Deadlock Prevention Policy Based On Petri Net For Flexible Manufacturing System

The competition for limited resources leads to deadlocks in flexible manufacturing systems (FMS). As a tool, Petri nets are an effective way to model, analyze, and control deadlocks in FMS. One trend of deadlock prevetion policy is the deadlock prevention method based on siphon theory. This method adds control places and related arcs to every strict minimal siphon (SMS). However the number of siphons grows in general exponentially with respect to the size of the Petri net, resulting in too many additional places and arcs. This thesis focuses on the deadlock prevention of S~3PR net, which is one subclass of Petri nets. A policy is developed, which can not only reduce the number of control places but also can ensure that the net system hold more permissive behavior.Based on Petri nets and siphon theory, strict minimal siphons are divided into elementary and dependent siphons. Different control policies will be taken toward elementary and dependent siphons. The dependent siphons will be divided by whether it includes center resource or not, and different control policies will be added also such that the strict minimal siphons in the original net will be sufficiently marked. Furthermore, the newly generated control-induced strict minimal siphon will not affect the liveness of the net. Finally, the characteristic of implicit place will be used for simpliyling the net system.The new deadlock prevention policy enables the supervisor's structure to be simpler, and more permissive behavior can be obtained in net system as well. In the final part of this research, the advantages and superiorities of this method can be proved through comparing with other kinds of deadlock prevention methods in FMS.