Concurrent Routing, Sequencing, and Setups for a Two-Machine Flexible Manufacturing Cell

An approach proposed for scheduling of Flexible Manufacturing Systems (FMS) is to sequentially solve three related subproblems, commonly referred to as the “FMS loading,” “job routing,” and “operation sequencing” problems. However, the use of this approach results in assigning a fixed set of resources for each machine prior to sequencing, and thus may unnecessarily restrict the capability of the flexible manufacturing system, especially if the machines are very versatile. In this paper, we present an approach which allows in-process “machine loading” through magazine setups, and which concurrently routes and sequences the jobs on the versatile machines. To illustrate the concurrent approach, a specific two-versatile-machine flowshop scheduling problem, referred to as 2-VFSP, is defined and studied in detail. Theoretical results show that the optimal schedule for 2-VFSP need not nave more than two in-process magazine setups, giving rise to the three possible scheduling configurations. Further, it is proven that to obtain the optimal schedule is an NP-complete problem. A heuristic is developed and tested on sets of random joblists, with different setup times corresponding to varying degrees of machine versatility. Results indicate that schedules which incorporate in-process magazine setup(s) may be more desirable when the setup time is small. Thus the use of concurrent scheduling approach which allows in-process magazine setups may be especially useful for systems with very versatile machines.