Warehouse design and control: framework and literature review
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paper_title: Design and operation of an order-consolidation warehouse: Models and application

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Abstract A warehouse is a service facility, often comprising the only view that customers actually have of a manufacturing firm. The management of this facility has significant leverage over order leadtimes and fill-rate reliability. As with other service facilities, system design and operation are decision problems that are closely interlinked. In this paper we describe and model in general terms the composite design and operating problems for a typical order-consolidation warehouse. These problems include warehouse layout, equipment and technology selection, item location, zoning, picker routing, pick list generation and order batching. The complexity of the overall problem mandates developing a new multi-stage hierarchical decision approach. Our hierarchical approach utilizes a sequence of coordinated mathematical models to evaluate the major economic tradeoffs and to prune the decision space to a few superior alternatives. Detailed simulation employing actual warehousing data is then used for validation and fine tuning of the resulting design and operating policies. We describe the application of this analytical approach to an automotive spare-parts distribution centre. The case study demonstrates substantial savings in operating costs and highlights several generic management tradeoffs.
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paper_title: Operational research and material handling

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Abstract A number of material handling research areas are reviewed and opportunities for further research are identified. Included in the review is a consideration of the following areas: robotics, conveyor theory, transfer lines, flexible manufacturing systems, equipment selection, storage alternatives, automated storage and retrieval systems, warehouse layout, palletizing, and order picking and accumulation.
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paper_title: Determining the size of a warehouse container

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The use of containers as basic handling units in warehousing systems is continuously expanding. A systematic procedure is proposed for finding the best container size for such systems. An approximating approach is developed which is valid under specific conditions. When these conditions do not hold, a simulation model is applied, yielding a minimum-cost container size that satisfies prescribed requirements.
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paper_title: Ranking Alternative Warehouse Area Assignments: A Multiattribute Approach

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Abstract The paper considers a choice problem among alternative space allocations. The choice is often made intuitively because of the difficulty in simultaneously considering multiple criteria (i.e., space categories), some of which are of conflicting nature. The paper employs the methodology of multi-attribute value functions to score and rank seven suggested area assignments. Through explicit consideration of trade-offs among the four space categories, the methodology yields a rank ordering which is consistent with the decision maker's preferences. In addition to ranking the alternatives, the formal analysis provided important insight into the trade-off and value structure over the space attributes to facilitate a new area assignment which was superior to the ones originally proposed.
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paper_title: A heuristic approach to warehouse layout with class-based storage

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This paper presents a procedure for warehouse layout. It employs the principles of class-based storage to increase floor space utilization and decrease material handling. Three phases of the procedure are outlined: (1) determination of aisle layout and storage zone dimensions, (2) assignment of material to a storage medium, and (3) allocation of floor space. An industrial case study illustrates the procedure for a warehouse required to store 739 different products totaling more than 10 000 pallets of material. An improved layout was developed and compared with the existing alternative. The proposed layout offered savings of more than 20 000 square feet of floor space and an approximately 45% reduction in material handling distance.
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paper_title: An empirical Evaluation of a General Purpose Automated Order Accumulation and Sortation System used in Batch Picking

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Batch picking of orders can yield higher productivity in high volume situations, but necessarily requires subsequent accumulation and sortation. What is the relative performance of the various approaches ?
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paper_title: A generalized design and performance analysis model for end-of-aisle order-picking systems

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In this paper we present an analytical design algorithm to determine the near-minimum number of pickers required in an end-of-aisle order-picking operation based on a miniload automated storage/retrieval system. The algorithm is based on an approximate analytical model we developed to estimate the expected picker utilization (and the storage/retrieval machine utilization) for general system configurations with two or more pick positions per aisle and/or two or more aisles per picker. For systems with two pick positions, we also investigate the possibility of improving the picker utilization by sequencing container retrievals within each order.
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paper_title: A study on multi-aisle system served by a single storage/retrieval machine

