Angled Laser Marking Verification Using Pattern Matching
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Solution Overview
Problem
Current methods for verifying angle-dependent laser markings on documents, such as CLI and MLI, are limited in detecting the existence, completeness, and positional accuracy of image and text features relative to the marking border, often failing to identify incorrect or incomplete features and offset errors.
Innovation Solution
A method and device using angled image capturing devices and illumination, combined with pattern matching and generalized Hough transformation, to capture and verify image and text features, and determine their positional accuracy relative to the marking border, ensuring accurate and complete verification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a simplified check of the laser marking's image features is performed to verify blackening, then the verification process is simple and quick, but it cannot detect incorrect or incomplete image features or misalignment between features and the laser marking outline
Solution Approach 1:
The verification process is divided into multiple independent analysis stages: initial simplified blackening check, detailed feature detection, completeness verification, and alignment checking. Each stage processes specific aspects of the laser marking separately, allowing the system to maintain high throughput while progressively improving detection accuracy without requiring complete re-verification of all features at maximum detail level
Solution Approach 2:
The system performs a basic verification level for all laser markings (simplified blackening check) and then applies enhanced verification (detailed feature analysis, completeness check, alignment verification) only to markings that fail the initial check or require higher scrutiny. This partial application of excessive verification action maintains overall productivity while ensuring measurement precision for critical cases
2Measurement precision
If multiple image acquisition devices and illumination devices are added to capture and verify image and text features from different angles, then detection accuracy and completeness are improved, but device complexity increases
Solution Approach 1:
Multiple image acquisition devices capturing images from different angles (including oblique and perpendicular views) are merged into a single integrated verification system. The illumination devices are similarly combined to provide coordinated multi-directional lighting. This merging allows the system to achieve comprehensive feature verification through coordinated operation of unified components rather than separate independent systems, reducing overall complexity while maintaining high measurement precision
Solution Approach 2:
The image acquisition devices are designed with multi-functionality to perform multiple verification tasks: capturing image features, detecting text features, verifying completeness, and checking alignment with laser marking outlines. The same devices serve multiple purposes across different verification stages, eliminating the need for dedicated specialized equipment for each function and thereby reducing device complexity while improving measurement precision through comprehensive analysis
3Reliability
If the document surface is illuminated by lighting devices positioned at an angle to eliminate interfering marking or printing elements, then verification quality is improved, but the setup becomes more complex
Solution Approach 1:
Illumination devices are positioned at specific angles to provide localized lighting quality optimized for different verification tasks. The lighting angle and intensity are tailored to highlight specific features (image elements, text, outlines) while suppressing interfering markings or printing elements in specific regions. This local optimization of illumination quality improves verification reliability without requiring complete redistribution of the entire illumination system, thereby limiting the increase in device complexity
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 reliable detection and verification of image and text features, improving quality assurance and throughput by allowing for precise matching and positional analysis without requiring document oblique alignment, thus enhancing the security features of identity and access cards.
Implementation Method 1
an image of a picture or text feature to be verified on a surface of the document is captured with an image capture device arranged at an angle alpha to a normal of the surface of the document
Implementation Method 2
The surface of the document is illuminated by at least one lighting device while the laser marking is being captured by the image capture device to verify the image
Data Source
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AI summary
The invention relates to a method and device for testing a laser marking (12) produced in accordance with an angle on a surface (14) of a document (15), in which an image of an image characteristic (29) or text characteristic (35) of the laser marking (12) is detected by the image detecting device (17) which is aligned at an angle α to the normal (18) of the surface (14) of the document (15). The image captured in perspective is equalized, an image pattern is produced in a evaluation device (27) from a data set provided by a document manager and associated with the document to be tested. The equalized image is searched for and determined using a pattern-matching method, and the equalized image is compared to the image pattern based on the concordance and a correlation value is determined.