Compensating for distortion in an electromagnetic tracking system
Inventors
Schneider, Mark Robert • Fujioka, Kenji
Assignees
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Publication Number
US-11360161-B2
Publication Date
2022-06-14
Expiration Date
Abstract
A system comprising: a magnetic transmitter configured to generate magnetic fields; a magnetic sensor configured to generate signals based on characteristics of the magnetic fields received at the magnetic sensor; and one or more computer systems configured to: receive the signals from the magnetic sensor; determine, based on the signals received from the magnetic sensor, an electromagnetic (EM) pose of the magnetic sensor relative to the magnetic transmitter; determine one or both of: i) an inertial pose of the magnetic sensor relative to the magnetic transmitter based on inertial data associated with the magnetic transmitter and the magnetic sensor, or ii) an optical pose of the magnetic sensor relative to the magnetic transmitter based on optical data associated with the magnetic transmitter and the magnetic sensor; determine an estimated pose of the magnetic sensor relative to the magnetic transmitter based on the EM pose and the one or both of the inertial pose or the optical pose; determine distorted magnetic fields based on the EM pose; determine estimated clean magnetic fields based on the estimated pose; determine estimated distorted magnetic fields based on the distorted magnetic fields and the estimated clean fields; and determine an improved EM pose of the magnetic sensor relative to the magnetic transmitter based on the estimated distorted magnetic fields.
Core Innovation
The invention relates to electromagnetic tracking in an environment that distorts magnetic fields. A magnetic sensor generates signals based on characteristics of magnetic fields generated by a magnetic transmitter and received at the magnetic sensor, and an EM tracker determines an EM pose of the magnetic sensor relative to the magnetic transmitter.
Using the EM pose, the system determines one or both of an inertial pose based on inertial data from an inertial measurement unit and an optical pose based on optical data from an optical sensor. The system then determines an estimated pose of the magnetic sensor relative to the magnetic transmitter based on the EM pose and the one or both of the inertial pose or the optical pose.
Based on the EM pose, the system determines distorted magnetic fields and determines estimated clean magnetic field values based on the estimated pose. The system determines estimated distorted magnetic field values based on differences between the distorted magnetic fields and the estimated clean fields, and then determines an improved EM pose of the magnetic sensor relative to the magnetic transmitter based on the estimated distorted magnetic fields.
The compensation workflow uses a distortion model and selects or fits model parameters to represent the distorted magnetic fields and derive the estimated clean and estimated distorted magnetic field values. The distortion compensation supports non-linear least squares, including Levenberg-Marquardt, with distortion model forms including a dipole model, a rectangular loop model, or spherical harmonics model, and tracking uses loosely coupled and tightly coupled implementations with an extended Kalman filter, pose fusion, and internal feedback.
Claims Coverage
The document provides two independent claims: one system claim and one method claim. Across these independent claims, the main inventive features are EM pose estimation, fusion with inertial and/or optical pose, derivation of clean and distorted magnetic field values, and use of estimated distorted magnetic fields to determine an improved EM pose.
Electromagnetic pose estimation from magnetic sensor signals
A magnetic transmitter generates magnetic fields, a magnetic sensor generates signals based on characteristics of magnetic fields received at the magnetic sensor, and an EM tracker determines an EM pose of the magnetic sensor relative to the magnetic transmitter.
Estimated pose fusion using EM pose and inertial and/or optical pose
The computer systems determine one or both of an inertial pose based on inertial data from an IMU and an optical pose based on optical data from an optical sensor, and determine an estimated pose based on the EM pose and the one or both of the inertial pose or the optical pose.
Clean and distorted magnetic field estimation from the estimated pose
The computer systems determine distorted magnetic fields based on the EM pose, determine estimated clean magnetic field values based on the estimated pose, and determine estimated distorted magnetic field values based on differences between the distorted magnetic fields and the estimated clean fields.
Improved EM pose determination using estimated distorted magnetic fields
The computer systems determine an improved EM pose of the magnetic sensor relative to the magnetic transmitter based on the estimated distorted magnetic fields.
Both independent claims follow the same core pipeline: determine an EM pose from magnetic sensor signals, fuse with inertial and/or optical pose to obtain an estimated pose, derive estimated clean and estimated distorted magnetic field values, and use the estimated distorted magnetic fields to determine an improved EM pose.
Stated Advantages
Compensates for distorted magnetic fields caused by the operating environment, by deriving estimated distorted magnetic fields and using them to determine an improved EM pose.
Documented Applications
Magnetic transmitter integrated into a controller and magnetic sensor integrated into a head-mounted display, with optional IMUs and optical sensors/cameras for electromagnetic tracking in a tracking environment.
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