Apparatus and method for measuring optical axis deflection

Abstract: In the apparatus for measuring optical-axis deflection angle of a headlight, according to the present invention, the optical-axis detecting means (3) detects the optical axis (ℓ'') of the light projected at the first location (E₁) from the headlight (7), and the screen box moving mechanism (2) moves until the position of the optical axis (ℓ'') coincides with the center of the screen (9). Then, the screen box is stopped there. Next, the screen moving mechanism (10) is put into operation to move the screen (9) from the first location (E₁) to the second location (E₂), the optical-axis detecting means (3) detects the optical axis (ℓ'') from the light projected onto the screen (9), and the controlling means (6) makes a predetermined calculation from the information on the optical-axis position, thereby calculating a deflection angle (α₁, α₂) of the optical axis.

Description: BACKGROUND OF THE INVENTION Field of the Invention: The present invention relates to an apparatus and a method for inspecting a vehicle headlight. Description of the Prior Art: While a car is running at night or in a similar condition. its headlight should not dazzle the driver of a car running in the opposite lane or people walking against the car but provide a sufficient illumination for the driver to have an easy viewing in front of the car. For these purposes. it is legally prescribed that the angles of an optical-axis deflection (deviation) of the light beam projected from the headlight in the horizontal and vertical directions should be within the respective predetermined allowable ranges. Accordingly, for example, after manufacture and assembling of a car or during inspection after the car has been used for a predetermined period, the optical-axis of the headlight is measured to check whether its angle of deflection is within the predetermined allowable range. For such measurement of the optical-axis deflection angle of the headlight, a variety of measuring apparatuses has been proposed so far. One of the well-known apparatuses for measuring the optical-axis deflection angle of light beam projected from an automotive headlight will be described by way of example with reference to Fig. 1. Referring to this Fig. 1, it is illustrated that a car 100 is stopped at a predetermined position while an optical-axis deflection angle measuring apparatus 102 is laid at a predetermined distance L apart from a headlight 101 of the car 100. As will be seen from Fig. 2, the optical-axis deflection angle measuring apparatus (will be referred to as "measuring apparatus" hereinbelow) 102 comprises a base 103 and a screen 104 freely movable vertically (in the Y-direction) and horizontally (in the X-direction). The light projected from the headlight 101 is collected into the main unit 106 through a converging lens 105, and projected onto the screen 104. For measurement of the optical axis of the light with the measuring apparatus 102, the screen 104 is positioned in the vertical and horizontal directions while viewing through the view-finders 107 and 108, the position of the optical axis of the light projected on the screen 104 is determined, and then the deflection angle of the optical axis is calculated from the measured position thereof. With such measuring apparatus, however, the inspecting worker positions the screen with respect to the headlight in a manual and visual manner using the finders. Thus, much labor and time are needed for attaining a positioning of the screen in a precisely aligned relationship with the headlight, and such positioning is possibly inaccurate in some cases. Also with such measuring apparatus, the inspecting worker visually locates the optical axis from the light projected on the screen for determination of the position of the optical axis. This work requires for the worker to a have a sharp sense, a high skill and much experience. That is, the work is difficult and thus likely to be erroneous. An apparatus very similar to the one just described is known from EP-A-0 296 856. This document is concerned with providing a more compact apparatus for inspecting and subsequently aiming vehicle headlights and suggests to install a screen within a housing mounted on a base, the screen being arranged opposite a converging lens. The lens is positioned opposite a vehicle headlight to be aimed by raising or lowering the housing as necessary, i.e. along the Y-direction, and by moving its base perpendicular thereto, i.e. in the X-direction. During the subsequent aiming operation the position of the screen remains unchanged. GB-A-2 179 180 discloses a device for aiming vehicle headlights which device includes a screen onto which light from a headlight to be aimed is projected. The light distribution pattern on the screen is evaluated by means of a TV-camera and adjustments may be made until the actual light distribution pattern matches a desired one. The screen is not moved during the adjustment operation. SUMMARY OF THE INVENTION Accordingly, the present invention has as an object to overcome the above-mentioned drawbacks of the prior art by providing an apparatus and a method for inspecting a vehicle headlight automatically, accurately and speedily. The above object is attained by providing an apparatus comprising the features as set out in claim 1 and also by providing a method comprising the steps as set out in claim 8. Further modifications and advantageous embodiments of the invention are specified in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and advantages of the present invention will be better seen from the ensuing description made, by way of example, of the embodiments of the present invention with reference to the drawings, in which: Fig. 1 is a side elevation of a conventional optical-axis deflection angle measuring system: Fig. 2 is a perspective view of a measuring apparatus used in the measuring system shown in Fig. 1; Fig. 3 is a schematic block diagram of an apparatus for measuring the optical-axis deflection angle of a headlight according to a first preferred embodiment of the present invention; Fig. 4 is a perspective view of the screen box moving mechanism according to the present invention; Fig. 5 is also a perspective view of the screen moving