Hybrid liveness-enforcing method for Petri net models of flexible manufacturing systems

This work presents a hybrid liveness-enforcing method for a class of Petri nets, which can well model many flexible manufacturing systems. The proposed method combines the theory of elementary siphons with a characteristic structure-based method to prevent deadlocks and enforce liveness in a Petri net model. It can identify and remove redundant monitors from a liveness-enforcing supervisor designed according to existing policies, reduce the structural complexity of a controlled system, improve the permissiveness, and save the control implementation cost. Several explanatory examples are used to illustrate this method.