Device and method for determining a characteristic of a path formed by consecutive positions of a triaxial accelerometer rigidly connected to a mobile element

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.