Method for determining the reference focal position of a laser beam
A method for determining a reference focal position of a laser beam for processing a plate-like member, the method comprising producing at least two incisions in the plate-like member with the laser beam set at different focal positions, irradiating the plate-like member with the laser beam, detecting edges of the incisions by measuring one or more parameters relating to the irradiation of the plate-like member, and establishing a width of the at least two incisions using the detected one or more parameters.
1. A method for determining a reference focal position of a laser beam for processing a workpiece that is a plate-like member, the method comprising:
producing at least two incisions in the workpiece with the laser beam set at a first laser power and at different focal positions for at least two of the incisions;
irradiating the workpiece with the laser beam at a second laser power lower than the first laser power;
detecting edges of the incisions by measuring one or more parameters of process radiation, one or more parameters of reflected laser radiation, or one or more parameters of both process radiation and reflected laser radiation caused by the irradiation of the workpiece at the second laser power;
establishing a width of each of the at least two incisions using the measured one or more parameters; and
fitting a mathematical curve to the established widths at associated different focal positions, determining a minimum of the curve, including between measurement locations of the different focal positions, as a minimal cutting gap width, and setting the associated focal position at the minimum of the curve as a reference focal position of the laser beam.
2. The method of claim 1 , comprising moving the laser beam relative to the plate-like member transversely to a longitudinal direction of the incisions.
3. The method of claim 2 , comprising moving the laser beam with a constant spacing between a processing head that emits the laser beam and the plate-like member and at a constant speed relative to the workpiece.
4. The method of claim 1 , wherein the incisions are produced with a width greater than a single cutting gap width of the laser beam.
5. The method of claim 1 , comprising moving the laser beam relative to the plate-like member in opposing directions twice, and detecting only one of the edges of the incision during each movement.
6. The method of claim 5 , wherein the second edge of the incision in the movement direction is detected.
7. The method of claim 1 , wherein producing the incisions comprises making a first single cutting gap in a longitudinal direction of the incision to be produced, subsequently making a second single cutting gap in a direction transverse to the longitudinal direction and then, making a third single cutting gap in the longitudinal direction but in an opposing direction to the production of the first single cutting gap.
8. The method of claim 1 , wherein the edge of an incision is detected when one of the one or more measured parameters exceeds or falls below a first reference value.
9. The method of claim 1 , comprising calculating a gradient of the measured parameter and identifying an edge of an incision when the gradient exceeds or falls below a second reference value.
10. The method of claim 1 , comprising calculating a gradient of the one or more measured parameters over a plurality of sampling points, calculating a mean value of the gradients, and comparing the mean value with a third reference value, wherein an edge of an incision is detected when the mean value exceeds or falls below the third reference value.
11. The method of claim 1 , comprising establishing a reference focal position as the focal position at which the incision with the smallest width was produced.