© 2008 prentice hall, inc.15 – 1 operations management chapter 15 – short-term scheduling...

© 2008 Prentice Hall, Inc. 15 – 1

Operations ManagementOperations ManagementChapter 15 – Chapter 15 – Short-Term SchedulingShort-Term Scheduling

PowerPoint presentation to accompany PowerPoint presentation to accompany Heizer/Render Heizer/Render Principles of Operations Management, 7ePrinciples of Operations Management, 7eOperations Management, 9e Operations Management, 9e


OutlineOutline

Global Company Profile: Global Company Profile: Delta Air LinesDelta Air Lines

The Strategic Importance of Short-The Strategic Importance of Short-Term SchedulingTerm Scheduling

Scheduling IssuesScheduling Issues Forward and Backward SchedulingForward and Backward Scheduling

Scheduling CriteriaScheduling Criteria


Outline – ContinuedOutline – Continued

Scheduling Process-Focused Scheduling Process-Focused FacilitiesFacilities

Loading JobsLoading Jobs Input-Output ControlInput-Output Control

Gantt ChartsGantt Charts

Assignment MethodAssignment Method



Sequencing JobsSequencing Jobs Priority Rules for Dispatching JobsPriority Rules for Dispatching Jobs

Critical RatioCritical Ratio

Sequencing N Jobs on Two Sequencing N Jobs on Two Machines: Johnson’s RuleMachines: Johnson’s Rule

Limitations of Rule-Based Limitations of Rule-Based Dispatching SystemsDispatching Systems

Finite Capacity Scheduling (FCS)Finite Capacity Scheduling (FCS)



Theory of ConstraintsTheory of Constraints BottlenecksBottlenecks

Drum, Buffer, RopeDrum, Buffer, Rope

Scheduling Repetitive FacilitiesScheduling Repetitive Facilities

Scheduling ServicesScheduling Services Scheduling Service Employees with Scheduling Service Employees with

Cyclical SchedulingCyclical Scheduling


Learning ObjectivesLearning Objectives

When you complete this chapter you When you complete this chapter you should be able to:should be able to:

1.1. Explain the relationship between short-Explain the relationship between short-term scheduling, capacity planning, term scheduling, capacity planning, aggregate planning, and a master aggregate planning, and a master scheduleschedule

2.2. Draw Gantt loading and scheduling Draw Gantt loading and scheduling chartscharts

3.3. Apply the assignment method for Apply the assignment method for loading jobsloading jobs


Learning ObjectivesLearning Objectives

When you complete this chapter you When you complete this chapter you should be able to:should be able to:

4.4. Name and describe each of the priority Name and describe each of the priority sequencing rulessequencing rules

5.5. Use Johnson’s ruleUse Johnson’s rule

6.6. Define finite capacity schedulingDefine finite capacity scheduling

7.7. List the steps in the theory of List the steps in the theory of constraintsconstraints

8.8. Use the cyclical scheduling techniqueUse the cyclical scheduling technique


Delta AirlinesDelta Airlines

About 10% of Delta’s flights are About 10% of Delta’s flights are disrupted per year, half because of disrupted per year, half because of weatherweather

Cost is $440 million in lost revenue, Cost is $440 million in lost revenue, overtime pay, food and lodging overtime pay, food and lodging vouchersvouchers

The $33 million Operations Control The $33 million Operations Control Center adjusts to changes and keeps Center adjusts to changes and keeps flights flowingflights flowing

Saves Delta $35 million per yearSaves Delta $35 million per year


Strategic Importance of Strategic Importance of Short-Term SchedulingShort-Term Scheduling

Effective and efficient scheduling Effective and efficient scheduling can be a competitive advantagecan be a competitive advantage Faster movement of goods through a Faster movement of goods through a

facility means better use of assets facility means better use of assets and lower costsand lower costs

Additional capacity resulting from Additional capacity resulting from faster throughput improves customer faster throughput improves customer service through faster deliveryservice through faster delivery

Good schedules result in more Good schedules result in more dependable deliveriesdependable deliveries


Scheduling IssuesScheduling Issues

Scheduling deals with the timing of Scheduling deals with the timing of operationsoperations

The task is the allocation and The task is the allocation and prioritization of demandprioritization of demand

