Scheduling n Jobs on m Machines Complex Job Shops
Complex job shops are characterized by multiple machine centers processing a variety of different jobs arriving at the machine centers in an intermittent fashion throughout the day. If there are n jobs to be processed on an machines and all jobs are processed on all machines. then there are (n !) alternative schedules for this job set. Because of the large number of schedules that exist for even small job shops, simulation is the only practical way to determi ne the relative merits of different priority rules in such situations. As in then job on one machine case, the 10 priority rules (and more) have been compared relative to their performance on the evaluation criteria previously mentioned. which priority rule should be used? We believe that the needs of most manufacturers are reasonably satisfied by a relatively simple priority scheme that embodies the following principles:
1. It should be dynamic, that is, computed frequently during the course of a job to reflect changing conditions.
2. It should be based in one way or another on slack time (the difference between the work remaining to be done on the time remaining to do it in).