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 9,068,842 B2
• Filed: 10/20/2009
• Issued: 06/30/2015
• Est. Priority Date: 10/22/2008
• Status: Active Grant

• Current Assignee: Commissariat a L'Energie Atomique (AES Corporation), Movea
• Original Assignee: Commissariat a L'Energie Atomique (AES Corporation), Movea
• Inventors: Youssef, Joe, Godin, Christelle, Denis, Benot
• Primary Examiner(s): Charioui, Mohamed
• Assistant Examiner(s): Zhang, Ruihua
• Application Number:
  US13/125,145
• Publication Number:
  US 20110264400A1
• Time in Patent Office: 2,079 Days
• Field of Search: 702/141, 702/160, 702/161, 735/10, 738/654, 734/90, 734/92, 734/89
• US Class Current: 1/1
• 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 of a mobile element, the device comprising:

a triaxial accelerometer attached to the mobile element;

an additional triaxial sensor for measuring a vector of a relatively constant vector field in a fixed global reference frame with respect to the terrestrial reference frame, said additional triaxial sensor being attached to said mobile element and fixed in a reference frame of the triaxial accelerometer; and

a control circuit, said control circuit comprising;

first determining means for determining a first instant of immobility and a second instant of immobility of the triaxial accelerometer, the second instant of immobility being subsequent to said first instant of immobility;

second determining means for determining a relatively invariant axis of rotation of the triaxial accelerometer between said first and second instants of immobility as the device moves between said first and second instants of immobility, and a plane orthogonal to said relatively invariant axis of rotation, in a mobile reference frame with respect to the accelerometer or to the additional triaxial sensor on the basis of vectors provided by the triaxial accelerometer, or on the basis of vectors provided by the additional triaxial sensor;

first calculating means for calculating at successive instants between said first and second instants of immobility first orthogonal projections onto said plane of the vectors provided by the triaxial accelerometer and of the vectors provided by the additional triaxial sensor in said mobile reference frame;

third determining means for determining at said successive instants a rotation for switching from said mobile reference frame to said fixed global reference frame, on the basis of said first orthogonal projections of the vectors delivered by the additional triaxial sensor;

second calculating means for calculating at said successive instants second orthogonal projections in said fixed global reference frame of the first orthogonal projections, provided by said first calculating means in said plane of the vectors delivered by the triaxial accelerometer

third calculating means for subtracting from each second orthogonal projection in said fixed global reference frame provided by the second calculating means a mean vector over said successive instants, so as to obtain accelerations centered in said plane relatively devoid of terrestrial gravitational influences and of drifts of said device, in said fixed global reference frame; and

fourth calculating means for calculating a characteristic of the trajectory utilizing the centered accelerations obtained from the third calculating means.

2. The device as claimed in claim 1, wherein said successive positions are relatively coplanar.

3. The device as claimed in claim 1, wherein said mobile element is a foot, the time interval separating said first and second instants of immobility of the triaxial accelerometer corresponding to a pace of said foot.

4. The device as claimed in claim 1, wherein said control circuit comprises first computing means for computing a direction vector, configured to link the respective positions, expressed in said fixed global reference frame, of the triaxial accelerometer to said first instant of immobility and to said second instant of immobility.

5. The device as claimed in claim 4, wherein said plane of the trajectory is vertical, and said control circuit further comprises second computing means for computing a displacement heading with respect to said vector field measured by the additional triaxial sensor, said second computing means configured to determine an orthogonal projection, of said vector field vector measured by the additional triaxial sensor, onto a horizontal plane orthogonal to said plane of the trajectory.

6. The device as claimed in claim 1, wherein said plane of the trajectory is vertical, and said second determining means is configured to determine a singular-value decomposition of a three-column matrix formed by vectors provided by the triaxial accelerometer at said successive instants, in said mobile reference frame, and extracting two vectors corresponding to two larger singular values.

7. The device as claimed in claim 1, wherein said plane of the trajectory is vertical, and said second determining means is configured to perform a decomposition into eigenvalues and eigenvectors, in said mobile reference frame, an autocorrelation matrix of a three-column matrix formed by vectors provided by the triaxial accelerometer at said successive instants, and extracting two eigenvectors corresponding to two larger eigenvalues.

8. The device as claimed in claim 1, wherein said second calculating means comprises fifth calculating means for switching to an intermediate reference frame with respect to the terrestrial reference frame, defined by a first vector delivered by said first calculation means on the basis of a vector provided by the additional triaxial sensor, and by a second vector, orthogonal to said first vector and within said plane of the trajectory.

