Autofocus System for High-NA Optical Inspection
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Solution Overview
Problem
Current optical inspection systems for electronic parts face challenges in maintaining focus due to height variations, leading to limited depth of field and resolution, which prevents the detection of small defects.
Innovation Solution
An intelligent autofocus system that dynamically computes and mechanically tracks the optimal focal plane by sampling surface heights in real-time, using a combination of visible and infrared light to identify and maintain focus on specific surfaces within the part's image field, allowing for high-resolution imaging despite height variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the depth of field is increased to cover height variations, then focus is maintained across the part surface, but image resolution deteriorates
Solution Approach 1:
The patent implements dynamic focus adjustment by continuously measuring the height of the part surface during scanning and adjusting the focal plane in real-time. The camera and optics system dynamically adapt their focus position to track the varying surface topography, enabling high-resolution imaging across height variations without requiring a compromised static depth of field.
Solution Approach 2:
The system employs a feedback mechanism where a height measurement device (such as a confocal sensor or triangulation sensor) continuously measures the surface profile ahead of the inspection camera. This height information is fed back to the focus control system, which adjusts the focal plane accordingly to maintain optimal focus on the measured surface features.
2Measurement precision
If high resolution optics are used to detect small defects, then defect detection capability is improved, but depth of field decreases
Solution Approach 1:
The system uses dynamic focus adjustment to maintain the shallow depth of field of high-resolution optics while compensating for surface height variations. By continuously tracking the surface profile and adjusting the focal plane in real-time, the system preserves the high resolution capability needed for detecting small defects without being limited by a fixed shallow depth of field.
3Productivity
If the part surface is scanned to inspect defects, then inspection coverage is improved, but focus maintenance becomes difficult due to height variations
Solution Approach 1:
The system performs preliminary height measurement of the part surface using a dedicated height measurement device that scans ahead of the inspection camera. This advance measurement of the surface profile allows the focus control system to pre-adjust the focal plane before the inspection camera reaches each region, ensuring continuous focus maintenance throughout the scanning process.
Solution Approach 2:
During the scanning process, the system continuously receives height feedback from the measurement device and dynamically adjusts the focal plane to track surface variations. This real-time feedback control enables maintained focus across the entire inspection area, allowing comprehensive defect inspection without focus degradation.
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
Enables high-speed autofocusing and high-resolution imaging across the entire inspection area, ensuring that all features of interest remain in focus, thereby improving defect detection capabilities.
Implementation Method 1
A confocal sensor measures a height of the part
Implementation Method 2
an imaging camera captures a image of the part with the imaging optics
Data Source
AI summary
A method and apparatus for optimizing inspection high-speed optical inspection of parts using intelligent image analysis to determine optimal focus using high numerical aperture (NA) optics, achieve a superior signal-to-noise ratio, resolution, and inspection speed performance with very limited depth of field lenses.