Abstract:
A light baffle arrangement for sensors is used to limit the sensing field of view. Arranging multiple said limited view sensors in a linear array provides a means to accurately locate and analyze the position of a beam pattern along said array axis as in checking vehicle headlamp beam alignment.

Description:
FIELD OF THE INVENTION 
     The present invention relates to systems and methods of industrial monitoring and quality control, and more specifically to systems and methods for detecting the alignment of vehicle headlamps. 
     BACKGROUND 
     At the end of World War II major building of the highway system we know today began in both the U.S. and Europe. In that era brightness of electric lamps was rated the same as commonly used today for the consumer, namely higher wattage produces higher brightness. It is important to understand that “brightness” is related to response of the human eye in the visible part of the spectrum which lies between the shorter wavelengths of ultraviolet and the longer wavelengths of infrared. 
     Freeways known today in the U.S. were only beginning to be built after the war; 
     therefore, nighttime road illumination was related to stopping safety in combination with close passing oncoming traffic. Therefore, for visibility safety the Department of Transportation (DOT) established vehicle headlamp wattage to be a maximum of  60  watts on the mainly two-way U.S. roads. In Europe of that reconstruction era the building of higher-speed roadways dictated vehicle headlamps at a maximum  65  watts for visibility safety. Those wattages remain in effect today. 
     In the mid to late  1990 ′s technology for manufacturing electric arc type headlamps evolved in Europe. These vehicle arc lamps produce approximately three times the brightness of incandescent vehicle lamps, and arc lamp power consumption is one half the incandescent wattage. Combining those statistics results in a total efficiency improvement approximately six times that of incandescent lamps in the visible spectrum. Under these circumstances  35 -watt electric arc lamps readily meet highway regulatory maximum wattage requirements both in the U.S. and Europe, even though they are much brighter to the eye! While that increased brightness is an improvement in night vision for drivers using arc lamps, at the same time there is a major risk of causing unsafe blindness in the oncoming traffic. Clearly there exists an ongoing nighttime vehicle headlamp lighting safety issue. 
     In order to establish nighttime road safety for both arc and incandescent sources 
     DOT established sharp headlamp beam pattern regulations. It is now required that the beam pattern top be accurately aimed to relatively strict standards by vehicle manufacturers. 
     Vehicle headlamp alignment requires significant quality control to assure meeting 
     DOT aiming standards. In the field of quality control it is necessary to measure at higher accuracy than the specified regulations. Variability of the human eye cannot meet the higher standards of accuracy and repeatability to evaluate headlamp beam vertical alignment; therefore, it is necessary to evaluate headlamp alignment with electro-optical instruments. In order to meet both quality and liability issues, it has become necessary to accurately measure headlamp alignment traceable to the U.S. National Institute of Standards and Technology (NIST). 
     By 1999 the U.S. vehicle producers began significant introduction of headlamp arc lamps in their products. In so doing quality control for headlamp aiming, also known as “headlamp audit”, became a prime concern at Ford Motor Company. Early headlamp audit equipment at Ford used Adroit Engineering beam sensors without baffling to eliminate spillover between left and right vehicle beams. This purposely created a need for the audit operator/driver to exit the vehicle and sequentially stand in front of each lamp while observing the audited position of the opposite lamp. Thereby variation of driver body weight was eliminated from the production statistical process control record. 
     To accomplish the foregoing this invention eliminates stray light sensor interference by introduction of sensor baffling. Having the driver exit the vehicle is still accomplished by a requirement to manually activate software recording of data from a position near the smart sensors. 
     BRIEF SUMMARY OF THE INVENTION 
     A light baffle arrangement for sensors is used to limit the sensing field of view. 
     Arranging multiple said limited view sensors in a linear array provides a means to accurately locate and analyze the position of a beam pattern along said array axis as in checking vehicle headlamp beam alignment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a vertical array configuration of sensing elements. 
         FIG. 2  illustrates a graphical display of light rays critical to operation of each sensing element. 
