Integrating order assignment and rack assignment in robotic mobile fulfillment system

In this paper, a three-phase hybrid heuristic algorithm based on product supply relationship (TP-HHA) is proposed to deal with the problem of order and rack assignment for picking stations (ORAPS). The ORAPS occurs in the order picking process of robotic mobile fulfillment system (RMFS). It is an NP-hard problem so that the optimal algorithm is difficult to effectively solve it with larger scale instances, which cannot meet the requirements of real applications. To overcome this difficulty, we propose the TP-HHA. It firstly uses a problem decomposition frame to divide the ORAPS into three subproblems. Then, in each stage, a meta-heuristic or constructive heuristic is designed to solve the corresponding subproblem. In addition, a post-optimization strategy is employed to find a better solution. The sufficient neighborhood search operators with problem-specific knowledge are designed for both subproblem optimization and post-optimization. The computational results are given to verify the effectiveness of our algorithm.