Deadlock avoidance algorithms for assembly processes with unreliable resources

This paper focuses on synthesis of controllers that can operate in the presence of machine failure. We formulate a deadlock avoidance controller synthesis problem for assembly production processes with unreliable machines based on resource unavailability models, which regard unavailability of resources as loss of tokens in nominal Petri net models. We define two types of token losses to model different modes of machine failure. For each type of token loss, we establish sufficient conditions that guarantee the liveness of the Petri nets after tokens are removed. An algorithm is proposed to conduct feasibility analysis by searching for recovery control sequence and to make the resources released from blocking situation so that all the remaining available resources can be effectively utilized for production. Our algorithm synthesizes control logics that try to minimize the recovery or reset operations that need to be conducted, so that the impacts on existing production schedule can be reduced.