Quản trị kinh doanh - Chapter 17: Scheduling

Chapter 17SchedulingLecture OutlineObjectives in SchedulingLoadingSequencingMonitoringAdvanced Planning and Scheduling SystemsTheory of ConstraintsEmployee SchedulingCopyright 2011 John Wiley & Sons, Inc.17-2What is Scheduling?Last stage of planning before production occursSpecifies when labor, equipment, and facilities are needed to produce a product or provide a serviceCopyright 2011 John Wiley & Sons, Inc.17-3Scheduled OperationsProcess IndustryLinear programmingEOQ with non-instantaneous replenishmentMass ProductionAssembly line balancingProjectProject -scheduling techniques (PERT, CPM)Batch ProductionAggregate planningMaster schedulingMaterial requirements planning (MRP)Capacity requirements planning (CRP)Copyright 2011 John Wiley & Sons, Inc.17-4Objectives in SchedulingMeet customer due datesMinimize job latenessMinimize response timeMinimize completion timeMinimize time in the systemMinimize overtimeMaximize machine or labor utilizationMinimize idle timeMinimize work-in-process inventoryCopyright 2011 John Wiley & Sons, Inc.17-5Shop Floor Control (SFC)Schedule and monitor day-to-day job shop productionAlso called production control and production activity control (PAC)Performed by production control departmentLoading - check availability of material, machines, and laborSequencing - release work orders to shop and issue dispatch lists for individual machinesMonitoring - maintain progress reports on each job until it is completeCopyright 2011 John Wiley & Sons, Inc.17-6LoadingProcess of assigning work to limited resourcesPerform work with most efficient resourcesUse assignment method of linear programming to determine allocationCopyright 2011 John Wiley & Sons, Inc.17-7Assignment MethodPerform row reductionssubtract minimum value in each row from all other row valuesPerform column reductionssubtract minimum value in each column from all other column valuesCross out all zeros in matrixuse minimum number of horizontal and vertical linesIf number of lines equals number of rows in matrix, then optimum solution has been found. Make assignments where zeros appearElse modify matrix:subtract minimum uncrossed value from all uncrossed valuesadd it to all cells where two lines intersectother values in matrix remain unchangedRepeat steps 3 and 4 until optimum solution is reachedCopyright 2011 John Wiley & Sons, Inc.17-8Assignment MethodCopyright 2011 John Wiley & Sons, Inc.17-9Initial PROJECTMatrix 1 2 3 4Bryan 10 5 6 10Kari 6 2 4 6Noah 7 6 5 6Chris 9 5 4 10 Row reduction Column reduction Cover all zeros 5 0 1 5 3 0 1 4 3 0 1 4 4 0 2 4 2 0 2 3 2 0 2 3 2 1 0 1 0 1 0 0 0 1 0 0 5 1 0 6 3 1 0 5 3 1 0 5 Number lines  number of rows so modify matrixCopyright 2011 John Wiley & Sons, Inc.17-10 1 2 3 4Bryan 1 0 1 2Kari 0 0 2 1Noah 0 3 2 0Chris 1 1 0 3PROJECT 1 2 3 4Bryan 10 5 6 10Kari 6 2 4 6Noah 7 6 5 6Chris 9 5 4 10PROJECTProject Cost = (5 + 6 + 4 + 6) X $100 = $2,100 Modify matrix Cover all zeros 1 0 1 2 1 0 1 2 0 0 2 1 0 0 2 1 0 3 2 0 0 3 2 0 1 1 0 3 1 1 0 3Number of lines = number of rows so at optimal solutionAssignment MethodAssignment Method - SetupCopyright 2011 John Wiley & Sons, Inc.17-11Solution goes hereOnly 1 leader canbe assigned to each projectClick “Solve” for solutionSum of all rows and columns = 1Assignment