An extensible multi-block layout warehouse routing optimization model

As a special Traveling Salesman Problem, the order picking problem is theoretically challenging and practically significant. Therefore, it has received the attention of many scholars for many years. Compared with a single block layout with parallel picking aisles, the optimal solution for a multi-block layout is much more difficult to find due to the increase in cross-aisles. In this paper, two mathematical optimization formulations are proposed to deal with the multi-block layout problem. One takes the picking position as a unit, and the other takes the picking aisle as a unit. Since picking aisles are connected to each other through specific cross aisles, different picking configurations, access modes, and constraints are introduced. The distance between picking positions is divided into horizontal distance and vertical distance, forming different parts in the objective function. On this basis, two mathematical planning models for the single picker routing problem are constructed. The scale and solution time of the two models are independent of the number of cross aisles, so they have good overall performance when compared with other optimization algorithms through numerical experiments. These models can be expanded to include important features of modern inventory systems, such as scattered storage.