Method And Apparatus For Correcting Magnetic Tracking Error With Inertial Measurement

• US 20160377451A1
• Filed: 07/13/2015
• Published: 12/29/2016
• Est. Priority Date: 07/11/2014
• Status: Active Grant

• Current Assignee: Penumbra, Inc.
• Original Assignee: Sixense Entertainment Incorporated
• Inventors: Pedrotti, Owen Walter, Zur, Oded Y.
• Granted Patent: US 10,378,921 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• 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, comprising:

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 true position of the receiver relative to the transmitter; and

directly composing by the processor the rotation error quaternion with the measured orientation to produce a corrected orientation of the receiver relative to the transmitter.

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, the method comprising:

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 true position of the receiver relative to the transmitter; and

directly composing by the processor the rotation error quaternion with the measured orientation to produce a corrected orientation of the receiver relative to the transmitter.