Deadlock-free optimal routing in flexible manufacturing cells via supervisory control theory

A typical problem in flexible manufacturing cells (FMCs) capable of producing multiple parts through multiple routes is optimal routing, where decisions regarding choosing alternative production routes have to be made at certain system states. This paper presents a novel method for determining deadlock-free decisions that optimize a given performance criterion. The approach employs automata, augmented by time labels, 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 maximally deadlock-free behavior and one that is capable of keeping track of time. This supervisor is utilized to determine the set of optimal decisions. The proposed approach is illustrated through a typical FMC simulation example.