Liveness enforcing supervisors for railway networks using ES/sup 2/PR Petri nets

Abstract

In this paper we consider a high-level description of a railway network using a skeleton net that belongs to the class of ES/sup 2/PR nets. The resource places of this model correspond to the action of a safeness enforcing supervisor. Liveness constraints may also be enforced for this class by adding appropriate monitor places designed using siphon analysis. We show how this can be done without an exhaustive computation of all siphons and characterize the cases in which this procedure can be recursively applied, giving a simple test for the closed loop net to remain an ES/sup 2/PR net.