gantry is above the Pre-stop, it is also above the Buffer as it has two arms.
Breakdowns If the Gantry Breakdowns, all the cell will be blocked since it is the Gantry which distributes parts and the control system calls maintenance. The machines finish their Cycle Time and wait.
If a machine Breakdowns the CNC cell will not be blocked since the machine are in parallel, but the flow through the cell is reduced.
Specific comment If the three first conditions are ok (Part at the Pre-stop, Machine Idle and Space available in the Buffer) the Gantry will load a part from the Pre-stop and unload to the Buffer at the same time.
The logic described above ensures the machines are never empty. Like the Transfer Operation, staff could empty the machine by manual intervention.
The Check Box is used to make quality checks on parts. This is a manual operation, at the end of this operation a button is pushed to call the Gantry.
Table 18: Real System Logic for Gantry: Reject Scen ario (Part 2)
The Gantries for the Crankshaft Machining Line are different to the Head Line. Here, a Gantry could distribute parts to several Operations. The Parts are loaded from the Pre-step, then go the first Operation (CNC Machine) then the second one and then the Buffer. The Gantry makes all the transportations.
The injection point is at the Pre-stop position and the rejection point is at the Buffer position. This is due to the Buffer characteristic (a section will describe later its characteristics).
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29
Figure 15: Crankshaft Gantry
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Flow Diagram for Gantry (Crankshaft): Injected Scen ario Diagram Description
1. Starting position is selected when the Gantry is reset and ready to load part from the Pre-stop. The Gantry could be above the Pre-stop or in an intermediate area. 2. The Gantry prioritises the injection of a part into the line.
3. The Gantry loads a part from the injection space at the Pre-stop.
4. The Gantry goes to the CNC Machine. In this case each Operation has one machine and the Gantry distributes part from one Operation to another. This makes that the steps 4-5-6-7 could be done several times. For example, if the Gantry distributes to 2 operations the steps 4-5-6-7 will be completed 2 times. 5. After loading parts and being above the CNC Machine the Gantry checks if the machine is idle. 6. The Gantry unloads parts from the CNC Machine. One arm takes parts from the CNC Machine. 7. The Gantry loads parts to the CNC Machine. The other arm puts part into the CNC Machine. The Gantry could go to the next Operation (the logic following the loop is represented with the discontinue arrow) or goes the next process. 8. The Gantry goes to the Buffer. 9. Before unloading parts the Gantry checks if there is space in the Buffer. If there is no space the flow will stay in the loop until there is a space. When there is space the Gantry goes to next step. 10. The Gantry could reject parts. The Gantry rejects parts for the quality checks. 11. If the parts do not need to be rejected, the Gantry unloads the parts in the Buffer.
12. The Gantry returns to the initial position above the Pre-stop or an intermediate position.
Table 19: Real System Logic for Gantry (Crankshaft) : Injected Scenario
1
2
3
4
5
6
7
8
9
10
11
12
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Flow Diagram for Gantry (Crankshaft): Through Flow Scenario Diagram Description
1. Starting position is select when the Gantry is reset and ready to load part from the Pre-stop. The Gantry could be above the Pre-stop or in an intermediate area. 2. The Gantry prioritises the injection of a part into the line.
3. The Gantry checks if there is part at the Pre-stop.
4. The Gantry loads parts from the Pre-stop.
5. The Gantry goes to the CNC Machine. In this case each Operation has one machine and the Gantry distributes part from one Operation to another. This makes that the steps 4-5-6-7 could be done several times. For example, if the Gantry distributes to 2 operations the steps 4-5-6-7 will be completed 2 times. 6. After loading part and being above the CNC Machine the Gantry checks if the machine is idle. 7. The Gantry unloads parts from the CNC Machine. One arm takes parts from the CNC Machine.
8. The Gantry loads parts to the CNC Machine. The Other arm puts parts into the CNC Machine. The Gantry could go to the next Operation (the logic follows the loop represented with the broken arrow) or goes the next process. 9. The Gantry goes to the Buffer. 10. Before unloading parts the Gantry checks if there is space in the Buffer. If there is no space the flow will stay in the loop until there is a space. When there is space the Gantry goes to next step. 11. Gantry checks if the part needs to be rejected. 12. Gantry unloads parts to the Buffer.
