Discussion on detection technology of automobile headlamp
Abstract: Automobile headlamp is the main lighting device for driving at night, and the shape and irradiation direction of far and near light play an important role in driving safely at night. Therefore, in order to ensure the safety of motor vehicles, the relevant performance of headlamps should be strictly tested. This paper analyzes the detection technology of far and near light of automobile headlights.
Keywords: automobile; Headlights; examination
China Library Classification Number: U46 Document Identification Number: A
Headlight is an important equipment to provide road lighting for drivers at night or in poor visibility, and it is also a light signal device for drivers to give warning and contact. Therefore, the headlamp must have sufficient luminous intensity and correct irradiation direction. At present, advanced CCD imaging technology and DSP image processing are widely used in major automobile inspection stations to detect the far and near light of automobile headlamps, so as to realize the automatic tracking of the optical axis, luminous intensity, center coordinates of high beam, inflection point coordinates of low beam and optical axis deviation angle detection of automobile headlamps.
1 Characteristics and functions of headlight far and near light emission
1. 1 Luminous Characteristics of Headlamp High Beam
In order to prevent the headlights from causing dazzling harm to drivers and passers-by, it is necessary to design the headlights specially to make their luminous performance reach a certain standard. The so-called luminous characteristics refer to the luminosity (illumination angle and luminous intensity) distribution of visible light emitted by lamps. The illumination angle varies with the direction and is often expressed by the luminous intensity distribution curve. In general, the luminous characteristics of car headlights's high beam, such as ellipse, are basically symmetrical in the up-and-down direction and the left-and-right direction, and the closer to the center point, the greater the irradiance.
1.2 luminous characteristics of headlamp low beam
Typical headlamp low beam has irregular geometry and obvious light-dark dividing line. There is a dark area on the upper left of the light-dark boundary, and a bright area on the lower right of the light-dark boundary. The area with the strongest luminous intensity is below the cut-off line of light and shade, and the central point of the area with the strongest luminous intensity has the highest illumination, and a certain isoillumination curve is formed around this central point. The low beam diagram of headlamp can be expressed as figure 1. The low beam produces obvious cut-off line between light and shade, and its horizontal part is in V-V? /kloc-about 0/5? Tilt or as high as 45? Slant line The turning point of the light and dark line is called the inflection point. According to the light shape distribution characteristics of the headlight, the traditional detection technology of the high beam of the headlight mainly focuses on instrument detection, mostly using the symmetry of the spot pattern of the high beam and using photovoltaic cells symmetrically distributed up and down, left and right to detect the optical axis center. However, due to the asymmetry of the spot pattern of the low beam, it is impossible to detect the low beam alone by measuring the high beam. Usually, the position of the inflection point of the cut-off line of light and shade is obtained by image analysis to measure various characteristic parameters of the low beam lamp, which provides accurate data for automobile drivers.
When the car is driving at night, the high beam of headlights can illuminate the object with a height of 2m within a certain range of 100m ahead, so as to ensure that the driver can take braking or bypassing measures in time when he finds an obstacle ahead, so as to keep the parking distance within the sight distance and ensure the driving safety.
2 Development of automobile headlamp detection technology
The detection technology of automobile headlights, from early screen observation to later instrument detection, has developed into the detection technology combining CCD and digital image processing (DSP), which has the level of intelligent and automatic detection technology.
2. 1 screening method detection
Simple screen inspection is to hang a screen in front of the tested lamp at 10m, draw the light beam irradiation position point and line on the screen according to the standard requirements, turn on the headlight of the tested vehicle to irradiate on the screen, and observe with naked eyes whether the light beam position meets the standard requirements, so as to measure the low beam and high beam. This method is characterized by simple equipment, no need for software processing system, high requirements for site and environment, but low efficiency, great dependence on people's subjective judgment, poor consistency of test results and large errors. Therefore, this detection method is rarely used in large flow detection lines.
2.2 CCD photosensitive detection technology is adopted.
Using the photosensitive technology of CCD camera, the collected optical signals are converted into electrical signals. Finally, the analog electrical signals are converted into digital signals through the image acquisition card, which are output to the computer and processed by the computer data processing system, so as to measure the high beam luminous intensity and low beam offset of the headlamp. Using CCD light detection technology, its detection accuracy can completely reach the national standard? 15? Requirements.
