Supervisory Control of Automated Manufacturing Systems Based on State-Tree Structures

Abstract

The automated manufacturing systems (AMS) can be regarded as a resource allocation system which can be abstracted as discrete event systems (DES) for analysis. Once an effective computational method is put forward to the DES, the corresponding real AMS, connected by networks or sensors, can be indirectly controlled. Supervisory control theory (SCT) of DES is developed with the intention of discovering the maximally permissible supervisor of AMS. The state-tree structure (STS) is an extension of SCT, whose application is mainly to solve the SCT state explosion of complicated AMS. The nonblocking supervisory control is investigated on the foundation of predicates in STS, of which the synthesis focuses on the states of the system but ignores the transition between events. In order to effectively solve the above problems, this paper puts forward a novel method based on state feedback control (SFBC) in the STS framework, by which the relation among events is discussed. First, following the definition of the SFBC for predicates, the algorithms to compute the SFBC under reachability, coreachability, and weak controllability are introduced. Second, it is proved that the nonblocking SFBC obtained by the proposed algorithm is equivalent to the one by computing predicates first, which ensures the satisfactory controllers for the supervisory control problems. To demonstrate the contribution of the proposed approach, which is designed considering the symmetry of the system behavior between the real system and its STS model, three examples are illustrated.