EM Tracking Pose Correction via IMU Weighting
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Solution Overview
Problem
Electromagnetic (EM) position tracking systems face inaccuracies and distortions due to metallic objects in the EM field, which are difficult to detect and correct, especially when these objects are introduced after calibration.
Innovation Solution
Incorporating an inertial measurement unit (IMU) in the mobile unit, such as a hand controller, to provide a secondary pose measurement, and adjusting the weighting of EM pose data and IMU pose data based on detected distortions, allowing the system to reduce pose errors and improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If EM field is used for position tracking, then position tracking capability is provided, but metallic objects cause field distortion leading to inaccurate pose values
Solution Approach 1:
The patent introduces an intermediary distortion correction process that mediates between the EM field measurements and the final pose calculation. A distortion correction module processes the raw EM field data to compensate for metallic object interference, using pre-characterized distortion maps or real-time correction algorithms to restore accurate pose values despite the presence of harmful metallic objects in the tracking volume.
Solution Approach 2:
The system implements feedback by continuously monitoring EM field measurements and comparing them against expected values based on the dipole model. When deviations indicating metallic object interference are detected, the system adjusts the pose calculation through distortion correction algorithms, creating a closed-loop system that actively compensates for harmful distortions to maintain measurement precision.
2Measurement precision
If distortion correction is implemented, then pose accuracy is improved, but system complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-characterizing the EM field distortion patterns during system calibration or manufacturing. Distortion correction maps or lookup tables are generated in advance for known metallic object configurations, allowing the runtime system to simply query and apply pre-computed corrections rather than performing complex real-time distortion analysis, thus reducing operational complexity while maintaining high accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively compensates for EM field distortions caused by metallic objects, enhancing the accuracy and reliability of position tracking in virtual reality applications by combining EM and IMU data, thereby improving user experience.
Implementation Method 1
a transmitter that generates an EM field using a tri-axis coil to induce a current on a second tri-axis coil located at a remote receiver
Implementation Method 2
Incorporating an inertial measurement unit (IMU) in the mobile unit, such as a hand controller, to provide a secondary pose measurement
Data Source
AI summary
An electromagnetic (EM) position tracking system identifies the pose of objects based on detected strength values of an EM field. To address distortions in the field, the system employs a pose sensor to provide a second pose of the mobile unit. Under conditions where no distortion in the EM field has been detected, the HMD applies a nominal set of corresponding weights to the EM pose data and the IMU pose data, respectively, and combines the weighted pose value to identify a combined pose of the mobile unit. In response to detecting conditions that indicate distortion in the EM field, the HMD can apply different weights to the EM pose data and IMU pose data to, for example increase the influence of the IMU pose data on the combined pose.