13. The Gantry returns to the initial position above the Pre-stop or an intermediate position.
Table 20: Real System Logic for Gantry (Crankshaft) : Through Flow Scenario
1
2 3
4
5
6
7
8
9
10
11
12
13
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Flow Diagram for Gantry (Crankshaft): Reject Scenar io Diagram Description
1. Starting position is select when the Gantry is reset and ready to load part from the Pre-stop. The Gantry could be above the Pre-stop or in an intermediate area. 2. The Gantry prioritises the injection of a part into the line.
3. The Gantry checks if there is parts at the Pre-stop.
4. The Gantry loads parts from the Pre-stop. 5. The Gantry goes to the CNC Machine. In this case each Operation has one machine and the Gantry distributes part from one Operation to another. This makes that the steps 4-5-6-7 could be done several times. For example, if the Gantry distributes to 2 operations the steps 4-5-6-7 will be completed 2 times. 6. After loading parts and being above the CNC Machine the Gantry checks if the machine is idle. 7. The Gantry unloads parts from the CNC Machine. One arm takes parts from the CNC Machine. 8. The Gantry loads parts to the CNC Machine. The Other arm puts parts into the CNC Machine. The Gantry could go to the next Operation (the logic follow the loop represented with the discontinue arrow) or goes the next process. 9. The Gantry goes to the Buffer. 10. Before unloading parts the Gantry checks if there is space in the Buffer. If there is no space the flow will stay in the loop until there is a space. When there is space the Gantry goes to next step. 11. Gantry checks if the part needs to be rejected. 12. Gantry checks if there is space in the Check Space in the Buffer. 13. If the part needs to be rejected the Gantry unloads the part in the Check Space.
14. The Gantry returns to the initial position above the Pre-stop or an intermediate position.
Table 21: Real System Logic for Gantry (Crankshaft) : Reject Scenario (Part 1)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
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Comments
Nature of Buffer
The Crankshaft Buffers are special; they are based on the principal of First In First Out. The Buffer is a magazine with a rotary system which moves to transport part.
Quality Check Space is included in the Buffer.
In some case the Buffer has a capacity of one (nest), this enables the Gantry store a part to allow it to go from an Operation which machines 2 parts at a time to an Operation which machines 1 part at a time.
Breakdowns If the Gantry breaks down, all the cell will be blocked since it is the Gantry which distributes part, the control system calls maintenance. The machines finish their Cycle Time and wait.
If a CNC Machine breaks down all the CNC Cell is blocked since machines are one after the other.
Specific comment Gantry can transport one or two parts depending on the Operation
The logic described above ensures that the CNC Machines never empty. Like the Transfer Operation, staff could empty the machine by manual intervention.
The Check Box is used the make quality checks on parts. Staff could calls part (after change over of the previous Operation). The Quality check is a manual operation, at the end of this operation a button is pushed to call the Gantry for injection part.
Table 22: Real System Logic for Gantry (Crankshaft) : Reject Scenario (Part 2)
Appendix D: Real System and Simulation Logic
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3.7.2 Gantry Logic Summary
Table 22 is a comparison of the real system logic for the Cylinder Head and Crankshaft Gantries for the CNC Cells.
Scenarios Similarities Differences Inject Part Both Gantries prioritise the
Injection of parts. • Crank Gantry injects part from it
Pre-stop position and injects parts to its associated Operations.
• Head Gantry injects parts from Its Check Box and injects parts to its associated Buffer, not to the Operation.
Through Flow
Both Gantries load from their Pre-stop, unload & load their CNC Machine and unload part to their Buffer.
• Crank Gantry loads parts from its Pre-stop even if its Buffer is full.
• Head Gantry does not load part from its Pre-stop if there is no space in its Buffer.
Reject Part Both reject parts after the Operation(s) is complete.
• The Head Gantry has a specific Check Box.
• The Crank Gantry has Check space located in its Buffer.
