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Chapter 17 Scheduling. Lecture Outline Objectives in Scheduling Loading Sequencing Monitoring Advanced Planning and Scheduling Systems Theory of Constraints.

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Presentation on theme: "Chapter 17 Scheduling. Lecture Outline Objectives in Scheduling Loading Sequencing Monitoring Advanced Planning and Scheduling Systems Theory of Constraints."— Presentation transcript:

1 Chapter 17 Scheduling

2 Lecture Outline Objectives in Scheduling Loading Sequencing Monitoring Advanced Planning and Scheduling Systems Theory of Constraints Employee Scheduling Copyright 2011 John Wiley & Sons, Inc.17-2

3 What is Scheduling? Last stage of planning before production occurs Specifies when labor, equipment, and facilities are needed to produce a product or provide a service Copyright 2011 John Wiley & Sons, Inc.17-3

4 Scheduled Operations Process Industry –Linear programming –EOQ with non- instantaneous replenishment Mass Production –Assembly line balancing Project –Project -scheduling techniques (PERT, CPM) Batch Production –Aggregate planning –Master scheduling –Material requirements planning (MRP) –Capacity requirements planning (CRP) Copyright 2011 John Wiley & Sons, Inc.17-4

5 Objectives in Scheduling Meet customer due dates Minimize job lateness Minimize response time Minimize completion time Minimize time in the system Minimize overtime Maximize machine or labor utilization Minimize idle time Minimize work-in-process inventory Copyright 2011 John Wiley & Sons, Inc.17-5

6 Shop Floor Control (SFC) Schedule and monitor day-to-day job shop production Also called production control and production activity control (PAC) Performed by production control department Loading - check availability of material, machines, and labor Sequencing - release work orders to shop and issue dispatch lists for individual machines Monitoring - maintain progress reports on each job until it is complete Copyright 2011 John Wiley & Sons, Inc.17-6

7 Loading Process of assigning work to limited resources Perform work with most efficient resources Use assignment method of linear programming to determine allocation Copyright 2011 John Wiley & Sons, Inc.17-7

8 Assignment Method 1.Perform row reductions – subtract minimum value in each row from all other row values 2.Perform column reductions – subtract minimum value in each column from all other column values 3.Cross out all zeros in matrix – use minimum number of horizontal and vertical lines 4.If number of lines equals number of rows in matrix, then optimum solution has been found. Make assignments where zeros appear ‾ Else modify matrix: ‾ subtract minimum uncrossed value from all uncrossed values ‾ add it to all cells where two lines intersect ‾ other values in matrix remain unchanged 5.Repeat steps 3 and 4 until optimum solution is reached Copyright 2011 John Wiley & Sons, Inc.17-8

9 Assignment Method Copyright 2011 John Wiley & Sons, Inc.17-9 Initial PROJECT Matrix1234 Bryan Kari6246 Noah7656 Chris95410 Row reduction Column reduction Cover all zeros Number lines  number of rows so modify matrix

10 Copyright 2011 John Wiley & Sons, Inc Bryan1012 Kari0021 Noah0320 Chris1103 PROJECT 1234 Bryan Kari6246 Noah7656 Chris95410 PROJECT Project Cost = ( ) X $100 = $2,100 Modify matrixCover all zeros Number of lines = number of rows so at optimal solution Assignment Method

11 Assignment Method - Setup Copyright 2011 John Wiley & Sons, Inc Solution goes here Only 1 leader can be assigned to each project Click “Solve” for solution Sum of all rows and columns = 1

12 Assignment Method - Solution Copyright 2011 John Wiley & Sons, Inc Assignments indicated by 1 Cost of solution

13 Sequencing Prioritize jobs assigned to a resource If no order specified use first-come first-served (FCFS) Other Sequencing Rules FCFS - first-come, first-served LCFS - last come, first served DDATE - earliest due date CUSTPR - highest customer priority SETUP - similar required setups SLACK - smallest slack CR - smallest critical ratio SPT - shortest processing time LPT - longest processing time Copyright 2011 John Wiley & Sons, Inc.17-13

14 Minimum Slack & Smallest Critical Ratio SLACK considers both work and time remaining CR recalculates sequence as processing continues and arranges information in ratio form Copyright 2011 John Wiley & Sons, Inc CR = = If CR > 1, job ahead of schedule If CR < 1, job behind schedule If CR = 1, job on schedule time remainingdue date - today’s date work remainingremaining processing time SLACK = (due date – today’s date) – (processing time)

