Due date based scheduling in a general flexible manufacturing system

This study considers two important issues. First, the authors investigate the impact of unequal machine workloads on the relative effectiveness of dispatching rules. This is significant because workloads are likely to be unbalanced in most real systems. The authors show that the performance of different dispatching rules does depend upon the degree of workload imbalance. They also propose and test a scheduling procedure which performs well in both balanced and unbalanced systems. Next, the authors develop a scheduling approach which shows promise as being an improved alternative to the use of dispatching rules. This approach decomposes the dynamic scheduling problem into a series of static problems. These static problems are then solved using an optimum-seeking method, and the solutions are implemented on a rolling basis. The authors show through a simulation experiment that adopting this approach over dispatching rules leads to an improvement in the overall solution quality, even in a dynamic envirionment. The two very practical implications of the present study are: (1) that commonly used dispatching rules in job shops or automated manufacturing systems may not be the best approach when capacity utilization is unbalanced; (2) a job shop or automated manufacturing system would likely benefit from implementing optimal-seeking scheduling rules instead of the traditional job dispatching rules.