Method - SolutionCopyright 2011 John Wiley & Sons, Inc.17-12Assignments indicated by 1Cost of solutionSequencingPrioritize jobs assigned to a resourceIf no order specified use first-come first-served (FCFS)Other Sequencing RulesFCFS - first-come, first-servedLCFS - last come, first servedDDATE - earliest due dateCUSTPR - highest customer prioritySETUP - similar required setupsSLACK - smallest slackCR - smallest critical ratioSPT - shortest processing timeLPT - longest processing time Copyright 2011 John Wiley & Sons, Inc.17-13Minimum Slack & Smallest Critical RatioSLACK considers both work and time remainingCR recalculates sequence as processing continues and arranges information in ratio formCopyright 2011 John Wiley & Sons, Inc.17-14CR = = If CR > 1, job ahead of schedule If CR < 1, job behind schedule If CR = 1, job on schedule time remaining due date - today’s date work remaining remaining processing timeSLACK = (due date – today’s date) – (processing time)Sequencing Jobs Through One ProcessFlow time (completion time) Time for a job to flow through systemMakespanTime for a group of jobs to be completedTardinessDifference between a late job’s due date and its completion timeCopyright 2011 John Wiley & Sons, Inc.17-15Simple Sequencing RulesCopyright 2011 John Wiley & Sons, Inc.17-16 PROCESSING DUE JOB TIME DATE A 5 10 B 10 15 C 2 5 D 8 12 E 6 8Simple Sequencing Rules: FCFSCopyright 2011 John Wiley & Sons, Inc.17-17 A 0 5 5 10 0 B 5 10 15 15 0 C 15 2 17 5 12 D 17 8 25 12 13 E 25 6 31 8 23 Total 93 48 Average 93/5 = 18.60 48/5 = 9.6 FCFS START PROCESSING COMPLETION DUE SEQUENCE TIME TIME TIME DATE TARDINESSSimple Sequencing Rules: DDATECopyright 2011 John Wiley & Sons, Inc.17-18 C 0 2 2 5 0 E 2 6 8 8 0 A 8 5 13 10 3 D 13 8 21 12 9 B 21 10 31 15 16 Total 75 28 Average 75/5 = 15.00 28/5 = 5.6 DDATE START PROCESSING COMPLETION DUE SEQUENCE TIME TIME TIME DATE TARDINESSSimple SequencingRules: SLACKCopyright 2011 John Wiley & Sons, Inc.17-19A (10-0) – 5 = 5B (15-0) – 10 = 5C (5-0) – 2 = 3D (12-0) – 8 = 4E (8-0) – 6 = 2 E 0 6 6 8 0 C 6 2 8 5 3 D 8 8 16 12 4 A 16 5 21 10 11 B 21 10 31 15 16 Total 82 34 Average 82/5 = 16.40 34/5 = 6.8 SLACK START PROCESSING COMPLETION DUE SEQUENCE TIME TIME TIME DATE TARDINESSSimple Sequencing Rules: SPTCopyright 2011 John Wiley & Sons, Inc.17-20 C 0 2 2 5 0 A 2 5 7 10 0 E 7 6 13 8 5 D 13 8 21 12 9 B 21 10 31 15 16 Total 74 30 Average 74/5 = 14.80 30/5 = 6 SPT START PROCESSING COMPLETION DUE SEQUENCE TIME TIME TIME DATE TARDINESSSimple Sequencing Rules: SummaryCopyright 2011 John Wiley & Sons, Inc.17-21FCFS 18.60 9.6 3 23DDATE 15.00 5.6 3 16SLACK 16.40 6.8 4 16SPT 14.80 6.0 3 16 AVERAGE AVERAGE NO. OF MAXIMUM RULE COMPLETION TIME TARDINESS JOBS TARDY TARDINESSBest valuesSequencing Jobs Through Two Serial ProcessCopyright 2011 John Wiley & Sons, Inc.17-22Johnson’s RuleList time required to process each job at each process. Set up a one-dimensional matrix to represent desired sequence with # of slots equal to # of jobs.Select smallest processing time at either process. If that time is on process 1, put the job as near to beginning of sequence as possible.If smallest time occurs on process 2, put the job as near to the end of the sequence as possible.Remove job from list.Repeat steps 2-4 until all slots in matrix are filled