AUTOMATICALLY UPDATING HARD IRON AND SOFT IRON COEFFICIENTS OF A MAGNETIC SENSOR

• US 20150241390A1
• Filed: 02/22/2015
• Published: 08/27/2015
• Est. Priority Date: 02/23/2014
• Status: Active Grant

• Current Assignee: PNI Sensor Corporation
• Original Assignee: PNI Sensor Corporation
• Inventors: Figaro, Davy J.
• Granted Patent: US 9,863,867 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses
• CPC Class Codes: G01N 19/00 Investigating materials by mechanical methods G01N3/00 - G01N17/00 take precedence
• CPC Class Codes: G01R 33/0035 Calibration of single magnetic sensors, e.g. integrated calibration
• CPC Class Codes: G01R 33/0064 comprising means for performing simulations, e.g. of the magnetic variable to be measured

Abstract

Apparatuses, methods and systems apparatus for automatically updating hard iron and soft iron coefficients of a magnetic sensor of a device are disclosed. One method includes making measurements of a magnetic field by the magnetic sensor during rotations of the device, determining by at least a criterion whether to input the measurements of the magnetic field into a coefficient estimator, calculating, by the coefficient estimator, new hard iron and soft iron coefficients upon receiving the measurements of the magnetic field, determining a quality of the newly calculated hard iron and soft iron calculated coefficients, and updating existing hard iron and soft iron coefficients to the newly calculated hard iron and soft iron coefficients only if the quality of the newly calculated hard iron and soft iron coefficients.

Claims

1. A method of automatically updating hard iron and soft iron coefficients of a magnetic sensor of a device, comprising:

making measurements of a magnetic field by the magnetic sensor during rotations of the device;

determining by at least a criterion whether to input the measurements of the magnetic field into a coefficient estimator;

calculating, by the coefficient estimator, new hard iron and soft iron coefficients upon receiving the measurements of the magnetic field;

determining a quality of the newly calculated hard iron and soft iron calculated coefficients; and

updating existing hard iron and soft iron coefficients to the newly calculated hard iron and soft iron coefficients only if the quality of the newly calculated hard iron and soft iron coefficients is better than a quality of the existing hard iron and soft iron coefficients.

2. The method of claim 1, wherein the rotations of the device are arbitrary.

3. The method of claim 2, wherein the measurements are opportunistically made depending upon the arbitrary rotations.

4. The method of claim 1, further comprising making additional measurements of the magnetic field for updating of the newly calculated hard iron and soft iron coefficients.

5. The method of claim 1, wherein the coefficient estimator operates recursively.

6. The method of claim 1, wherein the measurements include measuring a magnetic vector associated with the magnetic field, and further comprising tracking motion of the magnetic vector.

7. The method of claim 6, wherein the magnetic vector traces a surface of an ellipsoid, and wherein determining by at least the criterion comprises detecting that the magnetic vector traces the surface of the ellipsoid not traced since a prior hard iron and soft iron calculated coefficient update, and determining that the magnetic vector has moved more than a predetermined minimum displacement along the surface of the ellipsoid.

8. The method of claim 6, wherein the magnetic vector traces a surface of an ellipsoid, and wherein determining by at least the criterion comprises detecting that the magnetic vector traces the surface of the ellipsoid not traced since a predetermined period of time, and determining that the magnetic vector has moved more than a predetermined minimum displacement along the surface of the ellipsoid.

9. The method of claim 1, wherein determining the quality of the newly calculated hard iron and soft iron coefficients and only updating the existing hard iron and soft iron coefficients to the newly calculated hard iron and soft iron coefficients if the quality of the newly calculated hard iron and soft iron coefficients is better than a quality of existing hard iron and soft iron coefficients comprises:

measuring an angular rotation by a gyro;

taking successive magnetic sensor measurements simultaneously with the angular rotation as measured by the gyro;

applying the existing hard and soft iron coefficients to the successive magnetic sensor measurements to generate a first rotation calculation;

applying the newly calculated hard and soft iron coefficients to the successive magnetic sensor measurements to generate a second rotation calculation;

comparing the first calculated rotation and the second calculated rotation to angular rotation measured by the gyro;

selecting the one of the first calculated and the second calculated rotation that most closely matches the angular rotation measured by the gyro.

10. The method of claim 9, wherein if the newly calculated hard iron and soft iron coefficients more closely match the angular rotation measured by the gyro, then the updating the existing hard iron and soft iron coefficients.

11. The method of claim 9, wherein determining the quality of the newly calculated hard iron and soft iron coefficients additionally comprises:

comparing a difference of magnetic magnitude of successive measurements using the newly calculated hard iron and soft iron coefficients, with a difference of magnetic magnitude of successive measurements using the existing hard iron and soft iron coefficients;

determining if the magnetic magnitude difference for the newly calculated hard iron and soft iron coefficients is less than the magnetic magnitude difference for the existing hard iron and soft iron coefficients;

selecting either the newly calculated hard iron and soft iron coefficients or the existing hard iron and soft iron coefficients, depending on which results in a smallest magnitude difference over successive measurements.

12. The method of claim 10, wherein a sensed output of the magnetic sensor is received by an adaptive filter, and wherein the newly calculated hard and soft iron coefficients are updated within the adaptive filter.

