A Forward/Backward Scheduling Method Using Travel Time of AGV

Abstract

In this paper, we propose a scheduling method dealing with transportation time by automated guided vehicles (AGVs) in a production system. AGV transportation is classified into linear type, loop type and network type. We also formulate the travel distance of an AGV, which is controlled by three traffic control patterns, ground calling type (GCT), ground calling & specifying destination type (GCSD) and from-to calling type (FTCT). Firstly, scheduling is planned by only processing time and the critical transportation between work stations is obtained from this result. Secondly, according to the facility layout previously installed, the critical transportation time is calculated. From the time when the critical transportation occurs, rescheduling is obtained using both forward and backward methods. Finally the mean flow times resulting from the forward and backward rescheduling are compared and the scheduling which has the smallest mean flow time is selected. Simulation results on its application to the sample problem are discussed with regard to scheduling performance and the effect of transportation pattern and scheduling priority rules.