and all jobs are sequenced.SequencingWithExcelCopyright 2011 John Wiley & Sons, Inc.17-23Johnson’s RuleCopyright 2011 John Wiley & Sons, Inc.17-24 JOB PROCESS 1 PROCESS 2 A 6 8 B 11 6 C 7 3 D 9 7 E 5 10CEABDJohnson’s RuleCopyright 2011 John Wiley & Sons, Inc.17-25ABCDEEADBCProcess 1(sanding)511203138EADBCProcess 2(painting)51523303741Idle timeCompletion time = 41Idle time = 5+1+1+3=10Excel for Johnson’s RuleCopyright 2011 John Wiley & Sons, Inc.17-26User inputs processingtimes and sequenceExcel calculatescompletion timesand makespanWhen the set ofjobs is completedGuidelines for Selecting a Sequencing RuleSPT most useful when shop is highly congestedUse SLACK for periods of normal activityUse DDATE when only small tardiness values can be toleratedUse LPT if subcontracting is anticipatedUse FCFS when operating at low-capacity levelsDo not use SPT to sequence jobs that have to be assembled with other jobs at a later dateCopyright 2011 John Wiley & Sons, Inc.17-27MonitoringWork packageShop paperwork that travels with a jobGantt ChartShows both planned and completed activities against a time scaleInput/Output ControlMonitors the input and output from each work centerCopyright 2011 John Wiley & Sons, Inc.17-28Gantt ChartCopyright 2011 John Wiley & Sons, Inc.17-2912345689101112Days123Today’s DateJob 32BJob 23CJob 11CJob 12AFacilityKey:Planned activityCompleted activityBehind scheduleAhead of scheduleOn scheduleInput/Output ControlCopyright 2011 John Wiley & Sons, Inc.17-30Planned input 65 65 70 70 270Actual input 0Deviation 0Planned output 75 75 75 75 300Actual output 0Deviation 0Backlog 30 PERIOD 1 2 3 4 TOTAL20 10 5 0Input/Output ControlCopyright 2011 John Wiley & Sons, Inc.17-31Planned input 65 65 70 70 270Actual input 60 60 65 65 250Deviation -5 -5 -5 -5 -20Planned output 75 75 75 75 300Actual output 75 75 65 65 280Deviation -0 -0 -10 -10 -20Backlog 30 15 0 0 0PERIOD 1 2 3 4 TOTALExcel for Input/Output ControlCopyright 2011 John Wiley & Sons, Inc.17-32User inputsplanned andactual valuesExcel calculates deviationsand backlogAdvanced Planning and Scheduling SystemsInfinite scheduling - assumes infinite capacityLoads without regard to capacityThen levels the load and sequences jobsFinite scheduling - assumes finite (limited) capacitySequences jobs as part of the loading decisionResources are never loaded beyond capacityCopyright 2011 John Wiley & Sons, Inc.17-33Advanced Planning and Scheduling SystemsAdvanced planning and scheduling (APS)Add-ins to ERP systemsConstraint-based programming (CBP) identifies a solution space and evaluates alternativesGenetic algorithms based on natural selection properties of geneticsManufacturing execution system (MES) monitors status, usage, availability, qualityCopyright 2011 John Wiley & Sons, Inc.17-34Advanced Planning and SchedulingCopyright 2011 John Wiley & Sons, Inc.17-35Theory of ConstraintsNot all resources are used evenlyFinite scheduling approachConcentrate on the” bottleneck” resourceSynchronize flow through the bottleneckUse process and transfer batch sizes to move product through facilityCopyright 2011 John Wiley & Sons, Inc.17-36Drum-Buffer-RopeDrumBottleneck, beating to set the pace of production for the rest of the systemBuffer Inventory placed in front of the bottleneck to ensure it is always kept busyDetermines