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Abstract Multi-aisle S/R machine system (MASS) can substantially reduce high initial investment cost which is a major reason for the low popularity of AS/RS in manufacturing companies. The objective of this study is mainly related to the design aspects of MASS. With a travel time model developed, average travel time of S/R machine is determined. We propose rack-class-based storage assignment procedure and class selection procedure to find the minimum number of S/R machines required and identify the number of aisles each S/R machine serves. Example problems are solved to illustrate the procedures. The results show that MASS is effective in reducing initial installation cost, provided that the pallet demands are relatively low.
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paper_title: Internal Layout Design of a Warehouse

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Abstract Two configurations of shelves, in a homogeneous or a zoned warehouse, are compared. Handling costs as well as costs associated with the warehouse area and perimeter are taken into consideration. From these, expressions for optimal design parameters are developed. It is shown that, depending on ratios between the relevant costs, some general preference rules for the two layouts examined can be laid down.
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paper_title: Simulation-based design evaluation of unit load automated storage/retrieval systems

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Abstract The focus of this paper is unit load automated storage/retrieval (AS/R) systems. Two of the more important factors affecting the design of AS/R systems are system configuration and policies used for storing and retrieving items to and from the warehouse. Simulation results are obtained for six different single-dock layouts using three different scheduling policies. The results are compared using system throughput as the primary criterion; other performance measures investigated are storage and retrieval waiting times, and rejects due to the rack or input/output queues being fully utilized.
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paper_title: Travel-Time Models for Automated Storage/Retrieval Systems

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Abstract Travel-time models are developed for automated storage/retrieval (AS/R) machines. The S/R machine travels simultaneously horizontally and vertically as it moves along a storage aisle. For randomized storage conditions expected travel times are determined for both single and dual command cycles. Alternative input/output (I/O) locations are considered. Additionally, various dwell-point strategies for the storage/retrieval machine are examined.
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paper_title: Analytical Results for Miniload Throughput and the Distribution of Dual Command Travel Time

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Abstract We determine the throughput, the maximum rate at which a miniload automated storage and retrieval system can process requests, as a'function of the dimension of the storage racks, the speed of the s/r machine and the speed of die picker. As a byproduct, we determine the distribution function of me travel time for a storage/retrieval machine that stores one container and retrieves another container (“dual command cycle”) before returning to the I/O point. Our emphasis is on obtaining closed-form, computable expressions. Handled by the Department of Scheduling/PlanningyControl.
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paper_title: Algorithms for optimal material handling in automatic warehousing systems

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Abstract This paper presents four heuristic algorithms for handling orders in automatic warehousing systems. It is assumed that the orders will be handled by the use of an automatic storage and retrieval machine (S/R machine). The algorithms select, the orders that will be hand led in one tour in order to minimize the total distance travelled by the S7sol;R machine within the warehouse system. Computer programs are developed for the four algorithms and the optimal tours are found by using the travelling salesman algorithm. Optimal or near optimal solutions for the handling problem are found.
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paper_title: Order batching procedures

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Abstract Computer simulation is used to compare two new procedures for batching orders in an order retrieval system against a baseline procedure. The factors considered are the travel metric, warehouse representation, item location assignments, number of items per order, and the total number of orders considered. The results indicate that the two new procedures, in combination with skewed (ABC) item location assignments can reduce batch tour lengths by up to 44%.
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paper_title: A comparative study of order batching algorithms

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In a man-on-board storage and retrieval system, orders are combined into batches and each batch is processed in a tour of the storage/retrieval (S/R) machine. Batching policy determines the way to combine orders to form batches. Since batching is an NP-hard problem, heuristic algorithms have been proposed. The major steps of these algorithms include seed selection and addition of orders to a batch. This paper is a comparative study of order batching algorithms composed of four seed selection rules and four order addition rules for order batching problems. Together, they constitute 16 algorithms. In addition, another method, namely the SL (small and large) algorithm, is also considered. The performances of these algorithms are compared along the three dimensions of shape factor, capacity of the S/R machine, and storage assignment policy. The results indicate that the economic convex hull algorithm has the best performance.
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paper_title: Clustering algorithms for order picking in an automated storage and retrieval system

