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Process and apparatus for sensing magnitude and direction of lateral displacement

  • US 3,930,734 A
  • Filed: 04/26/1974
  • Issued: 01/06/1976
  • Est. Priority Date: 04/26/1974
  • Status: Expired due to Term
First Claim
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1. A process for sensing the magnitude and direction of lateral displacement of at least one line or slit element of an article comprising:

  • 1. producing two coherent light beams of the same intensity, one of said beams having a different frequency from said other beam, the frequency difference Δ

    f being within the radio frequency range;

    2. converging said beams to form an interference zone comprising a fringe pattern within the zone of convergence, said fringe pattern continuously moving laterally at a rate equal to Δ

    f;

    3. adjusting the fringe period λ

    s of the pattern to a width which is substantially wider than the width w of said element or the positive difference between the width of the element and an integer multiple of the fringe period nλ

    s ;

    4. positioning at least the portion of said article bearing said element within the interference zone in such manner that said article lies in a plane defined by the x-axis normal to the plane of the convergent beams and the y-axis normal to the fringe planes, and said element is in a position, relative to said article, such that the longitudinal axis of said element is substantially parallel to a fringe plane;

    5. laterally shifting the fringe zone and/or the article positioned within said fringe zone along the y-axis in such a manner as to produce relative lateral displacement between them while maintaining said element substantially parallel to the fringe plane at least at the central portion of the fringe zone;

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