Deadlock resolution strategy for automated manufacturing systems including conjunctive resource service

Automated manufacturing systems (AMSs) can process different parts according to operation sequences sharing a finite number of resources. In these systems, deadlock situations can occur so that the flow of parts is permanently inhibited, and the processing of jobs is partially or completely blocked. Hence, one of the tasks of the control system is ruling resource allocation to prevent such situations from occurring. A large part of the existing literature focused on systems in which every operation is performed by only one resource. This paper proposes a deadlock strategy to avoid deadlock conditions in more complex systems where multiple resource acquisitions are allowed to complete a working operation conjunctive resource service system (CRSS). The AMS structure and dynamics is described by a colored timed Petri net model, suitable for following resource changes and working procedure updating. Moreover, digraphs characterize the complex interactions between resources and jobs so that the conditions for the deadlock occurrence are derived. Finally, an event-based controller is defined to avoid deadlock in CRSSs on the basis of the system state knowledge and of the given priority law ruling the concurrent job selection.