Slotting the Complex Automated Picking System in tobacco distribution center

Tobacco distribution has the main features of fast-moving, high value, uniform dimension which requires high picking efficiency, accuracy and low labor intensity. In this case, traditional manual picking needs to be replaced by proper automated picking significantly. Complex Automated Picking System (CAPS) is a kind of automated order picking system, composed of the Horizontal Dispenser (HD) and A-frame to achieve the advantages of both. As the main order fulfillment area in tobacco distribution center, CAPS needs to be slotted significantly. Based on the classical forward-reserve model, multi-tier model and multi-mode model, we first present a comprehensive analysis of the general multi-tier, multi-mode inventory system of CAPS and analyze the restocking and picking activities of HD and A-frame. Considering the safety stock, we present the optimal number of channels assigned to each sku to minimize the restocking cost of Horizontal Dispenser (HD) based on fluid model and extend the results to A-frame. Rigorous proofs are presented for main theorems and corollaries. Then we develop a three-tier, four-mode inventory system and use it to identify the optimal proportion of picking buffer dedicated to HD and A-frame. Finally, we analyze the equivalent two-tier, three-mode inventory system and develop a practical Greedy Heuristic Strategy to slot the CAPS, which is of great significance for designing a new and measuring an already running CAPS in the tobacco distribution center.