chapter 12aggregate scheduling-Operations Scheduling.ppt

Operations Scheduling Advanced Operations Management Dr. Ron Tibben-Lembke Ch 16: 539-544, Job shop scheduling Personnel scheduling Facilities scheduling Vehicle scheduling Vendor scheduling Project scheduling Dynamic vs. static scheduling You are here Example Job Processing Time Due 1 6 18 2 2 6 3 3 9 4 4 11 5 5 8 What order should we do them in? Example Job Characteristics Arrival pattern: static or dynamic Number and variety of machines We will assume they are all identical Number of workers Flow patterns of jobs: all follow same, or many different Evaluation of alternative rules Objectives Many possible objectives: Meet due dates Minimize WIP Minimize average flow time through High worker/machine utilization Reduce setup times Minimize production and worker costs Terminology Flow shop: all jobs use M machines in same order Job shop: jobs use different sequences Parallel vs. sequential processing Flow time: from start of first job until completion of job I Makespan: start of first to finish of last Tardiness: = 0 Lateness: can be 0 or 0 Sequencing Rules First-come, first-served (FCFS) order they entered the shop Shortest Processing Time (SPT) longest job done last Earliest Due Date (EDD) job with last due date goes last Critical Ratio (CR) - processing time / time until due, smallest ratio goes first Other rules R - Random LWR - Least Work Remaining FOR - Fewest Operations Remaining ST - Slack Time ST/O-Slack Time per Operation NQ-Next Queue – choose job that is going next to the machine with smallest queue LSU - Least Setup Performance Quantities of interest Li Lateness of i: can be +/- Ti Tardiness of i: always = 0 Ei Earliness of i Tmax Maximum tardiness Example: FCFS Job Time Done Due Tardy 1 6 6 18 0 2 2 8 6 2 3 3 11 9 2 4 4 15 11 4 5 5 20 8 12 Total 50 20 Mean flow time = 50 / 5 = 10.0 Average tardiness = 20 / 5 = 4.0 Number of tardy jobs = 4 Max. Tardy 12 Example: SPT Job Time Done Due Tardy 2 2 2 6 0 3 3 5 9