Method for estimating the position of a magnet comprising a phase for identifying a magnetic disturbance

1. A method for estimating the position of a magnet by a tracking device comprising an array of magnetometers capable of measuring a magnetic field, the method being implemented by a processor, comprising the following phases:

determination of an initial state vector associated with the magnet, for an initial measurement instant, the state vector comprising variables representative of the position of the magnet relative to the array of magnetometers;

measurement by the array of magnetometers of a useful magnetic field, at a measurement instant, in the presence of the magnet;

estimation of a magnetic field generated by the magnet, as a function of the state vector obtained at a preceding measurement instant, on a basis of a predetermined model expressing a relationship between the magnetic field generated by the magnet and the state vector of the magnet;

calculation of a bias by a difference between the estimated magnetic field and the measured useful magnetic field;

updating of the state vector as a function of the calculated bias, thus making it possible to obtain an estimated position of the magnet at the measurement instant;

reiteration of the measurement, estimation, bias calculation and updating phases, on the basis of the updated state vector, by incrementing the measurement instant;

wherein the method also comprises the following phase:

identification, at at least one measurement instant, of a magnetic disrupter distinct from the magnet and situated in a vicinity of the array of magnetometers, comprising the following steps:

calculation of an indicator parameter from a deviation parameter defined as a function of a difference between an estimated magnetic field generated by the magnet for the state vector obtained at the preceding measurement instant or for the updated state vector, on the basis of the predetermined model, and the useful magnetic field measured at the measurement instant; and

comparison of the indicator to a predetermined threshold value, and identification of the magnetic disrupter when at least one of the values of the indicator is greater than or equal to the threshold value; and

wherein the indicator is equal to a ratio of the deviation parameter to a denominator term comprising at least the estimated magnetic field of the indicator, the measured useful magnetic field of the indicator, or at least one predetermined constant representative of a bias of at least one of the magnetometers.

2. The method of claim 1 , wherein the denominator term comprises the estimated magnetic field of the indicator and the predetermined constant.

3. The method of claim 1 , wherein the estimation, bias calculation and updating phases are performed by an optimization algorithm based on iterative minimization bias, called cost function, at the measurement instant.

4. The method of claim 1 , wherein the state vector also comprises variables representative of a magnetic moment of the magnet.

5. An information storage medium, comprising instructions for implementing the method as claimed in claim 1 , these instructions being executable by a processor.

6. A method for estimating the position of a magnet by a tracking device comprising an array of magnetometers capable of measuring a magnetic field, the method being implemented by a processor, comprising the following phases:

determination of an initial state vector associated with the magnet, for an initial measurement instant, the state vector comprising variables representative of the position of the magnet relative to the array of magnetometers;

measurement by the array of magnetometers of a useful magnetic field, at a measurement instant, in the presence of the magnet;

estimation of a magnetic field generated by the magnet, as a function of the state vector obtained at a preceding measurement instant, on a basis of a predetermined model expressing a relationship between the magnetic field generated by the magnet and the state vector of the magnet;

calculation of a bias by a difference between the estimated magnetic field and the measured useful magnetic field;

updating of the state vector as a function of the calculated bias, thus making it possible to obtain an estimated position of the magnet at the measurement instant;

reiteration of the measurement, estimation, bias calculation and updating phases, on the basis of the updated state vector, by incrementing the measurement instant;

wherein the method also comprises the following phase:

identification, at at least one measurement instant, of a magnetic disrupter distinct from the magnet and situated in a vicinity of the array of magnetometers, comprising the following steps:

calculation of an indicator parameter from a deviation parameter defined as a function of a difference between an estimated magnetic field generated by the magnet for the state vector obtained at the preceding measurement instant or for the updated state vector, on the basis of the predetermined model, and the useful magnetic field measured at the measurement instant; and

comparison of the indicator to a predetermined threshold value, and identification of the magnetic disrupter when at least one of the values of the indicator is greater than or equal to the threshold value,

wherein the estimation, bias calculation and updating phases are performed by a Bayesian recursive estimation algorithm;

wherein the estimation phase comprises:

a step of obtaining of a predicted state vector at the measurement instant as a function of a state vector obtained at a preceding measurement instant, and

a step of calculation of the estimated magnetic field for the predicted state vector; and

wherein the phase of bias calculation comprises:

a step of calculation of the bias, called innovation, as the difference between the estimated magnetic field for the predicted state vector and the measured useful magnetic field.

7. The method of claim 6 , wherein the deviation parameter is equal to the innovation.

8. The method of claim 6 , wherein the deviation parameter is equal to the difference between an estimated magnetic field generated by the magnet for the updated state vector, and the useful magnetic field measured at the measurement instant.

9. A method for estimating the position of a magnet by a tracking device comprising an array of magnetometers capable of measuring a magnetic field, the method being implemented by a processor, comprising the following phases:

determination of an initial state vector associated with the magnet, for an initial measurement instant, the state vector comprising variables representative of the position of the magnet relative to the array of magnetometers;

measurement by the array of magnetometers of a useful magnetic field, at a measurement instant, in the presence of the magnet;

estimation of a magnetic field generated by the magnet, as a function of the state vector obtained at a preceding measurement instant, on a basis of a predetermined model expressing a relationship between the magnetic field generated by the magnet and the state vector of the magnet;

calculation of a bias by a difference between the estimated magnetic field and the measured useful magnetic field;

updating of the state vector as a function of the calculated bias, thus making it possible to obtain an estimated position of the magnet at the measurement instant;

reiteration of the measurement, estimation, bias calculation and updating phases, on the basis of the updated state vector, by incrementing the measurement instant;

wherein the method also comprises the following phase:

identification, at at least one measurement instant, of a magnetic disrupter distinct from the magnet and situated in a vicinity of the array of magnetometers, comprising the following steps:

calculation of an indicator parameter from a deviation parameter defined as a function of a difference between an estimated magnetic field generated by the magnet for the state vector obtained at the preceding measurement instant or for the updated state vector, on the basis of the predetermined model, and the useful magnetic field measured at the measurement instant; and

comparison of the indicator to a predetermined threshold value, and identification of the magnetic disrupter when at least one of the values of the indicator is greater than or equal to the threshold value; and

wherein the phase of identification of the magnetic disrupter comprises a step of transmission of a signal to a user prompting separation of the magnetic disrupter from the array of magnetometers, as long as the indicator is greater than the predetermined threshold value.