Method and device for laser cutting a sheet metal blank from a continuously conveyed sheet metal strip

1. A method for cutting a sheet metal blank from a sheet metal strip continuously conveyed in a transport direction via at least one laser cutting device, the method comprising:

providing a laser cutting device with at least one laser cutting head having a cutting nozzle, which can be moved via a control unit along a predetermined cutting path corresponding to the geometry of the sheet metal blank;

cyclic measurement of a distance between the cutting nozzle and a surface of the sheet metal strip at at least one radially outer position with respect to the cutting nozzle via a first distance measuring device;

controlling a movement of the laser cutting head in such a way that, when the cutting nozzle is not in overlap with the sheet metal strip, the first distance measuring device always remains in overlap with the sheet metal strip;

wherein the first distance measuring device comprises one of (i) and (ii) below:

(i) comprises only one distance sensor attached to a rotatable cutting nozzle, wherein the distance sensor is rotated to a position in which the distance sensor remains in overlap with the sheet metal strip when the cutting nozzle is not in overlap with the sheet metal strip; and

(ii) comprises several distance sensors for measuring the distance between the cutting nozzle and the surface of the sheet metal strip at several different positions which are radially outside the cutting nozzle, wherein the distance between the cutting nozzle and the surface of the sheet metal strip is measured at a plurality of different positions which are radially outwardly located with respect to the cutting nozzle via the first distance measurement device; moving the cutting nozzle from a first position not in overlap with the sheet metal strip to a second position in overlap with the sheet metal strip, wherein a height of the cutting nozzle with respect to the surface of the sheet metal strip is controlled using first distance values provided by the first distance measuring device when the cutting nozzle is moved from the first position towards the second position; and

wherein at least a section of the cutting path starts at the edge of the sheet metal strip or of an aperture located in the sheet metal strip and runs to the interior of the sheet metal strip, wherein when the cutting nozzle is moved from the first to the second position, a laser beam passing through the cutting nozzle.

2. The method according to claim 1 , wherein the irradiation of a laser beam passing through the cutting nozzle during cutting operation is temporarily interrupted when the cutting nozzle is not in overlap with the sheet metal strip.

3. The method according to claim 1 , wherein cutting parameters for generating the laser beam are changed when the cutting nozzle is in the first position.

4. The method according to claim 1 , wherein the cutting nozzle is part of a second distance measuring device and second distance values are measured via the second distance measuring device.

5. The method according to claim 4 , wherein at least one of the first distance values and the second distance values are used to control the distance between the cutting nozzle and the surface of the sheet metal strip.

6. The method according to claim 1 , wherein a movement of the laser cutting head occurring from the second position to the first position is stopped when one of a first distance value and a second distance value or a difference between the first distance value and the second distance value is greater than a predetermined limit value.

7. The method according to claim 4 , wherein capacitive or optical distance measuring devices are used for measuring at least one of the first distance values and the second distance values.