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Manufacturing Systems Lab. Robot Cell

Manufacturing Systems Laboratory

Introduction to the Robot Cell

The robot cell in the Manufacturing Systems laboratory contains two industrial robotic arms made by Kuka Roboter which are designed for use in the automobile assembly industry. The cell also contains tools, equipment, conveyors, sensors and controllers which are connected to work with these two arms. These arms are used for teaching and student projects, including projects on prototyping and control systems.

The following documentation is intended as an introduction to the Kuka robot cell. More detailed documentation is available including a user guide, a tutorial guide, programming manuals and hardware specification sheets.

It is intended for distribution to staff, students and the general public.

Author: Ken Snow – 2012


Contents.Introduction to the Robot Cell Page 1Safety in the Kuka Robot Cell Page 3Size and Capacity of the robot Cell Page 4Controllers for the robot cell. Page 5Emergency Stop System Page 5Robot TCP Controllers and Cell Control Panel. Page 7Robot inputs and outputs Page 8Tool Power supplies and Grippers Page 9Conveyors Page 10Program Setup Page 11

TutorialsUser Programming Page 13Cartesian Co-ordinate Programming Page 15Sensor Examples Page 16Advanced Programming Techniques Page 19Auxiliary Control Page22



Safety in the Kuka Robot Cell

The Kuka robotic arms are heavy, powerful machines capable of inflicting serious harm by crushing or laceration. The machines each weigh around 250kg and draw a peak power of around 10 kilo-Watts. The robot cell is protected by a light gate rated by appropriate organisations for safety applications which triggers an emergency stop whenever anyone enters the cell, this prevents anyone from accidentally moving into the path of a moving robot.

It is essential that any operators are fully familiar with the safety requirements in the User Guide before operation the system. Only authorised people who have an adequate level of training are permitted to use the system.

It’s Big and Powerful!!!

Keep out of the robot cell when in operation.



Size and Capacity of the Robot Cell

Each of the robotic arms measures 2.2 metres in height when fully extended vertically and has a horizontal reach of 1.6 metres. Payload is up to 15 kilos and maximum speed is 2 metres per second with linear movement or a 180 degree rotation in 2 seconds with point to point movement. The robot arms each weigh in at around 250kg and draw up to 10kWatts of power at peak operation.


The robot cell measures 6 metres by 3.5 metres with the range of the two arms overlapping slightly. Conveyors with a capacity of up to 50kg allow work pieces to be translated between the two arms while a turntable with a similar capacity is located in the overlapping workspace.

Communication with the cell is through USB ports or re-writable CDs using plain text files. These can originate from scanner packages, graphic design or mathematical computer packages.

Communication with sensors and auxiliary motors and valves takes place through a Devicenet serial communication module.


Controllers for the robot cell.

Power is distributed through a controlling cabinet which contains motor drivers, PLC logic for monitoring position and computers for the human-machine interface.

Control Cabinet for KR16 . . . . and KR15

The cell also requires a 240V AC supply for a number of features, most essentially the emergency stop system, but also tools, conveyors and other auxiliary systems. The cell also uses compressed air for grippers and some tools.

Emergency Stop System

The emergency stop system for the robot cell is configured to trip an emergency stop on both of the robotic arms if any person enters the cell or reaches through the window.

The triggering mechanisms consist of a 40 beam SICK C4000 light gate rated for finger detection operating across the cell window and a 3 beam SICK M4000 light gate across the door plus a keyed stop with removable key on the control panel. Any one of these can trigger a stop.

3 Beam light gate for the door to the cell.



40 Beam Sick light gate covering the window of the cell



Robot TCP Controllers

The robot controllers can be monitored from the LCD screen of the controlling hand held TCP unit or from auxiliary screens or projections.

Cell Control Panel.

The cell control panel allows switching of the emergency stop system, conveyors, pneumatics and auxiliary 240V. Indicator lights and two LCD displays provide feedback in addition to the two TCP controllers.



Robot Inputs and Outputs

A number of digital inputs and outputs are available on all robots to allow them to detect the results of sensor processing and to communicate in a simple manner with one another. There are also two analogue inputs available for the Kr16 KrC2 controller.

Inputs and outputs for the Kr16 controller are handled by a Devicenet communication module which is located outside of the control cabinet and communicates with the robot computer through a five wire serial bus. Most sensors are processed by a PLC logic module which is capable of doing analogue to digital assessments, pulse counting, and frequency measuring. Outputs from the Kuka controllers also go to PLC logic which can be configured to do a number of tasks including the switching of motor controllers, solenoids and relays.

Video.

Cameras which include a miniature borescope camera are available to allow close up observation of processes from outside the cell.

