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Method and apparatus for measuring and controlling the surface characteristics of sheet materials such as paper

  • US 5,654,799 A
  • Filed: 05/05/1995
  • Issued: 08/05/1997
  • Est. Priority Date: 05/05/1995
  • Status: Expired due to Term
First Claim
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1. An apparatus for the continuous, on-line measurement of a property of a surface of a moving sheet, said property being characterized by surface features having various scale sizes and heights, the apparatus comprising:

  • a laser light source;

    means for focusing incident light from the laser source along an optical path intercepting the surface of the moving sheet to illuminate a light spot on said surface;

    means for collecting light scattered at a non-specular angle from the illuminated spot;

    a photosensitive detector responsive to a spectrum of frequencies produced by the various surface feature scale sizes, the detector having an output;

    means for focusing the collected scattered light on said photosensitive detector, the output of the detector providing an output signal representing variations of the height position of the light spot on the surface of the moving sheet; and

    a plurality of channels each including a filter responsive to the output signal of the detector, said filters having different cut-off frequencies for passing different frequency spectra representing different ranges of surface features scale sizes.

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