Phase Shift Interferometer Using Multiple Cameras
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Solution Overview
Problem
Phase shift interferometers face challenges in achieving high precision measurements due to shift errors caused by vibrations and air disturbances, requiring costly high-precision displacement stages and longer measurement times to reduce analysis errors, which can be affected by environmental factors.
Innovation Solution
A phase shift interferometer configuration using multiple cameras to capture and synthesize phase analysis results independently, with a phase difference of 90° between cameras, allowing for low-cost, low-precision displacement stages and minimizing phase analysis errors by averaging pixel results, while extending or shortening optical paths to achieve phase shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-precision displacement stages are used to shift the reference surface, then phase analysis precision is improved, but device cost and complexity increase
Solution Approach 1:
The patent uses multiple cameras to capture interference fringes at different phases simultaneously, creating optical copies of the fringe patterns. This eliminates the need for high-precision mechanical displacement stages, as the phase information is encoded in the optical paths rather than requiring precise mechanical positioning. The multiple camera system captures the necessary phase data without relying on expensive high-precision displacement mechanisms.
Solution Approach 2:
The patent replaces the mechanical displacement stage with an optical path length adjustment mechanism. Instead of physically moving the reference surface with high precision, the system adjusts the optical path length of one arm to introduce phase shifts. This substitution eliminates mechanical precision requirements while achieving the same phase shifting function through optical means.
2Measurement precision
If the number of images acquired is increased to reduce phase analysis errors, then measurement precision is improved, but measurement time increases
Solution Approach 1:
The patent performs preliminary phase shifting by adjusting the optical path length before capturing the interference fringes. By pre-establishing the phase differences through optical path adjustment rather than mechanical displacement during capture, the system can acquire multiple phase images simultaneously or with minimal time loss, reducing the total measurement time while maintaining precision.
Solution Approach 2:
The patent uses periodic optical path length adjustment to create phase shifts between the reference beam and measurement beam. This periodic modulation of the optical path introduces controlled phase differences that enable the extraction of surface shape information without requiring continuous or repeated mechanical displacement, thereby reducing measurement time while maintaining accuracy.
3Measurement precision
If measurement time is extended to reduce analysis errors, then phase analysis precision is improved, but reliability decreases due to environmental stability issues
Solution Approach 1:
The patent performs all necessary phase shifting and fringe capture operations during the initial measurement phase before environmental conditions can significantly change. By completing the data acquisition quickly through optical path adjustment rather than slow mechanical scanning, the system minimizes exposure to environmental disturbances such as temperature drift and vibrations, thereby maintaining both precision and reliability.
Solution Approach 2:
The patent replaces time-consuming mechanical displacement operations with rapid optical path length adjustment. This substitution dramatically reduces the time required to acquire interference fringe data, thereby minimizing the period during which the measurement system is exposed to environmental disturbances. The optical method achieves the same measurement goals much faster, improving reliability by reducing temporal exposure to unstable conditions.
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 shape measurement in a shorter time with reduced phase analysis errors, even with low-precision displacement stages, and is less susceptible to environmental disturbances, achieving accurate results with fewer images.
Implementation Method 1
The reference beam, which is a beam reflected from the reference surface 6, and the measurement beam, which is a beam reflected from the surface of the measurement object 7, are caused to interfere with each other using a beam splitter 4.
Data Source
AI summary
The phase shift interferometer is configured to measure the shapes of measurement objects by acquiring a plurality of images of interference fringes while shifting the phases of the interference fringes. The interference fringes are provided with a phase difference of 90° relative to each other utilizing polarization of light. Images of the interference fringes are captured by two respective cameras while, in accordance with a conventional phase shift method, mechanically displacing a reference surface or a reference optical path to shift the phases. The phases of the interference fringes are calculated independently from the respective images acquired by the cameras and an average of the two phase calculation results is calculated.