Types of Automated Storage and Retrieval Systems (AS/RS)

October 18, 2023
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Vertical lift modules (VLM)

A VLM consists of two parallel columns, each filled with shelves, and an automated lift at the center. No, we are not describing a pantry. This mechanism is controlled by integrated software that coordinates the entire process, from locating to retrieving items.

When you need to retrieve an item, the lift travels to the specific shelf, grabs the product, and brings it down to an access point. 

If you're dealing with smaller items that require quick retrieval, VLMs are a solid bet. They're commonly used in automotive parts stores, pharmaceutical facilities, and electronic component warehouses. 

Essentially, they're best suited for environments where high-frequency retrieval is more the rule than the exception.


  • Because they use vertical space, VLMs can significantly reduce your storage footprint.
  • The automated retrieval process is fast, cutting down on the time it would take for a human operator to locate and retrieve an item.


  •  VLMs aren't cheap. The initial investment could be a lot depending on the size and complexity of the system.
  • Due to their design, VLMs are generally not suitable for storing large, bulky items.

Horizontal Carousels

Imagine a conveyor belt with multiple bins attached, forming a closed-loop system. That's the basic structure of a horizontal carousel. 

The bins rotate horizontally, driven by a motor, to bring the required items to the operator at single or multiple pick stations. The system is usually controlled by a software interface that automates the retrieval process.

Horizontal Carousels are particularly useful when you need fast access to a wide array of items. They're commonly found in e-commerce fulfillment centers, parts distribution facilities, and even some retail environments. Basically, any operation with high throughput and quick order picking.


  • Because the bins are in constant motion, there is very little wait time for item retrieval.
  • They can be configured to fit your available space, making it a flexible storage solution.
  • As your business grows, you can integrate additional carousels into the system without a major overhaul.


  •  These systems can consume more energy than other types due to the constant motion of the carousel.
  • The carousel mechanism and control software may require specialized training, adding to your operational considerations.

Vertical Carousels

Picture a Ferris wheel of storage bins or shelves—this gives you a basic idea of what a Vertical Carousel looks like. These shelves or bins rotate up and down to bring the item to the operator at an access point. The entire operation is computer-controlled, so with a few clicks, the right product is on its way to you.

They are a good fit for environments where there is minimal floor space but lots of vertical space. They're often seen in medical facilities for storing pharmaceuticals, or in automotive parts stores where a wide variety of small to medium-sized items need to be accessed quickly.


  •  If you have more height than width in your facility, vertical carousels make the most of that.
  • Many models come with safety measures like locked access points, making them suitable for storing sensitive or hazardous items.


  • These systems often have weight limitations per shelf, restricting the kind of items that can be stored.
  • They can be quite pricey, especially at first.

Fixed Aisle AS/RS

The Fixed Aisle AS/RS is a more traditional system you might already associate with automated storage and retrieval. It's commonly used in large distribution centers and warehouses.

In a Fixed Aisle system, you have a set of racks and aisles with a Storage/Retrieval Machine (S/RM) that moves along each aisle. The S/RM is designed to navigate to specific locations in the rack to either store or retrieve pallets, boxes, or other types of containers. Everything is managed by a control system.

They're particularly useful where inventory turnover is less frequent but the volume of goods stored is large.


  • The system is excellent at maximizing space, so you can easily store large volumes of goods.
  • It can handle a variety of item types and sizes, making it a flexible choice.


  • These systems can be expensive to install and maintain. Plus, their operational complexity usually requires specialized training.
  • Because the aisles are fixed, making changes to the layout can be quite a task.
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Mobile shelving systems

Mobile shelving systems consist of rows of shelves mounted on wheeled bases that move along floor tracks. You can open and close aisles as needed by operating the system manually or through automated controls. 

When an item is required, the relevant aisle is opened, providing access to the stored materials.

They are particularly beneficial in environments where storage density is a priority, but quick access is not essential. Think archive rooms, libraries, or even museums, where the frequency of item retrieval may not be as high.


  • By eliminating the need for multiple fixed aisles, you can significantly increase your storage density.
  • The ability to open and close aisles gives you flexibility in how you use your storage space.
  • Unlike some other automated systems, mobile shelving generally uses less energy.


  • Because you need to open the aisles to access items, retrieval times can be slower compared to other AS/RS types.
  • Some systems require manual effort to move the shelves, which might not be ideal for all settings.

Compact AS/RS systems

Compact AS/RS Systems, also known as mini-load systems, are designed for smaller operations that need the benefits of automation without a large footprint.

It typically consists of a scaled-down Storage/Retrieval Machine (S/RM) that moves along narrow aisles between racks or shelves. These systems are best suited for handling small to medium-sized items, such as totes or cartons.

If you’re running a small to a medium-sized operation like an e-commerce fulfillment center, or if you have specific high-throughput areas within a larger facility, a Compact AS/RS System can be a great fit. 


  • Despite their smaller size, these systems offer fast access to stored items.
  • As your needs grow, it's easier to add more modules to a Compact AS/RS than to reconfigure a larger system.


  • These systems are generally not suitable for large or heavy items.
  • Given their smaller scale, the cost per item stored can sometimes be higher than in larger systems.

Micro-load AS/RS

Micro-load AS/RS systems are essentially a more specialized form of Compact AS/RS systems, designed for even smaller scales. They use small robotic arms or trays to handle items that are usually smaller than those in a mini-load system, like small electronic components, pharmaceuticals, or jewelry. 


  • The systems are designed for precision, making them ideal for handling high-value, small-sized items.
  • Given that they often store high-value items, many micro-load systems come with advanced security features.


  • These systems are not suitable for items outside their small size and weight parameters.


Automated Storage and Retrieval Systems (AS/RS) come in various shapes and sizes, each offering its own set of advantages and limitations. 

Choosing the right system involves a careful examination of several factors—storage density requirements, item types and sizes, operational speed, and budget constraints, to name a few. 

While the initial investment in AS/RS can be significant, the potential for increased efficiency and cost savings over time often makes it a worthwhile endeavor.

So, don't just pick a system because it's trendy or appears to be the most robust - Assess your specific needs, consider the trade-offs, and make an informed decision that aligns with your operational goals and constraints.

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