Magnetometer apparatus and associated methods

Patent metadata

Field	Value
Publication number	US-10094663-B2
Application number	US-201515129703-A
Country	US
Kind code	B2
Filing date	Mar 27, 2015
Priority date	Apr 3, 2014
Publication date	Oct 9, 2018
Grant date	Oct 9, 2018

Abstract

An apparatus comprising: a processor; and a memory including computer program code, the memory and the computer program code configured to, with the processor, cause the apparatus to perform at least the following: determine whether or not recalibration is required of a magnetometer configured to compensate for hard-iron and soft-iron effects by determining whether a plurality of magnetometer readings received from the magnetometer is consistent with: a scaled pre-calibrated matrix describing the soft-iron effect for at least one scaling factor of the pre-calibrated matrix; and a pre-calibrated vector describing the hard-iron effect.

First claim

The invention claimed is:

1. An apparatus comprising:
a processor; and
a memory including computer program code,
the memory and the computer program code configured to, with the processor, cause the apparatus to perform at least the following:
determine whether or not recalibration is required of a magnetometer configured to compensate for hard-iron and soft-iron effects by determining whether a plurality of magnetometer readings received from the magnetometer is consistent with:
a scaled pre-calibrated matrix describing the soft-iron effect for at least one scaling factor of the pre-calibrated matrix; or
a pre-calibrated vector describing the hard-iron effect; and

recalibrate the magnetometer based on the result from determining whether or not recalibration is required.

2. The apparatus of claim 1 , wherein recalibration of the magnetometer comprises at least one of:
adjusting the values of the pre-calibrated vector describing the hard-iron effect; and
adjusting the relative values of the matrix describing the soft-iron effect.

3. The apparatus of claim 1 , wherein the plurality of magnetometer readings correspond to different orientations of the magnetometer taken at substantially the same position.

4. The apparatus of claim 1 , wherein the pre-calibrated matrix is independent of the magnetic field strength corresponding to the calibration.

5. The apparatus of claim 1 , wherein the pre-calibrated matrix comprises information relating to the magnetic field strength corresponding to the calibration.

6. The apparatus of claim 1 , wherein the apparatus is configured to calibrate the magnetometer.

7. The apparatus of claim 1 , wherein the apparatus is configured to perform the determination in response to one or more of the following conditions being satisfied:
the number of received magnetometer readings exceeds a readings number threshold;
the range of orientations corresponding to the received magnetometer readings exceeds an orientation range threshold; and
the number of different orientations corresponding to the received magnetometer readings exceeds an orientation number threshold.

8. The apparatus of claim 1 , wherein the plurality of magnetometer readings comprise over 10 magnetometer readings.

9. The apparatus of claim 1 , wherein the plurality of magnetometer readings comprise more than 100 magnetometer readings.

10. The apparatus of claim 1 , wherein the apparatus is configured to determine that recalibration is not required if the received magnetometer readings are consistent, within a consistency threshold, with the scaled pre-calibrated matrix describing the soft-iron effect for at least one scaling factor of the pre-calibrated matrix; and the pre-calibrated vector describing the hard-iron effect.

11. The apparatus of claim 1 , wherein the apparatus is configured to store multiple sets of pre-calibration data, each set of pre-calibration data comprising a scaled pre-calibrated matrix describing the soft-iron effect; and a pre-calibrated vector describing the hard-iron effect.

12. The apparatus of claim 1 , wherein the apparatus is configured to determine whether or not recalibration is required of a magnetometer by determining whether a plurality of magnetometer readings received from the magnetometer is consistent with at least one of multiple sets of pre-calibration data, each set of pre-calibration data comprising a scaled pre-calibrated matrix describing the soft-iron effect; and a pre-calibrated vector describing the hard-iron effect comprising a scaled pre-calibrated matrix describing the soft-iron effect; and a pre-calibrated vector describing the hard-iron effect.

13. The apparatus of claim 1 , wherein the apparatus is configured to recalibrate the magnetometer based on the plurality of received magnetometer readings if the plurality of received magnetometer readings is not consistent with:
a scaled pre-calibrated matrix describing the soft-iron effect for at least one scaling factor of the pre-calibrated matrix; and
a pre-calibrated vector describing the hard-iron effect.

14. A method, the method comprising:
determining whether or not recalibration is required of a magnetometer configured to compensate for hard-iron and soft-iron effects by determining whether a plurality of magnetometer readings received from the magnetometer is consistent with:
a scaled pre-calibrated matrix describing the soft-iron effect for at least one scaling factor of the pre-calibrated matrix; and
a pre-calibrated vector describing the hard-iron effect.

15. A computer program, the computer program configured to:
enable determination of whether or not recalibration is required of a magnetometer configured to compensate for hard-iron and soft-iron effects by determining whether a plurality of magnetometer readings received from the magnetometer is consistent with:
a scaled pre-calibrated matrix describing the soft-iron effect for at least one scaling factor of the pre-calibrated matrix; and
a pre-calibrated vector describing the hard-iron effect.

Assignees

• Nokia Technologies Oy

Inventors

• Kesäniemi Martti

Classifications

• G01C17/38 Primary

  Testing, calibrating, or compensating of compasses · CPC title

• G01C17/02

  Magnetic compasses · CPC title

• G01R33/0035

  Calibration of single magnetic sensors, e.g. integrated calibration · CPC title

• G01C17/28 Primary

  Electromagnetic compasses (with north seeking magnetic elements and having electric pick-offs G01C17/26) · CPC title

• G01C25/00

  Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass (testing, calibrating or compensating compasses G01C17/38) · CPC title