Improvement order picking in mobile storage systems with a middle cross aisle

Mobile automated storage/retrieval system (M-AS/RS) is more efficient than mobile storage system (MSS). However, the problems of huge rack row movement and long travel distance have not been effectively solved, especially for heavy items. This study proposes the middle cross aisle model (MCAM) based on the perspective of warehouse layout of M-AS/RS. By designing the layout of cross aisle from front to middle, the warehouse was divided into two small blocks. Picker travel distance could thus be reduced significantly, reducing the huge rack row and making rack row movement more economic and safe. This study formulates the MCAM operation and decomposes the order picking process into three stages, integrating with routing algorithms to achieve better picking routes. Simulation results showed that the MCAM model outperformed the M-AS/RS model. It is suitable for application to lower order density, heavy items with deep racks rows. The optimal ratio for simulation experiment rack shape is 0.6 to 1. Finally, the authors compared typical M-AS/RS and MCAM and also raised some practical concerns regarding its application to industry and addressed future research directions.