Method for determining focal position

1. A method for determining a reference focal position of a focused laser beam passing through an opening in a nozzle body of a laser processing nozzle relative to a workpiece, the method comprising:

producing a continuous cutting line in the workpiece by simultaneously cutting off a portion of the workpiece using the focused laser beam and altering a distance between a focal point of the focused laser beam and the workpiece along a direction of a central axis of the laser beam, wherein a boundary of the continuous cutting line is defined by a continuous workpiece edge formed by the cutting;

determining coordinates of the edge, wherein determining coordinates of the edge comprises contacting the edge with a mechanical touch tool, and the mechanical touch tool comprises the nozzle body of the laser processing nozzle or a measuring probe mounted on a laser processing head, and wherein an extent to which the continuous edge protrudes from the workpiece varies based on a change in focal position of the focused laser beam during the cutting;

performing an operation selected from the list consisting of i) detecting a short circuit between the workpiece and the mechanical touch tool when the mechanical touch tool contacts the edge, ii) measuring a capacitance between the mechanical touch tool and the workpiece and detecting contact with the edge based on the capacitance measured, and iii) combinations thereof;

determining, based on the coordinates, a section of the edge that protrudes furthest from the workpiece; and

establishing a reference focal position (FL) of the laser beam based on the coordinates corresponding to the section of the edge that protrudes the furthest from the workpiece.

2. A method according to claim 1 , wherein altering the distance between the focal point of the focused laser beam and the workpiece comprises at least one of:

displacing focusing optics in the direction of the axis of the laser beam, the focusing optics being arranged in a beam path of the focused laser beam; and

changing a radius of curvature of at least one adaptive deflecting mirror disposed in the beam path of the laser beam.

3. A method according to claim 1 , wherein the workpiece comprises a thickness between about 1.5 mm and 2 mm.

4. A method according to claim 1 , wherein the workpiece comprises a shape of an elongated sheet.

5. A method according to claim 1 , wherein the workpiece comprises a metal sheet.

6. A method of using a laser processing machine, wherein the laser processing machine comprises (1) a laser beam processing head configured to direct a laser beam toward a workpiece during operation of the laser processing machine, the laser beam processing head comprising at least one deflecting mirror and a focusing mirror, wherein the focusing mirror is configured to alter a distance between a focal point of the laser beam and the workpiece in a direction of an axis of the laser beam during operation of the laser processing machine, (2) a laser processing nozzle mounted on the laser beam processing head, the laser processing nozzle comprising a laser nozzle body, and (3) a control unit, the method comprising:

moving the laser processing nozzle so that the nozzle body or a measuring probe mounted to the laser beam processing head laterally travels along and contacts a continuous edge of the workpiece during operation of the laser processing machine;

determining coordinates of the edge contacted by the laser nozzle body or by the measuring probe, wherein determining coordinates of the edge comprises performing an operation selected from the list consisting of i) detecting a short circuit between the workpiece and the nozzle body or the measuring probe when contacting the edge, ii) measuring a capacitance between the workpiece and the nozzle body or the measuring probe, and detecting contact with the edge based on the capacitance measured, and iii) combinations thereof;

based on the coordinates, determining a section of the edge that protrudes furthest from the workpiece; and

establishing a reference focal position FL of the laser beam based on the coordinates corresponding to the section of the edge that protrudes the furthest from the workpiece.