Laser Pulse Energy Control Filter for High-Contrast Marking
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Solution Overview
Problem
Pulsed laser systems, particularly diode-pumped fiber lasers, exhibit low-pass filter characteristics, leading to inadequate pulse energy control, which limits high-contrast marking of microscripts and fine patterns on plastic-based documents, as the actual pulse energy does not immediately match the requested changes from minimum to maximum.
Innovation Solution
A filter device is introduced to modify the control signals for the pulsed laser, using a comparator and gate circuit to generate a retrieval signal based on a threshold condition, allowing for precise pulse energy control and overcoming the low-pass filter properties, enabling high-contrast marking with adjustable pulse energy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a pulsed laser system with low-pass filter characteristics is used for marking, then the laser can operate with stable pulse energy, but the actual pulse energy cannot immediately match rapid changes in requested pulse energy, leading to inadequate control for high-contrast marking
Solution Approach 1:
The system pre-calculates and stores optimal pulse energy values in lookup tables before processing. When high-contrast marking is required, the control system retrieves pre-determined pulse energy values that compensate for the laser's low-pass filter characteristics, allowing the actual pulse energy to immediately match the desired values without gradual transition delays.
Solution Approach 2:
The system incorporates feedback mechanisms where the actual pulse energy output is monitored and compared with the requested pulse energy. Based on this feedback, the control system adjusts subsequent pulse energy commands to compensate for the low-pass filter effect, ensuring that the actual pulse energy rapidly converges to the desired value even when rapid changes are requested.
2Illumination intensity
If the pulse energy is rapidly changed from minimum to maximum to achieve high-contrast marking, then the marking contrast improves, but the low-pass filter characteristic causes the actual pulse energy to lag behind the requested energy, reducing marking quality
Solution Approach 1:
The system pre-calculates and stores optimal pulse energy values in lookup tables before processing. When high-contrast marking is required, the control system retrieves pre-determined pulse energy values that compensate for the laser's low-pass filter characteristics, allowing the actual pulse energy to immediately match the desired values without gradual transition delays.
Solution Approach 2:
The system incorporates feedback mechanisms where the actual pulse energy output is monitored and compared with the requested pulse energy. Based on this feedback, the control system adjusts subsequent pulse energy commands to compensate for the low-pass filter effect, ensuring that the actual pulse energy rapidly converges to the desired value even when rapid changes are requested.
3Manufacturing precision
If a filter device with comparator and gate circuit is introduced to control pulse energy, then the pulse energy control precision improves, but the device complexity increases
Solution Approach 1:
The filter device acts as an intermediary between the control system and the pulsed laser. It includes a comparator that compares the requested pulse energy with a threshold value and a gate circuit that selectively passes or blocks the pulse energy signal based on the comparison result. This intermediary structure enables precise control of pulse energy by filtering out unwanted variations while maintaining a relatively simple overall system architecture.
Solution Approach 2:
The filter device changes the parameter of pulse energy by selectively filtering signals based on threshold comparisons. The comparator converts the continuous pulse energy signal into a binary decision (pass or block) by comparing it with a predefined threshold, thereby transforming the control mechanism into a simpler on/off switching operation that achieves precise energy control without complex continuous adjustment circuits.
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 solution allows for high-contrast marking of microscripts and fine patterns on plastic-based documents, including security documents, by ensuring that the pulsed laser achieves the desired pulse energy immediately, thereby improving the quality of the marking process.
Implementation Method 1
The energy absorbed during the absorption of the laser radiation is used to alter the plastic material of the correspondingly prepared film, i.e. the layer formed from said film, in the document. In particular, chemical compounds of the polymers from which the plastic material is formed are broken up and carbonization is brought about.
Implementation Method 2
a pulsed laser which is controllable with regard to its pulse energy and a temporal retrieval of laser pulses
Data Source
AI summary
A laser processing apparatus, a filter device and a method are used for controlling a pulse laser, which is controllable in terms of its pulse energy and of a temporal triggering of laser pulses, during material processing of an object, in particular during the marking of a plastics-based document. The method includes comparing a pulse energy signal which assumes voltage values, in temporal correlation with a clock signal, which represent a pulse energy for the laser pulses for processing, with a threshold value condition and generating a logic result signal. The clock signal is passed to a gate and controlling the gate using the logic result signal and generating a retrieval signal thereby. An energy control signal is provided which has a voltage according to a specification of a control voltage. The retrieval signal and the energy control signal are used to control the pulse laser.