Research On The Performance Measurement And Operation Policies In Compact Storage Systems

As an important part of modern logistics, the efficiency of warehouse system has an important effects on the performance of the whole supply chain. On the one hand, the customer demand becomes more personalized and diversified, the improvement of warehouse systems operation efficiency plays an important role to satisfy the customer demand quickly and improve the customer service level; On the other hand, with the increase of land and labor costs, it is important to improve the utilization of storage space and the operation efficiency of the warehouse systems to reduce the overall operation costs of the warehouse systems. Based on these two points, the warehouse systems become storage space compact and service time quickly. Compact storage system in access, sorting, distribution of coordination and optimization, operation process and operation time for fast to meet customer diversification and personalized needs. The operation efficiency of warehouse systems is affected by many factors. Main factors affecting the efficiency of an AS/RS include storage assignment policy, the characteristics of S/R machine, command cycle and dwell point policy, etc.This dissertation intend to study the related problems about the operation efficiency and strategy on the compact storage systems. Firstly, we select two representative compact storage systems (Double-deep AS/RS and Three-dimensional Compact Storage System) as the research objects. For Double-deep Single-aisle AS/RS, considering the rearrangement operation, we use dual shuttle S/R machine to improve the efficiency of the systems. We develop analytical travel time models of dual command and quadruple command cycles under random storage policy. The results show that the efficiency of the system has a significantly improvement by using dual shuttle S/R machine. For Double-deep Multi-aisle AS/RS, we derive the single and dual command cycle time models and propose three rearrangement policies. Meanwhile, we developed a decision model to solve the tradeoff problem between space utilization and load travel time of the warehouse systems. For Three-dimensional Compact Storage System, we present a travel time model under the stay dwell point policy, with random storage strategy and single command cycles. We consider two level decisions in this system based on the proposed travel time model. At the strategic level, we derive the optimal ratio for the warehouse dimensions (length, height and depth) to minimize the expected travel time. At the operational level, we analyze the system performance as it is in influenced by the rack configuration and the types of operations.Secondly, considering the rapid development of the e-commerce and the warehouse usually congestion, the bottleneck of the whole distribution process usually occur in the internal operation efficiency of the distribution center, especially the sorting operation. The sorting efficiency is affected by main factors, such as the type and quantity of orders, sorting strategy, the sorting ability of sorting workers and other factors. The second part of this dissertation takes the sorting systems of compact storage systems as the research object, establish the mixed integer programming model to minimize the makespan and workload imbalance among sorting workers, improving the dynamic response of the distribution center. Meanwhile, we prove that the sorting problem is NP hard and then use some technical method to simplify the model which can be easily solved by some commercial softwares (such as CPLEX).The first two parts of this dissertation mainly focus on the internal operation optimization problem of warehouse systems. From the perspective of supply chain, the third part of this dissertation study the production lot sizing problem with the material-handling cost considerations to study the joint decision-making problem of warehouse system and production line.