Confusion avoidance for discrete event systems by P/E constraints and supervisory control

Non-deterministic firing of concurrent transitions in Petri nets (PNs) may lead to the information loss of conflicts. The phenomenon is called confusions that usually occur in the evolution of a PN containing interlaced conflicting and concurrent transitions, which generates incomplete and faulty system conflicting behaviour such that conflicts cannot be correctly resolved. This paper investigates detection and avoidance approaches of confusions in safe PNs. First, the structural features of confusions are characterized and two detection algorithms are proposed to capture confusion subnets in a PN according to their structural features. Secondly, amethod of supervisory control is developed to avoid the occurrence of confusions in a PN. It contains a policy of the generation of confusion avoidance constraints and a method to synthesize supervisors enforcing a class of place and enabling degree constraints, P/E constraints for short. Finally, an example of confusion detection and avoidance in an automated manufacturing system is presented.