"Functions and requirements of automobile headlamp inspection"
Headlamp is an important device for the driver to provide driving road lighting at night or under the condition of low visibility. It is also a light signal device for the driver to send out warning and contact. Therefore, the headlamp must have sufficient luminous intensity and correct irradiation direction. During driving, the vehicle is vibrated, which may cause the installation position of headlamp components to change, so as to change the correct irradiation direction of the beam. At the same time, the bulb will gradually age during use, and the reflector will be polluted, resulting in poor focusing performance, resulting in insufficient brightness of the headlamp. These changes will make the driver unable to recognize the road ahead, or dazzle the other driver when crossing with the opposite vehicle, resulting in accidents. Therefore, the luminous intensity of headlamp and the irradiation direction of beam are listed as the necessary inspection items for motor vehicle operation safety inspection. The requirements for headlamp safety inspection are as follows:
1、 Headlamp beam illumination position requirements
1. When the motor vehicle inspects the low beam irradiation position of the headlamp, the height of the corner or midpoint of the beam cut-off line at a distance of 10m from the screen shall be 0.6h-0.8h (H is the height of the headlamp reference center, the same below), and the deviation of its horizontal position from left to right shall not exceed 100mm.
2. The adjustment of the high beam single beam lamp of the four lamp headlamp requires that the height of the beam center from the ground on the screen is 0.85h-0.9oh, and the horizontal position requires that the left lamp shall not deviate more than 10o mm to the left and 170mm to the right; The deviation of the right lamp to the left or right shall not be greater than 170mm.
3. When motor vehicles are equipped with high beam and low beam dual beam lamps, the low beam beam shall be mainly adjusted. For lamps that can only adjust the high beam single beam, adjust the high beam single beam.
4. The luminous intensity of the main beam of each headlamp of a motor vehicle shall meet the requirements of Table 1. During the test, the power supply system shall be charged.
2、 Headlamp luminous intensity requirements
Table 1 requirements for luminous intensity of high beam of headlamp
For motor vehicles with four lamp system, two symmetrical lamps meeting the requirements of two lamp system shall be regarded as qualified.
Use the screen to detect the beam irradiation position of the headlamp
As shown in Figure 1, a special screen is set at the place LOM away from the headlamp. According to the inspection conditions specified above, three vertical lines and three horizontal lines are drawn on the screen, and the middle vertical line V-V is aligned with the longitudinal center line of the tested vehicle. The vertical lines V left-v left and V right-v right on both sides are the center lines of the left and right headlamps of the tested vehicle respectively; The horizontal line H-H is equal to the center of the headlamp of the tested vehicle, and the height from the ground is h (mm); The height of the next horizontal line is H1, which is equal to the upper limit value (0.9h) of the headlamp high beam center of the tested vehicle, and the height of the lowest horizontal line is H2, which is equal to the upper limit value (0.8h) of the headlamp low beam center of the tested vehicle. The standard specifies that the deviation range of the center height of the high and low beam is 0.05h and 0.2h respectively, that is, the lower limit values are 0.85h and 0.6h respectively.
During the inspection, cover the headlamp on one side first, and then turn on the low beam switch of the headlamp. The corner or beam center of the low beam dark cut-off line of the uncovered headlamp shall fall within the rectangular area surrounded by two horizontal lines with the height of H2 and h2-0.2h and two vertical lines with the freshness of 1 / 2S + 100 and 1 / 2s-100 (mm) in the longitudinal direction of the vehicle, Otherwise, it indicates that the irradiation position deviation of the passing beam is unqualified.
For the high beam single beam headlamp, the irradiation position of the high beam shall be detected with the same detection method as that of the front beam, but the beam center shall fall within the rectangular area surrounded by two horizontal lines with heights of H1 and h1-0.05h and two vertical lines 1 / 2S + 170 and 1 / 2s-170 (mm) from the longitudinal centerline of the vehicle (for the right lamp, 1 / 2S + 100 for the left lamp and 1 / 2s-170 for the right lamp).
Using the screen method to detect the headlamp is simple and easy, but it can only detect the deflection direction and amount of the beam, and can not detect the luminous intensity. In addition, in order to adapt to different vehicle models, the screen needs to be changed frequently, and the detection efficiency is low.
Check the luminous intensity and optical axis offset with the headlamp tester
1、 Detection principle of headlamp tester
The headlamp detector generally uses a photocell element that converts the absorbed light energy into current to measure the luminous intensity and optical axis deflection of the headlamp according to the proportion of current generated by the photocell irradiated by the main optical axis of the headlamp.
1. Detection principle of luminous intensity
As shown in Fig. 2, after connecting the photocell 3 with the photometer 1 and irradiating the photocell with the headlamp at an appropriate distance, the photocell generates a current according to the luminous intensity of the headlamp to make the photometer pointer act, so as to indicate the luminous intensity of the headlamp.
