Sub-pixel Feature Positioning for Non-contact Strain Monitoring
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Solution Overview
Problem
Existing methods for monitoring strains and displacements in objects, such as mechanical tests and large structures, face challenges including the need for direct contact with fragile or small structures, limited area coverage, and impracticality in extreme environments, as well as high costs and complexity in the aerospace industry for monitoring aircraft structures.
Innovation Solution
A method and apparatus using image processing techniques to determine the position of features within images to a high degree of accuracy, allowing for the measurement of dimensional changes and structural monitoring by capturing and comparing images, and applying Super Resolution techniques to enhance resolution and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If mechanical or electromechanical instruments (extensometers, strain gauges) are used to monitor strains and displacements, then measurement precision is improved, but device complexity and the need for direct contact with the object increase
Solution Approach 1:
The patent replaces mechanical extensometers and strain gauges with an optical system using video cameras to capture images of the object. The mechanical contact-based measurement system is substituted with a non-contact optical imaging system that uses image processing algorithms to calculate displacements and strains from sequential images, thereby eliminating the need for physical sensors attached to the object.
Solution Approach 2:
The patent creates a visual copy of the object's surface features through video imaging. By capturing images of natural surface patterns (without requiring artificial targets) and processing these visual copies through correlation algorithms, the system derives measurement data from the copied visual information rather than direct mechanical sensing.
2Measurement precision
If multiple extensometers or strain gauges are used to monitor a large area of the object, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent implements a universal measurement system where a single video camera can monitor multiple points and the entire field of view simultaneously. The image processing algorithm processes the entire image to identify and track multiple natural features, allowing one device to perform the function of multiple discrete sensors would have been required.
Solution Approach 2:
The patent transitions from point-based measurement (single extensometer at one location) to area-based measurement by capturing the entire object surface in a 2D image. The correlation-based image processing extends measurement capability across the whole field of view, adding spatial dimensionality to the monitoring coverage.
3Measurement precision
If mechanical or electromechanical instruments are used in extreme environments (hot, cold, corrosive), then measurement precision is maintained, but ease of operation deteriorates due to practical limitations
Solution Approach 1:
The patent replaces mechanical sensors that would physically degrade in extreme environments with an optical imaging system. The video camera and image processing system operate remotely without physical contact with the object, eliminating the operational constraints imposed by temperature, corrosion, and other environmental factors that would affect mechanical instruments.
4Device complexity
If prior art video monitoring systems use captured images for measurement, then device complexity is reduced, but measurement precision deteriorates due to inability to measure to sub-pixel accuracy
Solution Approach 1:
The patent changes the parameter of position measurement from discrete pixel values to continuous sub-pixel coordinates. By using correlation functions that can identify feature positions with fractional pixel precision (e.g., 0.01 pixel accuracy), the system transforms the measurement parameter from integer pixel coordinates to continuous spatial coordinates, thereby achieving high precision without increasing hardware complexity.
5Measurement precision
If artificial targets or known geometrical features are attached to the object for video monitoring, then measurement precision is improved, but ease of manufacture deteriorates due to additional preparation requirements
Solution Approach 1:
The patent enables the object to serve its own measurement function through its natural surface features. Instead of requiring artificial targets to be attached, the system uses the object's existing surface patterns (textures, markings, or any distinguishable features) as the measurement reference, allowing the object to provide its own measurement characteristics without external modification.
Data Source
AI summary
The position of a feature within an image is determined by determining an initial estimate of the feature position to within a fraction of a pixel, translating the feature by an amount equal to that fraction of a pixel, determining a further estimate of the translated feature position to within a fraction of a pixel and summing the pixel fraction of the previous estimate with the further estimate of the position to arrive at a refined estimate of the feature position.