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Abstract This paper deals with an order picking problem in an automated storage and retrieval system (AS/RS). We present heuristic algorithms for batching a set of orders such that the total distance travelled by the order picking machine is minimized. These algorithms are based on cluster analysis and their efficiency and validity are illustrated through computer simulation. The results show that the algorithms developed perform substantially better than those from previous studies.
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paper_title: Shared storage policies based on the duration stay of unit loads

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This paper addresses duration-of-stay-based shared storage policies for a unit load warehouse. We show that, for single command storage and retrieval, shared storage policies based on duration of stay of individual unit loads have the potential to significantly decrease travel time. An optimal storage policy with respect to travel time and storage space is developed for systems with balanced input and output. Based on the same principles, two heuristic policies are developed for more complex systems. Simulation results are provided which compare travel times for dedicated storage, random storage, turnover-based storage classes, and duration-of-stay-based storage classes.
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paper_title: Optimal Lane Depths for Single and Multiple Products in Block Stacking Storage Systems

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Abstract Block Stacking is one of the most common storage methods for warehousing large quantities of palletized or boxed products, when high space utilization is the main concern. Efficient algorithms are currently only available to compute the optimal lane depth for a single product, assuming that all lanes have equal depth. In most warehouses, the lane depth on each side of a single aisle is kept constant for layout arid material flow purposes. A layout procedure for selecting lane depths out of a limited number of allowable depths and for determining the number of lanes and aisles for each depth for the case of multiple products is developed. If the warehouse is perfectly balanced, then this procedure minimizes the required warehouse area. One component of the layout procedure is an algorithm to compute the optimal number of lanes and the optimal lane depths for a single product, when the lanes are allowed to have a limited number of different depths. The quality of this and other heuristics for the s...
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paper_title: A storage assignment policy in a man-on-board automated storage/retrieval system

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This paper deals with a man-on-board automated storage/retrieval system where each customer order consists of a number of different items and is picked one at a time. For the system the problem examined is to allocate storage locations dedicatedly to items so that the total travel time required to pick all the given orders per period is minimized. The problem is shown to be formulated as a variant of the generalized assignment model. A heuristic for the storage layout problem is developed based on the group technology concept considering both order structure and frequency. Through the heuristic, close relationships between items are identified from the order structure, and then based on the relationships the items are compelled to be stored closely in the storage rack following a space-filling curve. Experimental results are provided to describe the performance of the heuristic
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paper_title: Storage layout of AS/RS racks based on recurrent orders

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Abstract In many person-on-board AS/R systems, some very typical, recurrent orders have to be retrieved. In this paper, we present a straightforward methodology to design the storage layout of a rack when such recurrent orders represent a high percentage of total turnover. The approach makes use of sorting, assignment, and travelling salesman like algorithms. The resulting layouts are compared against more classical arrangements. Numerical simulations show that, in specific situations, more than 30% saving in travel time of the retrieval crane can be expected.
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paper_title: Expected travel time and optimal boundary formulas for a two-class-based automated storage/retrieval system

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Our paper studies a two-class-based rectangular-in-time automated storage/ retrieval system (AS/RS). We present explicit formulas for the optima! boundary of the two storage areas as well as for the expected single command cycle time for an optimally designed rack. In the basic model each crane handles a single aisle. These formulas provide the designer with a full picture of the quantitative effects of the various factors (i.e., access frequencies of the two storage areas, and dimensions of the rack) on the optimal boundary of the two storage areas and the achievable cycle lime in the warehouse. We also develop expected travel time formulas for the dual command AS/RS with two-class-based storage policies and obtain the optimal boundary with a one-dimensional search procedure. Similar developments (i.e., expected travel time formulas and optimal boundary search procedures) are discussed for AS/RS with a single command policy but with each crane handling multiple aisles.
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paper_title: Dynamic Operational Policies in an Automated Warehouse

