Powder Bed Surface Inspection Using Multi-Directional Illumination
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Solution Overview
Problem
Existing methods for inspecting the surface of a powder bed with a large number of metallic powder particles are hindered by numerous reflections and shadows, making it difficult to detect structural unevenness and grain size distribution accurately.
Innovation Solution
A method and device that combine multiple images of the object surface illuminated from different directions to produce a reflection-corrected and shadow-corrected image, using pixel value differences and a weighting function to minimize reflections and shadows, allowing for precise inspection of the object surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the object surface is illuminated from a single direction, then the imaging process is simple, but light reflections and shadows make it difficult to detect surface properties accurately
Solution Approach 1:
The illumination system is segmented into multiple independent light sources arranged at different positions around the object. Each light source illuminates the surface from a specific angle, and the corresponding image captures reflections and shadows from that particular direction. By dividing the illumination into multiple segments, the system can selectively combine or subtract these segmented images to eliminate reflections and shadows, thereby improving measurement precision without requiring a single complex illumination direction.
2Measurement precision
If multiple images are taken from different illumination directions, then reflections and shadows can be reduced, but the number of images and processing complexity increases
Solution Approach 1:
The system uses feedback-based image processing where the multiple images captured from different illumination directions are systematically combined or subtracted to eliminate reflections and shadows. The processing algorithm analyzes the patterns of reflections and shadows across multiple images and uses this feedback to compute a corrected image that enhances surface property detection. This feedback mechanism automates the complex processing of multiple images, reducing the burden of manual analysis while improving measurement precision.
3Measurement precision
If conventional reflection correction methods are used on powder bed surfaces, then some reflections are reduced, but shadows are intensified making inspection more difficult
Solution Approach 1:
The system employs asymmetric illumination arrangements where light sources are positioned at non-uniform angles around the object, specifically designed to illuminate shadowed regions while minimizing reflection hotspots. By using asymmetric illumination directions rather than symmetric uniform lighting, the system can selectively target and reduce shadows in critical inspection areas without uniformly intensifying all shadows. The image processing then combines these asymmetrically illuminated images to achieve balanced reflection and shadow reduction, improving overall surface feature visibility.
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 unevenness, small dents, and grain size distribution by reducing light reflections and shadows, thereby improving the inspection of the object surface in additive manufacturing processes.
Implementation Method 1
the numerous reflections and shadows that can be caused by the metallic powder particles
Implementation Method 2
the numerous reflections and shadows that can be caused by the metallic powder particles
Implementation Method 3
a camera is arranged to take a plurality of images of the object surface when the object surface is illuminated from the different directions
Data Source
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AI summary
An object surface (18) is illuminated from a first direction (26b) and from at least one further direction (26c, 28). A first image and at least one further image are recorded by a camera (30). The first image has a multiplicity of first pixel values, which represent the object surface (18) under illumination from the first direction (26b). The at least one further image has a multiplicity of further pixel values, which represent the object surface (18) under illumination from the corresponding further direction (26c, 28). A shadow-corrected and/or a reflection-corrected image of the object surface (18) is determined using the first and the further pixel values. Pixel values of the at least one further image are used for determining the corrected image, depending on whether or not they lie within a defined brightness value range. The method and a corresponding apparatus are particularly suitable for inspecting the surface (18) of a powder bed (16) with metallic powder particles (20).