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Indexed optical encoder, method for indexing an optical encoder, and method for dynamically adjusting gain and offset in an optical encoder

  • US 8,513,589 B2
  • Filed: 10/19/2012
  • Issued: 08/20/2013
  • Est. Priority Date: 08/28/2008
  • Status: Active Grant
First Claim
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1. An indexing method for use with an optical encoder, the indexing method comprising:

  • providing an encoder disk, comprising;

    a signal track comprising a diffraction grating formed as a ring on the encoder disk; and

    an index track formed as a ring on the encoder disk, the index track comprising an index mark provided at an index angular coordinate;

    providing an illumination system structured to direct light to the encoder disk;

    providing a detector structured to detect light diffracted from the encoder disk, the detector comprising;

    two offset detectors structured to detect light diffracted from the signal track and output a quadrature signal; and

    an index detector structured to detect light reflected from the index track and output an index pulse;

    calculating an estimated state count kest of quadrature states from a rising edge of the index pulse to a middle of the index pulse;

    calculating Qkest, wherein Qkest is the quadrature state at kest and corresponds to the quadrature state at an approximate center of the index pulse; and

    determining an offset correction to be applied to the optical encoder based on a value of Qkest.

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