M. B. M. de Koster

Routing orderpickers in a warehouse: a comparison between optimal and heuristic solutions

In this paper the problem of finding efficient orderpicking routes is studied for both conventional warehouses, where pickers have a central depot for picking up and depositing carts and pick lists, and modern warehouses, where orderpicking trucks can pick up and deposit pallets at the head of every aisle without returning to the depot. Such environments can be found in many warehouses where paperless picking is performed from pallet locations with pickers having mobile terminals receiving instructions one by one. In order to find orderpicking routes with a minimal length in both the situations of a central depot or decentralized depositing, we extend the well-known polynomial algorithm of Ratliff and Rosenthal [1] that considered warehouses with a central depot. In practice, the problem is mainly solved by using the so-called S-shape heuristic in which orderpickers move in a S-shape curve along the pick locations. The performance of the new algorithm and the S-shape heuristic are compared in three realistic orderpicking systems: (1) narrow-aisle high-bay pallet warehouse; (2) picking in shelf area with decentralized depositing of picked items; and (3) conventional orderpicking from wide-aisle pallet locations. The new algorithm gives a reduction in travel time per route of between 7 and 34%. It turns out that the reduction in travel time strongly depends on the lay-out and operation of the warehouse.

Efficient orderbatching methods in warehouses

In this paper, the orderbatching problem in warehouses is investigated. Batching, or clustering orders together in the picking process to form a single picking route, reduces travel time and, as such, this phenomenon can be encountered in many warehouses. The reason for its importance is that orderpicking is a labour intensive process and, by using good batching methods, substantial savings can be obtained. The batching and routing problems are complex to solve. In practice, simple methods are used for the batching problem, such as first-come first-served (FCFS), i.e. combine orders in the route in the arriving sequence until the pickdevice is full. Once clusters of orders have been formed, the calculation of the travel time for the routes requires the solution of a number of travelling salesman problems (one for each route). Two groups of heuristic algorithms are evaluated: the Seed algorithms and the somewhat more complex (and CPU time consuming) Time Savings algorithms. The performance of the algorithm...

Improving Order-Picking Response Time at Ankor's Warehouse

Ankor is a wholesaler of tools and garden equipment, carrying such well-known brands as Skandia. Its warehouse is under continuous pressure to improve its efficiency while it is confronted with several specific requirements in its order picking, like the requirement to retrieve heavy products first to prevent damage to other, breakable products. Our research goal was to determine a good combination of policies for storage assignment (assigning products to storage locations) and routing (determining the sequence in which to retrieve products from storage to meet customer demand) for Ankors situation. We adapted existing solution techniques for this problem, overcoming the special characteristics of Ankors operations. With these adapted techniques, we cut the average route length in the order-picking operation by 31 percent. As a result of our study, Ankor implemented a new storage and routing strategy. The study also showed further improvement potentials in the picking process, which Ankor adopted as well. All improvements led to a reduction in the number of order pickers of more than 25 percent.

On using DEA for benchmarking container terminals

Purpose – The purpose of this paper is to compare efficiency scores from the benchmarking exercise with those of previous studies and to discuss the reasons behind diverging results.Design/methodology/approach – This paper uses data envelopment analysis (DEA) on primary data of large container terminals.Findings – The results differ strongly from those available in the literature. Causes for these differences are: public (secondary) data are not always accurate; different terminal types are compared; terminals of different scale are compared; and terminals are mixed with ports.Practical implications – DEA may be appropriate for container terminal benchmarking, but only if better quality and additional input and output data can be obtained. In its application, the analysis should be controlled for terminal types.Originality/value – Summary of the state of play in the use of DEA methodologies for comparing the efficiency of container terminals at ports.

Factory Gate Pricing : an analysis of the Dutch retail distribution

Factory gate pricing (FGP) is a relatively new phenomenon in retail distribution. Under FGP, products are no longer delivered at the retailer distribution center, but collected by the retailer at the factory gates of the suppliers. Owing to both the asymmetry in the distribution networks (the supplier sites greatly outnumber the retailer distribution centers) and the better inventory and transport coordination mechanisms, this is likely to result in high cost savings. A mathematical model was used to analyze the benefits of FGP. The main contribution of this paper is its practical approach to transport consolidation in this recently emerging supply chain concept in retail distribution. Extensive numerical results for a large real-life case study of the Dutch retail distribution are presented to show the effect of the orchestration shift from supplier to retailer, the improved coordination mechanisms, and sector-wide cooperation.