mechanism provided inside the screen box, according to the present invention; Fig. 6 is an explanatory illustration of the determination of the optical-axis deflection angle when the light projected from a headlight travels, according to the present invention; and Fig. 7 is a flow chart showing the process of determining the optical-axis deflection angle using the apparatus for measuring the optical-axis deflection angle of a headlight according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One preferred embodiment of the measuring apparatus according to the present invention will be described herebelow with reference to the drawings. Referring now to Fig. 3, it is illustrated that the means for measuring the optical-axis deflection angle of a headlight (will be referred to as "measuring apparatus" also herebelow) comprises a screen box 1, a screen box moving mechanism 2, optical-axis detecting means 3, a deviation detecting means 4, a calculating means 5 and control means 6. The reference numeral 7 indicates an automotive headlight to be inspected, and note that the car provided with this headlight is precisely stopped at a predetermined positioned beforehand. The screen box 1 is disposed at a predetermined position in front of the automotive headlight 7 under inspection. As shown in Fig. 4, the screen box 1 has a large-diameter converging lens 8 at the front side thereof facing the headlight 7, and incorporates a screen 9 movable back and forth (in the Z-direction) in relation to the headlight 7. Further, the screen box 1 comprises a screen moving mechanism 10 which moves the screen 9 in the Z-direction from a first location (E₁) to second location (E₂) as will be seen from Fig. 5. The converging lens 8 used has a same curvature on both sides thereof, namely, it is a biconvex lens having a same focal distance f on both sides thereof. As shown in Fig. 5, the screen moving mechanism 10 comprises a base 11, a screw shaft 12 disposed rotatably in the Z-direction relative to the base 11, a slider 13 having formed therein a threaded hole 13a through which the screw shaft 12 is screwed and on which the screen is fixed, a screen moving drive motor 14 to rotationally drive the screw shaft 12, and a guide shaft 15 provided as passed through the slider 13 and supported in the base 11 parallelly with the screw shaft 12. The screen box moving mechanism 2 is provided to move the screen box 1 independently in two different directions, namely, in the X- and Y-directions which is parallel to the surface of the screen 9. The screen box moving mechanism 2 in this first embodiment of the present invention consists, as shown in Fig. 4, of an X-directional moving mechanism comprising a screw shaft 17 and guide shaft 18 disposed in the X-direction as supported in a base 16, a slider 19 having formed therein a threaded hole 19a through which the screw shaft 17 is screwed and a first screen-box moving drive motor 20 which rotationally drives the screw shaft 17; and a Y-directional moving mechanism comprising a feeding block 1a provided on the screen box 1 and having a threaded hole through which a screw shaft 21 provided as standing upright in the Y-direction (vertically) on the top of the slider 19 is screwed, and a second screen-box moving drive motor 22 which rotationally drives the screw shaft 21. The first and second screen-box moving drive motors 20 and 22 are feedback-controlled by the controlling means 6 so that the optical-axis position of the headlight, varying from one car to another under inspection, coincides with the center of the screen 9 set at the first location (E₁). The optical-axis detecting means 3 is provided to pick up the light emitted from the headlight 7 and incident upon the screen 9 through the lens 8 and optically detect from the picked-up light a hot point (point of a maximum illuminance) corresponding to the optical axis. This detecting means 3 used in this embodiment is a VTR camera using pickup elements such as CCD (charge coupled device) or the like. The hot point is detected through a predetermined image processing. Note that the optical-axis detecting means 3 is not limited to the device in this embodiment but that a hot point may be detected from a photo-current ratio or the similar signal outputted from, for example, photo-sensors or the like disposed symmetrically to each other with respect to the center of the screen 9. The deviation detecting means 4 is provided to accurately, detect a positional deviation of the optical axis in each of the X- and Y-directions between a position (X₂, Y₂) attained by activating the screen box moving mechanism 2 with the screen 9 kept set at the second position (E₂) to move the screen box 1 in each of the X-and Y-directions until the hot point coincides with the screen center, and a similar position (X₁, Y₂) at the first position (E₁). Namely, the deviation detecting means 4 detects Δx = (X₁ - X₂) and Δy =(Y₁ - Y₂) precisely. The deviation detecting means 4 in this embodiment is so arranged as to optically detect a positional deviation of the optical axis from each rotated amount of the screw shafts 17 and 21. This means 4 consists of a rotary body (not shown) provided on the outer circumference thereof a scale with regularly spaced divisions, and a photo-sensor (not shown) which supplies to the control means 6 pulse signals corresponding in number to the count of the scale divisions provided on the rotary body. Counting the pulse signals supplied from the above-mentioned deviation detecting means 4, the calculating means 5 calculates deviations Δ x and Δ y of the optical-axis position in the X- and Y-directions, and it also calculates each of the optical-axis deflection angles α₁ and α₂ from the data on the deviations Δ x and Δ y using the following equations. For example, the optical-axis deflection angle α₂ in the Y-direction can be calculated by the following equation (a) in the optical geometry shown in Fig. 6: α 2 = tan -1 [(f-S 1 ) · Δ y/ f · S 2 ] where f : Focal distance of converging lens 8 S₁ : Distance between conveging lens 8 and first location (E₁) S₂ : Distance between first location (E₁) and second location (E₂) Next, the equation (a) for the optical-axis deflection angle α₂ will be derived referring to Fig. 6. First, assume that the focal point