Millimeter-wave radar, as the only sensor that can work "all-weather, all-weather", is one of the indispensable core sensors for realizing automotive ADAS and autonomous driving! Learn more about it below:
â—â—â—The concept and principle of millimeter wave radar:
Radar (Radar, radio detecting and ranging), radio detection and ranging. The basic task of the radar is to emit electromagnetic waves to irradiate the target and receive its echo, thereby obtaining the state parameters such as the distance, direction, and speed that are of interest for the detection of the target to the electromagnetic wave launching point. According to the type of radiation, it can be divided into: pulse radar and continuous wave radar (FMCW).
Millimeter wave radar, as the name suggests, is a radar that works in the millimeter wave frequency band. Millimeter-Wave (Millimeter-Wave, abbreviation: MMW) refers to electromagnetic waves with a length of 1 to 10 mm, and the corresponding frequency range is 30 to 300 GHz. As shown in the figure below, millimeter waves are located in the overlapping wavelength range of microwaves and far-infrared waves, so millimeter waves have the advantages of these two spectrums, as well as their own unique properties. The theory and technology of millimeter wave are the extension of microwave to high frequency and the development of light wave to low frequency.
According to the wave propagation theory, the higher the frequency, the shorter the wavelength, the higher the resolution, and the stronger the penetration ability, but the greater the loss in the propagation process, the shorter the transmission distance; relatively, the lower the frequency, the longer the wavelength. , The stronger the diffraction ability, the longer the transmission distance. Therefore, compared with microwave, millimeter wave has high resolution, good directivity, strong anti-interference ability and good detection performance. Compared with infrared, millimeter waves have less atmospheric attenuation, better penetrability to smoke and dust, and are less affected by weather. These characteristics determine the millimeter-wave radar has the ability to work around the clock.
â—â—â—Millimeter wave radar detection principle:
The most important task of millimeter-wave radar is to find the target by radio and detect the distance, speed and direction of the target object.
The principle of millimeter wave radar ranging is very simple. It sends out radio waves (millimeter waves), then receives echoes, and measures the target's position data and relative distance based on the time difference between the transmission and reception. According to the propagation speed of the electromagnetic wave, the distance formula of the target can be determined as: s=ct/2, where s is the target distance, t is the time from when the electromagnetic wave is emitted from the radar to when the target echo is received, and c is the speed of light. Millimeter wave radar speed measurement is based on the principle of Doppler Effect. The so-called Doppler effect is that when vibration sources such as sound, light and radio waves move with the observer at a relative speed v, the frequency of vibration received by the observer is different from the frequency emitted by the vibration source. Because this phenomenon was first discovered by Austrian scientist Doppler, it is called the Doppler effect. In other words, when the emitted electromagnetic wave and the detected target move relative to each other, the frequency of the echo will be different from the frequency of the emitted wave. When the target approaches the radar antenna, the frequency of the reflected signal will be higher than the frequency of the transmitted signal; conversely, when the target moves away from the antenna, the frequency of the reflected signal will be lower than the frequency of the transmitted signal, as shown in the figure below. The frequency change formed by the Doppler effect is called the Doppler shift, which is proportional to the relative velocity v and inversely proportional to the frequency of vibration. In this way, by detecting this frequency difference, the moving speed of the target relative to the radar can be measured, that is, the relative speed of the target and the radar. According to the time difference between transmitting pulse and receiving, the distance to the target can be measured.
â—â—â—Industrial Research on Millimeter Wave Radar:
In 2017, the market size of China's millimeter wave radar was about 1.34 billion yuan, and it is expected to reach 9.67 billion yuan by 2021, with an average annual growth rate of about 70.6% in 2016-2021.
Since 2017, lidar has been sought after by the capital market. However, from the current market perspective, millimeter-wave radar is the fastest-growing market. From January to May 2018, the pre-installed market for passenger car millimeter-wave radars in China had 1.406 million units, an increase of 112.7 year-on-year. %.
