Method and apparatus for measuring and controlling the surface characteristics of sheet materials such as paper
First Claim
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.
1 Assignment
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Accused Products
Abstract
An on-line laser triangulation position sensing system provides measurements of the surface features of a moving sheet such as paper. The measurements are correlatable with measurements made with standard laboratory surface smoothness testers and provide predictions of the printability of paper during its fabrication. The sensing system includes a segmented balance detector having a high frequency response. The sensing system further includes signal processing circuitry comprising a plurality of channels, each channel including a filter. The various filters have different cutoff frequencies for passing different frequency spectra representing ranges of surface feature scale sizes. The cutoff frequency of each filter is varied in response to variations in sheet speed. The sheet sensing system further includes a sheet stabilizer to minimize flutter in the measurement region and a standardizing member permitting performance verification of the sensor system at at least one scale size spectrum. The sensing system may also be provided with a sheet compressor to compress the sheet in the measurement region so as to simulate the pressures applied to sheet samples by laboratory air leak smoothness testers. The output of the position sensing system may be used in conjunction with various kinds of papermaking machines to control one or more of the many papermaking process parameters that determine the smoothness or texture of the final product. The sensing system can be used to measure tissue crepe and such measurement can be utilized to control various crepe-determining stages in a tissue making machine and to monitor the condition of the creping or doctor blade in such a machine.
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Citations
45 Claims
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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:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. An apparatus for the continuous, on-line measurement of the topographical features of a surface of a moving sheet, said features having various scale sizes and heights, the apparatus comprising:
a laser triangulation position sensor for illuminating a light spot on the surface of the moving sheet and including a detector responsive to an image of the light spot reflected from the surface substantially along an optical axis of reflection, the detector comprising a pair of cells separated by a linear gap, the cells defining an active photosensitive area intercepting the reflection axis so that the image received by the detector bridges the gap to illuminate to a greater or a lesser extent the detector cells thereby sensing position deviations of the image substantially in accordance with variations in the height position of the light spot illuminating the surface of the moving sheet, the image being displaceable along an axis on the active area intercepting the linear gap, the detector having an output for providing a signal representing variations of the height position of the light spot illuminating the surface of the moving sheet, the linear gap being disposed at an angle lying between the image displacement axis and an axis orthogonal thereto, the angular orientation of the linear gap extending the measurement range of the detector. - View Dependent Claims (22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32)
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33. A method for measuring the surface features of a moving sheet, said surface features having various scale sizes and heights, said method comprising the steps of:
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focusing light from a source along an optical path intercepting the surface of the moving sheet to illuminate a light spot on said surface; collecting light scattered at a non-specular angle from the illuminated spot; providing, in response to the collected light, a signal representing variations in the heights of said surface features and having a frequency spectrum produced by the various scale sizes of said surface features; and processing the signal to produce a plurality of channels covering a total frequency range selected according to the total range of surface feature scale sizes of interest, each channel covering a surface feature scale size range that is different than the surface feature scale size ranges of the remaining channels. - View Dependent Claims (34, 35, 36, 37, 38, 39, 40)
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41. An apparatus for the continuous on-line measurement of a characteristic of a surface of a moving paper sheet having opposed surfaces, the apparatus comprising:
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a laser triangulation position sensor disposed adjacent one of the sheet surfaces for illuminating a light spot on said sheet surface, the sensor including a detector having an output for providing a signal representing variations of the height position of the light spot illuminating the surface of the moving sheet, the sensor further including a bottom, planar surface; and a backing platform positioned adjacent the other of said sheet surfaces, the backing platform including means for biasing the region of the sheet illuminated by the light spot toward the bottom surface of the sensor to compress said region of said moving paper sheet. - View Dependent Claims (42, 43)
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44. 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:
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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; at least one channel including a filter responsive to the output signal of the detector for filtering out low frequency variations in the detector output signal and passing frequencies in the detector output signal representing a range of surface feature scale sizes; means defining a reference surface along which the surface of the sheet is adapted to move in close proximity, said reference surface lying in a plane at which the incident light focusing means focuses the light spot illuminating the surface of the sheet; a standardizing member having an optical standardizing surface; and means for moving said standardizing member into an off-sheet standardizing position in which the optical standardizing surface is positioned substantially in the plane of the reference surface. - View Dependent Claims (45)
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Specification