Petri net dynamics-based scheduling of flexible manufacturing systems with assembly

Abstract

This paper presents a heuristic search method based on Petri nets for scheduling flexible manufacturing systems with assembly (FMSA) by partially generating the reachability graph. FMSAs are modeled by two types of timed place Petri nets, called generalized symmetric (GSN) and asymmetric nets (GAN). GSN is a sub-class of GAN. The special Petri net structures of GSN and GAN allow us to efficiently solve their state equations for solutions that constitute a part of the proposed heuristic function. Considering the dynamic information of nets such as concurrency and synchronization, the part of the heuristic function is adjusted since state equation solutions may over-estimate the real cost. The adjustment is based on a lower bound of the real cost and on dynamically comparing the partial estimated cost and partial real cost during the search process. Extensive simulation study shows that in most cases this work obtain better solutions than prior work.