Abstract
An automated manufacturing system (AMS) contains a number of versatile machines (or. workstations), buffers, and an automated material handling system (MHS). The MHS can be an automated guide vehicle (AGV) system, and/or a system that consists of multiple robots. Deadlock resolution in AMS is an important issue. For the AMS with an AGV system as MHS, the problems of deadlock resolution for part processing process and AGV system as an integrated system has been studied. It is shown that AGVs can serve as both material handling devices and central buffers at the same time to help resolve deadlocks. For AMS with robots as MHS, the existing work treated the robots just as material handling devices and showed that the robots had contribution to deadlock. In this paper, such AMS is modelled by resource-oriented Petri nets. Contrary to the existing work, it is shown that the robots have no contribution to deadlock by adopting such nets to control AMS. More interestingly, they can be used to resolve deadlock. by serving as temporary part storage devices. A new deadlock control policy is proposed by treating robots as both material handling devices and buffers. The new policy outperforms the existing ones.
Note to Practitioners-Robots have been widely used in manufacturing automation. This paper presents a unique Petri net formalism to model and control deadlock problems in automated manufacturing systems where robots are used as material handling devices. This formalism allows one to avoid the deadlocks that may arise due to the competition of part delivery processes for robots. More important, it allows robots to be used as temporary buffers to resolve otherwise deadlock situations. The proposed Petri net models and deadlock control method assume both theoretical and practical significance.