Laser Marking Grayscale Calibration via Absolute Power Measurement
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Solution Overview
Problem
Existing laser marking technologies for security documents require frequent calibration by trained technicians and complex optical equipment to achieve precise grayscale markings, which is time-consuming and inefficient, especially in decentralized settings.
Innovation Solution
A method and device equipped with a measuring head that measures laser power or pulse energy in absolute terms, using this measurement to adjust the laser control signal and generate an assignment function for precise grayscale markings, allowing for self-calibration and reduced technician intervention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If complex optical measuring equipment is used for calibration, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent uses a camera to capture an image of the marked security document and creates a digital copy of the grayscale markings. This digital image is then processed to extract grayscale values, replacing the need for complex optical measuring equipment while maintaining measurement precision through digital image analysis.
2Reliability
If frequent calibration cycles are performed, then reliability is improved, but loss of time increases
Solution Approach 1:
The system performs automatic self-calibration by capturing images of marked documents, processing the images to determine actual grayscale values, and automatically adjusting the assignment function. This eliminates the need for trained technicians and reduces calibration time while maintaining reliability through automated feedback control.
Solution Approach 2:
The patent implements a feedback mechanism where the actual grayscale values measured from marked documents are compared with target values, and the assignment function is automatically adjusted based on the deviation. This closed-loop feedback system ensures reliable grayscale markings while minimizing calibration time through automated correction.
3Manufacturing precision
If trained technicians are required for calibration, then manufacturing precision is improved, but ease of operation worsens
Solution Approach 1:
The calibration system is designed to perform automatic self-calibration without requiring trained technicians. The camera captures images, the processing unit extracts grayscale values, and the system automatically adjusts the assignment function, making the operation simple and accessible to untrained personnel while maintaining manufacturing precision.
Solution Approach 2:
The patent replaces manual technician operations with an automated digital system. Instead of technicians using complex optical equipment to measure and adjust grayscale values, a camera-based digital imaging system automatically captures, processes, and adjusts the markings, substituting mechanical/manual processes with automated digital control.
4Manufacturing precision
If laser control signal values are varied to achieve specific gray levels, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The system uses feedback from captured images to automatically adjust the laser control signal values. The processing unit analyzes the actual grayscale values from the image and automatically modifies the assignment function to correct deviations, achieving precise gray levels without complex manual calibration procedures.
Solution Approach 2:
The patent creates a digital model of the marking process through image capture and processing. By working with digital copies of the markings and their grayscale values, the system can precisely control laser parameters through software-based assignment functions, avoiding the need for complex physical calibration mechanisms.
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 and precise grayscale markings without the need for trained technicians, allowing for calibration of laser marking devices to maintain quality and reproducibility over time, particularly beneficial in decentralized operations.
Implementation Method 1
a measuring head 70 that measures absolutely and a decoupling unit 80 for decoupling a defined portion 42 of the laser light 40 from a beam path 41 for the laser marking and guiding the decoupled portion 42 to the measuring head 70 that measures absolutely, wherein the measuring head 70 is designed to have a power or energy of the guided to the measuring head to measure the extracted portion of the laser light in absolute terms
Implementation Method 2
In particular, security documents that are made on a plastic basis can be marked using laser radiation
Implementation Method 3
pigments are added to a transparent material layer, for example, which promote absorption of laser radiation
Implementation Method 4
The irradiated laser radiation is locally absorbed in the layer provided with the pigments and carbonization of the plastic is thereby effected
Data Source
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AI summary
The invention relates to a method for laser marking and to a device which comprises: a) a control device (10) for detecting graphics information which describes a graphic with different brightness values; b) wherein the control device (10) is configured to generate a position control signal (31) and a laser control signal (5) depending on the graphics information (16); c) a laser (3), the laser light output of which can be controlled by means of the laser control signal (5); and d) a beam guiding lens for guiding the laser light (40) which is emitted by the laser (3) onto the security document (2); and e) at least one position control device which can be actuated by means of the position control signal (31) for positioning the laser light (40) in a temporally adapted manner to the laser light output or laser pulse energy which is fixed by means of the laser control signal (5) relative to the security document (2), with the result that a precisely positioned marking of the security document with the graphic which has the different brightness values can be carried out, wherein the device (1) comprises an absolutely measuring measuring head (70) and a decoupling unit (80) for decoupling a defined proportion (42) of the laser light (40) from a beam path (41) for the laser marking, wherein the measuring head (70) outputs a calibration signal which represents the absolutely measured light output/pulse energy, wherein the control unit is configured to perform at least one calibration step during operation of the device, in which at least one calibration step the laser control signal (5) is generated for a brightness value and is kept constant during the calibration step, the power output or energy which is available for the marking is concluded from the measured power output or energy of the decoupled defined proportion (42) of the laser light (40) and is compared with the setpoint laser light output/setpoint laser pulse energy, and the calibration is performed via a change in the assignment function (18) if a difference above a predefined tolerance threshold is determined during the comparison.