on the optical axis of the converging lens 8 in the physical space (lefthand space of the lens) is D. Also assume that the intersection of the optical axis ℓ' of the light projected from the headlight 7 with a line normal to the optical axis on the focal point D is B. The angle  formed between a line OB connecting the point B and the center 0 of the lens 8 and the optical axis ℓ of the lens 8 is equal to the angle  formed between the optical path (optical axis ℓ'') along which the precedent light (optical axis ℓ') travels after refracted by the lens 8 and the optical axis ℓ of the lens 8. This is because when the light source (the point B is assumed to be the light source) lies in the focal position, each light emitted from the light source and traveling after passing by the center of the convex lens becomes parallel to the traveling direction of the light passing by the center of the convex lens. Also, the point E₁ where the light (optical axis ℓ') through the point B intersects the optical axis ℓ of the lens 8 after passing through and refracted by the lens 8 is set at the first location (E₁) of the screen 9. and a position on the optical axis ℓ and apart a distance S₂ from the first location (E₁) is set at the second location (E₂). Under these conditions, an elementary mathematics can be used derive the following equation (a) for Δ ABC: α 2 = tan -1 [BC/f] Also, the following equation can be obtained for Δ OBD: BD = f tan = BC + CD therefore, BC = f tan - CD The following equation can be obtained for Δ FE₁E₂: f tan = Δ y/S 2 Also, the following equation can be obtained for Δ OAE₁: OA ( = CD) = S 1 tan  Hence, by inserting the equations (c), (d) and (e) into the equation (b), the equation (a) coil be easily obtained. The derivation of α ₂ has been described in the foregoing, but the elementary mathematics can be similarly used to obtain an equation for derivation of α₁. The control means 6 is intended to provide a feedback control by activating the screen box moving mechanism 2 when there exists a deviation between the optical-axis position on the screen 9 and the center of the screen 9 and making the optical-axis position coincide with the center of the screen 9, and also to control the operation of the screen moving mechanism 10 for moving the screen 9 from the first to the second location. In this embodiment, a microcomputer is used as this controlling means. The control means 6 in this embodiment is connected to the first and second screen-box moving drive motors 20 and 22, and also to the calculating means 5. It should be noted that in the measuring apparatus according to the present invention, a foldable first screen and a second screen may be provided as fixed at the first and second locations, respectively, inside the screen box in lieu of the screen and the mechanism which moves the screen. Next, the measurement of the optical-axis s deflection angle using the measuring apparatus according to the embodiment in consideration will be discussed referring to Fig. 7. I . First, the screen box moving mechanism 2 is put into operation with the screen 9 kept set at the first location (E₁), namely, with the screen moving mechanism 10 not in operation. That is, the screen box 1 is appropriately moved in the X- and Y-di rect ions while controlling the first and second screen-box moving drive motors 20 and 22 by means of the control means 6 (at first step 30). II. Then, the image projected on the screen 9 through the converging lens 8 at this time is picked up by a VTR camera in the optical-axis detecting means 3 to detect the optical axis, namely, the hot point, on the screen 9 through a predetermined image processing (at second step 31). III. The control means 6 judges whether or not the hot point as detected lies in the center of the screen 9. If the optical axis is not coincident with the screen center, the similar operations are repeated again from the first step (3) (at third step 32). IV. If it is judged at the third step 32 that the hot point coincides with the screen center, the first and second screen-box moving drive motors 20 and 22 are stopped from operating and the screen moving mechanism 10 is put into action. When the screen 9 has been thus moved to the second location (E₂), the screen moving mechanism 10 is stopped (at fourth step 33). V. Then, the first and second screen-box moving drive motors 20 and 22 are put into operation with the screen 9 at the second location (E₂) to move the screen box 1 in the X- and Y-directions (at fifth step 34). VI. The hot point is detected as in the second step 31 (at sixth step 35). VII. It is judged as at the third step 32 whether or not the hot point lies in the center of the screen 9. If the hot point is not coincident with the screen center, the operation returns to the fifth step 34 and the similar operations are repeated (at seventh step 36). VIII. Further, if it is judged at the seventh step 36 that the hot point coincides with the screen center, the first and second screen-box moving drive motors 20 and 22 are stopped and the deviation detecting means 4 accurately detects a deviation (Δ x, Δ y) in each direction between the hot-point position with the screen at the first location (E₁) and the hot-point position where the hot point is thus coincident with the screen center (at eighth step 37). IX. Thus, the calculating means 5 automatically derives the optical-axis deflection angles α₁, and α₂ in the X- and Y-directions based on the deviation (Δ x, Δ y) detected at the eighth step 37 by using the predetermined equation (a) (at ninth step 38). As having been described in the foregoing, the calculating means in the measuring apparatus according to the present invention (as set forth in Claim 1) makes a predetermined calculation, based on a deviation between the position of the optical axis where the latter is made to coincide with the center of the screen set at the first location and the position of the optical axis projected on the screen set at the second location, to automatically detect the deflection angle of the optical axis accurately and speedily, whereby the automotive headlight can be inspected extremely accurately, speedily and thus efficiently without much labor at the car inspection shop. Thus, the inspection of the headlight can be automated.