15 Sequencing Jobs Through One Process Flow time (completion time) Time for a job to flow through system Makespan Time for a group of jobs to be completed Tardiness Difference between a late job’s due date and its completion time Copyright 2011 John Wiley & Sons, Inc.17-15

16 Simple Sequencing Rules Copyright 2011 John Wiley & Sons, Inc PROCESSINGDUE JOBTIMEDATE A510 B1015 C25 D812 E68

17 Simple Sequencing Rules: FCFS Copyright 2011 John Wiley & Sons, Inc A B C D E Total 9348 Average 93/5 = /5 = 9.6 FCFSSTARTPROCESSINGCOMPLETIONDUE SEQUENCETIMETIMETIMEDATETARDINESS

18 Simple Sequencing Rules: DDATE Copyright 2011 John Wiley & Sons, Inc C02250 E26880 A D B Total7528 Average75/5 = /5 = 5.6 DDATESTARTPROCESSINGCOMPLETIONDUE SEQUENCETIMETIMETIMEDATETARDINESS

19 Simple Sequencing Rules: SLACK Copyright 2011 John Wiley & Sons, Inc A(10-0) – 5 = 5 B(15-0) – 10 = 5 C(5-0) – 2 = 3 D(12-0) – 8 = 4 E(8-0) – 6 = 2 E06680 C62853 D A B Total8234 Average82/5 = /5 = 6.8 SLACKSTARTPROCESSINGCOMPLETIONDUE SEQUENCETIMETIMETIMEDATETARDINESS

20 Simple Sequencing Rules: SPT Copyright 2011 John Wiley & Sons, Inc C02250 A E D B Total7430 Average74/5 = /5 = 6 SPTSTARTPROCESSINGCOMPLETIONDUE SEQUENCETIMETIMETIMEDATETARDINESS

21 Simple Sequencing Rules: Summary Copyright 2011 John Wiley & Sons, Inc FCFS DDATE SLACK SPT AVERAGEAVERAGENO. OFMAXIMUM RULECOMPLETION TIMETARDINESSJOBS TARDYTARDINESS Best values

22 Sequencing Jobs Through Two Serial Process Copyright 2011 John Wiley & Sons, Inc Johnson’s Rule 1. 1.List 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.

23 Sequencing With Excel Copyright 2011 John Wiley & Sons, Inc.17-23

24 Johnson’s Rule Copyright 2011 John Wiley & Sons, Inc JOBPROCESS 1PROCESS 2 A68 B116 C73 D97 E510 CE A B D

25 Johnson’s Rule Copyright 2011 John Wiley & Sons, Inc ABCDE EADBC Process 1 (sanding) EADBC Process 2 (painting) Idle time Completion time = 41 Idle time = =10

26 Excel for Johnson’s Rule Copyright 2011 John Wiley & Sons, Inc User inputs processing times and sequence Excel calculates completion times and makespan When the set of jobs is completed

27 Guidelines for Selecting a Sequencing Rule SPT most useful when shop is highly congested Use SLACK for periods of normal activity Use DDATE when only small tardiness values can be tolerated Use LPT if subcontracting is anticipated Use FCFS when operating at low-capacity levels Do not use SPT to sequence jobs that have to be assembled with other jobs at a later date Copyright 2011 John Wiley & Sons, Inc.17-27

28 Monitoring Work package Shop paperwork that travels with a job Gantt Chart Shows both planned and completed activities against a time scale Input/Output Control Monitors the input and output from each work center Copyright 2011 John Wiley & Sons, Inc.17-28

29 Gantt Chart Copyright 2011 John Wiley & Sons, Inc Days Today’s Date Job 32B Job 23C Job 11CJob 12A Facility Key: Planned activity Completed activity Behind schedule Ahead of schedule On schedule

30 Input/Output Control Copyright 2011 John Wiley & Sons, Inc Planned input Actual input0 Deviation0 Planned output Actual output0 Deviation0 Backlog30 PERIOD1234TOTAL

31 Input/Output Control Copyright 2011 John Wiley & Sons, Inc Planned input Actual input Deviation Planned output Actual output Deviation Backlog PERIOD1234TOTAL

32 Excel for Input/Output Control Copyright 2011 John Wiley & Sons, Inc User inputs planned and actual values Excel calculates deviations and backlog

33 Advanced Planning and Scheduling Systems Infinite scheduling - assumes infinite capacity Loads without regard to capacity Then levels the load and sequences jobs Finite scheduling - assumes finite (limited) capacity Sequences jobs as part of the loading decision Resources are never loaded beyond capacity Copyright 2011 John Wiley & Sons, Inc.17-33

