Structured Light Projection for Specular Surface Height Measurement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Traditional optical phase profilometry systems face challenges in accurately measuring specular surfaces due to their reflective nature, which affects the precision of dimensional information, especially when the targets are tilted or have varying heights, leading to inaccurate height readings and vignetting issues.
Innovation Solution
The system employs a telecentric lens assembly with a variable focus optical system and multiple illumination source-imaging system pairs to capture specular reflections from tilted targets at different focus positions, using a controller to generate a three-dimensional height image by aligning the illumination source and camera relative to the target, and employing calibration methods to correct for lens aberrations and pupil vignetting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional optical phase profilometry systems are used to measure specular surfaces, then the system is simple and configured for diffuse surfaces, but measurement precision deteriorates due to reflective nature causing inaccurate height readings and vignetting
Solution Approach 1:
The patent employs a variable focus optical system that dynamically adjusts the focal position to capture images at multiple distinct focus positions. This dynamic focusing capability allows the system to compensate for tilt and height variations on specular surfaces, resolving the measurement precision issue while maintaining manageable system complexity through a single adjustable optical system rather than multiple fixed systems.
Solution Approach 2:
The patent segments the measurement process by capturing images at multiple distinct focus positions and processing them separately. The controller generates height images by combining information from these multiple focal planes, which allows the system to overcome the limitations of traditional single-focus systems when measuring tilted specular surfaces.
2Measurement precision
If multiple illumination source-imaging system pairs are used to capture specular reflections at different focus positions, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The patent makes a single illumination source-imaging system pair multi-functional by implementing variable focus capability. The same system captures images at multiple distinct focus positions, eliminating the need for multiple separate illumination-imaging pairs while achieving the same measurement accuracy improvement that would otherwise require multiple systems.
Solution Approach 2:
The patent changes the focal position parameter of the optical system to capture images at multiple distinct focus positions. This parameter change allows a single system to perform the function that would otherwise require multiple systems, reducing device complexity while maintaining measurement precision.
3Adaptability or versatility
If the system is aligned to capture specular images, then measurement capability for reflective surfaces improves, but vignetting and lens aberration errors increase
Solution Approach 1:
The patent incorporates calibration methods that provide feedback to correct for lens aberrations and pupil vignetting. By calibrating the system with known targets and using this calibration data to correct measurements, the system maintains its ability to handle reflective surfaces while compensating for the vignetting and aberration errors that arise from the optical alignment required for specular surface measurement.
Solution Approach 2:
The patent converts the harmful effects of vignetting and lens aberrations into correctable factors by implementing calibration procedures. The calibration process characterizes these optical imperfections and uses the information to correct measurements, thereby transforming what would be sources of error into opportunities for improved measurement accuracy through systematic correction.
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 enables accurate measurement of specular surfaces by compensating for tilt and height variations, improving the precision of dimensional information and reducing errors associated with lens aberrations and pupil alignment, thus enhancing the system's ability to handle complex reflective targets.
Implementation Method 1
the camera acquires a specular image of the patterned illumination
Implementation Method 2
a variable focus optical system configured to cause the camera to image the test target with at least two distinct focus positions
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A system (1100) for generating a three-dimensional height image of a reflective test target, the system comprising a plurality of illumination sources (1102) configured to generate a patterned illumination (1108) having a repeated pattern on the test target (1106); a plurality of cameras, each camera (1104) being configured to acquire an image of patterned illumination on the test target (1106) from a different azimuthal angle; the illumination sources (1102) and cameras (1104) being aligned relative to the test target (1106) and each other such that the camera (1104) acquires a specular image of the patterned illumination (1108) on the test target from at least one of the illumination sources. The system (1100) further including a controller (1454) coupled to the illumination sources (1102) and cameras (1104), the controller being configured to generate a height image of the test target (1106) by combining height images generated from each specularly aligned pattern illumination source and camera.