Optimal Supervisory Control for Flexible Manufacturing Systems Model with Petri Nets: A Place-Transition Control

Abstract

Supervisory control for discrete event systems that is widely studied in the literature to tackle the Petri net model's deadlock occurrence of flexible manufacturing systems. A supervisory structure constructed using control places imposed restrictions on the concurrent operation in the systems, which degrade the supervisor's efficiency. This study proposed a new method to construct a supervisory structure using combine control places and control transitions to ensure flexible manufacturing systems' smooth operation. Place-Transition controller is designed for each concurrent process of the systems. Three algorithms are proposed in this method. The algorithm 1 computes the loop markings at each process of the Petri net model. Algorithm 2 is used to sort the deadlock markings based on the concurrent processes of the Petri net model. The Transition-Place controller and Place-Transition controller are designed using algorithm 3. Transition-Place controller creates extra states in the reachability graph, which is called dump markings. Place-Transition controller projects the deadlock markings to the loop markings via dump markings. The number of states created by the Transition-Place controller depends on the number of concurrent states in the Petri net model. The final supervisory structure controls the deadlock occurrence of flexible manufacturing systems with zero restrictions of systems operation. This proposed method is efficient as it retains all the states generated in the controlled Petri net model.