1 Working principle of active collision avoidance system based on lidar
1.1 The working principle of lidar
The system mainly uses pulsed lidar as the data transceiver module to conduct distance measurement and speed measurement, and real-time monitoring of the vehicle in front. When there is a stopped or slow vehicle in front, it can detect the potential dangerous target ahead in time, and promptly alarm or make corresponding processing. action. The basic principle is: use the time difference between the laser emission and the echo when encountering obstacles to calculate the distance between the emission source and the target; compared to the phase ranging principle, it is simple, easy to implement, relatively low precision, and low product cost
(1) The controller drives the laser diode through the driver chip, and emits a laser beam of corresponding pulse width, which is scattered by the transmitting lens and illuminates forward; at the same time, it also passes through the electro-optical conversion circuit, and the pulse generated is directly received by the PIN photodiode, and then passes through the front Set amplification, main amplification, time discrimination circuit, generate a logic signal and transmit it to counter. This time is recorded as stoplo
(2) The echo signal reflected by the target is converged by the receiving lens to the photosensitive surface of the receiving PIN photodiode, and then subjected to pre-amplification, main amplification, and time point discrimination circuit to generate logic signals
(3) The counter calculates the result according to the time difference At and sends it to the microcontroller via the SPI bus
1.2 Working process of the active collision avoidance system
1.2, 1 warning
When the vehicle speed is lower than the set speed, the system will automatically start to monitor the traffic situation ahead through the lidar. If the vehicle in front has an emergency braking situation, and the system judges that there is a danger of collision, it will alert the driver.
1.22 Braking
When the front vehicle is in an emergency braking situation and the system judges that there is a danger of collision, if the driver does not respond, the system will pressurize the brakes and automatically brake without the driver's intervention, thereby reducing the front possibility of a rear-end collision
2 The key technology of active collision avoidance system
2.1 Lidar technology
The transmitting circuit is mainly to add a MOS tube driver chip between the MCU and the laser diode to play the role of isolation and shaping (see Figure 3). For the transmitting circuit, the greater the output power, the greater the energy obtained during the reception, which can reduce the difficulty of receiving circuit design and improve the signal-to-noise ratio. The response speed also has a greater impact on the test accuracy. The faster the response speed, the higher the measurement accuracy. The narrower the laser diode output pulse, the greater the optical power, the better the system. In addition, this part of the design also plays a key role in the cost of the system. Strong transmitting power has little effect on the cost of the transmitting circuit, but it has a great influence on the cost of the receiving circuit. Strong signals may save tens of yuan of amplifiers. Therefore, this part of the design needs to pay attention to In order to accurately generate the emission and reception laser pulse reference, the laser emission pulse should be as narrow as possible, and the rising edge slope should be as steep as possible; in the circuit board wiring, due to the large current and high frequency signal, the corresponding The signal line should be as short as possible, the trigger part and the drive part should be isolated, and the circuit board should be a common ground; when wiring, pay attention to the short lead from the decoupling capacitor C to the chip power and ground pins to effectively filter In addition to the instantaneous fluctuations on the power line; in order to prevent the CMOS latch-up phenomenon, it is necessary to limit the input-output signal amplitude and not exceed the supply voltage
(2) The receiving circuit, which is located between the receiving lens and the counting chip, transmits the echo signal to the counting chip after filtering, amplifying and shaping. This part of the circuit is the most workload part of the system, it directly affects the performance of the system: the accuracy can detect the size of the target
(3) (3) Perform braking strategy processing.
Active collision avoidance system is a development direction in the field of automotive active safety. Foreign research in this area has gradually matured, while domestic research is still in its infancy, and there are still many problems to be solved. The system uses lidar as the data transceiver module, and its design considers factors such as economic practicability and easy implementation. The system can quickly and accurately detect the information of the vehicle ahead, promptly detect dangerous targets and make an alarm or force braking, which contributes to the development of automobile collision avoidance radar and has certain theoretical significance and application value.www.isurestar.net