Design of a Petri Net Based Deadlock Prevention Policy Supervisor for S3PR

Siphons can be used to characterize deadlock states to solve deadlock problems in a class of Petri nets that represent models of flexible manufacturing system (FMS). This paper presents a deadlock prevention method for a class of FMS, where the unmarked siphons in their Petri net models cause the deadlocks. Based on Petri nets, a deadlock prevention policy is proposed for a special class of Petri nets called System of Simple Sequential Processes with Resources (S3PR) and the deadlock prevention problems can be characterized in terms of Petri net structural elements called siphons. The monitors are used to prevent the presence of unmarked siphons that are the direct cause of deadlocks in such a Petri net. Deadlock analysis and control techniques based on the structural theory of Petri nets attempt to find a relationship between liveness of a net and its structure, which relies on the concepts of elementary and dependent siphons. The siphon control has been applied in Petri nets by adding a control place for each elementary siphon to make sure it is deadlock-free.