Performance of Dual Stacker Automated Storage and Retrieval System (AS/RS) with Double-Deep Configuration

An automated storage and retrieval system (AS/RS) is one of the computer-controlled Material Handling Systems (MHSs), playing an important role in modern warehousing operations. With the rapid development of e-commerce, the efficiency and accuracy of warehousing operations are crucial to the competitiveness of enterprises. Among them, the stacker crane, as the core equipment of AS/RS, has a key role in storing and retrieving goods. However, maximizing its efficiency as well as improving storage space remains a challenging issue. In this study, dual stacker AS/RS was developed with parallel processing capabilities. Through the simulation-based experiment via FlexSim, the performance of dual stacker AS/RS was evaluated for the double-deep rack and compared to traditional AS/RS under different order rates, storage assignment methods, and input/output configurations. The experimental results showed that the dual stacker AS/RS had 21-78% higher throughput, and 22-51% lower travel distance, but 63-251% longer response time than single stacker AS/RS since it required longer exploration time. However, the faster the order rate, the response time impact became less obvious. The idle rate of dual stacker was consistently higher than single stacker leading to a more robust system to cope with order uncertainty and potentially lower energy consumption. The better performance of both single stacker and dual stacker AS/RS was achieved with class-based storage and double input/output configuration.