DEVICE AND METHOD FOR DETERMINING A CHARACTERISTIC OF A PATH FORMED BY CONSECUTIVE POSITIONS OF A TRIAXIAL ACCELEROMETER RIGIDLY CONNECTED TO A MOBILE ELEMENT

• US 20110264400A1
• Filed: 10/20/2009
• Published: 10/27/2011
• Est. Priority Date: 10/22/2008
• Status: Active Grant

• Current Assignee: Commissariat a L'Energie Atomique (French Alternative Energies and Atomic Energy Commission), Movea
• Original Assignee: Commissariat a L'Energie Atomique (French Alternative Energies and Atomic Energy Commission), Movea
• Inventors: Denis, Benoit, Youssef, Joe, Godin, Christelle
• Granted Patent: US 9,068,842 B2
• Time in Patent Office: Days
• US Class Current: 702/141
• CPC Class Codes: G01C 21/1654 with electromagnetic compass
• CPC Class Codes: G01C 22/006 Pedometers

Abstract

Device for determining a characteristic of a trajectory formed of successive positions of a triaxial accelerometer (3A) rigidly tied to a mobile element (EM), between a first instant of immobility (t₀) and a second instant of immobility (t_n) of the triaxial accelerometer (3A), subsequent to said first instant of immobility (t₀), said device comprising, furthermore, a triaxial additional sensor for measuring a vector of a substantially constant vector field between said first and second instants of immobility (t₀,t_n), in a fixed global reference frame (GE) tied to the terrestrial reference frame, said additional sensor being rigidly tied to said mobile element (EM) and fixed in the reference frame of the accelerometer (3A), and control means (CMD).

Claims

1. A device for determining a characteristic of a trajectory formed of successive positions of a triaxial accelerometer (3A) rigidly tied to a mobile element (EM), between a first instant of immobility (t₀) and a second instant of immobility (t_n) of the triaxial accelerometer (3A), subsequent to said first instant of immobility (t₀), said device comprising, furthermore, a triaxial additional sensor for measuring a vector of a substantially constant vector field between said first and second instants of immobility (t₀,t_n), in a fixed global reference frame (GF) tied to the terrestrial reference frame, said additional sensor being rigidly tied to said mobile element (EM) and fixed in the reference frame of the accelerometer (3A), and control means (CMD), characterized in that said control means (CMD) comprise:

first means (MD1) for determining said first and second instants of immobility (t₀,t_n) of the triaxial accelerometer (3A);

second means (MD2) for determining a substantially invariant axis of rotation of the triaxial accelerometer (3A) between said first and second instants of immobility (t₀,t_n), and a plane orthogonal to said substantially invariant axis of rotation, in a mobile reference frame (LF) tied to the accelerometer (3A) or to the additional sensor on the basis of the vectors delivered by the triaxial accelerometer (3A), or on the basis of the vectors delivered by the additional sensor;

first means (MC1) for calculating, at said successive instants (t₀, t₁, . . . , t_n), first orthogonal projections onto said plane of the vectors delivered by the triaxial accelerometer (3A) and of the vectors delivered by the additional sensor in said mobile reference frame (LF);

third means (MD3) for determining, at said successive instants (t₀, t₁, . . . , t_n), the rotation for switching from said mobile reference frame (LF) to said fixed global reference frame (GF), on the basis of said first orthogonal projections of the vectors delivered by the additional sensor;

second means (MC2) for calculating, at said successive instants (t₀, t₁, . . . , t_n), second orthogonal projections in said fixed global reference frame (GF), of the first orthogonal projections, provided by said first calculation means (MC1), in said plane of the vectors delivered by the triaxial accelerometer (3A);

third calculation means (MC3) for subtracting from each second orthogonal projection in said fixed global reference frame (GF) the mean vector over said successive instants (t₀, t₁, . . . , t_n), so as to obtain the accelerations centered in said plane, devoid of the influence of terrestrial gravity and of drifts of said device, in said fixed global reference frame (GF); and

fourth means (MC4) for calculating a characteristic of the trajectory on the basis of the centered accelerations.

