Time of Flight Sensor – What It Is and the Working Principle

What Is a Time of Flight Sensor?

Fig 1: Closeup of the laser sensor of a factory machine

First, the time of flight (TOF) is the time it takes a wave, object, or particle to travel a given distance. Now, the time of flight sensors use light detection and ranging (LiDAR) technology to get the depth of a surface. The sensors illuminate infrared light on a surface and get fast and precise reflections to calculate individual point distances. Consequently, they’re able to map out an object precisely. 

How does a Time of Flight Sensor work?

The basic principle in working a time of flight sensor is the time taken between transmission, reflection, and reception. In other words, TOF sensors emit infrared laser light, which bounces back upon hitting a target object and is received by the sensor. The sensor will then measure the distance between the sensor and the object. 

Here, let’s look at ways a TOF sensor determines distances using travel time. 

• Using Timed Pulses

Here, the sensor emits laser light toward an object and uses a scanner to measure the reflected light. It then deduces the distance to the object using the speed of light and travel time. Additionally, it makes precise 3D surface representations and characteristics of the target to map out individual features. 

It uses the following formula to get distance: 

Distance = (Speed of light x Time of flight) / 2 

• Using Phase Shift of an Amplitude Modulated Wave

Fig 2: A laser lens

Here, a TOF sensor detects the phase shift of the reflected light using continuous waves to determine depth and distance. Then, it modulates the amplitude to create an oscillating form having a known frequency. With this, it uses the formula below to determine the shift in phase of reflected light. 

C = λ * f

Where C = speed of light

            λ = wavelength (15m)

            f = frequency

With the information, it can easily find out the depth of a surface by calculating the distance to each point. 

Advantages and Limitations of Time of Flight Sensor

Advantages

• Compared to various distance sensors such as laser or ultrasonic, TOF sensors compute 3D images more quickly and precisely. 
• Second, It uses laser technology to measure long ranges and distances precisely. 
• Third, TOF sensors are safe as the low-power infrared laser light won’t harm your eyes. The sensors achieve Class 1 Laser Safety Standard to ensure your eyes are safe. 
• Fourth, It is relatively cheaper than other 3D depth range-finding technologies. 

Limitations

• TOF sensors may fail to work correctly when you use them close to very bright surfaces. External bright light can scatter excessive light into the receiver, resulting in wrong measurements.
• Second, It may give wrong measurements when used on areas of multiple reflections, including corners. 
• Third, TOF cameras are affected by intense sunlight and may give wrong measurements in sunny settings. 

Time of Flight Sensors Examples

Fig 3: Close-up of product, which is on a Smart factory assembly line equipped with sensors and pneumatic equipment

RPLiDAR A1M8-R6 360 Degree Laser Scanner Kit – 12M Range

It’s a cheap 360-degree 2D LiDAR scanner solution by SLAMTEC that can perform a 6-meter 360-degree scan.

Additionally, it’s a laser triangulation measurement system that excels in all sunlight-free settings. You can use it in localization, environmental/ object modeling, and mapping.

RPLiDAR S2 Low Cost 360 Degree Laser Range Scanner – 30M Range

It’s another low-cost 360-degree 2D LiDAR ranging radar that performs a 30-meter radius Omni-directional laser distance scan. It works best in practical applications, including map positioning, surveying, and navigation. 

DepthEye S2 -H67° x V51° VGA ToF Camera with Sony IMX556PLR DepthSense

Fig 4: Social distance alarm using a distance sensor

The DepthEye S2-H67 is a fully integrated optical TOF sensor with DepthSense VGA time of flight pixels.

The sensor measures reflectivity and distance with VGA resolution within 0.5m to 4m.

Additionally, they’re ideal for robot obstacle avoidance, object recognition, and volume measurement.

HPS-3D160-U Solid-State LiDAR

It is a modern, high-performance LiDAR TOF sensor with low-distortion infrared lenses.

They have an optimized lighting system and can rely on a 90 percent reflective white surface to measure up to 12m.

Furthermore, the TOF sensor has an advanced data process, excellent processor, compensation algorithm, and filter.

All these factors combine to give you stable and concurrent measure data output. 

TFmini S LiDAR module – Short-Range ToF LIDAR Range Finder

It’s a TOF sensor emitting near-infrared rays and measures phase differences between the incident and reflected rays to get the distance.

However, its LiDAR principle may trick it into giving wrong measurements between transparent objects like glass or water.

Regardless, it’s very sensitive to measuring real-time distances between moving objects.

Grove – Time of Flight Distance Sensor(VL53L0X)

The Grove is an excellent, fast, accurate, long-range TOF sensor based on the new generation VL53L0X module. It incorporates a Single Photon Avalanche Diodes (SPAD) array and other technologies to measure distances of up to 2m.

Furthermore, its emitter is invisible to the human eye and has excellent internal infrared filters. 

Slamtec Mapper M1M1 ToF Laser Scanner Kit – 20M Range

Fig 5: Robotic vision sensor camera system in intelligence factory

The Slamtec Mapper has a detection range between 20 and 40 meters. The M1M1 has real-time localization and navigation capabilities in addition to being a laser range scanner.

It has high-quality mapping and can readily map your house or place of business. 

It allows big working situations above 100,000 square meters and indoor and outdoor mapping.

The ideal laser scanner for robotic localization and navigation, environmental surveying, and mapping, among other things.

Opene8008B – QVGA Time-of-Flight Sensor Evaluation Kit

It’s an excellent TOF camera that you can use to get depth images. It has an Opene8008B – QVGA chip capable of achieving a 320×240 coupled with capable hardware.

You can connect it to your PC for the recording of depth map data and real-time data. Additionally, they have a range of 5 to 7 meters, with some achieving ranges of up to 10m.

Conclusion

You can use Time of flight (TOF) sensors in many practical applications.

They’re efficient for 3D mapping, obstacle detection, industrial automation, gesture recognition, volume measurement, and autonomous vehicles. 

You have to study your project and know the type of sensor to use. Finally, contact us today for more information about this sensor.