Abstract:
Method and apparatus for measuring the quality of a finished surface by projecting a pair of parallel light beams onto the surface and reflecting the beams onto an image screen where they are electronically recorded and analyzed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed to the field of analyzing the reflective quality of surfaces and more specifically to the area of apparatus and method used to inspect and determine the quality of surfaces. 
     2. Background Information 
     In the automotive and appliance industry where painted surfaces of products need to be inspected, the conventional method used is to pass the product through an area of high intensity light emitted from banks of elongated fluorescent tubes. Human inspectors visually scan the product and look for appearance attributes and flaws such as roughness, gloss, orange peel, waviness, dents and others that contribute to a degraded measure of quality in surface appearance. The inspectors are then able to provide a relative rating of the overall surface quality of each inspected product, based upon their subjective evaluation. While the aforementioned subjective technique may be used by an experienced inspector with some measure of reliability and consistency, it is subject to wide variations between different inspectors, and does not lend itself to high speed applications. Automation techniques are desired to Provide a quantitative, rapid and more consistent measure of quality. The high speed and distinctive repeatability are desired to provide a basis for statistical analysis and correction of quality degradation. 
     SUMMARY OF THE INVENTION 
     The present invention utilizes a laser-based optical projection apparatus to produce a profile image of a test surface that is being evaluated. The profile image has been found to contain readily discernable representations of physical features on a surface which are relevant to its appearance quality. The apparatus generates a pair of light beams that are directed toward the test surface and are parallelly incident thereto. The incident light is both dispersed and reflected from the test surface. The reflected light impinges upon a light dispersing screen where it is imaged by a video camera and electronically processed. The images appearing on the screen constitute profiles of the test surface and, by comparing variations in the line images, the distance between the images, thickness of the line images, curvatures and other comparative features, the electronics attached to the video camera is able to detect and identify those features. The identified features are then analyzed by an appropriately weighted algorithm to produce a numerical index which is configured to correlate with a human inspection expert&#39;s visual assessment of the overall surface quality, having been previously calibrated. 
     It is an object of the present invention to provide an apparatus and method for projecting a pair of light beams onto a test surface and imaging the reflected beams for quality analysis. 
     It is a further object of the present invention to provide a projection apparatus and method in which a pair of diverging light beams are directed to a test surface in a parallel arrangement and are imaged onto a light dispersing screen for comparison through electronic means. 
     It is a further object of the present invention to provide a projection apparatus and method in which a pair of diverging light beams are directed to a test surface in a parallel arrangement and imaged onto a dispersing screen. The images are recorded and analyzed to give a measure of the quality of the test surface with reference against predetermined levels of quality. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective cutaway view of the housing which contains the components of the preferred embodiment of the invention. 
     FIG. 2 is a block diagram of the image processing portion of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The embodiment of the invention shown in FIG. 1 includes a substantially light-tight housing 100 shown in a partial cutaway view. Housing 100 includes a top 102, a bottom 104 and end panels 106 and 108. The bottom 104 includes a rectangular aperture 118 through which projected lines of light L 1  and L 2  are projected onto an area 152 of a test surface 150 underlying the housing 100. 
     A laser 110 is enclosed within the housing 100 and generates a collimated monochromatic pencil beam L. The pencil beam L impinges on a cylindrical lens 112 where it is caused to be diverged in a single plane as a fan beam B. A partially reflecting planar mirror 114 serves to transmit a portion of the beam B and reflect the remainder towards the opening 118. 
     A second planar mirror 116 is located in line with the portion of beam B transmitted through partially reflecting mirror 114. The planar mirror 116 is angled substantially the same as planar mirror 114 so that it reflects a diverging beam B 1  in a plane parallel to B 2  . Beams B 1  and B 2  are both directed to the area defined by the open aperture 118 in the base of the housing 104 and impinge upon an area 152 of the test surface 150. Beams B 1  and B 2  are projected onto the surface 152 as line beams L 1  and L 2  at an acute angle of incidence that is preferrably greater than 45°. The light is reflected from the test surface 152 as B 1R  and B 2R  and is imaged onto a screen 105 as respective images I 1  and I 2 . Depending upon the unevenness, the dispersing characteristics, the curvature and other properties of the test surface effecting the light, the respective images I 1  and I 2  will vary. 
     The screen 105 on wall 106 is preferably a white planar surface that has light dispersion characteristics and is generally nonabsorbent of the light energy. A video camera 202 is mounted in wall 108 directly across from wall 106 and contains a lens which is focused upon the screen 105 in order that it may record the images I 1  and I 2  appearing on the screen 105. The output of the video camera 202 is connected to an image processor/computer 204 that contains peripherals such as a video monitor 206, a printer 208 and a keyboard 210. 
     In operation, the more closely the properties of the surface area 152 of the test sample 150 are to a planar mirror, the images I 1  and I 2  will appear on the screen 105 with a predetermined separation and approximate two line images without significant width. However, as dispersion characteristics are present in the the surface 152, those characteristics will result in the images I 1  and I 2  appearing as thicker lines. Dents or curvatures in the test surface 152 will affect the shapes and spacing of the images I 1  and I 2 . (Separate and distinguishable intensity levels for beams B 1  and B 2  may be provided in order to correspondingly distinguish images I 1  and I 2  with respect to each other.) In essence, the images I 1  and I 2  are profiles of the surface 152 and the variations in the images I 1  and I 2  from straight lines are detectable and measurable. 
     The image processor/computer 204 is programmed utilizing various test samples having known reflective properties inspected with the projector apparatus and compared with the subjective ratings of a human expert utilizing conventional techniques. Utilizing appropriate algorithms, and samplings at different areas of the surface 150, an overall quality measure can be obtained in a printed form through the printer 208 with a rating that will correspond to that provided by a human expert. 
     As indicated in FIGS. 1 and 2, the image that is electrically recorded by the video camera is provided to the image processor/computer 204. A Frame Digitizer Board converts the analog video to a digital signal. The digitized image is provided to a Frame Processor Board where filtering and enhancement eliminates noise. The computer section is programmed with appropriate algorithms to analyze the filtered and enhanced images and, in view of previous analysis made by a human inspection expert, provides a quality measure to the operator. 
     It will be apparent that many modifications and variations may be implemented without departing from the scope of the novel concept of this invention. Therefore, it is intended by the appended claims to cover all such modifications and variations which fall within the true spirit and scope of the invention.