A discrete cross aisle design model for order-picking warehouses

In this paper, we develop new warehouse designs that provide a reduction in travel distance for the order-picking operation, which is the most costly operation and the one most closely associated with order delivery time. For this purpose, we propose a new layout problem called “discrete cross aisle warehouse design”. In this problem, a linear middle cross aisle is divided into segments called tunnels on each picking aisle. In order to calculate average tour length for the proposed design problem, we develop an efficient algorithm that solves the order-picking problem optimally. A harmony search algorithm is used to find optimal tunnel positions that minimize the average tour length under a randomized storage policy by searching the space of all possible designs. A numerical study shows that, for small size order lists, the best-found solutions have similar layouts to the traditional two-block designs. As the number of locations to be visited increases, tunnel positions move away from the center of the warehouse and construct a segregated tunnels on the layout. Compared to the traditional two-block layouts, new, tunnel-based designs provide savings of up to 7% average savings in order-picking tour length.