Liveness-enforcing supervisor design for a class of generalised petri net models of flexible manufacturing systems

Abstract

The importance of siphons is well recognised in the analysis and control of deadlocks in Petri nets. Deadlock prevention problems are considered for S4PR, a class of generalised Petri nets, that can model well a large class of flexible manufacturing systems (FMS). Siphons in a plant net model are divided into elementary and dependent ones. Deadlock prevention is achieved by adding monitors (control places) to make every elementary siphon satisfy the maximal controlled-siphon property. Conditions are developed under which a dependent siphon is maximally controlled when its elementary siphons are so. The max-controllability of a dependent siphon is ensured by properly supervising the control depth variables of its elementary siphons via linear integer programming techniques. Compared with existing methods, this policy requires a much smaller number of supervisory monitors. Finally, the application of this approach is illustrated by an FMS example.