Non Hierarchical Control of a Flexible Manufacturing Cell

Abstract As hierarchically controlled computer-integrated manufacturing systems growthey tend to become complex and their designability, maintainability, expandability and fault tolerance deteriorate. As an alternative, herterarchical control architectures offer prospects of reduced compexity, reduced software development costs, high modularity, high flexibility, and improved fault tolerance. By locating decision making where information originates, global information is reduced to a minimum, scheduling becomes dynamic, machines and parts become “intelligent” entities that cooperatively interact, and the overall system is decomposed into functionally simplified, modular parts. Three flexible machining cell control systems have been constructed at the University of Wisconsin-Madison and are described in this paper: a centralized controller, a hierarchical controller with dynamic scheduling, and a fully distributed heterarchical controller with “intelligent parts”. Comparative results are reported showing that the heterarchical approach possesses a number of advantages including increased fault-tolerance, inherent adaptability and reconfigurability, decreased complexity, and reduced software development cost.