Shulou(Shulou.com)11/24 Report--

A recent measurement shows that

In the blind spot of a SUV

Can hold 75 children.

And I often see it in life.

Due to the existence of blind spots

And caused traffic accidents.

So is there any way to reduce the blind spot?

Or weaken the harm caused by the blind area?

Let's take an inventory today.

Related "intimate" technology ~

Part 1: before introducing the scientific and technological means to deal with the blind area, let's take a look at the blind area. The basic principle of the blind area is that the light propagates along a straight line. When the driver sits in the driving position, due to the limitation of the visual angle and the occlusion of the car body, there will inevitably be a large area of light reflected by the object can not be transmitted to the driver's eyes.

Fig. 1 the rearview mirror expands the field of vision. Although the rearview mirror can expand the driver's field of vision by reflecting light to a certain extent, there are still areas that cannot be covered due to the limitations of its size and location.

Fig. 2 car blind area for common car models, the blind area can be divided into: front blind area, rear blind area, bilateral rearview mirror blind area, bilateral AB column blind area and so on. The front blind area is mainly due to the blocking of the front area of the hood, while the rear blind area is because part of the rear part of the car is outside the rearview mirror. The blind area of the rearview mirror on both sides is difficult to be seen through the rearview mirror when turning at a large angle, while the blind area of the AB column is caused by the fact that the columns on both sides of the windshield block part of the front visual field.

On the other hand, large cars such as trucks have larger blind spots when driving than cars because of their larger body.

Fig. 4 the blind area of the truck is illustrated but it is worth noting that even the area designated outside the blind area does not mean that it is absolutely safe. Because even when the driver is focused, it is difficult to observe all directions at the same time, and it will be disturbed by real-time road conditions, weather conditions and the brightness of the lights on the opposite side of the car. It can be thought that the "blind area" in the real situation will only be larger than that described above! So, what can we do to help a bunch of drivers?

Part 2: more mirrors when we skillfully use the principle of specular reflection, we can create designs that reduce blind spots. Such as the auxiliary lens on the rearview mirror and the invisibility device that makes the A-pillar "transparent".

Fig. 5 the wide-angle mirror on the rearview mirror the auxiliary lens installed on the rearview mirror has become quite popular, and it is often referred to as the wide-angle mirror or blind spot mirror. Because this kind of lens is a small convex mirror, it can cover a larger field of view. The principle can be roughly understood through the following diagram.

Fig. 6 the principle of expanding the field of vision with a convex mirror so that the driver can observe the areas behind the rear wheels, such as the rear wheels, which cannot be covered by the original mirror, effectively reducing the size of the blind area on both sides. However, this convex mirror will also bring a potential problem, that is, the picture has a certain degree of deformation and distortion. When drivers observe the situation at the rear through a convex mirror, it is not easy to accurately grasp the actual distance of objects and vehicles behind, so it is easy to misjudge if they overtrust the picture in the wide-angle mirror.

Fig. 7 the visual field gain brought by the addition of a wide-angle lens, and the structure of the two lenses to be introduced below is actually similar to the principle of periscope in a submarine, that is, through a pair of parallel plane mirrors, the light emitted from an object that is not in the field of vision is reflected twice to the human eye, thus the object can be seen.

Fig. 8 the principle of periscope as described earlier, the AB column will block part of the field of vision in front of you while driving, which will bring great safety risks. If you borrow a similar idea and set two lenses in the right position and at the right angle, you can see the occluded object behind the AB column.

Figure 9 shows the principle of the A-pillar "invisible" device. Of course, when it is really used in cars, more complex designs are needed to ensure more practical requirements such as beauty. In this way, you can achieve the "invisible" effect of the A-column similar to the figure below.

Figure 10 invisibility effect illustration | the picture is derived from [4] of course, a similar effect can be achieved by displaying the outside picture on the inside of the A-pillar through the camera.

Part 3: let the car have the wide-angle lens described above and the A-pillar "invisibility" device mainly uses optical methods to reduce the driver's blind area while driving. However, for the wider visual dead corner, and considering the driver's limited energy, it is not enough to expand the driver's field of vision. As a result, people want to let the car have "eyes", that is, so that the car itself can actively judge the surrounding situation, and give drivers effective reminders and even intervention in driving operation. At this point, many readers may have thought of a word: radar.

Fig. 11 Radar is right. Radar is the most familiar tool for object location and velocity measurement. Its full name is literally translated as "radio detection and ranging". In the aspect of positioning, the radar will wait and receive the pulse reflected by the object after transmitting the radio pulse, and get the round-trip propagation time dt. Since radio is an electromagnetic wave, we can use the following formula to calculate its velocity in a certain medium.