Wide angle camera on the scorbot robotic arm Borescope camera on Kr16 robot



Tool Power Supplies.

A switchable AC 240V power supply exists inside the cell for the powering of tools that may be mounted in the robot cell. This can be switched from switches on the cell control panel including the auxiliary emergency stop.

240 Volt outlet

A 12 Volt, 8 Amp DC power supply is mounted on the shoulder of each robot arm and is intended for the powering of DC powered tools. There are also switchable compressed air supplies.

Grippers

The pneumatic grippers attached to the wrist of each robotic arm are intended to allow for a quick changeover of tools without the need to unscrew bolts or other mechanisms. When the air pressure is applied the grippers have a holding force in excess of 15 kilograms and therefore secure any tool that the robot can handle.

Gripper open and closed.

Tools need to have a baseplate with four notches which fit into lugs on the gripper. The baseplate is secured front and rear by lapping plates on the gripper to prevent any possibility of it falling out.



Baseplate of tool Mounted on the gripper

In addition to attaching the tool it will also be necessary to make any electrical power and communication connections and pneumatic connections.

Conveyors

Two conveyors and a turntable are available within the robot cell for the manoeuver of work pieces relative to the robotic arms. Each can be controlled from the control panel and each can be reached by both of the arms. They all have a maximum payload of 50kg.

Turn table and straight conveyor for mould making.

The loop conveyor allows work pieces to be moved to the robots in a continuous cycle, which is often used to represent a production process or to bring different work pieces to the robotic arms.



Program Setup

Base Frames of Reference.

Frames of reference can be established for the robotic arms to align their movement with the conveyors and tables within the cell and with the other machine, they allow both arms to be aligned.

An example of this is the mould making frame of reference.

For the Kr 16 this has the following offsets: X 1000, Y 0, Z 950, A 29, B 0, C -1.

For the Kr15 this has offsets: X 600, Y -950, Z 950, A -90, B 0, C 0.

This allows both machines to work on the same piece with the same data.


Y

X

ZZ

X

Y


Tool Definition

Tool definitions can be defined to allow orientation to take place about a point in space relative to the tool tip.

Tool 3 Grinder

This is intended for use with the pneumatic grinder.

USB Connection

The controlling computer for each of the KrC robot controllers have a number of USB ports available, which can take memory sticks.

It is possible to provide some ( but not all ) of the programming for the robots source files from a text ( .txt ) file on a memory stick or CD. This can be produced on any PC using a wide variety of programs. A thorough knowledge of expert programming is required to do this.

Tools

Tools need to be custom built for specific applications. However a number of tools exist in the lab including an electric router, a pneumatic grinder, DC powered hot wire for cutting polystyrene and vacuum suction pads.



A few of the robot tools

Tutorials

The tutorials and examples described in the following pages are used to introduce staff and students to the programming and control of the system. Those wishing to do a ‘project’ within the cell will probably need to spend 20 hours in the laboratory familiarising themselves with the system before starting the project. Those that wish to do ‘research’ will need to spend in excess of 100 hours.

See the Tutorial Guide for the details of each tutorial.

Programming manuals written by Kuka Roboter are available within the laboratory in paper and software versions. All programming must start with User programming even when more sophisticated routines will be included. Advanced programming will require Expert level programming and use of the editor.

The manuals available in the lab total 630 pages in 9 volumes in addition to this document.

User Programming – programming at the simplest level.

This tutorial is designed to introduce staff and students to programming of the Kuka robots at the simplest level.

The tutorial is designed to familiarise the user with control of the robotic arms through the TCP controller.



Tasks include reseting the emergency stop system, jogging the robot , starting a program and entering moves into a program.

The intended program should contain at least one point to point, one linear and one circular move. It should contain some continuous and non-continuous functions. Linear speeds should be around 0.3 m/sec and point to point should be around 30% but make changes to these values to suit the program. Acceleration should be around 30% and feel free to include some tool definitions.



Circular move with orientation change.

Cartesian Co-ordinate Programming – cutting a model car.

The model car cutting exercise is intended to familiarise staff and students with the cartesian co-ordinate system in the kuka robot and the method of programming designs into the system which can then be cut automatically.

Hotwire cutting of polystyrene is one of our quickest and simplest processes, once students are familiar with this they can move on to more complex systems within the robot cell.

