Inertial Sensor Attachment Posture Estimation via Acceleration Cross Products
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Solution Overview
Problem
Existing methods for estimating the attachment posture of inertial sensors relative to a target person are unreliable due to environmental influences on geomagnetism-based methods, and they fail to precisely determine the relative posture relationship between the measurement target portion and the inertial sensor.
Innovation Solution
A method involving the detection of acceleration vectors in a sensor coordinate system, where a first acceleration vector is measured while the target portion is still, and a second acceleration vector is measured during controlled changes in posture, allowing for the calculation of cross product vectors to identify the relative posture relationship between the measurement target portion and the inertial sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If geomagnetism-based method is used to estimate attachment posture, then the method is simple to implement, but the reliability and stability of estimation deteriorates due to environmental influences
Solution Approach 1:
The patent replaces the geomagnetism-based method with an acceleration-based mechanical sensing approach. By using the acceleration sensor to detect gravitational acceleration and motion-induced accelerations, the system determines attachment posture without relying on magnetic field measurements that are susceptible to environmental interference.
Solution Approach 2:
The patent introduces cross-product vectors as an intermediary computational element. By calculating the cross product of acceleration vectors detected at different postures, the system derives a vector that represents the attachment posture relationship, providing a stable intermediate representation that is insensitive to environmental factors.
2Measurement precision
If precise attachment posture is required, then measurement accuracy improves, but the ease of attachment deteriorates as degree of freedom increases
Solution Approach 1:
The patent performs preliminary calibration by detecting acceleration vectors at specific known postures (standing still, bending forward, turning sideways) before actual measurement. This preliminary action establishes the attachment posture relationship in advance, allowing the system to achieve precise measurements without requiring the user to precisely control attachment orientation.
Solution Approach 2:
The patent changes the parameter representation from direct spatial orientation to a transformation matrix derived from cross-product vectors. By representing attachment posture as a mathematical transformation relationship rather than fixed spatial coordinates, the system achieves precise posture measurement while maintaining flexibility in attachment orientation.
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
This method provides a reliable and stable estimation of the relative posture relationship, enhancing the accuracy of inertial sensor attachment and data collection during exercise monitoring.
Implementation Method 1
an acceleration sensor capable of detecting accelerations in the respective coordinate axes in a sensor coordinate system
Implementation Method 2
detecting a first acceleration vector that is an acceleration vector including a set of accelerations in three coordinate axis directions
Data Source
AI summary
An acceleration vector is detected in a kept-still state of a measurement target portion such as thighs of a target person to which an inertial sensor is attached, and further, another acceleration vector is detected in a state in which the target person is allowed to carry out exercise such that a posture of the measurement target portion is caused to change in a direction around a Yb axis with a Yb-axis direction of the measurement target portion maintained in a direction that perpendicularly intersects a vertical direction, direction in a sensor coordinate system the Yb-axis direction of the measurement target portion corresponds to is identified on the basis of a cross product vector of the acceleration vector and another acceleration vector.