# US 10,502,585 B2 · Gyro rate computation for an interferometric fiber optic gyro

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 10,502,585 B2
- Document ID: US10502585B2
- Status: Granted
- Kind: B2
- Application number: 14/522,462
- Filed: 2014-10-23
- Published: 2016-04-28
- Granted: 2019-12-10
- Earliest claimed: 2014-10-23
- Assignees: The Boeing Company
- Applicants: The Boeing Company
- Inventors: Shaun M. Detloff; James K. Gingrich
- Web page: https://patentgrep.com/patent/US10502585B2

## CPC

- G01C 25/00: Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass (testing, calibrating or compensating compasses G01C17/38)
- G01C 19/72: with counter-rotating light beams in a passive ring, e.g. fibre laser gyrometers
- G01C 19/721: {Details, e.g. optical or electronical details}
- G01C 25/005: {initial alignment, calibration or starting-up of inertial devices}
- G01C: MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY (measuring liquid level G01F; radio navigation, determining distance or velocity by use of propagation effects, e.g. Doppler effects, propagation time, of radio waves, analogous arrangements using other waves G01S)

## 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.

## Claims

### Claim 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.

### Claim 2 (depends on 1)

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

### Claim 3 (depends on 1)

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

### Claim 4 (depends on 1)

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.

### Claim 5 (depends on 4)

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.

### Claim 6 (depends on 1)

The method of claim 1, wherein the gyro rate (Ω) is computed as
Ω=((Δn1/Δt)−(Δn2Δt)−C)/(1/SF1−1/SF2)
where SF1 and SF2 are pre-determined IFOG scale factors corresponding to the first and second frequencies, C is the correction term, and (Δn1/Δt)−(Δn2/Δt)is the difference in responses of the IFOG to the optical input at the first and second frequencies.

### Claim 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.

### Claim 8 (depends on 7)

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

### Claim 9 (depends on 7)

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

### Claim 10 (depends on 7)

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.

### Claim 11 (depends on 10)

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.

### Claim 12 (depends on 7)

The system of claim 7, wherein the gyro rate (Ω) is computed as
Ω=((Δn1/Δt)−(Δn2Δt)−C)/(1/SF1−1/SF2)
where SF1 and SF2 are pre-determined IFOG scale factors corresponding to the first and second frequencies, C is the correction term, and (Δn1/Δt)−(Δn2/Δt)is the difference in responses of the IFOG to the optical input at the first and second frequencies.

### Claim 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.

### Claim 14 (depends on 13)

The method of claim 13, wherein the correction term (C) is computed from
Ω=((Δn1/Δt)−(Δn2/Δt)−C)/(1/SF1−1/SF2)
where Ω is the known rate, SF1 and SF2 are the scale factors corresponding to the first and second frequencies of the optical input, and (Δn1/Δt)−(Δn2/Δt) is the difference of the first and second IFOG phase variations.