Magnetic sensing for a polygon mirror using a hall sensor for LiDAR system

Patent metadata

Field	Value
Publication number	US-12265158-B2
Application number	US-202117238071-A
Country	US
Kind code	B2
Filing date	Apr 22, 2021
Priority date	Apr 22, 2021
Publication date	Apr 1, 2025
Grant date	Apr 1, 2025

Abstract

Embodiments of the disclosure provide magnetic sensing systems and methods for a polygon scanner. An exemplary magnetic sensing system includes a disc permanent magnet configured to provide a magnetic field. The magnetic sensing system further includes a Hall sensor configured to generate a voltage proportional to the strength of the magnetic field as the Hall sensor and the disc permanent magnet move relatively to each other when the polygon mirror rotates. One of the disc permanent magnet and the Hall sensor locates on and rotates with the polygon mirror and the other locates off the polygon mirror. The magnetic sensing system also includes at least one controller configured to determine a rotation angle of the polygon mirror based on the generated voltage by the Hall Sensor.

First claim

What is claimed is:

1. A magnetic sensing system for a polygon mirror,
comprising:
a disc permanent magnet configured to provide a magnetic field;
a Hall sensor configured to generate a voltage proportional to the strength of the magnetic field as the Hall sensor and the disc permanent magnet move relatively to each other when the polygon mirror rotates, wherein one of the disc permanent magnet and the Hall sensor locates on and rotates with the polygon mirror and the other locates off the polygon mirror, wherein the Hall sensor and the disc permanent magnet are placed such that a distance between the Hall sensor and the center of the disc permanent magnet changes, as they move relatively to each other; and
at least one controller configured to determine a rotation angle of the polygon mirror based on the generated voltage by the Hall Sensor.

2. The magnetic sensing system of claim 1 , wherein when the Hall sensor and the disc permanent magnet move relatively to each other, the distance between the Hall sensor and the center of the disc permanent magnet changes within a predetermined range between a first predetermined distance and a second predetermined distance.

3. The magnetic sensing system of claim 2 , wherein the strength of the magnetic field at the Hall sensor changes monotonically when the distance between the Hall sensor and the center of the disc permanent magnet changes monotonically between the first predetermined distance and the second predetermined distance.

4. The magnetic sensing system of claim 1 , wherein the Hall sensor is fixed on a substrate off the polygon mirror and the disc permanent magnet is mounted on the polygon mirror.

5. The magnetic sensing system of claim 4 , wherein the center of the disc permanent magnet moves around a rotation axis of the polygon mirror in a circular orbit when the polygon mirror rotates.

6. The magnetic sensing system of claim 1 , wherein the disc permanent magnet is fixed on a substrate off the polygon mirror and the Hall sensor is mounted on the polygon mirror.

7. The magnetic sensing system of claim 6 , wherein the center of the disc permanent magnet is not on the rotation axis of the polygon mirror.

8. The magnetic sensing system of claim 6 , wherein the Hall sensor is parallel to the surface of the disc permanent magnet.

9. The magnetic sensing system of claim 1 , wherein to determine a rotation angle of the polygon mirror based on the generated voltage by the Hall sensor, the at least one controller is further configured to:
determine a value of a magnetic flux density at a time point based on the generated voltage at the time point; and
determine a variation trend or rate of the value of the magnetic flux density at the time point.

10. The magnetic sensing system of claim 9 , wherein to determine a rotation angle of the polygon mirror based on the generated voltage by the Hall sensor, the at least one controller is further configured to:
determine the rotation angle of the polygon mirror at the time point based on a combination of the value and variation trend or rate of the magnetic flux density at the time point using a predetermined look-up table that maps the respective values of the magnetic flux density and the variation trends or rates of the value of the magnetic flux density to rotation angles of the polygon mirror.

11. The magnetic sensing system of claim 1 , wherein the at least one controller is further configured to adaptively control the rotation of the polygon mirror based on the determined rotation angle.

12. The magnetic sensing system of claim 11 , wherein to adaptively control the rotation of the polygon mirror based on the determined rotation angle, the at least one controller is further configured to:
compare the determined rotation angle with a target rotation angle; and
supply a control signal to an actuator of the polygon mirror to speed up or slow down the rotation of the polygon mirror based on the comparison.

13. A magnetic sensing method for a polygon mirror, comprising:
moving a disc permanent magnet and a Hall sensor relative to each other as the polygon mirror rotates, wherein one of the disc permanent magnet and the Hall sensor locates on and rotates with the polygon mirror and the other locates off the polygon mirror, wherein the Hall sensor and the disc permanent magnet are placed such that a distance between the Hall sensor and the center of the disc permanent magnet changes, as they move relatively to each other;
measuring a voltage generated by the Hall sensor caused by the relative movement; and
determining, by at least one controller, a rotation angle of the polygon mirror based on the voltage generated by the Hall sensor.

14. The magnetic sensing method of claim 13 , wherein when the Hall sensor and the disc permanent magnet move relatively to each other, the distance between the Hall sensor and the center of the disc permanent magnet changes within a predetermined range between a first predetermined distance and a second predetermined distance.

15. The magnetic sensing method of claim 14 , wherein the strength of a magnetic field at the Hall sensor changes monotonically when the distance between the Hall sensor and the center of the disc permanent magnet changes monotonically between the first predetermined distance and the second predetermined distance.

16. The magnetic sensing method of claim 15 , wherein determining, by at least one controller, a rotation angle of the polygon mirror based on the voltage generated by the Hall sensor further comprises:
determining a value of a magnetic flux density at a time point based on the voltage measured at the time point; and
determining a variation trend or rate of the value of the magnetic flux density at the time point.

17. The magnetic sensing method of claim 16 , wherein determining, by at least one controller, a rotation angle of the polygon mirror based on the voltage generated by the Hall sensor further comprises:
determining the rotation angle of the polygon mirror at the time point based on a combination of the value and variation trend or rate of the magnetic flux density at the time point using a predetermined look-up table that maps the respective values of the magnetic flux density and the variation trends or rates of the value of the magnetic flux density to rotation angles of the polygon mirror.

18. The magnetic sensing method of claim 14 , further comprising adaptively controlling the rotation of the polygon mirror, by the at least one controller, based on the determined rotation angle.

19. A polygon scanner assembly, comprising:
a polygon mirror configured to rotate around a rotation axis;
a disc permanent magnet configured to provide a magnetic field; and
a Hall sensor configured to generate a voltage proportional to the strength of the magnetic field as the Hall sensor and the disc permanent magnet move relatively to each other when the polygon mirror rotates, wherein one of the disc permanent magnet and the Hall sensor locates on and rotates with the polygon mirror and the other locates off the polygon mirror, wherein the Hall sensor and the disc permanent magnet are placed such that a distance between the Hall sensor and the center of the disc permanent magnet changes, as they move relatively to each other.

20. The polygon scanner assembly of claim 19 , wherein when the Hall sensor and the disc permanent magnet move relatively to each other, the distance between the Hall sensor and the center of the disc permanent magnet changes within a

Assignees

• Beijing Voyager Tech Co Ltd

Inventors

• Wang Youmin
• Wang Yufeng

Classifications

• H02K11/215

  Magnetic effect devices, e.g. Hall-effect or magneto-resistive elements · CPC title

• G01D5/145

  influenced by the relative movement between the Hall device and magnetic fields (see G01R33/06) · CPC title

• G01S7/4817

  relating to scanning · CPC title

• G01S7/484

  Transmitters · CPC title

• G02B26/121

  Mechanical drive devices for polygonal mirrors · CPC title