Triangulation Profilometry Defocusing Pixel Discretization
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Solution Overview
Problem
Triangulation-based three-dimensional optical profilometry systems suffer from non-physical artifacts such as 'jumps' or 'wiggles' in calculated surface profiles due to discretization issues with pixel-based image sensors, which are not adequately addressed by increasing resolution or forming thicker luminous lines, as these solutions compromise measurement accuracy and resolution.
Innovation Solution
An optical profilometry system with an objective lens assembly forming an out-of-focus image and a diaphragm with a non-circular aperture is used, where the image of the luminous line is asymmetrically spread over the image sensor, extending vertically over multiple pixels to reduce the effect of discrete pixel arrangement while maintaining lateral resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If higher resolution image sensors are used to capture finer surface details, then measurement precision is improved, but non-physical artifacts appear in the centroid calculation due to pixel discretization
Solution Approach 1:
The patent changes the focus parameter of the imaging system from in-focus to out-of-focus mode. By intentionally defocusing the imaging lens, the point spread function becomes larger than a single pixel, causing light from each point on the luminous line to be distributed across multiple pixels. This parameter change resolves the discretization problem while maintaining measurement precision.
Solution Approach 2:
The patent introduces the dimension of spatial distribution by spreading the image of each point across multiple pixels through defocusing. Instead of concentrating light into a single pixel (0-dimensional point), the out-of-focus condition creates a 2-dimensional distribution pattern that spans multiple pixels, thereby eliminating the discretization artifacts caused by pixel boundaries.
2Measurement precision
If the luminous line is made thinner to improve cross-sectional resolution, then measurement precision is improved, but the line covers fewer pixels vertically, worsening the discretization problem
Solution Approach 1:
The patent changes the focus parameter to out-of-focus mode, which transforms the image of each point from a concentrated spot into a distributed pattern across multiple pixels. This parameter change allows thin luminous lines to still activate multiple pixels vertically, resolving the discretization problem without requiring thicker lines.
3Reliability
If the luminous line is made thicker to cover more pixels, then discretization artifacts are reduced, but lateral resolution decreases
Solution Approach 1:
The patent changes the focus parameter to out-of-focus mode, which creates a controlled spread of light across multiple pixels. This allows the system to maintain thin luminous lines for high lateral resolution while still achieving sufficient vertical pixel coverage through the optical defocusing effect, thereby resolving both contradictions simultaneously.
4Reliability
If defocusing is used to spread the image over multiple pixels, then discretization artifacts are reduced, but lateral resolution decreases due to spreading
Solution Approach 1:
The patent optimizes the defocusing parameter to achieve a balance where the point spread function covers multiple pixels vertically (reducing discretization artifacts) while maintaining sufficient lateral confinement (preserving lateral resolution). This controlled parameter adjustment resolves the contradiction between reliability and precision.
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 minimizes non-physical artifacts in the calculated surface profile by ensuring the vertical centroid is calculated over multiple rows of pixels, thereby reducing the impact of pixel discretization without compromising lateral resolution.
Implementation Method 1
an objective lens assembly for imaging the luminous line, as projected on the sample plane, onto the image sensor, the objective lens assembly defining an optical axis extending between the sample plane and the image sensor... the objective lens assembly being arranged to form an out-of-focus image of the sample plane on the image sensor
Data Source
AI summary
A triangulation-based optical profilometry system for scanning a three-dimensional sample surface located at a sample plane includes a projection system; an image sensor; a processing unit; an objective lens assembly for imaging onto the image sensor a luminous line formed on the sample plane, a first direction orthogonal to an optical axis and being defined parallel to an extent of the luminous line, a second direction being defined perpendicular to the first direction; and a diaphragm defining a non-circular aperture defined by a first dimension and a second dimension greater than the first dimension, the diaphragm being rotationally oriented such that the first dimension is aligned with the first direction and the second dimension is aligned with the second direction, the objective lens assembly being arranged to form an out-of-focus image of the luminous line on the image sensor.