Optical Fourier Transform Surface Roughness Measurement
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Solution Overview
Problem
Current methods for quantifying surface roughness, such as profilometry and atomic force microscopy, are limited in their ability to efficiently and accurately measure full-field roughness of reflective surfaces, especially when flakes or particles are misaligned relative to the surface.
Innovation Solution
The use of light in conjunction with an optical Fourier transform to examine and quantify surface roughness by analyzing the degree of light scattering from flakes or particles on a reflective surface, where the scattered light is focused onto a light-sensitive array, allowing for the determination of surface roughness based on the angular distribution and intensity of the reflected light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If profilometry or atomic force microscopy is used to measure surface roughness, then measurement precision can be achieved in micrometer or nanometer realms, but the measurement process is time-consuming and cannot efficiently quantify full-field roughness
Solution Approach 1:
The patent replaces mechanical measurement systems (profilometry and atomic force microscopy) with an optical measurement system that uses light scattering and optical Fourier transform. This substitution enables full-field roughness measurement without the time-consuming point-by-point scanning required by mechanical methods, thereby improving measurement efficiency while maintaining precision through optical detection of surface irregularities
Solution Approach 2:
The patent transitions from one-dimensional or point-by-point mechanical scanning to two-dimensional full-field optical measurement. By capturing light scattering patterns across the entire surface simultaneously using a camera sensor, the system achieves comprehensive roughness quantification in a single measurement, dramatically increasing productivity while preserving measurement precision through spatial frequency analysis
2Reliability
If flakes are applied conformally to the surface, then surface coverage is improved, but the measurement system cannot distinguish surface roughness when flakes are perfectly aligned
Solution Approach 1:
The patent converts the previously problematic light scattering caused by misaligned flakes into a beneficial measurement signal. By analyzing the angular distribution and intensity of scattered light through optical Fourier transform, the system transforms the disorder introduced by flake misalignment into quantitative information about surface roughness, enabling precise measurement while maintaining reliable surface coverage
Solution Approach 2:
The patent changes the measurement parameter from direct optical reflection (which fails when flakes are conformal) to light scattering angular distribution. By measuring how light scatters at different angles and analyzing the spatial frequency content of the scattering pattern, the system can detect surface roughness even when flakes are perfectly aligned, thus maintaining both surface coverage reliability and measurement precision
3Area of stationary object
If light scattering is used to measure surface roughness, then full-field measurement capability is achieved, but the system becomes sensitive to flake alignment variations
Solution Approach 1:
The patent implements a feedback mechanism through optical Fourier transform analysis of the light scattering pattern. The system captures the angular distribution of scattered light, transforms it to spatial frequency domain, and uses the resulting spectrum to quantitatively determine surface roughness parameters. This feedback loop compensates for variations in flake alignment by referencing the characteristic scattering signature against known roughness standards, maintaining measurement precision across the full measurement field
Solution Approach 2:
The patent transforms the measurement from direct spatial observation of flakes to frequency domain analysis of light scattering patterns. By converting the scattering data through optical Fourier transform, the system extracts roughness information from the spatial frequency spectrum, which is insensitive to the absolute position or alignment of individual flakes. This parameter transformation enables accurate full-field roughness measurement despite variations in flake orientation
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 method effectively quantifies surface roughness by correlating the degree of light scattering with the alignment of flakes or particles, providing a precise measurement of surface irregularity, even when the flakes are misaligned, and allows for the differentiation between conformal and non-conformal surfaces.
Implementation Method 1
The reflected light will exhibit a degree of scattering that is correlated to degrees of tip and/or tilt of the flakes relative to surface plane of the target
Implementation Method 2
The reflected light passes through a lens and is collected at a light sensitive array (LSA)
Data Source
AI summary
The various embodiments presented herein relate to utilizing light in conjunction with an optical Fourier transform to examine and quantify roughness of a surface. The surface includes a plurality of flaked particles. The surface is illuminated with a light beam, wherein light reflected from the surface passes through an f-theta lens and is collected at a light sensitive array (LSA). The LSA comprises light sensitive pixels. For an arrangement where the flakes are conformal with the surface, a low degree of light scattering occurs at the surface. For a surface comprising tipped and/or tilted flakes, a correlating degree of scattering of the incident light beam occurs. The surface roughness is quantified based upon the distribution of angular reflections of the scattered light represented in an image formed through use of the LSA.