Overview of Research on Automotive HUD Display
1 What is a head-up display
When the vehicle is driving at high speed, especially at night, the driver may look down at the instrument display or the audio display of the center console. At this time, if there is an emergency ahead, it may be too late to take effective measures and cause an accident. . In order to avoid this situation, some high-end vehicles are equipped with a head-up display system, which can display relevant information on the driver's head-up range of the front windshield glass, so as to avoid looking down at the instrument, thereby shortening the blind spot time of the eyeball to the front, Has important value in reducing traffic accidents caused by bowing heads.
The head-up display system (Head-Up Display, HUD) is also called the head-up display system. HUD technology was developed on the basis of optical sighting and radar sighting in the 1960s and was first applied to fighter jets. HUD can project important information, such as speed, fuel level, rotation speed, navigation information, etc., into the driver's head-up range of the front windshield. The display position and display brightness are adjustable. The driver hardly needs to change the focal length and gaze range of the eyes, and can conveniently view the required information.
In 2003, DENSO introduced the world's first head-up display that can simultaneously display driving information and night vision system imaging information. The head-up display used in the Cadillac STS4.6, which was launched in 2006, can change the color of the projected words according to different vehicle speeds. This is the transformation of the onboard head-up display from monochrome display to composite color display. In May 2012, Pioneer of Japan launched the Pioneer projection head-up display, which is the first product in the world to apply a head-up display to car navigation. The product can analyze specific driving route information, determine important identification information and distance information between the car and its surroundings.
HUD can only display a few numbers such as vehicle speed on the first-generation product, and the display color is single, the field of view is small, and the contrast is poor. Nowadays, HUD functions are gradually diversified, including navigation functions, LBS information services, etc., and at the same time, the visual effect is greatly enhanced, and it is accepted by more and more drivers. In the future, HUD will combine "augmented reality" technology and expand the field of view to the entire panoramic car window. At that time, the onboard instrument panel may be completely replaced.
2 Head-up display classification
At present, the HUD can be divided into two types, hanging type and instrument table type, as shown in Figure 2.2. Most of the suspended HUD is installed on the sun visor on the side of the driver's seat in the car. This design causes the projected image to be displayed in the upper half of the windshield glass. The instrument desk HUD is installed above the instrument panel, and the projected image appears on the lower part of the windshield glass.
According to HUD imaging solutions, it can be divided into three categories: reflective, glass imaging, and virtual imaging. The reflective imaging solution is the earliest technology adopted by HUD. The image source is placed flat under the front windshield, and the light emitted by the image source is reflected by the front windshield or other glass medium and enters the driver's eyes. What the driver sees along the reverse extension line of the light is the virtual image of the image source. In order to improve the clarity of light reflection, coating treatment is often carried out on the front windshield.
The glass imaging type means that the HUD presents information to the driver through a transparent display. The transparent display is separated from the front windshield, so there is no need to coat the front windshield. The transparent display screen can be moved back and forth, and the projection angle is flexible. With the continuous development of technology and the popularization of mobile phones, head-up displays such as Garmin HUD and ADAYO can be connected to the mobile phone and project the navigation information on the mobile phone to the display panel.
The virtual imaging type refers to dissolving a variety of image information in the real scene, and the imaging picture is suspended in the air, which has a good sense of spatial depth. HUD information using virtual imaging technology can be integrated with the road environment. Virtual imaging HUD is more intuitive than traditional HUD so that the driver is immersed in the entire environment.
According to the three imaging solutions of the current vehicle head-up system: light reflection, glass imaging, and virtual imaging, through comparison, the glass imaging type HUD technology is mature, the price is moderate, and can provide a better driving experience, so the glass imaging type is selected for the head-up monitor.
3 HUD application and research status
HUD enables the driver to see the required information without looking down and reduces the distraction caused by the driver when he looks down on the instrument and mobile phone. Therefore, it has received extensive attention from the automotive industry. The front-mounted HUD is applied to a small number of high-end brand models, including BMW 5 Series Li, Lux Jetta 7 SUV, and Lexus GS. After-installation foreign products are represented by Jiaming and Japanese Pioneer, and domestic products are represented by car radish, but the overall assembly rate is not high, and the leading product has not yet been formed.
In the applied patent DE3712663A1, BMW of Munich proposed a set of HUD holographic optical elements to realize the holographic projection of HUD on the windshield window. The patent US4613200A applied by Ford Motor Company, which is also forward-looking, proposes the application of holographic optical elements to solve the problem of imaging quality. In the patent JPH1096776A, Honda proposed to display different colors on the HUD to mark the distance to the vehicle in front. The screen interactive HUD (WO0145080A) based on intelligent control recognition can realize the interaction of multiple screens in the car by the driver.
Kiefer et al. set up a comparative experiment by selecting two groups of experimenters of different ages (one group is 64-69 years old, and the other group is 19-22 years old). The study found that when the two groups of people use HUD, their sight staying on the road is significantly longer than when using mobile phones and onboard instruments. At the same time, it takes less time for the driver to increase the speed from 0 to 100km/h when using the HUD. The author compared and analyzed the impact of HUD and onboard instrumentation on truck driving performance through a driving simulator. The study found that there is no significant difference between the two in terms of cargo delivery efficiency, but in the event of an emergency, the response time of using HUD is shorter. In the high-speed state, the speed curve of the driver using the HUD is smoother. Participants believe that HUD is a measure that causes the least distraction from driving. Hammerschmidt et al. simulated HUD information prompt by appearing black squares in front of the car windows and found that drivers need to be distracted to observe the new information, which increases the misreading rate of information and interferes with the main driving task.
It can be seen that the current research on HUD in driving safety and driving distraction has just started, and even the research conclusions of some scholars are completely contradictory. There is no uniform reference standard in the experimental method, which leads to poor consistency of the conclusions. The research of quantitative indicators Mainly focuses on speed, acceleration, lane deviation, etc., so more researchers are waiting for more in-depth research.
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