Both AMRs and AVGs are efficient automated goods transportation systems

AMR vs. AGV: differences and which is better

24 June 2021

Implementing automated goods transportation systems, such as AGVs (automatic guided vehicles) or AMRs (autonomous mobile robots), is an extremely efficient way of connecting the various areas of a warehouse or logistics or production center. Just like automatic conveyors, they are used in environments with continuous and repetitive material flows, thereby saving time, boosting productivity, and reducing accidents. 

AGVs, automated vehicles that move in a guided way, have dominated the market over the past few decades. Nevertheless, in recent years, they’ve come up against a formidable competitor: AMRs, also known as autonomous intelligent vehicles (AIVs), which move and operate without preset routes.

But what are the differences between these two automated transportation systems? Will AMRs end up replacing AGVs? Which transportation system is better? We break it all down in this post.

Navigation system: guided vs. autonomous

The main difference between AMRs and AGVs lies in the navigation system they use. While AGVs travel along a predefined route that they detect with laser- or wire-guided systems, AMRs adapt their routes according to the information they receive from their environment in real time. Additionally, AMRs are connected with the warehouse management system (such as Easy WMS from Interlake Mecalux) as well as with the company’s ERP to determine where to go at every turn. 

This way, and with the help of technologies such as AI and machine learning, AMRs can configure their route through the facility by means of preloaded layouts, without the need for rails, wires, magnetic tape, or sensors. And that’s why these mobile robots are called autonomous. 

AGVs, meanwhile, incorporate minimum intelligence and move in a guided way along a closed circuit, obeying simple programming instructions that they read via RFID or receive by Wi-Fi.

Adaptability: closed circuit vs. open circuit

As AGVs move along a closed circuit, they’re highly efficient when traveling along a route that’s been defined in advance and doesn’t need to be changed. This means that, when they come across an object that obstructs their movement, such as a box or pallet, they stop immediately to avoid collision and wait for the object to be removed. 

On the other hand, by using AI and their integrated cameras, sensors, and laser scanners, AMRs, can create an alternative route if met with an obstacle. In fact, AMRs are constantly modifying their routes to follow the one that’s most efficient. Hence, they’re considered a more flexible automated transportation system than AGVs.

AGVs follow a closed, predefined circuit at all times
AGVs follow a closed, predefined circuit at all times

Price: cost per robot and cost of installation

Normally, the cost per robot of AGVs is lower than that of AMRs. Nevertheless, it’s important to note that AGVs make it necessary to modify the infrastructure to install the wires or magnetic tape that enable the vehicles to navigate. These adaptations to the warehouse account for an additional cost on top of the unit cost. 

In contrast, AMRs have a higher unit cost than AGVs, but no major changes to the facility are required. The warehouse flooring, however, does have to meet certain requirements to ensure that travel is smooth and steady.

When assessing the overall price of one system compared with the other, you need to consider the number of units to install and how easy it would be to make changes to the logistics center. If you’re planning on building a new warehouse with continuous material flows, you’ll get more bang for your buck with AGVs. If, on the other hand, you have a facility with variable flows that would be difficult to revamp, AMRs would be a more reasonable investment.

Safety: predefined route vs. improvisation 

Both systems are extremely safe thanks to their numerous safety devices and accessories, such as laser sensors, cameras, protectors, etc. 

AGVs provide an increased sense of safety by moving along a preset route, because the operators know the path by heart and just how the robots will behave at all times. 

The behavior of AMRs, meanwhile, is more unpredictable, with changes in direction and sudden stops when they come across an object in their path. They do, however, always ensure accident-free circulation.

In any case, it can be said that a robot or vehicle equipped with multiple sensors is generally safer than a human being at the wheel of a forklift, as this person is exposed to distractions and liable to make mistakes. Either way, employees should familiarize themselves with the way in which AGVs and AMRs work so that they know how to behave in their vicinity and how to stop them in the event of an emergency.

The path of AMRs is extremely flexible as well as safe
The path of AMRs is extremely flexible as well as safe

Speed and load capacity: heavy vs. light goods

In the beginning, AMRs were used especially for transporting lighter loads (for example, boxes), while AGVs were tasked with automatically moving pallets. Over time, AMRs were overhauled and tweaked, and nowadays, the major AMR manufacturers offer vehicles prepared to transport pallets bearing heavy weights. 