         FIG. 3  illustrates an engineering drawing cross section of each element in the sensing array. 
         FIG. 4  illustrates a typical layout of sensor arrays relative to a vehicle being tested for headlamp vertical alignment. 
         FIG. 5  illustrates plots of headlamp beam intensity as gathered by sensors for locating beam tops. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a front view of a typical arrangement of sensor elements is shown wherein the elements are accurately spaced along the linear axis of an array. In use the array axis is oriented in a vertical position. Location of a sectional view for  FIG. 2  is indicated by notation A-A. 
       FIG. 2  is a graphical representation of cross section A-A in  FIG. 1 . Light enters the element at circular aperture D 1  for detection by sensor D 2  at a distance of L 2  beyond D 1 . The sensing field of view is defined by conical frustum a-b-c-d. 
     In absence of any blocking baffle, undesirable stray light rays  1  and  2  entering D 1  are reflected on the inside tubular wall of D 3  such that reflected ray  1 ′ could intersect D 2  at point c, and reflected ray  2 ′ could intersects D 2  at point a. With said rays  1  and  2  falling outside the desired sensing field of view, it is necessary to block  1  and  2  from reaching points a and c at the edges of D 2 . 
     The location of intersection of rays  1 ′ and  2  at point e is controlled by inside diameter D 3  such that point e falls outside view field edge a-b at point f, an axial distance L 4  from aperture D 1 . It follows that an annular baffle located at said axial location L 4  blocks rays  1 ′ and  2  at point e when aperture D 4  edge is at point g, between points e and f. 
     Accurate construction of the foregoing baffling in combination with a relatively small finite detector size D 2  passes a small penumbra of annular rays defined by angle a-d-c thereby creating insignificant fuzziness of detection edge of sensing field of view a-b-c-d. 
     The baffling arrangement in  FIG. 2  prevents all rays outside the sensing Field of View and the aforementioned penumbra from reaching any part of detector D 2  without two or more reflections from low reflectance surfaces on the entire interior of the sensing element. 
     Referring to  FIG. 3 , this cross section shows typical element hardware at location A-A in  FIG. 1 . The packaging enclosure consists of a metal extrusion housing constructed in two halves  300 . Clamped to both interior and exterior of said enclosure  300  are two strips of plastic  301  and  302 . Said strips  301  and  302  enclose the components of a light baffle system consisting of baffle liners  303  comprised of two cylindrical portions and an aperture at an opening for photodiode sensor  304  electronically mounted on an electronic circuit board  305 . A means for mounting said circuit board  305  is a series of screw fasteners represented at insulated standoff  306 . 
     Sealing the sensing element enclosure cavity is window  307  held in place by a plastic set of rails  308  beneath which are resilient seals  309 . Adjacent to the inside window face is a spacer ring  310  clamping retaining baffle apertures  311  and  312  spaced between said cylindrical baffle liners  303 . 
     The resulting sensor  304  and baffle components  303 ,  311 , and  312  complete the means of sensing light in a limited cone view  313  as previously described in  FIG. 2 . 
     Referring to  FIG. 4 , an embodiment of the patent subject beam array is a means to detect vertical aiming of vehicle  400  headlamp beams  401  in a vertical direction  402 . The U.S. DOT specifies detection distance  403  between headlamps  401  and smart sensor arrays  404  as 25 feet. The basic ZERO reference for headlamp alignment is a horizontal plane emanating from headlamps  401  and intersecting sensor arrays  404 . The smart sensors accomplish sensing beam height deviations from the required reference plane at the sensors  404 . 
     Referring to  FIG. 5 , beam profile data in the form of illumination curves  50  and  55  from smart sensor arrays permits detection of headlamp beam vertical alignment (i.e. −Headlamp aim audit). Note that “UP” is on the LEFT, and detected beam intensity is on the RIGHT. 
     The foregoing descriptions of the embodiments of the present invention have been presented for purposes of illustration and description only. They are not intended to be exhaustive or to limit the present invention to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. The scope of present invention is defined by the appended claims.