Surface Inspection System for Glossy Sheet Elements
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Solution Overview
Problem
Existing surface inspection systems struggle to reliably detect defects like scratches on highly reflective surfaces of sheet elements moving at high speeds, as specular reflection complicates defect detection.
Innovation Solution
A surface inspection system using two light sources with different angles of incidence and a camera capturing line images, where the image evaluation unit compares the line images to detect differences caused by surface defects, allowing for reliable detection of scratches on glossy surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single light source is used to illuminate the surface, then the illumination setup is simple, but defects on highly reflective surfaces cannot be reliably detected due to specular reflection
Solution Approach 1:
The illumination system is segmented into multiple light sources positioned at different angles relative to the surface normal. Each light source illuminates the surface from a specific direction, creating distinct reflection patterns that help distinguish defects from specular reflections. The camera captures images under these different illumination conditions and compares them to detect defects.
Solution Approach 2:
Different regions of the surface are illuminated with light from specific angles tailored to highlight local defects. By positioning light sources at angles that create specular reflections away from the camera view, the system ensures that only scattered light from defects enters the camera, enhancing defect visibility while suppressing reflections from smooth surface areas.
2Productivity
If the sheet element moves at high speed through the inspection station, then productivity is high, but the exposure time for image capture is reduced making defect detection more difficult
Solution Approach 1:
The system uses periodic illumination with multiple light sources activated in sequence as the sheet element moves through the inspection station. Each light source is activated for a brief period to capture an image, and this periodic illumination continues as the sheet progresses, allowing multiple measurements to be taken during the short transit time and improving detection precision without reducing productivity.
3Reliability
If multiple illumination channels are used to detect defects, then defect detection reliability improves, but the device complexity and number of components increase
Solution Approach 1:
Multiple illumination channels are merged into a single camera system that captures images under different illumination angles. Instead of using separate cameras for each illumination channel, the system combines the illumination sources and uses one camera to capture all necessary views, then processes the images computationally to detect defects. This reduces device complexity while maintaining the reliability benefits of multiple illumination angles.
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 accurate detection of surface defects such as scratches on high-speed, glossy sheet elements by capturing and comparing line images from different illumination angles, effectively distinguishing defects from specular reflections.
Implementation Method 1
the reflection of the light coming from the two light sources is in theory specular (if the surface is assumed to be a mirror) and in practice close to specular
Implementation Method 2
the image evaluation unit compares the captured line images with each other, in particular subtracts the line images from each other
Data Source
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AI summary
The invention relates to a surface inspection system (10) for inspecting the surface of sheet elements (2) present in an inspection area (5), comprising an image evaluation unit (18), two light sources (12, 14) arranged adjacent each other on opposite sides of an illumination plane (O11 ) and oriented for illuminating the inspection area (5), and a camera (16) adapted for capturing line images (I12, I14) of the inspection area (5) along a viewing plane (O16), the illumination plane (O11) and the viewing plane (O16) being arranged on opposite sides of a median plane (M) which is perpendicular to an inspection plane, the angle (α) between the illumination plane (O11) and the median plane (M) being the same as the angle (α) between the viewing plane (O16) and the median plane (M). The invention further relates to a method of inspecting the surface of sheet elements (4) by using the surface inspection system (10) as defined above, wherein a first of the two light sources (12, 14) directs light onto the sheet element (4) to be inspected, and the camera (16) captures a line image (I12; I14) of the inspection area (5), and then the second of the two light sources (14, 12) directs light onto the sheet element (4) to be inspected, and the camera (16) captures a line image (I14; I12) of the inspection area (5), wherein the image evaluation unit (18) compares the captured line images (I14; I12) with each other, in particular subtracts the images images from each other.