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This paper develops a deadlock prevention policy for flexible manufacturing systems, which is based on iterative control of elementary siphons of Petri nets. Elementary siphons are a special topology structure of Petri nets. The number of them is bounded by the smaller of the place count and transition count in a Petri net. Siphons in a plant net model are first divided into elementary and dependent ones. Then a control place or monitor is added, for each elementary siphon, to make it invariant-controlled, while making dependent ones controlled as well. This implies that not all of the siphons need to explicitly control by adding monitors. Compared with existing methods that need to explicitly control all strict minimal siphons, the deadlock-free or liveness-enforcing Petri net supervisor obtained is structurally simple and has a less number of additional places and arcs but with more permissive behavior. Finally, the method presented in this paper is illustrated with an example.
Date of Conference: 19-22 March 2005