Method and apparatus for correcting magnetic tracking error with inertial measurement

• US 10,378,921 B2
• Filed: 07/13/2015
• Issued: 08/13/2019
• Est. Priority Date: 07/11/2014
• Status: Active Grant

• Current Assignee: Penumbra, Inc.
• Original Assignee: Sixense Enterprises Inc. (Penumbra Inc)
• Inventors: Pedrotti, Owen Walter, Zur, Oded Y.
• Primary Examiner(s): Macchiarolo, Peter J
• Assistant Examiner(s): Mercado, Alexander A
• Application Number:
  US14/797,983
• Publication Number:
  US 20160377451A1
• Time in Patent Office: 1,492 Days
• Field of Search: 73 175
• CPC Class Codes: G01C 25/00 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 Class Codes: G01R 33/0023 Electronic aspects, e.g. circuits for stimulation, evaluation, control; Treating the measured signals; calibration G01R33/0017 takes precedence
• CPC Class Codes: G01V 7/00 Measuring gravitational fields or waves; Gravimetric prospecting or detecting

Abstract

A method and apparatus is disclosed for synchronizing a magnetic field transmitter and receiver to resolve phase ambiguity so that phase information for the position and orientation of the receiver may be derived and maintained. A synchronization process allows for the phase information to be initially derived based upon known information from other sources, and then tracked from one measurement to the next. In another embodiment, information from an inertial measurement unit (IMU) is used to determine the phase information or to correct for errors in the determination from receiver data of the position and orientation of a receiver, and prevent such errors from accumulating as the receiver moves away from a transmitter.

Claims

1. A method of using an inertial measurement unit (IMU) to correct for error in a measured position vector and orientation of a tracking device containing a receiver in a magnetic tracking system having a transmitter and displaying the tracking device corresponding to an actual position and corrected orientation of the receiver, comprising:

displaying on a display the tracking device based on a measured position and orientation of the receiver relative to the transmitter;

receiving at a processor a gravity vector and position vector as measured by the receiver;

determining by the processor a true gravity vector from information from the IMU;

computing by the processor an angle of geodesic rotation between a gravity vector as measured by the receiver and the true gravity vector as a rotation error quaternion;

performing by the processor a spherical interpolation to reduce the angle of geodesic rotation by half to form a position correction quaternion;

rotating by the processor the measured position vector about an origin of the tracking space using the position correction quaternion to produce a corrected position vector indicating the actual position of the receiver relative to the transmitter; and

determining by the processor a corrected orientation of the receiver relative to the transmitter based upon the rotation error quaternion and the measured orientation; and

displaying on the display the tracking device in the actual position and corrected orientation of the receiver relative to the transmitter.

4. The method of claim 1 wherein rotating by the processer the measured position vector about an origin of the tracking space using the position correction quaternion is determined by a suitable curve fitting function.

2. A non-transitory computer readable storage medium having embodied thereon instructions for causing a computing device to execute a method of using an inertial measurement unit (IMU) to correct for error in a measured position vector and orientation of a tracking device containing a receiver in a magnetic tracking system having a transmitter and displaying the tracking device corresponding to an actual position and corrected orientation of the receiver, the method comprising:

generating instructions to display on a display device the tracking device based on a measured position and orientation of the receiver relative to the transmitter;

receiving a gravity vector and position vector as measured by the receiver;

determining a true gravity vector from information from the IMU;

computing an angle of geodesic rotation between a gravity vector as measured by the receiver and the true gravity vector as a rotation error quaternion;

performing a spherical interpolation to reduce the angle of geodesic rotation by half to form a position correction quaternion;

rotating the measured position vector about an origin of the tracking space using the position correction quaternion to produce a corrected position vector indicating the actual position of the receiver relative to the transmitter;

determining a corrected orientation of the receiver relative to the transmitter based upon the rotation error quaternion and the measured orientation; and

generating instructions to display on a display device the tracking device in the actual position and corrected orientation of the receiver relative to the transmitter.

5. The non-transitory computer readable storage medium of claim 2 wherein rotating the measured position vector about an origin of the tracking space using the position correction quaternion is determined by a suitable curve fitting function.

3. A system for using an inertial measurement unit (IMU) to correct for error in a measured position vector and orientation of a tracking device containing a receiver in a magnetic tracking system having a transmitter and displaying the tracking device corresponding to an actual position and corrected orientation of the receiver, comprising:

a transmitter comprising a plurality of source magnetic coils each configured to generate a magnetic field;

a tracking device comprising an inertial measurement unit (IMU) and a receiver, the receiver comprising a plurality of sensor magnetic coils configured to sense the magnetic fields and to generate a signal matrix representing the position and orientation of the receiver relative to the transmitter;

a processor configured to;

provide instructions to a display device to display the tracking device based on a measured position and orientation of the receiver relative to the transmitter;

receive a gravity vector and position vector as measured by the receiver;

determine a true gravity vector from information from the IMU;

compute an angle of geodesic rotation between a gravity vector as measured by the receiver and the true gravity vector as a rotation error quaternion;

perform a spherical interpolation to reduce the angle of geodesic rotation by half to form a position correction quaternion;

rotate the measured position vector about an origin of the tracking space using the position correction quaternion to produce a corrected position vector indicating the actual position of the receiver relative to the transmitter;

determine a corrected orientation of the receiver relative to the transmitter based upon the rotation error quaternion and the measured orientation; and

provide instructions to the display device to display the tracking device in the actual position and corrected orientation of the receiver relative to the transmitter.

6. The system of claim 3 wherein the processor configured to rotate the measured position vector about an origin of the tracking space using the position correction quaternion is configured to be determined by a suitable curve fitting function.