Optics: measuring and testing – By particle light scattering – With photocell detection
Patent
1992-10-28
1995-03-28
Rosenberger, Richard A.
Optics: measuring and testing
By particle light scattering
With photocell detection
G01N 2188, G01N 2186
Patent
active
054022282
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a dirt counter for measuring and recording dirt speck sizes and intensities on paper. More specifically, the invention relates to an on-line dirt counter which measures the dirt speck sizes and intensities on a surface of a web of moving paper.
BACKGROUND ART
Several off-line dirt counters have been developed. A typical one, such as the BIOTRAN.TM. (of New Brunswick Scientific) extracts measurements such as total area and total counts from two-dimensional incoming images. Recently, an off-line system PAPRICAN MICROSCANNER.TM. (of Noram Quality Control and Research Equipment Ltd.) image analyzer applies the medium-pass filter as well as visual impact principles to detect and measure dirt speck size of two-dimensional images. The INTEC.TM. (of Intec Corp.) on-line dirt counter uses a laser light source and fiber optic receivers. It can detect dirt specks as small as 0.05 mm.sup.2. However, this device is not designed to measure dirt speck size using visual impact principles similar to human judgment as defined in TAPPI (Technical Association of the Pulp and Paper Industry) count.
There are also issued patents of interest which deal with the detection of flaws on surfaces. U.S. Pat. No. 4,172,666, Clarke, Oct. 30, 1979 distinguishes between different types of faults detected on a moving web. A defect detector scans the surface of the web with a laser and views the reflected light with a view or several detectors at various angles. Sums and differences between signals are used to discern which defects scatter light and which absorb it. The signal processing is not specifically related to the emulation of visual inspection as is the present invention.
U.S. Pat. Nos. 4,794,264 and 4,794,265, Quackenbos et al, Dec. 27, 1988, relate to an apparatus and method for uniquely detecting pits on a smooth surface. The moving surface is illuminated with a point source of laser light through a pair of beam splitters. Flaws and pits reflect specularly with different patterns. An annular mask shields one detector to view the neighborhood of a focal point and a window on the other detector constrains the signal to the central focus.
The invention in the above patents uses a beam splitter to view the same spot with a pair of detectors and to difference a central spot signal with a wider surround. However, Quackenbos et al illuminate the sample with a laser through the same beam splitter in order to observe glossy specular reflectance but does not illuminate diffusely outside the beam splitter to observe the fuse reflectance. Further, Quackenbos et al use a single detector in each beam rather than a linear array of detectors, and Quackenbos et al mask the two detectors to see only their intended domains of view rather than having the two beams differ only in sharpness of focus. Finally, Quackenbos et al use the difference of detector signals to distinguish flaws from pits but does not have a system wherein the signal differences correspond to a sharpening operation.
U.S. Pat. No. 4,740,079, Koizumi et al, Apr. 26, 1988, teaches a method and apparatus for detecting foreign substances, e.g. dirt specks or smudges, on the glossy surface of a semi-conductor chip which already contains delivered etches of the circuit. In the Koizumi et al patent, a circuit component is illuminated at near grazing incidence with a laser or a pair of lasers as the chip is physically moved past the detection configuration. A beam splitter divides the View of the surface of the chip in two identical beams with different polarization. Each beam is viewed at the same focus by a linear array of detectors. The difference signal corresponds to the diffused scattering from dirt on the chip. However, Koizumi et al does not calculate the integrated optical density as a visual impact parameter.
U.S. Pat. No. 4,724,481, Nishioka, Feb. 9, 1988, teaches a flaw detector for detecting a flaw in a sheet. The apparatus includes an array camera or series of array cameras which view a moving sheet. A circuit employs an electro
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patent: 3883436 (1975-05-01), Fletcher
patent: 4172666 (1979-10-01), Clarke
patent: 4226541 (1980-10-01), Tisue
patent: 4237539 (1980-12-01), Piovoso et al.
patent: 4253768 (1981-03-01), Yaroshuk et al.
patent: 4665317 (1987-05-01), Ferriere et al.
patent: 4724481 (1988-02-01), Nishioka
patent: 4740079 (1988-04-01), Koizumi et al.
patent: 4794264 (1988-12-01), Quackenbos et al.
patent: 4794265 (1988-12-01), Quackenbos et al.
Jordan Byron D.
Nguyen Nam G.
Pulp and Paper Research Institute of Canada
Rosenberger Richard A.
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