A REAL TIME SIMULATION BASED STUDY OF DEADLOCKS IN AUTOMATED MANUFACTURING SYSTEMS

Abstract

Automated manufacturing systems (AMS) which are equipped with several CNC machines and AGV based material handling system are designed and implemented to gain the flexibility and efficiency of production. However a situation arises when movement of the parts to the subsequent stages is stopped. The deadlock arises when a set of two or more parts keep waiting indefinitely for the other parts in the set to release resources. There are some serious consequences due to occurrence of deadlock like-complete halting of the system, reduced/zero throughput, loss of production hours, increased WIP, increased make span time of parts, increased number of parts in the queue, increased average waiting time of the parts in the queue etc. There are three strategies for handling deadlocks, these are- Deadlock prevention, Deadlock avoidance and Deadlock detection and resolution. In the present work different cases of deadlock have been studied in AGV based automated manufacturing system. A discrete event dynamic simulator has been developed for automated manufacturing system under simplified assumptions. A deadlock avoidance and deadlock detection and resolution algorithm has been developed to handle deadlocks in automated manufacturing systems by categorising the deadlock in automated manufacturing systems as: - deadlock among machines, deadlock among AGVs and deadlock among machines and AGVs. To handle the deadlocks in such type of system an integrated approach of deadlock avoidance and deadlock detection and resolution technique has been applied in the developed algorithm. Apart from the deadlock handling algorithms an algorithm for optimal routing of AGVs from its starting point'to destination based on minimum travelling time has also been developed. The software is developed using Visual Basic 6 under its limitations; it is a user friendly program apart from this feature the software can also be used to check the performance of the different manufacturing system layout and different path network of AGV delivery system. Some case studies have been done to demonstrate the effectiveness of the developed algorithm.