Grid Surface Deformation Measurement via Phase Analysis
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Solution Overview
Problem
Conventional methods for measuring displacement and strain distribution, such as single-point measurement using displacement meters or strain gauges, are time-consuming and costly, while digital image correlation methods require a large area for correlation, limiting precision and increasing data processing complexity.
Innovation Solution
A two-dimensional grid is used, with images from each direction being Fourier transformed to analyze phase components, allowing for high-precision displacement measurement in both x and y directions without the need for precise cosine waves, thereby reducing noise and simplifying the process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If single-point measurement using displacement meters or strain gauges is used, then measurement cost is low for individual points, but measurement time and data processing complexity increase significantly when measuring multiple points
Solution Approach 1:
The patent uses a two-dimensional grid pattern as a visual copy/mark on the object surface, which can be captured by a camera to obtain displacement information for multiple points simultaneously. This eliminates the need for physical displacement meters at each measurement point, reducing measurement time while maintaining precision through phase analysis of the grid pattern.
Solution Approach 2:
The patent utilizes phase shifting of the grid pattern (analogous to color/brightness changes) to encode displacement information. By capturing multiple images with different grid phase shifts and analyzing the phase changes, the system can measure displacement at numerous points concurrently, significantly reducing measurement time compared to sequential single-point measurements.
2Productivity
If digital image correlation method is used, then multiple points can be measured simultaneously, but a large area is required for correlation which limits precision and increases gauge length
Solution Approach 1:
The patent divides the measurement area into smaller units by using a two-dimensional grid pattern with specific periods in x and y directions. Each grid intersection or small region can be analyzed independently for phase information, allowing precise displacement measurement at multiple points simultaneously without requiring a large correlation area, thus improving both productivity and precision.
Solution Approach 2:
The patent transitions from one-dimensional correlation methods to two-dimensional grid-based phase analysis. By utilizing phase information in both x and y directions through two-dimensional Fourier transformation, the system achieves higher precision with shorter gauge lengths while maintaining high measurement speed across the entire field of view.
3Measurement precision
If conventional grid method with phase shift or Fourier transform is used, then high precision phase analysis is achieved, but data for multiple periods is required which complicates the process
Solution Approach 1:
The patent extracts only the necessary phase information from a single grid period by using two-dimensional Fourier transformation to identify specific frequency components (1,0) and (0,1). This eliminates the need to capture and process multiple grid periods, simplifying the measurement process while maintaining high precision through targeted frequency analysis.
Solution Approach 2:
The patent changes the approach from requiring multiple periods of grid data to achieving accurate phase measurement from a single period by utilizing two-dimensional Fourier transformation. This parameter change in the data requirement (from multiple periods to one period) simplifies the measurement process while preserving measurement precision through efficient frequency domain analysis.
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
This approach enables high-precision, fast, and noise-resistant measurement of displacement and strain distribution, with a shorter gauge length compared to other methods, suitable for both static and moving objects.
Implementation Method 1
an image of a two-dimensional grid on a surface of an object is taken by a camera
Implementation Method 2
a pixel region which corresponds to one period in the x direction and the y direction is cut out, and two-dimensionally Fourier transformed so as to find a phase of a component with a frequency 1
Data Source
Figure 1~2
Figure 3A~3B
AI summary
A phase of a specific frequency is found by carrying out a two-dimensional Fourier transformation on an image of a two-dimensional grid image on the surface of an object taken by a camera, and the displacement of the surface of the object is measured from the phase. As a result, measurement that is strong against noise can be carried out without projecting a grid having a brightness distribution of precise cosine waves. In addition, the process is simple and the number of pixels used for the measurement is smaller than that in the sampling moire method. The displacement can be found at a high speed.