Apparatus and method for enhanced beat note detection
AssigneeHoneywell International Inc.
InventorsMarc Smiciklas, Chuck Croker, Norman Gerard Tarleton, Glen A. Sanders
Life of this patent
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Abstract
Lower noise and complexity techniques are disclosed for compensating for time varying phase changes in fiber optics in a resonant fiber optic gyroscope (RFOG). Orthogonal components derived from an electrical beat note signal and a difference between clockwise and counterclockwise resonant frequencies of an optical resonator coil of the RFOG are determined. The orthogonal products are converted to a phase which is differentiated with respect to time to obtain a beat note correction signal.
Claims20
A method for generating a beat note correction signal configured to reduce bias error in a resonant fiber optic gyroscope including an optical source optically coupled to an optical resonator coil, wherein the optical source is configured to generate a clockwise optical signal configured to propagate clockwise around the optical resonator coil and a counterclockwise optical signal configured to propagate counterclockwise around the optical resonator coil, the method comprising:
- receiving a resonant frequency in each of a clockwise direction and a counterclockwise direction of the optical resonator coil;
- receiving a beat note electrical signal derived from a portion of the clockwise optical signal and a portion of the counterclockwise optical signal;
- determining a difference frequency which is a function of the resonant frequency in the clockwise direction of the optical resonator coil and the resonant frequency in the counterclockwise direction of the optical resonator coil;
- generating (a) a sine signal which is a function of the difference frequency and (b) a cosine signal which is the function of the difference frequency;
- digitizing the beat note electrical signal;
- generating a first low pass filtered signal by mixing the sine signal with a digitized beat note electrical signal and removing first set of mixing products other than a first mixing product closest to zero Hertz;
- generating a second low pass filtered signal by mixing the cosine signal with the digitized beat note electrical signal and removing a second set of mixing products other than a second mixing product closest to zero Hertz;
- using the first and the second low pass filtered signals, generating a phase signal using a rectangular to polar coordinates converter;
- and
- generating the beat note correction signal by differentiating the phase signal with respect to time.
A non-transitory machine readable medium storing data that when loaded into a programmable circuit, causes the programmable circuit to instantiate an instantiated circuit configured to generate a beat note correction signal configured to reduce bias error in a resonant fiber optic gyroscope including an optical source optically coupled to an optical resonator coil, wherein the optical source is configured to generate a clockwise optical signal configured to propagate clockwise around the optical resonator coil and a counterclockwise optical signal configured to propagate counterclockwise around the optical resonator coil, wherein the instantiated circuit is configured to:
- receive a resonant frequency in each of a clockwise direction and a counterclockwise direction of the optical resonator coil;
- receive a beat note electrical signal derived from a portion of the clockwise optical signal and a portion of the counterclockwise optical signal;
- determine a difference frequency which is a function of the resonant frequency in the clockwise direction of the optical resonator coil and the resonant frequency in the counterclockwise direction of the optical resonator coil;
- generate (a) a sine signal which is a function of the difference frequency and (b) a cosine signal which is the function of the difference frequency;
- digitize the beat note electrical signal;
- generate a first low pass filtered signal by mixing the sine signal with a digitized beat note electrical signal and removing a first set of mixing products other than a first mixing product closest to zero Hertz;
- generate a second low pass filtered signal by mixing the cosine signal with the digitized beat note electrical signal and removing a second set of mixing products other than a second mixing product closest to zero Hertz;
- using the first and the second low pass filtered signals, generate a phase signal using a rectangular to polar coordinates converter;
- and
- generate the beat note correction signal by differentiating the phase signal with respect to time.
A resonant fiber optic gyroscope (RFOG), comprising:
- an optical source comprising at least one laser and configured to generate a clockwise (CW) optical signal and a counterclockwise optical (CCW) signal;
- a beat note detector configured to receive a first portion of the CW optical signal and a first portion of the CCW optical signal, and to generate a beat note electrical signal using the first portions of the CW and the CCW optical signals;
- an optical resonator coil;
- resonator closure optics configured to couple a second portion of the CW optical signal and a second portion of the CW optical signal into the optical resonator coil, and to transmit a third portion of the CW optical signal and a third portion of the CCW optical signal from the optical resonator coil;
- a CW rate detector configured to convert a portion of the third portion of the CW optical signal to a CW electrical signal;
- a CCW rate detector configured to convert a portion of the third portion of the CCW optical signal to a CCW electrical signal;
- a CW resonance tracking loop circuit configured to determine a resonant frequency of the optical resonator coil in a CW direction;
- a CCW resonance tracking loop circuit configured to determine a resonant frequency of the optical resonator coil in a CCW direction;
- and
- first circuitry configured to:
- receive the resonant frequency in each of a clockwise direction and a counterclockwise direction of the optical resonator coil;
- receive the beat note electrical signal;
- determine a difference frequency which is a function of the resonant frequency in the clockwise direction of the optical resonator coil and the resonant frequency in the counterclockwise direction of the optical resonator coil;
- generate (a) a sine signal which is a function of the difference frequency and (b) a cosine signal which is the function of the difference frequency;
- digitize the beat note electrical signal;
- generate a first low pass filtered signal by mixing the sine signal with a digitized beat note electrical signal and removing a first set of mixing products other than a first mixing product closest to zero Hertz;
- generate a second low pass filtered signal by mixing the cosine signal with a digitized beat note electrical signal and removing a second set of mixing products other than a second mixing product closest to zero Hertz;
- using the first and the second low pass filtered signals, generate a phase signal using a rectangular to polar coordinates converter;
- and
- generate a beat note correction signal by differentiating the phase signal with respect to time.
Dependencies are inferred from the claim text.