13. A sensing system that automatically updates hard iron and soft iron coefficients of a magnetic sensor of the system, comprising:

the magnetic sensor operative to make measurements of a magnetic field during rotations of the device;

electronic control circuitry, the electronic control circuitry operative to;

determine by at least a criterion whether to input the measurements into a coefficient estimator to generate a new hard iron and soft iron coefficient calculation;

calculate a quality of the new hard iron and soft iron coefficients;

update existing hard iron and soft iron coefficients to the newly calculated hard iron and soft iron coefficients only if the quality of the newly calculated hard iron and soft iron coefficients is better than a quality of the existing hard iron and soft iron coefficients.

14. The system of claim 13, wherein the measurements include measuring a magnetic vector associated with the magnetic field, and further comprising tracking motion of the magnetic vector.

15. The system of claim 14, wherein the magnetic vector traces a surface of an ellipsoid, and wherein determining by at least the criterion comprises detecting that the magnetic vector traces the surface of the ellipsoid not traced since a prior hard iron and soft iron calculated coefficient update, and determining that the magnetic vector has moved more than a predetermined minimum displacement along the surface of the ellipsoid.

16. The system of claim 14, wherein the magnetic vector traces a surface of an ellipsoid, and wherein determining by at least the criterion comprises detecting that the magnetic vector traces the surface of the ellipsoid not traced since a predetermined period of time, and determining that the magnetic vector has moved more than a predetermined minimum displacement along the surface of the ellipsoid.

17. The system of claim 13, further comprising a gyroscope operative to measure an angular rotation, and

wherein determining the quality of the newly calculated hard iron and soft iron coefficients and only updating existing hard iron and soft iron coefficients to the newly calculated hard iron and soft iron coefficients if the quality of the newly calculated hard iron and soft iron coefficients is better than a quality of existing hard iron and soft iron coefficients comprises the electronic control circuitry being operative to:

take successive magnetic sensor measurements simultaneously with the angular rotation as measured by the gyroscope;

apply the existing hard and soft iron coefficients to the successive magnetic sensor measurements to generate a first rotation calculation;

apply the newly calculated hard and soft iron coefficients to the successive magnetic sensor measurements to generate a second rotation calculation;

compare the first calculated rotation and the second calculated rotation to angular rotation measured by the gyroscope;

select the one of the first calculated and the second calculated rotation that most closely matches the angular rotation measured by the gyro.

18. The system of claim 17, wherein determining the quality of the newly calculated hard iron and soft iron coefficients additionally comprises:

comparing a difference of magnetic magnitude of successive measurements using the newly calculated hard iron and soft iron coefficients, with a difference of magnetic magnitude of successive measurements using existing hard iron and soft iron coefficients;

determining if the magnetic magnitude difference for the newly calculated hard and soft iron coefficients is less than the magnetic magnitude difference for the existing hard iron and soft iron coefficients;

selecting either the newly calculated hard iron and soft iron coefficients or the existing hard iron and soft iron coefficients, depending on which results in a smallest magnitude difference over successive measurements.

19. A method of automatically updating coefficients of a magnetic sensor input to a Kalman filter of a device, comprising:

sensing, by a magnetic sensor, a magnetic vector of an ambient magnetic field;

tracking motion of the magnetic vector, wherein a tip of the magnetic vector traces to a surface of an ellipsoid;

detecting whether the tip is tracing a new surface area of the ellipsoid, wherein a new surface area has not been previously traced;

detecting whether the tip trace moves more than a predetermined minimum angular rotation;

recording a certain number of magnetic measurements while the tip is tracing the new surface area and moving more than the a predetermined minimum angular rotation;

for each new magnetic measurement;

a. comparing angular rotation between successive new measurements and an angular rotation of a gyroscope measurement, and comparing angular rotation between successive prior measurements and angular rotation of the gyroscope measurement, and determine if the new magnetic measurements more closely match the gyroscope measurement;

b. comparing a difference of a magnetic magnitude of successive measurements using newly calculated hard iron and soft iron coefficients, with a difference of magnetic magnitude of successive measurements using the previously calculated hard iron and soft iron coefficients, and determining if a magnitude difference for the newly calculated hard iron and soft iron coefficients is less than a magnitude difference for the previous calculated hard iron and soft iron coefficients;

updating magnetic coefficients of the Kalman filter with the newly calculated hard iron and soft iron coefficients if the difference based on the newly calculated hard iron and soft iron coefficients more closely match, and differ by less.

20. A method of tracking a magnetic field, comprising:

measuring, by a magnetic sensor, successive magnetic vectors of a magnetic field;

comparing an angular rotation between successive new measurements and angular rotation of gyro measurement, and comparing angular rotation between successive prior measurements and angular rotation of gyro measurement, and determining if the new measurements more closely match the gyro measurement;

comparing a difference of magnetic magnitude of successive measurements using newly calculated hard iron and soft iron coefficients, with a difference of magnetic magnitude of successive measurements using previously calculated hard iron and soft iron coefficients, and determining if a magnitude difference for the newly calculated hard iron and soft iron coefficients is less than a magnitude difference for the previously calculated hard iron and soft iron coefficients; and

updating magnetic coefficients of an adaptive filter with new coefficients if a difference based on the newly calculated hard iron and soft iron coefficients more closely match, and differ by less.