Deadlock avoidance for flexible manufacturing systems with choices based on digraph circuit analysis

Due to the existence of concurrent part flow and resource sharing in modern automated flexible manufacturing systems, deadlock is a common problem and its occurrence causes loss of productivity. When a manufacturing system is modeled by a digraph, existence of circuits in such a graph is a necessary condition for deadlock. Our research further shows that the knot and order of a circuit is closely related to impending deadlocks - a type of deadlock that is more difficult to detect. A deadlock avoidance method for flexible manufacturing systems with flexible part routing is presented together with new concepts such as broken circuit and supremal circuit. The new method is highly permissive since the effective free space calculation captures more part flow dynamics, especially when there exist multiple knots in the digraph model. The online policy runs in polynomial time once the set of basic circuits of the digraph is computed offline. Simulation results on selected examples are given.