Comparison of deadlock prevention policies in FMS based on Petri nets siphons

In the former paper (Huang, Y. S. et al, Jan. 2001), we have proposed a deadlock prevention policy based on Petri net siphons for flexible manufacturing systems (FMS). This paper presents an analysis to show that in terms of control, the proposed policy appears to be more permissive than previous one and siphon-based approaches published recently. In other words, the proposed policy may allow a controlled FMS to contain more reachable, nondeadlocked states. Specifically, three siphon-based methods are compared with this approach. One is Ezpeleta ´s work (1995) for S³PR nets and another is Li ´s approach (2004) using elementary siphons and the other is our previous work, called two-stage policy due to its two stages of preventing deadlocks. All these three rely on the addition of control places to the original net model to prevent siphons from being unmarked. The differences lie in the exact locations and sequences of adding the control places. Our analysis starts with the development of several theoretical results followed by an experimental study. Through reachability analysis, all of the experiments indicate that the proposed policy appears to be more permissive than the other two