Elastic-Wave Defect Inspection With Fixed-Phase Interferometry
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Solution Overview
Problem
Conventional defect inspection methods using laser interferometry require multiple measurements at different phase differences, leading to prolonged inspection times due to the need to change the phase difference between interfered laser light for each measurement.
Innovation Solution
A defect inspection apparatus and method that approximates the difference value or absolute value between pixel values in captured images at different phases of the elastic wave, allowing defect inspection without changing the phase difference between interfered laser light, thereby reducing the number of necessary measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser interferometry is used to measure displacement at each point in the measurement region, then measurement precision is improved, but inspection time increases due to requiring at least nine measurements with different phase differences
Solution Approach 1:
The patent changes the measurement parameter from displacement (requiring multiple phase difference measurements) to intensity of interference light (measurable with fixed phase difference). By using the intensity distribution of interference light and elastic wave phase information, the system achieves defect detection without needing to vary the phase difference multiple times, thus reducing inspection time while maintaining measurement capability.
2Measurement precision
If multiple measurements are performed at different phase differences, then measurement accuracy is improved, but device complexity increases due to phase adjustment mechanisms
Solution Approach 1:
The patent extracts only the necessary information (intensity of interference light and elastic wave phase) from the full displacement measurement process. By eliminating the need for mechanical phase adjustment mechanisms and using only intensity measurements combined with phase information from the elastic wave, the system achieves accurate defect detection with significantly reduced device complexity.
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 faster defect inspection by reducing the number of measurements required, while maintaining accuracy, and allows for a simpler apparatus configuration without the need for complex phase adjustments, thus shortening inspection time and improving detection efficiency.
Implementation Method 1
an exciter (vibrator) 1 configured to excite an elastic wave in a measurement region Pa of an inspection target P
Implementation Method 2
an interference unit (speckle shearing interferometer) 3 configured to cause interference of the laser light reflected at the measurement region Pa by laser interferometry
Data Source
AI summary
A defect inspection apparatus (100) is configured to approximate a difference value or an absolute value (Iα) of the difference value between a pixel value in at least three captured images (A) captured by an imager in at least three different phases of an elastic wave and a pixel value in a reference image (Aave) separate from the captured images (A) so as to acquire an approximate value for defect inspection corresponding to an amount of change in the pixel value in the captured images (A).