Stress Measurement for Optical Materials Using Phase Shift
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Solution Overview
Problem
Conventional stress measurement methods for planar optical components, such as glass substrates, face challenges in accurately measuring low-level residual stresses due to insufficient resolution and complexity, particularly in flexible display and MEMS semiconductor manufacturing, where thin glass substrates with low temporary birefringence complicate the measurement process.
Innovation Solution
A stress measurement method and system that captures four light intensity images at different phase angles, performs phase shift calculations, and enhances isochromatic retardation values through intensified imaging, allowing for precise stress transformation, even in low-stress conditions, using a setup with a polarizer, analyzer, light source, and image capturing device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional photoelasticity method is used to measure residual stress of thin planar glass, then measurement can be performed, but resolution and accuracy are insufficient due to low temporary birefringence and thin thickness
Solution Approach 1:
The patent applies preliminary action by performing calibration measurements on a reference sample with known stress properties before measuring the actual sample. This calibration step establishes baseline parameters (k-factor, optical path difference relationships) that are then used to accurately interpret measurements of thin planar glass with low birefringence, thereby improving measurement precision for difficult-to-measure low-level stresses
Solution Approach 2:
The patent changes measurement parameters by using multiple wavelength lights and capturing images at different phase angles (0°, 45°, 90°, 135°). This multi-parameter approach allows calculation of isochromatic retardation through phase shift algorithms, significantly improving the accuracy of stress measurements for thin glass substrates with low temporary birefringence compared to conventional single-wavelength methods
2Loss of information
If point-to-point scan is performed to construct whole-field stress map using low-level stress measurement instrument, then stress information can be obtained, but space resolution is low and measurement time is huge
Solution Approach 1:
The patent replaces the mechanical point-to-point scanning system with an optical field-based measurement system. By using a digital camera to capture the entire stress field simultaneously through photoelasticity effects, and processing images taken at four phase angles, the system obtains whole-field stress distribution instantly without mechanical scanning, eliminating time loss and improving spatial resolution
Solution Approach 2:
The patent employs periodic action by capturing images at four different phase angles (0°, 45°, 90°, 135°) in a systematic sequence. This periodic phase shifting allows extraction of complete stress information (isochromatic and isoclinic data) through computational algorithms, achieving comprehensive whole-field stress mapping efficiently without requiring continuous mechanical scanning
3Adaptability or versatility
If conventional reflection photoelasticity method is used to measure stress on reflective region, then measurement can be performed, but regions with no reflection film or partial reflection film cannot be measured
Solution Approach 1:
The patent achieves universality by designing a measurement system that can handle multiple measurement scenarios (transmissive and reflective regions) within a single experimental setup. By capturing images at four phase angles and using computational photoelasticity, the system extracts stress information from both transmissive and reflective regions uniformly, eliminating the need for separate measurement procedures and improving adaptability across different surface regions
Solution Approach 2:
The patent effectively uses a composite measurement approach by combining transmissive photoelasticity (for non-reflective regions) and reflective photoelasticity (for reflective regions) within the same imaging system. The computational algorithm processes both types of optical information uniformly, creating a composite measurement capability that reliably measures stress across heterogeneous surface regions with different optical properties
4Measurement precision
If conventional stress measurement system is used, then measurement can be performed, but complicated image processing and recognition procedures are required making it difficult for rapid online inspection
Solution Approach 1:
The patent applies self-service by using the measured stress field information to automatically determine the principal stress directions (isoclinic parameters). The computational algorithm extracts both isochromatic (magnitude) and isoclinic (direction) information from the same set of four phase-angle images, eliminating the need for separate, complex recognition procedures and simplifying the overall measurement process while maintaining precision
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 efficient, whole-field stress measurements with high accuracy and simplicity, effectively addressing the limitations of existing methods by providing precise stress values for both transmission and reflection properties of optical materials, particularly suitable for thin glass substrates.
Implementation Method 1
a polarizer, an analyzer, a light source, and an image capturing device
Implementation Method 2
glass material has a low temporary birefringence
Implementation Method 3
A photoelasticity method is an efficient method for measuring an internal stress of an object that is transparent and has a temporary birefringence
Data Source
AI summary
A stress measurement method is provided of the present disclosure. The stress measurement method includes an image capturing procedure, a phase shift calculation procedure, an isochromatic intensifying procedure and a transformation procedure. The image capturing procedure is used to capture four light intensity images with four different phase angles of a sample. The phase shift calculation procedure is used to obtain an isochromatic retardation of the sample when the four light intensity images have sufficient light intensity values. The isochromatic intensifying procedure is used to calculate two enhanced light intensity values, the background of intensified isochromatic light intensity value and the amplitude of intensified isochromatic light intensity value to obtain an isochromatic retardation when the sample is in a low stress condition. The transformation procedure is used to transform the isochromatic retardation to a stress value of the sample.