On-line dispatching rules for vehicle-based internal transport systems

On-line vehicle dispatching rules are widely used in many facilities such as warehouses and manufacturing facilities to control vehicles’ movements. Single-attribute dispatching rules, which dispatch vehicles based on only one parameter, are usually used. However, multi-attribute dispatching rules prove to be better in general. In this paper, we study the impact of reassigning moving vehicles on some good dispatching rules, both single- and multi-attribute, in the literature. Results suggest that reassigning moving-to-park vehicles has a significant positive effect on reducing the average load waiting time. We evaluate the dispatching rules’ performance using the experimental design of a real-life case study. The performance criteria are: minimizing the average load waiting time, keeping the maximum load waiting time as short as possible and utilizing better vehicles. The results show that the combined dispatching rules which integrates multi-attribute dispatching and vehicle reassignment yields the best performance overall.

American, Asian and third‐party international warehouse operations in Europe

Purpose – This paper aims to report a survey carried out among European distribution centres (EDCs) in The Netherlands. EDCs are forerunners in implementing advanced logistics systems, since they are responsible for the distribution of a manufacturers products to customers in a larger part of Europe, Middle East and Africa, often with strict service level agreements.Design/methodology/approach – Warehouses with different outsourcing relations (own‐account, dedicated outsourced and public outsourced) are compared on operational aspects, performance, and future developments. Moreover, within the group of own‐account warehouses, especially Asian and American operations are tested for differences.Findings – Outsourced warehouse operations appear to have a higher percentage of error‐free deliveries and to be more flexible than own‐account operations. Based on the literature it was expected that a difference in productivity and quality between American and Asian EDCs would be found. Some differences in operati...

E-business models for reverse logistics: contributions and challenges

Reverse logistics, i.e. all operations related to the extension of a useful lifecycle for used products, commercial returns, excess inventory and packaging materials, is gaining increasing attention globally for its promising financial potential, its sustainable growth alternatives and the environmentally positive impact that it could have. In this paper, we include a brief discussion of the major reverse logistics issues and we present the new e-business models in this field. We identify key factors for their competitive advantages, and we discuss conceptual and current opportunities for these e-business models to thrive and advance. Finally, we outline some possible future developments of e-commerce tools for reverse logistics.

Organizing warehouse management

Purpose – The purpose of this paper is to investigate how warehouse management, understood as a cluster of planning and control decisions and procedures, is organized and driven by task complexity (TC) and market dynamics (MD).Design/methodology/approach – A multi‐variable conceptual model is developed based on the literature and tested among 215 warehouses using a survey.Findings – The results suggest that TC and MD are the main drivers of warehouse management, measured by planning extensiveness (PE), decision rules complexity, and control sophistication. Differences between production and distribution warehouses are found with respect to the relationship between assortment changes and PE. Furthermore, TC appears to be a main driver of the specificity of the warehouse management (information) system (WMS).Research limitations/implications – This paper is based on 215 warehouses in The Netherlands and Flanders (Belgium); future research may test the model on a different sample. More research should be con...

Estimating performance in a Robotic Mobile Fulfillment System

This paper models Robotic Mobile Fulfillment Systems and analyzes their performance. A Robotic Mobile Fulfillment System is an automated, parts-to-picker storage system where robots bring pods with products to a workstation. It is especially suited for e-commerce distribution centers with large assortments of small products, and with strong demand fluctuations. Its most important feature is the ability to automatically sort inventory and to adapt the warehouse layout in a short period of time. Queueing network models are developed for both single-line and multi-line orders, to analytically estimate maximum order throughput, average order cycle time, and robot utilization. These models can be used to quickly evaluate different warehouse layouts, or robot zoning strategies. Two main contributions are that the models include accurate driving behavior of robots and multi-line orders. The results show that: (1) the analytical models accurately estimate robot utilization, workstation utilization, and order cycle time, (2) maximum order throughput is quite insensitive to the length-to-width ratio of the storage area and (3) maximum order throughput is affected by the location of the workstations around the storage area.