Modeling And Optimization Of Multi-tier Shuttle Warehousing System

Taking into account improvement of flexibility and robustness in logistics engineering, a new type of Automated Storage and Retrieval System (AS/RS) has been gaining popularity over time, named by Multi-tier Shuttle Warehousing System (MSWS). This new storage system consists of multi-tier shuttle sub-system which is in charge of horizontal movement and lift sub-system which takes charge of vertical movement, while the combination of shuttles and lifts undertakes inbound/outbound tasks instead of stacker crane in conventional AS/RS. In this context, this thesis analyzes the operations process and handover sequence of outbound task execution based on the tier-captive Multi-tier Shuttle Warehousing System. Then, two main research contents are taken into consideration. The first research content is storage assignment optimization based on Open Queuing Networks and Ant Colony Clustering Algorithm, while the second one is task scheduling problem which is optimized based on the Elitist Non-dominated Sorting Genetic Algorithm (NSGA-II).The main thesis outlines are listed as follows:(1) A time sequence model of MSWS is proposed based on the fact of parallel retrieval of shuttles and progressive transfer of the lift. This thesis analyzes the operations process of MSWS taking into account movement characteristics of shuttles and the lift. According to the time sequence model, the main impact factors are outlined and analyzed in this chapter.(2) An open queuing networks model is established to describe the idle time of the lift and the waiting time of shuttles while the handover operation happens. The decomposition method is used to analyze operation performance and queuing characteristics. Subsequently, the storage keeping unit (SKU) relevancy matrix and ant colony clustering algorithm are both used for initial storage partitions. Then, this thesis presents several basic principles for permutation and combination of initial storage partitions, depending on analysis results of the open queuing networks. After these steps, storage assignment problem of MSWS can be addressed. In the end, this thesis applies these algorithms to a practical engineering project for storage assignment problem.(3) The multi-objective optimization model for operation performance of MSWS is established based on parallel retrieval of shuttles and progressive transfer of the lift, which consists of the minimal outbound operation time, shortest idle time of the lift and minimal waiting time of shuttles during the whole outbound operation process. Based on Pareto Optimum, NSGA-â…¡ is applied to model solution. At last, case study is used for model verification.In the end, the graduation thesis presents the research conclusion and innovations. In addition, the future research contents in this area also are outlined.