Application of Petri nets for deadlock analysis and avoidance in flexible manufacturing systems

Abstract

Unreasonable dispatching resources to jobs inflexible manufacturing system (FMS) may result in a deadlock situation. This serious situation is studied and avoided through Petri net (PN) analysis techniques in this paper. Firstly, a production Petri net (PPN) model for a given FMS is developed. Based on a certain set of resources in PPN,. the concepts of a deadlock state and a potential deadlock state are introduced. Then, we present a deadlock avoidance method that consists of two parts. One is the construction of a deadlock state equation that describes the intrinsic relationship between resources assignation and a deadlock state in PPN. This equation is a necessary and sufficient condition for the occurrence of a deadlock situation. The other is the construction of a restrictive PN controller for each deadlock state equation. This restrictive PN controller can control the resources dispatching by excluding some enabled transitions from firing, consequently avoiding the deadlock. This method is minimally restrictive and allows the maximal use of resources not only for normal FMS, but also for special FMS with cyclic deadlock structure chain (i.e., a pathological type of circular waiting structure). Finally, two applications are given to illustrate the validity of this method. The results show that this method can be efficiently implemented in practical FMS.