An interleaving policy in automated storage/retrieval systems

In order to improve their service level many automated storage/retrieval systems have adopted a dual command policy. In a dual command policy both storage and retrieval of pallets are done within one roundtrip of the crane. The expected travel time for a dual command policy is composed of two one-way travel time elements used for storage and retrieval, and an interleaving time element used for moving from a storage location to a retrieval location. In this study the authors apply the nearest-neighbour policy to a class-based warehouse in order to decrease the interleaving time. They develop the methodology for determining the interleaving time for both square and rectangular (time-wise) warehouses. The authors show that using the nearest-neighbour policy in a class-based environment can decrease the interleaving time, resulting in a significant increase in the total throughput.