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Automated Storage and Retrieval Systems (AS/RS)

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Automated or semi-automated systems for chemical or biological library storage are now commonplace[1]. However, laboratory applications of such technology are but a tiny part of a much larger industry. Automated storage and retrieval systems (AS/RS) are inventory management systems that are widely used in distribution centers and warehouses throughout the United States and the world[2]. There is a professional AS/RS industry group, part of the Material Handling Industry of America (MHIA).  An automated storage/retrieval system (AS/RS) can be defined as a storage system under which a defined degree of automation is to be implemented to ensure precision accuracy and speed in performing storage and retrieval operations[3]. These automated storage and mechanized systems eliminate human intervention in performing basic sets of operations that includes :

  • Removal of an item from a storage location automatically
  • Transferring the above item to a specific processing or interface point
  • After receiving an item from a processing or interface point, it is automatically stored at a predetermined location.

Systems vary from relatively simple, manually controlled order-picking machines operating in small storage structures to extremely large, computer-controlled storage/retrieval systems totally integrated into a manufacturing and distribution process. These systems provide users with increased inventory control and tracking, including greater flexibility to accommodate changing business conditions. They can be comprised of modular subsystems that are easily replaced to minimize downtime and extend the service life of the overall system. AS/RS systems also reduce labor costs, lowering necessary workforce requirements, increasing workplace safety, and removing personnel from difficult working conditions (such as cold storage environments). AS/RS systems can produce major savings in inventory storage costs via improved space utilization and storage density - both vertically and horizontally.

Automated storage and retrieval systems do require considerable investments of a company's resources, however. Maintaining a large and highly integrated system requires training and experience. The cost of purchasing and implementing an effective automated storage/retrieval system is significant as well, encompassing everything from the actual purchase price of AS/RS equipment and software to modifying existing facilities or creating new ones. In addition, experts in the use and maintenance of AS/RS systems note that companies often experience significant ongoing costs for maintenance and updating of various subsystems. Businesses are urged to examine the long-term implications of their choices when they incorporate an automated storage and retrieval system into their operations.

Contents

Terminology

The AS/RS industry has its own unique terminology. Because the purchase of such a system for chemical or biological storage may be a once-per-career event for most scientists, it’s not likely they are conversant in all the terms of the trade.

  • Storage Structure: The rack framework that supports the loads contained in the AS/RS and is used to store inventory items.
  • Storage Racks: This structural entity comprises storage locations, bays, rows, etc.
  • Storage Space: The three-dimensional space in the storage racks used to store a single load unit of material.
  • Bay: The height of the storage rack from floor to the ceiling.
  • Row: A series of bays placed side by side.
  • Aisle: The spacing between two rows for the machine operations of AS/RS.
  • Aisle Unit: Encompasses aisle space and racks adjacent to an aisle.
  • Storage/Retrieval Machine: Used to move items in and out of inventory. An S/R machine is generally capable of both horizontal and vertical movement. In the case of fixed-aisle storage systems, a rail system along the floor guides the machine along the aisle and a parallel rail at the top of the storage structure is used to maintain its alignment.
  • Storage Modules: The unit load containers used to hold the inventory items. In the industrial world these include pallets, steel wire baskets and containers, pans and special drawers. In the laboratory environment, these may include vials, plates, bottles, etc. These modules are generally made to a standard base size capable of being stored in the structure and moved by the S/R machines.
  • Pickup and Deposit (P/D) Stations : Where inventory are transferred into and out of the AS/RS. They are generally located at the end of the aisles to facilitate easy access by the S/R machines from the external material-handling system. The location and number of P/D stations depends upon the origination point of incoming loads and the destination of output loads.
  • Cherry Picking: The process of the AS/RS accessing any individual unit load container, regardless of location in the storage system and position in access sequence. In the laboratory environment, cherry picking may also involve randomly accessing a given sub-unit within a load container, i.e. a given sample within a multi-sample container, such as a microplate or array of vials.

