Research On Scheduling Optimization Of Four-way Shuttle-based Storage And Retrieval Systems

Fifth-generation mobile communication(5G)technology has been started commercially available and laser radar has been used widely,moreover,the pursuit of the ultimate limits of time and space for the modern logistics,this situation provides a great opportunity for the development of intelligent equipment and opens a vast market for these smart devices.It,as we all know,is not only the traditional industries but the new Internet e-commerce companies have built logistics centers(such as China Tobacco,FAW Group,Tmall Mall and JD.com)that can be used for many SKUs(Standard Product Units).Using the equipment with three-dimensional high-rise racks as the main storage device has developed into the main method of intelligent logistics system storage,and the main spaces of work also have transformed from shelves into robots or shuttles + shelves.The storage system integrated with hardware and software including shelves + shuttle cars + elevators + picking system + warehouse management system has become one of the most popular storage modes at present.In order to break through the city's last-mile delivery issue or meet the massive demand for festivities promotional activities,higher requirements are needed on the flexibility of warehousing operations.A new type of shuttle system,four-way shuttle system,is more and more popular using.The four-way shuttle system can dynamically adjust the task according to the workloads,which gives the users strong flexibility.However,the concurrent operation of multiple shuttle vehicles on the same floor may cause path conflicts also the system control scheduling is much more complicated.In this paper,taking the four-way shuttle system for the research object,aiming at set up a mathematical model for scheduling optimization based on the shortest time usage,focus on the four-way shuttle system which has multi-elevators and multi-four-way shuttles,reaching input and output tasks scheduling optimization issues and the optimizations and scheduling of the path for the four-way shuttles.Combining with the characteristics of the model,it's used an optimized genetic algorithm to solve input and output task issues,and modified A * algorithm to find out and optimize the path on one floor.First,based on the analysis of the physical layout restrict of the four-way shuttle system and the flow of input and output task operations,the input operation could be divided into three methods,while the output is into two methods,according to the time consumed in different steps of the four-way shuttle and elevator operation,establish an optimal scheduling model based on the shortest time.Secondly,combined with the aspects of the scheduling optimization model in this paper,we design an optimized genetic algorithm to solve the scheduling model issues.A matrix format coding is designed to carrying on the information including task indexes,the location of the four-way shuttles and elevator information,etc.figure out the optimal path based on the coding.to get better results and more efficient,optimize and improve the operator probability and fitness functions in the algorithm.In the end,introduce and classify all of the scheduling conflict scenarios in the four-way shuttle system,then according to these situations giving a new method to find out the shortest path based on graph theory and set up an improved a * algorithm with time window.According to the simulations,it shows that the methods in this paper give a significant optimization effect on the batch input and output tasks.