2.3 Digital image processing DSP detection technology
This new detection technology mainly converts the analog video signal collected by CCD camera into digital video signal, and then uses the processing system of digital video acquisition card and DSP (Digital Signal Processor) to perform digital operation and processing on the digital video signal as needed to obtain the parameters to be measured.
As can be seen from the development of the above lighting detection technology, with the continuous development and popularization of electronic technology and computer technology, digital image processing technology has also developed rapidly. Up to now, most major automobile inspection stations use CCD photosensitive system for accurate imaging, and DSP system for image analysis and electronic control technology to accurately detect the technical parameters of car headlights. DSP (Digital Signal Processing) Digital signal processing has the characteristics of high speed, high integration and convenient interface.
Measurement principle of 3 CCD photosensitive system
3. 1 imaging principle
Based on the correspondence between object and image in geometric optics, the light intensity distribution in a large range in the distance is made into a small measurable real image, and the light intensity distribution on the whole plane can be obtained at one time by using area CCD as image sensor.
According to the requirements of the screen method in GB7258-2004 "Technical Conditions for Motor Vehicle Operation Safety", the headlamp uses the corresponding relationship between objects and images in geometric optics to make the large-scale light intensity distribution on the distant screen (10m) into a smaller measurable real image (the imaging screen at 1m), and uses the area array CCD as the image sensor to obtain the whole plane at one time.
Headlights can be considered as surface light sources with a certain light intensity distribution. Headlights are imaged as AB at 10m. After inserting a Fresnel lens group in the optical path (assuming the equivalent is L), the rays of AB actually converge into a real image as AB, as shown in Figure 2.
If it is assumed that the focal length of the Fresnel lens is f, the following relationship exists:
Select the appropriate ratio of L and F to get the appropriate image, which is convenient for measurement.
3.2 aiming mode during measurement
The position of two points must be obtained in the detection of spatial angle, and it is no exception in the measurement of beam deflection angle. Before measuring, we must first find the position of the headlight or the position of the first reference point. Fig. 3 shows the measuring principle of aiming headlights. This measurement method firstly uses CCD camera 1 to find the position of the headlight, then uses CCD camera 2 to shoot the spot image of the headlight imaged by the lens, and analyzes the optical axis position (high beam or low beam) to get the deviation compared with the zero point, so as to get the angle deviation value of the actual headlight according to the calibrated data.
Directly aim at the headlights:
This measurement method is to find the position of the car lamp with a camera, then shoot the imaged spot image, and analyze the optical axis position (high beam or low beam) to get the deviation compared with the zero point, so as to get the actual angle deviation value according to the calibrated data.
3.3 light intensity measurement and analysis
Because there is a good linear relationship between the output voltage of CCD and illumination under low illumination, the digital quantity of CCD bin signal can be related to the illumination value of external light source shining on the detection screen. According to the relational database established during measurement and the digital quantity of each pixel after spatial sampling, the illumination intensity of each point is obtained.
3.4 Angle measurement and analysis
Mainly using the light (the center point of the high beam and the corner point near the cutoff line) to have X displacement on the screen, after the lens is imaged, the displacement of the imaging point on the square focal plane of the lens image is X? By analyzing the digital image obtained by CCD, the deflection angle of the optical axis can be calculated. Using the symmetry of high beam illumination, the symmetry center of high beam spot is found, and then the judgment process of human eyes is simulated under the illumination condition of low beam, and the inflection point of low beam is analyzed. Similarly, when detecting low beam angle, because CCD graphics have the advantage of high resolution, combined with computer technology, compared with the photoelectric cell scanning method, more accurate inflection points can be found.
Concluding remarks
To sum up, choosing a professional image processing chip to analyze and process the headlamp low beam distribution image can accurately determine the corner of the low beam cut-off line and the low beam irradiation direction.
refer to
Zou Ying, Wu Yong. Discussion on detection distance of headlamp detector [J]. Automobile Maintenance, 2005, 12.
[2] Zhao Bin. Problems and countermeasures in the detection of automobile headlights [J]. Journal of Wuxi Commercial Vocational and Technical College, June 2008.
Click the next page for details >>& gt Technical paper on automobile headlights.