2008 Prentice Hall, Inc. 15 – 1 Operations Management Chapter 15 – Chapter 15 – Short-Term Scheduling Short-Term Scheduling PowerPoint presentation to accompany PowerPoint presentation to accompany Heizer/Render Heizer/Render Principles of Operations Management, 7e Principles of Operations Management, 7e Operations Management, 9e Operations Management, 9e
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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
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
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
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
Forward and Backward Forward and Backward SchedulingScheduling
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
Forward and Backward Forward and Backward SchedulingScheduling
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
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
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
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
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)
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.
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
TypesetterTypesetter
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
TypesetterTypesetter
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.
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.
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
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
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
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.
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
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
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
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
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
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
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
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
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