Evaluation of scheduling rules with commensurate customer priorities in job shops

Mucht of the existing job shop scheduling literature has focussed on scheduling rules and heuristics that typically do not incorporate customer specific characteristics into their scheduling decisions. This paper specifically considers the situation in which depending upon the identity of the customer, different jobs have different tardiness penalties associated with them. In addition, the tardiness penalties associated with different customers are comparable in magnitude with one another. The authors propose here and test four differnt types of scheduling rules which utilize the jobs’ tardiness penalty information, and show that the performance of the shop is only mildly affected by the shape and dispersion of the weighting scheme used in determining the tardiness penalties. The performance of scheduling rules is however contingent on due-date tightness. In general, apart from the traditionally well performing shortest processing time rule, the ATC rule works well on the mean flow time measure in loose due-date situations, while COVERT performs well on mean flow time under tight due-date conditions. Lesser differences are seen to exist between mean tardiness and root mean square tardiness performance of different scheduling rules. Weighted mean tardiness deteriorates with increasing due-date tightness and coefficient of variation of job tardiness penalties. Finally, customer service performance worsens considerably with weighted dispatching rules when the performance criteria are not weighted by each job’s tardiness penalty. Implications of the present results for providing more effective management of job shops, and exploring future research directions in this area are also presented and discussed.