LASER MACHINING HEAD AND METHOD FOR MACHINING A WORKPIECE

Abstract

A laser machining head for machining a workpiece by means of a laser beam, includes: a scanning device for directing the laser beam at a plurality of positions on a workpiece surface; an image acquisition device for acquiring an image of the workpiece surface, said image acquisition device including an objective with a lens having an adjustable focal length; and a control configured to adjust a focal length of the lens based on a measurement value.

Claims

1. A laser machining head for machining a workpiece by a laser beam, comprising: a scanning device for directing said laser beam at a plurality of positions on a workpiece surface; an image acquisition device for acquiring an image of said workpiece surface, said image acquisition device comprising an objective with a lens having an adjustable focal length; and a control configured to adjust a focal length of said lens based on a measurement value.

2. The laser machining head according to claim 1, wherein said lens is a liquid lens and/or has a focal length range between 500 mm and +500 mm, between 500 mm and +333 mm or between 100 mm and +100 mm.

3. The laser machining head according to claim 1, wherein said image acquisition device comprises a camera or a gray image camera.

4. The laser machining head according to claim 1, wherein a beam path of said image acquisition device extends at least partially coaxially with said beam path of said laser beam.

5. The laser machining head according to claim 4, wherein said scanning device is arranged in an area in which said beam path of said image acquisition device extends coaxially with said beam path of said laser beam.

6. The laser machining head according to claim 1, wherein the measurement value is a distance measurement value of a distance between said laser machining head and said workpiece surface.

7. The laser machining head according to claim 6, further comprising: a distance measuring device for measuring the distance value.

8. The laser machining head according to claim 7, wherein said distance measuring device comprises at least one of the following devices: an optical coherence tomography (OCT) device, a lidar device, a ladar device, a ToF device, a conoscopy device, a light section device, a triangulation measuring device and a capacitive distance measuring device.

9. The laser machining head according to claim 1, wherein the measurement value is a contrast value of an image of said workpiece surface acquired by said image acquisition device.

10. The laser machining head according to claim 9, wherein said control is configured to determine a distance value of said laser machining head to said workpiece surface from the contrast value of the acquired image and a focal length set when acquiring the image.

11. The laser machining head according to claim 1, wherein: said control is configured to adjust the focal length of said lens in such a way that an area of said workpiece surface in which the measurement value was acquired lies in the focal plane of said image acquisition device; and/or said control is configured to control said image acquisition device in order to carry out an autofocus function.

12. The laser machining head according to claim 1, further comprising: a collimating optics for collimating said laser beam; and a focusing optics for focusing said laser beam; wherein at least a part of the focusing optics and/or the collimating optics is displaceable by means of an actuator; and wherein said control is configured to adjust a focal position of said laser beam based on the measurement value by controlling the actuator.

13. A method for machining a workpiece a laser beam via a laser machining head with an image acquisition device, which includes an objective with a lens having an adjustable focal length, said method comprising: acquiring a measurement value; adjusting the focal length of said lens based on the measurement value; and acquiring an image of said workpiece surface by means of said image acquisition device with the adjusted focal length.

14. The method according to claim 13, further comprising: acquiring the measurement value at a position on said workpiece surface which is to lie in the focal plane of said image acquisition device.

15. The method according to claim 13, wherein acquiring a measurement value comprises: acquiring a distance measurement value, wherein the focal length of said lens is adjusted based on the acquired distance measurement value; and/or acquiring a contrast value in an image of said workpiece surface, wherein the focal length of said lens is adjusted based on the acquired contrast value.

16. The method according to claim 13, further comprising: evaluating the acquired image and determining a machining position on the workpiece surface for said laser beam.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0059] FIG. 1 is a schematic view of a laser machining head according to an embodiment;

[0060] FIG. 2 is a schematic view of a laser machining head according to another embodiment;

[0061] FIG. 3 is a schematic view of a laser machining head according to yet another embodiment;

[0062] FIG. 4 is a schematic view of a laser machining head according to yet another embodiment; and

[0063] FIG. 5 is a flowchart that schematically illustrates a method according to an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0064] Unless otherwise noted, the same reference symbols are used below for the same elements and those with the same effect. A redundant description of recurring features and possibly a redundant use of recurring reference symbols are avoided as far as possible. The various embodiments and features of the figures described below can be expressly combined and are not to be understood as complete implementations.