AS/RS layouts

  • Horizontal Carousels: Consists of a fixed number of adjacent storage columns or bays that are mechanically linked to an oval track which rotates horizontally, on an overhead or floor mounted drive mechanism. Each column is divided into a fixed number of storage locations or bins. Loads consisting of containers may be inserted and retrieved either manually or by an automatic inserter/extractor mechanism. However, rotation of the carousel, whereby a specific storage location is brought to the picking location, is almost always controlled automatically.
  • Rotary Carousels: Consists of a fixed number of adjacent storage columns or bays that are mechanically attached to a rotary positioning stage. Each column is divided into a fixed number of storage location or bins. Loads consisting of containers may be inserted and retrieved either manually or by an automatic inserter/extractor mechanism. However, rotation of the carousel, whereby a specific storage location is brought to the picking location, is almost always controlled automatically.
  • Vertical Carousels: Consists of a number of horizontal shelves, trays or bins that are mechanically linked to an oval track which rotates vertically. Because storage is vertical, such systems are popular when conserving floor space. Although automatic insertion and extraction of individual items or loads is possible, it is not as common as it is with horizontal carousel applications.
  • Vertical Lift Modules (VLM): A storage system that consists of two parallel columns each of which is divided into fixed shelf locations that can hold a single storage module or container. The shelving locations are single deep. A container is inserted, extracted and transported between storage levels and picking locations via an elevator-like device with an automatic shuttle that travels up and down within the space between the storage columns.  The storage container is presented to a fixed P/D station by the elevator mechanism. 
  • Fixed-Aisle (F/A) Storage Retrieval Systems: Consists of one or more long, narrow aisles framed on both sides by a steel or extruded aluminum storage rack structure from which loads are automatically stored and retrieved under computer control. The storage/retrieval function in each aisle can be performed a variety of ways. However, the most common way is by a machine that consists of a floor running, traveling structural frame or vertical mast that guides and supports a hoisting carriage on which loads are carried. One or more shuttles or insertion/extraction devices on the hosted carriage manipulates loads into and out of adjacent or opposing storage rack positions. All three machine motions; horizontal (down aisle), vertical and shuttle action are independently and automatically controlled.
AS/RS Layouts
ASRS Horizontal Carousel.png ASRS Rotary carousel2.jpg ASRS Veritical Carousel 2.jpg ASRS Vertical Lift.jpg  ASRS Aisle System.jpg 
Horizontal Carousel Rotary Carousel Vertical Carousel Vertical Lift Fixed Aisle
Image:ASRS_Vertical_Underground.jpg
Multiple vertical lifts installed underground

AS/RS in the laboratory

AS/RS are used in the laboratory environment primarily to manage collections of chemicals or biologics. Collections of small molecules, stored neat or in solution (often in Dimethyl Sulfoxide - DMSO)  are used to support drug discovery screening efforts[4]. Large collections of DNA, RNA, cell cultures and tissues are now common. The key factors influencing the specifications of laboratory AS/RS installation are:

Size of collection, frequency of access, desired turnaround

Storage collections can range from several thousand to millions of samples. Small collections with a low frequency of demand can be managed manually, but as collection sizes and access frequency increase, AS/RS becomes desirable and then essential to avoid errors. This is especially true if the process involves return of samples to the collection, which is the most error prone operation. Some laboratory focused AS/RS advertise capacity as large as tens of millions of samples, depending on storage format. Systems capable of storing thousands of samples can often fit into a standard laboratory with minor facility modifications. Systems capable of storing 100’s of thousands up to millions of samples will generally require significant facility modification, up to and in some cases including the building of a specialized facility for very large collections. AS/RS can be designed to present and retrieve individual samples directly to/from a person if frequency of access is moderate. In cases of high access frequency, an automated front-end to the AS/RS may be necessary. Similarly, the specification for turnaround time from request to receipt of sample will influence the degree of front-end automation and also the degree of multiplexing within the main AS/RS. A requirement for high frequency/high turnaround may necessitate a modular design, where the collection is split among multiple, smaller AS/RS.

Laboratory AS/RS
ASRS - Lab Scale.png Image:ASRS_MatriStore.jpg Haystack.JPG  ASRS- Fixed Aisle Lab.png
Lab-scale AS/RS Automated front end to main AS/RS unit Multiple automated front ends to AS/RS units Fixed Aisle AS/RS



Sample type, physical state and format of the collection

Small molecule collections are stored in solution (most often dissolved in DMSO) to facilitate repeated access by downstream screening operations. Neat collections (most often dry compounds) tend to be more archival in nature and thus may not be accessed with the same frequency as solution collections.  Both present unique environmental constraints (see below). Dry, neat compound collections may vary widely in format, ranging from bottles, to screw-cap vials, to microvials.  A key workflow consideration is whether the entire neat sample container will be sent to the laboratory requesting the compound, or only a portion. In the latter case, either provisions for dispensing/weighing of compounds must be part of the retrieval operation, or a volitile solve transfer procedure must be used.


