Abstract:
A standalone gradient detector system, utilizing a gradient detector with a several photodetectors, is disclosed. A lamp emits light toward a screen. The light strikes the photodetectors on a photodector array, which communicate the light intensity to a gradient circuit. The gradient circuit compares the intensity values from each photodetector with the intensity value for the photodetector immediately adjacent, and computes a gradient value. The maximum gradient value is displayed using a display device, and the position of the photodetector with the maximum gradient value is indicated by an adjacent light source. The gradient of an automobile headlamp may thus be found easily, assisting in headlamp positioning during headlamp and vehicle manufacture.

Description:
BACKGROUND  
       [0001]     Automobile headlamps are aimed on the vehicle near the end of the vehicle manufacturing process to ensure that the light beams emitted from the headlamp will be properly positioned with respect to the vehicle. Proper aim of the headlamps is important, as the headlamps must illuminate large portions of the roadway for the driver, but avoid glare in the eyes of oncoming traffic. One import criteria in aiming headlamps is measurement of the gradient of the beam pattern near the horizon. Headlamp manufacturers use a similar process to test new lamp designs and correct errors in the reflector before wide-scale manufacturing.  
         [0002]     The gradient, in the instance of headlamp aiming and manufacture, is a measure of the change of the light intensity between two or more points from the center of the beam to the vertical limits of the beam. The center of the headlamp beam is ideally positioned to project light onto the road surface. Light incident to the main beam, or any light located above the horizon (assuming a flat driving plane), may cause glare light for oncoming drivers. Therefore, it is desirable for a large amount of light to be directed just below the horizon (and on the road) and very little light to be directed just above the horizon (in the face of oncoming traffic). Accordingly, it is desirable for the largest light gradient to be found at or near the horizon.  
         [0003]     A gradient calculation requires at least two measurements of light intensity in two different places on the beam pattern. Typically, this is accomplished by using a single fixed intensity detector, or photodetector, and subsequently moving the headlamp through the use of a gonio-photometer system. The value of the maximum gradient, and the position of the maximum gradient on the beam pattern, are determined through the use of an external software-driven computer system that interprets the intensity values of the detector and calculates the gradient between any two detector readings. This process, including the use of the gonio-photometer system to move the headlamp, is time consuming. The process is especially time consuming during headlamp manufacture, when many small changes are typically made to the headlamp reflector or other geometries.  
         [0004]     A desirable feature of a gradient detector would be the inclusion of a plurality of photodetectors. A system utilizing a plurality of photodetectors would be operable to sample the light intensity from several points on the headlamp beam simultaneously, and then compute and locate the maximum gradient value. Such a system would greatly increase the speed and efficiency of measuring the gradient of the beam pattern by providing nearly instantaneous feedback regarding the location and value of the maximum light gradient. The prompt feedback would be especially helpful when manufacturing headlamps, as changes could be made to the headlamp much more quickly, without the delay of the gonio-photometer system. The prompt feedback would also be helpful when aiming headlamps during the manufacturing process, as adjustments to the aim of the headlamp could be made based on the location of the maximum gradient value.  
       SUMMARY  
       [0005]     A light beam gradient detector comprises a photodetector array positioned in front of a light beam. The photodetector array includes a plurality of photodetector elements each operable to provide a signal that corresponds to the light received by photodetector element. A gradient circuit is in communication with the photodetector array and operable to determine a light gradient measured between two adjacent photodetector elements. The gradient circuit is further operable to determine the maximum light gradient of all the measured light gradients. A display device is in communication with the gradient circuit and operable to display the value of the maximum measured light gradient near the location of the photodetector array. A plurality of light sources are also provided in association with the photodetector array. Each of the plurality of light sources is positioned adjacent to one of the plurality of photodetector elements. To indicate the location of the maximum measured light gradient, one of the plurality of light sources is illuminated when the maximum measured light gradient is displayed. The light beam gradient detector, including photodetector array, associated light sources and display device may be a free-standing unit or may alternatively be mounted on a screen or a wall, such as a wall having markings representative of a roadway. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a front perspective view of a gradient detector system;  
         [0007]      FIG. 2  is a component view of the gradient detector as shown in  FIG. 1 ;  
         [0008]      FIG. 3  is a side view of the gradient detector system as shown in  FIG. 1 ; and  
         [0009]      FIG. 4  is a block diagram overview of the electrical components included in the gradient detector system. 
     
    
     DETAILED DESCRIPTION  
       [0010]     One embodiment of a standalone light beam gradient detector is provided as shown in  FIG. 1 , and is generally indicated as numeral  12 . The standalone gradient detector  10  comprises a gradient detector  16  suspended by a support device  12  to allow the gradient detector to receive light emitted from a vehicle lamp. The gradient detector  16  is comprised of a display device  18 , a photodetector array  20 , and a plurality of light sources  24 . The photodetector array  20  includes a plurality of photodetectors  22  arranged in a vertical column, with the plurality of light sources  24  adjacent to the photodetectors  22 .  
         [0011]     The support device  12  may take a number of different forms. For example, the support device may be a tripod, pole, or other device that properly positions the gradient detector  16  in the air to receive light from the lamp. Alternatively, the support device  12  may be a screen having a plurality of markings thereon. The screen  12  may be positioned on a fixed structure or portable. For example, the screen may be attached to or part of a wall, or the screen may be attached to a moveable screen stand, as is well known in the art, to increase portability. The markings on the screen  12  are representative of a roadway  30  and a flat horizon  36 . The roadway  30  includes a driver&#39;s lane  32  and an oncoming traffic lane  34 . The markings on the screen are used to adjust the beam pattern of an automobile headlamp so that it conforms to the desired shape, size and direction. The markings are well known and practiced in the art.  
