The Ultimate Beginner's Guide to AS/RS

Short history

The first AS/RS was developed by the German company Demag in the 1950s. Demag installed the world’s first AS/RS fully automated warehouse for the Bertelsmann publishing house in 1962. This twenty-meter-high (65.6-foot-high) design held and retrieved nearly 7 million books and heralded a new era in warehouse technology. Traditional warehouses were labor intensive with limited shelving designed for human access and required a large amount of space. Demag’s revolutionary design was to combine the benefits of automation with the ability to access more vertical space for storage.

Over the next few decades, while the AS/RS design remained essentially unchanged, the technology spread globally across a range of different warehouse types, offering clear advantages for high density storage, especially in areas with labor and land constraints. Since the 1980s, developments in processor power and affordability, alongside improved Warehouse Control Systems (WCS) software, such as the Controller, have catapulted AS/RS to the forefront of warehouse solutions. Together, these developments have enabled today’s AS/RS technologies to manage complex tasks far removed from Demag’s pioneering work, revolutionizing storage worldwide.

What is an Automated Storage & Retrieval System?

An AS/RS integrates a variety of different digital, robotic, and racking elements to provide a tailored automated warehouse capable of handling an enormous variety of goods, all controlled via digital automation software. A tailored AS/RS solution can be assembled from a wide variety of options, including Cube Storage, Autonomous Mobile Robots (AMRs), horizontal and vertical carousels, cranes, shuttles, Vertical Lift Modules (VLMs), Micro-, Unit-, and mini-Loads, among other systems. All of these systems are managed by a Warehouse Management System (WMS) ⁠— the brain of the operation.

Furthermore, an AS/RS is not limited by size, and can support small, large, or multi-site warehouses, leveraging the various technologies and vehicles to automate the retrieval and deposition of high-volume loads, accurately and at speed. This type of solution is especially popular for warehouses handling high volume loads, where storage density is a key factor due to the cost or lack of space, and where items are not processed or altered in any way.

Benefits of AS/RS

An AS/RS brings a range of benefits for a company willing to invest in a system that meets their requirements. These systems offer unparalleled accuracy, efficiency, and productivity, with very low error rates combined with the ability to handle high volumes, day or night. They also reduce repetitive and physically demanding tasks, freeing labor to be used in more productive pursuits. This is becoming more and more important as all advanced economies are seeing labor shortages, which drive up labor costs, as various populations age across advanced economies. Relying on variable seasonal workers is becoming increasingly problematic as well, due to increased competition for their work. AS/RS technology can also help to reduce the physical cost of working with heavy items day in, day out, and can handle goods in environments with extra physical demands, such as freezers. Systems like Cube Storage AS/RS also offer higher density storage compared to traditional warehouses, saving significant space and real estate costs.

Nevertheless, it is no doubt that AS/RS installations require significant changes to working practices, warehouse infrastructure, and layout. Alongside changes to the warehouse, they also require regular maintenance to operate at peak performance and in case breakdowns do occur, productivity can suffer accordingly, bringing the line to a stop. There is, however, variation in terms of the different AS/RS installations’ need for maintenance and ability to handle such breakdowns.

How does an automated storage and retrieval system work?

An AS/RS is, in essence, an automated system designed to store and retrieve inventory or products. It typically replaces large areas of shelving to save floor space, improve safety, and increase overall productivity. With AS/RS, warehouse robots are used to bring the goods to workers (Goods-to-Person, GTP automation), nearly eliminating workers’ need to walk, while significantly improving efficiency, safety, and ergonomics.

There are several different types of AS/RS, as outlined above, depending on the size and weight of the product in question and purpose of the warehouse. With the different technologies available, nearly every warehouse can be automated. An installation can involve a combination of unit-load, mini-load, carousel-based, vertical lift, and shuttle and robots, tailored to meet the needs of the company. Underlying these different parts are four key elements in common: storage structure, physical automation, conveyance interface, and a control software.

