Method for correcting optical path length measurement errors of measurement scanners in laser processing optics

Abstract

The invention relates to a method for correcting optical path length measurement errors of a measurement scanner (15) in a laser machining optics (10), in which a measurement beam (18) of the measurement scanner (15) for distance measurement is coaxially coupled into a machining laser beam (14) and is moved laterally on a workpiece in the surroundings of the machining laser beam (14) in an x-y plane, the method is characterized in that the distance values measured by the measurement scanner (15) at different measurement points (M1-M5) of the workpiece are corrected in the z direction by variation values ([delta] I1, [beta], [delta] I2, [beta], [delta] I3, [beta], [delta] I4, [beta]), the variation value is determined on the basis of a calculated or previously known optical path length of the measurement beam (18) at different selection points in the x-y plane.

Description

Background Art

[0001] In laser material processing, measuring scanners, in particular OCT measuring scanners, are increasingly being used as distance measuring sensors on laser processing devices. These sensors can be used to ensure that laser welding or laser marking takes place where desired. The measuring scanner scans the workpiece almost coaxially with the processing laser beam direction. In this case, the measuring beam can be deflected on the workpiece independently of the processing laser beam. The measured values ​​are evaluated by image processing facilities, which allows optical control of the process.

[0002] The optical path length of the measuring beam changes when the measuring beam is deflected laterally relative to the beam axis of the processing laser beam. One reason for the change in the optical path length is a geometric change in the path length due to an adjustment of the deflection angle of the measuring scanner mirror and / or the mirror of the laser processing optics. Another reason for the change in the optical path length of the measuring beam is that the glass penetration length of the measuring beam changes when the measuring beam passes through an optical element, such as an F-Theta objective. These two causes add up and lead to measurement errors. For example, if the measuring beam moves along a line over a flat upper surface, this line will appear curved in the image produced by the measuring scanner, even though it is straight.

[0003] The deflection of the measuring beam in the entire working volume of the laser processing device by the deflection mirrors of the laser processing optics is called a global change in the optical path length. This global change is usually a few millimeters. In contrast, if the measuring beam is only deflected in the surroundings of the processing laser beam by the deflection mirrors of the measuring scanner, the change in the optical path length is called a local change. The local changes are in the range of several hundred micrometers. For measuring systems that should have a resolution of ±50 micrometers, changes in this size range are a problem. Summary of the invention

[0004] The object of the present invention is to eliminate the influence of local optical path length changes on the measurement results of a measuring scanner in laser processing optics.

[0005] The object is achieved by a method for correcting optical path length measurement errors of a measuring scanner in laser processing optics, wherein the measuring beam of the measuring scanner for distance measurement is coupled coaxially into the processing laser beam and is moved laterally over the workpiece in the xy plane, characterized in that the distance values ​​measured by the measuring scanner at different sampling points of the workpiece are corrected in the z direction by variation values, wherein these variation values ​​are obtained based on calculated or previously known optical path lengths of the measuring beam at different selected points in the xy plane. Furthermore, the object is achieved by using an image processing facility of a laser processing device according to independent claim 9.

[0006] By carrying out this correction of the measured values ​​of the measuring scanner, distortions in the image of the workpiece generated by the measuring scanner can be eliminated. After this correction, the distance data of the workpiece are also accurate to a few micrometers in the z direction. In this case, the correction of the image is carried out directly after the measured values ​​are received.

[0007] The selected points correspond to different deflection angles of the measuring beam in the measuring scanner and / or in the laser processing optics. They are therefore directly related to the adjustment of the deflection mirrors in the measuring scanner and / or in the laser processing optics.

[0008] In a first method variant, the change values ​​for selected points can be stored in an image processing facility of the laser processing device. For this purpose, the image processing facility can contain various optics-specific correction data sets. With knowledge of the laser processing optics and the measuring scanner used, a corresponding correction data set can be selected and the change values ​​extracted from it, which are then applied to the measured values. Each correction data set contains the change values ​​of the optical path length for a large number of angular positions of the laser processing optics and the deflection mirrors of the measuring scanner, wherein the change values ​​can be stored in the form of a table.