Breakdown If the Gantry breaks down, all the cells will be blocked since it is the Gantry which distributes part. The control system calls maintenance. The machines finish their Cycle Time and wait.
• Crank: If a machine breaks down all the CNC Cell is blocked since machines are one after the other.
• Head: If a machine breaks down the CNC Cell will not be blocked since the machines are in parallel, but the flow is reduced.
Table 23: Comparison of Gantry Logic between Machin ing Lines
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3.7.3 Gaps between Simulation Logic and Reality Simulation logic Gaps
In the simulation Gantry with its Pre-stop, Buffer and Operation(s) is represented like a Transfer Operation. This means that the logic loads & unloads a part at the same time when a part is at the Pre-stop and a Space is at the Buffer.
The Crank Gantries could load when the Buffer is full. This gap makes that 1 or 2 parts enter into the element in the reality and not in the simulation.
The head Gantry follow the logic without gap.
A Transfer Operation CNC Machine always has parts inside except during a manual intervention
No gap
Loading and unloading is done at the same moment.
For the Head Gantry this is right as there is a part at the Pre-stop when the Gantry unloads to its Buffer. If there is no part at the Pre-stop the Gantry will unload without loading a new part.
For the Crank Gantry, the load and unload Buffer positions are at opposite ends of the Cell. This means that the gantry loading and unloading actions are carried out with a significant time delay between them. Between the Pre-Stop and Buffer positions there could be several machines which will increase the delay.
Breakdowns Head Gantry supports the CNC cell and several machines are in parallel doing the same operation. If one machine breaks down all Cell will not be blocked but the flow will be reduced. The throughput time for the same number of parts through the CNC Cell will increase.
Crank Gantry supports the CNC Cell, several CNC Machines are one after the other. This means that if one of them breaks down the whole cell will be blocked.
In Both cases if the gantry breaks the CNC Cell will be blocked.
Whatever component breaks down, all other component of the Cell will complete their operation Cycle Times.
Table 24: Real System and Simulation Logic Gap Obse rvation for Gantry
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4 GENERAL CASES AND SPECIFIC OBSERVATIONS
In this section issues that have been observed that are common to both the Lion Machining Line and Lion Assembly Line are presented. The specific observations relating to the individual lines are also shown.
4.1 General Logic Issues
This section describes the observations and factors that apply to both lines.
4.1.1 Breakdowns
When a Breakdown occurs the scenario followed is generally the same:
1. The control system establishes a diagnostic and sends it to the control system and calls operator.
2. If the operator cannot fix the Breakdown within 10 minutes, the operator has to call maintenance.
4.1.2 Antenna
Real Life
The RFID Antenna is used to read and write information on to an RFID tag in the base of the platen. The tag holds information about the type of engine that is mounted on the platen. The information contained on this tag can be used automatically by a machine to set itself up ready for the platen arriving, for example.
The Antenna puts information into the quality system.
A Breakdown an Antenna system stops the assembly line. The Breakdown may prevent information transfer to the quality system and could potentially change the sequencing of the parts.
The Antennas determine what path and operations are carried out on a part.
The Antennas are not mentioned in the work standard.
Simulation
The Antennas are not included in the simulation and hence the model does not contain Breakdown data specifically for it. The stop at an Antenna after a machine is not included in the Cycle Time of an operation as it is recorded as the time interval between parts entering the machine. They are also outside the physical operation boundary.
4.1.3 Frequency Event
A frequency event is something that happens every x number of cycles. This can be built into the simulation model and depends on the element and the
Appendix D: General Cases and Specific Observation
37
work content at that element.
4.2 Specific Issues from Machining Line Analysis
This section describes some specific issues related to the Machining Lines, based on observed scenarios.
4.2.1 Changeover
In the Block Machining Lines, Changeovers are necessary when the engine derivative is changed. As the engines are not exactly similar they require Changeover.
The Changeover scenario is for Transfer Machines:
• Empty the Transfer Machine. • Stop the Machine. • Change the tools (some of the tools are directly on the machine and
other in the tool room). A Poke yoke system prevents tool change mistakes: right tool for right engine.
• Restart the Machine. • The Machine is fills full of part automatically.
