Deadlock analysis in automated manufacturing systems with conjunctive resource service

The use of shared resources by multiple part types in automated manufacturing systems (AMSs) can cause deadlock, i.e., a situation in which the flow of parts is permanently inhibited and the processing of jobs is partially or completely blocked. Most of the work existing in literature focuses on systems in which every operation is performed by only one resource. The paper analyzes deadlock conditions for systems in which multiple resource acquisitions are allowed to complete a working operation (conjunctive resource service, CRS). Extending a digraph representation already used for systems with one-resource operation to the case of CRS allows us a formal characterization of deadlock. This leads to an easy solving approach, consisting of a detection/recovery policy. The paper also shows that some results on the safe states of systems with one-resource operation cannot be extended to CRS. As a consequence, some maximally permissive policies for deadlock avoidance cannot be applied to this kind of system.