Method of determining an absolute angle of a magnetic field

Patent metadata

Field	Value
Publication number	US-11467225-B2
Application number	US-201916296581-A
Country	US
Kind code	B2
Filing date	Mar 8, 2019
Priority date	Mar 8, 2019
Publication date	Oct 11, 2022
Grant date	Oct 11, 2022

Abstract

A method of determining an absolute angle of a magnetic field includes receiving a first digital measurement value Bx of a first magnetic field component indicating intensity of the magnetic field along a first axis; receiving a second digital measurement value Bz of a second magnetic field component indicating the intensity of the magnetic field along a second axis, orthogonal to the first axis; determining absolute values for the first and second magnetic field components; and determining the angle of the magnetic field with respect to the first or second axis. The angle is determined so that the angle is derivable from the value of arcsin of Bz or of its approximation, when the absolute value of Bz≤ the absolute value of Bx, and derivable from the value of arccos of Bx or of its approximation, when the absolute value of Bz> the absolute value of Bx.

First claim

What is claimed is:

1. A method of determining an absolute angle of a magnetic field from a magnetic field sensor, the method comprising the following steps carried out by a digital signal processor:
receiving a first digital measurement value of a first magnetic field sensor (Bx), indicating intensity of the magnetic field along a first axis,
receiving a second digital measurement value of a second magnetic field sensor (Bz), indicating intensity of the magnetic field along a second axis, orthogonal to the first axis,
determining absolute values for the first and second magnetic field sensors, and
determining, using a digital signal processor, the angle of the magnetic field with respect to the first or second axis, wherein the angle is derivable by the digital signal processor from the value of arcsin of Bz or of its approximation, where Bz is 1 or less, when the absolute value of Bz<the absolute value of Bx, and derivable from the value of arccos of Bx or of its approximation, wherein Bx is 1 or less, when the absolute value of Bz>the absolute value of Bx.

2. The method according to claim 1 , wherein determining the angle of the magnetic field comprises fetching the value of arcsin of Bz or of its approximation or arcsin of Bx or of its approximation from a first lookup table.

3. The method according to claim 2 , wherein the first lookup table comprises different values of Bz, such that each value of Bz in the first lookup table is identified by the value of its arcsin if the angle is determined with respect to the first axis, or different values of Bx, such that each value of Bx in the first lookup table is identified by the value of its arcsin if the angle is determined with respect to the second axis.

4. The method according to claim 3 , wherein the first lookup table comprises different values of Bz or Bx for the angles from 0° to 45°.

5. The method according to claim 4 , wherein a number N of the values Bz or Bx in the first lookup equals (1+45)/(angle precision in degrees).

6. The method according to claim 2 , wherein the method further comprises:
determining which one of the absolute values of the magnetic field sensors Bz and Bx is smaller,
selecting the magnetic field sensor with the smaller absolute value,
accessing the first lookup table by using the selected magnetic field sensor, and
selecting the value Bz or Bx from the first lookup table corresponding to the selected magnetic field sensor.

7. The method according to claim 6 , wherein the selected value Bz or Bx in the first lookup table corresponds to the selected magnetic field sensor if the selected magnetic field sensor is smaller or equal to the selected value of Bz or Bx and greater than the value of Bz or Bx in the preceding memory location in the first lookup table.

8. The method according to claim 1 , wherein the angle is determined by performing a given mathematical operation involving subtracting the obtained value of arcsin from a given angle value or adding the obtained value of arcsin to the given angle value.

9. The method according to claim 8 , wherein the method further comprises:
determining which one of the absolute values of the magnetic field sensors Bx and Bz is smaller,
determining signs of Bx and Bz, and
accessing a second lookup table for fetching the given mathematical operation from the second lookup table based on the signs of Bx and Bz and based on which one of the absolute values of the magnetic field sensors Bx and Bz is smaller.

10. The method according to claim 1 , wherein the method further comprises compensating the first and second digital measurement values before the angle determination in order to remove effects due to temperature variations and due to parasitic magnetic fields.

11. A system comprising:
a digital signal processor configured to determine an absolute angle of a magnetic field, the digital signal processor being further configured to:
receive a first digital measurement value of a first magnetic field sensor, referred to as Bx, indicating intensity of the magnetic field along a first axis,
receive a second digital measurement value of a second magnetic field sensor, referred to as Bz, indicating intensity of the magnetic field along a second axis, orthogonal to the first axis,
determine absolute values for the first and second magnetic field sensors, and
determine the angle of the magnetic field with respect to the first or second axis, wherein the angle is derivable by the digital signal processor from the value of arcsin of Bz or of its approximation, wherein Bz is 1 or less, when the absolute value of Bz≤the absolute value of Bx, and derivable from the value of arccos of Bx or of its approximation, wherein Bx is 1 or less, when the absolute value of Bz >the absolute value of Bx.

12. The system comprising the digital signal processor according to claim 11 , and further comprising a first magnetic sensor for measuring the first magnetic field sensor, a second magnetic sensor for measuring the second magnetic field sensor, and an analogue-to-digital converter for converting analogue measurements signals of the first and second magnetic sensors to the first and second digital measurement values.

13. The system according to claim 12 , wherein the magnetic sensors are Hall effect sensors.

14. The system according to claim 12 , wherein the system further comprises a third magnetic sensor for measuring a third magnetic field sensor, referred to as By, indicating the intensity of the magnetic field along a third axis, which is orthogonal to the first and second axes.

15. The system according to claim 14 , wherein only two of the magnetic sensors are operative at a time.

Assignees

• Em Microelectronic Marin Sa

Inventors

• Pierobon Lorenzo
• Deschildre Alexandre
• Lojewski Evan
• Schlachter Jeremy

Classifications

• G01R33/0094 Primary

  Sensor arrays · CPC title

• G01R33/07

  Hall effect devices · CPC title

• G01R33/0023 Primary

  Electronic aspects, e.g. circuits for stimulation, evaluation, control; Treating the measured signals; calibration (G01R33/0017 takes precedence) · CPC title