Research On Modeling And Optimization Of Four-way Multi-tier Shuttle-based Storage And Retrieval System

Under the background of German Industry 4.0 and Intelligent Manufacturing in China,warehousing automation technology has aroused a research upsurge at home and abroad.In recent years,the flourishing development of e-commerce industry has changed customer's shopping habits,and fragmented orders show exponential growth,but consumers have higher and higher requirements on order response speed.In addition to the rising cost of land and labor,the multi-tier shuttle-based storage and retrieval systems,with storage and sorting functions,has become the most popular logistics automation solution.In the general multi-tier shuttle-based storage and retrieval systems,the shuttle does linear reciprocating motion on the fixed tier of the fixed aisle.However,in four-way multi-tier shuttle-based storage and retrieval systems,the shuttle can achieve cross-aisle and cross-tier operations to any storage location.Therefore,four-way multi-tier shuttle-based storage and retrieval systems has strong flexibility and the number of four-way shuttles of the system can be adjusted according to business requirements.However,at the same time,the control scheduling of the system is more complex,and the difficulty and time of a single operation of the four-way shuttle are also increased accordingly.This paper takes four-way multi-tier shuttle-based storage and retrieval systems as the research object,and takes the system performance analysis,configuration optimization and order sequencing optimization strategy as the research points to carry out the research work:1.Performance analysis modeling of four-way multi-tier shuttle-based storage and retrieval systems.By studying the warehouse layout structure and the operation characteristics of the main equipment of the systems in the engineering practice application,the inbound and outbound operation flows are analyzed in detail,and the operation characteristics of the picking workstation in processing a group of small batch orders are analyzed.According to the different operation actions of the four-way shuttle and the lift,the average service time was calculated,and the system outbound and inbound operations were divided into 16 different operation scenarios.Considering the influence of the number of aisles(that is,the number of lifts),the number of tiers and the number of four-way shuttles,the occurrence probability of 16 scenarios has been analyzed and calculated.Considering the order queue and four-way shuttle fleet queue at the same time,the semi-open queuing network model under small batch task is established,and the service rate of two service nodes in the queuing network model of four,way shuttle system is solved.2.Configuration optimization of four-way multi-tier shuttle-based storage and retrieval systems.The matrix geometry method is selected to solve the queueing network,and the reliability is verified by simulation experiment.The data changes of four important system performance indexes of the system were analyzed under a certain system scale but with different task arrival rates and different number of four-way shuttle configurations.According to the practical engineering application experience,taking the average utilization rate equal to 80%as the basis for the selection of the optimal configuration number of four-way shuttle in the system,the configuration number of four-way shuttle is analyzed under different arrival rates of inbound and outbound tasks.3.Order sequencing optimization strategy of four-way multi-tier shuttle-based storage and retrieval systems.According to the cross-aisle and cross-tier movement of four-way shuttle,by making two orders containing more identical SKU or more SKU distributed in the same aisle or tier be picked together,the frequency of "In-Out Stock" and the frequency of cross-aisle and cross-tier operation can be reduced.The mathematical model was established with the objective of minimizing the total order picking time,and a heuristic order sequence algorithm with improved coupling degree was proposed to solve the model.Through numerical example analysis,it is concluded that the order sequencing optimization strategy can greatly reduce the completion time of batch orders,and the optimization effect is different under different order quantity and order structure.