The nature of the line (transfer) makes Changeovers follows the flow of the part. Changeovers are done operation by operation starting at the beginning of the line.
For all CNC Machines no Changeover is required. The machines have tool magazines and change automatically. All tool changes for CNC Machines are for the withdrawal of worn tools, it is considered as maintenance.
4.2.2 Zones
The control system is divided into Zones for the lines. If a piece of automation or a machine Breakdown within a Zone, there will not be an impact on this Zone. For normal fault conditions the standard approach is to allow different components of the line to continue as far as they can if a fault occurs elsewhere.
4.2.3 Washing Machine
Washing machines are considered as Transfer Machines. There is one difference, if new parts do not arrive after a certain time period the washing machine unloads parts automatically. This avoids parts spending too much time in the machine preventing damage to the parts.
4.2.4 Crankshaft Buffer
The Crankshaft Buffers are special as they are based on the principal of First In First Out. The Buffer is a magazine with a rotary system which moves to transport parts.
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Quality Check Space rejection positions and injection positions are included in the Buffer. The rotary system moves to transport the part to the Pre-stop position.
A part is generally rejected after tool change to check the machine setup.
4.2.5 Specific Crank Gantry - OP140 in Head
On the Cylinder Head Machining Line Operation 140 is an Manual Assembly Operation.
Figure 16: Operation 140 Drawing
Several elements compose this Operation (two Sub-Operations and Automation Equipment).
The Gantry has one arm and puts part into the loop. In this loop parts are put on a new platen, this is done on the Divert. Several parts could be in the loop.
The scenario is:
1. If a part must be unloaded from the loop (part ready to be unload from the Divert), the Gantry unloads the Divert and goes to the Buffer (This empties the platen in the Divert). If there is a space in its Buffer, the Gantry unloads the part to the Buffer.
2. If the is part at the Pre-stop the Gantry goes to the Pre-stop, loads a part, goes to the Divert and loads the part to the Divert.
3. The Divert rotates to enable a robot to put protection on the part. When the protection is in place and if the Divert has a space in its Buffer, the Divert unloads the part. The part goes through the loop until the Manual Operation (no specific logic).
4. After the Manual Operation the part goes through the loop following the logic of the elements until the Automatic + Test Operation.
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5. After the Automatic + Test Operation parts return to the Divert. If the part is OK the Divert rotates to enable the robot to withdraw the protection. Then the Gantry unloads this part. If the part is not OK the Divert does not rotate and “re-inject” the part into the loop.
The time required to go through the loop depends on the number of parts in the loop and the number of re-tests necessary.
4.2.6 Elevator 2 Parts
On the Cylinder Head machining Line, a special Elevator could elevate parts 2 at a time or 1 by 1 according to the part flow. This Elevator is located between the Operation 80 and 100. If enough parts arrive, the Elevator will wait for 2 parts to be on the Pre-stop before loading them. If the Part flow is too low the Elevator will load 1 by 1. From observation it appears that the sensor located at the opposite extremity of the previous Buffer give this information.
Pre-stop
Figure 17: Special Elevator Drawing
4.2.7 Turntable – Elevator - Lowerator Reset
The Reset of these elements takes a few seconds, but Breakdowns could occur during the reset, this makes the element block without a part inside. This could build a queue at this point.
4.2.8 Orientator Could Have Two Different Logic Pat terns
Several Orientators have the “regular” logic called Gap (Section 4.1) logic. However one of them located after the final wash (OP 170, Lion Head Machining Line) has the same logic as a Turntable – Elevator – Lowerator.
The principal difference is that this special Orientator could hold a part.
4.2.9 Crankshaft Gantry Special Logic: OP100
For OP100 on the Crankshaft Machining Line the Gantry has a special logic. The Pre-stop is an Operation (Marker Operation) and is loaded by the
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40
previous Gantry.
• The OP100 Gantry unloads the Marker Operation and puts the part into the Buffer 1.
• The Gantry loads a different part from Buffer 1 (following FIFO rules) and goes to the CNC Machine.
