Abstract: We develop a novel deadlock control policy to add monitors to ensure the controllability of elementary siphons of Petri nets, and the controllability of dependent siphons is ensured by properly selecting the control depth variables of elementary siphons, which can be obtained by linear programming techniques. The control policy can model concurrent execution of manufacturing assembly processes in FMS (Flexible Manufacturing Systems) through a class of nets, called the G-system that is a large class of discrete event systems. A relevant property of the system behavior is to be non-blocking, i.e., from any reachable state, a desirable state can be always reached under supervision. Compared with the existing policies, the advantage of ours is that a much smaller number of monitors are added with unnecessary iterative processes avoided.

Key words: flexible manuufacturing systems(FMS), Petri net, deadlock prevention, elementary siphon, non-blocking