A forward/backward scheduling method using travel time of automated guided vehicles

In this paper, we propose the forward and backward re-scheduling method to determine the scheduling by considering the transportation time in the given facility layout in which an automated guided vehicle (AGV) is controlled by three traffic control patterns. Firstly the scheduling is performed by using only the operation time under the criterion of FCFS (First Come First Served), DUEDATE (Due Date), SPT (Shortest Processing Time) or SLACK (Slack Time). Secondly in the forward re-scheduling method, the time at the pairs of facilities (critical transportation) which do not have idle time is arranged in ascending order. Re-scheduling is done by using the transportation time of one of the traffic patterns at the obtained ascending ordered time, and is continued until the critical transportation does not occur. Thirdly in the backward re-scheduling method, the time at the critical transportation is arranged in descending order and the forward re-scheduling method is applied to this order. Finally the mean flow times of the results of the forward and backward re-scheduling are compared and the scheduling which has the smaller mean flow time is selected.