Deadlock Control for Flexible Assembly Systems With Multiple Resource Requirements and Separately-Loaded Parts

This work addresses the problem of deadlock control in flexible assembly systems (FASs) with multiple resource requirements and parts loaded separately into the system. We use generalized Petri nets to model, analyze, and control these FASs. Two kinds of structural objects in the Petri net model, namely A-circuits and closed Ω-structures, can characterize deadlocks. Then a necessary and sufficient condition is derived for the liveness of FAS based on these two objects. By using integer linear programs, we compute all the problematic closed Ω -structures and A-circuits that are related to deadlocks. A specific design of the monitor is developed for each of these objects so as to prevent it from causing deadlock. By composing all these monitors, a deadlock prevention controller is proposed for a subclass of FASs under consideration. Importantly, this work generalizes the liveness condition of ordinary Petri net models to broader non-ordinary ones. Finally, an example can illustrate the usefulness and correctness of the proposed concepts and methods.