1. 16 Scheduling (focus on sequencing; FCFS, SPT, EDD pages 731-736, and Johnson’s rule pages 738- 740) Homework; 6, 7, 11

2. Scheduling Scheduling has to do with establishing the timing of the use of equipment, workstations, facilities, and personnel. Sequencing is the determination of of order in which jobs waiting at a workstation are to be processed. Simple Scenario: Workstation A3 B10 C20 D2 E5

3. Terms/Performance Measures Job flow time - length of time a job is at a particular work center, actual processing time and any waiting time. Job lateness Makespan - total time needed to complete a group of jobs Average number of jobs – total flow time / makespan (at a work center)

4. Possible Priority Rules First come, first served (FCFS): Jobs are processed in the order in which they arrive. Dominant in service, mainly because of fairness and inability to estimate processing times. Shortest processing time (SPT): Jobs are processed shortest job first. Low average number of jobs at a workstation. Low average tardiness. Lower inventories. Earliest due date (EDD): Jobs are processed earliest due date first. Addresses lateness and minimizes lateness. Minimizes job tardiness. Critical ratio (CR): Jobs are processed according to the smallest ratio of time remaining until due date to processing time remaining. Low average tardiness. Slack per operation (S/O): Jobs are processed according to slack time divided by number of remaining operations. Jobs with little slack and a large number of remaining operations will be processed first. Used when considering remaining processing time and remaining number of operations.

5. Example Jobs (in order of arrival) Processing Time (days) Due Date (days hence) A35 B46 C27 D69 E12 FCFS Job Sequence Processing Time Flow Time Due Date Days Tardy A B C D E Makespan Avg. Flow Time Avg. Tardiness Avg. Number of jobs at the work center

6. Example Jobs (in order of arrival) Processing Time (days) Due Date (days hence) A35 B46 C27 D69 E12 SPT Job Sequence Processing Time Flow Time Due Date Days Tardy E C A B D Makespan Avg. Flow Time Avg. Tardiness Avg. Number of jobs at the work center

7. Example Jobs (in order of arrival) Processing Time (days) Due Date (days hence) A35 B46 C27 D69 E12 EDD Job Sequence Processing Time Flow Time Due Date Days Tardy E A B C D Makespan Avg. Flow Time Avg. Tardiness Avg. Number of jobs at the work center

8. Example RuleAvg. FlowAvg. Tardiness Avg. Jobs FCFS SPT EDD

9. Johnson’s rule A sequencing technique for minimizing total completion time for a group of jobs. -Job times must be know in advance -All jobs follow the same two-step sequence -Two work centers that each job must go through Example: JobMach1Mach2 A32 B68 C56 D74