2. The device as claimed in claim 1, in which said successive positions are substantially coplanar.

3. The device as claimed in claim 1, in which said mobile element (EM) is a foot, the time interval separating said first and second instants of immobility (t₀,t_n) of the triaxial accelerometer (3A) corresponding to a pace of said foot.

4. The device as claimed in claim 1, in which said control means (CMD) comprise first means (MEL1) for computing a direction vector, adapted for linking the respective positions, expressed in said fixed global reference frame (GF), of the triaxial accelerometer (3A) to said first instant of immobility (t0) and to said second instant of immobility (t_n).

5. The device as claimed in claim 4, in which said plane of the trajectory being vertical, said control means (CMD) comprise, furthermore, second means (MEL2) for computing a displacement heading with respect to said vector field measured by the additional sensor, said second computation means (MEL2) being adapted for performing an orthogonal projection, of said vector field vector measured by the additional sensor, onto a horizontal plane orthogonal to said plane of the trajectory.

6. The device as claimed in claim 1, in which said plane of the trajectory being vertical, said second means (MD2) for determining the plane of said trajectory of the triaxial accelerometer (3A) are adapted for performing a singular-value decomposition of the three-column matrix (A_p^LF(t₀ . . . t_n) formed by the vectors delivered by the triaxial accelerometer (3A) at said successive instants (t₀, t₁, . . . , t_n), in said mobile reference frame, and extracting the two vectors corresponding to the larger two singular values.

7. The device as claimed in claim 1, in which said plane of the trajectory being vertical, said second means (MD2) for determining the plane of said trajectory of the triaxial accelerometer (3A) are adapted for performing a decomposition into eigenvalues and eigenvectors, in said mobile reference frame (LF), the autocorrelation matrix of the three-column matrix formed by the vectors delivered by the triaxial accelerometer (3A) at said successive instants (t₀, t₁, . . . , t_n), and extracting the two eigenvectors corresponding to the larger two eigenvalues.

8. The device as claimed in claim 1, in which said second calculation means (MC2) comprise fifth calculation means (MC5) for switching to an intermediate reference frame (IF), tied to the terrestrial reference frame, defined by a first vector delivered by said first calculation means (MC1) on the basis of a vector provided by the additional sensor, and by a second vector, orthogonal to said first vector and belonging to said plane of the trajectory.

9. The device as claimed in claim 1, in which said third means (MD3) for determining the rotation for switching from said mobile reference frame (LF) to said fixed global reference frame (GF) comprise means (MEST) for estimating an angle (α

), said switching rotation being defined by an orthogonal projection onto said substantially constant vector field, followed by a rotation by said estimated angle (α

) in said plane of trajectory of the triaxial accelerometer (3A).

10. The device as claimed in claim 9, in which said estimation means (MEST) are adapted for estimating said angle (α

) on the basis of the slope (θ

) of the contact surface of the mobile element (EM), and of the vector transmitted by said fifth calculation means (MC5) on the basis of the vector transmitted by the triaxial accelerometer (3A).

11. The device as claimed in claim 9, in which said estimation means (MEST) are adapted for estimating said angle (α

) on the basis of a singular-value decomposition of the three-column matrix provided by said fifth calculation means (MC5) on the basis of the matrix (A^IF) formed by the vectors delivered by the triaxial accelerometer (3A) at said successive instants (t₀, t₁, . . . , t_n).

12. The device as claimed in claim 9, in which said estimation means (MEST) are adapted for estimating said angle (α

) as the angle, at said first or second instant of immobility (t₀,t_n), between the vector delivered by said first calculation means (MC1) on the basis of the vector provided by the additional sensor, and the vector delivered by said first calculation means (MC1) on the basis of the vector provided by the triaxial accelerometer (3A).

13. The device as claimed in claim 1, in which said control means (CMD) comprise third means (MEL3) for computing the distance traveled between said first and second instants of immobility (t₀,t_n), and/or during a set of successive time intervals separating two successive instants of immobility (t₀,t_n) of the triaxial accelerometer (3A), on the basis of the data provided by said fourth calculation means (MC4).

