Abstract: The online supermarket has become one of the most powerful engines that drive the online retailing market in China. It always sells huge number of fast-moving consumer goods (FMCG) and normally has to store enormous stock-keeping units (SKUs) at multiple zones. How to efficiently and accurately pick up the ordered items from tens of thousands of commodities and package them? From the perspective of JIT assembly line, a new optimization method is proposed to streamline the processing of order fulfillment operations in warehouses, including order picking, order sorting (item collecting and checking) and order packing. Three working time calculation formulations are present first and then a joint optimization model of order batching and sequencing is formulated. The model is solved by a two-stage heuristic solution procedure, which decomposes the original model into a batching model with the consideration of the workload balance of multiple storage zones, and a Permutation Flow Shop Problem (PFSP) to sequence the order batches. The batching model is solved by improved relocate and exchange operations in Local Search algorithm while the PFSP is solved by the NEH algorithm. Finally numerical analysis is conducted to verify the effective of the proposed method. The results indicate that compared with the traditional wave picking method, the proposed method can substantially increase the efficiency of order picking for online supermarkets. The principle of JIT assembly line is introduced to order picking. A new problem solution idea is present for order picking and a theoretical guide for optimizing the whole process of order picking in online retailing is provided.

Key words: online supermarket, order picking, assembly line, order batching, sequencing