Method and device for laser marking with grayscale calibration

Abstract

The invention relates to a method for laser marking and a device comprising: a) a control device (10) for detecting graphic information describing graphics 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) according to the graphic information (16); c) a laser (3), whose laser power can be controlled by means of the laser signal (5) control; and d) beam guiding optics for directing the laser light (40) irradiated by said laser (3) onto said security document (2); and e) at least one A position control device controlled by the position control signal (31), the position control device is used to match the laser power or laser pulse energy determined by means of the laser control signal (5) in time relative to the security document ( 2) positioning of the laser (40) in such a way that a positionally correct marking of the security document by means of graphics with different brightness values ​​can be carried out, wherein the device (1) comprises an absolutely measuring measuring head (70) and A coupling-out unit (80) for coupling out a defined fraction (42) of the laser light (40) from the beam path (41) for the laser marking, wherein the measuring The head (70) outputs a calibration signal representing the absolutely measured optical power / pulse energy, wherein the control unit is configured to carry out at least one calibration step during operation of the device, wherein the laser control for brightness values A signal (5) is generated and kept constant during the calibration step, from the measured power or energy of a defined fraction (42) of the outcoupling of the laser light (40) the power available for the marking is deduced or energy and compare it with the desired laser power / desired laser pulse energy, and if a difference above a predefined tolerance threshold is determined in the comparison, the assignment function (18) is carried out Changed calibration.

Description

technical field [0001] The invention relates to a method for laser marking of security documents and a corresponding device, whereby graphic information describing graphics with different brightness values ​​can be stored in the security document. Background technique [0002] It is known from the prior art to mark security documents using laser radiation. In particular, security documents produced on the basis of plastic can be marked by means of laser radiation in such a way that graphic information is stored on the surface or in the interior of the security document. For storage in the interior of the security document, for example, pigments are added to the transparent material layer which, although they facilitate the absorption of the laser radiation, do not at all or only insignificantly impair the general transparency of the material. The incident laser radiation is locally absorbed in the layer provided with the pigment and thus causes, for example, carbonization o...

AI Technical Summary

Problems solved by technology

This means that the exact laser power or laser pulse energy may not be specified precisely

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