Outdoor Mobile Robots

Outdoor autonomous robots WANTED ? .. it's true... ?I receive many enquiries every year.

It makes sense: ?When is it suitable to deploy a mobile robot system?

Mobile Robots are best deployed when they perform low value-added tasks.

In fact, outdoor transportation sometimes requires long distances needing extended periods of time for performing missions.

In Movincar, we have installed several AGVs/AMRs in for outdoor applications.

?Check the video here

For example, this is the first outdoor tractor that we installed 5 years ago… yes… long time for such an innovative and changing industry. As you can see this agv has a safety bumper and follows a track...

Many things have changed since then.

Mobile Robots (AGVs or AMRs) are a great option for outdoor applications but must overcome specific challenges such weather conditions, floor wear or heavy load vehicles traffic. ???????????.

Of course, the WEATHER is the main driver that will define the self-driving robot performance.

Regardless its "shape": Tow tractor, Last Mile Delivery Robot, Forklift, Plarform, etc.

An Outdoor Mobile Robot System must drive safely and independently considering all types of weather conditions.

It seems obvious, but it isn’t.

There are two key elements to consider:

I said that they must “Drive”: ?How do robots navigate? What are the best navigation technologies for outdoor applications?

I also said “Safely”: Very simple: Mobile Robots must avoid the risk of personal injury.

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Outdoor Mobile Robot Safety

Let’s start with the big boss. The Safety Scanner of the Autonomous Vehicle

You already know it, safety is essential.

Mobile Robots must comply with the most exigent safety rules regardless the weather conditions or other area considerations for the application.

There are two main types of Safety Sensors for mobile robots:

• Sensors that avoid contact (safety laser scanners)
• Contact Sensors (bumpers, safety edges, etc)

I will not explain the second type at length, because even if bumpers are considered safety certified, the mobile robot must travel very slowly to avoid harming someone in case of contact.

Let’s focus on Safety Laser Scanners.

Nowadays, almost every self-driving robot counts on Safety Laser Scanners to avoid any or all contact between the robot and the surrounding people or structures.

The detection field dimension and shape must be coordinated with and match the vehicle speed and load inertia.

So, if the robot is running fast, protection field must be longer than a protection field at low speed.

Obviously, Safety Laser Scanners must be reliable and sensible.?Like other Safety Sensors, they must comply with the Standard 62998-1:2019 (Safety of machinery – Safety-related sensors used for the protection of persons).

So, here is the first problem related to weather: “The Sensibility” of the Safety Laser.?

If it rains, the Safety Laser could detect raindrops and identify them as obstacles. We have the same problem with fog, snow, natural sunlight or due to dust or particles in the air.

An Outdoor Safety Laser must be sensible and smart enough to identify real obstacles, but it must be able to filter environmental influences that are not a real risk.

Luckily, SICK has developed the outdoorScan3 safety laser scanner that protects people in a wide range of mobile and stationary outdoor applications in harsh weather conditions.

Click here to watch the video

The outdoorScan3 is rated PLd accordingly with ISO 13849-1 (Safety-relted parts of control systems)?and with IEC 62998 (Safety of machinery - Safety-related sensors used for the protection of persons) specially for outdoor areas.?

Ok, let’s imagine that we have a Safety Laser like the outdoorScan3 able to filter those external influences.?

The first question would be: Your sensors filter rain... but: How much rain?

Some Outdoor Safety Scanners ensure 10 mm/hour. Great again! But how much is that??

I have only found this explanation:

• ?Moderate rain: Greater than 0.5 mm per hour, but less than 4.0 mm per hour.-
• ?Heavy rain: Greater than 4 mm per hour, but less than 8 mm per hour.
• Very heavy rain: Greater than 8 mm per hour.

If you are managing a factory, you probably won’t have time to discuss with your robot supplier situations in which the AGV stops because of rain… it was raining 10 or maybe 20 mm/hour? Who knows?... and who cares?

If possible, you should define with your supplier from the start what are the possible and acceptable weather limitations.

Another solution is to place a Weather Station to justify the limits of the vehicle.?

I’m talking about rain, but the external weather influence happens the same with fog or sunlight. How “dense” is fog? How to measure lumens? How does sunlight direction influence the performance? Critical moments are sunrise and dawn when sunlight arrives parallel and “blind” to the scanner.

The weather conditions will also define the way that the AGV/AMR works in general. Is the floor wet? How slippery is the wet floor? A wet floor is very important to how the AGV/AMR moves and navigates.

