Points-From-Focus Metrology With Multi-Position Glare Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing precision non-contact metrology systems face challenges in achieving micron or sub-micron accuracy for Z-height measurements due to complex best focus determination processes, which are often compromised by lighting issues, particularly in deriving 3-dimensional surface reconstructions.
Innovation Solution
A metrology system utilizing a variable focus lens and multiple lighting positions to acquire image stacks with glare reduction, determining pixel intensity values to generate composite stacks for precise focus curve data, indicating three-dimensional surface points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple lighting positions are used to acquire image stacks, then glare reduction and measurement precision are improved, but device complexity increases
Solution Approach 1:
The lighting system is segmented into multiple independent lighting positions arranged around the workpiece. Each lighting position can be independently controlled to illuminate specific regions, allowing the system to acquire multiple image stacks with different lighting conditions. This segmentation enables glare reduction by selecting appropriate lighting positions while maintaining manageable system complexity through modular design.
Solution Approach 2:
The system transitions from single-point lighting to multi-position lighting by adding a spatial dimension to the illumination configuration. Lighting positions are distributed in three-dimensional space around the workpiece, creating multiple illumination directions. This dimensional expansion enables the system to capture images from various lighting angles, improving measurement precision while the computational complexity is managed through automated image stack processing algorithms.
2Manufacturing precision
If focus position is varied along the optical axis to determine best focus, then Z-height measurement capability is enabled, but measurement precision deteriorates due to complex best focus determination
Solution Approach 1:
The system employs feedback mechanisms to automatically determine the best focus position for each lighting condition. By analyzing the image stacks and comparing focus metrics across different focal planes, the system identifies optimal focus positions and uses this feedback to refine Z-height measurements. This automated feedback loop eliminates manual focus determination and improves measurement precision while reducing the complexity of focus analysis.
Solution Approach 2:
The system changes the lighting parameters (lighting position, illumination angle) while maintaining consistent focus determination methods. By varying lighting conditions rather than relying solely on complex focus position analysis, the system simplifies the best focus determination process while improving overall measurement precision through the combined effect of multiple lighting-condition image stacks.
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 precision in Z-height measurements by improving focus curve data accuracy and reducing glare effects, thereby facilitating reliable 3-dimensional surface point determination.
Implementation Method 1
The objective lens has an optical axis and is configured to input image light arising from a workpiece and to transmit the image light along an imaging optical path
Implementation Method 2
The camera has a sensor array including pixels, and the camera is configured to receive image light transmitted along the imaging optical path and to provide images of the workpiece
Implementation Method 3
The lighting configuration is configured to provide light from a plurality of different lighting positions toward the workpiece
Data Source
AI summary
A metrology system is provided including a lighting configuration and camera which are controlled to acquire image stacks of a workpiece, wherein each image stack is acquired utilizing different lighting (e.g., corresponding to different lighting positions). Sets of pixel intensity values from the image stacks are utilized to determine a composite stack which includes one pixel intensity value for each pixel position and focus position. At least some of the pixel intensity values of the composite stack are determined according to a glare reduction process which determines a corresponding pixel intensity value for the composite stack that is less than a maximum pixel intensity value of the corresponding set of pixel intensity values. Focus curve data is determined based at least in part on the pixel intensity values of the composite stack, wherein the focus curve data indicates three dimensional positions of a plurality of surface points on the workpiece.