Three novel deadlock recovery policies for [Formula: see text]-based manufacturing systems.

Manufacturing systems are supposed to operate flawlessly and not to cease functioning due to the deadlocks. Petri nets as a formal specification language, and in particular their subclass known as systems of simple sequential processes with resources ([Formula: see text] nets), are well suited to model modern flexible manufacturing systems. They allow for formal analysis of the production processes and checking whether a system can suspend its functionality under some circumstances. In such a case, deadlock recovery policies can be applied to enforce the liveness of the [Formula: see text] models. In the study, we propose, analyze and discuss some new approaches to deadlock recovery. Three methods are presented and compared: one of them is based on the reachability graph traversal, the second is based on restarting of the process instances, and in the third method the cycles in the resource flow graphs are considered. All the proposed policies allow for the obtaining of acceptable solutions which are similar to or better than the ones provided by other known methods. Furthermore, the problem of phantom deadlocks in [Formula: see text] nets is identified and formally analyzed. Some new results on reachability in [Formula: see text] nets are presented.