Applying Supervisory Control Theory to Discrete Event Systems Modeled by Object Oriented Principles

Implementation of complex discrete event manufacturing systems can be considerably simplified by use of general reusable software modules, representing the physical components. At the same time, construction of the control system can be facilitated by use of formal methods for automatic generation of the control laws. These two aspects can be joined into a general concept with object oriented modeling and control law synthesis as foundations. The goal is to allow an operator to specify the product routes through the system, for each type of product, irrespective of any other type of product that may be simultaneously present within the production system. Control laws guaranteeing production according to those product specifications can then be synthesized, given the model of the system. We will describe such an object oriented modeling approach to discrete event manufacturing systems. Based on the supervisory control theory, using interleaved product routes as specification, it is shown how control laws can be synthesized. An added complexity is that such a specification becomes nondeterministic in the sense that the same string of events can lead to different system states. We have shown that the supervisory control theory can indeed be used with nondeterministic specifications, but also that the notion of controllability is not strong enough to guarantee an implementable supervisor.