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Incremental measuring instrument

  • US 4,253,021 A
  • Filed: 12/20/1978
  • Issued: 02/24/1981
  • Est. Priority Date: 12/30/1977
  • Status: Expired due to Term
First Claim
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1. In an instrument for measuring the movement of a first object with respect to a second object along a measuring direction, said instrument including first means, mounted on the first object, for defining a rotatable first pattern of spirally formed stripes, second means mounted on the second object, for defining a second pattern of stripes oriented substantially perpendicularly to the measuring direction, means for generating an optical image of one of said patterns on the other of said patterns at an image zone, means for generating a measurement signal representative of the intensity of light given off from said other pattern, means for generating a reference signal, and means for evaluating the measurement signal in comparison with the reference signal, the improvement comprising:

  • the stripes of the rotatable spirally striped pattern are formed substantially in the form of involutes proceeding from a base circle centered at the center of rotation of the spirally striped pattern; and

    said means for generating an optical image includes means for orienting the stripes of the second pattern substantially perpendicular to a line tangent to the base circle passing through the image zone;

    said means for generating an optical image operating to generate a reduced image of said one pattern on said other pattern.

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