Syntax Example; X-Z profile for a Aston Martin DB4LIN { X -35.0, Z 0.}LIN { X -35.0, Z 31.0}CIRC { X -32.0, Z 34.5},{ X -27.0, Z 36.0}…………LIN { X 35.0, Z 0.}

; Y-Z profile of Aston Martin DB4



LIN { Y 0.0, Z 10.}LIN { Y 14.0, Z 10.}…………….CIRC { Y 138.0, Z 44.0},{ Y 168.0, Z 33.0}LIN { Y 168.0, Z 17.0}

Sensor Examples

Non-contact sensors in the lab include infrared, ultrasonic and inductive sensors. These need to be installed for specific applications and connected to the appropriate robot controller inputs if they are to trigger automatic reactions.

Infra-red Sensors

Two tutorial examples are available using infra-red reflactive sensors. These cover sensors mounted on the conveyor and on a tool, to detect the arrival of a pallet and whether a path is clear or blocked.



Infra-red Sensor on the conveyor and three on a tool

Pallet in position with inputs 3 and 4 True.

Infra-red sensors preventing a collision with a mag wheel and two 2 meter range sensors.

Ultrasonic sensors

The two ultrasonic range finders located in the cell monitor the loop conveyor and can be used to locate the position of items on the conveyor. The sensors are connected to analogue input channels 1 and 2 on the Kr16 controller.

Ultrasonic rangefinders monitoring a mag wheel.



Laser Referencing

Laser referencing is used to establish tool offsets and to provide accurate alignment of frames of reference to known lines. It uses a laser diode and light receiver to create a through beam with the reciever connected to the robot inputs.

Laser beam masked by a tool tip.



Light reciever Laser Diode

Advanced Programming Techniques

Inverse Kinematics

The Inverse Kinematics example is intended as a simple display of how to derive complex relationships between axes. This program takes known angles of three of the robot axes and uses these values to derive the three equations which will establish a straight line in space parallel to one of the conveyors.

Curve Fitting

In this example a smoothly curved surface is created from a number of known points. The first example is in two dimensions however it is relatively easy to expand the system out to three dimensions. The example which we use is an aircraft wing with the cross sectional profile shown below:

Cross sectional curve of aircraft wing

The cutting part of the program is shown below.

I=0WHILE I<4POSITION.X=STARTX+(12*I*I)POSITION.Z=STARTZ+(18.67*I)-(2.0*I*I)-(0.67*I*I*I)POSITION.A=5-(1*I*I)LIN POSITION C_VELI=I+0.1ENDWHILE



This is a fairly simple two dimensional example with an orientation in the A co-ordinate to produce a tapered wing.

More complex arrangements are possible to create three dimensionally curved surfaces. Examples that have been done in the robot cell include ‘Spitfire’ wings with the curved plan view and cross section, yacht hull models, fan blades and aerodynamic cockpit canopys.

Downloading Data Arrays

Data from a variety of sources including scanners, design packages and mathematical software can be loaded into the robot for operational purposes.

Rapidform computer graphic model

For this example Rapidform was used to create the model and ASCI Point files are used to pass the point data to the robot controller.

Cutting the wax mould



A program is written to cut a mould from the data points available. This mould was then used to create a fibreglass part.

The finished piece



Auxiliary Control

I/O for auxiliary control

Connection to all of the auxiliary systems within the robot cell is done via the I/O system which consists of a Devicenet communication module which is wired to a Programmable Logic Controller. The PLC recieves signals from the robot programming and from control panel switches and can switch on output relays to start other units.

Three Phase AC Motors

Three phase motors are driven from a controller which provides forward/reverse, on/off and speed and acceleration control. The example here is made by Telemecanique and uses a 240 Volt single phase supply.

Three phase motor controller with the control panel open .

Our example motor is a 360W motor being driven by 240V from the motor control unit. Also attached to the motor are an inductive sensor which detects the passing of a lug on the shaft of the motor and an incremental sensor unit which is attached via a belt drive to the shaft and gives 500 pulses per revolution of the shaft. Both the incremantal sensor and the inductive unit are connected to the controlling PLC with the incremental sensor connected to a fast counter and the inductive sensor connected to a normal counter.

The three phase motor used in our example



Inductive sensorConnection to controller Incremental sensor

Although the system always requires significant amounts of tuning it is possible to have auxiliary systems such as tools, conveyors and turntables operating in this manner. Much more sophisticated versions of these systems are also available.

Pneumatics

Pneumatics are frequently used for grippers, reciprocating systems and some linear actuation. They are controlled by the electronic switching of solenoid valves from the robot controller.

Solenoid triggered pneumatic valve. Restrictor valve.

Pneumatic Cylinders retracted with the electrical limit switches.



Hydraulics

Hydraulic systems are generally used for high load operations involving payloads of hundreds or thousands of kilos. Pumps are driven by three phase electric motors, while directional valves are switched electronically with solenoid valves.

Hydraulic pump Return Out Solenoid valves

25mm and 40mm cylinders with a 300mm stroke.


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