A U-shaped layout for manual order-picking systems

In manual order-picking systems, order pickers walk or ride through a warehouse in order to collect items required by customers. When designing such a warehouse, two conflicting goals have to be considered, namely the maximization of space utilization and the minimization of the average length of the tours on which the requested items are collected. The achievement of these goals is significantly dependent on the layout of the warehouse. Whereas in a traditional warehouse layout, the picking aisles run in parallel to each other, the picking aisles in the warehouse layout presented here are arranged around a U-shaped central aisle. This type of layout, so-called U-shaped layout, provides a kind of compromise solution with respect to the above-mentioned goals. It has recently been implemented for spare-parts warehouses in practice, but has not been studied in the scientific literature so far. In this paper, we present a new routing strategy for the order pickers who operate in such a warehouse, and we derive an analytical expression for the expected tour length per picking order. By comparing this estimation with those of routing schemes for traditional warehouse layouts, it is demonstrated under which conditions such U-shaped layouts allow for operating warehouses more efficiently.