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Journal ArticleDOI

A survey of literature on automated storage and retrieval systems

TL;DR: A comprehensive explanation of the current state of the art in AS/RS design is provided for a range of issues such as system configuration, travel time estimation, storage assignment, dwell-point location, and request sequencing.
About: This article is published in European Journal of Operational Research.The article was published on 2009-04-16 and is currently open access. It has received 533 citations till now. The article focuses on the topics: Automated storage and retrieval system & RSS.

Summary (4 min read)

1 Introduction

  • Between 1994 and 2004, there has been a significant increase in the number of AS/RSs used in distribution environments in the United States (Automated Storage Retrieval Systems Production Section of the Material Handling Industry of America, 2005).
  • In designing an AS/RS, many physical design and control issues have to be addressed in the right way to fully take advantage of all its pros.
  • The authors conclude that their paper seems to be the first overview paper in over ten years devoted exclusively to AS/RSs, and the first ever to give a broad overview of all design and control issues in AS/RSs.
  • Section 10 presents conclusions and issues for further research.

2 AS/RS types

  • An AS/RS system is defined as a storage system that uses fixed-path storage and retrieval machines running on one or more rails between fixed arrays of storage racks (Automated Storage Retrieval Systems Production Section of the Material Handling Industry of America, 2005).
  • Unit loads arrive at the I/O-point of the AS/RS from other parts of the warehouse by means of, for example, automated guided vehicles, conveyors, or forklift trucks.
  • A picker at this workstation takes the required amount of products from the unit load after which the AS/RS moves the remainder of the load back into the storage rack.
  • Storage in the racks may occur single or double deep.
  • Modifications to the crane may be required to be able to store and retrieve loads from both positions.

3 Overview of design decisions

  • Various options for AS/RS types are displayed in Figure 1, however, little research is available to select the best type of system from the available options.
  • Even when the number of aisles is given, there is still a trade-off between rack height and length.
  • A good design procedure should simultaneously address both physical design and control issues of the system.
  • In a single command cycle the crane performs either a single storage or a single retrieval request.

4 Physical design

  • Only a few papers address the design of AS/RSs in combination with the design of other material handling systems in the facility.
  • Inman (2003) studies the usage of AS/RSs in the automotive industry.
  • These authors examine the effect of different sequencing rules on six layout configurations (with a varying I/O-point, item distribution over racks, rack configuration and rack dimensions).
  • Mathematical programming models, queueing theory and heuristics have been mostly used in developing analytical design models.
  • From the overview in Table 2 the authors conclude that all models address some, but certainly not all physical design aspects.

5 Storage Assignment

  • Several methods exist for assigning products to storage locations in the racks.
  • For the dedicated storage method each product type is assigned to a fixed location.
  • The full-turnover storage policy determines storage locations for loads based on their demand frequency.
  • The COI rule assigns loads with the lowest COI to the locations closest to the I/O-point.
  • Malmborg and Krishnakumar (1989) show that the COIrule is optimal for person-aboard AS/RSs with respect to order-picking costs if there are fixed inventory levels and a fixed balanced assignment of order pickers to items.

5.1 Class-based storage

  • This storage assignment method divides the available warehouse space into a number of areas.
  • Graves et al. (1977) demonstrate through simulation that this L-shaped configuration is close to optimal for dual command scheduling in square-in-time racks.
  • Figure 3 presents examples of zone shapes for both types of racks for three classes.
  • XXX INSERT FIGURE 3 XXX Some variations of the class-based storage policy have been studied.

