There are a number of methods currently in use to detect the alignment of vehicle headlamps. Traditionally, a vehicle was positioned on a level surface a certain distance (e.g. 25 feet) from a flat, white wall. The pattern of the beams was observed by a human observer, who would then determine the top edge of each beam. The location of the top edge of the beam is typically specified in terms of the height above the ground and is measured along a certain vertical line specified in terms of an angle left or right of the center of the lamp.
FIG. 1 illustrates a vehicle headlamp alignment setup. Vehicle 10 is positioned a specified distance from wall 11. Headlamps 18 and 19 are activated and beams 16 and 17 illuminate wall 11. The top edge of each beam is generally measured at a prescribed position along wall 11. FIG. 1 illustrates four measurement points 12, 13, 14 and 15. Any given vehicle utilizes only two such positions, but which two depends on the particular headlamp. In certain cases the vertical locations are defined to be 2.0 degrees to the left (known as VOL) or 2.0 degrees to the right (known as VOR) of the centerline of the headlamp. In FIG. 1, locations 12 and 14 are the VOL positions and locations 13 and 15 and the VOR positions. Whether or not a headlamp is a VOL type or a VOR type depends on the headlamp manufacturer and how the headlamp has been designed to be audited. Both types of headlamps are in common use today.
Other than traditional manual observation of headlamp illumination, there are other systems in use today that rely on video cameras to observe the illumination pattern. Some of these systems attempt to locate the brightest point, or “hot-spot,” of the beam and then determine the top edge of the beam based on a horizontal and vertical offset from the hot-spot. Unfortunately the top edge of the beam is not always positioned the same with respect to the hot-spot as beam illumination patterns vary. Additionally, any time both headlamps simultaneously illuminate a flat surface, the light from one headlamp mixes with the light from the other headlamp, complicating the measurement.
Another system is use today is illustrated in FIG. 2, which is a system built and sold by Adroit Engineering, Inc. Two sensor units 20 and 22 are mounted on a wall and controlled by control unit 25. The system of FIG. 2 detects beam illumination and reports the top of each beam on the front panel using LED readouts and a LED vertical bar display. Sensor units 20 and 22 are not intelligent, independent sensor units; they are directly controlled by control unit 25 via point to point cables. The system is limited to two sensor units and is not networked to any other system, which requires that the audit data be manually recorded.