The camera for the lane departure warning system is often mixed up with the LiDaR module. In fact, these are two independent sensors. In this article I will explain what exactly the LiDaR sensor does.
The word "LiDaR" means "Light Detection and Ranging". The LiDaR uses the principle of direct time-of-flight measurement of light as well as infrared waves for scanning in a light wave range between 840 - 950 nm. Dust and fog can have a negative impact on the measurement result of infrared waves.
There are two types of LiDaR systems:
1. Flash-LiDaR: The entire field of vision is scanned at once (this is used in brands like Ford and Volvo)
2. Scanning-LiDaR: The entire field of view is scanned point by point with a high precision and sampling rate (this is used in the brand Audi A8 2018 laser scanner)
Today, we’ll look at the Flash-LiDaR.
The LiDaR system operates according to the ToF runtime method (Time of Flight). The time between the light being emitted and arriving back is measured and the distance to the object is calculated. This is a fundamental difference to the FMCW radar, which we already know from the radar blog entry (see
chapter 8). The LiDaR system is used in conjunction with assistance systems such as the "City Emergency Brake Assist" at Ford, Mazda, and Volvo.
A characteristic feature of the Flash-LiDaR is the trapezoidal transducer and receiver unit in the windscreen. The smaller trapezoid is at the bottom and forms the transmitting unit. The larger trapezoid is at the top and forms the receiving unit.
A laser emitter sends light pulses through a diffuser, which are received again through two lenses in the receiver. The lower transmitter unit is divided into three channels, the center, left and right. As mentioned above, the receiver unit has two lenses. The right lens (from a driving point of view) receives the pulses from the left and right channels and the left lens receives the pulses from the center channel.
As a scattered lens is used, the resolution decreases with increasing distance. This is the reason why a Flash-LiDaR is used in the range between 1 – 15 meters as an Emergency Brake Assistant (Short Range LiDaR).
In the LiDaR module itself, there is a computing unit that processes the received signal and can output the data on various interfaces. The best known is CAN bus and USB. CAN bus is the preferred interface.
By analysis of data from this sensor, the data can be processed to such an extent that a 3D image is made available in real time. Thus, the "Flash-LiDaR" becomes the "3D-Flash-LiDaR". This development is a further step towards autonomous driving and offers an alternative to the "Scan-LiDaR" systems. The Flash-LiDaR does not need to be calibrated unless the manufacturer specifically requires it.
Image: Continental