Synthesis of feedback control logic for discrete manufacturing systems

This paper concerns the supervisory coordination and control of concurrent activity cycles in automated manufacturing facilities. In contrast to commonly used simulation models which integrate the control policy with the system model, the state transition logic for the manufacturing equipment is represented by a class of controlled Petri nets (CtlPN) with external inputs to be determined by the control synthesis algorithm. We formulate the forbidden state control problem in the CtlPN context and present an algorithm for generating maximally permissive controls which guarantee the system will avoid the forbidden states while permitting a maximal amount of flexibility in the system operation. The problem formulation and control synthesis algorithm is illustrated for an example of AGV co-ordination, and several classes of manufacturing control problems which can be addressed within this framework are identified.