Significant issues areSignificant issues are The type of scheduling, forward or The type of scheduling, forward or

backwardbackward

The criteria for prioritiesThe criteria for priorities


Scheduling DecisionsScheduling Decisions

OrganizationOrganization Managers Must Schedule the FollowingManagers Must Schedule the Following

Arnold Palmer Arnold Palmer HospitalHospital

Operating room useOperating room usePatient admissionsPatient admissionsNursing, security, maintenance staffsNursing, security, maintenance staffsOutpatient treatmentsOutpatient treatments

University of University of MissouriMissouri

Classrooms and audiovisual equipmentClassrooms and audiovisual equipmentStudent and instructor schedulesStudent and instructor schedulesGraduate and undergraduate coursesGraduate and undergraduate courses

Lockheed Martin Lockheed Martin factoryfactory

Production of goodsProduction of goodsPurchases of materialsPurchases of materialsWorkersWorkers

Hard Rock CafeHard Rock Cafe Chef, waiters, bartendersChef, waiters, bartendersDelivery of fresh foodsDelivery of fresh foodsEntertainersEntertainersOpening of dining areasOpening of dining areas

Delta Air LinesDelta Air Lines Maintenance of aircraftMaintenance of aircraftDeparture timetablesDeparture timetablesFlight crews, catering, gate, ticketing personnelFlight crews, catering, gate, ticketing personnelTable 15.1Table 15.1


Figure 15.1Figure 15.1

Scheduling Scheduling FlowFlow


Forward and Backward Forward and Backward SchedulingScheduling

Forward scheduling starts as soon Forward scheduling starts as soon as the requirements are knownas the requirements are known

Produces a feasible schedule Produces a feasible schedule though it may not meet due datesthough it may not meet due dates

Frequently results in Frequently results in buildup of work-in-buildup of work-in-process inventoryprocess inventory

Due Due DateDateNowNow



Backward scheduling begins with Backward scheduling begins with the due date and schedules the final the due date and schedules the final operation firstoperation first

Schedule is produced by working Schedule is produced by working backwards though the processesbackwards though the processes

Resources may not Resources may not be available to be available to accomplish the accomplish the scheduleschedule




Backward scheduling begins with Backward scheduling begins with the due date and schedules the final the due date and schedules the final operation firstoperation first

Schedule is produced by working Schedule is produced by working backwards though the processesbackwards though the processes

Resources may not Resources may not be available to be available to accomplish the accomplish the scheduleschedule


Often these approaches are

Often these approaches are

combined to develop a trade-off

combined to develop a trade-off

between a feasible schedule and

between a feasible schedule and

customer due dates

customer due dates


Different Processes/ Different Processes/ Different ApproachesDifferent Approaches

Process-focused Process-focused facilitiesfacilities

Forward-looking schedulesForward-looking schedulesMRP due datesMRP due datesFinite capacity schedulingFinite capacity scheduling

Work cellsWork cells Forward-looking schedulesForward-looking schedulesMRP due datesMRP due datesDetailed schedule done using work cell Detailed schedule done using work cell priority rulespriority rules

Repetitive facilitiesRepetitive facilities Forward-looking schedule with a Forward-looking schedule with a balanced linebalanced linePull techniques for schedulingPull techniques for scheduling

Product-focused Product-focused facilitiesfacilities

Forward-looking schedule with stable Forward-looking schedule with stable demand and fixed capacitydemand and fixed capacityCapacity, set-up, and run times knownCapacity, set-up, and run times knownCapacity limited by long-term capital Capacity limited by long-term capital investmentinvestmentTable 15.2Table 15.2


Scheduling CriteriaScheduling Criteria

1.1. Minimize completion timeMinimize completion time

2.2. Maximize utilization of facilitiesMaximize utilization of facilities

3.3. Minimize work-in-process (WIP) Minimize work-in-process (WIP) inventoryinventory

4.4. Minimize customer waiting timeMinimize customer waiting time

Optimize the use of resources so Optimize the use of resources so that production objectives are metthat production objectives are met


Scheduling Process-Scheduling Process-Focused FacilitiesFocused Facilities

1.1. Schedule incoming orders without Schedule incoming orders without violating capacity constraintsviolating capacity constraints

