Skin Strain Measurement via Motion Capture and 3D Tracking
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Solution Overview
Problem
Current methods for understanding skin material properties during natural movements are limited, as they do not account for biaxial prestress and anisotropic behavior, making it difficult to quantify strains and identify lines of non-extension (LONEs) effectively, especially in vivo.
Innovation Solution
A system combining motion capture and 3D tracking technologies to record body movements, calculate strain fields, and derive three-dimensional contours and patterns, using second-order Lagrangian strains and eigenvector analysis to identify LONEs and project strains onto tangential planes, allowing for quantitative analysis of skin strains during dynamic and static movements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If in vitro tensile testing is used to measure skin material properties, then material property data can be obtained, but the skin behaves differently when removed from surrounding tissues
Solution Approach 1:
The patent introduces motion capture systems and 3D tracking technology as intermediary tools to measure skin deformation in vivo without removing the skin from the body. These systems capture marker positions on the skin surface and calculate strains through computational methods, serving as a bridge between non-invasive measurement and accurate material property assessment.
Solution Approach 2:
The patent replaces direct mechanical tensile testing with a computational mechanics approach. Instead of physically pulling skin samples in the lab, the system uses motion capture data and finite element analysis to calculate strains and stress distributions in vivo, substituting physical mechanical testing with computational modeling.
2Measurement precision
If in vivo techniques with external loads are used to measure skin deformation, then material property data can be obtained, but biaxial prestress is not taken into account
Solution Approach 1:
The patent creates a multi-functional measurement system that simultaneously captures skin deformation in multiple directions and calculates multiple strain components. The motion capture system tracks markers in 3D space, enabling calculation of both longitudinal and transverse strains, as well as principal strains and their orientations, all within a single in vivo measurement session.
Solution Approach 2:
The patent transitions from uniaxial to biaxial strain measurement by utilizing three-dimensional motion capture data. The system calculates not only the magnitude of strains in two principal directions but also the orientations of these principal strain directions, adding the dimensional aspect of orientation to the strain measurement.
3Difficulty of detecting and measuring
If previous work methods are used to find non-extending lines, then qualitative identification is possible, but quantitative strain measurement is not achieved
Solution Approach 1:
The patent implements a feedback loop where motion capture data is continuously processed to calculate strain fields, which are then used to identify LONEs. The system provides quantitative feedback on strain magnitudes and directions, allowing for precise identification and verification of non-extending line locations and orientations based on measured principal strain directions.
Solution Approach 2:
The patent changes the measurement parameters from qualitative visual inspection to quantitative strain field analysis. By calculating principal strains and their orientations at each point on the skin surface, the system transforms the identification of LONEs from a subjective qualitative process to an objective quantitative process based on measured strain parameters.
Data Source
AI summary
Described herein are systems and techniques for a motion capture system and a three-dimensional (3D) tracking system used to record body position and/or movements/motions and using the data to measure skin strain (a strain field) all along the body while a joint is in motion (dynamic) as well as in a fixed position (static). The data and technique can be used to quantify strains, calculate 3D contours, and derive patterns believed to reveal skin's properties during natural motions.