From the comparison of the three sensors in the figure below, the current overall performance of millimeter-wave radar is stronger than that of lidar.
The millimeter wave radar market continues to be subdivided, and 24GHz millimeter wave radar is still the largest type of shipment. The early 24GHz millimeter-wave radar was mainly used for short- and medium-range detection, and the 77GHz millimeter-wave radar was mainly used for long-distance detection. With technological progress and cost reduction, coupled with performance advantages, 77GHz radar has a tendency to gradually replace 24GHz radar. It will be used in 2017. Shipment volume of 77GHz radar for LCA/RCTA increased significantly.
In terms of total volume, on the one hand, the side SRR 24GHz is still the mainstream, and some of the front-view LRR OEMs such as Mercedes-Benz and PSA also use 24GHz radars. In the short term, the growth of 24GHz radars is still considerable; on the other hand, mainstream global suppliers such as Bosch and Continental's next-generation products mainly use the 76-77GHz frequency band. It is expected that by 2020, the 77GHz radar market will exceed the market size.
The millimeter wave radar market is still the main share of the traditional Tier1 market controlled by Bosch, Continental, and Hella. Domestic millimeter-wave radar manufacturers started from the after-installation market, and then gradually entered the pre-installation market through domestic car companies.
Mu Niu Technology has received tens of thousands of orders in the aftermarket. Sunstech 24Ghz side-rear radar has received pre-installation orders from its own brand Changfeng Cheetah. By 2019, it is expected that more than ten new models will be equipped with Sunstech millimeter-wave radars.
Lidar has become an innovation hotspot in the field of autonomous driving at home and abroad. Traditional automobile giants and start-ups have increased their investment in this field, and investment and mergers are frequent. In terms of technology, mechanical multi-line lidar has been widely used in unmanned prototype cars, but solid-state lidar is more in line with the demand for automobile mass production and represents the future development direction.
At present, Lidar still has problems such as uncertain technical route, high price, and difficulty in meeting vehicle-level requirements. At the same time, the next generation of high-precision imaging millimeter-wave radar is also becoming mature and will compete with lidar in the future.
However, the rapid technological advancement of lidar has made lidar manufacturers increasingly confident. Louay Eldada, the co-founder and CEO of Quanergy, said at the beginning of the year that Quanergy will use its partner Sensata's factory in Changzhou, Jiangsu to produce lidar in 2018. It is expected to have an initial annual production capacity of 10 million units. Later, as market demand increases, the factory's production capacity is expected to gradually increase. Expanded to hundreds of millions of units.
In addition to Quanery, domestic lidar manufacturers such as Sagitar Juchuang, Beiketianhui, Leishen Intelligent, and Hesai Technology have also established their own factories and are continuously expanding their production capacity. The lidar market is expected to start large-scale growth in 2021.
Millimeter wave radar, lidar and cameras have their own advantages and disadvantages in terms of size, price, adaptation to the scene, imaging, ranging, positioning, and object recognition. No single sensor can independently support future self-driving cars' perception of the external environment Requirements. The fusion of radar and camera can obtain more accurate environmental data, improve redundancy, and ensure the stability and safety of ADAS and autonomous driving systems to the greatest extent.
â—â—â—Application of millimeter wave radar in ADAS:
For vehicle safety, the most important basis for judging is the relative distance and relative speed information between two vehicles. Especially when the vehicle is running at high speed, if the distance between the two vehicles is too close, it is easy to cause a rear-end collision. With excellent ranging and speed measurement capabilities, millimeter wave radar is widely used in adaptive cruise control (ACC), forward collision avoidance warning (FCW), blind spot detection (BSD), assisted parking (PA), assisted lane change (LCA) ) Waiting for the car ADAS.
Generally, in order to meet the detection needs of different distance ranges, a car will install multiple short-range, medium-range and long-range millimeter wave radars. Among them, the 24GHz radar system mainly realizes short-range detection (SRR, below 60 meters), and the 77GHz radar system mainly realizes medium and long-distance detection (MRR, about 100 meters; LRR, above 200 meters). Different millimeter-wave radars "perform their duties" and play different roles in the front, body, and rear of the vehicle.
