Transient multiple hoist scheduling of consecutive cyclic schedules

Abstract

This paper addresses the transient multi-hoist scheduling problem in flexible manufacturing facilities and focuses on the Lot Switching procedure. The problem arises in automated electroplating lines where multiple hoists are operating on a shared track and due to a flexible production different product types needs to be manufactured which differ in the routing through the facility. The considered processing sequences may contain loops, i.e. multiple usages of single machines within a sequence. In addition the electroplating line may be equipped with identical machines used as parallel resources. A mixed integer linear programming (MILP) model for optimizing the Lot Switching schedule is presented considering in particular collisions of hoists. A real world example indicating that the model finds schedules for the transition in reasonable time is presented.