Scheduling Production Planning and Control Varun Babu Lecture

Scheduling Production Planning and Control Varun Babu

Lecture Outline w w w w Objectives in Scheduling Loading Sequencing Monitoring Advanced Planning and Scheduling Systems Theory of Constraints Employee Scheduling bvarun. weebly. com 16 -2

What is Scheduling? w Last stage of planning before production occurs w Specifies when labor, equipment, facilities are needed to produce a product or provide a service bvarun. weebly. com 16 -3

Scheduled Operations w Process Industry n n Linear programming EOQ with non-instantaneous replenishment w Mass Production n n Assembly line balancing w Project n w Batch Production Project -scheduling techniques (PERT, CPM) bvarun. weebly. com n Aggregate planning Master scheduling Material requirements planning (MRP) Capacity requirements planning (CRP) 16 -4

Objectives in Scheduling w Meet customer due dates w Minimize job lateness w Minimize response time w Minimize completion time w Minimize time in the system bvarun. weebly. com w Minimize overtime w Maximize machine or labor utilization w Minimize idle time w Minimize work-inprocess inventory 16 -5

Shop Floor Control w Loading n w Check availability of material, machines and labor Sequencing n w Release work orders to shop and issue dispatch lists for individual machines Monitoring n Maintain progress reports on each job until it is complete bvarun. weebly. com 16 -6

Loading w Process of assigning work to limited resources w Perform work on most efficient resources w Use assignment method of linear programming to determine allocation bvarun. weebly. com 16 -7

Assignment Method 1. Perform row reductions n 4. If number of lines equals number of rows in matrix then optimum solution subtract minimum value in each row from all other row values 2. Perform column reductions has been found. Make assignments where zeros appear subtract minimum value in each 5. Else modify matrix n subtract minimum uncrossed value from column from all other column all uncrossed values n add it to all cells where two lines 3. Cross out all zeros in matrix intersect use minimum number of n other values in matrix remain horizontal and vertical lines unchanged n § 6. Repeat steps 3 through 5 until optimum solution is reached bvarun. weebly. com 16 -8

Assignment Method: Example Initial Matrix Bryan Kari Noah Chris 1 10 6 7 9 Row reduction 5 4 2 5 0 0 1 1 1 2 0 0 5 4 1 6 PROJECT 3 6 4 5 4 2 5 2 6 5 4 10 6 6 10 Column reduction Cover all zeros 3 2 0 3 0 0 1 1 1 2 0 0 4 3 0 5 Number lines number of rows so modify matrix bvarun. weebly. com 16 -9

Assignment Method: Example (cont. ) Modify matrix 1 0 0 3 1 1 2 2 0 Cover all zeros 2 1 0 3 1 0 0 3 1 1 2 2 0 2 1 0 3 Number of lines = number of rows so at optimal solution Bryan Kari Noah Chris 1 1 0 0 1 PROJECT 2 3 0 1 0 2 3 2 1 0 4 2 1 0 3 Bryan Kari Noah Chris 1 10 6 7 9 PROJECT 2 3 4 5 6 10 2 4 6 6 5 4 10 Project Cost = (5 + 6 + 4) X $100 = $2, 100 bvarun. weebly. com 16 -10

Sequencing § Prioritize jobs assigned to a resource § If no order specified use first-come firstserved (FCFS) § Many other sequencing rules exist § Each attempts to achieve to an objective bvarun. weebly. com 16 -11

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 - critical ratio SPT - shortest processing time LPT - longest processing time bvarun. weebly. com 16 -12

Critical Ratio Rule CR considers both time and work remaining CR = time remaining work remaining = due date - today’s date remaining processing time If CR > 1, job ahead of schedule If CR < 1, job behind schedule If CR = 1, job on schedule bvarun. weebly. com 16 -13

Sequencing Jobs Through One Process w Flowtime (completion time) n Time for a job to flow through the system w Makespan n Time for a group of jobs to be completed w Tardiness n Difference between a late job’s due date and its completion time bvarun. weebly. com 16 -14

Simple Sequencing Rules bvarun. weebly. com JOB PROCESSING TIME DUE DATE A B C D E 5 10 2 8 6 10 15 5 12 8 16 -15

