IMU Heading Error Correction via Joint Axis Plane
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Solution Overview
Problem
Motion tracking systems using inertial measurement units (IMUs) face heading errors due to cumulative errors and magnetic disturbances, leading to inaccurate movement sequence assessments, particularly in physical rehabilitation applications, where soft tissue artifacts and IMU misplacement exacerbate these issues.
Innovation Solution
A method involving a computing device that processes orientation measurements from IMUs on body members to compute a heading rotation value, correcting heading errors by digitally modifying the orientation measurements to ensure they are contained within a joint axis plane, thereby reducing errors and improving the accuracy of movement sequence analysis without requiring calibration procedures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If IMUs are used for motion tracking, then movement sequence can be determined, but heading errors occur due to cumulative errors and magnetic disturbances
Solution Approach 1:
The system uses the joint axis plane as a reference constraint to continuously correct heading estimates. The computing device calculates the deviation of IMU measurements from the expected joint axis plane and applies corrective rotations to maintain accuracy throughout the motion tracking process.
Solution Approach 2:
The system changes the reference frame parameters by defining a joint axis plane based on anatomical constraints. By transforming the heading estimation problem into a plane-containing problem, the system can correct measurements by applying parameter adjustments that ensure the IMU data conforms to the expected anatomical plane.
2Measurement precision
If calibration procedures are implemented to correct heading errors, then measurement precision improves, but device complexity and setup time increase
Solution Approach 1:
The system performs self-calibration by using the joint axis plane constraint inherent to the human body anatomy. The computing device automatically determines the plane from the IMU measurements and anatomical relationships without requiring external calibration equipment or procedures, making the system self-sufficient.
Solution Approach 2:
The system pre-defines the joint axis plane based on anatomical knowledge before actual motion tracking begins. This preliminary establishment of the reference plane allows for immediate correction of heading errors without requiring calibration procedures during setup.
3Productivity
If IMUs are placed on body members, then motion tracking is enabled, but soft tissue artifacts and misplacement cause additional heading errors
Solution Approach 1:
The joint axis plane acts as an intermediary reference that mediates between the IMU measurements and the true body segment orientation. By using this intermediate plane defined by anatomical constraints, the system can filter out errors caused by soft tissue artifacts and misplacement.
Data Source
AI summary
A method comprising: digitally processing orientation measurements provided by each of first and second inertial measurement units, the first and second units being arranged on first and second body members of a person, respectively, according to a predetermined unit arrangement, and the first and second body members being connected by a joint; the measurements are digitally processed such that the computing device at least: computes a length vector of a segment of the first body member based on a first orientation measurement of the first unit; defines a joint axis plane of the joint based on a second orientation measurement of the second unit; and computes a heading rotation value for making the first orientation measurement to be contained within the joint axis plane defined; and the method further comprising digitally modifying the first orientation measurement or the second orientation measurement by applying a rotation at least based on the heading rotation value computed. Also, a motion tracking system and a computer program product.