Dual Fringe Moiré Profilometry for Accurate Phase Demodulation
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Solution Overview
Problem
Conventional geometric moiré methods suffer from poor visibility of moiré fringes, which decreases measurement precision, and phase demodulation methods are inaccurate for moiré patterns with few fringes and low local frequencies.
Innovation Solution
A moiré profilometry method involving simultaneous dual fringe projection from two symmetric directions, followed by spatial or temporal extraction and phase demodulation of the moiré pattern using spatial or temporal methods, including Fourier transforms, band-pass filters, and phase shifting algorithms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional geometric moiré methods are used, then measurement resolution is improved, but fringe visibility deteriorates
Solution Approach 1:
The patent combines FPP and geometric moiré methods into a hybrid system where a reference grating is projected onto the object surface along with the fringe pattern. The camera captures both the topography-modulated fringes and the moiré pattern generated by the reference grating, merging the advantages of both methods to achieve high-resolution measurements with improved fringe visibility
Solution Approach 2:
The reference grating acts as an intermediary element that mediates between the projected fringe pattern and the camera observation. It introduces additional periodic structure that generates moiré fringes, serving as a carrier that enhances the visibility of topography information while maintaining the high sensitivity of geometric moiré methods
2Measurement precision
If phase demodulation methods are applied to moiré patterns with few fringes, then phase extraction is attempted, but accuracy deteriorates
Solution Approach 1:
The patent applies preliminary spatial filtering and frequency domain processing to the captured fringe pattern before phase demodulation. By pre-processing the image to enhance moiré fringe contrast and separate it from the carrier frequency components, the system prepares the data in advance to make subsequent phase extraction accurate even when moiré patterns have few fringes
Solution Approach 2:
The patent transforms the problem from spatial domain to frequency domain using Fourier transform. This dimensional change allows separation of the moiré pattern from the carrier fringes in the frequency spectrum, enabling accurate phase demodulation by isolating the relevant frequency components that contain topography information
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
Enhances phase demodulation accuracy and measurement precision by generating a moiré pattern with high fringe visibility, allowing for more accurate phase retrieval and out-of-plane displacement determination.
Implementation Method 1
The two sinusoidal patterns superimpose and generate a fringe pattern that contains a moiré pattern, the moiré pattern having a phase that is modulated according to the topography of the object
Implementation Method 2
recording its reflection from a certain direction
Data Source
AI summary
In alternative embodiments, provided are moiré profilometry methods for analyzing a topography of an object comprising use of dual patterns that are simultaneously projected onto a surface of the object from two symmetric directions. In alternative embodiments, the projected dual patterns superimpose and generate a fringe pattern that contains a moiré pattern, the moiré pattern having a phase that is modulated according to the topography of the object. In alternative embodiments, the moiré pattern is extracted from the fringe pattern using a spatial or temporal method, and the phase is demodulated from the extracted moiré pattern using a spatial or temporal method.