2.2. Check availability of tools and materials Check availability of tools and materials before releasing an orderbefore releasing an order

3.3. Establish due dates for each job and Establish due dates for each job and check progresscheck progress

4.4. Check work in progressCheck work in progress

5.5. Provide feedbackProvide feedback

6.6. Provide work efficiency statistics and Provide work efficiency statistics and monitor timesmonitor times


Planning and Control FilesPlanning and Control Files

1.1. An item master file contains information about An item master file contains information about each componenteach component

2.2. A routing file indicates each component’s flow A routing file indicates each component’s flow through the shopthrough the shop

3.3. A work-center master file contains information A work-center master file contains information about the work centerabout the work center

Planning FilesPlanning Files

Control FilesControl Files

Track the actual progress made against Track the actual progress made against the planthe plan


Loading JobsLoading Jobs

Assign jobs so that costs, idle Assign jobs so that costs, idle time, or completion time are time, or completion time are minimizedminimized

Two forms of loadingTwo forms of loading Capacity orientedCapacity oriented

Assigning specific jobs to work Assigning specific jobs to work centerscenters


Input-Output ControlInput-Output Control

Identifies overloading and Identifies overloading and underloading conditionsunderloading conditions

Prompts managerial action to Prompts managerial action to resolve scheduling problemsresolve scheduling problems

Can be maintained using ConWIP Can be maintained using ConWIP cards that control the scheduling cards that control the scheduling of batchesof batches


Input-Output Control Input-Output Control ExampleExample

Week Ending 6/6 6/13 6/20 6/27 7/4 7/11

Planned Input 280 280 280 280 280

Actual Input 270 250 280 285 280

Cumulative Deviation –10 –40 –40 –35

Planned Output 320 320 320 320

Actual Output 270 270 270 270


Cumulative Change in Backlog

0 –20 –10 +5


Work Center DNC Milling (in standard hours)



Work Center DNC Milling (in standard hours)

Week Ending 6/6 6/13 6/20 6/27 7/4 7/11

Planned Input 280 280 280 280 280

Actual Input 270 250 280 285 280


Planned Output 320 320 320 320

Actual Output 270 270 270 270


Cumulative Change in Backlog

0 –20 –10 +5

Explanation:270 input, 270 output implies 0 change

Explanation: 250 input,270 output implies –20 change




Options available to operations Options available to operations personnel include:personnel include:

1.1. Correcting performancesCorrecting performances

2.2. Increasing capacityIncreasing capacity

3.3. Increasing or reducing input to Increasing or reducing input to the work centerthe work center


Gantt ChartsGantt Charts

Load chart shows the loading and Load chart shows the loading and idle times of departments, machines, idle times of departments, machines, or facilitiesor facilities

Displays relative workloads over Displays relative workloads over timetime

Schedule chart monitors jobs in Schedule chart monitors jobs in processprocess

All Gantt charts need to be updated All Gantt charts need to be updated frequently to account for changesfrequently to account for changes


Gantt Load Chart ExampleGantt Load Chart Example


Day Monday Tuesday Wednesday Thursday FridayWork Center

Metalworks

Mechanical

Electronics

Painting

Job 349

Job 349

Job 349

Job 408

Job 408

Job 408

ProcessingProcessing UnscheduledUnscheduled Center not availableCenter not available

Job 350

Job 349

Job 295


Gantt Schedule Chart Gantt Schedule Chart ExampleExample


Job Day 1

Day 2

Day 3

Day 4

Day 5

Day 6

Day 7

Day 8

A

B

C

NowNow

Maintenance

Start of an Start of an activityactivity

End of an End of an activityactivity

Scheduled Scheduled activity time activity time allowedallowed

Actual work Actual work progressprogress

Nonproduction Nonproduction timetime

Point in time Point in time when chart is when chart is reviewedreviewed



A special class of linear A special class of linear programming models that assign programming models that assign tasks or jobs to resourcestasks or jobs to resources

Objective is to minimize cost or Objective is to minimize cost or timetime

Only one job (or worker) is Only one job (or worker) is assigned to one machine (or assigned to one machine (or project)project)



Build a table of costs or time Build a table of costs or time associated with particular associated with particular assignmentsassignments

