Abstract
Automated guided vehicles (AGVs) have long been identified as a potential driver to improve system efficiency and lower labour costs in material handling systems. Accordingly, the reliability and availability of AGV systems is crucial to assure the stability and efficiency of these systems. However, the reliability issues and maintenance strategies of AGVs have not previously been studied sufficiently. This is even more marked in the case of multi-AGV systems that consist of fleets of AGVs. To fill this knowledge gap, research is conducted considering a multi-AGV system, consisting of three AGVs, in order to develop a scientific methodology for optimising the layout design, operation and maintenance of a multi-AGV system. Once an AGV is failed, it will be towed to the maintenance site for repair by a recycle vehicle to prevent deadlock and conflict. The efficiency of the recycling process of failed AGVs in a multi-AGV system, with respect to the change of location of the maintenance site, is analysed by the approach of coloured Petri nets (CPNs). A CPN model simulating the corrective and periodic preventive maintenance processes of failed AGVs is also developed in order to investigate the impact of different AGV maintenance strategies on the operation efficiency of the multi-AGV system. The simulation results obtained clearly show that the location of maintenance sites and maintenance strategies do have significant influence on the performance of a multi-AGV system, where corrective maintenance is an effective measure to maintain the long-term reliability and stability of the system.
Highlights
Automated Guided Vehicles (AGVs), a type of vehicles that are driverless and programmed to travel on predefined routes to transfer loads, are being widely used in modern material handling systems due to their ability to improve the efficiency and productivity of the systems and decrease human labour
The Master Petri nets (MPN) links the path with the mission; the Recycle Petri nets (RPN) is connected to locate the failed AGVs and find the optimal recycle route; and the Corrective maintenance Petri nets (CMPN) to send the failed AGV back to the base
In order to develop an efficient and reliable approach to find the optimal design, operation, and maintenance strategy of a multi-AGV system, coloured Petri nets (CPNs) simulation models are developed in this research
Summary
Automated Guided Vehicles (AGVs), a type of vehicles that are driverless and programmed to travel on predefined routes to transfer loads, are being widely used in modern material handling systems due to their ability to improve the efficiency and productivity of the systems and decrease human labour. A method was proposed in [6] to solve the deadlock problem, when AGVs are unable to make further progress, the potential in reducing both the material handling time and the cost was demonstrated by the approach of simulation The impact of both empty and loaded vehicles on the operation of AGV system was researched in [7] in order to optimise the direction of unidirectional routes. The influences of the location of the maintenance site and maintenance plan of the failed AGV on the system efficiency can be investigated through modelling the system using coloured Petri nets (CPNs) Such comprehensive research paves the way to achieve more successful layout design, operation and maintenance of multi-AGV systems.
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