Deadlock avoidance for production systems with flexible routing

Avoiding deadlock is essential in the operation of highly automated manufacturing systems. Many of these systems support sufficient redundancy to permit flexible part routing. Although flexible routing improves the inherent operational flexibility of these systems, it also requires more highly sophisticated supervisory control techniques. The objective of this work is to characterize the deadlock avoidance problem for systems with flexible routing capabilities. Specifically, the paper addresses deadlock avoidance for single capacity systems (each machine has a single unit of buffer capacity), and mixed capacity systems (some machines have multiple units of buffer capacity). For each of these, we characterize deadlock and prove the correctness of several methods of suboptimal deadlock avoidance. We also address two interesting special cases. The first assumes that every stage of every part type can be performed on at least one multiple capacity machine, whereas the second provides a finite central buffer that can be revisited after every processing stage. For the first case, we present two suboptimal deadlock avoidance approaches, while for the second, we show optimal deadlock avoidance to be computationally tractable.