Storage of DMSO-solution small molecule collections in various forms of microplate formats are giving way to storage in microvials or "cryovials" because of the concern about the detrimental effects of the freeze-thaw cycle on compound stability and solubility. These microvials will be removed from the cold storage environment only once and their contents used entirely. Once thawed, liquid samples are most often arrayed into a microplate format for testing. Automation of this arraying process is essentially mandatory to avoid errors.


Biobank collections may contain DNA, RNA, blood, tissue, cells, antibodies and proteins. The storage formats tend to be more variable than for small molecule collections and most often in individual vessels (vacutainers, cryovials) rather than microplate wells, although the individual vessels may be arrayed in a microplate footprint.  Biobanks containing any type of human tissue are subject to many guidelines and restrictions having to do with donor consent, privacy and security. 

Environmental constraints (temperature, atmosphere, humidity)

In the case of neat chemical compounds there may be concern about compound volatility, i.e. vapors. Even well sealed vessels will tend to allow the escape of some volatile components over time and when multiplied by the size of a compound collection, air quality can be a serious concern. Thus adequate facility ventilation must be considered. Neat compound collections are generally stored at either constant room temperature or cooler, but not below freezing. Humidity control and minimal exposure to light is also desirable. The latter can be achieved via opaque containers or a dark storage environment or both.
The significant environmental concern associated with DMSO-dissolved collections is the high hygroscopicity of DMSO, since the absorption of water by such compound collections has been shown to be detrimental to compound stability. The solubility of compounds will change as the % water changes and the melting point of the solution will change[5]. Most long-term DMSO collections are stored frozen, at 4°C or -20°C. Even though storage at -80°C might lend increased stability, it is generally a complication not considered necessary. As with neat collections, minimized exposure to light is desirable. The collection may be maintained in an inert atmosphere, such as nitrogen. Avoiding the formation of frost is essential to the good operation of the AS/RS.
Collections of biological samples, or “biobanks” are often stored at -80°C or colder to ensure long-term stability and suspension of biological activity. This presents a highly challenging environment for mechanical systems, thus a more limited range of automation will be suitable for such an environment. Although biological samples are frozen, biohazard precautions must be maintained. The conditions of the entire storage and retrieval process for biological samples must suitable to maintain the biological viability of the retrieved sample. Heat, light and the physical shearing of the freeze/thaw process can have a much more profound impact that is the case with small molecules. The specifics are very case dependent.

Desired request turnaround, degree of automation and interface to other systems

The desired degree of automation for collection management is dependent on a number of factors that are interdependent.

  • Frequency of access: Just about any collection in any storage environment can be managed manually for low frequency access. Small biological collections have been managed in standard laboratory -80°C freezers for many years. However, as the frequency of access ramps up so do the undesirable effects of manual access. Special environmental conditions will not be well maintained. The potential for human error will increase, especially if the process involves return of samples back into the collection, which is the most error-prone activity.
  • Desired request turnaround: This is the elapsed time between a sample request and presentation of that sample. Turnaround times increase as the collection size and the frequency of access (i.e. requests) increases. At some point, these factors may dictate use of AS/RS to maintain the desired turnaround. Furthermore, continued collection size and/or access demand growth may dictate use of a modular, multi-AS/RS approach, in which the collection is split into subparts, each with it’s own AS/RS.
  • Interfaces: Depending on the type and use of the collection, it may be desirable to directly interface the AS/RS P/D station to additional sample preparation automation, such as automation to thaw, reformat and/or weigh samples. One must weigh the benefits of interfacing multiple automated systems against the added complication of such an approach. For instance, at one time it was popular to envision directly interfacing AS/RS automation with HTS automation to create a completely automated “smart” loop of sample request, assay, secondary sample request, secondary assay, etc. The complexity of such an approach has generally been found to outweigh the benefits. However some degree of automation at the P/D station may be required to manage the transition of samples from a very cold, inert atmosphere environment to a room temperature, regular atmosphere environment.
    • Any collection of any size almost certainly must have an associated collection-tracking database together with an automated identification (i.e. bar coding) approach. Interface of collection informatics to other systems, such as chemical or screening data management systems, LIMS or a laboratory notebook system is almost as certainly to be required.

