Confusion diagnosis and avoidance of discrete event systems using supervisory control

Nondeterministic firing of concurrent transitions in Petri nets (PNs) may lead to the disappearance of conflicts. The disappearance implies that the partial conflicting transitions in a conflict become disabled before the resolution of the conflict. The phenomenon is called confusions that are caused by the interlacement of conflicting and concurrent transitions in PNs, which generates incomplete and faulty system conflicting behavior such that conflicts cannot be correctly resolved. In this paper, conflict-increasing confusions (CICs) and conflict-decreasing confusions (CDCs) in a PN are investigated. The relation graph of conflicts and confusions (RGC(2)) in a PN is proposed to detect the structure of confusions. To avoid the occurrence of confusions in a PN, an algorithm based on generalized mutual exclusion constraints (GMECs) is proposed, which can generate confusion-avoidance supervisors such that the occurrence of conflicts can be ensured in a PN. Finally, an example of confusion detection and avoidance in a flexible assembly system is presented. (c) 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.