output or throughput of the systemRopeCommunication signal; tells processes upstream when they should begin productionCopyright 2011 John Wiley & Sons, Inc.17-37TOC Scheduling ProcedureIdentify bottleneckSchedule job first whose lead time to bottleneck is less than or equal to bottleneck processing timeForward schedule bottleneck machineBackward schedule other machines to sustain bottleneck scheduleTransfer in batch sizes smaller than process batch sizeCopyright 2011 John Wiley & Sons, Inc.17-38Synchronous ManufacturingCopyright 2011 John Wiley & Sons, Inc.17-39BACDB1 1 5B2 2 3B3 1 7C1 3 2C2 1 10C3 2 15D1 3 10D2 2 8D3 3 5Item iKey:iIj k lOperation j of item i performed at machine center k takes l minutes to processCopyright 2011 John Wiley & Sons, Inc.17-40Synchronous ManufacturingDemand = 100 A’sMachine setup time = 60 minutes MACHINE 1 MACHINE 2 MACHINE 3 B1 5 B2 3 C1 2 B3 7 C3 15 D3 5 C2 10 D2 8 D1 10 Sum 22 26* 17* BottleneckSynchronous ManufacturingCopyright 2011 John Wiley & Sons, Inc.17-41Machine 1Machine 3SetupCompletion time100223221227320200126019402737C2B1B3C3B2D2C1D1D3IdleSetupSetupSetupSetup156215121872SetupMachine 2Idle2Employee SchedulingLabor is very flexible resourceScheduling workforce is complicated, repetitive taskAssignment method can be usedHeuristics are commonly used17-42Copyright 2011 John Wiley & Sons, Inc.Employee Scheduling HeuristicCopyright 2011 John Wiley & Sons, Inc.17-43Let N = no. of workers available Di = demand for workers on day i X = day working O = day offAssign the first N - D1 workers day 1 off. Assign the next N - D2 workers day 2 off. Continue in a similar manner until all days are have been scheduledIf number of workdays for full time employee < 5, assign remaining workdays so consecutive days off are possibleAssign any remaining work to part-time employeesIf consecutive days off are desired, consider switching schedules among days with the same demand requirementsEmployee SchedulingCopyright 2011 John Wiley & Sons, Inc.17-44 DAY OF WEEK M T W TH F SA SU MIN NO. OF WORKERS REQUIRED 3 3 4 3 4 5 3 Taylor Smith Simpson Allen Dickerson Employee SchedulingCopyright 2011 John Wiley & Sons, Inc.17-45 DAY OF WEEK M T W TH F SA SU MIN NO. OF WORKERS REQUIRED 3 3 4 3 4 5 3 Taylor O X X O X X X Smith O X X O X X X Simpson X O X X O X X Allen X O X X X X O Dickerson X X O X X X OCompleted schedule satisfies requirements but has no consecutive days offCopyright 2011 John Wiley & Sons, Inc.17-46 DAY OF WEEK M T W TH F SA SU MIN NO. OF WORKERS REQUIRED 3 3 4 3 4 5 3 Taylor O O X X X X X Smith O O X X X X X Simpson X X O O X X X Allen X X X O X X O Dickerson X X X X O X ORevised schedule satisfies requirements with consecutive days off for most employeesEmployee SchedulingAutomated Scheduling SystemsStaff SchedulingAssign workers to standardize shift patternsSchedule Bidding Workers bid for certain shift positions or schedulesSchedule OptimizationCreates demand-driven forecast of labor needsAssigns workers to variable schedulesUses mathematical programming and artificial intelligence techniquesCopyright 2011 John Wiley & Sons, Inc.17-47Copyright 2011 John Wiley & Sons, Inc.17-48Copyright 2011 John Wiley & Sons, Inc.All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. 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