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Abstract In this paper we consider the optimal relocation of pallets with a high expectancy of retrieval within each storage rack of an automated warehouse to meet the fluctuating, short-term throughput requirements imposed on the automated storage-retrieval machines. The prepositioning of these pallets closer to the input/output point of each rack during off-peak periods will reduce the expected travel time for the storage/retrieval machines during future peak periods of the planning horizon. As the model has been abstracted from an actual operating environment, we first describe the environment in which the problem has been posed. We then exploit the special structure of the problem to develop conditions that an optimal relocation policy should satisfy. Based on these optimality conditions, we develop a very efficient optimal relocation algorithm. Finally, we present the performance of several relocation policies in the warehouse studied. Handled by the Department of Manufacturing and Automated Production.
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paper_title: Optimal product layout in an order picking warehouse

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Abstract The purpose of this paper is to provide a basis for locating product in an order picking warehouse such that average order picking time will be minimized. A stochastic model is developed to ensure that optimal, rather than just “good,” results are obtained. It is shown that, for a class of order picking warehouse, simple, but general, assignment algorithms may be used to optimally allocate product to locations. The results are then used to explore the effects of average order size and the shape of the inventory curve on order picking efficiency.
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paper_title: Scheduling of storage/retrieval orders under a just-in-time environment

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We consider the problem of scheduling storage and retrieval orders under dual-command operations in a unit-load automated storage/retrieval system. The objective is to minimize the weighted sum of earliness and tardiness penalties about a common due date. We propose four heuristics based upon a two-step approach where dual-command cycles are formed first and then optimally scheduled. A mixed-integer programming model is also formulated to obtain an optimal solution. Performances of the heuristics are compared in the simulation tests. Computational results show that some heuristics perform favourably.
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paper_title: DISTANCE APPROXIMATIONS FOR ROUTING MANUAL PICKERS IN A WAREHOUSE

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This paper evaluates and compares strategies for routing a manual picker through a simple warehouse. It expands on previous work, in which optimization algorithms were developed, by deriving equations which relate route length to warehouse attributes. Several rules of thumb are derived for selection of order picking strategies and optimization of warehouse shape.
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paper_title: On Sequencing Retrievals In An Automated Storage/Retrieval System

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Abstract This paper addresses throughput improvement by retrieval sequencing in conventional unit load automated storage/retrieval systems when several retrieval requests are available and dual command cycles are performed. Taking first-come-first-served as the reference sequencing rule, the potential for improvement is identified. A “nearest-neighbor” sequencing rule is proposed as an alternative, an analytic model for its expected performance is developed, and Monte Carlo simulation is used for evaluation. In addition, a lower bound on dual command cycle times is developed, and the dynamic behavior of two heuristic sequencing rules is discussed.
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paper_title: Routing orderpickers in a warehouse: a comparison between optimal and heuristic solutions

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textabstractThe 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, the well-known polynomial algorithm of Ratliff and Rosenthal (1983) that considered warehouses with a central depot is extended. 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.
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paper_title: Intelligent control schemes for automated storage and retrieval systems

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A new information system approach to the operational controls of automated storage and retrieval systems (AS/RS) is developed and examined. This approach is based on artificial intelligence, state-operator framework for problem solving. Gradually increasing the information level, several operational goal functions are identified for an industrial unit-load food produce AS/RS. These functions use real-time statistical interpolations to select the desired storage and retrieval bins. As a result the AS/RS response adapts itself to stochastic perturbations in the system conditions. Experimental evaluations using multiple variance analysis technique and detailed simulations have shown that the proposed dynamic approach is superior to the common industrial control method currently used in those industrial systems characterized by batch arrivals (and retrievals) of the UL's and non-stationary demand patterns, These evaluations further suggest that improved performance is realized with the increase in the informa...
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paper_title: Geometric Approaches to Solve the Chebyshev Traveling Salesman Problem

