Outline of TOF sensor
TOF (Time of Flight) is a method of measuring the distance to an object by measuring the time it takes for the light emitted from the light source to reflect off the object and return to the sensor (photodetector). is called
The direct translation of “Time of Flight” is “flight time”, but as the name suggests, distance is measured by the time of flight of light.
TOF focuses on the fact that the speed of light in the air (300,000 km/s) is always constant, and measures the distance based on the round trip time of light.
For example, if the time it takes for the light source to return to the sensor is 10 nanoseconds (hereafter, n seconds), the distance is measured by multiplying the one-way time of 5 nanoseconds and the speed of light of 300,000 km/second. . The calculation formula is as follows, and the distance between the sensor and the object is 1.5m.
- 5n (0.000000005) seconds x 300,000km = 1.5m
Conventional TOF sensors have the characteristic of being vulnerable to ambient light.
Ambient light is ambient light. For example, changes in light caused by non-lighting equipment such as factories affect distance measurement.
However, TOF type sensors that are resistant to ambient light have also appeared, and for this reason, the application of TOF type sensors is expanding beyond security cameras to automobiles and factories.
Advantages of TOF sensors
For distance measurement, there are BGS-type sensors in addition to TOF-type sensors. The BGS method is a method of detecting the distance between a sensor and an object at the light-receiving position on the light-receiving element. The longer the distance, the smaller the difference in the light-receiving position, resulting in a drop in long-distance measurement accuracy.
However, TOF always converts the constant time difference of the speed of light into the distance, so the detection accuracy is constant at both short and long distances. Therefore, distance measurement with high accuracy can be performed. In addition, you can measure the distance without problems even in a dark environment.
It also consists of a sensor (photodetector) and a light source and has the advantage of being easy to introduce with a simple device configuration.
Application of TOF sensor
Application of TOF sensor
| Application example | Purpose | Other requests |
|---|---|---|
| car monitor | Collision prevention/contact prevention | High reliability |
| smart airbag | child identification | Small |
| surveillance camera | Measurement of actual dimensions and prevention of prying eyes | outdoor installation |
| Automatic door | child protection | auto detect |
| store | People count in store | automatic counting |
| game equipment | contactless operation | Highly reliable and inexpensive |
| Vending machine/Information board | Gesture operation | inexpensive |
| robot | Automatic control | small speed of light |
| plant | automatic inspection | On-the-go measurement |
There are a wide range of fields in which TOF sensors are expected to play an active role, from automobiles to robots.
Other measurement methods have problems such as reduced accuracy in long-distance measurement and inability to use in dark places, so the TOF sensor, which can always maintain constant accuracy even when the measurement distance is long, is attracting attention. .
We have introduced the applications of the TOF sensor, but the application to automobiles cannot be put into practical use until it is confirmed that there is no danger in driving under the illumination of a light source. Due to reliability standards and legal issues, full-scale automotive applications are said to take time.
However, using a TOF sensor in a surveillance camera has attracted a great deal of attention as it is possible to easily calculate the actual size of an object. In recent years, TOF sensors have attracted attention due to the release of a gesture game called Kinect by Microsoft. If a game uses a TOF sensor like Microsoft’s Kinect, it must be a cheap product.
In addition, for quality identification in factories, it is necessary to use a TOF sensor that can measure while moving. Therefore, each manufacturer is developing various original sensors.
