Tracking position and movement using a magnetic field

• US 10,151,606 B1
• Filed: 02/20/2017
• Issued: 12/11/2018
• Est. Priority Date: 02/24/2016
• Status: Active Grant

• Current Assignee: Ommo Technologies, Inc.
• Original Assignee: Ommo Technologies, Inc.
• Inventors: Memarzanjany, Fathollah, Zheng, Minjie
• Primary Examiner(s): Shah, Neel
• Application Number:
  US15/436,967
• Time in Patent Office: 659 Days
• CPC Class Codes: A61B 2034/2051 Electromagnetic tracking systems
• CPC Class Codes: G01D 5/145 influenced by the relative movement between the Hall device and magnetic fields see G01R33/06
• CPC Class Codes: G01D 5/2046 by a movable ferromagnetic element, e.g. a core

Abstract

In a general aspect, a position tracking system includes a sphere magnet that produces a magnetic field in a space. A magnetic field control system is configured to change the magnetic field by rotating the sphere magnet through a time-series of rotations over a time period. A position marker includes a magnetic field sensor that is configured to measure the magnetic field in the space during the time period. A data processing apparatus is configured to determine the position of the position marker based on magnetic field measurements obtained by the magnetic field sensor in the space during the time period.

Claims

1. A position tracking system comprising:

a sphere magnet that produces a magnetic field in a space;

a magnetic field control system configured to change the magnetic field by rotating the sphere magnet through a plurality of rotations over a time period, wherein the magnetic field control system comprises a plurality of coils configured to rotate the sphere magnet, the plurality of coils comprising;

a first pair of coils aligned, along a first axis, on first and second opposite sides of the sphere magnet;

a second pair of coils aligned, along a second axis that is orthogonal to the first axis, on third and fourth opposite sides of the sphere magnet; and

a third pair of coils aligned, along a third axis that is orthogonal to the first and second axes, on fifth and sixth opposite sides of the sphere magnet;

a position marker comprising a magnetic field sensor configured to measure the magnetic field in the space during the time period; and

a data processing apparatus configured to determine a position of the position marker based on magnetic field measurements obtained by the magnetic field sensor in the space during the time period.

2. The position tracking system of claim 1, wherein the magnetic field control system is configured to:

change the magnetic field by rotating the sphere magnet through a time-series of rotations over the time period; and

hold the sphere magnet in static orientations during time intervals between rotations in the time-series of rotations.

3. The position tracking system of claim 2, wherein determining the position of the position marker comprises identifying, from the magnetic field measurements, the time intervals between the rotations.

4. The position tracking system of claim 2, wherein rotating the sphere magnet through the time-series of rotations comprises:

rotating the sphere magnet by 180 degrees about a first axis;

rotating the sphere magnet by 90 degrees in a clockwise direction about a second axis that is orthogonal to the first axis;

rotating the sphere magnet by 180 degrees about a third axis that is orthogonal to the first and second axes; and

rotating the sphere magnet by 90 degrees in a counter-clockwise direction about the second axis.

5. The position tracking system of claim 1, wherein rotating the sphere magnet comprises activating the plurality of coils in succession.

6. The position tracking system of claim 1, wherein the magnetic field sensor is configured to measure the strength of the magnetic field along three orthogonal axes, and the data processing apparatus is configured to determine the position of the position marker with millimeter-scale precision.

7. The position tracking system of claim 6, wherein the magnetic field control system is configured to rotate the magnetic field by at least 180 degrees in a rotation time of less than 10 milliseconds, and the magnetic field sensor is configured to obtain multiple magnetic field measurements during the rotation time.

8. The position tracking system of claim 1, comprising multiple position markers each comprising a respective magnetic field sensor configured to measure the magnetic field in the space during the time period, wherein the data processing apparatus is configured to determine the respective positions of the position markers based on magnetic field measurements obtained by the respective magnetic field sensors in the space during the time period.

9. The position tracking system of claim 1, wherein the position marker is a wireless device that includes a power source.

10. The position tracking system of claim 9, comprising a main processing unit that includes the data processing apparatus, wherein the main processing unit is configured to communicate with the position markers through a wireless communication link.

11. A position tracking method comprising:

by operation of a magnetic field control system, changing a magnetic field in a space by rotating a sphere magnet through a plurality of rotations over a time period, wherein the magnetic field control system comprises a plurality of coils configured to rotate the sphere magnet, and the plurality of coils comprises;

a first pair of coils aligned, along a first axis, on first and second opposite sides of the sphere magnet;

a second pair of coils aligned, along a second axis that is orthogonal to the first axis, on third and fourth opposite sides of the sphere magnet; and

a third pair of coils aligned, along a third axis that is orthogonal to the first and second axes, on fifth and sixth opposite sides of the sphere magnet;

obtaining, during the time period, magnetic field measurements at a position marker comprising a magnetic field sensor in the space;

receiving the magnetic field measurements at a data processing apparatus; and

by operation of the data processing apparatus, determining a position of the position marker based on the magnetic field measurements.

12. The position tracking method of claim 11, comprising:

changing the magnetic field by rotating the sphere magnet through a time-series of rotations over the time period; and

maintaining the sphere magnet in a static orientation during a time interval between two sequential rotations in the time-series of rotations.

13. The position tracking method of claim 12, wherein determining the position comprises identifying, from the magnetic field measurements, the time interval between the rotations.

14. The position tracking method of claim 12, wherein rotating the sphere magnet through the time-series of rotations comprises:

rotating the sphere magnet by 180 degrees about a first axis;

rotating the sphere magnet by 90 degrees in a clockwise direction about a second axis that is orthogonal to the first axis;

rotating the sphere magnet by 180 degrees about a third axis that is orthogonal to the first and second axes; and

rotating the sphere magnet by 90 degrees in a counter-clockwise direction about the second axis.

15. The position tracking method of claim 11, wherein rotating the sphere magnet comprises controlling current through the plurality of coils.

16. The position tracking method of claim 11, wherein rotating the sphere magnet comprises activating the plurality of coils in succession.

17. The position tracking method of claim 11, comprising, at a main processing unit comprising the data processing apparatus, receiving the magnetic field measurements from the position marker through a wireless communication link.