Method for correcting the image-field plane of an optical scanner unit of a laser system

Abstract

The invention relates to a method for correcting the image-field plane (22) of an optical scanner unit (12) of a laser system with respect to a reference plane (24), which method comprises the method steps: a) identifying the position of the image-field plane (22) with respect to the reference plane (24), b) determining a correction value on the basis of the identified position of the image-field plane (22), c) correcting the image-field plane (22) using the correction value, in particular when the scanner processing head comprising the optical scanner unit (12) is stationary.

Description

[0001] Method for correcting the image field plane of a scanner optics of a laser system

[0002] The invention relates to a method for correcting the image field plane of a scanner optics of a laser system with respect to a reference plane.

[0003] Due to optical and mechanical tolerances, the scan field of a scanner optics of a scanner processing head can be tilted to a reference surface, which can lead to different focal positions in the scan field when processing flat components. This reduces the process window and can, for example, lead to different welding depths. A scan field is the area that can be scanned by a scanner optics by adjusting the focal point in two spatial directions. The scan field lies parallel to an image field plane. If it was previously determined that the image field plane was tilted to a reference plane, the scanner processing head was mechanically adjusted to align the image field plane as parallel to the reference plane as possible. It was often sufficient to align the image field plane with an accuracy of + / - 1 degree to the reference plane.Due to the development of lenses with large scan fields and increased requirements of the processes to be carried out, especially in electromobility, e.g. with regard to the welding depth when welding thin sheets, the inclination of the image field plane is becoming increasingly critical.

[0004] A mechanical correction of the alignment of the scanner processing head is known, for example, from WO 2020 / 161 462 A1.

[0005] The object of the present invention is to provide a method for correcting the image field plane, with which an image field misalignment can be corrected quickly and easily without additional mechanical components. This object is achieved according to the invention by a method for correcting the image field plane of a scanner optics of a laser system with respect to a reference plane, comprising the method steps: a. detecting the position of the image field plane with respect to the reference plane, b. determining a correction value based on the detected position of the image field plane, c. correcting the image field plane using the correction value, in particular with a stationary scanner processing head having the scanner optics.

[0006] A correction of the image field plane is, in particular, a change in the position or alignment of the image field plane. By “correction with a stationary scanner processing head having the scanner optics” is meant that the correction is carried out in particular without mechanically changing the connection of the scanner processing head, the alignment and / or position of the scanner processing head. The aim of the correction is to align the image field plane parallel to the reference plane. With the method according to the invention, it is possible to align the image field plane with an accuracy of 0.01 degrees relative to the reference plane without additional mechanical devices. The reference plane is, for example, the processing plane, in particular a workpiece surface of a flat workpiece. In particular, the invention makes it possible to tilt the image field plane of an objective without having to change the mechanical connection of the scanner processing head.

[0007] It has proven advantageous to record the position of the image field plane by taking a measurement value at at least three measuring points. By recording three measurement values ​​at three measuring points, it is possible to determine the orientation of the image field plane and thus determine how much the image field plane is tilted relative to a reference plane.

[0008] In particular, the measured values ​​can be recorded along one spatial direction.

[0009] For example, the measured values ​​can be recorded along an X-direction or a Y-direction of a Cartesian coordinate system. This makes it particularly easy to determine how the image field plane is tilted along a spatial direction.

[0010] If the measurement values ​​are recorded with the same radial deflection of the scanner optics, the influence of a scan field curvature of the lens can be neglected when determining the position of the image field plane.

[0011] If at least four measurements are taken, a tilt of the image field plane can be determined around both the Y and X axes. For example, the measurements can be taken at the largest possible + / - X deflection and + / - Y deflection.

[0012] Even greater accuracy is achieved when at least two measurement values ​​are acquired in one edge region of a scan field. The measurement values ​​are preferably acquired in two opposite edge regions of the scan field.

[0013] The tilt about the X or Y axis can be determined particularly easily if at least two measured values ​​are recorded along a first spatial direction, for example the X direction, and at least two measured values ​​are recorded along a second spatial direction, for example the Y direction.