• If the Operation if finished, the Gantry unloads & loads the CNC Machine, then goes to Buffer 2 and if a space is available the Gantry unloads part to the Buffer 2.
• The Gantry returns to its initial position.
Figure 18: Diagram of Crankshaft Gantry Special Log ic OP100
4.2.10 Crankshaft Gantry Special Logic: OP200
Figure 19: Diagram of Crankshaft Gantry Special Log ic OP200
The Operation is supported by 2 Gantries (Gantry 1 and Gantry 2) they distribute parts to one CNC Machine decomposed in several steps (4 Stations). Gantry 1 distributes part to Stations 1 to 3 and Gantry 2 to Stations 3, 41 and 42. Gantry 2 has priority over Station 3.
• If there is a part at the Pre-stop, Gantry 1 loads it, goes to the Station 1 unloads & loads it’s the same for Station 2.
• The Gantry 1 goes to Station 3 and waits if the station is not idle. • The Gantry 2 unloads Station 3, unloads & loads a part in station 41 or
42, and then returns in Station 3 loads Station 3 (re-test). • If the test is OK, the Gantry 2 will unload Station 3 and goes to the
Buffer. If there is space in the Buffer the Gantry 2 will unload a part to it.
• If the re-test is no OK, Gantry 2 will load a part from the Station 3 and load again into Station 41 or 42.
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5 SUMMARY OF THE GAPS
The matrix in Table 32 summarises the identification of gaps and similarities between the simulation model and the interpretation of the real life logic.
Table 25: Gap and Similarities Summary
This document and the table above show that the simulation represents the reality closely for the majority of the elements. There are however a number of elements where greater attention should be paid when modelling as there could be differences in reality.
More detail is provided on these cases in their respective sections above.
Real Element
GapTurntable Elevator
LoweratorDivert Operation
Transfer Operation
Orientator OK
Elevator OK
Elevator Turntable
OK
Turntable OK
Lowerator Turntable
OK
Lowerator OK
Swing GateAdd
Frequency Event
DivertCheck
Scenario Cycle Time
Manual Operation
OK
Machine Operation
OK
CNC Cell
Crank Gantry (Load if
Buffer Full)Transfer Machine
Washing Machine
Simulation Element
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6 CONCLUSION
6.1 Summary of Work
The aim of this document was to allow a reader to understand the behaviour of components of the real systems to represent them accurately in a simulation model.
Section 2 is dedicated to presenting the relevant level of logic and the elements boundaries. The level of logic presented here was not the deepest level that was possible to represent. The level chosen is deep enough to match the real system element logic with the logic of the simulation elements.
n Section 3 each elemental component of the real system were studied using the selected boundaries and level of logic. When observing some apparently dissimilar elements (such as Turntable/Elevator) the logic was analysed to find a common pattern.
In Section 4 the general issues relating to Ancillary Logic was presented. Special cases for the Assembly and Machining Lines have been shown and a comparison with the simulation and real logic has been presented.
6.2 Difficulties Encountered
The following difficulties and problems where encountered and solved:
• Defining a common vocabulary that relates to the simulation model and the real system.
• The identification of a common structure of the flow diagrams was an issue because what was observed in reality differed from case to case. The actions performed in reality by an element can differ but the underlying logic principles remain constant. The difficulty arises when translating these differences into common patterns of logic flow.
• It is less difficult to represent what occurs in real life in a textual description. However the length of the descriptions would make them indigestible. The diagrams are produced to lighten the text and make the explanation friendlier. The sketches with colour coding assist in conveying this message.
Overcoming these three important difficulties have enabled this document and the information contained in it to be communicated as simply as possible without loosing the message.
6.3 Limits of the Specification Document
This document is the first attempt of the specification of the Lion Assembly and Machining Lines. There are therefore some inherent weaknesses and room for improvement:
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43
• The framework of this document is in Word format which occupies a lot of pages. A more user friendly solution is obtainable using other frameworks such as an interactive Web based or PDF document with hyperlinks, videos and pictures
• It is possible that there are Ford logic components missing from this specification as a limited number of lines where observed. When people in the future use this document there may be gaps in the logic specified due to lack of total immersion in the real system.
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