Performance approximation of pick-to-belt orderpicking systems

In this paper, an approximation method is discussed for the analysis of pick-to-belt orderpicking systems. The aim of the approximation method is to provide an instrument for obtaining rapid insight in the performance of designs of pick-to-belt orderpicking systems. It can be used to evaluate the effects of changing the layout of the system, the number of picking stations, the number of pickers, the conveyor speed, the number of bins to be processed per day, the number of orderlines per bin, etc. Especially in the design phase, modeling and analysis speed is more important than accuracy. The method presented in this paper is based on Jackson network modeling and analysis. The method is fast and sufficiently accurate. The method is used by Ingenieursbureau Groenewout B.V., for early-stage evaluation of design alternatives of pick-to-belt orderpicking systems and general transportation systems

Open Location Management in Automated Warehousing Systems

A warehouse needs to have sufficient open locations to be able to deal with the change of item inventory levels, but due to ongoing storage and retrieval processes, open locations usually spread over storage areas. Unfavorable positions of open locations negatively impact the average load retrieval times. This paper presents a new method to manage these open locations such that the average system travel time for processing a block of storage and retrieval jobs in an automated warehousing system is minimized. We introduce the effective storage area (ESA), a well-defined part of the locations closest to the depot; where only a part of the open locations –the effective open locations-, together with all the products, are stored. We determine the optimal number of effective open locations and the ESA boundary minimizing the average travel time. Using the ESA policy, the travel time of a pair of storage and retrieval jobs can be reduced by more than 10% on average. Its performance depends hardly on the number or the sequence of retrievals. In fact, in case of only one retrieval, applying the policy leads already to beneficial results. Application is also easy; the ESA size can be changed dynamically during storage and retrieval operations. Keywords: Distribution science, warehousing; AS/RS; storage and retrieval; open locations

On the Reversibility of Manufacturing Networks

In this paper it is shown that in many production networks it is possible to reverse the flow direction in one or more buffers without changing the throughput and buffer content distributions of other buffers in the network. If a network possesses the property that simultaneous reversal of the flow direction in all buffers reverses all the buffer contents, then it is called reversible. If it possesses the property that flow reversal in a single buffer b reverses the buffer content of b and leaves all other buffer contents unchanged, then it is called b-reversible. The reversibility of a production network depends, for the discrete product situation, on the blocking rule used. For networks having a continuous product flow the blocking rule is only important for so-called buffersharing networks. b-reversibility is shown to hold for all buffers b for so-called assembly-disassembly networks. Reversibility is shown to hold for buffersharing networks

Supply-Chain Culture Clashes in Europe. Pitfalls in Japanese Service Operations

Japanese companies value service and quality highly and they put much effort in realising this. However, survey research carried out in 2001 among senior managers of Japanese logistics companies in the Netherlands, indicated that these efforts do not result in significant performance differences compared to western companies. In this exploratory paper, we report of company visits and interviews with managers of Japanese logistics companies in Western Europe. They described a clash of cultures underlying their operations, prohibiting them from achieving performance excellence. The causes focus around two key factors: the unique concept of Japanese service, based on future rewards which are absent in Western Europe; different employment circumstances in Western Europe, which make Japanese human resource management ineffective, and the Japanese career development system which makes that Japanese managers do not always have the right focus in their job abroad. We conclude that Japanese subsidiaries in Western Europe should keep on nourishing their uneq

Class-based Storage With a Finite Number of Items

ABC class-based storage is widely studied in literature and applied practice. It divides all stored items into a limited number of classes according to their demand rates (turnover per unit time). Classes of items with higher turnovers are stored in a region closer to the warehouse depot. In literature, it is commonly shown that the use of more storage classes leads to shorter travel time for storing and retrieving items. A basic assumption in this literature commonly is that the required storage space of items equals their average inventory levels, which is right if an infinite number of items are stored in each storage region. However, if a finite number of items are stored in the warehouse, more storage classes need more space to store the items: more classes lead to fewer items stored per class, which have less opportunity to share space with other items. This paper revisits ABC class-based storage by relaxing the common assumption that the total required storage space of all items is independent of the number of classes. We develop a travel time model and use it for optimizing the number and the boundaries of classes. Our numerical results illustrate that a small number of classes is optimal

Product Return Handling

In this article we focus on product return handling and warehousing issues. In some businesses return rates can be well over 20% and returns can be especially costly when not handled properly. In spite of this, many managers have handled returns extemporarily. The fact that quantitative methods barely exist to support return handling decisions adds to this. In this article we bridge those issues by 1) going over the key decisions related with return handling; 2) identifying quantitative models to support those decisions. Furthermore, we provide insights on directions for future research

Open Location Management in Automated Warehousing Systems

A warehouse needs to have sufficient open locations to be able to store incoming shipments of various sizes. In combination with ongoing load retrievals open locations gradually spread over the storage area. Unfavorable positions of open locations negatively impact the average load retrieval times. This paper presents a new method to manage these open locations such that the average system travel time for processing a block o

On the Suboptimality of Full Turnover-Based Storage

In the past thirty years the full turnover-based storage policy as described by Hausman et al. (1976, Management Science 22(6)) has been widely claimed to outperform the commonly used ABC class-based storage policy, in terms of the resulting average storage and retrieval machine travel time. In practice however, ABC storage is the dominant policy. Hausman et al. (1976) model the turnover-based policy under the unrealistic assumption of shared storage, i.e. the stor

Optimal Storage Rack Design for a 3D Compact AS/RS with Full Turnover-Based Storage

Compact, multi-deep (3D) automated storage and retrieval systems (AS/RS) are becoming increasingly popular for storing products with relatively low turnover on a compact area. An automated storage/retrieval crane takes care of movements in the horizontal and vertical direction in the rack, and a gravity conveying mechanism takes care of the depth movement. An important question is how to layout such systems to minimize the pr

Sequencing Heuristics for Storing and Retrieving Unit Loads in 3D Compact Automated Warehousing Systems

Sequencing unit load retrieval requests has been studied extensively in literature for conventional single-deep automated warehousing systems. A proper sequence can greatly reduce the makespan when carrying out a group of such requests. Although the sequencing problem is NP-hard some very good heuristics exist. Surprisingly the problem has not yet been investigated for compact (multi-deep) storage systems, which have greatly