A PETRI-NET BASED DEADLOCK PREVENTION POLICY FOR FLEXIBLE MANUFACTURING SYSTEMS

In this paper we illustrate a compositional method for modeling the concurrent execution of working processes in flexible manufacturing systems (FMS) through a special class of Petri Nets that we call S-3 PR. In essence, this class is built from state machines sharing a set of plates modeling the availability of system resources. The analysis of S-3 PR leads us to characterize deadlock situations in terms of a zero marking for some structural objects called siphons. In order to prevent the system from deadlocks, we propose a policy for resource allocation based on the addition of new places to the net imposing restrictions that prevent the presence of unmarked siphons (direct cause of deadlocks). Finally, we present the application of this technique to a realistic FMS case.