1 Overview of automotive lidar
1 Vehicle-mounted Lidar (Light Detection And Ranging) is developed from microwave radar and originally originated from the research and development of NASA in 1970. Traditional radars use microwave and millimeter wave band electromagnetic waves as carrier waves. Their working principles are basically similar. They first transmit a carrier detection signal carrying information to the measured target, and then measure the arrival time of the reflected signal, the direction of the beam, and the frequency. Change and other parameters to determine the distance direction and speed of the target . Compared with microwave, the wavelength of laser is several orders of magnitude shorter and the beam is narrower. Therefore, compared with microwave radar, lidar is smaller, lighter, and has higher angular resolution and better anti-interference. .
With the development of GPS positioning technology to centimeter-level positioning accuracy and the significant improvement of inertial measurement unit (IMU) accuracy, lidar measurement technology has begun to move towards commercial development, and was first applied to airborne (aircraft) Lidar systems. , National defense and other fields have been widely used .
In recent years, from the ground-based unmanned vehicles that were initially promoted to meet the needs of military applications, to several major car companies in the world have successively invested in the research and development of civilian autonomous vehicles. The development trend of autonomous vehicles is constantly being confirmed. From a demand perspective, the research and development of autonomous vehicles is to meet people’s higher requirements for driving technology and the urgent need for intelligent transportation. From a technical perspective, research and development of autonomous vehicles is a homeopath for breakthroughs in related technical fields. The development of perception technology, new energy technology, artificial intelligence and other fields has brought new development directions to the traditional automobile industry. The environment perception of self-driving cars is like the vision and hearing of cars, which can help cars quickly and accurately obtain driving environment information. It is the prerequisite and basis for vehicles to achieve advanced intelligent behaviors such as obstacle avoidance, positioning, and path planning . According to the classification standards established by the Society of American Engineers (SAE, Society of American Engineers), autonomous driving is divided into six levels, Level 0 to Level 5, corresponding to full manual driving (Level 0), assisted driving (Level 1), and partial Automatic driving (Level 2), automatic driving under certain conditions (Level 3), highly automatic driving (Level 4) and fully automatic driving (Level 5) . Three types of sensors are indispensable to the realization of autonomous vehicles’ environmental perception: cameras, radars, and lidars. Sensors have been equipped on Level 1 and Level 2 autonomous vehicles. The current consensus in the industry recognizes that it is necessary to achieve Level 3 unmanned driving must be equipped with a higher-precision lidar sensor. This article sorts out the main technical branches of vehicle-mounted lidar in recent years, and introduces the main patent applications of each technical branch in recent years, hoping to summarize the development trend of vehicle-mounted lidar technology.
2. Technology development trend
From May 2012 when Google officially obtained the first license for autonomous vehicles in the history of the United States, it is estimated that the lidar market will reach 270 million U.S. dollars in 2020. From the initial Google equipped with Velodyne’s 64-line mechanical Rotate LiDAR (Light Detection And Ranging), until more and more research and development institutions are committed to realizing vehicle-level lidar as soon as possible. We have become more aware that as one of the key sensors for environmental perception, the development of vehicle-mounted lidar technology is It plays a very important role in the tide of autonomous driving, and the industry demand for autonomous driving also promotes the rapid development of the automotive lidar field.
Through the above combing through the main technical branches of vehicle-mounted lidar in recent years, it can be seen that vehicle-mounted lidar has evolved along the technical route of miniaturization and low cost as a whole. Relying on mature mechanical scanning technology, mechanical rotating lidar is the first technical branch to be applied in vehicle lidar. Its main improvement difficulty lies in the natural contradiction between the miniaturization of equipment and the improvement of vertical resolution, and its commercialization The biggest obstacle to mass production lies in a series of high costs such as high prices and high assembly cycles brought about by complex mechanical structures.
From the perspective of the research and development situation of the main developers, the complete elimination of the technical branch of the mechanical rotating structure (ie, the "solid-state lidar") is the mainstream development trend of the vehicle lidar in the future. To analyze the reasons, solid-state lidar has the advantages of low cost and small size due to the use of electronic components instead of mechanical rotating components to achieve scanning. Low cost means mass production is possible. Small size can be separated from the top-mounted installation method and integrated into the traditional The appearance of the vehicle (for example, it can be installed in the vehicle's air intake grille, rearview mirror, etc.). In addition, because the mechanical rotating parts that require precise optical registration are eliminated, the service life of the solid-state lidar becomes longer, and the difficulty of assembly is reduced because it can be controlled by software. On the whole, solid-state automotive lidar is the most likely technology branch to produce automotive-grade products in the future. However, it needs to be realized that the current solid-state lidar branch is still in the research stage, and the technical route has not been finalized. The mainstream solutions include optical phased array (OPA) lidar and flash (Flash) lidar, and the technical problems that need to be solved There are a lot more. This is mainly reflected in the fact that a single solid-state lidar sensor cannot achieve 360° scanning detection, and multiple sensors need to be arranged in different directions to complete omnidirectional scanning. Therefore, although the cost of a single sensor is declining, whether there is still a price advantage after the overall configuration remains to be considered; For OPA lidar, its manufacturing process is more difficult, and it is necessary to study how to eliminate the influence of side lobes; for Flash-type lidar, how to improve the detection range is an urgent problem to be solved. The MEMS method of changing the rotating scanning structure from "macro" to "micro" is considered to be the transitional stage of vehicle-mounted lidar to solid-state, so it is also called "hybrid solid-state" lidar, but because the all-solid-state lidar has not been determined, Therefore, it is not excluded that hybrid solid-state lidar will find new breakthroughs with technological progress.
In terms of ranging principles, most vehicle-mounted lidars use the TOF mechanism, but in order to improve the accuracy of long-distance detection, FMCW (Frequency Modulated Continuous Wave) lidar has also become the main technical branch of current vehicle-mounted lidars, due to the complexity of the FMCW mechanism, It has higher requirements for computing power, slower imaging speed, and detection accuracy is highly dependent on the linearity of "chirp". In general, the development time of vehicle-mounted lidar is not long. In order to meet the urgent needs of autonomous driving, low-cost, miniaturization, and solid-stateization are the overall development trends in the future.www.isurestar.net