Industrial job-shop scheduling with random operations and different priorities

Industrial job-shop scheduling with random operations and different priorities

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Article ID: iaor1996854
Country: Netherlands
Volume: 40
Issue: 2/3
Start Page Number: 185
End Page Number: 195
Publication Date: Aug 1995
Journal: International Journal of Production Economics
Authors: , ,
Keywords: heuristics
Abstract:

A classical job-shop scheduling problem with n jobs (orders) and m machines is considered. Each job-operation equ1 (the equ2 operation of job equ3) has a random time duration equ4 with the average value equ5 and the variance equ6. Each job equ7 has its due date equ8 and its priority index equ9. Given equ10, the desired probability for job J i to be accomplished on time, and equ11 the least permissible probability for the job to meet its due date on time, the problem is to determine starting time values equ12 for each job-operation equ13. Those values are not calculated beforehand and are values conditioned on our decisions. Decision-making, i.e., determining values equ14 is carried out at the moments when at least one of the machines is free for service and at least one job is ready to be processed on that machine. If at a certain moment t more than one job is ready to be processed, these jobs are compared pairwise. The winner of the first pair will be compared with the third job, etc., until only one job will be left. The latter has to be chosen for the machine. The competition is carried out by calculating the job's delivery performance, i.e., the probability for a certain job to meet its due date on time. Such a calculation is carried out by determining the probability to meet the deadline for a chain of random operations. Two different heuristics for choosing a job from the line will be imbedded in the problem. The first one is based on examining delivery performance values together with priority indices equ15. The second one deals with examining confidence possibilities equ16 and equ17 and does not take into account priority indices. A numerical example is presented. Both heuristics are examined via extensive simulation in order to evaluate their comparative efficiency for practical industrial problems.

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