34 Advanced Planning and Scheduling Systems Advanced planning and scheduling (APS) Add-ins to ERP systems Constraint-based programming (CBP) identifies a solution space and evaluates alternatives Genetic algorithms based on natural selection properties of genetics Manufacturing execution system (MES) monitors status, usage, availability, quality Copyright 2011 John Wiley & Sons, Inc.17-34

35 Advanced Planning and Scheduling Copyright 2011 John Wiley & Sons, Inc.17-35

36 Theory of Constraints Not all resources are used evenly Finite scheduling approach Concentrate on the” bottleneck” resource Synchronize flow through the bottleneck Use process and transfer batch sizes to move product through facility Copyright 2011 John Wiley & Sons, Inc.17-36

37 Drum-Buffer-Rope Drum Bottleneck, beating to set the pace of production for the rest of the system Buffer Inventory placed in front of the bottleneck to ensure it is always kept busy Determines output or throughput of the system Rope Communication signal; tells processes upstream when they should begin production Copyright 2011 John Wiley & Sons, Inc.17-37

38 TOC Scheduling Procedure Identify bottleneck Schedule job first whose lead time to bottleneck is less than or equal to bottleneck processing time Forward schedule bottleneck machine Backward schedule other machines to sustain bottleneck schedule Transfer in batch sizes smaller than process batch size Copyright 2011 John Wiley & Sons, Inc.17-38

39 Synchronous Manufacturing Copyright 2011 John Wiley & Sons, Inc B A C D B1 1 5 B2 2 3 B3 1 7 C1 3 2 C C D D2 2 8 D3 3 5 Item i Key: i Ij k l Operation j of item i performed at machine center k takes l minutes to process

40 Copyright 2011 John Wiley & Sons, Inc Synchronous Manufacturing Demand = 100 A’s Machine setup time = 60 minutes MACHINE 1MACHINE 2MACHINE 3 B15B23C12 B37C315D35 C210D28D110 Sum2226*17 * Bottleneck

41 Synchronous Manufacturing Copyright 2011 John Wiley & Sons, Inc Machine 1 Machine 3 Setup Completion time C2B1B3 C3B2D2 C1D1D3Idle Setup Setup Machine 2 Idle 2

42 Copyright 2011 John Wiley & Sons, Inc. Employee Scheduling Labor is very flexible resource Scheduling workforce is complicated, repetitive task Assignment method can be used Heuristics are commonly used 17-42Copyright 2011 John Wiley & Sons, Inc.

43 Employee Scheduling Heuristic Copyright 2011 John Wiley & Sons, Inc Let N = no. of workers available D i = demand for workers on day i X = day working O = day off 2. 2.Assign the first N - D 1 workers day 1 off. Assign the next N - D 2 workers day 2 off. Continue in a similar manner until all days are have been scheduled 3. 3.If number of workdays for full time employee < 5, assign remaining workdays so consecutive days off are possible 4. 4.Assign any remaining work to part-time employees 5. 5.If consecutive days off are desired, consider switching schedules among days with the same demand requirements

44 Employee Scheduling Copyright 2011 John Wiley & Sons, Inc DAY OF WEEKMTWTHFSASU MIN NO. OF WORKERS REQUIRED Taylor Smith Simpson Allen Dickerson

45 Employee Scheduling Copyright 2011 John Wiley & Sons, Inc DAY OF WEEKMTWTHFSASU MIN NO. OF WORKERS REQUIRED TaylorOXXOXXX SmithOXXOXXX SimpsonXOXXOXX AllenXOXXXXO DickersonXXOXXXO Completed schedule satisfies requirements but has no consecutive days off

46 Copyright 2011 John Wiley & Sons, Inc DAY OF WEEKMTWTHFSASU MIN NO. OF WORKERS REQUIRED TaylorOOXXXXX SmithOOXXXXX SimpsonXXOOXXX AllenXXXOXXO DickersonXXXXOXO Revised schedule satisfies requirements with consecutive days off for most employees Employee Scheduling

47 Automated Scheduling Systems Staff Scheduling Assign workers to standardize shift patterns Schedule Bidding Workers bid for certain shift positions or schedules Schedule Optimization Creates demand-driven forecast of labor needs Assigns workers to variable schedules Uses mathematical programming and artificial intelligence techniques Copyright 2011 John Wiley & Sons, Inc.17-47

48 Copyright 2011 John Wiley & Sons, Inc Copyright 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. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publisher assumes no responsibility for errors, omissions, or damages caused by the use of these programs or from the use of the information herein.


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