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Method of optically detecting position of object and position detecting apparatus using the method

  • US 5,129,725 A
  • Filed: 09/17/1991
  • Issued: 07/14/1992
  • Est. Priority Date: 11/04/1986
  • Status: Expired due to Term
First Claim
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1. A displacement measuring device, comprising:

  • a movable scale for measuring displacement, said scale having a plurality of codes thereon, each code being formed by a plurality of bit patterns arranged in a predetermined direction, said scale also having thereon an incremental pattern having a plurality of diffraction grating patterns arranged with a smaller pitch than the arrangement of the codes, and a reference pattern corresponding to each of the plurality of codes;

    reference signal detecting means including first and second light-receiving elements for detecting the reference pattern by comparing outputs of said first and second light-receiving elements, and generating a reference signal;

    code detecting means for subsequently detecting the codes in response to the reference signal output from said reference signal detecting means;

    incremental signal detecting means for detecting interference light formed by diffracted light from the diffraction grating patterns in response to the displacement of the scale to output an incremental signal;

    counting means for counting the incremental signal output from said incremental signal detecting means, said counting means being reset in response to the reference signal; and

    position detecting means for detecting an absolute position of said scale on the basis of detected codes and the counting of said counting means.

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