Both automated transportation systems can be personalized, adapted to the needs of each customer. As a rule, AMRs have capacities of between 1.65-2.2 tons, while AGVs can transport up to 5.5 tons. 

As for speed of movement, this feature is similar in both transportation systems, reaching 6.5'/s. The speed is also subject to the particular needs, the load, and the space for which the vehicles are used. 

Other types of automated transportation systems

In addition to AMRs and AGVs, there are two other automated goods transportation systems on the market that are often found in warehouses with a high degree of automation and product movement:

  • Conveyors. Conveyors consist of a set of rollers that carry the load and propel it along a circuit. The system is equipped with electric motors that move the unit loads in a safe, controlled way. They work by means of the warehouse control system (WCS), which is responsible for executing the movements and following the orders given by the WMS. 
  • Electrified monorails. This system is comprised of automated trolleys with two modes: aerial and floor-mounted. They move along an electrified rail and, just like conveyors, require a powerful WCS connected to the warehouse management system (WMS). 

Both automated transportation systems can be integrated with various elements (roller, chain, turntable, and vertical conveyors, among others) that combine or connect different areas in the facility, according to the load handling needs.

The main advantage of these systems compared to AGVs or AMRs is their high transportation capacity and speed. Their most evident drawbacks are that the conveyors form a fixed circuit (leaving little room for improvisation), and they can occasionally hinder the passage of operators.

AGV vs. AMR: which is better?

All in all, the factors that really determine which automated transportation system is best are those having to do with the company’s objective, scope of application, and logistics planning. AGVs and AMRs both have their strengths and weaknesses, so depending on the application and environment, one of them will be the most appropriate. 

In other words, if the project requires long trips with various routes that don’t always follow the same pattern, or the center has multiple obstacles, AMRs are the most suitable. An example of this is the new warehouse of Normagrup, the leading Spanish firm in the emergency lighting market. Our company equipped the center with an automated storage and retrieval system (AS/RS) connected to the production lines by four autonomous intelligent vehicles (AIVs). Every time a kit is assembled, Easy WMS notifies the software that runs the AMR for a vehicle to pick up the kit and bring it to the production line that requires it.

As for AGVs, they’re ideal when it comes to traveling long distances free of obstacles that are defined in advance and aren’t expected to be changed. They’re also more economically viable when implemented in new buildings, as warehouse activity doesn’t have to be halted when installing the wire-guided system in the floor. This is the case of the project our company carried out for French paper manufacturer Clairefontaine. An aisle was opened up on one side of the warehouse where only the AGVs that move the goods from the production center to the warehouse can circulate.

So, when should conveyors and electrified monorails be used? Both systems have the same benefits as AGVs and AMRs in terms of automated goods transportation, their versatility when designing different routes, and their safety, in addition to being more affordable. That said, their disadvantage is that they limit the space available for the passage of operators and forklifts. 

Conveyors are especially useful for covering long distances, although they do occupy a fixed space. This is illustrated in the warehouse our company built for Venis (Porcelanosa Group), where an underground tunnel equipped with roller conveyors spanning over half a mile long connects the facility with the production plant. 

Electrified monorails, meanwhile, are recommended when you need more agility. This can be seen in Sokpol’s juice warehouse in Poland, connected to the production center by an electrified monorail circuit. This transportation system reaches 328'/min and guarantees continuous goods flows.

Automatic roller conveyors for pallets serve the same function as AMRs and AGVs
Automatic roller conveyors for pallets serve the same function as AMRs and AGVs

Automated transportation system for every need

All automated transportation systems have their pros and cons, which you should take into account when setting up any kind of logistics facility. AGVs will help you to speed up internal transportation between areas where the path is free from obstacles, while AMRs will be very efficient at connecting zones with busier traffic and changing routes. 

To make the right choice that will let you increase your throughput and minimize costs, it’s advisable to consult a company that’s an expert in logistics support and that can set up your project with any type of automated transportation system on the market. Interlake Mecalux fits the bill: we’re specialists in integrated logistics solutions, providing highly tailored storage systems that aim to maximize the efficiency of each process. Looking to boost your supply chain? Get in touch. We’ll give you advice and come up with the best solution for your needs.