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Encoder

  • US 4,933,673 A
  • Filed: 03/21/1988
  • Issued: 06/12/1990
  • Est. Priority Date: 03/24/1987
  • Status: Expired due to Term
First Claim
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1. A position detecting apparatus for detecting a position of a scale, with the scale having a plurality of tracks thereon and each of the tracks having a predetermined pattern arrangement to form a code, comprising:

  • a radiation source;

    an illumination system for illuminating the scale with a radiation beam from said radiation source, said illumination system including diffraction means for generating a plurality of diffracted beams from said radiation beam, said illumination system directing a first beam group to the plurality of tracks, with the first beam group having a diffracted beam corresponding to each of the plurality of tracks, and said illumination system directing a second beam group to a predetermined track of the plurality of tracks, with the beams in the second beam group being aligned along a direction of movement of the scale on which the predetermined track extends such that all of the beams of the second beam group are incident on the pattern of the predetermined track; and

    a detecting system for detecting said first and second beam groups modulated by each pattern on the plurality of tracks, said detecting system including a first sensor array for receiving the first beam group and outputting a first signal corresponding to the code, and a second sensor array for receiving the second beam group and outputting a second signal corresponding to the displacement of the pattern of the predetermined track, wherein the position of the scale is determined on the basis of said first and second signals.

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