2. Detection principle of optical axis deflection
As shown in Figure 3, the photocell is divided into four parts: s up, s down, s left, s right. The upper and lower deflection indicators 3 are connected to s up and s down, and the left and right deflection indicators 1 are connected to s left and s right. When the photocell is irradiated by the headlamp, each photocell generates current respectively, and the current is not equal when the light receiving amounts of s up and s down or s left and s right are different. According to the difference, the upper and lower deflection indicator 3 or the left and right deflection indicator 1 can be operated, so that the deflection of the headlamp optical axis can be measured.
The flexibility of photocells will decrease after a long time, whether they are used or not.
2、 Type of headlight tester
There are four types: spotlight type, screen type, automatic tracking optical axis type and projection type.
Working principle of automatic headlamp tester
1、 Shape and structure principle
The outline of the instrument is shown in Figure 4. The light receiving box is guided by the column and pulled up and down by the chain. Wheels are installed under the bottom box of the instrument, which can move the whole equipment left and right along the ground guide rail. Inside the light receiving box is a lens assembly (Fig. 5), a photocell and a light detection system. A drive system in two directions is installed in the bottom box (Fig. 6).
Four photocells, up, down, left and right, are installed on the front of the light receiving box for optical axis tracking. The principle is as described above. When the illuminance received by the upper and lower photocells is different, the generated deviation signal drives the motor in the upper and lower transmission parts to pull the light receiving box to the position of light balance. Similarly, the deviation signal of the left and right photocells will drive the motor in the left and right transmission parts to make the instrument move upward or right until the optical axis position deviation signal is zero.
Behind the lens is a set of four image limiting photocells. When the headlamp beam is focused through the lens and irradiated in the center of the photocell pack, the deviation signal generated by the four photocells is zero (the upper and lower tables and the left and right tables indicate zero). If the beam passing through the condenser lens deviates from the center when the instrument is positioned at the main optical axis, a deviation signal will inevitably be generated. The deviation signal of the left-right deviation drives the left-right motor (Fig. 5) to move the lens to reduce this deviation, even if the converged beam approaches the center of the photocell pack. Similarly, the up and down offset deviation signal drives the lens to adjust in the vertical direction so that the light spot can approach the center of the photocell pack in the vertical direction. The displacement of the lens in two directions is detected by displacement sensors installed in two directions respectively, and sent to the detection circuit for processing.
In Figure 7, I1 and I2 respectively represent the loop current generated by each photocell in the same group of photocells. According to the electrical principle, under the conditions of R1 = R2 and R3 = R4, the output voltage ex is:
Ex=（E2-E1）/2
Where E1 = I1, R1, E2 = R2, I2. When I1 = I2, there is ex = 0. When the light receiving amount of photocell 1 is greater than that of photocell 2, I1 > I2 and circuit output ex < 0; On the contrary, ex > 0.
2. Motor steering control principle
The motor steering control circuit is assembled on a circuit board. The error signal ex generated by the photocell detection circuit is sent to the preamplifier after filtering the 5ohz interference signal through the T-type filter circuit. The amplified deviation signal is then determined by the state comparator to control the state output circuit in three states of ex "0", ex "0" or ex = 0 to generate motor forward rotation signal and motor reverse rotation signal, or no signal output (i.e. motor stalling).
The circuit is equipped with two potentiometers: zero adjustment and gain adjustment, which is an important link in the positioning accuracy of the instrument transmission system. Zero position drift directly affects the positioning accuracy, and too small gain will reduce the detection sensitivity of the instrument and increase the zero error, but too high gain will reduce the stability of the instrument and produce oscillation.
3. Principle of optical axis angle measurement
As shown in Fig. 9, the amplifier and three state comparator constitute the steering control circuit of the lens motor. In.adj is the zero adjustment potentiometer of the amplifier and gain is the gain adjustment potentiometer of the comparator. Under the measurement conditions, relay J8 is turned on, its normally open contacts j8.1 and j8.2 connect the signals of photocell Pu and PD to the amplifier, and adjust its balance point with potentiometer BAL. During calibration (the luminous intensity of the calibration lamp is 20000 CD), set the optical axis angle to 0 °, and adjust BAL so that the reading of the corresponding optical axis angle indicator is zero. During operation, if the signals of PU and PD are unbalanced, the lens motor is driven, and the displacement sensor detects the displacement and sends it to the optical axis angle indicator circuit to deflect the pointer of the indicator until Pu and PD reach a new balance. At this time, the reading of the indicator is the deflection of the optical axis of the headlamp.
When exiting the measurement, J8 is released, and its normally closed contacts j8.1 and j8.2 are connected to potentiometer zero and displacement sensor respectively. If the lens is not at the origin at this time, they will generate a signal to return the lens to the origin and drive the lens motor to rotate accordingly.
4. Others
The tester uses the same group of photocells to measure the luminous intensity and optical axis angle of the headlamp. Therefore, the photocell signal is not only sent to the optical axis angle measurement circuit, but also sent to the addition circuit for signal superposition to generate the signal of luminous intensity.
