Deadlock analysis and control using Petri net decomposition techniques

Abstract

Petri nets are an effective tool for modeling and analyzing deadlock problems of flexible manufacturing systems (FMSs). Based on Petri nets, this paper proposes a decomposition method for deadlock control of a class of Petri net modeling FMSs. It first decomposes a Petri net into two (or more) subnets via shared transitions and designs a liveness-enforcing Petri net supervisor for each subnet. Then the root of causing deadlocks is analyzed when merging the controlled subnets. Finally, control places are adjoined to the merged net to obtain a liveness-enforcing Petri net supervisor. The proposed method only needs to calculate the reachability graphs of the subnets, which are in general much smaller than that of the whole original net system. This method in general reduces significantly the computational overhead of designing a liveness-enforcing Petri net supervisor. A subnet can be further decomposed in a hierarchical way, which can further mitigate the computational burden. Typical examples are used to demonstrate the proposed methods.