Evaluation of scheduling rules for single- and dual-dock automated storage/retrieval system

Abstract

The effect of the number of pick-up delivery stations (or docks or input/output points) is analyzed and compared for three different unit load automated storage and retrieval (AS/R) systems operating under dual command cycle. The AS/R system layouts differ in the number of docks per aisle, and the relationship between the storage and retrieval sources. A simulation model was used to evaluate the systems on three performance criteria—system throughput, mean waiting time and maximum waiting time. The efficiency of the AS/R system can be improved by the introduction of two docks per aisle with the input/output pallets for each dock being independent of each other, the input pallet storage based on closest open location policy, and output pallet withdrawal based on a nearest neighbour policy (or its variant, with a maximum waiting time limit).