Rectangular Hand Marker for Wrist Rotation Tracking
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Solution Overview
Problem
Existing single-camera and marker-based systems struggle to accurately track hand and wrist rotation movements, particularly in post-stroke rehabilitation exercises, due to difficulties in detecting 3 degrees of freedom with arbitrary-shaped markers, often requiring additional markers or sensors.
Innovation Solution
A method and apparatus using a specifically designed rectangular-shaped hand-worn marker that can be line-fitted, allowing for both line-fitting and area-angle mapping algorithms, enabling accurate tracking of hand and wrist rotations with a single marker, thereby simplifying the system and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If arbitrary-shaped markers (circular or square) are used for hand/wrist rotation tracking, then the marker can be easily manufactured and worn, but the line-fitting algorithm cannot be applied and rotation tracking becomes inaccurate
Solution Approach 1:
The patent applies asymmetry by designing the marker with a specific rectangular shape where the length along the forearm direction is significantly different from the width perpendicular to the forearm. This asymmetric rectangular shape enables the line-fitting algorithm to accurately distinguish the forearm direction from other directions, resolving the contradiction between ease of manufacture and measurement precision.
2Measurement precision
If multiple markers or additional sensors (accelerometers) are added to improve rotation tracking accuracy, then measurement precision improves, but device complexity and cost increase
Solution Approach 1:
The patent applies universality by designing a single rectangular marker that can track all three degrees of freedom of hand/wrist rotation (forearm pronation/supination, wrist dorsiflexion/palmar flexion, and wrist radial/ulnar deviation) using only one marker combined with line-fitting and area-angle mapping algorithms. This eliminates the need for multiple markers or additional sensors, reducing device complexity while maintaining measurement precision.
3Device complexity
If a single marker is used for all three degrees of freedom of hand/wrist rotation, then device complexity is reduced, but it becomes difficult to distinguish different rotation directions and planes
Solution Approach 1:
The patent applies asymmetry by designing the rectangular marker with specific orientation relative to the hand anatomy, where the length is along the forearm direction and width is perpendicular to it. This asymmetric shape allows the line-fitting algorithm to identify the forearm direction and distinguish different rotation planes (sagittal, coronal, transverse planes), enabling accurate detection of all three rotation degrees of freedom with a single marker.
4Ease of manufacture
If circular or square markers are used, then the marker shape is simple and easy to manufacture, but the projection to camera cannot be line-fitted into a line for rotation identification
Solution Approach 1:
The patent applies asymmetry by rejecting symmetric shapes (circular or square) and adopting an asymmetric rectangular shape where length ≠ width. This asymmetric rectangular shape ensures that the marker projection can be line-fitted into a line by the algorithm, as the line-fitting process can identify the major axis of the rectangle corresponding to the forearm direction, enabling accurate rotation tracking.
Data Source
AI summary
The present invention provides a method and apparatus for tracking hand and/or wrist rotation of a user performing exercise. An aspect of the present invention proposes a method of tracking hand and/or wrist rotation of a user performing an exercise, wherein the user wears a marker on his/her hand, the method comprising the steps of: acquiring a first image and a second image of the marker by means of a camera when the hand is in a first posture and a second posture respectively; deriving the angle change of the hand and/or wrist from the change from the first posture to the second posture, based on the first image and the second image and the type of the exercise that the user is performing; and outputting the angle change of the hand and/or wrist, wherein the marker approximates a rectangular block, the marker has an opening for accommodating the palm(s) of the user and the side of the marker along the direction perpendicular to the palm is substantially shorter than two other sides. In this way, a single hand-worn marker is adequate for hand/wrist rotation tracking, so that the system implementation may be simplified and the cost for markers or other accelerometers can be saved.