[0014] The measured values ​​can be recorded, for example, by machining a workpiece using the scanner optics and then determining the welding depth at the measuring points. If, for example, a welding depth of 2.7 mm is measured at a measuring point along the Y-axis at +207 mm and a welding depth of 0.7 mm is measured at a measuring point along the Y-axis at -200 mm, the inclination of the image field plane is approximately 0.3 degrees. The image field plane is therefore tilted by 0.3 degrees with respect to the machining plane. To avoid having to mechanically tilt the scanner optics by exactly 0.3 degrees, a correction value corresponding to the 0.3 degree tilt can be determined to adjust the image field plane. As a result, i.e. when the correction value is applied, the welding depth is the same at all points in the scan field. The following generally applies: The welding depth can change in the scan field due to the curvature of the scan field and the angle of incidence of the laser beam on the workpiece.Before correction, the welding depth may be asymmetrical to the scan axes of the scanning optics. After correction, the welding depth may be symmetrical to the scan axes, especially taking into account the remaining scan field curvature and, for example, the incidence angle of the laser beam.

[0015] Alternatively, the measured values ​​can be determined by recording the distance of the focal point from the reference plane at the measuring points.

[0016] The measured values ​​can be used to determine the angle by which the image field plane is tilted relative to the reference plane. This angle can be used as a correction value.

[0017] Particular advantages arise when the focal point can be adjusted in a first and second spatial direction, particularly by two mirrors, and the correction of the image field plane is achieved by adjusting the focal point in a third spatial direction. This adjustment in the third spatial direction can be achieved, for example, by a telescopic arrangement with a first and second lens that are adjustable relative to one another. To correct the image field plane, it is therefore not necessary to adjust the entire scanner optics or the scanner processing head. The correction of the image field plane can be achieved by a correction in a third spatial direction, particularly in the Z direction.

[0018] The invention also includes a scanner processing head for a laser system with scanner optics, which is configured to carry out the method according to the invention. The scanner processing head can, for example, have a controller. Software can be implemented in the controller that, based on the acquired measured values ​​as described above, determines the inclination of the image field plane and a correction value that is taken into account in further processing tasks. Furthermore, the invention includes the use of a scanner processing head for the three-dimensional processing of workpieces for processing a two-dimensional workpiece, wherein the image field plane is aligned parallel to the workpiece when the scanner processing head is stationary.Such a scanner processing head for three-dimensional processing of workpieces is disclosed, for example, in EP 1 643 284 A1, the contents of which are incorporated by reference and which is incorporated into the subject matter of this patent application. When using the scanner processing head according to the invention, the method described above can be carried out.

[0019] Further advantages of the invention will become apparent from the description and the drawings. Likewise, the above-mentioned and further listed features can be used individually or in combination. The embodiments shown are not intended to be exhaustive, but rather serve as examples for describing the invention.

[0020] Fig. 1 shows a highly schematic view of a scanner processing head.

[0021] Figure 1 shows a scanner processing head 10 of a laser system. A focal point 18 of a laser beam 20 can be moved along an image field plane 22 via scanner optics 12, which in the illustrated embodiment has two scanner mirrors 14, 16. A scan field that can be traversed by the scanner optics 12 is parallel to the image field plane 22. Due to optical and mechanical tolerances, the image field plane 22 can be inclined with respect to a reference plane 24, as shown here. The reference plane 24 can, for example, be the surface of a flat workpiece. The scanner processing head 10 and the reference plane 24 are generally aligned to one another such that an ideal image field plane, i.e. when no optical or mechanical tolerances exist, is parallel to the reference plane 24.If a workpiece whose surface corresponds to the reference plane 24 were to be machined without correction of the image field plane 22, the laser beam 20 would be in focus at point 26. At point 28, however, the focal point 18 would be below the reference plane 24, and at point 30 the focal point 18 would be above the reference plane 24. By recording a measured value, for example the position of the focal point 18 at points 26, 28, 30, or by measuring a welding depth at points 26, 28, 30, it is possible to determine the angle a by which the image field plane 22 is tilted relative to the reference plane 24. From this angle, a correction value can be determined, according to which a device 32 is adjusted. In particular, a controller 34 can be provided in which software is implemented which determines a correction value from the recorded measured values ​​and uses the correction value to control the device 32.With the device 32, in particular the focusing of the laser beam 20, in particular the focus position, can be changed.

