Implementation of a deadlock avoidance policy for multipart reentrant flow lines using a matrix-based discrete event controller

Abstract

A deadlock avoidance supervisory controller for Discrete Event (DE) Systems is implemented. The DE controller uses a novel rule-based matrix dispatching formulation (US patent received). This matrix formulation makes it direct to write down the DE controller from standard manufacturing tools such as the bill of materials or the assembly tree. It is shown that the DE controller's matrix form equations plus the Petri Net marking transition equation together provide a complete dynamical description of DE systems. Deadlock-free dispatching rules are derived by performing circular wait analysis (CW) for possible deadlock situations. We analyze the so-called critical siphons, certain critical subsystems and resources to develop a DE controller that guaranties deadlock-free dispatching by limiting the work-in-progress in the critical subsystems associated with each CW. This is the least-restrictive dispatching policy that avoids deadlock. The deadlock-free dispatching rules are implemented by the DE controller on a three-robot, two machine reentrant flow line, the Intelligent Material Handling cell at the Automation and Robotics Research Institute of UTA. Technical information given includes the development of the deadlock-free controller in LabVIEW®. Copyright © 2002 by ASME.