Abstract
Deadlocks are a rather undesirable phenomenon in flexible manufacturing systems (FMSs). This work, by adding monitors, develops a deadlock prevention policy for FMSs that can be modeled by a class of Petri nets called alpha-(SPR)-P-3 with xi-resources. First, an algorithm is presented to reduce an (SPR)-P-3 via a xi-resource. Based on the algorithm, xi-resources in alpha-S(3)PRs are classified into two types: 1) A-xi-resources and 2) B-xi-resources. Next, for an alpha-(SPR)-P-3 with only B-xi-resources, it is proved that a maximally permissive liveness-enforcing supervisor can be designed by controlling all emptied strict minimal siphons. For an alpha-(SPR)-P-3 containing A-xi-resources, a liveness-enforcing supervisor can be designed by iteratively reducing the net via A-xi-resources and adding the corresponding monitors. Finally, a deadlock prevention algorithm for alpha-S(3)PRs is presented. Two FMS examples are used to illustrate its application. Its comparison results with other state-of-the-art deadlock prevention policies validate its overall advantages in terms of computational complexity, structural complexity, and behavior permissiveness.