Structured Light Z-Height Measurement in Machine Vision
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Solution Overview
Problem
Precision non-contact metrology systems, such as machine vision inspection systems, face challenges in achieving high accuracy and speed for Z-height measurements, as determining the best focus position is complex and often results in less precise Z-height measurements compared to X and Y measurements.
Innovation Solution
The method involves illuminating a workpiece surface with structured light of high spatial frequency, collecting multiple image stacks at different X-Y positions, and determining Z values based on intensity values at the same Z heights, where the X-Y position is changed at a slower rate than the Z height, either continuously or fixed during each stack, to enhance measurement speed and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If structured illumination microscopy (SIM) or white light interferometer (WLI) techniques are used to improve measurement resolution and accuracy, then measurement precision is improved, but measurement speed deteriorates
Solution Approach 1:
The patent changes the illumination parameters by using structured light with high spatial frequency content (small period) and systematically varying the X-Y position parameters across multiple image stacks. This allows extraction of precise Z-height information through intensity analysis while maintaining faster acquisition compared to traditional SIM or WLI methods
2Reliability
If best focus position is determined using traditional autofocus tools combining multiple images, then measurement reliability is improved, but device complexity and measurement time increase
Solution Approach 1:
The patent uses parameter changes in the structured light illumination pattern and systematic X-Y position variation to encode depth information directly in the intensity values of image stacks, enabling simpler and faster Z-height determination compared to traditional autofocus methods that combine and analyze multiple images
Solution Approach 2:
The patent replaces the mechanical/complex process of traditional autofocus with an optical approach using structured light modulation and intensity analysis, substituting a complex image combination process with a more direct intensity-based Z-value determination method
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 improves the speed and accuracy of Z-height measurements in machine vision inspection systems, providing high spatial frequency content and reduced measurement time compared to existing SIM or WLI techniques.
Implementation Method 1
illuminating a workpiece surface with structured light which has high spatial frequency content
Data Source
AI summary
A method for measuring Z height values of a workpiece surface with a machine vision inspection system comprises illuminating a workpiece surface with structured light, collecting at least two stacks of images of the workpiece, each stack including a different X-Y position between the structured light and the workpiece surface at a corresponding Z height in each of the stacks, and determining Z values based on sets of intensity values of a pixel corresponding to the same workpiece position in the X-Y plane which are at the same Z heights. The X-Y position is changed at a slower rate than the Z height in each stack of images, and is changed either continuously during each of the at least two stacks at a slower rate than the Z shift, or fixed to a different value during each of the at least two stacks.