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Absolute optical encoder system

  • US 4,445,110 A
  • Filed: 07/28/1980
  • Issued: 04/24/1984
  • Est. Priority Date: 07/28/1980
  • Status: Expired due to Term
First Claim
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1. An optical angular encoder system including a code disc having a plurality of concentric optical code tracks thereon, illuminating means for illuminating the code tracks, detecting means for detecting illumination which passes through the code tracks and decoding circuitry for providing an angular output in response to the output of the detecting means, the system characterized by:

  • the code tracks comprising a fine code track, at least one more significant track encoded for a natural binary output, and at least two most significant coarse tracks encoded for Gray code output;

    a plurality of illuminators associated with respective groups of code tracks, each illuminator being optically isolated from those code tracks with which it is not associated;

    means for sequentially enabling at least some of the illuminators to optically multiplex code track signals, common detector outputs associated with groups of multiplexed code tracks, and decoder circuitry for demultiplexing the common detector outputs;

    multiplier circuitry for providing a multi-bit digital output from sinusoidal outputs of the fine track by deriving a family of phase shifted sinusoids in parallel circuits, converting the family of sinusoids to square waves and logically combining the square waves from parallel circuits, the multiplier circuitry being designed to provide a multi-bit digital output directly from the sinusoidal detector outputs only through one of a plurality of segments of the fine track cycle, there being means for selectively modifying the sinusoidal inputs to the multiplier circuitry such that those inputs are identical though each of said segments of the fine track cycle;

    the detecting means associated with the more significant tracks including at least a lead detector and a lag detector, the locations of which are phased with respect to signals from said fine track, and which generate signals which, respectively, lead and lag the signal of the next lower order track, and the decoding circuitry associated with those tracks including means to select either the lead or the lag detector output as a function of the logic state of the next lower order track signal to synchronize each track to the preceding track; and

    the decoding circuitry associated with the most significant Gray code tracks including means to synchronize those tracks to the natural binary tracks.

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