Design and specification of a low-level control software for an FMC using supervisory control theory

Supervisory control is an approach based on formal language. It is used to model and control discrete event systems in which each discrete event process is represented as an automaton. A supervisor is a generator that switches control patterns in such a way that a given discrete event process behaves in obedience to various constraints. A flexible manufacturing cell (FMC) is one of discrete event systems. Functions necessary for the operation of an FMC are characterized by operational components and informational components. The operational components can be modeled using the finite state machines and the informational components can be modeled using the abstract formalism which describes supporting operations of the cell controller. In this paper, the authors addressed functions required for FMC control specification, software engineering aspects on FMC control based on supervisory control, a concept of event queue for resolving synchronization problem, and complexity reduction. Based on the mathematical model of an FMC, they synthesized the controller by integrating a supervisor for FMC with control specification that specifies event-driven operation of the cell controller. The proposed control scheme is stable mathematically so that the system always behaves on a controlled way even under the existence of uncontrollable events. Furthermore, using an event queue concept, the authors can solve a synchronization problem caused by the violation of instantaneity assumption of supervisory control theory in real life situation. And also, they can propotype a control software rapidly due to the modularity of the proposed control scheme.