Abstract: To solve the problem of deadlock prevention for a class of Petri nets, S³PR, an effective deadlock prevention policy is proposed. The deadlock avoidance policy of Conjunctive／Disjunctive Resources Upstream Neighborhood (C／D-RUN) is applied to the siphon-based deadlock prevention policy, and the resources of the control places are allocated reasonably to guarantee the absence of deadlock states and processes. First, strict minimal siphons of an S³PR are divided into elementary and dependent ones. From the set of elementary siphons, a set of linear inequality constraints expressed by the state vector can be formalized, and after being modified by the C／D-RUN policy, a set of generalized mutual exclusion constraints(GMEC) expressed by the marking vector can be found. Then monitors based on the marking constraints are added to the plant model to ensure that all elementary siphons in the S³PR net are invariant-controlled, thus leading to a deadlock freedom liveness-enforcing supervisor with a simple structure and much permissive behavior can be realized.

Key words: flexible manufacturing system, deadlock prevention, Petri net, elementary siphon, S³PR