A Set-based Scheduling Problem for Square Rack Automated Storage and Retrieval Systems

Many researchers have studied AS/RS scheduling problems that sequence the storage and retrieval requests to maximize the system throughput. These studies assume that each retrieval request is fixed with a pre-determined bin position in the AS/RS rack. However, in reality, a retrieval request is associated not with a specific bin position but with a specific product item which is available in various bin locations. In this paper, we address a generalized sequencing problem that determines both specific bin locations for the retrieval requests and sequencing with the chosen bin locations. To solve this new complex combinatorial problem, we introduce heuristic methods and present their computational results. We also derive the cycle time distributions and their mean values for the single command under both squared and non-squared rack shapes