Dynamic sequencing of jobs on conveyor systems for minimizing changeovers

This research investigates the problem of minimizing setup costs in resequencing jobs having first-in, first-out (FIFO) constraints conveyorized production or assembly systems. Sequence changing at conveyor junctions (with or without off-line buffers) in these systems is limited due to FIFO restriction. We first define the general problem of resequencing jobs to workstations satisfying precedence relationships between jobs (generalized sequential ordering problem, GSOP). Then we limit our scope to FIFO precedence relationships which is the conveyor selection problem at a diverging junction (diverging sequential ordering problem, DSOP), modeling it as a 0-1 integer program. With load balancing constraints removed, we show that the problem can be modeled as an assignment problem. We also define buffered sequential ordering problem (BSOP) as resequencing problem at a junction point of an off-line buffer, modeling it as a mixed integer program and propose a simple rule-based heuristic. Finally, we discuss the case study which motivated this research, details of the discrete event simulation model we developed, and numerical results.