According to the wave propagation theory, the higher the frequency, the shorter the wavelength, the higher the resolution, and the longer the detection distance, but the detection angle (horizontal field of view) will become smaller. Therefore, the 77GHz millimeter-wave radar can achieve a longer detection range and higher accuracy than the 24GHz. However, as the frequency increases, the design and manufacturing of the corresponding chip becomes more difficult, and the 77GHz millimeter-wave radar is more expensive. Usually the detection angle and the detection distance are contradictory. Figure 1 shows the comparison of the detection range and detection angle of the Continental Group 77GHz ARS 310 millimeter wave radar in the short, medium and long range. So although 77GHz can replace 24GHz functionally, it is the mainstream in the future, but from the perspective of cost performance, the current short-range radar is mainly borne by 24GHz.
The picture above shows the detection range of Continental's ARS 310 short-range, medium-range, and long-range radars. In order to fully realize the various functions of ADAS, comprehensively cover the sensing of the car's surrounding environment, and take into account performance and cost, a car will install multiple short-range, medium-range and long-range millimeter wave radars. Different millimeter-wave radars "perform their duties" and play different roles in the front, body, and rear of the vehicle. The current main standard configuration: 1-2 77GHz MRR/LRR+4 24GHz SRR. Although the detection range of 24GHz SRR is relatively short, it has the advantage of large detection angle and relatively low cost. It can be configured with multiple units to achieve close-range and all-round coverage of the vehicle body. MRR/LRR functions are equivalent. The advantage of LRR is that its detectable distance is relatively long, and the applicable speed can reach 250km/h. However, in most countries with limited speed, the use cost is relatively lower and the applicable speed is within 160km/h. It is more cost-effective to realize the adaptive cruise (ACC) function with mid-range radar.
For example, the Mercedes-Benz S-Class uses 6 millimeter wave radars (1 long + 1 medium + 4 short), as shown in the figure above, which are respectively distributed in one forward dual-mode long-range millimeter wave radar, and one backward medium and long-range millimeter wave radar. There are 4 short-range radars on the left and right of the front/rear bumper. "Short-range + medium-range + long-range" millimeter wave radars combine to complete adaptive cruise (ACC), automatic emergency braking (AEB), front/rear collision warning (FCW/BCW), lane change assist (LCA), Blind spot detection (BSD), reverse assist (BPA), parking assist (PA) and other ADAS functions. Among them, ACC, AEB, FCW and LCA are the most important anti-collision warning functions in automotive ADAS. How are they realized? It will be described in detail below. Adaptive Cruise Control (ACC) Adaptive Cruise Control (ACC) is a vehicle that can follow the vehicle ahead according to the set speed or distance, or actively control the speed of the vehicle according to the speed of the vehicle ahead, and finally connect the vehicle with the vehicle ahead. The driving assistance function that keeps the car at a safe distance, the biggest advantage of this function is that it can effectively liberate the driver's feet and improve driving comfort.
The realization principle of ACC: When the vehicle is running, the millimeter wave radar sensor installed in the front of the vehicle continuously scans the road in front of the vehicle, while the wheel speed sensor collects the vehicle speed signal. When the distance to the vehicle in front is too small, the ACC system can coordinate with the anti-lock braking system and the engine control system to properly brake the wheels and reduce the output power of the engine, so that the vehicle and the vehicle in front are always Keep a safe distance. When the ACC system controls the braking of the vehicle, it usually limits the braking deceleration to a level that does not affect the comfort. When a greater deceleration is required, the ACC system will issue an audible and optical warning signal to inform the driver to take the initiative to take the braking operation. Automatic emergency braking (AEB) Automatic emergency braking (Autonomous Emergency Braking, AEB) is an active safety assist function for automobiles. The AEB system uses millimeter-wave radar to measure the distance to the vehicle or obstacle in front, and then uses the data analysis module to compare the measured distance with the alarm distance and the safety distance. When the distance is less than the alarm distance, an alarm is given, and when the distance is less than the safety distance Even if the driver does not have time to step on the brake pedal, the AEB system will start to make the car brake automatically to ensure driving safety.
