(246g) Hierarchic Cyclic Hoist Scheduling for Multi-Stage Material Handling Processes

In multi-stage material handling processes (MSMH), such as electroplating process and polymeric coating, the minimization of cycle duration under a customized production requirement, which is equivalent to the maximization of productivity, is the ultimate goal. Cyclic hoist scheduling (CHS) can provide a complete hoist movement plan, including pick-up and drop-off time points as well as the transportation sequence of each job. This CHS plan will be very practical for large amount of jobs in continuous production.  In recent studies, CHS has been coupled with perspectives of customized productivity-ratio (CPR) and production line arrangement (PLA) to simultaneously address optimal scheduling, operation, and design issues.

In this paper, we developed a new hierarchic CHS methodology based on the previous studies.  The idea is that we allow the outer CHS will contain several pseudo inner job processing cycles.  The inner pseudo cycles make the cyclic hoist movement independent from cyclic job movement, so that the job processing and hoist movement can be virtually separated.  In the outer CHS, job processing and hoist movement will be finally synchronized.  Such arrangement will help identify better opportunities for scheduling the load of multi-job processing tanks and thus bring better solutions of CHS.  Based on the proposed idea, a new integer linear programming (MILP) model has also been developed. A CHS case with considerations of CPR and PLA has been studied.  The efficacy of the proposed methodology is demonstrated by compared with the previous studies.