Interferometric Surface Shape Measurement With Fourier Phase Analysis
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Solution Overview
Problem
Conventional surface shape measurement devices require significant computational power and time due to the need for extensive analysis of numerous interference fringe images, and parallel processing of fine peak detection is not feasible.
Innovation Solution
The method employs an interferometer optical head to divide incoherent light into reference and measurement paths, acquiring multiple interference fringe images while scanning, and uses discrete Fourier transforms to determine the surface shape based on phase analysis of specific wavelengths, allowing for reduced computational load and parallel processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional surface shape measurement devices capture hundreds to thousands of interference fringe images and perform extensive analysis processing, then measurement precision is improved, but measurement time and computational power requirements increase significantly
Solution Approach 1:
The patent extracts only the necessary information from interference fringe images by using phase analysis on a limited number of images. Instead of analyzing all hundreds to thousands of captured images, the method extracts phase information from selectively captured images to determine surface shape, significantly reducing the number of images that need to be processed while maintaining measurement precision.
Solution Approach 2:
The patent performs preliminary phase analysis on a small subset of interference fringe images to obtain initial surface shape information. This preliminary action allows the system to avoid the time-consuming process of analyzing all captured images, as the phase information from the limited set of images is sufficient to determine the surface shape with adequate precision.
2Measurement precision
If conventional devices perform rough peak detection and fine peak detection processing on all captured images, then measurement precision is improved, but computational power requirements and work memory increase
Solution Approach 1:
The patent extracts phase information directly from a limited number of interference fringe images using Fourier transform methods. This extraction approach eliminates the need for computationally intensive rough peak detection and fine peak detection processing on all captured images, reducing computational power requirements while obtaining the necessary surface shape information.
Solution Approach 2:
The patent replaces the mechanical-like iterative peak detection process with a mathematical Fourier transform approach. Instead of performing sequential rough and fine peak detection operations that require significant computational resources, the method uses phase analysis of the interference signal, which is computationally more efficient and requires less work memory.
3Measurement precision
If conventional fine peak detection processing is performed sequentially after rough peak detection, then measurement precision is improved, but measurement time increases
Solution Approach 1:
The patent merges the functions of rough peak detection and fine peak detection into a single phase analysis operation. By using Fourier transform to extract phase information directly from the interference signal, the method combines what were previously separate sequential processing steps into one unified operation, improving measurement speed while maintaining precision.
Solution Approach 2:
The patent replaces the sequential mechanical-like detection process with a parallel mathematical computation approach. The phase analysis can be performed simultaneously on multiple pixels and wavelengths using Fourier transform, enabling parallel processing that significantly reduces measurement time compared to the sequential rough and fine peak detection methodology.
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 significantly reduces measurement time and computational requirements by optimizing analysis processing, enabling efficient and rapid surface shape measurement.
Implementation Method 1
Surface shape measurement devices that precisely measure surface shapes of measurement targets, and the like, using luminance information of interference fringes caused by light interference
Implementation Method 2
acquires an interference fringe image generated by a light path difference between light reflected from the reference mirror and light reflected from the measurement target surface
Data Source
AI summary
A measurement method of a surface shape and a surface shape measurement device uses an interferometer optical head that acquires an interference fringe image generated by a light path difference between the reference light and the measurement light, acquires N interference fringe images by scanning from a start point to an end point in the Z-axis direction, and measures the surface shape of the measurement target surface based on the interference fringe images. For a common position in the N interference fringe images, regarding an interference signal including values of N points that indicates a change in the interference light intensity along the Z-axis direction, a phase of an interference fringe produced by the light of a predetermined analysis wavelength is determined, and the relative position in the Z-axis direction of the measurement target surface within the range of the analysis wavelength is determined based on the phase.