Hybrid-grouping-matching Heuristic for the Storage Assignment in Gravity AS/RSs with Duration-of-stay Storage Policy

The gravity automated storage and retrieval systems (the gravity AS/RSs) has high space utilization and high storage density. In the gravity AS / RSs, unit-loads in each bin slide from storage end to retrieval end driven by the gravity. The unit-load in each bin follow the first-in-first-out principle, which means that the improper sequences of stored unit-loads brings extra travel time for removing blocking unit-loads. In duration-of-stay (DOS) storage policy, arrivals and departures of unit-loads are determined in advance. Therefore, a hybrid grouping-matching heuristic (hybrid-GM) is proposed in this paper to generate appropriate sequences of stored unit-loads in bins. Simulation experiments are conducted to evaluate the performance of the proposed heuristic.