TypesetterTypesetter

JobJob AA BB CC

R-34R-34 $11$11 $14$14 $ 6$ 6

S-66S-66 $ 8$ 8 $10$10 $11$11

T-50T-50 $ 9$ 9 $12$12 $ 7$ 7



1.1. Create zero opportunity costs by Create zero opportunity costs by repeatedly subtracting the lowest costs repeatedly subtracting the lowest costs from each row and columnfrom each row and column

2.2. Draw the minimum number of vertical Draw the minimum number of vertical and horizontal lines necessary to cover and horizontal lines necessary to cover all the zeros in the table. If the number all the zeros in the table. If the number of lines equals either the number of of lines equals either the number of rows or the number of columns, rows or the number of columns, proceed to step 4. Otherwise proceed to proceed to step 4. Otherwise proceed to step 3.step 3.



3.3. Subtract the smallest number not Subtract the smallest number not covered by a line from all other covered by a line from all other uncovered numbers. Add the same uncovered numbers. Add the same number to any number at the number to any number at the intersection of two lines. Return to intersection of two lines. Return to step 2.step 2.

4.4. Optimal assignments are at zero Optimal assignments are at zero locations in the table. Select one, draw locations in the table. Select one, draw lines through the row and column lines through the row and column involved, and continue to the next involved, and continue to the next assignment.assignment.


Assignment ExampleAssignment Example

AA BB CCJobJob

R-34R-34 $11$11 $14$14 $ 6$ 6

S-66S-66 $ 8$ 8 $10$10 $11$11

T-50T-50 $ 9$ 9 $12$12 $ 7$ 7


AA BB CCJobJob

R-34R-34 $ 5$ 5 $ 8$ 8 $ 0$ 0

S-66S-66 $ 0$ 0 $ 2$ 2 $ 3$ 3

T-50T-50 $ 2$ 2 $ 5$ 5 $ 0$ 0


Step 1a - RowsStep 1a - Rows

AA BB CCJobJob

R-34R-34 $ 5$ 5 $ 6$ 6 $ 0$ 0

S-66S-66 $ 0$ 0 $ 0$ 0 $ 3$ 3

T-50T-50 $ 2$ 2 $ 3$ 3 $ 0$ 0


Step 1b - ColumnsStep 1b - Columns



Step 2 - LinesStep 2 - Lines

AA BB CCJobJob

R-34R-34 $ 5$ 5 $ 6$ 6 $ 0$ 0

S-66S-66 $ 0$ 0 $ 0$ 0 $ 3$ 3

T-50T-50 $ 2$ 2 $ 3$ 3 $ 0$ 0


Because only two lines Because only two lines are needed to cover all are needed to cover all the zeros, the solution the zeros, the solution is not optimalis not optimal

Step 3 - SubtractionStep 3 - Subtraction

AA BB CCJobJob

R-34R-34 $ 3$ 3 $ 4$ 4 $ 0$ 0

S-66S-66 $ 0$ 0 $ 0$ 0 $ 5$ 5

T-50T-50 $ 0$ 0 $ 1$ 1 $ 0$ 0


The smallest uncovered The smallest uncovered number is 2 so this is number is 2 so this is subtracted from all other subtracted from all other uncovered numbers and uncovered numbers and added to numbers at the added to numbers at the intersection of linesintersection of lines



Because three lines are Because three lines are needed, the solution is needed, the solution is optimal and optimal and assignments can be assignments can be mademade

Step 2 - LinesStep 2 - Lines

AA BB CCJobJob

R-34R-34 $ 3$ 3 $ 4$ 4 $ 0$ 0

S-66S-66 $ 0$ 0 $ 0$ 0 $ 5$ 5

T-50T-50 $ 0$ 0 $ 1$ 1 $ 0$ 0


Start by assigning R-34 to Start by assigning R-34 to worker C as this is the only worker C as this is the only possible assignment for possible assignment for worker C.worker C.

Step 4 - AssignmentsStep 4 - Assignments

AA BB CCJobJobR-34 $ 3$ 3 $ 4$ 4 $ 0S-66 $ 0$ 0 $ 0 $ 5$ 5T-50 $ 0 $ 1$ 1 $ 0$ 0


Job T-50 must Job T-50 must go to worker A as worker C go to worker A as worker C is already assigned. This is already assigned. This leaves S-66 for worker B.leaves S-66 for worker B.



