A Deadlock-Avoidance Dispatching Method for Multiple-Load AGVs Based Transportation System; [基于多载量AGV的运输系统死锁避免调度方法]

In recent years, multiple-load automatic guided vehicle (AGV) is increasingly used in the logistics transportation fields, owing to the advantages of smaller fleet size and fewer occurrences of traffic congestion. However, one main challenge lies in the deadlock-avoidance for the dispatching process of a multiple-load AGV system. To prevent the system from falling into a deadlock, a strategy of keeping the number of jobs in the system (NJIS) at a low level is adopted in most existing literatures. It is noteworthy that a low-level NJIS will make the processing machine easier to be starved, thereby reducing the system efficiency unavoidably. The motivation of the paper is to develop a deadlock-avoidance dispatching method for a multiple-load AGV system operating at a high NJIS level. Firstly, the deadlock-avoidance dispatching method is devised by incorporating a deadlock-avoidance strategy into a dispatching procedure that contains four sub-problems. In this strategy, critical tasks are recognized according to the status of workstation buffers, and then temporarily forbidden to avoid potential deadlocks. Secondly, three multi-attribute dispatching rules are designed for system efficiency, where both the traveling distance and the buffer status are taken into account. Finally, a simulation system is developed to evaluate the performance of the proposed deadlock-avoidance strategy and dispatching rules at different NJIS levels. The experimental results demonstrate that our deadlock-avoidance dispatching method can improve the system efficiency at a high NJIS level and the adaptability to various system settings, while still avoiding potential deadlocks. © 2021, Editorial Department of Transactions of NUAA. All right reserved.