5.2 Performance of storage assignment rules

  • Travel time estimates (see Section 9) for both single and dual command scheduling in different types of AS/RS configurations are an appropriate analytical tool for comparing control rules (e.g., Hausman et al., 1976; Graves et al., 1977).
  • With simulation more extensive experiments under stochastic conditions can be performed (e.g., Schwarz et al., 1978; Kaylan and Medeiros, 1988; Kulturel et al., 1999; Van den Berg and Gademann, 2000).
  • Kulturel et al. (1999) compare a three class-based policy with a duration of stay policy, which was originally introduced by Goetschalckx and Ratliff (1990).
  • Sadiq et al. (1996) propose a dynamic storage assignment policy to reassign items to storage locations in systems with a rapidly changing product mix and short product life cycles.
  • It is shown that this dynamic policy outperforms the static COI rule.

6 Batching

  • Batching problems for person-on-board AS/RSs are quite similar to batching problems for order pickers in warehouses.
  • XXX INSERT FIGURE 4 XXX XXX INSERT TABLE 4 XXX Contrary to a single seeding rule a cumulative seeding rule (e.g., Elsayed and Stern, 1983) uses all orders that are already in the batch as the seed.
  • In the experiments the shape and the capacity of the cranes as well as the storage assignment policies have been varied.
  • Both Elsayed et al. (1993) and Elsayed and Lee (1996) discuss the batching problem with due dates in combination with the scheduling problem of orders.

7 Dwell point location

  • Several methods have been proposed to deal with the decision where to position an idle crane, i.e., how to determine the crane’s dwell-point.
  • XXX INSERT TABLE 5 XXX Egbelu (1991) proposes linear programming models that are capable of responding to fluctuations in types of requests.
  • Chang and Egbelu (1997) consider a single crane serving multiple aisles.
  • Park (1999) developed an optimal dwell point policy for square-in-time racks under dedicated storage.
  • Most approaches address static positioning of single unit-load capacity AS/RSs and do not study other types of AS/RSs.

8 Sequencing of storage and retrieval requests

  • Storage requests in distribution or production environments are usually not time-critical.
  • The list of retrievals is continuously changing over time.
  • Firstly, select a block of the most urgent storage and retrieval requests, sequence them and when they are completed select the next block, and so on.
  • The performance of both approaches differs per situation.
  • Therefore, the authors first discuss sequencing methods for this basic sequencing problem.

8.1 The basic sequencing problem

  • For the sequencing problem of unit load AS/RSs, the two common types of cycles to be addressed are single command and dual command cycles (see also Section 3).
  • If arriving and leaving trucks overlap in time, dual command cycles can be performed.
  • For the dynamic sequencing problem various methods, as summarised in Table 7 have been formulated.
  • Several studies, including simulation studies, have been performed to compare the 14 performance of these heuristics in combination with several storage assignment policies (see, e.g., Linn and Wysk, 1987).
  • These methods can be applied in situations with high uncertainty and little information.

8.2 Extensions of the basic sequencing problem

  • An extension of the previously described basic scheduling problem is the problem in which storage and retrieval requests with release and due times need to be scheduled.
  • Other configurations of an AS/RS such as multiple I/O-points per aisle might require new solution approaches.
  • Randhawa et al. (1991) use simulation to evaluate various scheduling rules for systems with one input/output station at each aisle and systems with two input/output stations at each aisle.
  • Kanet and Ramirez (1986) add location selection to the scheduling problem in case products are stored at multiple locations.
  • Jaikumar and Solomon (1990) study the prepositioning of pallets in periods the AS/RS would otherwise be idle.

8.3 Sequencing for other types of AS/RSs

  • Some research has been done to the scheduling of storage and retrieval requests for other types of AS/RSs.
  • Due to the double capacity of the crane, more routing options emerge since cycles can be performed in which at most four locations are visited before returning to the I/O-point.
  • Simple nearest-neighbour heuristics (Sarker et al., 1991 and 1994) and a minimum perimeter heuristic (Keserla and Peters, 1994) have been developed.
  • Retrieval requests are rearranged such that successive requests are located close to each other.
  • Abdel-Malek and Tang (1994) and Hwang et al. (1999) study the sequencing problem for automated single and double shuttle carrousel storage and retrieval systems.