Generally speaking, there are three main load types:

• Unit-Load AS/RS (such as pallets)
• Mid-Load AS/RS (tailored automation for particular types of inventory)
• Mini-Load AS/RS (such as split case picking)

Alongside these load types are a variety of AS/RS options, including:

• Cube Storage AS/RS
• Unit-Load AS/RS Cranes (Fixed-Aisle & Moveable Aisle)
• Mini-Load AS/RS Cranes (Fixed-Aisle)
• Shuttle AS/RS
• Carousel-based AS/RS
• Vertical, Horizontal, and Robotic Vertical Lift Module (VLM) AS/RS
• Micro-Load (Stocker) AS/RS
• Vertical Sequence Systems (VSM) AS/RS

This daunting list may seem complex, but they break down into several optimized parts working together through control software to order the warehouse. Below is an overview of the different elements, and variations within these.

Cube Storage AS/RS

The Cube Storage AS/RS offers high density storage by removing all of the empty space found in traditional shelving. Consisting of only 5 modules, items are stored in Bins which are stacked next to and on top of each other like building blocks within an aluminum Grid. Robots drive on tracks along the top, continuously digging, retrieving, and delivering Bins to Ports (warehouse workstations) as directed by the system. Workers access the inventory at the Port for order fulfillment or stock replenishment. Robots then collect the Bins to return to the Grid. This automatically slots products by popularity and ensures that high runners stay on top and low runners sink to the bottom, ensuring high picking speed. Cube Storage AS/RS combines highly efficient space usage with modular robots and a building block design that enables ease of installation as well as expansion. One limiting factor to consider with cube storage AS/RS is that products need to fit into the Bins, (e.g. the largest AutoStore Bin size measures 449 mm x 649 mm x 425 mm).

Unit-Load AS/RS

Unit-load AS/RS systems are designed to cope with cumbersome and/or heavy loads covering weights between 1,000 and just over 5,000 pounds (about 2267.96 kg). They are ideal for heavy pallets and often employ tall racks with narrow avenues accessed via a fixed-aisle or moveable-aisle crane to transport the goods in storage. They are ideal for locations where space for pallets is limited and where larger items need to be accessed at speed.

Fixed-Aisle & Moveable Aisle Crane Unit-Load AS/RS

With this system, narrow aisles of pallet racks are accessed via a mobile crane that can move vertically and horizontally along a set aisle to quickly access, collect, and move items in storage. A Moveable Aisle Unit-Load AS/RS differs in that the crane is not limited to one aisle, which avoids duplicating the crane for each and every aisle, thus saving on space and cost. One limiting factor is that the system relies completely on the mobile crane, and an aisle will be inaccessible during maintenance. 

Mini-Load AS/RS

A Mini-Load AS/RS is ideal for handling smaller items, usually weighing no more than 75 pounds, compared to Unit-Load systems that can handle much heavier or larger loads. This AS/RS model often employs totes, trays, or cartons (or a combination of these elements) to transport inventory at speed, and is sometimes identified as a "case-handling/tote-stacking" AS/RS. It is a popular choice for Stock Keeping Units (SKU) where space is at a premium, causing traditional carton shelving to be problematic. Area Mini-Load AS/RS is also a versatile option as a buffer for ordering products destined for picking or packaging, and can be used to replenish pick storage. These systems are limited by weight as well as size, which makes them less versatile than other systems.

Shuttle-based AS/RS

This model transports items via shuttle or robot following a track between the different areas in the warehouse/workspace, both horizontally and vertically. They can operate across a range of levels and deliver a wide variety of items via a tote or carton to a required location. Shuttles are instructed to retrieve items and deliver them via the exterior of the rack to a workstation or to a secondary conveyor. They come in a wide variety of designs, depending on the product and warehouse requirements. Limiting factors include that aisles of products can be inaccessible during maintenance and shuttles require more space than other systems.

