Method and device for detecting a substantially invariant rotation axis

• US 7,890,291 B2
• Filed: 04/24/2008
• Issued: 02/15/2011
• Est. Priority Date: 04/25/2007
• Status: Active Grant

• Current Assignee: Commissariat a L'Energie Atomique (French Alternative Energies and Atomic Energy Commission), Institut National Polytechnique de Grenoble, Universite Joseph Fourier
• Original Assignee: Commissariat a L'Energie Atomique (French Alternative Energies and Atomic Energy Commission), Institut National Polytechnique de Grenoble, Universite Joseph Fourier
• Inventors: Bonnet, Stèphane, Lesecq, Suzanne, Barraud, Alain, Godin, Christelle
• Primary Examiner(s): BHAT, ADITYA S
• Application Number:
  US12/108,981
• Publication Number:
  US 20080281555A1
• Time in Patent Office: 1,027 Days
• Field of Search: 702/153
• US Class Current: 702/153
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• CPC Class Codes: A61B 2562/0219 Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches
• CPC Class Codes: A61B 5/1126 using a particular sensing technique
• CPC Class Codes: A61B 5/6824 Arm or wrist
• CPC Class Codes: G01C 21/16 by integrating acceleration or speed, i.e. inertial navigation
• CPC Class Codes: 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

Abstract

A method for detecting a substantially invariant rotation axis of a motion of a mobile body equipped with at least one inertial or magnetic sensor with three sensitive axes that includes acquiring physical measurements with respect to the three sensitive axes of the sensor, the physical measurements including at least three samples at different times, estimating a substantially invariant rotation axis in the physical measurements space, and identifying the estimated axis as the substantially invariant rotation axis of the motion. In one aspect, the method is applicable for estimating the motion of a mobile body rotating about a substantially invariant axis.

Claims

1. A method for detecting a substantially invariant rotation axis of a motion of a mobile body equipped with one of an inertial or magnetic sensor with three sensitive axes, the method comprising the following steps:

acquiring physical measurements with respect to the three sensitive axes by the inertial or magnetic sensor, the physical measurements comprising at least three samples at different times during motion of the mobile body;

estimating from the at least three samples a substantially invariant rotation axis in the physical measurements space; and

identifying the estimated substantially invariant rotation axis as the substantially invariant rotation axis of the motion.

2. The method according to claim 1 further comprising the following steps:

calculating an indicator of variations of the rotation axis;

comparing the value of the indicator with a predetermined threshold value; and

validating the estimated substantially invariant rotation axis as the substantially invariant rotation axis of the motion if the value of the indicator is less than the predetermined threshold value, which is substantially equal to the value of the noise affecting the physical measurements from the inertial or magnetic sensor.

3. The method according to claim 1, wherein the inertial or magnetic sensor comprises one of an accelerometer with three sensitive axes, a magnetometer with three sensitive axes, or a rate gyro with three sensitive axes.

4. The method according to claim 3, wherein the estimated substantially invariant rotation axis corresponds to the axis for which the standard deviation of the values of the physical measurements projected onto the axis is minimized for a magnetometer or an accelerometer, and maximized for a rate gyro.

5. The method according to claim 4, wherein estimating a substantially invariant rotation axis comprises a step of calculating by analysis into principal components, the third principal component corresponding to the coordinates of the substantially invariant rotation axis in the physical measurements space.

6. The method according to claim 4, wherein estimating a substantially invariant rotation axis comprises a step of calculating least squares applied to a linear combination of the physical measurements.

7. The method according to claim 4, further comprising, if the standard deviation is substantially equal to the standard deviation of noise affecting the inertial or magnetic sensor, the estimated rotation axis is validated as the substantially invariant rotation axis of the motion.

8. The method according to claim 1, wherein the inertial or magnetic sensor comprises a magnetometer or an accelerometer and estimating a substantially invariant rotation axis comprises a step of vectorial calculation on the physical measurements.

9. A method for estimating a motion of a mobile body equipped with one of an inertial or magnetic sensor with three sensitive axes, the motion comprising rotation about a substantially invariant axis, the method comprising the following steps:

detecting a substantially invariant rotation axis by the detection method according to claim 1; and

determining a rotation angle of the mobile body about the substantially invariant rotation axis.

10. The method according to claim 9, wherein the inertial or magnetic sensor comprises a magnetometer or a goniometer and the mobile body is also equipped with an accelerometer, and wherein the method further comprises a step of determining the acceleration of the mobile body.

11. A method for calibrating an inertial or magnetic sensor with three sensitive axes for determining a rotation matrix suitable for transforming coordinates expressed in a measurement frame of reference of the sensor into coordinates expressed in a predetermined frame of reference stationary with respect to a mobile body carrying the sensor, the method comprising the following steps:

acquiring at least two series of physical measurements by the sensor respectively corresponding to the rotation of the mobile body with respect to at least two of the three axes of the predetermined frame of reference;

determining from each of the two series of coordinates of each of the rotation axes corresponding to one of the at least two axes of the predetermined frame of reference in the frame of reference of the physical measurements from the sensor according to the detection method of claim 1; and

generating a rotation matrix from the determined coordinates of the at least two rotation axes.

12. The method according to claim 11, wherein the sensor is integrated into a casing, and wherein axes of the predetermined frame of reference are defined by edges of the casing.

13. The method according to claim 11, wherein the sensor is positioned on an anatomical feature, and wherein the predetermined frame of reference corresponds to an anatomical frame of reference defined by three anatomical rotation axes of the anatomical feature.

14. A method for detecting a substantially invariant rotation axis of a motion of a mobile body equipped with one of an inertial or magnetic sensor with three sensitive axes, the method comprising the following steps:

acquiring physical measurements with respect to the three sensitive axes by the inertial or magnetic sensor, the physical measurements comprising at least three samples at different times during motion of the mobile body;

estimation from the at least three samples a substantially invariant rotation axis in the physical measurement space; and

identifying the estimated substantially invariant rotation axis as the substantially invariant rotation axis of the motion; and

transforming coordinates of the estimated substantially invariant rotation axis in a measurement frame of reference of the inertial or magnetic sensor into coordinates in a geophysical frame of reference.

15. A method for detecting a substantially invariant rotation axis of a motion of a mobile body, wherein the mobile body is equipped with a magnetometer having three sensitive axes and an accelerometer having three sensitive axes, the method comprising the following steps:

acquiring physical measurements with respect to the three sensitive axes by the magnetometer and the accelerometer, respectively, the physical measurements comprising at least three samples at different times during motion of the mobile body;

estimating from the at least three samples a substantially invariant rotation axes in the physical measurements spaces of said magnetometer and said accelerometer, respectively; and

validating the substantially invariant rotation axis of the motion of a linear combination of the estimated rotation axes for said physical measurements from the magnetometer and from the accelerometer, wherein coefficients of the combination are not limited between 0 and 1, their sum being equal to 1, and wherein the coefficients are a function of the values of the indicators of the variations of the rotation axes of the magnetometer or the accelerometer, or both.

16. A device for detecting a substantially invariant rotation axis of a motion of a mobile body equipped with one of an inertial or magnetic sensor with three sensitive axes, wherein the device comprises:

a sensor acquiring physical measurements with respect to the three sensitive axes of the inertial or magnetic sensor, the physical measurements comprising at least three samples at different times during motion of the mobile body;

means for estimating from the at least three samples a substantially invariant rotation axis in the physical measurements space; and

means for identifying the estimated substantially invariant rotation axis as the substantially invariant rotation axis of the motion.