Issues and bottlenecks

As with any “industrial” operation, the entire workflow must be carefully understood and managed to maintain smooth flow. The following are some issues that may have to be managed.

  • Consumables: A steady, high volume supply of consumables (i.e. vials, microplates, pipette tips, solvent, etc.) is necessary. An inventory management system may be necessary, perhaps linked to the companies purchasing department. Storage space for consumables must be provided. A “just-in-time” approach to consumable supply may minimize storage requirements and help to manage costs. The disposal of a high volume of consumables must also be planned for and managed. The cost of purchasing, storing and disposing of consumables may be significant enough to dictate the use of methodologies that minimize their use, such as reformatting of samples using washable pipetting components or non-contact technologies, such as ultrasonic droplet ejection.
  • Weighing: The bottleneck for any dry compound collection is often the dispensing and weighing of samples. Automated techniques exist for this operation, but none span all the different potential physical characteristics posed by solid samples. Thus some degree of manual intervention is almost always going to be required. Strict attention must be given to eliminating the exposure of individuals to these dry compounds during such a weighing process.
  • Centralized vs. decentralized: The debate over the merits of a large, centralized sample collection vs. multiple, decentralized collections is ongoing. Many companies have decided to have both, with a single, large collection providing samples to smaller, decentralized facilities on a “campaign” basis. In this scenario, the decentralized facilities have a smaller capacity and are highly focused on providing the samples in a format and throughput consistent with their specific downstream needs. This mode of operation has been made more feasible by the increasing commercial offerings of “lab-scale” AS/RS systems, some no larger than a large laboratory freezer.
  • Sample identification: The use of some form of Automatic Identification technology is essential for sample identification.  Two or three - dimensional bar coding are the most common methods.  Radio Frequency ID tags (RFID) are also a viable choice, although likely more expensive.  Any label technology must be capable of staying adhered to the vessel and remaining readable under the storage conditions, i.e. very cold, potential frost (see Bar code labels).  A choice must be made between a ID strategy in which the identifier is simply a pointer to information in a data base, or one in which the identifier actually contains information about the sample (see Automatic Identification - strategy).
  • Support and maintenance: A large, fully automated AS/RS is an industrial scale system and operation. Each installation of such a system involves some degree of customization, so none of these systems can be considered to be commercial-off-the-shelf (COTS). Successful installation and operation of such systems is made much more likely by the presence of in-house laboratory automation specialists. Although the system is almost certainly to be provided and integrated by a commercial entity, internal resources are essential for all the aspects of managing a highly custom laboratory automation project.
  • Changing requirements: Such large, industrial operations take much time to put into place. The R&D process supported by these large systems change and evolve constantly, sometimes rapidly, not only in terms of science, but also organizationally. Therefore one must carefully weigh the timelines of implementing such a system vs. the potential timelines of change within the organization. It is not unknown for such projects to be overtaken by events and change and rendered irrelevant. Any system must be capable of evolving to meet changing requirements once installed. It is also not unknown for the sources of such highly custom systems to go out of business. A buyer must be prepared to make an investment in understanding the system and also take appropriate contractual precautions to assure the system IP remains accessible even if the original developer is no longer available.
  • Changing viewpoints on stability: Over the history of compound collections, opinions and information about sample stability has evolved, and will likely continue to evolve as more long-term data is obtained. This may cause an evolution in the desired storage conditions or format, which may necessitate system modification.
  • Changing formats: The downstream formatting requirements may evolve and change over time, necessitating changes in the collection format.

Related articles

Organizations

References

  1. Industrialization of drug discovery: from target selection through lead optimization, Jeffrey S. Handen, CRC Press, 2005 ISBN 0824723910
  2. Handbook of Industrial Engineering: Technology and Operations Management, Gavriel Salvendy, Wiley-IEEE, 2001 ISBN 0471330574
  3. Automated Storage and Retrieval Systems, in Fundamentals of CIM.
  4. High throughput screening: methods and protocols, William P. Janzen, Humana Press, 2002, ISBN 0896038890
  5. | Chris Lipinsky, LRIG New Jersey, Feb 2006
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