AMR-Based High-Density AS/RS

An autonomous mobile robot (AMR) uses independent robots to navigate the racking, using multiple pathways to retrieve items for a specified tote or location. AMRs deliver these items to the ordering workstation, before taking on the next task. This versatile system offers excellent flexibility and efficiency, and the nature of AMRs means they can be easily scaled to meet changing demand, by adding more AMR units. The systems are highly complex, with advanced sensor packages and other autonomous elements demanding a higher level of technical support.

Go-Fer Bot AMR

The Go-Fer system, named after burrowing gophers, uses specially designed shelves and racks that are moved via the AMR from below to the workstation. The shelves can be configured to take a wide variety of options such as boxes, pallets, or hanging arrangements depending on the items in question. The AMRs lift and transport the whole unit to the workstation, before returning. This offers a high-density storage solution, and can be easily and affordably scaled to meet the needs of the business. This system, like the shuttle system, requires more floor space to move the shelves and store them in queues.

Stacker-Bot

A newly developed AMR AS/RS stacker-bot extracts several totes or cases from a shelving rack, then delivers the totes or cases to an awaiting conveyor, secondary AMR, or workstation. The Stacker-Bot can combine delivery and returns on the fly, providing a nimble, efficient, and cost-effective system. They require more space to operate, as the units vary in size, and so require more space set aside for navigation.

Carousel-Based AS/RS

Carousel-based AS/RS systems are the oldest form of AS/RS, consisting of a track suspending a variety of items or storage options (think of dry cleaners with hanging clothes). This will cycle to deliver a particular item or bin to a workstation as required. They come in a variety of designs, from a horizontal model delivering items in a line to a vertical carousel where bins move in an up-and-down loop. These systems are ideal for smaller items that can move at speed. Another variation includes the Robotic Horizontal Carousel AS/RS, which offers an automated system involving up to three tiers of carousel with totes at every level. Limiting factors are that they can be more difficult to expand and they demand a considerable amount of space.

Vertical Lift Module (VLM)

This system is characterized by a picker at the center of a stack of racks, which moves back and forth to select ordered items and deliver them to a workstation or conveyor. They are often enclosed with the arm moving freely within the racking space. Once the order is fulfilled, the VLM will return the storage unit to the correct location, before taking on the next task. The trays themselves can be fixed or mobile, leading to highly efficient management of a complex inventory. A Micro-Load Stocker is very similar to a VLM, and is ideal for high density warehouses requiring an AS/RS for buffering, sequencing, and point-of-use goods. A micro-load stocker can consist, for example, of a series of robots operating within an enclosed storage grid, delivering bins to a conveyor. Like the aisle-based cranes, the VLM/stocker is highly reliant on certain parts that can cause the system to grind to a halt during maintenance.

Vertical Sequence Module (VSM)

This system orders retrieved bins in a sequence, providing an efficient solution for high-density, high-volume warehouse spaces. The order sequence can be retrieved via another system such as an AMR or conveyor and delivers them in a specific order. This system can also be added as an enhancement to existing AS/RS installations, thus improving efficiency and productivity and reducing demands on floor space. Like the VLM above, the system can be subject to delays during maintenance when certain components are out of action.

Conclusion

In summary, AS/RS systems have come a long way since they were invented and have transformed warehouse operations by offering increased storage density, improved efficiency, and reduced labor costs. When considering an AS/RS system, there are several factors to keep in mind and a tailored AS/RS solution can consist of a combination of various systems. Some of the systems listed above are complex and demand significant changes to the warehouse building. Systems which rely on a few key parts can be vulnerable to downtime during maintenance, whereas others, requiring more floorspace, can suffer from difficulties in expansion or are less suitable for areas with a high land cost, such as urban areas.

There is no doubt that AS/RS systems are far superior to manually operated warehouses, and by leveraging automation, robotics, and digital control, these systems optimize space, accuracy, and productivity. However, careful consideration of maintenance requirements and system limitations is essential to ensure smooth operations and maximize the benefits of AS/RS technology in the long run.