Surface Defect Inspection Using Rotating Polarized Illumination
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Solution Overview
Problem
Current surface defect inspection apparatuses struggle to effectively inspect concave-shaped flaws parallel to the plane of incidence and fail to secure a sufficient signal-to-noise ratio due to weak scattered light intensity and insufficient removal of diffracted light.
Innovation Solution
A surface defect inspection apparatus and method that includes an illumination unit, a changing unit, and a light reception unit, where the object and illumination unit are rotated around a perpendicular axis to change illumination conditions, and the light reception unit is set to exclude specular light while capturing scattered light, using linearly polarized light and telecentric structures to enhance image processing and SN ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If illumination light is incident at a specific angle to receive scattered light, then surface defects can be detected, but concave-shaped flaws parallel to the plane of incidence cannot be properly inspected due to weak scattered light intensity
Solution Approach 1:
The patent applies the dynamics principle by rotating the illumination unit and object around an axis perpendicular to the front surface, changing illumination conditions dynamically. This allows the system to capture images from multiple illumination angles, ensuring that concave-shaped flaws parallel to the plane of incidence are properly inspected by receiving scattered light from different directions.
Solution Approach 2:
The patent introduces a new dimension by adding rotation around an axis perpendicular to the front surface. Instead of fixed-angle illumination, the system now operates in multiple angular dimensions, capturing images at various illumination conditions to comprehensively detect surface defects including those that would otherwise be invisible.
2Object-affected harmful factors
If angle conditions are adjusted to remove diffracted light, then noise is reduced, but scattered light intensity becomes weak and SN ratio is insufficient
Solution Approach 1:
The patent uses dynamic rotation of the illumination unit and object to change illumination conditions. By capturing images at multiple angles and combining them, the system maintains sufficient scattered light intensity while the light reception unit selectively receives only the necessary scattered light, achieving both diffracted light removal and adequate SN ratio.
Solution Approach 2:
The patent merges multiple images captured under different illumination conditions to generate a combined image. This combining process enhances the signal from scattered light while the light reception unit's angular selection continues to filter out diffracted light, resulting in improved SN ratio without compromising defect detection capability.
3Productivity
If only scattered light is received in a predetermined direction, then inspection can be performed, but concave-shaped flaws with weak scattered light emission are not detected
Solution Approach 1:
The patent applies dynamic illumination by rotating the illumination unit and object around an axis perpendicular to the front surface. This enables the system to receive scattered light from multiple directions rather than a single predetermined direction, ensuring that concave-shaped flaws with weak scattered light emission in any direction can be detected while maintaining inspection efficiency.
Solution Approach 2:
The patent makes the illumination system universal by enabling it to operate at multiple angles around the axis perpendicular to the front surface. This multi-functional capability allows the same apparatus to detect various types of surface defects including concave-shaped flaws that would require specialized single-angle inspection 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
The solution enables proper inspection of concave-shaped flaws and secure removal of diffracted light, achieving a necessary SN ratio for defect detection, improving inspection quality and throughput by generating combined images from varied illumination conditions.
Implementation Method 1
receives scattered light emitted from the front surface when the front surface is illuminated with the illumination light in each of the illumination conditions
Implementation Method 2
the intensity of scattered light emitted from the flaw is very weak... diffracted light may be insufficiently removed
Implementation Method 3
even if the concave-shaped flaw is curved and a part thereof is substantially in parallel with the plane of incidence, the apparatus cannot inspect for the entire flaw
Implementation Method 4
using linearly polarized light and telecentric structures to enhance image processing and SN ratio
Data Source
AI summary
The present invention aims to provide a surface defect inspection apparatus and a surface defect inspection method for properly inspecting for a concave-shaped flaw (or a part thereof) substantially in parallel with a plane of incidence. The apparatus includes an illumination unit 10 illuminating a front surface (surface under inspection 5a) of an object to be inspected 5 with illumination light for inspection, a changing unit 1, 33 which relatively rotating the object to be inspected and the illumination unit around an axis AX1 perpendicular to the surface under inspection 5a and changing illumination conditions of the illumination light, a light reception unit 20 receiving scattered light emitted from the surface under inspection when illuminated with illumination light in each illumination condition, to capture images thereof, and a combining unit 32 combining images captured by the light reception unit to generate a combined image.