双旋转货架拣货作业优化设计

Optimal Order Picking in the Double Carousel Storage System

本文讨论了由一个拣货员负责的双旋转货架系统,目标是寻找一种最优拣货顺序使得总拣货时间。该问题被证明为强NP-难问题,文章提出了启发式算法寻找最优拣货顺序,并对相关模型及算法进行模拟测试以证明其有效性,为方法选择与应用提供了依据。

Carousel systems have been used in different parts of a supply chain, including manufacturing, distribution, and retail. Carousel is a computer warehousing system used for storing and order-picking small to medium sized products. In this system, the picker （human or robot） stands in a fixed position before the carousel. When picking a product, the carousel system will automatically rotate the bin with the requested product to the position of the operator. The advantages are： （ 1 ） automatically moving products to pickers, （2） storing and picking goods in high speed, （3） operating at low cost, （4） effectively utilizing space, （5） minimizing the number of theft incidents, and （5） more space utilization, less chance of theft by employees, and no heating and lighting requirement in the storage area. This paper mainly studies order-picking optimization in a double carousel system with a single picker. Each carousel rotates individually either clockwise or counterclockwise. In the first part, this paper describes the order-picking problem in a double carousel system. Different from the single carousel system, the sequence of picking items will not only impact the rotation time of carousels, but also the waiting time and the walking time between the two carousels for the picker. Changes in the sequence can result in different order picking route, and the different picking route results in different picking time. Therefore, in a double carousel system, it is necessary to consider how to arrange items in the storage locations and order-picking schedule （the picking routing problem） to minimize the total order picking time and improve the order-picking efficiency. In the second part, this paper discusses how to get the optimal order-picking sequence in order to minimize the picking time, and provide the algorithm and validation. This order-picking problem is NP-hard. Based on the characteristics of the double carousel system, this paper provides a pseudo-polynomial algorithm. The algorithm uses recursion method, breaks down the original problem to the corresponding sub-problems, and obtains the final solution by resolving all sub-problems. Meanwhile, simulated testing is taken to validate the performance and reliability of each algorithm, which provides a reference for the application and the choice of order picking method. In the third part, this paper gives a summary for the optimal order picking in a double carousel storage system. Because of the complexity in the order picking system, different systems and different configurations will have different problems. A small change in the system configuration will create different order picking problems, and show a different pattern. These findings warrant future study.