The luminous intensity signal and optical axis angle signal are sent to their respective indicator circuits at the same time to drive the deflection of the indicator pointer. Each indicator circuit is equipped with an adjusting potentiometer to adjust the gain of the circuit, the zero point of the amplifier and calibrate the scale value of the indicating ammeter. In order to facilitate computer processing, these signals are also output as sampling signals and connected with the computer through connecting cables.
In order to facilitate manual adjustment, operation and calibration, the instrument is also equipped with relevant relay control circuit, operation switch and button.
In order to adapt to the rapid movement of the instrument to the detection position or return from the detection position, the movement of the bottom box of the instrument (i.e. the left and right movement of the whole machine) adopts AC reversible gear deceleration servo motor and fast braking device, which can ensure the stability of the light receiver under the measurement state. The AC speed regulating circuit makes the motor run at high speed under non measurement conditions, while the motor runs at low speed under measurement conditions, and accurately and stably align the instrument with the main optical axis of the headlamp.
Use of headlamp tester
1、 Preparation before testing
1. Preparation of tester
(1) When the headlamp tester is not receiving light, check whether the pointers of the photometer and the optical axis deflection indicator can be aligned with the mechanical zero point. If the pointer is out of alignment, it can be adjusted at the zero point with the zero adjustment screw.
(2) Check whether the mirror surfaces of the condenser lens and reflector are dirty or blurred. If any, wipe it with a soft cloth or lens paper.
(3) Check the technical condition of the level. If the level has no bubbles, repair it; If the bubble is not in the red line frame, it can be adjusted with a level regulator or gasket.
(4) Check whether the guide rail is stained with dirt or small stones. When there are sundries, clean them up.
2. Vehicle preparation
(1) Remove oil from the headlamp.
(2) The tire pressure shall comply with the regulations of the automobile manufacturer.
(3) The vehicle battery shall be in sufficient cushion state.
2、 Test method of automatic tracking optical axis headlamp tester
1. Keep the vehicle perpendicular to the guide rail as far as possible and drive close to the tester so that the headlamp is 3M away from the light receiver of the tester.
2. Align the vehicle with the aligner to align the tester with the vehicle.
3. Turn on the headlamp, turn on the power supply of the tester, and move the tester position with the up, down, left and right control switches to make the headlamp beam shine on the light receiver.
2、 Detection principle
4. Press the measuring switch, the light receiver can track the headlamp light state, and the and luminous intensity can be measured according to the indicated values of the optical axis deflection indicator (marked with scale) and the photometer.
If the deflection of headlamp axis needs to be adjusted, the irradiation direction of headlamp can be adjusted while observing the optical axis deflection indicator to make the pointer return to the specified range.
Taking the automatic headlamp detector as an example, its application in the automatic detection line is briefly discussed below.
First of all, in order to avoid the shadow of external light, the headlamp tester shall be arranged at the middle station of the automatic detection line. In order to ensure the perpendicularity between the optical axis of the headlamp and the light receiving surface of the instrument, an appropriate lead wire shall be provided in front of the detector. In order to ensure the detection distance of 3M, a parking space control device, such as photoelectric detection device, shall be set in front of the detector. The guide rail and light receiving box of the instrument must be installed correctly according to the requirements of the operation manual.
There are two types of interface signals of the tester: analog signal and switching signal. The analog signal includes luminous intensity signal, up and down deflection angle of optical axis and left and right deflection angle signal. The luminous intensity signal is 0-5V and the optical axis angle signal is - 2.5 - + 2.5V, which are all collected from their respective indicator circuits, and their amplitude can be adjusted by the corresponding output voltage adjustment potentiometer. The switching value signal is used to control the instrument to quickly enter or exit the measurement position, and to provide the detection tracking signal when the instrument is in the illumination area and enters the automatic tracking state of the optical axis and the automatic sampling signal when aligning the optical axis.
The signals controlling the movement of the instrument and the optical receiving box have three different sources, as shown in Figure 10. One is the moving key signal on the manual control box; The second is the optical axis tracking signal output by the motor steering control board; The third is the control signal output by the computer. Therefore, during manual operation, computer control should be cancelled. To avoid accidents, the control box can be removed during normal operation of the instrument. In order to reduce the interference of external signals to the computer, an isolation circuit must be added between the computer and the instrument.
After the instrument enters the lighting area, the automatic tracking state of the optical axis shall be started. Therefore, the manual control and computer control must be cancelled, that is, the manual switch shall be released and the intermediate relay Ju shall be cut off, and the steering control circuit drives the power relay J4. Therefore, it is necessary to sample and process the detection and tracking signal during computer control.
In order to collect the analog signals (light intensity and optical axis angle) output by the instrument, the computer must be equipped with an A / D conversion circuit, which must be equipped with at least three analog channels, one 0-5V channel for sampling luminous intensity, and two
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