Method for estimating scattering coefficients of a laser gyro in operation and associated gyroscopic system

Patent metadata

Field	Value
Publication number	US-10859378-B2
Application number	US-201715453818-A
Country	US
Kind code	B2
Filing date	Mar 8, 2017
Priority date	Mar 18, 2016
Publication date	Dec 8, 2020
Grant date	Dec 8, 2020

Abstract

An iterative method for determining scattering coefficients of the cavity of a laser gyro in operation supporting two counter-propagating modes, comprises steps of: determining a set of variables dependent on characteristic physical quantities of the laser gyro, one reference variable per dependency relationship being selected from the variables; measuring values of the characteristic physical quantities of the laser gyro in operation; determining measured values of the variables; estimating, via an iterative method, estimated values of the coefficients minimising a discrepancy between the measured values of the reference variables and estimated values of the reference variables, which are estimated from the values of the coefficients and the measured values of the variables other than the reference variables; and determining estimated values of the scattering coefficients from the estimated values of the coefficients.

First claim

The invention claimed is:

1. A method of determining an angular rotation (Δθ) of a laser gyro in operation, the method comprising:
implementing a real time iterative method for determining scattering coefficients (m, ξ) of the cavity of a laser gyro in operation supporting two counter-propagating modes, comprising steps of:
determining a set of variables dependent on characteristic physical quantities of the laser gyro,
the characteristic physical quantities comprising a first and second light intensity corresponding to the first and second counter-propagating modes, respectively, and a phase difference (φ) between said modes,
said variables being determined so that they are related to one another by at least a first and a second dependency relationships (R1 (u, {dot over (u)}, cos φ), R2 (v, {dot over (v)}, sin φ)) modelling the behaviour of the laser gyro and using a plurality of coefficients, said coefficients depending on parameters of the laser cavity including said scattering coefficients, the first dependency relationship relating variables, referred to as the first set of variables, to one another, and the second dependency relationship relating variables, referred to as the second set of variables, to one another, the first and second dependency relationships being such that one variable of a set is equal to a linear combination of the other variables of the same set;
one reference variable ({dot over (u)}, {dot over (v)}) per dependency relationship being selected from the variables;
measuring values of the characteristic physical quantities of the laser gyro in operation;
determining measured values of the variables, deduced from the measured values of the characteristic physical quantities and from the first and second dependency relationships;
estimating, via an iterative method, estimated values of the coefficients ({circumflex over (F)}) minimising a discrepancy between the measured values ({dot over (u)}, {dot over (v)}) of the reference variables and estimated values ({dot over (û)}, {dot over ({circumflex over (v)})}) of the reference variables, which are estimated from the values of the coefficients, the measured values of the variables (u, cos φ v, sin φ) other than the reference variables and from the first and second dependency relationships;
determining estimated values of the scattering coefficients ({circumflex over (m)}, {circumflex over (ξ)}) from the estimated values ({circumflex over (F)}) of the coefficients; and
determining the angular rotation (Δθ) of the laser gyro from the estimated values of the scattering coefficients ({circumflex over (m)}, {circumflex over (ξ)}).

2. The method according to claim 1 , wherein the step of determining a set of variables comprises determining the first and the second dependency relationships between the variables from Lamb's differential equations.

3. The method according to claim 1 , wherein the step of determining a set of variables defines the following variables:

u
=

1
2

⁢

(

I
1

+

I
2

)

v
=

1
2

⁢

(

I
1

-

I
2

)

u
.

=

du
dt

v
.

=

dv
dt

cos
⁢

⁢
φ

sin
⁢

⁢
φ

where:
I 1 , I 2 are the light intensities of the two counter-propagating modes; and cos φ and sin φ are respectively the cosine and sine of the phase difference between the two modes.

4. The method according to claim 3 , wherein the first dependency relationship R1(u, {dot over (u)}, cos φ) relates the variables u, {dot over (u)} and cos φ, to one another, and the second dependency relationship R2(v, {dot over (v)}, sin φ) relates the variables v, {dot over (v)}, and sin φ, to one another.

5. The method according to claim 3 , wherein {dot over (u)} is selected as reference variable for the first dependency relationship and {dot over (v)} is selected as reference variable in the second dependency relationship.

6. The method according to claim 1 , wherein the phase difference (φ) between the two counter-propagating modes is determined from a first beat signal (yc) and a second beat signal (ys) in phase quadrature with the first beat signal.

7. The method according to claim 6 , wherein the cosine and sine of the phase difference (φ) are determined as follows:

cos
⁡

(
φ
)

=

y
c

-

I
1

-

I
2

2
⁢

I
1

⁢

I
2

sin
⁡

(
φ
)

=

y
s

-

I
1

-

I
2

2
⁢

Assignees

• Thales Sa
• Association Pour La Rech Et Le Developpement De Methodes Et Processus Industriels Armines

Inventors

• Hamze El Badaoui Noad
• Rouchon Pierre
• Feugnet Gilles
• Schwartz Sylvain
• Martin Philippe

Classifications

• G01C19/664 Primary

  means for removing the dither signal · 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

• G01C19/661 Primary

  details · CPC title

• G01C19/64

  Gyrometers using the Sagnac effect, i.e. rotation-induced shifts between counter-rotating electromagnetic beams · CPC title