Abstract: The quicker responding time of orders demands a more efficient order fulfilment system in the distribution centre. The automated vehicle storage/retrieval system (AVS/RS) has been widely used in recent years due to its flexibility and high efficiency. The AVS/RS has two mechanical structures-one is based on cross-aisle shuttles and another is based on a ring-shaped conveyor. Both of above systems can fulfill the orders rapidly,however,there are differences in two aspects including the system throughput and order cycle time which makes the warehouse manager hard to make decision when choosing the systems. Based on the above reasons,this paper compares the performance differences of two kinds of AVS/RS. The open queuing network models of two systems are built,and then the system throughput and order cycle time are calculated. The open queuing network models are verified by simulation. The performance of the two systems are compared. The results show that the system throughput is related to the number of tiers and lanes of AVS/RS. The AVS/RS with cross-aisle has more advantages when there are more tiers and fewer lanes. Similarly,the order cycle time is related to the number of tiers and order arrival rate. The AVS/RS with cross-aisle has more advantages when there are more tiers and smaller order arrival rate.

Key words: automated vehicle storage/retrieval system, cross-aisle shuttle, ring-shaped conveyor, open queuing network, system performance