3D Surface Profile Measurement Using Multi-Polarization Phase Shifting
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Solution Overview
Problem
Conventional 3D surface inspection methods face inaccuracies due to limited image phase generation and assumptions about fringe modulation and surface flatness, particularly when dealing with objects of varying materials or uneven color spectrum distributions, leading to inconsistent reflectivity and inaccurate height measurements.
Innovation Solution
An apparatus utilizing three light sources with different polarization directions to project patterned images onto a surface, capturing images separately with each light source to determine the surface profile, employing a polarization beam splitter and birefringence plate to achieve accurate height information without mechanical motion or additional patterned images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional methods use only two phase-shifted images, then the system complexity is reduced, but the measurement precision and reliability deteriorate due to insufficient phase information
Solution Approach 1:
The patent changes the parameter of phase shift by using multiple light sources with different polarization states (0°, 45°, 90°, 135°) to generate multiple phase-shifted patterns. This allows obtaining sufficient phase information for accurate height measurement without requiring mechanical movement or complex moving parts, thus improving measurement precision while maintaining system simplicity.
2Measurement precision
If assumptions about fringe modulation or surface flatness are made, then the device complexity is reduced, but the measurement precision deteriorates when objects have varying materials or uneven color spectrum distributions
Solution Approach 1:
The patent uses multiple light sources with different polarization states to project multiple phase-shifted patterns simultaneously. By capturing images under these different polarization conditions and processing them through specific algorithms, the system can determine accurate surface profiles without making assumptions about fringe modulation or surface flatness, thereby improving both measurement precision and adaptability to varying materials.
3Productivity
If different color patterns are projected for phase shifting, then the productivity is improved by simultaneous projection, but the measurement precision deteriorates due to inconsistent reflectivity from objects with uneven color spectrum distributions
Solution Approach 1:
Instead of using different colors for phase shifting, the patent changes the polarization state of light (0°, 45°, 90°, 135°) while maintaining the same wavelength. This approach enables simultaneous projection of multiple phase-shifted patterns with consistent reflectivity characteristics, improving both productivity and measurement precision by avoiding the reflectivity inconsistency problem associated with color-based methods.
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 generates reliable and accurate 3D surface profiles by overcoming limitations of previous methods, providing consistent results across varying materials and color distributions, with improved accuracy and reduced manufacturing costs through a simpler apparatus design.
Implementation Method 1
a second light source operative to project a patterned image produced from a first polarized light from the second light source onto the object, the first polarized light being polarized in a first polarization direction; a third light source operative to project the patterned image produced from a second polarized light from the third light source onto the object, the second polarized light being polarized in a second polarization direction which is different from the first polarization direction
Data Source
AI summary
An apparatus for inspecting a surface of an object has a first light source operative to illuminate the object without producing a patterned image onto the object. A second light source projects a patterned image produced from a first polarized light from the second light source onto the object, wherein the first polarized light is polarized in a first polarization direction. A third light source projects the patterned image produced from a second polarized light from the third light source onto the object, wherein the second polarized light is polarized in a second polarization direction different from the first polarization direction. An imaging device views the surface of the object when the object is illuminated separately by the first, second and third light sources respectively for determining a profile of the surface of the object.