Due-Date Oriented Production Scheduling Including Pre-emption and Job Splitting

Aiming at an excellent schedule with respect to due-date related criteria, we propose a method that allows a large lot-size job to be effectively pre-empted and split by a smaller job. In order to determine the best pre-emption strategy, it is necessary to review the jobs and the possible timings for pre-emption. The proposed method involves two basic procedures within a general search procedure. The first procedure gives an initial configuration schedule where large lot-size jobs are assigned by the GA method so as to maximize due-date earliness, and where small lot-size jobs are appended to the large-lot size job assignments. The second procedure is a schedule generated by a forward simulation where every large lot-size is split into 'unit jobs' and small lot-size jobs can mix among the unit jobs. At the end of the procedure, the unit jobs are rejoined to create a larger job. The search procedure introduces three parameters to determine the jobs and the timings to pre-empt and split the larger job. The parameter-space-search-improvement (PSSI) method is used to efficiently search for an excellent schedule. The performance of the proposed method is investigated using a simple flow-shop model by comparing results obtained by different methods. The characteristics of the job pre-emption are also discussed by assuming different scheduling conditions such as release times and due-dates.