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Method and apparatus for measuring distance to a target

  • US 5,589,928 A
  • Filed: 09/01/1994
  • Issued: 12/31/1996
  • Est. Priority Date: 09/01/1994
  • Status: Expired due to Term
First Claim
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1. A device for measuring the distance to a target comprising:

  • means for generating an optical signal;

    means for producing a plurality of modulation signals;

    means for combining said optical signal with said modulation signals to produce a modulated output signal which is intensity modulated at a plurality of frequencies;

    optical elements for directing said modulated output signal to said target and directing back a return signal reflected from said target, said optical elements including a mirror and a gimbal upon which said mirror is mounted for movement to a position where it reflects said modulated output signal onto said target;

    a detector for detecting the return signal reflected back from said target;

    a gimbal position control;

    a power meter for measuring the power of the return signals;

    a signal generator which generates reference signals, each of which is offset in frequency from a corresponding one of the intensity modulation frequencies by a predetermined amount;

    means for combining the return signals with the reference signals to form a first set of intermediate frequency signals, each of which corresponds to one of said intensity modulation frequencies;

    means for combining the modulation signals with the reference signals to form a second set of intermediate frequency signals, each of which corresponds to one of said intensity modulation frequencies; and

    a computer for calculating a set of phase differences between said output beam and said return signals for each of said modulation frequencies from the first and second set of intermediate frequencies, and determining the distance to the target from said phase differences, and for receiving input from said power meter and to output instructions to said gimbal control so as to adjust the position of said gimbal to maximize the power of said return signals.

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