According to research, 90% of traffic accidents are caused by drivers’ inattention. AEB technology can reduce rear-end collisions by 38% in the real world, whether on urban roads (speed limit 60km/h) or When driving on suburban roads, the effect is significant. Therefore, the European New Car Safety Evaluation Association (Euro NCAP) took the lead to include the AEB system in the overall safety rating in 2014, and my country also added AEB to the NCAP scoring system in 2018. Forward Collision Warning (FCW) Forward Collision Warning (FCW) uses millimeter-wave radar and front-facing camera to continuously monitor the vehicle in front to determine the distance, orientation and relative speed between the vehicle and the vehicle in front. When a potential collision hazard ahead is detected, when the driver does not take braking measures, the instrument will display an alarm message and an audible alarm to warn the driver that he must take countermeasures. When it is judged that an accident is about to occur, the system will let the brakes automatically intervene in the work, thereby avoiding the accident or reducing the risk that the accident may cause.
AEB uses sensors to detect obstacles such as vehicles and pedestrians in front. If it finds that the distance is too close and there is a risk of collision, it will automatically brake. FCW can be understood as an early warning function before automatic braking. In fact, FCW and AEB systems are in a complementary relationship, and the purpose is to avoid or reduce the occurrence of collisions while driving. Lane change assist (LCA) lane change assist (LCA) uses sensors such as millimeter-wave radar and cameras to detect the lanes and the rear of the adjacent two sides of the vehicle, and obtain the movement information of the objects on the side and the rear of the vehicle. Combined with the current state of the vehicle for judgment, the driver is finally reminded by sound, light, etc., so that the driver can grasp the best time to change lanes, prevent traffic accidents caused by lane change, and also have a better preventive effect on rear collisions. The lane change assist system includes three functions: "Blind Spot Detection (BSD)", "Lane Change Warning (LCA)", and "Rear Collision Warning (RCW)". It can effectively prevent traffic accidents such as lane change, turning, rear-end collision, etc., and greatly improve the safety performance of the car lane change operation.
Among them, the BSD judges the relative position of the moving object and the relative speed with the vehicle. When it is within the blind zone of the vehicle, it promptly reminds the driver to pay attention to the risk of changing lanes. LCA detects that the target vehicle is approaching the vehicle at a relatively large relative speed in the adjacent area, and when the time distance between the two vehicles is less than a certain range, the driver is reminded by sound, light, etc. When RCW detects that there is a fast approaching moving object behind the same lane and there is a risk of collision, it will promptly warn the driver to wear a seat belt through sound, light and other methods to reduce the damage caused by the collision. In fact, in the process of implementing these driving assistance functions, it is not difficult to find that although the millimeter wave radar plays the core role of object detection, ranging and speed measurement, the whole process also needs the assistance of other sensors, such as lasers. Radar, camera, ultrasonic radar, inertial sensor, etc. As more and more car manufacturers begin to integrate different sensors into automotive ADAS, the industry generally believes that "sensor fusion" is the key to the safety of highly automated driving. In environmental perception, each type of sensor has unique strengths and weaknesses. For example, millimeter-wave radar can work around the clock without being affected by the weather, but the resolution is not high and cannot distinguish between people and objects; while the camera has a higher resolution and can perceive colors, but it is greatly affected by strong light; lasers Radar can provide three-dimensional-scale sensing information and has a strong ability to reconstruct the environment, but it is greatly affected by weather. Sensors have their own advantages and disadvantages, and it is difficult to replace each other. In order to realize automatic driving in the future, it is necessary for multiple sensors to cooperate with each other to form a car's perception system. As shown in Figure 7, with the development of autonomous driving from L2 to L5 autonomous driving, the number and types of sensors integrated in cars continue to increase. Only in this way can it be possible to ensure sufficient information acquisition and redundancy, and to achieve the requirements of OEM manufacturers. safety standard.