9. The device as claimed in claim 8, wherein said third determining means comprises estimating means for estimating an angle, wherein said switching rotation is determined by an orthogonal projection onto said relatively constant vector field, followed by a rotation by said angle in said plane of trajectory of the triaxial accelerometer.

10. The device as claimed in claim 9, wherein said estimation means is configured to estimate said angle utilizing a slope of a contact surface of the mobile element, and of the vector transmitted by said fifth calculating means on the basis of a vector transmitted by the triaxial accelerometer.

11. The device as claimed in claim 9, wherein said estimation means is configured to estimate said angle utilizing a singular-value decomposition of a three-column matrix provided by said fifth calculation means on the basis of a matrix formed by vectors delivered by the triaxial accelerometer at said successive instants.

12. The device as claimed in claim 9, wherein said estimation means is configured to estimate said angle as an angle, at said first or second instant of immobility, between a vector delivered by said first calculating means on the basis of a vector provided by the additional triaxial sensor, and a vector delivered by said first calculating means on the basis of a vector provided by the triaxial accelerometer.

13. The device as claimed in claim 1, wherein said control circuit comprises third computing means for computing a distance traveled between said first and second instants of immobility, or during a set of successive time intervals separating two successive instants of immobility of the triaxial accelerometer, utilizing data provided by said fourth calculating means.

14. The device as claimed in claim 1, wherein said control circuit comprises fourth computing means for computing a trajectory during a set of successive time intervals separating two successive instants of immobility of the triaxial accelerometer, utilizing data provided by said fourth calculating means.

15. The device as claimed in claim 1, wherein said additional triaxial sensor is a triaxial magnetometer for measuring the terrestrial magnetic field, which is relatively constant between said first and second instants of immobility.

16. The device as claimed in claim 1, wherein said triaxial accelerometer is disposed so as to be positioned relatively at a level of a contact surface of the mobile element at an instant of immobility of said triaxial accelerometer.

17. The device as claimed in claim 1, wherein said additional triaxial sensor is disposed so as to be positioned at a predetermined distance from a contact surface of said mobile element, at an instant of immobility of said triaxial accelerometer.

18. The device as claimed in claim 1, wherein said control circuit is connected to the mobile element or disposed at a predetermined distance from the mobile element, and is 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 the video game system comprises at least one device as claimed in claim 3.

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

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

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

23. The device as claimed in claim 1, wherein said characteristic of the trajectory of the triaxial accelerometer comprises a velocity of the triaxial accelerometer.

24. The device as claimed in claim 1, wherein said characteristic of the trajectory of the triaxial accelerometer comprises a trajectory of the triaxial accelerometer.

25. A method for determining a characteristic of a trajectory obtained from successive positions of a triaxial accelerometer attached to a mobile element, between a first instant of immobility and a second instant of immobility of the triaxial accelerometer, the second instant of immobility being subsequent to said first instant of immobility, the method further comprising utilizing an additional triaxial sensor for measuring a vector of a relatively constant vector field in a fixed global reference frame with respect to the terrestrial reference frame, said additional triaxial sensor being connected to said mobile element and fixed in a reference frame of the triaxial accelerometer, said method further comprising, using a data processor, performing the following steps:

determining said first and second instants of immobility of the triaxial accelerometer;

determining, as the mobile element moves between said first and second instants of immobility, a relatively invariant axis of rotation of the triaxial accelerometer between the first and second instants of immobility, and determining a plane orthogonal to said relatively invariant axis of rotation, in a mobile reference frame with respect to the accelerometer or to the additional triaxial sensor, utilizing vectors provided by the triaxial accelerometer or utilizing vectors provided by the additional triaxial sensor;

calculating, at successive instants between said first and second instants of immobility, first orthogonal projections in said plane, of the vectors provided by the triaxial accelerometer and of the vectors provided by the additional triaxial sensor in said mobile reference frame;

determining, at said successive instants, a rotation for switching from said mobile reference frame to said fixed global reference frame, utilizing said first orthogonal projections of the vectors provided by the additional triaxial sensor;

calculating, at said successive instants, second orthogonal projections in said fixed global reference frame of the first orthogonal projections in said plane of the vectors provided by the triaxial accelerometer;

subtracting from each second orthogonal projection in said fixed global reference frame, a mean vector over said successive instants so as to obtain accelerations centered in said plane, relatively devoid of influence of terrestrial gravity and of drifts of said device, in said fixed global reference frame; and

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