Max-controlled Property Of Petri Nets Siphons And Its Application

This thesis investigates deadlock problems for a special class of Petri nets, which is called G-systems that can well model flexible manufacturing systems (FMS). Two different deadlock prevention policies that are based on max-controlled property of siphons are developed. One is parameterized supervisor control design policy based on and the other is an improved parameterized supervisor control design policy.The first supervisor design policy purposes a way making every strict minimal siphon max-controlled by adding a control place to every elementary siphon. 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. Compared with the existing policies, the advantage of ours is that a much smaller number of monitors are added and unnecessary iterative processes are avoided. 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.An improved parameterized supervisor control design policy aims at improving the parameterized supervisor control design policy, where the output arcs of the additional monitors are not directly moved to the postposition transitions of idle places. It withdraws the output arcs to the transitions until the controlled system does not generate new emptiable minimal siphons. Consequently, dynamic behavior is improved. It is also an effecitve policy from control performance point of view.Two deadlock prevention policies are adequate to larger and medium net systems. Finally, the application of the two approaches is illustrated by a G-system example.