Thickness measurement
First Claim
1. In an apparatus for use in measuring the position of a surface in a direction normal to said surface, as said position is related to a datum, wherein a beam of light is projected onto said surface along a first axis with the light reflecting from said surface along a second axis, said axes being in a common plane, the improvement comprising:
- a photodiode strip comprising a plurality of photodiodes positioned sequentially along a line, said strip being positioned transverse to said second axis with said line in said plane, whereby a change in the position of said surface in said direction will cause said second axis to move along said line with the result of a change in which of the photodiodes are illuminated by the reflected light; and
means connected to said photodiode strip for determining which photodiodes are illuminated to a predetermined degree, said means being arranged to repetitively scan the strip in a given direction to determine the voltage output of each diode in sequence along said line to thereby create a composite voltage signal which is a composite, as related to time, of the voltage output of each photodiode, as related to the direction of scan said beam having a leading edge and a trailing edge, said means connected to said photodiode strip producing a square wave initiated by that part (TA) of the composite voltage signal corresponding to the voltage output of the first diode to be illuminated to said degree and terminated (at TS) by the termination of said scan, the width of said beam between said leading edge and said trailing edge being sufficient to simultaneously illuminate a plurality of said diodes, said means determining which of the diodes, with respect to the direction of scan, is the first to be illuminated to said predetermined degree thereby determining the position of the reflected beam along said line, said means producing a sensible indication of the position of the reflected beam along said line calibrated in terms of the dimension between the part of said one surface at which the axes converge and said datum, said sensible indication being related to the time difference between said signals TA and TS.
5 Assignments
0 Petitions
Accused Products
Abstract
For detecting changes of level of a moving surface, a sharply defined light pattern is directed on to the surface and an image of the pattern is formed on a multiple photodiode strip so that a predetermined point of reference of the image is variably located on the strip depending on variation in level of the surface, the photodiode strip is repetitively scanned to create a voltage waveform repetitively defining the variable position of the point of reference on the image in relation to the fixed position of a point of reference on the photodiode strip, and the waveform is analysed to determine the variations in level of the moving surface.
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Citations
7 Claims
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1. In an apparatus for use in measuring the position of a surface in a direction normal to said surface, as said position is related to a datum, wherein a beam of light is projected onto said surface along a first axis with the light reflecting from said surface along a second axis, said axes being in a common plane, the improvement comprising:
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a photodiode strip comprising a plurality of photodiodes positioned sequentially along a line, said strip being positioned transverse to said second axis with said line in said plane, whereby a change in the position of said surface in said direction will cause said second axis to move along said line with the result of a change in which of the photodiodes are illuminated by the reflected light; and means connected to said photodiode strip for determining which photodiodes are illuminated to a predetermined degree, said means being arranged to repetitively scan the strip in a given direction to determine the voltage output of each diode in sequence along said line to thereby create a composite voltage signal which is a composite, as related to time, of the voltage output of each photodiode, as related to the direction of scan said beam having a leading edge and a trailing edge, said means connected to said photodiode strip producing a square wave initiated by that part (TA) of the composite voltage signal corresponding to the voltage output of the first diode to be illuminated to said degree and terminated (at TS) by the termination of said scan, the width of said beam between said leading edge and said trailing edge being sufficient to simultaneously illuminate a plurality of said diodes, said means determining which of the diodes, with respect to the direction of scan, is the first to be illuminated to said predetermined degree thereby determining the position of the reflected beam along said line, said means producing a sensible indication of the position of the reflected beam along said line calibrated in terms of the dimension between the part of said one surface at which the axes converge and said datum, said sensible indication being related to the time difference between said signals TA and TS. - View Dependent Claims (2, 3, 4, 5, 6)
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6. In an apparatus as set forth in claim 1, wherein the beam has a length transverse to said width greater than the dimension in the corresponding direction of the photodiodes of said strip and is positioned so that the photodiodes are intermediate the ends of said length whereby irregularities in said surface will not result in the beam moving transversely even partially off the photodiodes in a direction transverse to said line.
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7. In an apparatus for use in measuring the position of a surface in a direction normal to said surface, as said position is related to a datum, wherein a beam of light is projected onto said surface along a first axis with the light reflecting from said surface along a second axis, said axes being in a common plane, said apparatus utilizing a device for forming said beam of light, the improvement comprising:
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a photodiode strip comprising a plurality of photodiodes positioned sequentially along a line, said strip being positioned transverse to said second axis with said line in said plane, whereby a change in the position of said surface in said direction will cause said second axis to move along said line with the result of a change in which of the photodiodes are illuminated by the reflected light; said device being constructed and arranged so that during the course of measuring said surface position the beam of light is wholly within the limits of the length of said strip; and means connected to said photodiode strip for determining which diodes are illuminated to a predetermined degree, thereby indicating the position of said surface with respect to said datum, said means repetitively scanning the strip in a given direction to determine the voltage output of each diode in sequence along said line to thereby create a composite voltage signal which is a composite, as related to time, of the voltage output of each photodiode, as related to the direction of scan said beam having a leading edge and a trailing edge falling within said limits of length, the width of said beam between said leading edge and said trailing edge being sufficient to simultaneously illuminate a plurality of said diodes, said means determining which of the diodes are illuminated to said predetermined degree, determining the median of the diodes illuminated to said degree, and relating said median to a point of reference along the length of the line thereby determining the position of the reflected beam along said line, said means producing a sensible indication of the position of the reflected beam along said line calibrated in terms of the dimension between the part of said one surface at which the axes converge and said datum.
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Specification