Transfer from [ http://www.sohu.com/a/127225089_296134]
TOF technology principle
ToF is the Time of Flight Abbreviation, literally translated as time of flight, by the target transmission optical pulse succession , then the sensor receives light returned from the object , by detecting the transmitted and received light pulses flight (round-trip) time to obtain the object distance .
Military and industrial laser radar (the LiDAR) used on unmanned vehicles ToF technique to be employed, the feature quantity with a laser beam to detect the target position, velocity, etc., in conjunction with the laser, a global positioning system GPS and Inertial Measurement Unit ( action Inertial Measurement Unit, IMU) three, the depth information acquired point by point scanning of the entire object detection.
Our main concern here is to be integrated in consumer electronics miniaturization ToF camera. Common ToF camera and the camera imaging process is similar, mainly by the light source, a light-sensitive chip, a lens, a sensor, the drive control circuit and a processing circuit parts key modules and components. ToF camera includes a two part core modules, 发射照明模块and 感光接收模块generates according to the linkages between the two core module depth information. ToF camera sensor chips are classified according to the number of pixel units 单点and a 面阵式light-sensitive chip, in order to measure the entire surface of the three-dimensional position of the object depth information may be acquired using a single-point ToF camera 3D object geometry is detected by scanning point by point, the surface may be by Zhenshi ToF camera, shooting a scene image to obtain real-time information about the surface geometry of the whole scene, surface Zhenshi ToF cameras are more susceptible to consumer electronics system built of all ages, but the technical difficulty is greater.
Then after the TOF light irradiation unit is a high frequency modulation transmitter, the general LED or laser (laser diode and comprising VCSEL) for emitting a high-performance pulse light, the pulse can reach 100MHz, mainly using infrared light. Most of the current existing market ToF camera technology is based on 连续波(continuous wave) intensity modulation method, and some are based 光学快门approach, the principle is slightly different. The principle are shown below:
The method based on the principle of the optical shutter is very simple, emitting a pulsed light, to obtain information of the time difference t reflected light waves irradiated to the three-dimensional object by fast optical shutter, known since the speed of light c, just know the irradiation light and the light receiving time difference , back and forth from the public by d = t / 2 · c. This method looks very simple principle, but in practice to achieve high accuracy still can be challenging, as the control clock of the optical shutter switches require a very high precision, but also can generate high precision and high repeatability ultrashort pulse irradiation unit and the TOF sensor requires high-speed control signal, so as to achieve a high precision depth measurement. If the irradiation light 10ps shift occurs between the clock signal and the ToF sensor, equivalent to the displacement error of 1.5mm.
Another prior ToF-based intensity modulation continuous wave works as follows:
Emits a beam of illumination light emitted lightwave signal using the reflected light wave signal phase change for distance measurement. Wherein the wavelength of the illumination module is typically the infrared band, and a high-frequency modulation is required. ToF photosensitive module and the like ordinary mobile phone camera module, a chip composed of a member, a lens, circuit board, each chip ToF photosensitive pixel between the camera and from the optical wave emitted by the object 具体相位were recorded, the data extracted by the processing unit out 相位差, the depth information is calculated by the formula. The CMOS image sensor chip and the sensor structure ordinary mobile phone camera module used in a similar, but more complex, comprising 调制控制单元, A/D转换单元, 数据处理单元and the like, so ToF chip than the average pixel image sensor pixel size is much larger, generally around 20um. Also it requires a lens to collect light, but different from ordinary optical lens is a need to add this 红外带通滤光片to ensure the 只有与照明光源波长相同light to enter. Since the scene at different distances from the respective optical imaging system 不同直径的同心球面, rather than parallel planes, so that in actual use, the data processing unit requires a subsequent correction of the error. ToF camera 校正is essential to the production process in the most important step, no correction process, ToF camera will not work.
TOF technology advantages
- Small size, small error
TOF camera requires the receiving end and the transmitting end as close as possible, the closer, because the smaller transmit different reception paths brought error, has a natural advantage from the perspective of the volume of the compact; - Direct output depth information
TOF depth information can be output directly, you do not need to binocular stereo vision or similar structures that require light to obtain depth information calculated by the algorithm. - Strong anti-
TOF not affect the surface characteristics and gradation, because the sun is not modulated, the anti-glare TOF ability better. TOF accuracy does not vary with change in the distance varies, basically stable in cm order.
TOF technology disadvantage
- Low resolution, large power
consumption section to be improved. - Solutions are not mature enough