From the original cost table

Minimum cost = $6 + $10 + $9 = $25

Step 4 - AssignmentsStep 4 - Assignments

AA BB CCJobJobR-34 $ 3$ 3 $ 4$ 4 $ 0S-66 $ 0$ 0 $ 0 $ 5$ 5T-50 $ 0 $ 1$ 1 $ 0$ 0

TypesetterTypesetterAA BB CC

JobJob

R-34R-34 $11$11 $14$14 $ 6$ 6

S-66S-66 $ 8$ 8 $10$10 $11$11

T-50T-50 $ 9$ 9 $12$12 $ 7$ 7



Sequencing JobsSequencing Jobs

Specifies the order in which jobs Specifies the order in which jobs should be performed at work centersshould be performed at work centers

Priority rules are used to dispatch or Priority rules are used to dispatch or sequence jobssequence jobs FCFS: First come, first servedFCFS: First come, first served

SPT: Shortest processing timeSPT: Shortest processing time

EDD: Earliest due dateEDD: Earliest due date

LPT: Longest processing timeLPT: Longest processing time


Sequencing ExampleSequencing Example

JobJob

Job Work Job Work (Processing) Time(Processing) Time

(Days)(Days)

Job Due Job Due DateDate

(Days)(Days)

AA 66 88

BB 22 66

CC 88 1818

DD 33 1515

EE 99 2323

Apply the four popular sequencing rules Apply the four popular sequencing rules to these five jobsto these five jobs



Job Job SequenceSequence

Job Work Job Work (Processing) (Processing)

TimeTimeFlow Flow TimeTime


Job Job LatenessLateness

AA 66 66 88 00

BB 22 88 66 22

CC 88 1616 1818 00

DD 33 1919 1515 44

EE 99 2828 2323 55

2828 7777 1111

FCFS: Sequence A-B-C-D-EFCFS: Sequence A-B-C-D-E








AA 66 66 88 00

BB 22 88 66 22

CC 88 1616 1818 00

DD 33 1919 1515 44

EE 99 2828 2323 55

2828 7777 1111

FCFS: Sequence A-B-C-D-EFCFS: Sequence A-B-C-D-E

Average completion time = = 77/5 = 15.4 daysSum of total flow time

Number of jobs

Utilization = = 28/77 = 36.4%Total job work time

Sum of total flow time

Average number of jobs in the system = = 77/28 = 2.75 jobs

Sum of total flow timeTotal job work time

Average job lateness = = 11/5 = 2.2 daysTotal late daysNumber of jobs








BB 22 22 66 00

DD 33 55 1515 00

AA 66 1111 88 33

CC 88 1919 1818 11

EE 99 2828 2323 55

2828 6565 99

SPT: Sequence B-D-A-C-ESPT: Sequence B-D-A-C-E








BB 22 22 66 00

DD 33 55 1515 00

AA 66 1111 88 33

CC 88 1919 1818 11

EE 99 2828 2323 55

2828 6565 99

SPT: Sequence B-D-A-C-ESPT: Sequence B-D-A-C-E

Average completion time = = 65/5 = 13 daysSum of total flow time

Number of jobs













BB 22 22 66 00

AA 66 88 88 00

DD 33 1111 1515 00

CC 88 1919 1818 11

EE 99 2828 2323 55

2828 6868 66

EDD: Sequence B-A-D-C-EEDD: Sequence B-A-D-C-E








BB 22 22 66 00

AA 66 88 88 00

DD 33 1111 1515 00

CC 88 1919 1818 11

EE 99 2828 2323 55

2828 6868 66

EDD: Sequence B-A-D-C-EEDD: Sequence B-A-D-C-E


Number of jobs













EE 99 99 2323 00

CC 88 1717 1818 00

AA 66 2323 88 1515

DD 33 2626 1515 1111

BB 22 2828 66 2222

2828 103103 4848

LPT: Sequence E-C-A-D-BLPT: Sequence E-C-A-D-B








EE 99 99 2323 00

CC 88 1717 1818 00

AA 66 2323 88 1515

DD 33 2626 1515 1111

BB 22 2828 66 2222

2828 103103 4848

LPT: Sequence E-C-A-D-BLPT: Sequence E-C-A-D-B


Number of jobs








RuleRule

Average Average Completion Completion Time (Days)Time (Days)

