A graph-based deadlock prevention technique for FMSs Petri nets

This paper proposes a method to synthesize supervisors for a class of sequential resources allocation system for flexible manufacturing systems. The class of Petri nets, called the simple sequential processes with resources (S³PR) where deadlocks are related to empty siphons. The proposed policy first constructs a reachability tree (also called reachability graph) of the S³PR net in order to find its dead markings. Then it controls the dead markings by using a graph-based technique. Finally, the control policy adds a controlled transition to the net such that it make the control net into a live one. Based on the independent dead states, a new deadlock policy is developed by using reachability graph technique. The new control policy is to handle I/O variation to get all the independent dead states of the system nets. By way of the independent dead states, we can obtain the control transitions. Notably, this study is different from previous control policies which are adding additional control places policies. Comparison with experimental results, our new control policy will obtain the maximally permissive reachability states than the conventional place-control ones. As a result, one can infer that our control policy can be used in Petri nets deadlock systems and obtain the maximum permissive states. To our knowledge, this is the first work that employs independent dead states to obtain the deadlock policy.