Elliptical Reflector for Uniform Dark-Field Illumination
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Solution Overview
Problem
Conventional dark-field illumination systems for optical testing devices face challenges in achieving uniform and homogeneous illumination of reflecting surfaces, as light sources are perceived as individual spots due to being within the sharp-focus range of the sensor, and struggle to provide illumination from a wide angular range without increasing the light source size or number.
Innovation Solution
A device with a reflector in the shape of a segment of an ellipse is used, where the first focal point is on the object's surface and the light source is located at the reflected second focal point, allowing light to be directed efficiently onto the scanning area, enabling a high level of illumination with a linear light source made of several diodes, even at a greater distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the light source is placed close to the object surface to achieve high illumination intensity, then the illumination level is sufficient, but the light-emitting diodes are perceived as individual spots by the sensor due to being within the sharp-focus range
Solution Approach 1:
A reflector is introduced as an intermediary component between the light source and the object surface. The reflector redirects light from the source positioned at a distance to illuminate the scanning line, preventing direct viewing of the LED spots by the sensor while maintaining high illumination intensity and uniformity across the scanned line.
2Manufacturing precision
If the light source is placed far from the object surface to avoid being in the sharp-focus range, then uniform illumination is achieved, but the illumination intensity becomes insufficient
Solution Approach 1:
The reflector serves as a mediator that enables the light source to be positioned at a distance from the object surface for uniform illumination, while simultaneously concentrating and redirecting the light to maintain high illumination intensity on the scanning line.
Solution Approach 2:
The reflector utilizes a curved surface (cylindrical or conical geometry) to redirect light rays from the distant light source onto the scanning line. The curvature of the reflector focuses and distributes light uniformly across the line while maintaining the source at a distance to avoid spot perception.
3Device complexity
If conventional linear light sources are used for dark-field illumination, then the setup is simple, but the illumination angular range is limited and cannot provide wide-angle illumination
Solution Approach 1:
The reflector is designed to perform multiple functions: it redirects light from the light source, expands the illumination angular range, and maintains uniform illumination across the scanning line. This single component replaces the need for multiple light sources or complex illumination arrangements.
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 configuration ensures nearly all light is directed onto the scanning area, providing homogeneous illumination and enhancing defect detection by illuminating from a wider angular range, with minimal reflection losses and improved luminance, even on low-reflection surfaces.
Implementation Method 1
a reflector (6), wherein the reflector has in cross-section the form of a segment of an ellipse
Data Source
AI summary
The invention relates to a device for dark-field illumination for an optical testing device for scanning a plane surface of an object together with a method for optical scanning of a plane surface of an object in which the device according to the invention is used. The illumination device according to the invention has a reflector which has in cross-section the form of a segment of an ellipse, while the illumination device may be arranged with a first focal point of the ellipse on the surface of the object, and the light source located at a point which results from reflection of the second focal point of the ellipse on the surface of the object. By this means, dark-field illumination with a high level of illumination at the first focal point is obtained, even when the light source is located a good distance away from the object.