14. The device as claimed in claim 1, in which said control means (CMD) comprise fourth means (MEL4) for computing a trajectory during a set of successive time intervals separating two successive instants of immobility (t₀,t_n) of the triaxial accelerometer (3A), on the basis of the data provided by said fourth calculation means (MC4).

15. The device as claimed in claim 1, in which said additional sensor is a triaxial magnetometer (3M) for measuring the terrestrial magnetic field, substantially constant between said first and second instants of immobility (t₀,t_n).

16. The device as claimed in claim 1, in which said triaxial accelerometer (3A) is disposed so as to be positioned substantially at the level of the contact surface of the mobile element (EM) at an instant of immobility of said triaxial accelerometer (3A).

17. The device as claimed in claim 1, in which said additional sensor is disposed so as to be positioned some distance from the contact surface of said mobile element (EM), at an instant of immobility of said triaxial accelerometer (3A).

18. The device as claimed in claim 1, in which said control means (CMD) are tied to the mobile element (EM) or disposed some distance from the mobile element (EM), and adapted for operating in real or non-real time.

19. A video game system comprising a visual or auditory indicator for indicating at least one pace to be taken by the player, characterized in that it comprises at least one device as claimed in claim 3.

20. A jump analysis system, characterized in that it comprises at least one device as claimed in claim 3.

21. An outdoor or indoor geolocation system, characterized in that it comprises at least one device as claimed in claim 3.

22. A system for calculating energy expenditure of a user, characterized in that it comprises at least one device as claimed in claim 3.

23. The device as claimed in claim 1, in which said characteristic of the trajectory of the triaxial accelerometer (3A) comprises the velocity of the triaxial accelerometer (3A).

24. The device as claimed in claim 1, in which said characteristic of the trajectory of the triaxial accelerometer (3A) comprises the trajectory of the triaxial accelerometer (3A).

25. A method for determining a characteristic of a trajectory formed of successive positions of a triaxial accelerometer (3A) rigidly tied to a mobile element (EM), between a first instant of immobility (t₀) and a second instant of immobility (t_n) of the triaxial accelerometer, subsequent to said first instant of immobility (t₀), by means furthermore of a triaxial additional sensor for measuring a vector of a substantially constant vector field between said first and second instants of immobility (t₀,t_n) in a fixed global reference frame (GF) tied to the terrestrial reference frame, said additional sensor being rigidly tied to said mobile element (EM) and fixed in the reference frame of the accelerometer (3A), said method comprising the following steps:

determining said first and second instants of immobility (t₀,t_n) of the triaxial accelerometer (3A);

determining a substantially invariant axis of rotation of the triaxial accelerometer between the first and second instants of immobility, and determining a plane orthogonal to said substantially invariant axis of rotation, in a mobile reference frame (LF) tied to the accelerometer (3A) or to the additional sensor, on the basis of the vectors delivered by the triaxial accelerometer (3A) or on the basis of the vectors delivered by the additional sensor;

calculating, at said successive instants (t₀, t₁, . . . , t_n), first orthogonal projections in said plane, of the vectors delivered by the triaxial accelerometer (3A) and of the vectors delivered by the additional sensor in said mobile reference frame;

determining, at said successive instants (t₀, t₁, . . . , t_n), the rotation for switching from said mobile reference frame (LF) to said fixed global reference frame (GF), on the basis of said first orthogonal projections of the vectors delivered by the additional sensor;

calculating, at said successive instants (t₀, t₁, . . . , t_n), second orthogonal projections in said fixed global reference frame of the first orthogonal projections in said plane of the vectors delivered by the triaxial accelerometer;

subtracting from each second orthogonal projection in said fixed global reference frame, the mean vector over said successive instants (t₀, t₁, . . . , t_n) so as to obtain the accelerations centered in said plane, devoid of the influence of terrestrial gravity and of the drifts of said device, in said fixed global reference frame (GF); and

determining a characteristic of the trajectory on the basis of the centered accelerations.