Software is one of the cores of multiple sensor fusion. The algorithm is the "blocker" of multi-sensor fusion leading to more advanced automatic driving technology, because the use of multiple sensors will greatly increase the amount of information that needs to be processed, and there may even be conflicting information. How to ensure that the system can quickly process data? It is critical to filter useless and wrong information to ensure that the system finally makes timely and correct decisions. At present, many theoretical methods of sensor fusion include Bayes criterion method, Kalman filter method, DS evidence theory method, fuzzy set theory method, artificial neural network method and so on. Therefore, in the case of using a variety of sensors, in order to ensure safety, it is necessary to perform information fusion on the sensors. Multi-sensor fusion can significantly improve the redundancy and fault tolerance of the system, thereby ensuring the speed and correctness of decision-making. It is an inevitable trend for ADAS to move toward advanced automatic driving and ultimately realize unmanned driving at this stage.
â—â—â—Other applications and development trends of millimeter wave radar:
In addition to automotive ADAS applications, millimeter-wave radar also plays a very important role in UAV, security, intelligent transportation, industrial and military fields. • UAV: ​​The main application is embodied in two aspects: height fixation and obstacle avoidance. • Security: It is mainly used for security alert in some important areas. • Intelligent transportation: Mainly used in vehicle detection, traffic volume investigation, traffic incident detection, traffic guidance, speeding monitoring, electronic checkpoints, electronic police and traffic light control, etc. • Industry: Mainly used in industrial level gauges, excavators, heavy bulldozers, safe construction near high-voltage power line towers, production safety monitoring, etc. • Military: Mainly used in radar detection, missile guidance, satellite remote sensing, electronic countermeasures, etc.
In summary, the development trend of millimeter-wave radar technology is toward smaller size, lower power consumption, higher integration, and the coexistence and integration of multiple technologies (higher cost performance). From the frequency band, since 77GHz has a smaller wavelength than 24GHz, the antenna size can be further reduced, making it easier to install and deploy. At the same time, the 77GHz band has a larger bandwidth, longer detection range, and higher accuracy, which is gradually becoming the mainstream. However, 24GHz has obvious cost advantages in applications such as short-range BSD/LCA, and will complement and coexist with 77GHz for a long time. In the front-end transceiver components, highly integrated MMICs have become the mainstream. In the process, SiGe first replaced GaAs, and it is now slowly developing in the direction of CMOS. Because GaAs, SiGe and CMOS each have their own advantages and disadvantages, CMOS is still inferior to GaAs in the ultra-high-speed and ultra-high-frequency fields. There is a demand for several processes in the market at the same time. For automotive applications, not only the front-end integration of the millimeter-wave radar and the integration with other sensors must be considered, but also the "cooperation" with the main processor. Is it integration or separation, or a flexible compromise? From the perspective of product trends, one is the fusion or high integration of the sensors themselves, such as the integration of millimeter wave radar front ends with cameras and other sensors; the other is a single-chip system solution, that is, "multi-sensor + main processor + digital signal "Processor", the future battle will also revolve around these two aspects, of course, cost-effectiveness is the premise. At the level of market demand, both radar front-end integrated chips and single-chip system solutions are required to meet the differentiated needs of customers. In short, the final result of the above-mentioned technological development is to realize a "smaller, cheaper, and smarter" millimeter wave radar, serving ADAS, autonomous driving and ultimate unmanned driving!
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Application:
The high speed machines mainly used for stranding copper wire, aluminum wire, steel wire, ACSR and wire rope. Accompanied with taping head, it can used for insulation cores and some control cable stranding process.
Component:
Central pay-off, cage host, taping device(optional), capstan, take-up and traverse device and electric control system.
Main Character:
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