Robustness of deadlock control for a class of Petri nets with unreliable resources

A variety of deadlock control policies based on Petri nets have been proposed for automated manufacturing systems (AMSs). Most of them prevent deadlocks by adding monitors for emptiable siphons that, without an appropriate control policy, can cause deadlocks, where the resources in a system under consideration are assumed to be reliable. When resources are unreliable, it is infeasible or impossible to apply the existing control strategies. For systems of simple sequential processes with resources (S^3PR), this paper bridges the gap between a divide-and-conquer deadlock control strategy and its application to real-world systems with unreliable resources. Recovery subnets and monitors are designed for unreliable resources and strict minimal siphons that may be emptied, respectively. Normal and inhibitor arcs are used to connect monitors with recovery subnets in case of necessity. Then reanalysis of the original Petri net is avoided and a robust liveness-enforcing supervisor is derived. Examples are presented to illustrate the proposed methodology.