         [0012]     Referring now to  FIG. 1 , the gradient detector  16  is attached to the screen  12 . The gradient detector  16  is positioned near the center of the screen  12 , with the photodetector array  20  positioned vertically. As shown in  FIG. 2 , the gradient detector  16  is comprised of a photodetector array  20  including a plurality of adjacent photodetectors  22 , each in electrical communication with a gradient circuit  40  (see  FIG. 4 ). The gradient detector also comprises a plurality of light sources  24  associated with each of the photodetectors  22  and a display device  18 . The light sources  24  and display device  18  are both in electrical communication with the gradient circuit.  
         [0013]     The display device  18  comprises an LED display including a plurality of individual number displays  26 . As shown in  FIG. 2 , four individual number displays  26  are shown. The individual number displays  26  are operable to display a full range of alphanumeric characters. Of course, alternate embodiments may include any number of individual number displays  26  attached to the display device  18 , or may include a cathode-ray tube (“CRT”) screen  12 , liquid crystal display, or an array of light emitting diodes, operable to display a plurality of alphanumeric characters. Each of the individual number displays  26  is in electrical communication with the gradient circuit  40 .  
         [0014]     The photodetector array  20  is comprised of a plurality of photodetectors  22 . A plurality of light sources  24  are positioned next to the plurality of photodetectors. The photodetectors  22  are positioned in a substantially straight vertical line on the photodetector array  20 , and are spaced equally apart on the array. Each of the photodetectors is capable of providing a signal related to the light received by the photodetector. For example, each of the photodetectors may provide a signal that corresponds to the intensity of light at the photodetector. Adjacent to each of the photodetectors  22  is a corresponding light source  24 , such that an equal number of photodetectors  22  and light sources  24  are present on the gradient detector  16 . The light sources  24  may be light emitting diodes or any other light source as commonly used to indicate a particular location. Each of the plurality of photodetectors  22  and light sources  24  is in electrical communication with the gradient circuit.  
         [0015]     As shown in  FIG. 4 , the gradient circuit  40  is an electrical circuit, such as a software controlled microchip. Of course, the gradient circuit could be comprised solely of hardware devices. The gradient circuit  40  may be located within the gradient detector  16 , or may be located separately. The gradient circuit  40  is in electrical communication with the photodetectors  22  on the photodetector array  20 , the display device  18 , and the light sources  24 . Through a multiplexer  42 , the gradient circuit receives electrical signals from each of the plurality of photodetectors  22  attached to the photodetector array  20 , and converts each of the electrical signals into a discrete intensity value. The gradient circuit then compares the values to determine the location of the largest light gradient in the array  20 . The microchip  40  instructs the LED display  18  to display the value of the largest light gradient, and the microchip also provides a signal to a LED driver  44  that lights the LED in the LED array that is associated with the largest gradient value.  
         [0016]     Operation of the disclosed embodiment of a standalone light beam gradient detector  10  is now described as shown in  FIGS. 1-3 . With reference to  FIG. 3 , an automobile is positioned at a pre-selected distance from the standalone light beam gradient detector  10 . Alternatively, an automobile headlamp may be positioned at a distance from the standalone light beam gradient detector  10 , if the headlamp is to be tested and measured apart from the automobile. The automobile headlamp is illuminated, and projects light  14  onto the gradient detector  16  and associated screen  12  or other support device. Light  14  from the lamp strikes the screen  12 , and the photodetector array  20  of the gradient detector  16 . Referring also to  FIG. 2 , light thus strikes each of the plurality of photodetectors  22 , which individually transmit intensity information to the gradient circuit  40 . The gradient circuit  40  compares the intensity value from each of the photodetectors  22  with the intensity value received from the immediately adjacent photodetector, and calculates a gradient value for each of the plurality of photodetectors  22 . The gradient circuit  40  transmits the largest gradient value calculated to the display device  18  for display using the plurality of individual number displays  26 . The gradient circuit  40  also energizes the light source  24  adjacent to the photodetector with the largest gradient value, providing a visual indication of the location of the largest gradient value. The gradient circuit  40  may be operable repeat the process of collecting intensity values from the photodetectors  22  and displaying the maximum gradient value over any frequency, including several times a second. The standalone light beam gradient detector may also be triggered to operate as described above by a switch or other means.  
         [0017]     With the position of the maximum gradient detected, the headlamp may be adjusted to better position the light beam emitted from the headlamp with respect to the horizon. Also, if the headlamp is being tested for conformity with certain specifications, locating the maximum gradient value will assist in completing the test and determining whether changes need to be made in the headlamp. If the gradient circuit includes a software program having a user interface, the display device may be used to display other information in addition to the maximum gradient value. For example, the intensity of the light beam at any of the plurality of photo detectors  22  may be displayed on the display device  18 . This will further assist the user in testing the headlamp for conformity with certain specifications.  
         [0018]     While the above operation has been described with respect to one embodiment of the standalone gradient detector, it should be understood that the functions and features of the gradient detector  16  may vary. For example, the gradient detector  16  and the gradient circuit  40  may be operable to display the smallest gradient value obtained from the plurality of photodetectors  22 , along with the light source adjacent to the photodetector with the smallest gradient value. Further, an alternate embodiment may display the average gradient value from the photodetector array  20 , or any other desirable data as obtained from the plurality of photodetectors  22 . As another example, the plurality of light sources may be associated with and positioned adjacent to the photodetectors in a location that is in-between each of the plurality of photodetectors as opposed to directly beside any one photodetector.  
         [0019]     Although other advantages may be found and realized and various modifications may be suggested by those versed in the art, it is understood that the present invention is not to be limited to the details given above, but rather may be modified within the scope of the appended claims.