Utilization Utilization (%)(%)

Average Number Average Number of Jobs in of Jobs in

SystemSystem

Average Average Lateness Lateness

(Days)(Days)

FCFSFCFS 15.415.4 36.436.4 2.752.75 2.22.2

SPTSPT 13.013.0 43.143.1 2.322.32 1.81.8

EDDEDD 13.613.6 41.241.2 2.432.43 1.21.2

LPTLPT 20.620.6 27.227.2 3.683.68 9.69.6

Summary of RulesSummary of Rules


Comparison of Comparison of Sequencing RulesSequencing Rules

No one sequencing rule excels on all criteriaNo one sequencing rule excels on all criteria SPT does well on minimizing flow time and SPT does well on minimizing flow time and

number of jobs in the systemnumber of jobs in the system But SPT moves long jobs to But SPT moves long jobs to

the end which may result the end which may result in dissatisfied customersin dissatisfied customers

FCFS does not do especially FCFS does not do especially well (or poorly) on any well (or poorly) on any criteria but is perceived criteria but is perceived as fair by customersas fair by customers

EDD minimizes latenessEDD minimizes lateness


Critical Ratio (CR)Critical Ratio (CR)

An index number found by dividing the An index number found by dividing the time remaining until the due date by the time remaining until the due date by the work time remaining on the jobwork time remaining on the job

Jobs with low critical ratios are Jobs with low critical ratios are scheduled ahead of jobs with higher scheduled ahead of jobs with higher critical ratioscritical ratios

Performs well on average job lateness Performs well on average job lateness criteriacriteria

CR = =CR = =Due date - Today’s dateDue date - Today’s date

Work (lead) time remainingWork (lead) time remaining

Time remainingTime remaining

Workdays remainingWorkdays remaining


Critical Ratio ExampleCritical Ratio Example

JobJobDue Due DateDate

Workdays Workdays RemainingRemaining Critical RatioCritical Ratio

Priority Priority OrderOrder

AA 3030 44 (30 - 25)/4 = 1.25(30 - 25)/4 = 1.25 33

BB 2828 55 (28 - 25)/5 = .60(28 - 25)/5 = .60 11

CC 2727 22 (27 - 25)/2 = 1.00(27 - 25)/2 = 1.00 22

Currently Day Currently Day 2525

With CR < 1, Job B is late. Job C is just on schedule With CR < 1, Job B is late. Job C is just on schedule and Job A has some slack time.and Job A has some slack time.


Critical Ratio TechniqueCritical Ratio Technique

1.1. Helps determine the status of specific Helps determine the status of specific jobsjobs

2.2. Establishes relative priorities among Establishes relative priorities among jobs on a common basisjobs on a common basis

3.3. Relates both stock and make-to-order Relates both stock and make-to-order jobs on a common basisjobs on a common basis

4.4. Adjusts priorities automatically for Adjusts priorities automatically for changes in both demand and job changes in both demand and job progressprogress

5.5. Dynamically tracks job progressDynamically tracks job progress


Sequencing N Jobs on Two Sequencing N Jobs on Two Machines: Johnson’s RuleMachines: Johnson’s Rule

Works with two or more jobs that Works with two or more jobs that pass through the same two pass through the same two machines or work centersmachines or work centers

Minimizes total production time and Minimizes total production time and idle timeidle time


Johnson’s RuleJohnson’s Rule

1.1. List all jobs and times for each work List all jobs and times for each work centercenter

2.2. Choose the job with the shortest activity Choose the job with the shortest activity time. If that time is in the first work center, time. If that time is in the first work center, schedule the job first. If it is in the second schedule the job first. If it is in the second work center, schedule the job last.work center, schedule the job last.

