EVALUATING VARIANCE CONTROL, ORDER REVIEW RELEASE AND DISPATCHING - AREGRESSION-ANALYSIS

The challenge of improving performance in the job shop can be met in a number of ways. We can rely on variance control to reduce variances c reated either in the planning system (through uneven or fluctuating lo ads) or on the shop floor (through varying processing times for releas ed batches). We can rely on Order Review/Release(ORR). Finally, we can turn to one of the various dispatching rules that are available. Each option has been previously examined. However, this study examines all of these options simultaneously within the context of a simulated sim ple job shop. Based on a regression analysis of the data generated, se veral interesting results are uncovered. First, the results show that the presence of variance control at both the planning and shop floor l evels can greatly enhance the effectivess of ORR. This result partiall y helps resolve the controversy surrounding ORR. Second, the results s how that Shortest Processing Time (SPT), while extremely effective in an uncontrolled environment, reacts adversely to the presence of varia nce control. Finally, if used effectively, variance control can greatl y reduce the need for complex dispatching rule.