Sub-pixel Corner Detection for Specimen Deformation Measurement
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Solution Overview
Problem
Traditional deformation measurement methods for geotechnical specimens are limited by their contact nature, low accuracy, and inability to capture whole deformation images, making them unsuitable for studying local deformation properties, especially in sensitive environments like underwater pressure vessels.
Innovation Solution
A digital image measurement system using sub-pixel corner detection with a CMOS camera, image pressure cell, and flexible lens hood to track deformation of specimens with printed grids, allowing non-contact, high-precision measurement of axial, radial, and volumetric strains through finite element analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional contact measurement methods (strain gauges, sensors) are used, then measurement can be performed, but measurement accuracy is low and test points are insufficient
Solution Approach 1:
The patent replaces traditional mechanical contact measurement methods (strain gauges, sensors) with optical non-contact measurement. A digital camera captures images of the specimen surface, and image processing algorithms calculate deformation and strain fields without physical contact, thereby improving measurement accuracy and avoiding disturbance to the specimen.
Solution Approach 2:
The patent creates a digital copy of the specimen surface by capturing images with a camera. The actual physical specimen is replaced by its optical image, which is then processed through image analysis algorithms to extract deformation information. This copying approach enables non-contact, high-precision measurement of the entire surface.
2Reliability
If traditional contact measurement methods are used, then deformation can be measured, but the specimen is disturbed and operation in underwater pressure environment is difficult
Solution Approach 1:
The patent replaces mechanical contact sensors with optical measurement systems that can operate through transparent walls of underwater pressure vessels. The camera and lighting system capture images of the specimen without requiring physical access to the high-pressure environment, making the measurement process both non-intrusive and easily operable in challenging environments.
3Loss of information
If traditional measurement methods are used, then overall deformation can be measured, but local deformation properties and strain field cannot be obtained
Solution Approach 1:
The patent transitions from point-based or line-based measurement to surface-wide two-dimensional measurement. By capturing the entire specimen surface with a camera and processing images to identify characteristic points and calculate displacements across the surface, the system obtains complete strain field information including local deformation properties that traditional methods cannot provide.
4Measurement precision
If digital image measurement technology is used, then non-contact and high precision measurement is achieved, but measurement accuracy needs to be improved to sub-pixel level
Solution Approach 1:
The patent applies preliminary image processing steps including calibration, coordinate transformation, and characteristic point identification before final deformation calculation. By pre-processing images to establish accurate coordinate systems and identify key feature points, the system achieves sub-pixel measurement accuracy while managing processing complexity through systematic preliminary actions.
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
Enables non-disturbing, high-accuracy measurement of specimen deformation, suitable for unsaturated soil specimens, with real-time monitoring and automatic data recording, improving measurement precision and reducing labor intensity.
Implementation Method 1
there are two flat mirrors 3 are settled at a 120° angle inside the pressure chamber at the back of the cylindrical specimen 4
Implementation Method 2
Specially designed circular light-emitting diodes (LEDs) 6 which are to withstand high pressure are placed on the inside top and bottom of the semi-cylindrical cavity 10 to ensure an unchanged lighting environment for photographing of the CMOS camera
Data Source
AI summary
A digital image measurement device and method for the surface deformation of specimen based on sub-pixel corner detection is disclosed. This digital image measurement device is composed of a new type of image pressure cell, a complementary metal-oxide-semiconductor (CMOS) camera, a camera bracket, a flexible lens hood, a computer and matching measurement software. This method discretizes the specimen into several four-node finite elements by printing grids on the specimen and takes corners of the grids as the nodes of the finite elements; tracks the deformation of the feature points in real time by edge detection and corner detection based on sub-pixel; captures the deformation of the whole surface of the specimen by the two flat mirrors which are at an 120° angle behind the specimen; achieves the observation of the deformation of the whole surface by conducting splicing and error correction on the three images.