A survey of literature on automated storage and retrieval systems

Abstract

Automated Storage and Retrieval Systems (AS/RSs) are warehousing systems that are used for the storage and retrieval of products in both distribution and production environments. 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. The majority of the reviewed models and solution methods are applicable to static scheduling and design problems only. Requirements for AS/RSs are, however, increasingly of a more dynamic nature for which new models will need to be developed to overcome large computation times and finite planning horizons, and to improve system performance. Several other avenues for future research in the design and control of AS/RSs are also specified.

Introduction

Automated storage and retrieval systems have been widely used in distribution and production environments since their introduction in the 1950s. An automated storage and retrieval system (AS/RS) usually consists of racks served by cranes running through aisles between the racks. An AS/RS is capable of handling pallets without the interference of an operator, thus the system is fully automated. Both in production and distribution environments AS/RSs are used for putting products (e.g., raw materials or (semi-) finished products) in storage and for retrieving those products from storage to fulfill an order. 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). The usage of AS/RSs has several advantages over non-automated systems. Examples are savings in labour costs and floor space, increased reliability and reduced error rates. Apparent disadvantages are high investments costs (approximately $634,000 for a single aisle AS/RS, Zollinger, 1999), less flexibility and higher investments in control systems (about $103,000, Zollinger, 1999).

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. This paper intends to present a critical overview of all important issues concerning AS/RS design and control in both production and distribution environments while studying recent and past literature. Previously, several overview papers have been published that discuss part of the AS/RS literature. Almost all of these overview papers, however, have a focus different from AS/RSs, for example, general warehouse design. Because of this, only a limited number of aspects of AS/RSs and a limited number of references with respect to AS/RSs are presented in those papers. Matson and White (1982) review a number of material handling research areas one of which is concerned with AS/RSs. Kusiak (1985) describes design and operational decision problems for flexible manufacturing systems with a focus on automated guided vehicles and AS/RSs. The author discusses design, storage and batching (i.e., consolidation of orders) policies for AS/RSs. Johnson and Brandeau (1996) discuss stochastic models for the design and control of automated guided vehicles and AS/RSs. Manda and Palekar (1997) discuss some papers on travel time estimation for AS/RSs and storage assignment rules.

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, Gu et al., 2007. Due to their broad scope, these five papers only discuss a fraction of the AS/RS issues and literature. To our 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. We conclude that our paper seems to be the first overview paper in over 10 years devoted exclusively to AS/RSs, and the first ever to give a broad overview of all design and control issues in AS/RSs.

The main structure of the paper can be described as follows. First, we present a general description of AS/RSs and a classification of related design and control issues. The main body of the paper consists of an overview of literature discussing solution methods for these design and control problems. At the end, we indicate relevant open research questions. In more detail, Section 2 defines various types of AS/RSs and describes some important technical characteristics. Section 3 presents a classification of both physical design and control issues. This broad introduction will be followed in Section 4 by a more detailed description of methods that support each of the discussed physical design issues. Papers addressing individual control policies for storage assignment (Section 5), batching (Section 6), parking of idle AS/RSs (Section 7) and sequencing (Section 8) will be discussed in subsequent sections. Travel time estimates and other performance measures will be treated in Section 9. Section 10 presents conclusions and issues for further research.