[0009] In an alternative method variant, the change value can be obtained based on a simulation of the optical system formed by the laser processing optics and the measuring scanner by calculating the local change of the optical path length of the measuring beam at a plurality of selected points and determining a polynomial therefrom, which contains the coordinates of the laser processing optics and the measuring scanner and uses this polynomial to calculate the optical path length of the measuring beam at the measuring points of the measuring scanner. In this case, the actual optical path length of the measuring beam at the corresponding measuring point during the measurement is calculated and the change value of the measured value is determined therefrom.

[0010] In all method variants, the distance data of the measuring beam in the z direction at a measuring point not coinciding with a selected point can be corrected by a change value calculated by interpolating the change values ​​of the nearest selected points. It is therefore not necessary to determine these values ​​for a very large number of points in the method variant in which the change values ​​are stored, or to calculate the local change of the optical path length at a large number of selected points in order to determine a polynomial in the second method variant in order to achieve sufficient accuracy for the correction of the measured values.

[0011] In order to obtain an undistorted image of the workpiece, the image of the workpiece generated on the basis of the measurement data of the measuring scanner can be corrected by the image processing system by means of a geometric shearing method using a change value in the z direction. The shearing of the image is preferably performed row-wise in that each row is offset in the z direction by the change value of the optical path length.

[0012] In order to achieve the most precise possible correction result, the optical path length calculation is preferably carried out taking into account the geometry of the laser processing optics and the optical elements and their materials used in the laser processing optics and the measuring scanner, ie taking into account all parameters relevant to the optical path length. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] An exemplary embodiment of the method according to the present invention is explained in further detail below with reference to the accompanying drawings.

[0014] The accompanying drawings show:

[0015] Figure 1a , 1b Schematic diagram of the laser processing optics with a measurement scanner to account for global and local variations in the optical path length of the measurement beam;

[0016] Figure 2 A block diagram for correcting the measured values ​​for local variations in the optical path length;

[0017] Figure 3a -c Schematic diagram of the correction for local variations in the optical path length in the example of a line scan. DETAILED DESCRIPTION

[0018] 1 schematically shows a laser processing optical system 10 with three deflection mirrors 11, 12 and 13 for a processing laser beam 14 and a measuring scanner 15 with two deflection mirrors 16, 17 for a measuring beam 18. The deflection mirror 11 is fixed, but the deflection mirrors 12, 13 are adjustable. The measuring beam 18 is coupled coaxially into the processing laser beam 14 via the deflection mirror 11.

[0019] exist Figure 1a In the embodiment, the measuring beam 18 is deflected together with the processing laser beam 14 by the deflection mirror 13 relative to the vertical by an angle α, in that the deflection mirror 13 is adjusted by an angle α1. This results in an optical path length I of the measuring beam 18. 1,0 becomes a larger optical path length I 1,α The change value is ΔI 1,α =I 1,α -I 1,0 This is called the global change in optical path length and is typically a few millimeters.

[0020] On the contrary, Figure 1b In the embodiment, the measuring beam 18 is deflected by the deflection mirror 16 in the measuring scanner 15 relative to the vertical line by an angle β, in that the deflection mirror 16 is adjusted by an angle β1. This deflection results in that the optical path length I of the measuring beam 18 is 1,0 Change to I 1,β , where the change value is ΔI 1,β =I 1,β -I 1,0 This variation is called the local variation of the optical path length and is significantly smaller than the global variation of the optical path length and is in the range of 100 microns.

[0021] use Figure 2 The method shown eliminates the influence of local changes in the optical path length of the measuring beam 18 on the measured values ​​of the measuring scanner 15. The block diagram schematically shows the measuring scanner 15 with a drive 19 for the deflection mirrors 16, 17 of the measuring beam 18 and an image processing device 20. The image processing device 20 has a correction data set 21 for the optical path length, a calculation unit 22 for calculating the corrected measured values, and a memory 23 for the corrected measured values. With the help of the known angle adjustments α1, α2 of the deflection mirrors 13 and 12 of the laser processing optical system 10 and the angle adjustments β1, β2 of the deflection mirrors 16 and 17 of the measuring scanner 15, the change value ΔI of the optical path length can be read out from the correction data set 21. 1,β , ΔI 2,β , ΔI 3,β ..., and in the calculation unit these changes are applied to the measured values ​​from the memory of the drive 19 of the measuring scanner 15. The corrected measured values ​​resulting from the calculation are then stored in the memory 23 of the image processing facility 20. Based on the corrected measured values, an undistorted image of the workpiece to be machined by the machining laser beam 14 can be generated.

