Distance estimate for order picking systems in manual warehouses

Given the importance of warehouse processes, this paper proposes an estimate of the order picking distance in a warehouse as a function of the number of items in the picking list, the warehouse shape factor and the number of cross-aisles. Two routing policies, i.e. SShape and combined, are taken into account in the evaluation. A model developed in Excel™ is first used to identify the warehouse configuration that generates the best (shortest) distance for each of the policies analysed. Then, an estimate of the picking distance is obtained through a linear regression model. For validation purpose, the results provided by the simulation model for the SS policy are compared with those resulting from the application of an analytic model available in literature. In terms of picking distance, results generally indicate that the S-Shape policy performs better in the absence of cross-aisles and with a warehouse shape factor high for a few order lines, while the COMB policy reaches the best results with an odd number of cross aisles, that decreases as the number of order lines increases; the optimal shape factor instead increases with the number of order lines.