Method for correcting a predetermined cutting path for cutting a sheet metal blank

1. A method for cutting a metal blank from a metal strip continuously transported in a transport direction x, comprising:

preparing a laser cutting apparatus comprising at least one laser moving in a transport direction x and in a transverse direction y running perpendicular to the transport direction x, and a computer storing cutting path coordinates describing a predetermined cutting path for moving the at least one laser;

simultaneously determining a first x coordinate x 1 and a first y coordinate y 1 of an arbitrary point on a surface of the metal strip with respect to an x and a y reference, the arbitrary point not being a separate mark put on the metal strip;

determining a second coordinate y 2 of the point with respect to the y reference precisely when the metal strip has been moved in the transport direction x by a predetermined first distance dx 1 with respect to the first x coordinate x 1 ;

determining a first y correction value K y 1 by taking a difference between the first y coordinate y 1 and the second y coordinate y 2 ;

using the first y correction value K y 1 to correct cutting path coordinates describing the predetermined cutting path; and

cutting the metal blank by moving the at least one laser along the predetermined cutting path corrected by the first y correction value K y 1 while the metal strip is continuously transported in the transport direction x.

2. The method according to claim 1 , further comprising:

providing a first y measurement device (M y 1 ) to measure the first y coordinate y 1 of the metal strip with respect to the y reference;

providing a second y measurement device (M y 2 ) to measure the second y coordinate y 2 of the metal strip with respect to the y reference, the second y measurement device (M y 2 ) being arranged at the predetermined first distance dx 1 downstream of the first y measurement device (M y 1 ); and

providing a first displacement measurement device (M x 1 ) to measure the x coordinates of the metal strip with respect to the x reference.

3. The method according to claim 1 , further comprising:

determining a third y coordinate y 3 at a predetermined second distance dx 2 from a place of determination of the second y coordinate y 2 ;

determining a second y correction value K y 2 by taking a difference between the second y coordinate y 2 and the third y coordinate y 3 ; and

correcting the cutting path coordinates describing the predetermined cutting path by taking into consideration change in the second y correction value K y 2 with respect to the first y correction value K y 1 over the transport path or over time.

4. The method according to claim 3 , further comprising:

providing a third y measurement device (M y 3 ) to measure the third y coordinate y 3 of the metal strip with respect to the y reference, the third y measurement device being arranged at the predetermined second distance dx 2 downstream of the second y measurement device (M y 2 ).

5. The method according to claim 1 , wherein in the step of simultaneously determining the first x coordinate x 1 and the first y coordinate y 1 of the arbitrary point, one point on the surface of the metal strip is detected as the arbitrary point, and the one point is a part of the surface of the metal strip.

6. The method according to claim 1 , wherein in the step of simultaneously determining the first x coordinate x 1 and the first y coordinate y 1 of the arbitrary point, the arbitrary point is not physically marked on the metal strip.

7. A method for cutting a metal blank from a metal strip continuously transported in a transport direction x, comprising:

preparing a laser cutting apparatus comprising at least one laser moving in a transport direction x and in a transverse direction y running perpendicular to the transport direction x, and a computer storing cutting path coordinates describing a predetermined cutting path for moving the at least one laser;

simultaneously determining a first x coordinate x 1 and a first y coordinate y 1 of an arbitrary point (P) of a surface of the metal strip with respect to an x and a y reference, the arbitrary point not being a separate mark put on the metal strip, this determination being done by means of a strip flow measuring device (BF), which allows a determination of positional coordinates xy of the point and their change over time or travel;

simultaneously determining a second x coordinate x 2 and a second y coordinate y 2 of the point (P) of the surface of the metal strip with respect to the x and y reference by means of the strip flow measuring device (BF), if the metal strip has been moved in the transport direction x by a predetermined third distance dx 3 ;

determining a third y correction value K y 3 using a vector (V) determined by the strip flow measuring device (BF) from coordinate pairs (x 1 , y 1 ) and (x 2 , y 2 );

using the third y correction value K y 3 to correct cutting path coordinates describing the predetermined cutting path; and

cutting the metal blank by moving the at least one laser along the predetermined cutting path corrected by the third correction value K y 3 while the metal strip is continuously transported in the transport direction x.

8. The method according to claim 7 , further comprising:

measuring a fourth y coordinate y 4 of the metal strip by means of a fourth y measurement device (M y 4 ) arranged at a predetermined fourth distance dx 4 from the strip flow measuring device (BF) and correcting the third y correction value K y 3 using the fourth y coordinate y 4 .

9. The method according to claim 7 , further comprising:

measuring a fourth x coordinate x 4 of the metal strip by means of a second displacement measurement device (M x 2 ) and using the fourth x coordinate x 4 for correction of the third y correction value K y 3 .

10. The method according to claim 7 , wherein the first coordinate pair (x 1 , y 1 ) is determined from a surface structure detected at a time point t 1 with the strip flow measuring device (BF).

11. The method according to claim 10 , wherein the surface structure is determined from a 2- or 3-dimensional surface image produced at time point t 1 .

12. The method according to claim 11 , wherein the surface image is produced using a strip flow measuring device (BF), which comprises one of the following components: a camera, an optical mouse sensor, a distance sensor, or a confocal chromatic distance sensor.

13. The method according to claim 10 , wherein the second coordinate pair (x 2 , y 2 ) is calculated from another surface structure detected at other time points to following the time point t 1 with the strip flow measuring device (BF).

14. The method according to claim 7 , wherein in the step of simultaneously determining the first x coordinate x 1 and the first y coordinate y 1 of the arbitrary point, one point on the surface of the metal strip is detected as the arbitrary point, and the one point is a part of the surface of the metal strip.