Control and navigation of AGVs and AMRs

Transport trolleys are nothing new in production facilities, but as automation solutions develop, self-driving vehicles are slowly starting to dominate this space. AGVs have evolved rapidly in recent years and initially could only move between well-defined points along a set route. AMR vehicles, also known as mobile transport robots, are becoming increasingly popular. Not only can they autonomously determine the most ideal route, but they can also modify it in real time if unexpected obstacles arise along the way.

At first glance, automated guided vehicles (AGVs) and their evolution, autonomous vehicles (AMRs), are no different. So are the tasks they face. The main difference between these vehicles is how they are controlled and navigated. In this regard, the greater flexibility of AMR vehicles makes them the transport vehicle of the future for industrial plants or warehouses.

●Self-propelled transport vehicles are increasingly popular in production plants and warehouses

●The main difference between AGV and AMR comes down to their control and navigation.

●AGV requires additional markers to move.

●AMR is an autonomous vehicle that can decide the best route independently.

The basic difference between AGV and AMR

AGV (Automated Guided Vehicle) consists of a main controller, data communication unit and loading station. These vehicles (usually forklifts of electromechanical design) move on prescribed routes and are oriented using free navigation of natural features (geographical coordinates). Some older technology AGVs still use laser-guided navigation systems with external targets.

AMRs( autonomous mobile robots or autonomous forklifts) on the other hand, rely more on flexible navigation (SLAM, AI or perceptual learning systems) with LiDAR (Light Detection and Ranging) and camera technology and do not require additional infrastructure. QR codes posted on the warehouse floor can also be used for fine positioning.

How does AGV move?

As you can see, the basic difference between AGV and AMR trolleys is the way they move, more precisely the control and navigation. The AGV trolley keeps moving along the same route, which is correctly marked. If any modifications to the route are required (because of changes in the production process or the emergence of new facilities in a given hall), it will be necessary to adapt the infrastructure accordingly. Depending on the AGV navigation method, the setup of this new path may be more or less time-consuming and may even require structural changes to a given hall.

In order for traditional AGV transport vehicles to move independently, lines or special markings need to be installed on the floor;

Standard AGVs move along pre-marked paths, but the way they are laid out may vary. Therefore, every time you change the route, you need to set up a new route.

Induction Loop

In this method, cables are embedded in the floor of a hall through which a current of a certain frequency flows. It then generates a magnetic field, which is detected by magnetic sensors on the vehicle. By continuously measuring the magnetic field strength, the AGV moves in the direction in which its value is always as high as possible. Interestingly, using modulated magnetic fields, specific commands can be sent to the AGV controller.

Magnetic Ring

Thanks to the magnetic tape (made of ferromagnetic material) attached to the floor, the magnetic sensors placed on the trolley transmit the appropriate signals to the vehicle's control unit. This approach is very precise, allowing for example the detection of intersections and better positioning of AGVs. Therefore, higher travel speeds can be developed. The disadvantage of this solution is the relatively low durability of the magnetized tape stuck to the floor. It needs to be updated regularly.

Reflective and Optical Circuits

Also in this method, tape is placed on the floor of the hall or a line is painted. The reflection method utilizes the reflection of light emitted from the vehicle. After sending and receiving reflected light, determine the position of the cart relative to the painted or glued line.

In the optical method, the path is painted in a color that has a different contrast with the rest of the floor. Cameras on the vehicles constantly monitor the route of the main line, allowing the position of the AGV relative to the path to be determined. Like magnetic rings, lines that are glued or painted onto the floor will need to be updated from time to time.

Location-Specific Markers

This method is not based on tracking paths, but on points (markers) placed at specific locations in the hall. The AGV vision system or laser scanner finds these points and uses them to determine the truck's current position. The more markers placed on the hall, the more accurate this method will be. The greater the distance between these points, the greater the risk of positioning errors.

How does AMR move?

Developments in the field of AGVs mean that their levels of autonomy are increasing so that they do not require physically marked paths. What's more, they can quickly adapt to changing environments and emerging objects.

For navigation, AMR vehicles use preloaded maps of a given facility, or so-called natural navigation. To do this, a test drive is first carried out, during which precise terrain mapping is carried out (so-called environmental mapping). For this purpose, the necessary elements of an AMR device are sensors, software to process the acquired data, and a vision system that can be created by cameras, lasers, a combination of cameras and lasers, or LiDAR technology.

With such an accurate map of the facility, AMR can set a different optimal route every time. This is important if there are people in the facility, other vehicles are moving, or various factors may be in the way. Each time the AMR carefully scans the surrounding environment in front of it and compares it with the map produced in real time. It is therefore able to detect obstacles and avoid collisions, and the control unit can quickly correct its trajectory. Even if a facility is very crowded, if there is any free corridor, the AMR will be able to find it and proceed, maneuvering between obstacles. If the road is completely blocked, the vehicle will stop and start again as soon as the road clears.

Any major changes to facilities are not a big deal when using self-driving cars. All you have to do is do another test run, during which AMR will remap the space. After this treatment, he will again be able to move accurately within a given area. Importantly, each new AMR vehicle takes a relatively short implementation time, is free, requires no changes to infrastructure, and can be executed without disrupting production.

The future of self-propelled transport vehicles

Autonomous transport vehicles are still in the development stage, so you can expect more great solutions in the near future. Of course, fast, precise and conflict-free routing will remain the primary requirement for AMR vehicles, but in factories with large numbers of such trucks, high throughput of the transport system will also become increasingly important. Of course, internal transportation will develop in this direction. This is important because AMR vehicles will be an important part of Industry 4.0 and future smart factory concepts, where the role of humans will be restricted to a minimum.

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