A study of storage assignment problem for an order picking line in a pick-and-pass warehousing system

Order picking is one of the most crucial factors for efficient warehouse management. Most of previous research in order picking in a warehouse considered only the picker-to-part or part-to-picker system; however, the pick-and-pass system plays an increasingly important role because of the growth of e-commerce and time-based competition. This paper develops an analytical model for the pick-and-pass system by describing the operation of a picker as a Markov Chain for the estimation of the expected distance traveled of the picker in a picking line. Based on the proposed analytical model, this study derives properties of storage assignment and proposes three algorithms that optimally allocate items to storages for the cases of a single picking zone, a picking line with unequal-sized zones, and a picking line with equal-sized zones in a pick-and-pass system.