Whatever the “weather” reason, be ready to have a backup plan in case the mobile robot stops.

I have said that the mobile robot must stop as soon as the Safety Scanner detects an obstacle in the Emergency Area, before contacting that obstacle.

The distance from the stop command to the effective vehicle stop, will depend on “reaction time” (that it is certified), the vehicle speed, the vehicle load inertia and the floor conditions (roughness, slippery, etc).

Your mobile robot supplier must perform a Safety Risk Assessment, together with the Customer HSE people to determine max speed on each track and related Scanner Safety Field.

This analysis must be done taking into consideration any possible floor conditions.

Of course, it is necessary to think of what happens in case of icy floors as well. Human operators can decide to go faster, slower or to brake before or later.

What is the best Navigation technology for an Outdoor Mobile Robot?

We already have a Safe Robot. Now we need self-driving robot able to “drive”. In the mobile robot world, “drive” means “navigate”.

There are several Navigation Technologies available for Outdoor applications.

1. Magnetic
2. SLAM or Natural with 2D or 3D LiDARs
3. GPS
4. Combination of different technologies

Outdoor AGV with Magnetic Navigation

Magnetic Navigation is very reliable. It simply works well and works consistently.

The robot has a magnetic sensor and follows a magnetic tape embedded in the floor.

If you have an AGV with magnetic navigation you can be sure that you will not have any kind of problems related to navigation. Magnetic navigation does not care about weather… rain, fog… it does not matter.?It simply and efficiently works.

Nevertheless, there are several disadvantages.

The main drawback is the installation cost. Because of the necessity to embed the magnetic tape in the ground there is a high cost for installation, particularly related to longer tracks.

Another drawback is that it is not flexible, I mean, it’s hard to modify after installation.

It is necessary to mill the floor and replace the magnetic tape in its new location.

There are two types of magnetic tape, the “flat” and the “square”.

• The flat tape is 2’’ wide x 0,12’’ thick (50 mm x 3 mm). It is necessary to perform milling of 4’’ wide x 2,6’’deep (100 mm X 60 mm) to place the tape in. Once the tape is placed it is necessary to protect the track with specific outdoor resins.??

You can spend around 20 USD every 3,2 feet (near 20 €/m) for the milling and resin work. If you add around 9 USD each 3,2 feet for magnetic tape cost, you’ll have nearly 10 USD/ft of installation cost.

• There’s another type of tape that is smaller and squared with dimensions near 0,2 inch x 0,2 inch (5mmx5mm). In this case you only have to mill a slot of 0,15” wide and 0,5” deep (4,5mmx7mm) and embed the tape. The tape remains fitted in the slot and it is not necessary to resin the surface. This is a cheaper option though alteration is still difficult.????

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LiDAR, SLAM, Natural for Outdoor Navigation

The term SLAM is the acronym for Simultaneous Localization And Mapping.

Check Navya-Charlatte Tow tractor video

A SLAM AGV is able to map the environment and localize itself in that map without using fixed navigation elements such magnetic tapes or laser reflectors.

SLAM is a calculation technique that considers inputs arriving from navigation sensors.

Autonomous Vehicles perform LiDAR sensor technology. A LiDAR measures distance to a target by illuminating it with laser light and measuring the reflected light with a sensor.

Differences in laser return specifications (timing, wavelengths, etc) can then be used to make digital 2-D or 3-D representations of the target.

Outdoor applications generally have well defined contours (walls) and generally are less chaotic than indoor applications. Of course, there will be external traffic but, in general, it’s easier to find fixed references to perform the navigation.

Nevertheless, LiDAR+SLAM should be implemented together with other IMU sensors (inertial measurement unit) and GPS technology to provide better accuracy in the vehicle positioning.

The main problem with LiDAR in outdoor are wide open spaces with far walls or contours that could be difficult to reach with laser. As anticipated, in this case, you'd probably need other natural navigation such GPS.

One of the most important advantages of this Navigation Technique is that the associated installation is relatively easy and not too expensive. It is possible to track several miles in one day.

Another important advantage is that it is easy to modify these tracks.

Same as the Safety Sensors, the LiDAR sensors must be good enough to avoid outdoor problem.

