Navigational aid method, computer program product and inertial navigation system therefor

Patent metadata

Field	Value
Publication number	US-10401177-B2
Application number	US-201715840139-A
Country	US
Kind code	B2
Filing date	Dec 13, 2017
Priority date	Dec 13, 2016
Publication date	Sep 3, 2019
Grant date	Sep 3, 2019

Abstract

The invention relates to a navigational aid method for an inertial navigation system including at least one inertial sensor (4) having a sensitive axis (X-X), each inertial sensor (4) comprising an ASG gyroscope (8) able to deliver an ASG signal representative of a rotation about the corresponding sensitive axis (X-X), and a MEMS gyroscope (10) able to deliver a MEMS signal representative of a rotation about the corresponding sensitive axis (X-X), the method including the steps of: between a first date and a subsequent third date, calculating a path from the MEMS signals; from the third date, calculating the path from the ASG signals; estimating a bias vector introduced by the MEMS gyroscopes (10), from the MEMS signals and ASG signals; at a fourth date subsequent to the third date, resetting the path.

First claim

The invention claimed is:

1. A navigational aid method for an inertial navigation system fixed with respect to a solid, the inertial system including at least one inertial sensor having a sensitive axis, each inertial sensor comprising an ASG gyroscope and a MEMS gyroscope integral with each other, the ASG gyroscope being able to deliver an ASG signal representative of a rotation about the corresponding sensitive axis, the MEMS gyroscope being able to deliver a MEMS signal representative of a rotation about the corresponding sensitive axis, the method including the steps of:
calculating, between a first date and a subsequent third date, a path and, for each inertial sensor, a corresponding biased path, from the MEMS signals, assuming, for the biased path, that the inertial sensor has a predetermined unit bias;
calculating, from the third date, the path and each biased path from the ASG signals, assuming, for the biased path, that the inertial sensor has a predetermined unit bias;
estimating a bias vector introduced by the MEMS gyroscopes, from the MEMS signals and ASG signals;
resetting, at a fourth date subsequent to the third date, the path as a function of each biased path, the unit biases and the estimated bias vector, to obtain a nominal path which is not affected by the bias of the MEMS gyroscopes.

2. The method according to claim 1 , wherein, for each MEMS gyrometer, a corresponding component of the bias vector is equal to an average, between a second date and the fourth date, of a difference between an angular velocity from the corresponding MEMS signal and an angular velocity from the corresponding ASG signal, the second date being included between the first date and the third date.

3. The method according to claim 1 , wherein the nominal path is obtained by subtracting a reset from the path, the reset being a vectorial corrective term calculated according to:

δ
⁢

⁢
Xn

=

b

0
⁢
x

⁢

∂

∂
D

⁢

⁢
0
⁢
x

+

b

0
⁢
y

⁢

∂

∂
D

⁢

⁢
0
⁢
y

+

b

0
⁢
z

⁢

∂

∂
D

⁢

⁢
0
⁢
z

where δXn is the reset;
b 0i is the i-th component of the bias vector; and
the quantity

∂

∂
D

⁢

⁢
0
⁢
i

is calculated according to:

∂

∂
D

⁢

⁢
0
⁢
i

=

XnDi
⁡

(

t
rec

)

-

Xn
⁡

(

t
rec

)

D
⁢

⁢
0
⁢
i

where XnDi(t rec ) is the i-th biased path taken at the fourth date; and
D0i is the predetermined unit bias associated with the component i.

4. The method according to claim 1 , comprising an overlap step, the overlap step including:
between the second date and the third date, the second date being included between the first date and the third date, a first phase for calculating the path and each biased path from the MEMS signal;
at the third date, a switching for calculating the path and each biased path from a corresponding angle increment, the angle increment being obtained, for each sensitive axis, by the relationship:
dθ com =θ ASG ( t com )−θ MEMS ( t com −T e )−Δθ

where dθ com is the angle increment;
θ ASG (t com ) is a quantity equal to a cumulation of rotation angle increments about the sensitive axis between the second date and the third date, which are calculated from the ASG signal upon switching;
θ MEMS (t com −T e ) is a quantity equal to a cumulation of rotation angle increments about the sensitive axis between the second date and a duration T e before the third date, which are calculated from the MEMS signal;
each increment being equal to an integral, between two successive instants, of the angular velocity of a rotation about a sensitive axis from the corresponding MEMS or ASG signal,
Δθ is a predetermined angular correction; and
T e is a predetermined duration;
between the third date and the fourth date, a second phase for calculating the trajectory and each biased trajecto

Assignees

• Commissariat Energie Atomique
• Safran

Inventors

• Morales Sophie
• Palacios Laloy Augustin
• Leger Jean-Michel
• Remillieux Georges
• Gramlich Marc
• Brunstein Etienne

Classifications

• G01C19/60

  Electronic or nuclear magnetic resonance gyrometers · CPC title

• G01C19/56 Primary

  Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces · CPC title

• G01C19/5776

  Signal processing not specific to any of the devices covered by groups G01C19/5607 - G01C19/5719 · CPC title

• G01C25/005

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

• G01C21/18 Primary

  Stabilised platforms, e.g. by gyroscope · CPC title