Document Surface Inspection Using Multi-Angle Static Illumination
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Solution Overview
Problem
Current methods for detecting raised structures on documents are inefficient due to the need for dynamic illumination, limiting throughput and making real-time quality control during production economically unfeasible.
Innovation Solution
The method involves successively illuminating the document surface in different areas with fixed lighting, capturing areal images for each illumination type, and evaluating these images to identify raised structures, allowing for increased throughput and robust mechanical design without dynamic light sweeping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dynamic illumination with linear light strip is used to scan the document surface, then raised structures can be detected through reflection deviations, but the throughput is limited and real-time quality control during production is not economically feasible
Solution Approach 1:
The illumination is segmented into multiple discrete light sources arranged at different positions and angles around the document surface, allowing simultaneous multi-point illumination rather than sequential scanning with a single linear light strip
Solution Approach 2:
The inspection system transitions from one-dimensional linear scanning to two-dimensional areal illumination by arranging light sources and cameras in a planar configuration that illuminates and captures the entire document surface simultaneously
2Measurement precision
If dynamic illumination with moving light strip is used, then raised structures can be detected, but the mechanical structure becomes complex and less robust
Solution Approach 1:
The system eliminates dynamic moving parts by using fixed, stationary light sources and cameras. The illumination geometry is fixed in space, and document movement is controlled by the transport mechanism rather than requiring dynamic illumination adjustment
Solution Approach 2:
The mechanical scanning system with moving light strips is replaced by a static optical system with multiple fixed light sources. The detection is achieved through fixed geometric relationships between light sources, document surface, and cameras rather than mechanical movement
3Measurement precision
If multiple images are captured sequentially with linear illumination, then raised structures can be identified through evaluation, but the inspection time increases and throughput decreases
Solution Approach 1:
Multiple light sources are pre-positioned at optimal angles and locations to simultaneously illuminate the entire document surface. The geometric arrangement is predetermined to capture all necessary reflection information in a single exposure rather than requiring sequential captures
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 approach significantly reduces the number of images needed for evaluation, enhancing the method's efficiency and enabling real-time quality control during document production.
Implementation Method 1
the surface is illuminated from different directions with light at a grazing angle of incidence
Data Source
Figure 1
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AI summary
The invention relates to an apparatus (1) and to a method for detecting three-dimensional elevated structures (2) on a surface (3) of a document (4). The method comprises the steps of: illuminating the surface (3) with light; capturing an image of the surface (3) during the illumination of the surface (3), and evaluating the captured image to ascertain the elevated structures (2), wherein the surface (3) is illuminated areally in at least two different ways and at least one areal image (71, 81) of the surface (3) is captured for each of the different illumination ways and the plurality of areal images (71, 81) of the surface (3) thus captured are evaluated together.