On deadlock control for a class of generalised Petri net models of flexible manufacturing systems

Abstract

This paper develops a deadlock prevention policy for a class of Petri nets that can model flexible manufacturing systems with assembly and disassembly operations. Siphons in a plant Petri net model are divided into elementary and dependent siphons according to the linear dependency of their characteristic T-vectors. The proposed approach is to make every siphon satisfy the controlled-siphon property (the cs-property), i.e., at any reachable marking, any siphon is max-marked, so that no deadlock states can be reached. The satisfiability of the cs-property is achieved by explicitly adding a monitor for each elementary siphon. The max-controllability of a dependent siphon is ensured by properly supervising its elementary siphons. More permissive behaviour of the non-blocking supervisor is obtained through the rearrangement of the output arcs of the monitors. Compared with existing policies reported in the literature, the advantage of the present method is that a small number of monitors are added and the iterative computing process is accordingly avoided. Finally, the application of the proposed method to an FMS example is presented.

Keywords:

• Petri net
• flexible manufacturing system
• non-blocking; deadlock prevention
• elementary siphon

Acknowledgements

The authors would like to thank the National Nature Science Foundation of China under grants 60474018 and 60773001, and the Laboratory Foundation for Returned Overseas Chinese Scholars, State Education Ministry of China, under grant 030401.