3.3. Once a job is scheduled, it is eliminated Once a job is scheduled, it is eliminated from the list from the list

4.4. Repeat steps 2 and 3 working toward the Repeat steps 2 and 3 working toward the center of the sequencecenter of the sequence


Johnson’s Rule ExampleJohnson’s Rule Example

JobJobWork Center 1 Work Center 1

(Drill Press)(Drill Press)Work Center 2 Work Center 2

(Lathe)(Lathe)

AA 55 22

BB 33 66

CC 88 44

DD 1010 77

EE 77 1212


BB EE DD CC AA




(Lathe)(Lathe)

AA 55 22

BB 33 66

CC 88 44

DD 1010 77

EE 77 1212





(Lathe)(Lathe)

AA 55 22

BB 33 66

CC 88 44

DD 1010 77

EE 77 1212

TimeTime 00 33 1010 2020 2828 3333

B ACDEWC 1

WC 2

BB AACCDDEE





(Lathe)(Lathe)

AA 55 22

BB 33 66

CC 88 44

DD 1010 77

EE 77 1212

TimeTime 00 33 1010 2020 2828 3333

TimeTime 0 0 11 33 55 77 99 1010 1111 1212 1313 1717 1919 21 22 2321 22 232525 2727 2929 3131 33333535

B ACDE

B ACDE

WC 1

WC 2

BB EE DD CC AA

BB AACCDDEE


Limitations of Rule-Based Limitations of Rule-Based Dispatching SystemsDispatching Systems

1.1. Scheduling is dynamic and rules Scheduling is dynamic and rules need to be revised to adjust to need to be revised to adjust to changeschanges

2.2. Rules do not look upstream or Rules do not look upstream or downstreamdownstream

3.3. Rules do not look beyond due Rules do not look beyond due datesdates


Finite Capacity SchedulingFinite Capacity Scheduling

Overcomes disadvantages of rule-based Overcomes disadvantages of rule-based systems by providing an interactive, systems by providing an interactive, computer-based graphical systemcomputer-based graphical system

May include rules and expert systems or May include rules and expert systems or simulation to allow real-time response to simulation to allow real-time response to system changessystem changes

Initial data often from an MRP systemInitial data often from an MRP system

FCS allows the balancing of delivery FCS allows the balancing of delivery needs and efficiencyneeds and efficiency



MRP Data• Master

schedule• BOM• Inventory

Priority rules

• Expert systems

• Simulation models

• Routing files• Work center

information

Tooling and other resources

Setups and run time


Interactive Finite Capacity SchedulingInteractive Finite Capacity Scheduling


Theory of ConstraintsTheory of Constraints

Throughput is the number of units Throughput is the number of units processed through the facility and soldprocessed through the facility and sold

TOC deals with the limits an organization TOC deals with the limits an organization faces in achieving its goalsfaces in achieving its goals

1.1. Identify the constraintsIdentify the constraints

2.2. Develop a plan for overcoming the constraintsDevelop a plan for overcoming the constraints

3.3. Focus resources on accomplishing the planFocus resources on accomplishing the plan

4.4. Reduce the effects of constraints by off-Reduce the effects of constraints by off-loading work or increasing capacityloading work or increasing capacity

5.5. Once successful, return to step 1 and identify Once successful, return to step 1 and identify new constraintsnew constraints


BottlenecksBottlenecks

Bottleneck work centers are constraints Bottleneck work centers are constraints that limit outputthat limit output Common occurrence due to frequent changesCommon occurrence due to frequent changes

Management techniques include:Management techniques include: Increasing the capacity of the constraintIncreasing the capacity of the constraint

Cross-trained employees and maintenanceCross-trained employees and maintenance

Alternative routings, procedures, or Alternative routings, procedures, or subcontractorssubcontractors

Moving inspection and testMoving inspection and test

Scheduling throughput to match bottleneck Scheduling throughput to match bottleneck capacitycapacity


Drum, Buffer, RopeDrum, Buffer, Rope

The drum is the beat of the system and The drum is the beat of the system and provides the schedule or pace of provides the schedule or pace of productionproduction

The buffer is the inventory necessary to The buffer is the inventory necessary to keep constraints operating at capacitykeep constraints operating at capacity

The rope provides the synchronization The rope provides the synchronization necessary to pull units through the necessary to pull units through the systemsystem


