Deadlock control policy for a class of automated manufacturing systems with key resources

For automated manufacturing systems (AMSs) without center resources that are one-unit resources shared by two or more maximal perfect resource transition circuits, the optimal Petri net-based polynomial complexity deadlock avoidance policies are synthesized in our previous work. Based on Petri net models of AMSs, this work focuses on the deadlock control problem for AMSs with center resources. First, the concepts of key resources and key transitions are presented. It can prove that key transitions can bring AMSs with key resources into secondary-deadlock, i.e. the controlled Petri nets of AMSs with key resources are not live. Second, for a class of AMSs with key resources, secondary-deadlock can be characterized by maximal perfect control transition circuits (MPCT-circuits) that are saturated at a reachable marking of the controlled system. Then, by adding a control place and related arcs to each MPCT-circuit, secondary-deadlock can be prevented. Thereby, a deadlock control policy for a class of AMSs with center resources is synthesized. Finally, a few examples are provided to demonstrate the presented policy and used to compare them with the state-of-the-art methods.