Claims: An apparatus for inspecting a vehicle headlight, comprising at least one screen (9) for projecting thereon the light beam of a vehicle headlight (7) to be inspected, the at least one screen (9) being arranged in or parallel to a plane and being movable independently in two different X- and Y-directions therein by associated first displacement means (17, 19a and 21, 1a), and means (3) for detecting the position of the optical axis of the light beam projected onto the screen (9) by detecting the point of maximum illuminance on the screen (9), characterized in that at at least two positions in the Z-direction perpendicular to said plane one of said at least one screen is positioned or postionable the first displacement means (17, 19a and 21, 1a) for moving the at least one screen (9) in the X- and Y- directions is controlled by feedback-control means (6) to center the point of maximum illuminance on the at least one screen (9), means (4) are provided for detecting the displacement of the at least one screen (9) in both X- and Y-directions, and means (5) for calculating the deflection angle (α₁, α₂) of the light beam's optical axis relative to a horizontal plane from the distance between two positions in the Z-direction and from the respective displacement amounts (ΔX, ΔY) required for centering the point of maximum illuminance on the screen (9) at said two positions. An apparatus according to claim 1, characterized in that there is provided a screen box (1) accomodating the screen (9) and having a converging-lens (8) mounted therein opposite the screen (9). An apparatus according to claim 1 or 2, characterized in that said at least one screen includes fixed screens disposed at said at least two positions in the Z-direction, wherein all of said screens but one are foldable. An apparatus according to claim 1 or 2, characterized in that said at least one screen comprises only a single screen (9) positionable at said at least two positions in the Z-direction by second displacement means (12, 13a). An apparatus according to claim 4, characterized in that said means (4) are adapted to calculate the amount (ΔX, ΔY) of displacement necessary for recentering said light beam on said screen (9) upon the screen (9) having been displaced, in the Z-direction, from a first position (E₁) into a second position (E₂). An apparatus according to claim 2 and 5, characterized in that the first displacement means (17, 19a and 21, 1a) are operatively connected to the screen box (1). A method for inspecting a vehicle headlight, comprising the steps of: a) placing a screen for projecting thereon a light beam of a vehicle headlight to be inspected and adapted to be moved independently in two different directions in its own XY-plane at a first position along the Z-direction, the Z-direction being perpendicular to the XY-plane, b) detecting the point of maximum illuminance of the light beam incident onto the screen for determining the light beam's optical axis, characterized by the steps of c) centering the light beam's optical axis on the screen by moving the latter in X- and/or Y-direction and measuring the amount of displacement (ΔX, ΔY) required for centering, d) placing a screen at a second position along the Z-direction spaced apart from the first position, e) repeating steps b) and c) and f) calculating the headlight optical axis angle relative to a horizontal plane from the distance between the first and second position along the Z-direction and from the amount of displacement (ΔX, ΔY) required for centering the light beam's optical axis in the second position with respect to the amount of displacement determined in step c) at the first position. A method according to claim 7, characterized in that detecting the point of maximum illuminance is performed using a VTR camera and image processing.

Inventors: KAYA TOSHIYUKI, MATSUSHITA NOBUO, TAKAO OSAMU, KAYA, TOSHIYUKI, MATSUSHITA, NOBUO, TAKAO, OSAMU, Kaya, Toshiyuki, c/o Chuo Electronic Measurement, Matsushita, Nobuo, c/o Chuo Electronic Measurement, Takao, Osamu, c/o Chuo Electronic Measurement
Applicants: CHUO DENSHI KEISOKU KK, CHUO ELECTRIC MEASUREMENT CO., LTD.
Application year: 1991
Main classification: G01M11
IPC codes: G01M11