Order Picking in Rack Moving Mobile Robot Systems

Rack moving mobile robots provide a new solution for e-commerce retailers to fulfill customers’ orders. In these systems, racks are moved by robots to workstations where pickers retrieve the purchased products from the racks and put them into totes corresponding to the customers’ orders. Such modern parts-to-picker warehouse operations are leading to the order picking problem that is different from those in traditional picker-to-parts order picking systems. This chapter focuses on the order- and rack-sequencing decision challenges with multiple picking stations in such systems. We first formulate the problem as a mixed-integer program. We then propose a two-stage heuristic solution procedure that provides competitive solutions within a short run time. Computational experiments on small cases and large-scale real-world cases demonstrate significant performance improvement with our algorithm. The results in this chapter provide comprehensive insights into modeling and solution approaches for solving the order- and rack-sequencing decision problem in rack-moving mobile robot systems.