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Abstract: Several heuristic procedures based on geometric concepts have been developed for the Chebyshev (or too) Traveling Salesman Problem (CTSP),which has numerous applications in materials handling and information storage-retrieval. The following study is concerned with evaluating the performance of geometric approaches as a function of the shape of the service region and the number of points to be sequenced. A new approach, the band insertion heuristic, is also introduced and compared with existing procedures. Trade-offs in tour quality and solution effort are the primary focus of the study, which is empirical in nature; however, the results generally apply to a wide range of configurations.
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paper_title: Deriving an optimal dwell point of the storage/retrieval machine in an automated storage/retrieval system

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Abstract The selection of the dwell point of the storage/retrieval (S/R) machine when it becomes idle in an automated storage/retrieval system (AS/RS) is discussed. Two existing models for dynamic control of the S/R machine are adopted for the analysis. They are transformed to the single-facility location problem with Tchebyshev distance, and the Tchebyshev minimax facility location problem, respectively. Algorithms are presented utilizing well known research results in location theory. Through computational tests, the algorithms are shown to be quite suitable for real-world applications.
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paper_title: Storage-Retrieval Interleaving in Automatic Warehousing Systems

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This paper extends work previously reported on storage assignment rules for automatic warehousing systems to include interleaving; that is, the sequencing of storage and retrieve requests. Using both continuous analytical models and discrete evaluation procedures, this paper compares the operating performance of several storage assignment/interleaving policies. The results indicate that significant reductions in crane travel time and distance are obtainable in some real-world and/or previously modeled situations via the proposed storage assignment/interleaving policies. These reductions may be directly translated into increased throughput capacity for existing systems. The storage assignment/interleaving policies may also be used to improve the design of proposed systems to achieve a more desirable balance between throughput and storage capacity. Although the system examined is a high-rise automatic warehouse, the results presented have implications for the warehousing function in general.
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Title: Warehouse Design and Control: Framework and Literature Review

Section 1: Introduction
Description 1: Provide an overview of the importance of warehouse design and control in logistic operations, emphasizing the need for a systematic design approach.

Section 2: Warehouse Characterizations
Description 2: Discuss the characterization of warehouses from three angles: processes, resources, and organization.

Section 3: Warehouse Processes
Description 3: Detail the various processes involved in warehouse operations, including receiving, storage, order picking, sorting, and shipping.

Section 4: Warehouse Resources
Description 4: List and describe the different resources necessary for warehouse operations, such as storage units, storage systems, retrieval equipment, and personnel.

Section 5: Warehouse Organization
Description 5: Explain the organizational policies and decisions related to warehouse operations, including process flow design, assignment policies, storage policies, and various control policies.

Section 6: Warehouse Design
Description 6: Present a hierarchical framework for making warehouse design decisions and discuss relevant performance criteria.

Section 7: Warehouse Design Methods
Description 7: Outline the various phases of the warehouse design process and discuss the integration of analytical and simulation approaches.

Section 8: Warehouse Performance Criteria
Description 8: Identify and elaborate on the performance criteria used to evaluate warehouse designs, such as costs, throughput, storage capacity, and response time.

Section 9: Warehouse Design Problems
Description 9: Discuss the key design problems encountered at strategic, tactical, and operational levels, including their interrelations and specific challenges.

Section 10: A Review of Warehousing Models
Description 10: Provide an overview of existing models and algorithms for warehouse design, planning, and control, classified by strategic, tactical, and operational levels.

Section 11: Warehouse Literature Overviews
Description 11: Summarize previous literature reviews on warehouse design and identify gaps and needs in current research.

Section 12: Warehouse Design Problems: Strategic Level
Description 12: Review literature dealing with strategic-level design problems, focusing on system selection and process flow design.

Section 13: Warehouse Design Problems: Tactical Level
Description 13: Review literature addressing tactical-level design problems, including resource dimensioning and organizational issues.

Section 14: Warehouse Design Problems: Operational Level
Description 14: Review literature discussing operational-level design problems, focusing on task assignment, scheduling, and control of personnel and equipment.

Section 15: Design Oriented Research
Description 15: Emphasize the need for design-oriented research in warehouse systems and offer guidelines for future research.

Section 16: Conclusions
Description 16: Summarize the findings of the paper, highlight the need for an integrated design approach, and suggest areas for future research.