Rotating a permanent magnet in a position detection system
In a general aspect, a position detection system includes a magnetic field generator configured to generate a time-varying magnetic field. The magnetic field generator includes a carrier assembly that defines a first axis of rotation and comprises a permanent magnet having a center of mass. The magnetic field generator also includes a drive assembly that is coupled to the carrier assembly and configured to act on the carrier assembly to rotate the permanent magnet simultaneously about the first axis of rotation and a second axis of rotation. The second axis of rotation intersects the first axis of rotation at an intersection that is offset from the center of mass of the permanent magnet. The position detection system additionally includes a computer device configured to determine a position of a sensor based on magnetic field measurements obtained by the sensor in the time-varying magnetic field.
1. A position detection system comprising:
a magnetic field generator configured to generate a time-varying magnetic field, the magnetic field generator comprising:
a carrier assembly that defines a first axis of rotation and comprises a permanent magnet having a center of mass; and
a drive assembly coupled to the carrier assembly and configured to act on the carrier assembly to rotate the permanent magnet simultaneously about the first axis of rotation and a second axis of rotation, the second axis of rotation intersecting the first axis of rotation at an intersection that is offset from the center of mass of the permanent magnet;
a computer device configured to determine a position of a sensor based on magnetic field measurements obtained by the sensor in the time-varying magnetic field.
2. The position detection system of claim 1 , wherein the drive assembly is configured to act on the carrier assembly to rotate the permanent magnet an integer number of full rotations about the first axis for each individual full rotation of the permanent magnet about the second axis.
3. The position detection system of claim 1 , wherein the drive assembly is configured to act on the carrier assembly to rotate the permanent magnet an integer number of full rotations about the second axis for each individual full rotation of the permanent magnet about the first axis.
4. The position detection system of claim 1 , wherein the carrier assembly further comprises a non-magnetic counterweight having a center of mass offset from the intersection along the first axis of rotation and opposite the center of mass of the permanent magnet.
5. The position detection system of claim 4 , wherein the drive assembly is configured to act on the carrier assembly to simultaneously:
rotate the non-magnetic counterweight about the first axis and the second axis, and
rotate the permanent magnet about the first axis and the second axis.
6. The position detection system of claim 5 , wherein the drive assembly is configured to act on the carrier assembly to simultaneously rotate the non-magnetic counterweight and the permanent magnet such that a gyroscopic effect of the permanent magnet and a gyroscopic effect of the non-magnetic counterweight offset each other.
7. The position detection system of claim 1 , wherein the permanent magnet is part of a permanent magnet assembly that comprises one or more permanent magnets and produces a dipole magnetic field, and the drive assembly is configured to act on the carrier assembly to rotate the dipole magnetic field simultaneously about the first axis and the second axis.
8. The position detection system of claim 7 , wherein the dipole magnetic field defines a dipole axis of symmetry perpendicular to the first axis, and the drive assembly is configured to act on the carrier assembly to rotate the dipole axis of symmetry simultaneously about the first axis and the second axis.
9. The position detection system of claim 7 , wherein the dipole magnetic field defines a center point that is offset from the intersection between the first axis and the second axis.
10. The position detection system of claim 1 , wherein the drive assembly comprises a motor and a drive shaft coupled to the carrier assembly, and the motor is configured to rotate the drive shaft about the second axis.
11. The position detection system of claim 10 , wherein the drive shaft is configured to act on the carrier assembly to rotate the carrier assembly about the second axis, and the drive assembly further comprises a torque converter configured to act on the carrier assembly to rotate the permanent magnet about the first axis while the carrier assembly rotates about the second axis.
12. The position detection system of claim 11 , wherein the carrier assembly further comprises a non-magnetic counterweight, and the torque converter is configured to act on the carrier assembly to rotate the non-magnetic counterweight about the first axis while the carrier assembly rotates about the second axis.
13. The position detection system of claim 12 , wherein the carrier assembly comprises a first pinion gear associated with the permanent magnet and a second pinion gear associated with non-magnetic counterweight, and the torque converter comprises a ring gear operatively coupled to the first and second pinion gears.
14. The position detection system of claim 1 , wherein the carrier assembly comprises a carrier shaft extending along the first axis, and the drive assembly comprises a motor configured to rotate the carrier shaft about the first axis.
15. The position detection system of claim 1 , wherein the second axis is perpendicular to the first axis.
16. A method for position detection, comprising:
generating a time-varying magnetic field by operation of a magnetic field generator, wherein the magnetic field generator generates the time-varying magnetic field by rotating a permanent magnet simultaneously about a first axis of rotation and a second axis of rotation, the second axis of rotation intersecting the first axis of rotation at a location that is offset from a center of mass of the permanent magnet;
at a computer system, receiving magnetic field measurements obtained by a sensor in the time-varying magnetic field; and
by operation of the computer system, determining a position of the sensor based on the magnetic field measurements.
17. The method of claim 16 , wherein the magnetic field generator comprises:
a carrier assembly that defines the first axis of rotation and comprises the permanent magnet; and
a drive assembly that acts on the carrier assembly to rotate the permanent magnet simultaneously about the first axis of rotation and the second axis of rotation.
18. The method of claim 16 , wherein the magnetic field generator generates the time-varying magnetic field by rotating the permanent magnet an integer number of multiple full rotations about the first axis for each individual full rotation of the permanent magnet about the second axis.
19. The method of claim 16 , wherein the magnetic field generator generates the time-varying magnetic field by rotating the permanent magnet an integer number of multiple full rotations about the second axis for each individual full rotation of the permanent magnet about the first axis.
20. The method of claim 16 , wherein the magnetic field generator further comprises a non-magnetic counterweight, and the magnetic field generator generates the time-varying magnetic field by simultaneously:
rotating the non-magnetic counterweight about the first axis and the second axis, and
rotating the permanent magnet about the first axis and the second axis.
21. The method of claim 20 , wherein the magnetic field generator generates the time-varying magnetic field by simultaneously rotating the non-magnetic counterweight and the permanent magnet such that a gyroscopic effect of the permanent magnet and a gyroscopic effect of the non-magnetic counterweight offset each other.
22. The method of claim 16 , wherein the permanent magnet is part of a permanent magnet assembly that comprises one or more permanent magnets and produces a dipole magnetic field, and the magnetic field generator generates the time-varying magnetic field by rotating the dipole magnetic field simultaneously about the first axis and the second axis.
23. The method of claim 22 , wherein:
the dipole magnetic field defines a dipole axis of symmetry perpendicular to the first axis, and the magnetic field generator generates the time-varying magnetic field by rotating the dipole axis of symmetry simultaneously about the first axis and the second axis, and
the dipole magnetic field defines a center point that is offset from the intersection between the first axis and the second axis.
24. The method of claim 16 , wherein the magnetic field generator generates the time-varying magnetic field by rotating the permanent magnet simultaneously:
about the first axis of rotation at a speed of 30 rotations per minute (RPM) or higher, and
about the second axis of rotation at a speed of 30 rotations per minute (RPM) or higher.