[0022] Figure 3a This is illustrated in the example where the measuring scanner 15 performs a line scan in the y direction. Figure 3a 3 shows an image of the line 30 without correction of the measured values ​​of the measuring scanner 15. Since no change in the optical path length of the measuring beam 18 is taken into account, the originally straight line appears curved in the z direction. The curvature is greatest at the end of the line 30, since the measuring beam 18 experiences its greatest deflection there.

[0023] Figure 3b The correction of the measured values ​​detected by the measuring scanner 15 is explained, which in the example shown are obtained by the measuring beam 18 at five measuring points M1 to M5 on the line 30. Here, the measuring points M1 to M5 are selected points on the line 30. At the measuring point M3, the measuring beam 18 is not deflected. In the measuring point M3, the optical path length has not changed, the measured value is correct and is not corrected. In contrast, at the other measuring points M1, M2, M4 and M5, the measured values ​​of the line 30 are changed in the z direction by the change ΔI of the optical path length of the measuring beam 18. 1,β , ΔI 2,β , ΔI 3,β , ΔI 4,β The result is Figure 3c 3c shows that after the correction of the measured values ​​of line 30, the line acquires a straight course according to straight line 30', as shown in 3c. After the correction, the z coordinates of all measuring points M1 to M5 are the same.

Claims

1. A method for correcting optical path length measurement errors of a measuring scanner (15) on a laser processing optical device (10), wherein: The measuring beam (18) of the measuring scanner (15) for distance measurement is coaxially coupled into the machining laser beam (14) and is moved transversely on the workpiece in the surroundings of the machining laser beam (14) in the xy plane, characterized in that the distance values ​​measured by the measuring scanner (15) at different measuring points (M1-M5) of the workpiece are varied in the z direction by a change value (ΔI 1,β , ΔI 2,β , ΔI 3,β , ΔI 4,β ) is corrected, wherein the variation value is obtained based on calculated or previously known optical path lengths of the measuring beam (18) at different selected points in the xy plane.

2. The method according to claim 1, characterized in that The selected points correspond to different deflection angles (β1, β2; α1, α2) of the measuring beam (18) in the measuring scanner (15) and / or in the laser processing optics (10).

3. The method according to claim 1 or 2, characterized in that: The change value (ΔI) for the selected point 1,β , ΔI 2,β , ΔI 3,β , ΔI 4,β ) is stored in an image processing facility (20) in the laser processing device.

4. The method according to claim 1 or 2, characterized in that: The change value (ΔI 1,β , ΔI 2,β , ΔI 3,β , ΔI 4,β ) is obtained based on a simulation of an optical system formed by the laser processing optical device (10) and the measuring scanner (15), in which the local changes of the optical path length of the measuring beam (18) at a plurality of selected points are calculated and a polynomial is determined therefrom, the polynomial containing the coordinates of the laser processing optical device (10) and the measuring scanner (15), and the optical path length of the measuring beam (18) at the measuring points (M1-M5) of the measuring scanner (15) is calculated using the polynomial.

5. The method according to any one of the preceding claims, characterized in that By the following change value (ΔI 1,β , ΔI 2,β , ΔI 3,β , ΔI 4,β ) to correct the distance data in the z direction at the measuring point (M1-M5) of the measuring beam (18) that is inconsistent with the selected point: the change value is obtained by calculating the change value (ΔI 1,β , ΔI 2,β , ΔI 3,β , ΔI 4,β ) is calculated by interpolation.

6. The method according to any one of the preceding claims, characterized in that Using the change value (ΔI 1,β , ΔI 2,β , ΔI 3,β , ΔI 4,β ), the image of the workpiece generated by the measurement data (19) of the measurement scanner (15) is corrected by the image processing facility (20) by a shearing method.

7. The method according to claim 6, characterized in that The image cropping method is performed in a column-by-column manner by calculating the change value (ΔI 1,β , ΔI 2,β , ΔI 3,β , ΔI 4,β ) for offset.

8. The method according to any one of the preceding claims, characterized in that An optical path calculation is performed taking into account the geometry of the laser processing optics (10) and the optical elements and their materials used in the laser processing optics (10) and the measuring scanner (15).

9. An image processing facility (20) of a laser processing device, for implementing the method according to claim 1.

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