Abstract: We develop an effective control policy to prevent deadlocks from occurring in a class of Petri nets, ES³PR, where deadlocks are related to unmarked siphons. Strict minimal siphons are divided into elementary and dependent ones. For each elementary siphon, a monitor is added to ensure that it is sufficiently marked without gnerating emptiable control-induced siphons. The controllability of a dependent siphon is guaranteed by changing the control depth variables of its related elementary siphons, which leads to a liveness-enforcing supervisor for a plant model. Furthermore, by checking the redundancy of the additional monitors, some control-redundant monitors can be removed, which leads to a more permissive and structurally simple net supervisor.

Key words: FMS, Petri net, deadlock prevention, elementary siphon, ES³PR