The fragmented warehouse: Location assignment for unit-load picking

In traditional warehouses, all items of the same stock-keeping units (SKUs) are usually co-located. However, the emergence of automatic identification and tracking technologies like RFID, enables us to consider free-form storage. We consider the strategy of storing identical items in a fragmented manner. The storage of identical SKUs in different locations creates new optimization opportunities by enabling more numerous picking route choices beyond standard unique location sets. Multiple storage location problems are not as well understood as the co-located storage case, and the complexity is greater. We present an abstract warehouse model to explore the storage location assignment problem in warehouse systems involving unit-load order picking and illustrate how multiple copies of items affect optimal location assignment. We introduce a provably optimal strategy involving a concept called ¿order pressure.¿ We provide an optimal arrangement method for unit-load pick-orders and show how relative item probabilities affect clustering and distribution.