Rigid Upper Arm Model for Shoulder Rotation Center Positioning
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Solution Overview
Problem
Existing methods for positioning the functional rotation center of the shoulder (FRCS) in human motion measurement are inadequate in accuracy, especially when establishing dynamic models, due to reliance on static anatomical knowledge and geometric limitations, leading to positioning errors and deviations.
Innovation Solution
A positioning method based on a rigid upper arm model, abstracting the human upper arm into a cylinder with the FRCS as the center, determining a reference axis vector, correcting the central axis direction, and applying height compensation to accurately locate the FRCS.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the GHAC method is used to locate the rotation center based on static anatomical knowledge, then the measurement can be completed under static conditions with anatomical reference, but the positioning accuracy is insufficient for establishing dynamic models
Solution Approach 1:
The patent transitions from static anatomical measurement to dynamic motion-based measurement. The FRCS is determined by analyzing the motion trajectories of multiple markers on the upper arm during actual movement, making the measurement adaptive to dynamic conditions rather than relying on static anatomical references.
Solution Approach 2:
The patent replaces the mechanical/anatomical reference system (GHAC based on bone structure) with a kinematic calculation system based on motion trajectories and geometric algorithms. The rotation center is computed from marker motion data rather than inferred from anatomical landmarks.
2Measurement precision
If the cadaver method with three rotation axes is used to locate FRCS, then the rotation center can be determined by intersection of axes, but the non-subjective movement of cadaver results in insufficient accuracy
Solution Approach 1:
The system uses the subject's own motion to determine the rotation center. Multiple markers placed on the upper arm automatically trace their trajectories during natural movement, and the FRCS is computed from these self-generated motion data, eliminating the need for external manipulation or non-subjective cadaver preparation.
3Adaptability or versatility
If the Japan Digital Human Research Center method is used that abandons anatomical knowledge restrictions, then the FRCS can be calculated according to moving human body, but positioning errors from systematic error and skin deformation are transmitted and amplified
Solution Approach 1:
The patent introduces a rigid upper arm model as an intermediary between the skin-mounted markers and the FRCS calculation. This model serves as a reference frame that filters out skin deformation errors, allowing the system to maintain adaptability to motion while reducing the amplification of measurement errors through geometric calculation.
Data Source
AI summary
A positioning method of functional rotation center of shoulder based on rigid upper arm model includes: step 1: abstracting a human upper arm into a cylinder with FRCS as a center of top surface; step 2: determining a reference axis vector of the cylinder; step 3: determining an axis vector of the cylinder and a displacement from the reference axis vector to the axis vector; step 4: correcting a central axis direction of the cylinder; step 5: determining a height compensation of the cylinder, and positioning the FRCS. The method has higher accuracy for the positioning result of FRCS, the positioning result of FRCS has better stability relative to the upper arm and trunk, and can be used to establish a more accurate human digital dynamic model and predict more accurate human posture.