Angle Independent Optical Surface Inspector for Glass
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Solution Overview
Problem
Current techniques face challenges in accurately inspecting glass samples due to their low reflectivity and high transparency, particularly in separating signals from the top and bottom surfaces, and in scanning various shapes and sizes of transparent samples for defects.
Innovation Solution
An optical scanning system that irradiates the transparent sample at or near the Brewster's angle, using a combination of time-varying beam reflectors, phase retardance detectors, and spatial filters to differentiate signals from the top and bottom surfaces, allowing for sensitive defect detection and scanning of diverse sample shapes and sizes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If glass samples are spun for inspection, then inspection coverage is improved, but fragile or large samples are damaged or become impractical to test
Solution Approach 1:
The patent replaces the mechanical spinning system with a stationary sample inspection system using optical scanning. The light source and detectors remain stationary while the sample remains fixed on the substrate, eliminating mechanical stress on fragile samples while maintaining comprehensive inspection coverage through optical field scanning.
Solution Approach 2:
The patent changes the inspection parameters by using Brewster's angle incidence (approximately 57 degrees for glass) to optimize light reflection characteristics. This parameter change enables effective detection on stationary samples without requiring mechanical movement, thus protecting sample integrity while maintaining inspection effectiveness.
2Difficulty of detecting and measuring
If light is reflected from transparent glass samples, then defect detection is enabled, but low reflectivity and high transparency cause signal separation difficulties
Solution Approach 1:
The patent changes the angle of incidence parameter to Brewster's angle (approximately 57 degrees for glass), which optimizes the reflection characteristics of transparent materials. At this angle, the reflected light contains enhanced information about surface defects while minimizing the effects of bulk transparency, enabling better signal separation between top and bottom surface reflections.
Solution Approach 2:
The patent introduces phase retardance detectors as an intermediary measurement mechanism. These detectors measure the phase difference between light reflected from the top and bottom surfaces, providing a indirect but precise method to separate and identify defects on each surface individually, overcoming the limitation of direct reflectivity measurement.
3Measurement precision
If incident angle is varied for inspection, then sensitivity to different defect types is improved, but polarization change and reflectivity variations increase
Solution Approach 1:
The patent selects a specific parameter value (Brewster's angle of approximately 57 degrees) that optimizes the balance between detection sensitivity and polarization stability. At this angle, the system achieves maximum sensitivity to surface defects while minimizing unwanted polarization changes and reflectivity variations that would complicate the measurement and reduce measurement accuracy.
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 enhances sensitivity and accuracy in detecting defects on transparent samples by minimizing polarization change and reflectivity variations, enabling effective inspection of glass samples regardless of their shape or size.
Implementation Method 1
irradiates the transparent sample at an incident angle that is not more than one degree greater or less than Brewster's angle of the transparent sample
Implementation Method 2
The output of the phase retardance detector is usable to determine if a defect is present on the transparent sample
Data Source
AI summary
An angle independent optical surface inspector capable of generating a light beam, directing the light beam to a sample, and de-scanning a reflected light beam that is reflected from the sample, thereby generating a first de-scanned light beam. The de-scanning is performed at approximately one focal length of a de-scanning lens from an irradiation location where the light beam irradiates the sample. The optical inspector also capable of focusing the first de-scanned light beam, thereby generating a focused light beam, and measuring the location of the focused light beam. The measuring of the location is performed at approximately one focal length of a focusing lens from the focusing lens. The incident angle of the light beam is within ten degrees of Brewster's angle. The focusing is performed by an achromatic lens.