Online Scheduling of 2-Re-entrant Flexible Manufacturing Systems

Abstract

Online scheduling of operations is essential to optimize productivity of exible manufacturing systems (FMSs) where manufacturing requests arrive on the y. An FMS processes products according to a particular ow through processing stations. This work focusses on online scheduling of re-entrant FMSs with ows using processing stations where products pass twice and with limited bu ering between processing stations. This kind of FMS is modelled as a re-entrant ow shop with due dates and sequence-dependent set-up times. Such ow shops can bene t from minimization of the time penalties incurred from set-up times. On top of an existing greedy scheduling heuristic we apply a meta-heuristic that simultaneously explores several alternatives considering trade-o s between the used metrics by the scheduling heuristic. We identify invariants to e ciently remove many infeasible scheduling options so that the running time of online implementations is improved. The resulting algorithm is much faster than the state of the art and produces schedules with on average 4.6% shorter makespan.

A Heuristic for Variable Re-Entrant Scheduling Problems

“…Schedulers for job sets with fixed flows (i.e. simplex, or duplex, but not mixed), have been proposed for the LSP in [1], [2]. The MFL and MNEH heuristics [13] are also able to schedule 2-re-entrant flowshops with sequence dependent setup times and relative due dates.…”

“…In this paper we focus on the scheduling problem where sheets can take the duplex and simplex route. Schedulers have been developed for the LSP [1], [2], but these approaches support only print jobs that are fully simplex or fully duplex. They cannot schedule mixed-plexity print jobs in an LSP, i.e.…”

“…4) Check feasibility and compute start times: The function CHECK FEASIBILITY CHOICE(ot, cg) checks the feasibility of the minimum ranked schedule option in OT j . The BFA [1], [2] is used to check feasibility and compute starting times after inserting the schedule option constraints. If it detects a positive cycle in the constraint graph, then the schedule with the inserted schedule option is not feasible.…”