Modeling and scheduling of flexible manufacturing systems using timed/stochastic petri nets

Abstract

This paper deals with methodologies for modeling and scheduling of Flexible Manufacturing Systems (FMS) which are the typical discrete event dynamic systems. Since Petri nets provide a powerful tool for modeling dynamical behavior of discrete concurrent processes, we use them for modeling FMS. For the purpose of off-line scheduling of FMS we use timed Petri nets, and for on-line real-time scheduling of FMS we use timed-stochastic Petri nets with hierarchical structure where we deal with uncertain events in FMS such as variation of processing time, failure of machine tools, variation of repairing time, and so forth.We deal with off-line and on-line rule-based scheduling. The role of the rule base is to generate an appropriate priority rule for resolving conflicts, that is for selecting one of enabled transitions to be fired in a conflict set of the Petri net. This corresponds to select a part type to be processed in FMS.Towards developing more Intelligent Manufacturing Systems (IMS) we propose a conceptual framework of a futuristic intelligent scheduling system.