Joint Storage Location Assignment And Order Batching In Mobile-pods Warehouse Systems

As the e-commerce develops dramatically,the warehouse’s level of intelligence enhances gradually.The warehouse system which is based on mobile-pods is becoming a hotspot for research.The typical example is the Kiva system used by Amazon warehouse.This system proves that the mobile-pods can help company save spending,and enhance operation efficiency.The operation of warehouse mainly includes receiving,stocking,selecting,sorting,packaging and shipping.In these operations,selection is order picking,which is supposed to be the most time-consuming and labor-intensive operation.The efficiency of warehouse operation mainly depends on efficiency of order picking.Therefore,enhancing efficiency of order picking is the main goal of our research.Picking orders in the mobile-pods warehouse system means that a robot moves the storage pod to station operation staff based on demands of orders waiting for order picker to take off stock and then the robot sends mobile-pod back to storage area.The area does not have to be the original one,so the spot of mobile-pod keeps changing all the time.This method of order picking is the “Things to People” pattern.Currently,there are few researches on this field.In the actual operation,the robot has to go there and back frequently moving mobile-pods to compete a batch of orders.So deceasing back and forth frequency of robot is our main strategy of order picking.This is an effective method of increasing order picking efficiency.We think that storage location assignment strategy(SLAS)and order combination strategy(OCS)both have influence on order picking.In the context of mobile-pods warehouse system,the SLAS is deciding which stock should be stored in a shelf,the OCS is that whether we should batch picking,and which orders are suitable to be picked in the same batch.Researching SLAS and OCS at the same time also has innovative theoretical significance.This essay is aimed at storage location assignment problem(SLAP)and order batching problem(OBP)in mobile-pods warehouse system.Different similarity indexes are introduced,and a clustering model is built for the two problems.Besides,a strategy evaluation model based on the mobile-pods warehouse system is given,and detailed numerical experiments are carried out to evaluate the performances of the six proposed strategies which jointly consider SLAP and OBP.After visual and variance analysis of the data,we can compare the strategies and draw instructive conclusions.