9 Performance measurement

  • In evaluating the design and control rules of an AS/RS several performance measures can be used.
  • Numerous research has been done in this area.
  • First the authors discuss travel time models for single unit-load aisle-captive AS/RSs.

9.1 Travel time models for single-shuttle unit-load AS/RSs

  • Hausman et al. (1976) were one of the first to present travel time models for single-shuttle unitload AS/RSs.
  • The authors proposed estimates for single command scheduling in square-in-time continuous racks.
  • Other authors since then mainly continue the research of Hausman et al. (1976), Graves et al. (1977) and Bozer and White (1984) by studying different control policies, configurations of AS/RSs and/or operational characteristics.
  • Hwang and Lee (1990) incorporate both the maximum velocity of a crane and the time required to reach the peak velocity or to come to a halt.
  • Wen et al. (2001) extend the work of Chang et al. (1995) by considering class-based and full-turnover-based storage assignment policies.

9.2 Travel time models for other types of AS/RSs

  • New travel time estimates are required for multi-shuttle AS/RSs to deal with quadruple and even sextuple (e.g., Meller and Mungwattana, 1997) command scheduling.
  • Foley and Frazelle (1991) consider a miniload square-in-time AS/RS operating under a FCFS dual command scheduling policy and random storage.
  • Authors (e.g., Elsayed and Unal, 1998; Guenov and Raeside, 1992; Chiang et al., 1994) typically derive expressions for upper and lower bounds for travel times based on the number of locations to be visited given a storage assignment and sequencing policy.
  • Summarising, it can be concluded that travel time models for both square-in-time and rectangular racks have been developed for unit-load AS/RSs operating under most common storage assignment policies and two sequencing heuristics derived from practice.
  • So far no studies have been performed that include dwell-point rules in travel time estimates.

10 Conclusions and further research issues

  • In both manufacturing and distribution environments, AS/RSs are used to store products and to retrieve products from storage in response to production orders or customers’ orders.
  • Journal of Manufacturing Science and Engineering, 1997; 119; 841—848. Mansuri M. Cycle—time computation, and dedicatated storage assignment, for AS/R systems.
  • Analytical models and optimal stategies for automated storage/retrieval system operations.

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References
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TL;DR: In this paper, a literature overview on typical decision problems in design and control of manual order-picking processes is given, focusing on optimal (internal) layout design, storage assignment methods, routing methods, order batching and zoning.

1,603 citations

Journal ArticleDOI
TL;DR: The purpose is to provide a bridge between academic researchers and warehouse practitioners, explaining what planning models and methods are currently available for warehouse operations, and what are the future research opportunities.

847 citations


"A survey of literature on automated..." refers background in this paper

  • ...General overviews of warehouse design and control include Cormier and Gunn (1992), Van den Berg (1999),Rouwenhorst et al. (2000), De Koster et al. (2007) and Gu et al. (2007)....

    [...]

Journal ArticleDOI
TL;DR: It is shown that significant reductions in crane travel time and distance are obtainable from turnover-based rules, and these improvements can be directly translated into increased throughput capacity for existing systems, and may be used to alter the design of proposed systems.
Abstract: In the past few years, increasing numbers of automatic warehousing systems using computer-controlled stacker cranes have been installed. Our research concerns the scientific scheduling and design of these systems. There are three elements to scheduling: the assignment of multiple items to the same pallet Pallet Assignment; the assignment of pallet loads to storage locations Storage Assignment; and rules for sequencing storage and retrieve requests Interleaving. This paper deals with optimal storage assignment. Results are obtained which compare the operating performance of three storage assignment rules: random assignment, which is similar to the closest-open-location rule used by many currently operating systems; full turnover-based assignment: and class-based turnover assignment. It is shown that significant reductions in crane travel time and distance are obtainable from turnover-based rules. These improvements can, under certain circumstances, be directly translated into increased throughput capacity for existing systems, and may be used to alter the design e.g., size and number of racks, speed of cranes, etc. of proposed systems in order to achieve a more desirable system balance between throughput and storage capacity.