Simple Sequencing Rules: FCFS START SEQUENCE TIME A B C D E 0 5 15 17 25 bvarun. weebly. com PROCESSING COMPLETION DUE TIME DATE 5 10 2 8 6 5 15 17 25 31 10 15 5 12 8 TARDINESS 0 0 12 13 23 16 -16

Simple Sequencing Rules: DDATE START SEQUENCE TIME C E A D B 0 2 8 13 21 bvarun. weebly. com PROCESSING COMPLETION DUE TIME DATE 2 6 5 8 10 2 8 13 21 31 5 8 10 12 15 TARDINESS 0 0 3 9 16 16 -17

Simple Sequencing Rules: SLACK START SEQUENCE TIME E C D A B 0 6 8 16 21 bvarun. weebly. com 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 PROCESSING COMPLETION DUE TIME DATE 6 2 8 5 10 6 8 16 21 31 8 5 12 10 15 TARDINESS 0 3 4 11 16 16 -18

Simple Sequencing Rules: CR CR START SEQUENCE TIME E D B A C 0 6 14 24 29 bvarun. weebly. com A(10)/5 = 2. 00 B(15)/10 = 1. 50 C (5)/2 = 2. 50 D(12)/8 = 1. 50 E (8)/6 = 1. 33 PROCESSING COMPLETION DUE TIME DATE 6 8 10 5 2 6 14 24 29 31 8 12 15 10 5 TARDINESS 0 2 9 19 26 16 -19

Simple Sequencing Rules: SPT START SEQUENCE TIME C A E D B 0 2 7 13 21 bvarun. weebly. com PROCESSING COMPLETION DUE TIME DATE 2 5 6 8 10 2 7 13 21 31 5 10 8 12 15 TARDINESS 0 0 5 9 16 16 -20

Simple Sequencing Rules: Summary RULE AVERAGE COMPLETION TIME FCFS DDATE SLACK CR SPT bvarun. weebly. com 18. 60 15. 00 16. 40 20. 80 14. 80 AVERAGE NO. OF MAXIMUM TARDINESS JOBS TARDY TARDINESS 9. 6 5. 6 6. 8 11. 2 6. 0 3 3 4 4 3 23 16 16 26 16 16 -21

Sequencing Jobs Through Two Serial Process Johnson’s Rule 1. List time required to process each job at each machine. Set up a one-dimensional matrix to represent desired sequence with # of slots equal to # of jobs. 2. Select smallest processing time at either machine. If that time is on machine 1, put the job as near to beginning of sequence as possible. 3. If smallest time occurs on machine 2, put the job as near to the end of the sequence as possible. 4. Remove job from list. 5. Repeat steps 2 -4 until all slots in matrix are filled and all jobs are sequenced. bvarun. weebly. com 16 -22

Johnson’s Rule JOB PROCESS 1 PROCESS 2 A B C D E 6 11 7 9 5 8 6 3 7 10 E bvarun. weebly. com A D B C 16 -23

Johnson’s Rule (cont. ) E E A 5 A D D 11 B C B Process 1 (sanding) C 20 31 38 Idle time E 5 A 15 D 23 B 30 Process 2 (painting) C 37 41 Completion time = 41 Idle time = 5+1+1+3=10 bvarun. weebly. com 16 -24

Guidelines for Selecting a Sequencing Rule 1. 2. 3. 4. 5. 6. 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 bvarun. weebly. com 16 -25

Monitoring w Work package n Shop paperwork that travels with a job w Gantt Chart n Shows both planned and completed activities against a time scale w Input/Output Control n Monitors the input and output from each work center bvarun. weebly. com 16 -26

Gantt Chart Job 32 B Behind schedule Facility 3 Job 23 C Ahead of schedule 2 Job 11 C Job 12 A On schedule 1 1 2 Key: 3 4 5 6 8 Today’s Date 9 10 11 12 Days Planned activity Completed activity bvarun. weebly. com 16 -27

Input/Output Control Input/Output Report PERIOD Planned input Actual input Deviation Planned output Actual output Deviation Backlog 30 bvarun. weebly. com 1 2 3 4 65 60 70 65 75 70 75 65 TOTAL 16 -28

