Abstract: Mobile-rack warehousing system has greatly enhanced the flexibility of product storage. It is conducive to significantly improving the efficiency of picking e-commerce orders with the characteristic that an order contains multiple products. However, just because of the mobility of racks, how to locate racks to effectively meet the challenges of picking e-commerce orders becomes a new and difficult problem that must be handled by decision makers of e-commerce warehouses. It is also a problem that constrains the advantages of this type of warehousing system. Since each rack in the warehousing system stores products of different types and numbers, the key of solving the problem is to reasonably locate racks in a warehouse in order to maximize the order picking efficiency based on the patterns that customers order products. To handle the problem, the model that generates the degrees of rack popularity and relevance is constructed based on customer orders. And a two-objective integer programming model is constructed by considering the minimization of heavy-load and no-load travelling distance of robots based on the two attributes. A tabu search heuristic algorithm is developed. Instances with different sizes are respectively applied to verify the scientificity and effectiveness of the proposed models and algorithm. Managerial insights are provided for decision makers of the warehouses of this type by sensitivity analysis.

Key words: Mobile rack, Rack location optimization, Degrees of popularity and relevance, Goal programming, Tabu search