Dispatching-driven deadlock avoidance controller synthesis for flexible manufacturing systems

Abstract This paper develops a new method for synthesizing deadlock avoidance controllers (DACs) that realize job and machine dispatching policies of a flexible manufacturing system (FMS) into deadlock free control actions. Our methodology is based on an untimed, deterministic Petri net formalism. It consists of four ingredients: (1) a bottom up approach for synthesizing a controlled production Petri net (CPPN) model of a FMS, (2) a necessary and sufficient liveness condition based on decomposition of the CPPN into production subnets and the concept of minimal resource requirements, (3) a sufficient procedure to test whether the liveness condition is kept after a control action is executed and (4) an algorithm that combines the test procedure with the given dispatching policy to generate valid and utilization maximizing control actions. Such controllers not only keep the FMS capable of repeating any of its operations, i.e., live, but also achieve a high resource utilization under any given dispatching policy.