Deadlock-free scheduling of flexible manufacturing workcells using automata theory

This paper presents a novel method for the scheduling and control of flexible manufacturing cells (FMCs). The approach employs automata. Augmented by time labels proposed in the paper, for the modeling of machines, transportation devices, buffers, part types, precedence constraints, and part routes. The Ramadge-Wonham´s supervisory-control theory is then used to synthesize a controller for the workcell representing its deadlock-free behaviour and capable of keeping track of time. For any given batch of parts to be processed by the FMC, a best-first (BF) graph-search strategy is subsequently employed to determine an optimal, or near-optimal, deadlock-free schedule using a novel heuristic function. The proposed approach is illustrated through a typical FMC example, adopted from [HH Xiong, M Zhou, and RJ Caudil IEE Conf. On Robotics and Automation, Albuquerque, USA, Vol. 3, pp. 2793-2797, 1996] to demonstrate the significant reduction in node generation.