Input/Output Control (cont. ) Input/Output Report PERIOD Planned input Actual input Deviation Planned output Actual output Deviation Backlog 30 bvarun. weebly. com 1 2 3 4 60 60 0 75 70 -5 20 65 60 -5 75 70 -5 10 70 65 -5 75 65 -10 10 TOTAL 270 250 -20 300 270 -30 16 -29

Advanced Planning and Scheduling Systems w Infinite - assumes infinite capacity n n Loads without regard to capacity Then levels the load and sequences jobs w Finite - assumes finite (limited) capacity n n Sequences jobs as part of the loading decision Resources are never loaded beyond capacity bvarun. weebly. com 16 -30

Advanced Planning and Scheduling Systems (cont. ) w Advanced planning and scheduling (APS) n n 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 bvarun. weebly. com 16 -31

Theory of Constraints w w Not all resources are used evenly Concentrate on the” bottleneck” resource Synchronize flow through the bottleneck Use process and transfer batch sizes to move product through facility bvarun. weebly. com 16 -32

Drum-Buffer-Rope w Drum n Bottleneck, beating to set the pace of production for the rest of the system w Buffer n n Inventory, placed in front of the bottleneck to ensure it is always kept busy Determines output or throughput of the system w Rope n Communication signal, tells processes upstream when they should begin production bvarun. weebly. com 16 -33

TOC Scheduling Procedure w Identify bottleneck w Schedule job first whose lead time to the bottleneck is less than or equal bottleneck processing time w Forward schedule the bottleneck machine w Backward schedule the other machines to sustain the bottleneck schedule w Transfer in batch sizes smaller than the process batch size bvarun. weebly. com 16 -34

A B Synchronous Manufacturing bvarun. weebly. com C D B 3 1 7 C 3 2 15 D 3 3 5 B 2 2 3 C 2 1 10 D 2 2 8 B 1 1 5 C 1 3 2 D 1 3 10 Key: i ij k l Item i Operation j of item i performed at machine center k takes l minutes to process 16 -35

Synchronous Manufacturing (cont. ) Demand = 100 A’s Machine setup time = 60 minutes MACHINE 1 MACHINE 2 MACHINE 3 B 1 B 3 C 2 Sum 5 7 10 22 B 2 C 3 D 2 3 15 8 26* C 1 D 3 D 1 2 5 10 17 * Bottleneck bvarun. weebly. com 16 -36

Synchronous Manufacturing (cont. ) Setup Machine 1 C 2 Setup B 1 2 B 3 1002 1562 2322 Idle Setup Machine 2 C 3 B 2 12 1512 Machine 3 Setup C 1 0 200 bvarun. weebly. com Setup D 2 1872 2732 Setup D 1 Idle 1260 D 3 1940 Completion time 2737 16 -37

Employee Scheduling w Labor is very flexible resource w Scheduling workforce is complicated repetitive task w Assignment method can be used w Heuristics are commonly used bvarun. weebly. com 16 -38

Employee Scheduling Heuristic 1. Let N = no. of workers available Di = demand for workers on day i X = day working O = day off 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. If number of workdays for full time employee < 5, assign remaining workdays so consecutive days off are possible 4. Assign any remaining work to part-time employees 5. If consecutive days off are desired, consider switching schedules among days with the same demand requirements bvarun. weebly. com 16 -39

Employee Scheduling DAY OF WEEK MIN NO. OF WORKERS REQUIRED M T W TH F SA SU 3 3 4 5 3 Taylor Smith Simpson Allen Dickerson bvarun. weebly. com 16 -40

Employee Scheduling (cont. ) DAY OF WEEK MIN NO. OF WORKERS REQUIRED Taylor Smith Simpson Allen Dickerson M T W TH F SA SU 3 3 4 5 3 O O X X X X X O O O X X X X O O Completed schedule satisfies requirements but has no consecutive days off bvarun. weebly. com 16 -41

Employee Scheduling (cont. ) DAY OF WEEK MIN NO. OF WORKERS REQUIRED Taylor Smith Simpson Allen Dickerson M T W TH F SA SU 3 3 4 5 3 O O X X X X X O O X X X X O O Revised schedule satisfies requirements with consecutive days off for most employees bvarun. weebly. com 16 -42

Automated Scheduling Systems w Staff Scheduling w Schedule Bidding w Schedule Optimization bvarun. weebly. com 16 -43

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