Re-entrant Manufacturing Systems

Re-entrant manufacturing systems differ from traditional manufacturing systems in the sense that a job may visit a service station more than once, at various stages of the product development cycle. Several parts at different stages of processing may be in contention for service at the same machine, which gives rise to the need to solve scheduling problems. This document surveys some of the facets of such systems presented in the literature. A variety of scheduling policies for re-entrant lines is presented and their stability and performance discussed. Approximate Mean Value Analysis is carried out on a closed re-entrant line under two different scheduling schemes to compute the mean cycle time and mean throughput rate for different number of parts in the system. The results of this exercise are compared with the output of a linear program that provides an upper bound on the throughput rate. In the last section, the mean value analysis and dynamic programming techniques are compared in the context of re-entrant lines.