Interference Analysis Apparatus Phase Shift Error Correction
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Solution Overview
Problem
Conventional laser interferometers face challenges in accurately controlling phase shift due to errors from piezoelectric element operating errors, optical imperfections, and external factors like vibration and air fluctuations, leading to difficulties in achieving precise surface geometry measurements.
Innovation Solution
An analysis apparatus that acquires and analyzes interference images by calculating sine and cosine wave components, detects errors using Lissajous figures, and corrects these components to calculate the surface geometry of the object, thereby reducing phase shift errors and improving measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If phase shift is controlled using mechanical movement or polarization methods, then phase difference can be changed between reference light and measurement light, but phase shift error occurs due to operating errors of piezoelectric elements, optical imperfections, and external factors such as vibration and air fluctuation
Solution Approach 1:
The patent applies feedback by detecting the actual phase shift amount through interference image analysis and using this information to correct the phase shift error. The error detection unit calculates the phase shift amount from interference images and the correction unit adjusts the phase shift based on the detected error, creating a closed-loop system that compensates for piezoelectric element errors, optical imperfections, and external factor disturbances.
Solution Approach 2:
The patent substitutes mechanical phase shift control methods with an optical measurement and calculation-based approach. Instead of relying solely on mechanical movement of optical elements or polarization changes, the system uses interference image analysis to detect and correct phase shift errors, replacing mechanical precision requirements with optical measurement and computational correction.
2Productivity
If conventional interference image analysis is performed without error correction, then analysis can be performed, but phase shift error affects the analysis result of the interference image
Solution Approach 1:
The patent applies preliminary action by performing error detection and correction before the final surface geometry analysis. The error detection unit first calculates the phase shift amount and detects errors from interference images, then the correction unit adjusts the phase shift values before the geometry calculation unit performs the final analysis, ensuring high precision without requiring complex iterative processes.
3Measurement precision
If iterative processes are used to correct phase shift error, then measurement precision can be improved, but computational cost increases
Solution Approach 1:
The patent substitutes iterative computational processes with a direct calculation approach. Instead of using iterative methods to converge on corrected phase shift values, the system directly calculates the phase shift amount from interference images and applies correction based on detected errors, achieving high precision error correction without the computational burden of iterative processes.
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
The apparatus enables high-precision interference measurements with reduced computational cost, capable of analyzing ten or fewer interference images, and effectively corrects phase shift errors without iterative processes, enhancing measurement accuracy and efficiency.
Implementation Method 1
an interference measurement apparatus for generating the interference image of reference light and measurement light reflected by irradiating a reference surface and a surface of an object to be measured with a laser light
Implementation Method 2
an amount of change in the phase difference between the reference light and the measurement light has been sometimes treated as a known parameter when analyzing a plurality of interference images generated by a laser interferometer
Data Source
AI summary
An analysis apparatus includes an acquisition part that acquires a plurality of interference images of the object to be measured from the interference measurement apparatus, a calculation part that calculates a sine wave component and a cosine wave component of an interference signal for each pixel in the plurality of interference images, respectively, an error detection part that detects an error between a first Lissajous figure constructed on the basis of the sine wave component and the cosine wave component for each pixel and an ideal second Lissajous figure, a correction part that corrects the sine wave component and the cosine wave component for each pixel on the basis of the error, and a geometry calculation part that calculates surface geometry of the object to be measured on the basis of the corrected sine wave component and cosine wave component.