606 citations


"A survey of literature on automated..." refers background or methods in this paper

  • ...Hausman et al. (1976) prove that a L-shaped configuration with square-in-time boundaries for classes A, B and C is optimal when single command scheduling is applied in square-intime racks....

    [...]

  • ...Travel time estimates (see Section 9) for both single and dual command scheduling in different types of AS/RS configurations are an appropriate analytical tool for comparing control rules (e.g., Hausman et al., 1976; Graves et al., 1977)....

    [...]

  • ...Hausman et al. (1976) were one of the first to present travel time models for single-shuttle unit-load AS/RSs....

    [...]

  • ...Thonemann and Brandeau (1998) alter the algorithms of Hausman et al. (1976) such that they can be A B C A B C Fig....

    [...]

  • ...Other authors since then mainly continue the research of Hausman et al. (1976), Graves et al. (1977) and Bozer and White (1984) by studying different control policies, configurations of AS/RSs and/or operational characteristics....

    [...]

01 Jan 1998
TL;DR: A reference framework and a classification of warehouse design and control problems and the need for design oriented studies is emphasized, as opposed to the strong analysis oriented research on isolated subproblems that seems to be dominant in the current literature.
Abstract: In this paper we present a reference framework and a classification of warehouse design and control problems Based on this framework, we review the existing literature on warehousing systems and indicate important gaps In particular, we emphasize the need for design oriented studies, as opposed to the strong analysis oriented research on isolated subproblems that seems to be dominant in the current literature

574 citations

Journal ArticleDOI
TL;DR: In this article, the authors present a reference framework and a classification of warehouse design and control problems based on this framework, and emphasize the need for design oriented studies, as opposed to strong analysis oriented research on isolated subproblems that seems to be dominant in the current literature.

521 citations

Frequently Asked Questions (9)
Q1. What contributions have the authors mentioned in the paper "A survey of literature on automated storage and retrieval systems" ?

This paper provides an overview of literature from the past 30 years. A comprehensive explanation of the current state of the art in AS/RS design is provided for a range of issues such as system configuration, travel time estimation, storage assignment, dwell point location, and request sequencing. 

Except for those general issues, further detailed research can also be advised for each of the following issues. A further digression on the over—automated warehouse: some evidence. 

As common in cluster analysis, both attribute vectors related to storage locations of an order and similarity measures, based on, for example, the boundaries of the area in which the crane needs to travel to reach all locations of an order, are used in formulating heuristics. 

In order to deal with one or more design issues for AS/RSs, methods ranging from simulation, analytical models, artificial intelligent approaches (e.g., Knapp and Wang, 1992; Chincholkar et al., 1994; Hsieh et al., 1998) to experimental approaches (e.g., Lim et al., 1996) have been proposed in the literature. 

For the sequencing problem of unit load AS/RSs, the two common types of cycles to be addressed are single command and dual command cycles (see also Section 3). 

Important drawbacks of this dynamic approach are the facts that LP solution techniques need to be implemented in the AS/RS control system and that computation times may be too high to be of practical value. 

XXX INSERT TABLE 7 XXXOther approaches to find solutions to the sequencing problem include neural networks (e.g., Wan and Yih, 1997), expert systems (e.g., Linn and Wysk, 1990a and 1990b), artificial intelligence (e.g., Seidmann, 1988), genetic algorithms (e.g., Krishnaiah Chetty et al., 2003) and the Taguchi method (e.g., Lim et al., 1996). 

To their knowledge, Sarker and Babu (1995) is the only paper discussing exclusively AS/RSs, however, this paper only reviews some design aspects of AS/RSs while focussing on travel time models. 

it can be concluded that travel time models for both square-in-time and rectangular racks have been developed for unit-load AS/RSs operating under most common storage assignment policies and two sequencing heuristics derived from practice.