AN OBJECT-ORIENTED MODEL FOR FMS CONTROL

The flexible manufacturing system (FMS) is a distributed network of he terogeneous programmable manufacturing machinery, such as assembly lin es and numerically controlled machines. Despite these interconnected, programmable hardware elements, the success of building a truly flexib le manufacturing system has been limited so far, owing to the lack of flexibility in its control software layer. In integrating heterogeneou s machinery, many existing FMS control software systems depend structu rally on specific machinery and job-scheduling strategies, and thus it is difficult to incorporate new developments in FMS organization and operational requirements. In searching for an open architecture for th e FMS control software system, this paper presents an object-oriented FMS data model. Among others, it represents each physical cluster of r elated machinery (called a flexible manufacturing cell) as an object. To facilitate the integration of heterogeneous physical cells, such ce ll objects share a common protocol of interacting with the main contro l process through inheritance from the abstract cell class. Other rela ted physical and abstract entities in FMS are also modelled as objects , with their similarity and difference captured in inheritance hierarc hies. To verify the proposed approach experimentally, a prototype FMS control software system named FREE (FMS Runtime Executive Environment) has been implemented on top of a commercial object-oriented database system.