Making ToF Sensor Arrays for Collision Avoidance Systems in Mobile Robots

Mobile robots are fast becoming a vital tool to maximize operational efficiency. However, to ensure their safety and reliability, collision avoidance systems are required, which can be complicated and expensive. Flexible Time-of-Flight (ToF) sensor arrays can offer an easy and cost-effective solution to this challenge.  

Today, automation and robotics are trending topics in operational efficiency. Robots seem to be making an appearance everywhere, from warehouses to laboratories and even homes. Robots help get things done more efficiently, while also ensuring less money is spent in the process. Robots provide additional advantages – like the fact that they can do dangerous tasks and reach places humans can’t. These include tight spaces and remote sites. Additionally, robots can even operate in the air.1,2

Sectors like transportation, logistics and manufacturing already widely use mobile robots for inspection tasks. It is critical to note that mobile robots are here to stay – and avoiding them could leave any organization at a significant disadvantage compared to their competitors. 1,2

Mobile Robots Need to Move Quickly and Accurately

To function safely and efficiently, mobile robots require real-time anti-collision systems. These robot collision avoidance systems ensure enhanced safety for people that work in the same areas, while also preventing expensive repairs to the robot and the goods they are carrying. 1,2

Anti-collision systems are not just for indoor ground robots. Air-borne drones also need to avoid objects that may be in their path while flying, including branches, buildings, and even other drones. Furthermore, drone collision avoidance systems can help prevent drones that inspect facilities and infrastructure from crashing into the object they are examining.3

For mobile robot obstacle avoidance, laser technologies can prove highly effective. However, these technologies can pose a risk to eyesight. While some drones use rotating LIDAR anti-collision systems, since the moving parts in these systems could be more prone to failure, this can result in costly repairs.1-3

Time-of-Flight Sensors Provide a Complementary Anti-Collision System

Beams of light are used by ToF technology to detect objects. Assuming there is an obstacle in front of the robot, the sensor sends continuous, modulated beams of light and measures the phase of the reflected light. The light then bounces back to the sensor, utilizing the phase shift between emitted and received light. This provides a calculation of the distance between the robot and the obstacle.4

However, a ToF single module is only able to provide limited coverage by using beams of light. To overcome this disadvantage, careful placement of multiple sensors can be used to increase coverage significantly. This is a cost-effective solution that identifies obstacles that are above or below the coverage of the 2D laser scanner.

As compared to existing 3D technologies, ToF multi-directional arrays are equipped to provide a simple obstacle detection system with the help of careful sensor placement. What’s more, this arrangement also consumes less energy and can be manufactured at a fraction of the cost. The use of multiple ToF sensor modules ensures a complementary system that is capable of covering blind spots that may exist in the main anti-collision system.

Further, the presence of multiple beams pointed in different directions allows the system to scan the ground for small obstacles below the laser’s field of view. This also ensures detection of objects above its field of view – which could potentially collide with the chassis or payload of the robot.

Lastly, ToF solutions using infrared light, such as those produced by Terabee, are safe for the eyes, and function well in all indoor lighting conditions.

Figure 1. Left: Anti-collision system using a laser scanner. Right: Example of object detection using TeraRanger sensor arrays. Image Credits: Terabee


Building the Perfect ToF Sensor Array for an Anti-Collision System

Terabee’s TeraRanger Hub Evo is the ideal platform for the development of multi-sensor ToF arrays. The TeraRanger is a lightweight, compact board connecting up to eight ToF sensors. Furthermore, this platform provides almost unlimited sensor placement flexibility, ensuring the construction of a lean, custom sensor array with the exact coverage needed. The Hub Evo can even be combined with other technologies to improve coverage.5

Combining the TeraRanger Hub Evo with other complementary technologies for improved coverage.

Figure 2. Combining the TeraRanger Hub Evo with other complementary technologies for improved coverage. Image Credit: Terabee.

The Hub Evo adopts a plug and play approach that is compatible with the Evo 60m, Evo 3m, and Evo 600Hz. This ensures a choice between sensors, which can be plugged in and the system can then be tested.

For any reason, if the fit isn’t right, the configuration can be changed just as quickly and easily to optimize the ToF sensor array for anti-collision applications. Any problems with cross-talk are eliminated because the Hub Evo synchronizes the distance measurements from each sensor.5

Custom sensor arrays with TeraRanger Hub Evo.

Figure 3. Custom sensor arrays with TeraRanger Hub Evo. Image Credit: Terabee.


In the case of smaller robots that require indoor anti-collision solutions, the TeraRanger Multiflex provides a flexible multi-directional sensor ToF system. The equipment weighs just 20g. The pack features up to eight short-range (up to 2 m) ToF sensor modules on flexible ribbons, ensuring the right placement of sensors as per requirements. The hub can simultaneously measure distances from all the sensors, while it skillfully avoids cross-talk.6

custom sensor arrays

Image Credit: Terabee.

For both large and small indoor mobile robots that operate on the ground, the TeraRanger Hub Evo and TeraRanger Multiflex are both great anti-collision systems. But what about robots that operate in the air?

ToF Sensor Arrays for Drones

A great, lightweight anti-collision system for drones is the TeraRanger Tower Evo. This system can detect multiple objects in a range of 0.5 to 60 m, while being fully operational both indoors and outdoors, as well as in complete darkness or bright sunlight. Owing to its rapid update rate (up to 120Hz), drones using this technology can even detect and avoid moving objects.7

Unlike a rotating system, the TeraRanger Tower Evo does not depend on moving parts to provide complete coverage, so it is not prone to failure. What’s more, being lightweight (132g) helps minimize battery drain and maximize flight times. The system is modular, providing a choice between 4 or 8 sensors depending on a client’s needs.7

sensor arrays drones

Image Credit: Terabee.

Terabee Provides a Cost-Effective Solution for Every Robot

White it is clear that robots are the future of efficient operations, it is critical to ensure that they can work safely and effectively. To achieve this, robot collision avoidance systems are essential, but they do not need to be expensive or complicated.

ToF sensor arrays have a demonstrated track record in getting the job done easily and cheaply. As leaders in the ToF industry, Terabee provides a range of flexible, lean solutions that works for all robots and all companies.

References and Further Reading

  1. ‘Industrial Automation and Robotics: An Introduction’ — Gupta AK, Arora SK, Riescher Westcott J, Mercury Learning & Information, 2016.
  2. ‘Introduction to Autonomous Mobile Robots’ — Siegwart R, Nourbakhsh IR, Scaramuzza D, MIT Press, 2011.
  3. ‘Drone Collision Avoidance for Beginners’
  4. ‘Time-of-flight principle’
  5. ‘TeraRanger Hub Evo’
  6. TeraRanger Multiflex
  7. TeraRanger Tower Evo

This information has been sourced, reviewed and adapted from materials provided by Terabee.

For more information on this source, please visit Terabee.


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