On the Determinations of Class-Based Storage Assignments in AS/RS having two I/O Locations

This paper presents the use and extension of a geometrical-based algorithmic approach for determining the expected S/R machine cycle times, and therefore warehouse throughput, for class-based storage assignment layouts in an AS/RS.The approach was designed for the purpose of solving a practical storage assignment design problem for a major European manufacturer.The algorithm may be used to layout racks that are either "square-in-time (SIT)" or "non-square in time (NSIT)" with single or multiple I/O points.It is believed that use of this approach can result in the expedient evaluation of warehouse throughput resulting from new layouts, or re-layouts, of AS/R system racks, thus making these systems more appealing for use in integrated supply chain systems in general.production management;manufacturing;supply chain mangement;warehousing;storage

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

Sequencing approaches for multiple-aisle automated storage and retrieval systems

Automated storage and retrieval systems (AS/RS) are used in high velocity distribution centres to provide accurate and fast order processing. While almost every industrial system is comprised of many aisles, most of the academic research on the operational aspects of AS/RS is devoted to single-aisle systems, probably due to the broadly accepted hypothesis proposing that an m aisles system can be modelled as m 1-aisle independent systems. In this article, we present two multi-aisles sequencing approaches and evaluate their performance when all the aisles are managed independently first, and then in a global manner. Computational experiments conducted on a multi-aisle AS/RS simulation model clearly demonstrate that a multi-aisle system cannot be accurately represented by multiple single-aisle systems. The numerical results demonstrate that, when dealing with random storage, globally sequencing multi-aisle AS/RS leads to makespan reductions ranging from 14 to 29% for 2- and 3-aisle systems, respectivelyKeywords: automated storage and retrieval systems; multi-aisle; sequencing; simulatio

A survey on performance analysis of warehouse carousel systems

This paper gives an overview of recent research on the performance evaluation and design of carousel systems. We discuss picking strategies for problems involving one carousel, consider the throughput of the system for problems involving two carousels, give an overview of related problems in this area, and present an extensive literature review. Emphasis has been given on future research directions in this area

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

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

Robotized Warehouse Systems: Developments and Research Opportunities

Robotized handling systems are increasingly applied in distribution centers. They require little space, provide flexibility in managing varying demand requirements, and are able to work 24/7. This makes them particularly fit for e-commerce operations. This paper reviews new categories of robotized handling systems, such as the shuttle-based storage and retrieval systems, shuttle-based compact storage systems, and robotic mobile fulfillment systems. For each system, we categorize the literature in three groups: system analysis, design optimization, and operations planning and control. Our focus is to identify the research issue and OR modeling methodology adopted to analyze the problem. We find that many new robotic systems and applications have hardly been studied in academic literature, despite their increasing use in practice. Due to unique system features (such as autonomous control, networked and dynamic operation), new models and methods are needed to address the design and operational control challenges for such systems, in particular, for the integration of subsystems. Integrated robotized warehouse systems will form the next category of warehouses. All vital warehouse design, planning and control logic such as methods to design layout, storage and order picking system selection, storage slotting, order batching, picker routing, and picker to order assignment will have to be revisited for new robotized warehouses

On sequencing policies for unit-load automated storage and retrieval systems

Automated Storage and Retrieval System (AS/RS) performance high ly depends on the characteristics of the mechanical equipment. However, once the system has been physically implemented, achieving its maxim um efficiency depends on the wa y the system is operated. This paper it shows that request sequencing (i.e., planning the orde r in which storage and retrieval requests are performed) is of p aramount importance in AS/RS per formance. This paper reviews and adapts the most popular storage and sequencing policies to dynamic contexts, and then it proposes a “sequencing mathematical model” (SMM) to simultaneou sly solve the sequencing and storage location problems. Extensive computational results based on a thorough simulation experiment plan confirm that performing the requests in the rig ht sequence can have a positive impact on AS/RS performance. O ur results show that the proposed sequencing mathematical model regularly outperforms other methods. When used in a dynam ic context, the proposed SMM may yield up to a 25% reducti on in average travel-time comp ared to the situation where a no-sequencing method is applied