Patent ID: 9539840
Date: 2017-01-10
CPC Classifications: B23K,B41M

Claim:
1. A method for laser marking security documents comprising the following steps: a) capturing graphic information which describes a graphic having different brightness values; b) generating a position control signal and a laser control signal dependent on the graphic information, wherein each brightness value is assigned a nominal laser light output or nominal laser pulse energy which is needed to induce a laser marking with the corresponding brightness value in a security document and, wherein the laser control signal is generated by means of an assignment function, wherein each brightness value is assigned a control value which is provided for generating laser light with the corresponding laser light output according to the nominal laser light output or laser pulse energy according to the nominal laser pulse energy, c) controlling a laser by means of the laser control signal and emitting laser light with a laser light output or laserpulse energy according to the laser control signal; and d) temporally adapted controlling of at least one position control device by means of the position control signal, so that the emitted laser light is positioned relative to the security document, so that, by iteratively performing the method steps b) to d), a correctly positioned marking of the security document with the graphic having the different brightness values is performed, characterized in that at least one calibration step is performed, wherein, when performing the calibration step, the laser control signal with a control value for a brightness value is generated and held constant during the calibration step, wherein a defined proportion of the laser light is decoupled from a beam path for the laser marking and is guided into a measuring head, the measuring head measuring absolutely, the decoupled proportion of the laser light output, or energy thereof, that is, guided onto the measuring head, and wherein a calibration signal is generated, and, wherein from the measured output or energy of the decoupled proportion of the laser light represented by the calibration signal, the output or pulse energy available for the marking is ascertained, and wherein (i) the output ascertained is compared to the nominal laser light output or (ii) the pulse energy ascertained is compared to the nominal laser pulse energy, and wherein the calibration is performed by a change of the assignment function if, in the comparison, a difference above a specified tolerance threshold is ascertained.