Hierarchical Modeling and Control of Discrete Event Control Systems based on Rule Description Method

A new approach: rule description method, is proposed for discrete event control systems (DECS) modeling in order to reduce the exponential complexity existing in design and implementation of DECS. In the method, objects of a system are divided into two or more layers according to their constitution and dependency. In hierarchical structure of DECS, the overall control task of a DECS is divided into two or more subtasks and distributed into supervisors of all-layer objects. Logic rule expression, which is similar to natural language, is adopted to describe internal logic relation of the controlled system. Message is used to transfer logic control relation between objects of high and low level. Rule description method is easy for technicians to understand, grasp and apply. Procedure of system design and implementation using this method for three-layer DECS modeling are introduced. An example is used to illustrate the method.