[0022] In the illustrated embodiment, the controller 34 is shown as a component of the scanner processing head 10. However, it can also be located at another location in the laser system.

[0023] In the illustrated embodiment, the scanner mirrors 14, 16 are arranged between a collimating lens 36 and a focusing lens 38, which constitute a first telescope arrangement. Arranged in the beam path in front of the first telescope arrangement is the device 32, which is designed as a second telescope arrangement with a first lens 40 and a second lens 42, wherein the first lens 40 and the second lens 42 are displaceable relative to one another in the beam direction. The second telescope arrangement can be arranged near an exit surface of a laser light cable. The second telescope arrangement can be designed as a Keppler telescope. In particular, the lenses 40, 42 can be designed as converging lenses. The second telescope arrangement can adjust the focal point 18 in one spatial direction, in particular a third spatial direction, which is perpendicular to the two spatial directions that span the image field plane 22.Because the lenses 40, 42 are small and lightweight, they can be adjusted particularly easily and quickly, allowing the image field plane 22 to be adjusted with the scanner processing head 10 stationary so that it lies parallel to the reference plane 24. The scanner processing head 10 can be provided, in particular, for three-dimensional workpiece processing. According to the invention, it can be used to machine a two-dimensional workpiece, in particular a flat workpiece surface, and to align the image field plane 22 parallel to the reference plane 24 by adjusting it in the Z-axis (by the device 32).

Claims

Patent claims 1 . Method for correcting the image field plane (22) of a scanner optics (12) of a laser system with respect to a reference plane (24), comprising the method steps: a. detecting the position of the image field plane (22) with respect to the reference plane (24), b. determining a correction value based on the detected position of the image field plane (22), c. correcting the image field plane (22) with the aid of the correction value, in particular in the case of a stationary scanner processing head (10) having the scanner optics (12).

2. Method according to claim 1, characterized in that in order to detect the position of the image field plane (22) a measured value is detected at at least three measuring points.

3. Method according to claim 2, characterized in that the measured values ​​are recorded with the same radial deflection of the scanner optics (12).

4. Method according to one of the preceding claims 2 or 3, characterized in that the measured values ​​are recorded along a spatial direction.

5. Method according to one of the preceding claims 2 to 4, characterized in that at least four measured values ​​are recorded.

6. Method according to one of the preceding claims 2 to 5, characterized in that at least two measured values ​​are recorded in an edge region of a scan field.

7. Method according to one of the preceding claims 2 to 6, characterized in that at least two measured values ​​are recorded along a first spatial direction and at least two measured values ​​are recorded along a second spatial direction.

8. Method according to one of the preceding claims 2 to 7, characterized in that the measured values ​​are recorded by machining a workpiece by means of the scanner optics (12) and determining the welding depth at the measuring points.

9. Method according to one of the preceding claims 2 to 7, characterized in that the measured values ​​are determined by detecting the distance of the focal point (18) from the reference plane (24) at the measuring points.

10. Method according to one of the preceding claims, characterized in that it is determined by which angle (a) the image field plane (22) is tilted relative to the reference plane (24).

11. Method according to one of the preceding claims, characterized in that the focal point (18) is adjustable, in particular by two mirrors, in a first and second spatial direction and the correction of the image field plane (22) is carried out by adjusting the focal point (18) in a third spatial direction.

12. The method according to claim 11, characterized in that the adjustment in the third spatial direction is carried out by a device (32), in particular a telescopic arrangement with a first and second lens (40, 42) which are adjustable relative to one another.

13. Scanner processing head (10) for a laser system with a scanner optics (12), which is designed to carry out the method according to one of the preceding claims.

4. Use of a scanner processing head (10) for three-dimensional Machining of workpieces for machining a two-dimensional Workpiece, wherein the image field plane (22) is aligned parallel to the workpiece when the scanner processing head is stationary.

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