Analysis and optimization for automated vehicle routing on a single loop

This paper treats with an automated material handling system called a permutation circulation-type vehicle routing system (denoted PCVRS). In the PCVRS a fleet of vehicles unidirectionally and repeatedly circulate on a single loop to carry items to stations located along by the loop where items are served. No passing is allowed between vehicles on the loop. This may induce interferences or blocking between vehicles which may deteriorate the performance of the PCVRS. One of the most serious interferences is the one lap behind (denoted OLB) interference which occurs when the first vehicle is interfered by the last vehicle in a fleet of vehicles. Once the OLB interference occurs, the system can not reach the steady state in which no interference occurs. This paper theoretically analyzes the steady state with no interference and the transient state with interferences including the OLB one. This paper considers both the infinite acceleration and deceleration and the finite ones on the vehicles, and four vehicle routing rules by which each job (and each vehicle) is allocated to a processing station for service. Two of them are existing ones and the other two are newly introduced to improve the existing ones. This paper adopts the throughput and the mean interference time for evaluating the vehicle routing rules. This paper confirms the theoretically obtained results by means of numerical simulation.