ELECTRONIC COMPASS

• US 20120022823A1
• Filed: 08/25/2009
• Published: 01/26/2012
• Est. Priority Date: 10/21/2008
• Status: Abandoned Application

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Bennini, Fouad
• Application Number:
  US12/998,376
• Publication Number:
  US 20120022823A1
• Time in Patent Office: Days
• US Class Current: 702/141
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses
• CPC Class Codes: G01R 33/0206 Three-component magnetometers

Abstract

A method for determining a null drift (Hx0, Hy0) of an electronic compass includes steps for ascertaining first magnetic field strengths in a first coordinate system of the electronic compass via a triaxial magnetic sensor; for calculating from the first magnetic field strengths incline-compensated second magnetic field strengths (200) in a second coordinate system (x, y) parallel to the Earth'"'"'s surface; for adjusting a trial function (210) to the incline-compensated second magnetic field strengths (200); and for determining a null drift (Hx0, Hy0) from the adjusted trial function (210). A method for operating the electronic compass includes steps for calculating an incline-compensated magnetic field strength (Hx, Hy) in the second coordinate system (x, y) from a first magnetic field strength measured by the magnetic sensor, for calculating a zero-point-corrected third magnetic field strength (Bx, By) by subtracting the null drift (Hx0, Hy0) determined by the above-described method from the incline-compensated second magnetic field strength (Hx, Hy); and for calculating an azimuth angle by which an axis (x) of the second coordinate system (x, y) deviates from a north-south direction.

Claims

1-14. -14. (canceled)

15. A method for determining a null drift (Hx0, Hy0) of an electronic compass, comprising:

ascertaining a plurality of first magnetic field strengths (Mx′

, My′

, Mz′

) in a first coordinate system (KS′

) of the electronic compass via a triaxial magnetic sensor;

calculating a plurality of incline-compensated second magnetic field strengths (Hx, Hy) in a second coordinate system (KS) parallel to the Earth'"'"'s surface from the plurality of first magnetic field strengths (Mx′

, My′

Mz′

);

adjusting a trial function to the plurality of incline-compensated second magnetic field strengths (Hx, Hy); and

determining a null drift (Hx0, Hy0) from the adjusted trial function.

16. The method as recited in claim 15, wherein the plurality of incline-compensated second magnetic field strengths (Hx, Hy) for each first magnetic field strength (Mx′

, My′

, Mz′

) are calculated by;

determining a bank angle (θ

) and a pitch angle (φ

) of the first coordinate system (KS′

) relative to the second coordinate system (KS); and

calculating the incline-compensated second magnetic field strength (Hx, Hy) from the first magnetic field strength (Mx′

, My′

, Mz′

), the bank angle (θ

) and the pitch angle (φ

).

17. The method as recited in claim 16, wherein the incline-compensated second magnetic field strengths (Hx, Hy) are calculated using the following formula:

Hx=Mx′

cos(φ

)+My′

sin(φ

)sin(θ

)−

Mz′

sin(φ

)cos(θ

);

Hy=My′

cos(θ

)+Mz′

sin(θ

).

18. The method as recited in claim 16, wherein the bank angle (θ

) and the pitch angle (φ

) are determined by;

ascertaining an acceleration value (ax′

, ay′

, az′

) in the first coordinate system (KS′

) via a triaxial acceleration sensor (120); and

calculating the bank angle (θ

) and the pitch angle (φ

) of the first coordinate system (KS′

) relative to the second coordinate system (KS).

19. The method as recited in claim 18, wherein the bank angle (θ

) and pitch angle (φ

) are calculated according to the following formulas;

θ

=1/tan(ay′

/sqrt(ax′

ax′

+az′

az′

));

φ

=1/tan(ax′

/sqrt(ay′

ay′

+az′

az′

)).

20. The method as recited in claim 18, wherein the ascertained acceleration value (ax′

, ay′

, az′

) is filtered via a low-pass filter prior to further processing.

21. The method as recited in claim 15, wherein a circular function is used as a trial function.

22. The method as recited in claim 15, wherein the electronic compass is moved during the ascertaining of the plurality of first magnetic field strengths (Mx′

, My′

, Mz).

23. A method for operating an electronic compass, comprising:

determining a null drift (Hx0, Hy0) of the electronic compass according to the method recited in claim 15;

ascertaining a first magnetic field strength (Mx′

, My′

, Mz′

) in a first coordinate system (KS′

) of the electronic compass via a triaxial magnetic sensor;

calculating an incline-compensated second magnetic field strength (Hx, Hy) in a second coordinate system (KS) parallel to the Earth'"'"'s surface from the first magnetic field strength (Mx′

, My′

Mz′

); and

calculating a zero-point-corrected third magnetic field strength (Bx, By) by subtracting the null drift (Hx0, Hy0) from the incline-compensated second magnetic field strength (Hx, Hy); and

calculating an azimuth angle (α

) by which an axis (x) of the second coordinate system (KS) deviates from a north-south direction.

24. The method as recited in claim 23, wherein the azimuth angle (α

) is calculated from the third magnetic field strength (Bx, By) according to the following formula;

α

=arctan(By/Bx).

25. An electronic compass having a triaxial magnetic sensor and triaxial acceleration sensor, the electronic compass being designed to implement a method for determining a null drift (Hx0, Hy0) as recited in claim 15.

26. The electronic compass as recited in claim 25, the electronic compass being designed to implement the method as recited in claim 23.

27. The electronic compass as recited in claim 25, the magnetic sensor including at least one GMR sensor.

28. The electronic compass as recited in claim 25, the acceleration sensor including at least one micromechanical acceleration sensor.