• Resistance to Ambient Light. Intense sunlight could blind the LiDAR sensor making it unable to identify its own light beam. It should be necessary to have LiDAR resisting around 70.000 lumens.
• Resistance to Environnmental Noise. LiDAR sensors must be able to filter environmental noise such raindrops that could create navigation issues. These false inputs are called ECHOs and LiDAR that is able to deal with this issue performs Multi-echo technology.
• Environmental IP protection. IP is a two-digit number established by the International Electro Technical Commission, is used to provide an Ingress Protection rating to a piece of electronic equipment or to an enclosure for electronic equipment. LiDAR laser should be IP65 or IP67.??
• Temperature Operation Range. Temperature affects laser functionality. Extreme cold or heat could damage sensors. Ask your mobile robot supplier to indicate the Operating Temperature Range of its robot

One of the main drawbacks of ?many LiDAR based vehicles is its reliability in chaotic indoor applications.

If you keep the robot outdoor with well-defined contours, everything should work. The problem is if you wish to use the robot also indoors in an extremely variable environment. If the indoor application is complex and chaotic, the vehicle could have navigation problems without any environmental reference.

Outdoor mobile robot with GPS Navigation

GPS systems provides accurate position and speed in all weather conditions anywhere when at least four satellites are available.

Galileo is the European Global Navigation Satellite System. There are currently three other systems: from the US (#GPS), Russia (#GLONASS), and China (#BEIDOU).

However, GPS could have problems in urban and indoor areas where satellite signals are unreliable or unavailable.

Combination of different Navigation Systems – Sensor fusion

Mobile Robot Suppliers use to work on multi-sensor integrated navigation systems for both outdoor and indoor environments that uses GPS or LiDAR as aiding systems to alternatively provide periodic corrections to Inertial Measurements.?

It is also possible to switch from LiDAR or GPS to magnetic navigation when passing from outdoor to indoor.

Outdoor Mobile Robot Management System?

?I have to say that this is a pain point. ????

? How do you send orders to a mobile robot that is working outdoor?

? How do you manage traffic?

Whatever the type of robot or navigation technology, you need a “brain” that manages the mobile robot system.

In general, the indoor robots are connected to a Management System that assigns missions, manages traffic, and interfaces the robotic System with other Local Systems such PLCs, ERPs, WMS, etc.

Typically, these Management Systems are connected via WiFi.

So, What happens if you are outdoors?

There are three options:

1. You can install an outdoor wifi net… of course it is a complex and expensive solution if you have to cover a large working area.
2. ?You could use a cloud-based management system. This solution is more and more reliable and it can deliver high security connections together with top technical features. ?The problem is that there’s still some reluctancy to have an “external” or “cloud” management system.
3. ?You simply could have stand-alone robots without central server or Management System, but in this case, you will have limited management options.

Think about this situation:

You have a big Automotive Production Area where there is a main Automotive Manufacturer and several TIER1 suppliers in the same industrial area connected with internal roads (not public). There would be hundreds of Tow tractors transporting material from Tier1 suppliers to the Automotive Manufacturer.

Imagine that you want to deploy some outdoor tow tractors to cut logistics cost. Well, you’d probably have a problem because the Tier1 will have its own WiFi net, then the AGV will go outdoor where probably there is not good WiFi coverage and in the Automotive Manufacturer there will be a different WiFi net.

In which WiFi net would you install a centralized Management System?

Types of Mobile Robots for Outdoor Applications

There are three main types of mobile robots for outdoor applications:

Tow tractors

Some suppliers can convert a manual tow tractor into a driverless outdoor tow tractor.

Check here TLD-Easymile Tractor

A manual Tow Tractor able to work in outdoor conditions should be able to do it in Automatic mode.

Tow tractors are already equipped for outdoor with rubber wheels and cabins where electronic cabinets can be installed. Moreover, tow tractors are widely used to transport convoys up to 44.000 lbs (near 20 Ton).

Unit Load Robots

There are several Unit Load mobile robots in Outdoor applications already existing. In general, these vehicles are “custom made” and transport material with roll conveyors or other transfer devices.

Check here DTA Video

Automatic forklifts

There aren’t many, but there are some outdoor forklifts working out there. In fact there isn't reason why an automated forklift should not work outdoor.

Outdoor Service AMRs

Autonomous Navigation enables many new applications:

• Security Robots
• Las Mile Delivery Robots
• Military Robots

etc...

Conclusions

Summing up, while mobile robotics is improving and becoming user friendly, some new applications are rising.

Outdoor mobile robotics is already here… there are many challenges to overcome… but there are tons of applications where mobile robotics can support outdoor activities.

Do not hesitate to contact me if you wish to know more about Outdoor AGVs and AMRs