Gyro rate computation for an interferometric fiber optic gyro

Patent metadata

Field	Value
Publication number	US-10502585-B2
Application number	US-201414522462-A
Country	US
Kind code	B2
Filing date	Oct 23, 2014
Priority date	Oct 23, 2014
Publication date	Dec 10, 2019
Grant date	Dec 10, 2019

Abstract

A method comprises supplying an optical input to an interferometric fiber optic gyro (IFOG) at a first frequency and then a different second frequency; detecting a difference in responses of the IFOG to the optical input at the first and second frequencies; and computing a gyro rate as a function of the difference and a correction term.

First claim

The invention claimed is:

1. A method comprising:
supplying an optical input to an interferometric fiber optic gyro (IFOG) at a first frequency and then a different second frequency;
detecting a first phase variation between counter-propagating optical signals at the first frequency;
detecting a second phase variation between counter-propagating optical signals at the second frequency;
detecting a difference in the first phase variation and the second phase variation of the IFOG to the optical input at the first and second frequencies;
determining a rotation of the IFOG based on a gyro rate, wherein the gyro rate is a function of the difference and a correction term.

2. The method of claim 1 , wherein the correction term represents a sum of time-dependent errors in the IFOG responses.

3. The method of claim 1 , wherein the gyro rate is not computed as a function of a calibrated scale factor.

4. The method of claim 1 , wherein the correction term is pre-computed according to initial first and second scale factors corresponding to the first and second frequencies.

5. The method of claim 4 , further comprising continuing to repeat computing the gyro rate without calibrating both scale factors if time-dependent errors or an event occurs that causes both scale factors to shift equally.

6. The method of claim 1 , wherein the gyro rate (Ω) is computed as
Ω=((Δ n 1 /Δt )−(Δ n 2 Δt )− C )/(1/SF 1 −1/SF 2 )

where SF 1 and SF 2 are pre-determined IFOG scale factors corresponding to the first and second frequencies, C is the correction term, and (Δn 1 /Δt)−(Δn 2 / Δt )is the difference in responses of the IFOG to the optical input at the first and second frequencies.

7. A system comprising:
an interferometric fiber optic gyro (IFOG);
a fiber optic light source for supplying an optical input to the IFOG at a first frequency and then a different second frequency;
a photodetector for detecting a first phase variation between counter-propagating optical signals at the first frequency and a second phase variation between counter-propagating optical signals at the second frequency of the IFOG to the optical input; and
a processor for determining a rotation of the IFOG based on a gyro rate as a function of a difference of the first and second phase variation and a correction term.

8. The system of claim 7 , wherein the correction term represents a sum of time-dependent errors in the IFOG responses.

9. The system of claim 7 , wherein the gyro rate is not computed as a function of a calibrated scale factor.

10. The system of claim 7 , wherein the correction term is pre-computed according to original first and second scale factors at the first and second frequencies.

11. The system of claim 10 , further comprising repeatedly computing the gyro rate without calibrating both scale factors if time-dependent errors or an event occurs that causes both scale factors to shift equally.

12. The system of claim 7 , wherein the gyro rate (Ω) is computed as
Ω=((Δ n 1 /Δt )−(Δ n 2 Δt )− C )/(1/SF 1 −1/SF 2 )

where SF 1 and SF 2 are pre-determined IFOG scale factors corresponding to the first and second frequencies, C is the correction term, and (Δn 1 /Δt)−(Δn 2 /Δt)is the difference in responses of the IFOG to the optical input at the first and second frequencies.

13. A method for an interferometric fiber optic gyro (IFOG) comprising:
applying a known rate to the IFOG and determining IFOG scale factors for optical inputs at first and second frequencies;
providing an optical input to the IFOG at the first frequency and detecting a first phase variation between counter-propagating optical signals at the first frequency of the IFOG;
switching the optical input to the second frequency and detecting a second phase variation between counter-propagating optical signals at the second frequency of the IFOG; and
using a difference between the first and second phase variations, the known rate, and the scale factors to determine an IFOG correction term representing a sum of time-dependent errors in the first and second IFOG phase variations.

14. The method of claim 13 , wherein the correction term (C) is computed from
Ω=((Δ n 1 /Δt )−(Δ n 2 /Δt )− C )/(1/SF 1 −1/SF 2 )

where Ω is the known rate, SF 1 and SF 2 are the scale factors corresponding to the first and second frequencies of the optical input, and (Δn 1 /Δt)−(Δn 2 /Δt) is the difference of the first and second IFOG phase variations.

Assignees

• Boeing Co

Inventors

• Detloff Shaun M
• Gingrich James K

Classifications

• G01C25/005

  initial alignment, calibration or starting-up of inertial devices · CPC title

• G01C21/005 Primary

  with correlation of navigation data from several sources, e.g. map or contour matching (G01C21/30 takes precedence) · CPC title

• G01C25/00 Primary

  Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass (testing, calibrating or compensating compasses G01C17/38) · CPC title

• G01C19/72 Primary

  with counter-rotating light beams in a passive ring, e.g. fibre laser gyrometers · CPC title

• G01C19/721

  Details, e.g. optical or electronical details · CPC title