Towards a fault tolerant cell controller for flexible assembly systems: An approach using colour Petri-Nets

Abstract

Colour Petri-Nets (CPN) can be used within distributed cell controllers for the design, control and monitoring of flexible assembly systems. This paper presents a methodology using CPN to enhance the flexibility, usability and fault tolerance of assembly systems. In particular, flexible process plans and a Genetic Algorithm based scheduler are derived to improve the operational versatility of the system. Moreover, a novel method is described which enables non-Petri-Net experts to automatically generate the CPN based controller from the input of the system parameters within a suite of graphical editors. This approach demonstrates tremendous versatility in the operation of the cell controller, including being able to respond to fault conditions and re-configuring the cell to allow continued operation in most circumstances by dynamically modifying the routings and operation schedules. The proposed methods are seen to be highly effective for small batch production, in particular, where reconfiguration of the physical systems is frequently required.