ON FORBIDDEN STATE PROBLEMS FOR A CLASS OF CONTROLLED PETRI NETS

This paper treats the forbidden state problem for the class of discrete event dynamical systems (DEDS's) which can be modeled as controlled state machines (CtlSM's), CtlSM's constitute a special class of controlled Petri nets (CtlPN's) where no synchronization requirements are included in the system model. Synchronization and other safety requirements are modeled via sets of forbidden states. In this paper we study methods guaranteeing these constraints by disabling some of the controllable transitions. We assume that the full state is observable. Control logic synthesis taking into account the graphical representation of CtlSM's and the distributed state representation in terms of markings is proposed and justified. Two examples-the cat-and-mouse game and a model of a metro line-illustrate the theoretical results.