Patent ID: 8379194

Claim:
A method for focusing a laser in the laser processing of a workpiece, the method comprising the following steps: (a) adjusting the focal distance f of a laser to a starting value A; (b) resetting a continuous index i to an initial value; (c) producing a focal spot on a workpiece to be processed; (d) storing the current value of the continuous index i together with the corresponding value of the focal distance f i and the corresponding value of the focal spot position pos i ; (e) moving the workpiece by one path increment Δx along a predetermined track; (f) adjusting the focal distance f in the direction of a final value B by one infeed increment Δf; (g) incrementing the continuous index i and repeating the steps (c) to (f) until reaching one of (i) a previously determined number i max of focal spots; (ii) the final value B; and (iii) the end of the predetermined track; (h) determining the focal spot with the smallest focal spot diameter d opt ; (i) determining the optimal continuous index i opt belonging to the focal spot having smallest focal spot diameter d opt ; and (j) adjusting the focus of the laser to the optimal focal distance f opt belonging to the optimal continuous index i opt ; wherein the steps of determining the focal spot with the smallest focal spot diameter d opt and of determining the associated continuous index i opt comprise the following sub-steps (1) resetting the continuous index i to the initial value; (2) examining the particular value of the stored focal spot position pos i ; (3) determining and storing the particular focal spot diameter d i corresponding to the stored focal spot position pos i ; (4) incrementing the continuous index i and repeating the sub-steps (2) to (4) until reaching the previously determined number i max of focal spot positions pos i ; (5) determining an interpolating or approximating function that reproduces the focal spot diameter d i as a function of the continuous index i; (6) determining the minimum of the interpolating or approximating function; (7) determining the continuous index i opt located closest to the minimum of the interpolating or approximating function.