A performance evaluation model for order picking warehouse design

Abstract

This paper is concerned with a performance evaluation model for the order picking facility for warehouse design in a supply center (SC) by reducing the travel distance of transporters. This study includes important detail aspects of warehouse design and operational parameters such as warehouse size, rack size, number of transporters, and the system performance. In this study, we develop both mathematical and simulation modes considering probabilistic demand and picking frequency, and using simulation S/W, AutoMod. The results are compared and validated via simulation methods using AutoMod simulator. Finally, we developed a systematic and practical computer program and it was known that the proposed method is potentially efficient and useful in performance analysis for order picking warehouse problems.

Introduction

Recent studies among various activities taking place in order picking warehouse have shown various researches to reduce the order picking costs occupying more than half the total costs (Caron et al., 2000, Jang et al., 1999, Jarvis and McDowell, 1991). Order picking warehouse, a special class of warehouse, generally deals with a large number of small, fast-moving products (Rouwenhorst et al., 2000). The orders filled in order picking warehouse usually contain many different products that individually do not constitute a full unit load. In this study we consider freight terminals that serve as bases for pickup and delivery operations. It can be thought as a warehouse through which inventory transfers to customers by pickup, sort, and delivery operations. Fig. 1 shows typical freight terminal flows (Van den Berg & Zijm, 1999). There are three major areas in the freight terminal system: (1) first, arrival area represents incoming vehicles with freight to be unloaded, (2) sort and transfer area is equipped with auto-sort devices and transporters such as conveyer systems and carts. The facilities in auto-sort system reads the information on the freight arrived by barcode sensing or by the other methods and based on these freight information this system sort the freights by those destinations to send pre-assigned chutes, and finally, (3) delivery area load/unload freights arrived from auto-sort area through predetermined chutes by destinations and loads to vehicle to deliver the freights to destinations. The major functions of the freight terminal system are: (1) pickup and arrival, (2) auto-sensing the freight information, (3) auto-sorting, and (4) delivery. The purpose of this study is to design order picking warehouse to minimize the number of transporters and the expected travel time to improve the performance of transporters. To solve this problem, we developed a mathematical model and also we demonstrated the system performance by simulation model using AutoMod simulator (Auto Simulations, 2000) and verify the results to compare mathematical results of the system performance of warehouse system.

One of the significant changes in warehouse systems design is the optimizing design and automation of order picking facilities such as optimizing the performance of order picking transporters to reduce the freight terminal process cost and increasing the system throughputs. Brynzer and Johnsson (1995) summarized the factors that affect the performance of order picking system, including the composition of orders in a batch, the sequence in which the items will be retrieved, where to store each item, the division of the picking area into zones, layout design, and picking equipment. Roodbergen and Koster (2001) considered a parallel aisle warehouse, where order pickers can change aisles at the ends of every aisle and also at a cross aisle halfway a long the aisles. This paper focuses on the performance evaluation for optimizing the performance of transporters for the design and layout factors of integrated order picking warehouse system. A systematic approach is introduced for the performance evaluation considering mathematical and simulation methods as: (1) a mathematical model to analyze the performance of order picking warehouse system and the transporters performance evaluation. The travel time of transporters is one of the warehouse performance measures and it has to meet the required throughput considering the design of strip and stack doors. We develop a performance evaluation model based on the material handling cost for both cases of throughput and waiting due to congestion and (2) we develop a simulation model using the AutoMod simulator, and we validate the mathematical model using this simulation model. Fig. 2 shows a systematic approach for order picking warehouse performance evaluation.