Distortion correction for tracking an object in a magnetic field
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Publication Number
US-11397220-B2
Publication Date
2022-07-26
Expiration Date
Abstract
A system is configured to model a magnetic field by measuring a first value for characteristics of a magnetic field at a first position in the magnetic field. The system measures a second value characteristics of the magnetic field at a second position in the magnetic field. The system determines a distance between the first position and the second position. The system estimates a distortion component of the magnetic field at approximately the second position in the magnetic field based on each of the distance, the first value for each of the one or more characteristics, and the second value for each of the one or more characteristics. The system outputs a model of at least a region of the magnetic field.
Core Innovation
The invention relates to modeling a magnetic field and compensating magnetic distortions in electromagnetic tracking. A magnetic sensor measures one or more characteristics of a magnetic field at a first position, motion data representing movement of the magnetic sensor from the first position to a second position is obtained, and the magnetic sensor measures the one or more characteristics at the second position. A computing device determines a distance between the positions based on the motion data, the first values, and the second values.
Using the determined distance and the measured magnetic-field characteristics, the computing device estimates a distortion component of the magnetic field at approximately the second position. The distortion estimation is based on the distance, the first value for each characteristic, and the second value for each characteristic, and the computing device outputs a model of at least a region of the magnetic field based on the estimating. In related system embodiments, the second position is in a relatively more distorted region than the first position.
In specific embodiments, the distortion component is estimated by retrieving a model of the magnetic field corresponding to the second position and determining a value of the magnetic field corresponding to an undistorted received magnetic field at the second position according to the model. A difference is then determined between that model-based value and a value of the second magnetic data measured at the second position, and the difference represents the distortion component. The output includes an error field map for at least a region of the field.
Claims Coverage
The independent claims are 1, 11, and 16. Across these claims, the core coverage includes two-position magnetic-field measurement, determination of distance between positions using motion data or a known separation between sensors, estimation of a distortion component at approximately the second position, and outputting a model of at least a region of the magnetic field based on the distortion component.
Distance-determined two-position magnetic-field measurement
Measuring, by a magnetic sensor, first value(s) of one or more characteristics of a magnetic field at a first position; obtaining motion data representing movement from the first position to a second position; measuring second value(s) at the second position; and determining, by a computing device based on the motion data, the first value(s), and the second value(s), a distance between the first position and the second position.
Distortion-component estimation at approximately the second position
Estimating a distortion component of the magnetic field at approximately the second position based on the distance, the first value(s), and the second value(s), and using the estimating to output a model of at least a region of the magnetic field.
Undistorted model-based differencing for distortion component
Estimating the distortion component by retrieving a model of the magnetic field corresponding to the second position, determining a value of the magnetic field corresponding to an undistorted received magnetic field at the second position according to the model, determining a difference between that value and a value of the second magnetic data measured at the second position, and using the difference as the distortion component.
Multi-sensor and IMU-based magnetic tracking system
A magnetic tracking system including a source device configured to generate a magnetic field, a tracked device having a magnetic sensor configured to measure the magnetic field and generate magnetic data, and an inertial measurement unit (IMU) coupled to the magnetic sensor to generate motion data based on motion of the IMU, with a computing device configured to receive first and second magnetic data at first and second positions, determine a distance between the positions based on IMU motion data, determine a distortion component, and output a model of the magnetic field based on the distortion component.
Two fixed-position sensors with known separation for distortion modeling
A magnetic tracking system including a first magnetic sensor at a first position and a second magnetic sensor coupled to the first sensor at a particular distance, with the second sensor measuring magnetic data at a second position relatively more distorted than the first, where the computing device determines a distortion component by retrieving a model corresponding to the second position, determining an undistorted received magnetic-field value at the second position according to the model, determining a difference between that value and the measured second magnetic data value, and outputting a model of the magnetic field based on the distortion component.
Taken together, the independent claims cover measuring magnetic-field characteristics at two positions, determining distance between the positions using motion data or based on a particular distance between two magnetic sensors, estimating a distortion component at approximately the second position, and outputting a model of at least a region of the magnetic field based on the distortion component.
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