Design and Evaluation of the Class-based Multi-aisle As/rs

In this paper, the design and evaluation of the multi-aisle automated storage and retrieval systems (AS/RS) is presented. In comparison with the well known single-aisle systems, the multi-aisle systems, where the storage and retrieval machine serves more than one picking aisle, can substantially reduce the investment cost. The objective of this study is to exploit the benefits of the class-based multi-aisle system for reducing the average travel time for a transaction and consequently to increase the throughput capacity. For the storage operation, the random location assignment policy was applied, while for the retrieval operation the "first come first served" and "nearest neighbour" request selection rules were applied. The performance comparison of the single-class and class-based multi-aisle systems is contrasted with the alternative combination of the storage rack configuration and the number of picking aisles. The results show that class-based multi-aisle systems are effective in reducing the average travel time and also show large improvements in throughput capacities. (Received in August 2005, accepted in December 2005. This paper was with the author 2 months for 2 revisions.)