Rule-based controller design algorithm for discrete event manufacturing systems

Abstract

A modern system theory point of view is offered for the design of sequencing controllers for discrete event manufacturing systems, whereby the controller is considered as separate from the workcell. The controller has a rule-based structure with inner loops where no shared-resource conflict resolution is required, and extra control inputs in an outer loop to resolve conflict and remove deadlock (where needed). The controller design is based on the required task sequence and the available resources; it is described by linear (i.e. matrix) and nonlinear logical equations. The controller-workcell interaction expressed both in qualitative and quantitative terms supports a rigorous analysis of conflicts and deadlock. Three methods for conflict and deadlock resolution related to current work are efficiently incorporated in the general design framework. The design algorithm naturally accommodates a performance analysis in terms of the (R,max,+) representation as a consequence of the link established between that approach and the rule-based controller equations. Compatibility with other analysis/design techniques is briefly addressed.