Scheduling Repetitive Scheduling Repetitive FacilitiesFacilities

Level material use can help Level material use can help repetitive facilities repetitive facilities Better satisfy customer Better satisfy customer

demanddemand

Lower inventory Lower inventory investmentinvestment

Reduce batch sizeReduce batch size

Better utilize equipment Better utilize equipment and facilitiesand facilities


Scheduling Repetitive Scheduling Repetitive FacilitiesFacilities

Advantages include:Advantages include:

1.1. Lower inventory levelsLower inventory levels

2.2. Faster product throughputFaster product throughput

3.3. Improved component qualityImproved component quality

4.4. Reduced floor-space requirementsReduced floor-space requirements

5.5. Improved communicationsImproved communications

6.6. Smoother production processSmoother production process


Scheduling ServicesScheduling Services

Service systems differ from manufacturingService systems differ from manufacturing

ManufacturingManufacturing ServicesServices

Schedules machines Schedules machines and materialsand materials

Schedule staffSchedule staff

Inventories used to Inventories used to smooth demandsmooth demand

Seldom maintain Seldom maintain inventoriesinventories

Machine-intensive and Machine-intensive and demand may be smoothdemand may be smooth

Labor-intensive and Labor-intensive and demand may be variabledemand may be variable

Scheduling may be bound Scheduling may be bound by union contractsby union contracts

Legal issues may constrain Legal issues may constrain flexible schedulingflexible scheduling

Few social or behavioral Few social or behavioral issuesissues

Social and behavioral Social and behavioral issues may be quite issues may be quite importantimportant



Hospitals have complex scheduling Hospitals have complex scheduling system to handle complex processes system to handle complex processes and material requirementsand material requirements

Banks use a cross-trained and flexible Banks use a cross-trained and flexible workforce and part-time workersworkforce and part-time workers

Retail stores use scheduling Retail stores use scheduling optimization systems that track sales, optimization systems that track sales, transactions, and customer traffic to transactions, and customer traffic to create work schedules in less time and create work schedules in less time and with improved customer satisfactionwith improved customer satisfaction



Airlines must meet complex FAA and Airlines must meet complex FAA and union regulations and often use linear union regulations and often use linear programming to develop optimal programming to develop optimal schedulesschedules

24/7 operations like police/fire 24/7 operations like police/fire departments, emergency hot lines, and departments, emergency hot lines, and mail order businesses use flexible mail order businesses use flexible workers and variable schedules, often workers and variable schedules, often created using computerized systemscreated using computerized systems


Demand ManagementDemand Management

Appointment or reservation Appointment or reservation systemssystems

FCFS sequencing rulesFCFS sequencing rules

Discounts or other promotional Discounts or other promotional schemesschemes

When demand management is not When demand management is not feasible, managing capacity feasible, managing capacity through staffing flexibility may be through staffing flexibility may be usedused


Scheduling Service Employees Scheduling Service Employees With Cyclical SchedulingWith Cyclical Scheduling

Objective is to meet staffing Objective is to meet staffing requirements with the minimum requirements with the minimum number of workersnumber of workers

Schedules need to be smooth and Schedules need to be smooth and keep personnel happykeep personnel happy

Many techniques exist from simple Many techniques exist from simple algorithms to complex linear algorithms to complex linear programming solutionsprogramming solutions


Cyclical Scheduling ExampleCyclical Scheduling Example

1.1. Determine the staffing requirementsDetermine the staffing requirements

2.2. Identify two consecutive days with the Identify two consecutive days with the lowest total requirements and assign lowest total requirements and assign these as days offthese as days off

3.3. Make a new set of requirements Make a new set of requirements subtracting the days worked by the first subtracting the days worked by the first employeeemployee

4.4. Apply step 2 to the new row Apply step 2 to the new row

5.5. Repeat steps 3 and 4 until all Repeat steps 3 and 4 until all requirements have been metrequirements have been met



MM TT WW TT FF SS SS

Employee 1Employee 1 55 55 66 55 44 33 33

Capacity (Employees)Capacity (Employees)

Excess CapacityExcess Capacity










Employee 7Employee 7 11












Employee 7Employee 7 11

Capacity (Employees)Capacity (Employees) 55 55 66 55 44 33 33

Excess CapacityExcess Capacity 00 00 00 00 00 11 00

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