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.
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