Where c and n represent the speed of light in a vacuum and the refractive index of a medium, such as air, respectively. Therefore, the distance of the object from the radar can be expressed as:

If you need to achieve positioning in three-dimensional space, you can adopt the method of multi-base stations, which has been interpreted in detail in previous articles. If you are interested, you can review ~ then, how does radar achieve speed measurement? This refers to the Doppler effect as we know it.

Fig. 12 Doppler effect of sound waves Doppler effect means that the wavelength of radiation from an object changes with the relative motion of the wave source and the observer. For example, for mechanical waves represented by sound waves, when a car (wave source) is coming to you, it sounds like the sound tone of the car will become higher, that is, the frequency will increase; if the wave source is far away, the tone will become lower, that is, the frequency will decrease. A similar phenomenon will occur in light waves, but the situation is slightly complicated: if the wave frequency emitted by the wave source is f and the wave frequency received is f, there is a relationship between the two:

Where θ is the angle between the connection between the wave source and the receiver and the velocity direction of the wave source. Of course, the situation will be more complicated when the on-board radar determines the position and speed of the surrounding vehicles or pedestrians. Because the device that emits the pulse and the receiving device are in the moving car, and the object that reflects the pulse may also be moving. However, as long as we seriously consider the relative motion between the two, we can still make a judgment based on the above principles.

Fig. 13 comparison of types of vehicle radar | Picture is derived from [5] in the actual broad sense, radar can not only emit radio, but also emit infrared, ultrasonic and even lasers. The principles of positioning and speed measurement are similar. According to the types of transmitted pulses, they can be divided into infrared radar, ultrasonic radar, millimeter wave radar and so on.

Fig. 14 the work flow of vehicle radar | the picture is from [5] with such a positioning and speed measuring device, the car can scan the surrounding environment and transmit the signal to the algorithm chip for analysis. Once you find that the surrounding objects are approaching quickly, you can warn the driver or notify the surrounding cars and pedestrians through the alarm device. When necessary, if it is found that the distance between the car and the car is rapidly approaching, the car can also start the automatic braking system to complete the braking process, which greatly increases the safety factor of the driver.

Part 4: can be smarter in recent years, the technical term self-driving technology has become familiar to people, which means that in the future era when self-driving is fully realized, drivers will be completely liberated and there will no longer be the concept of "blind zone". So how do you do all this? This mainly depends on two aspects: positioning system and environmental awareness.

Figure 15 how Google driverless cars work | Pictures are from [8] due to the development of Internet technology, we are gradually able to exchange information with the Internet in real time. This means that a moving car can also get its own location and traffic information through the Internet in real time. It is conceivable that if all cars are connected to the Internet, they can have a global perspective to some extent.

Fig. 16 the popularity of lidar with the advantages of high resolution, high precision and strong anti-jamming ability of Beidou and other satellite positioning systems makes the vehicle's ability to detect the surrounding environment by no means a simple positioning and speed measurement. For example, the vehicle-mounted three-dimensional lidar can draw the three-dimensional space map around the vehicle in real time through high-speed rotation, and measure the distance, velocity, acceleration, angular velocity and other information of other vehicles in three directions.

Fig. 17 3D modeling given by lidar | the picture is derived from [9] in addition to the positioning system and environmental awareness mentioned above, we can also associate with the recent development of computer vision. Cars in the future can not only fully perceive the surrounding environment, but also extract and recognize different elements, and selectively respond, warn, avoid and other operations.

Fig. 18 concept map of self-driving scene | Picture is from [8] when technology really strikes, we can not only reduce blind areas, but even eliminate blind areas; we can not only help drivers, but even liberate drivers. Expect more science and technology to become mature, popularized and eventually become the patron saint of everyone's travel safety. We also hope that on the way to this idealized end, we can all take responsibility for ourselves and others with a better sense of security.

references

[1] explanation of the schematic diagram of automobile blind area-Zhihu (zhihu.com)

[2] do you know how dangerous blind spots are? 10 pictures-Zhihu (zhihu.com)

[3] what is the function of the small round mirror on the rearview mirror of the car? Is it necessary to install?

[4] US20170227781A1-Apparatuses and methods for making an object appear transparent-Google Patents

[5] vehicle-mounted millimeter wave radar-- standard for high-order autopilot-zhihu.com

[6] Radar (electronic equipment using electromagnetic waves to detect targets) _ Baidu Encyclopedia (baidu.com)

[7] Doppler effect _ Baidu Encyclopedia (baidu.com)

[8] the development process and bottleneck technology of self-driving technology and its future development trend-zhihu.com

[9] uncover the three sensor systems of autopilot (camera, radar, lidar)-sensor / Mems-EETOP- core network

This article comes from the official account of Wechat: Institute of Physics, Chinese Academy of Sciences (ID:cas-iop), author: Yun Kai Ye Luo

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