Performance analysis of single shuttle and twin shuttle AS/RS

An Automated Storage and Retrieval System (AS/RS) can be equipped with the traditional single shuttle or the newly developed twin shuttle. There has been a significant literature on the comparison of single shuttle versus twin shuttle systems. Researchers agree that the twin shuttle system has better operating performance. However, constructing a twin shuttle system costs 40% more than constructing a single shuttle system. Therefore, given the same environment, we believe that the capacity or effectiveness of a twin shuttle system should outperform a single shuttle system by at least 40% to justify its cost. This study uses Arena 8.0 to conduct the simulation experiment. We assume different rack shapes, time periods of storage and retrieval operations may or may not overlap, locations of input and output stations may not be close, and there may be batch demands for storage and retrieval operations. Simulation results suggest that twin shuttle systems would be the better investment if the input/output stations are in separate locations, time periods of storage/retrieval operations do not overlap, and/or there are significant batch demands.