AMRs vs. ASRS: which are best for warehouse automation?

Understanding AMRs (Autonomous Mobile Robots)

AMRs have had a surge in popularity in the last few years, with maybe the most popular and visible adopter being Amazon. An AMR is a robot that can move products around a warehouse environment without being controlled by a human operator or following a fixed path. 

AMRs use onboard sensors, cameras, and software to perceive their surroundings, navigate autonomously, and avoid obstacles. They can perform various warehouse tasks, such as picking, sorting, transporting, and delivering goods. For picking purposes they are usually used to carry shelving units or palletised goods and navigate using QR codes fixed to the warehouse floor. 

One of the benefits of AMRs is their relatively low costs, coupled with their ease of scalability. Where some traditional warehouse automation solutions are only viable in spaces with large internal clear height, AMRs can be used in areas with reduced ceiling heights and even on mezzanines. From a contingency point of view, a single AMR failure shouldn’t have a significant impact on the operation.

Exploring ASRS (Automated Storage and Retrieval Systems)

Unlike the relatively recent popularity of AMRs, ASRSs have been available in the warehouse automation market for over half a century. An ASRS (Automated Storage and Retrieval System) is a type of warehouse automation that usually uses cranes, shuttles and/or lifts to store and retrieve goods. 

An ASRS typically consists of racks, aisles, bins, shelves, and other storage units, An ASRS can increase the efficiency, accuracy, and safety of warehouse operations, as well as reduce labour costs and space requirements. An ASRS can also be integrated with other warehouse technologies, such as barcode scanners, RFID tags, or inventory management software.

Comparing AMRs and ASRS

Some of the key differences between AMRs and ASRS are:

– Flexibility and modular growth – An AMR system uses robots that can move freely around the warehouse floor, while ASRS use fixed infrastructure meaning they can only move along predefined paths or rails. 

You can increase the throughput of an AMR system by introducing more robots or increase the storage capacity by building more racks and extending the footprint. These works can take place over the space of a few weeks. With an ASRS, you can expand the system, but it will be more costly, more invasive and take significantly longer. 

– Implementation: AMRs are more flexible and scalable, as they can be easily added or removed depending on the demand, and they do not require major changes in the warehouse layout or infrastructure. ASRS are more rigid and costly, as they require a high initial investment, a large amount of space, and a complex installation and maintenance process.

– Space constraints: If you are constrained by a low roof or small chamber, AMR’s will likely be a more suitable solution. When a high roof is available in a larger chamber, ASRSs will provide a significantly denser storage solution, minimising the overall space requirement. 

Applications and Use Cases

AMRs are best suited to operations that require flexibility, scalability, and adaptability. AMRs can handle a variety of tasks, such as picking, sorting, transporting, replenishing, and inventorying. They can also adjust to changing demand, layout, or inventory without requiring fixed infrastructure or extensive reconfiguration. AMRs will usually be best suited to smaller products, which fit in the typical AMR racks. 

ASRSs are best suited to operations that require high-density storage, fast retrieval, and high throughput. ASRSs can optimise the use of vertical and horizontal space, reduce labour costs, and improve inventory accuracy and security. 

Factors to Consider When Choosing Between AMRs and ASRS

Are your products suitable for totes?

Many GTP (Global Technology Platform) technologies use totes to store items. If your products are not tote-friendly, this will limit your options and push you towards a system that can handle larger items or pallets such as shelf-based AMR systems.

How much height do you have available?

Technologies like AMRs are suited to low-height warehouses, while crane-based systems (mini-loads and pallet cranes) may prove more viable in sites that have 15m+ headroom and are better for taller warehouses.

Mezzanines

Mezzanines may suit your manual processes but how will they affect your automation choice? If you have mezzanines, you need to consider their strength and space for automation. AMRs may fit on a mezzanine but is it strong enough? You also need to consider the columns and cross bracing. If you have automation on multiple mezzanine floors, you will need a way to consolidate your orders, such as automated put walls or sortation AMRs.

How much space do you have available?

The warehouse footprint will determine the stock volume. Technologies like GTP shelf-based AMRs offer dense storage solutions but only use 2.5m of headroom. Technologies like case handling AMRs (ACRs) use up to 12m of height.

Automation of a site vs a process

You can connect silos of automation with technologies like AGVs (Automated Guided Vehicle) or AMRs. You can analyse each process independently to see if automation is worthwhile. Some processes may be better done manually. Typical processes to automate include boxing and bagging, piece picking, transportation and sortation.

CAPEX vs REVEX

The payback period guides you on the potential values and automation technology. Some automation companies offer Robots-as-a-Service models, which allow you to lease the automation from REVEX instead of buying it from CAPEX, however these vendors are few and far between.

Future Trends and Technologies

The future for AMR technologies seems to be heading down the path of systems that combine all the different types of AMR together. You may store pallets on the ground and retrieve them with a shelf-based AMR system, whilst storing totes or individual cartons above in a mast-based ACR system. Ground based totes handling AMRs move individual boxes around on the floor and pass them to pick stations where items are picked and packed and then placed onto sortation AMRs.

There is also a push for mast based ACR systems to go higher and higher. However, with these systems you must be careful about the density of robots you have in a particular area, so going higher may not provide the desired benefits in some cases as you may hit throughput restrictions. 

Call to Arms

As shown in this article, different products, business requirements and constraints, directly impact the suitability of any automated solution. When searching for a new operational solution, it is crucial that you have an impartial third party to work with you, to help you navigate the options available.

Hatmill have run dozens of tenders and managed installations, for small AMR systems through to fully automated warehouses. When working with a customer, we ensure that:

• The relevant data is cleansed, analysed and shared with the bidders 
• Regular check-ins and workshops are held to ensure the bidders are proposing the most suitable technology 
• The bidders are challenged on both price and solution, ensuring that the technology provided is suited to the customer’s specific needs 
• A robust scoring system is used to remove bias from the equation and recommend the best solution
• A robust business case is developed which can be used for Board sign off and project approval

If you need any support with warehouse automation, please don’t hesitate to contact us.