[0065] FIG. 1 is a schematic view of a laser machining head 1 according to an embodiment. The laser machining head 1 for machining a workpiece, in particular a workpiece surface 3, by means of a laser beam 4 comprises a housing 6, in which at least one optics for guiding the laser beam 4 is arranged, e.g. a focusing optics 18 for focusing the laser beam 4 and/or a collimating optics 17 for collimating the laser beam 4. The laser beam 4 is coupled into the laser machining head 1 by means of a light guide 12, for example. In FIG. 1 the laser beam 4 is directed at a position on the workpiece surface 3 via a deflection minor 22. During the laser machining process, the laser machining head 1 may be guided over the workpiece surface 3 at a speed {right arrow over (v)} in order to guide the laser beam 4 along a machining path on the workpiece surface 3. The focusing optics 18 may be an F-Theta lens. A focal position of the laser beam 4 may be achieved by a motorized adjustment of at least a part of the collimation optics 17 and/or the focusing optics 18. For this purpose, at least a part of the collimation optics 17 and/or the focusing optics 18 may be displaced along the propagation direction of the laser beam 4 by a motor, for example by means of an actuator (not shown here). The laser beam 4 runs along the optical path 11 (of the laser beam).

[0066] Although the laser machining head 1 is shown as a fixed optics head in FIG. 1, the laser machining head 1 may be a scanner laser machining head. In this case, the laser machining head 1 may include a scanning device instead of the deflection mirror 22, for example as shown in FIG. 3.

[0067] Moreover, the laser machining head 1 of FIG. 1 includes an image acquisition device 5 for acquiring an image of the workpiece surface 3. The image acquisition device 5 may be a gray image camera, for example. The image acquisition device 5 includes an objective 52 with a lens 9 having an adjustable focal length. The lens 9 may be a liquid lens, for example. The lens 52 is used to project an image onto a sensor 51 of the image acquisition device 5. The beam path of the image acquisition device 5, i.e. the imaging beam path 8, extends between the sensor 51 and the workpiece surface 3 via the deflection mirror 16, through the lens 9, the beam splitter or dichroic mirror 15, the deflection mirror 22, the focusing optics 18 and the exit opening 19 of the laser machining head 1. Of course, the imaging beam path 8 may be configured without the deflection minor 16, e.g. when the sensor 51 is arranged on the optical axis of the lens 9. The imaging optical path 8 has a portion that is not overlapped with the optical path 11 of the laser beam 4 and a portion that is coaxial with the optical path 11 of the laser beam 4.

[0068] In addition, the laser machining head 1 of FIG. 1 includes a control 10 configured to adjust the focal length of the lens 9 based on a measurement value, for example in such a way that with the adjusted focal length of the lens 9, the focal position FL of the image acquisition device 5 corresponds to the current position of the laser beam 4 on the workpiece surface 3. The focal position FL may be changed, for example, by a change in focal length z. Focusing times of up to 5 ms can be achieved depending on the size of the focus tracking or focal length change of the lens 9.

[0069] The measurement value may comprise a measured distance value of a distance 7 between the laser machining head 1 and the workpiece surface 3. Optionally, an optional distance measuring device 13 for measuring the measured distance value may be provided as an external element or an element integrated into the laser machining head 1. The optional distance measuring device 13 is not specified in more detail in FIG. 1 and is arranged next to the laser machining head 1 by way of example. The distance measuring device 13 may be one of the following devices: an optical coherence tomography (OCT) device, a lidar device, a ladar device, a ToF device, a conoscopy device, a light section device, a triangulation measuring device or a capacitive distance measuring device. In this case, the lens 9, e.g. the liquid lens, may be driven on the basis of measured distance values, which are obtained, for example, by an OCT measurement.

[0070] The control 10 may be configured to determine a contrast value from the image acquired by the image acquisition device 5 and to adjust the focal length of the lens 9 based on the contrast value in an autofocus function. A distance value of the distance 7 between the laser machining head 1 and the workpiece surface 3 may also be determined from the contrast value and a focal length of the lens 9 set when acquiring the underlying image. Thus, as an alternative to control based on a measured distance value, the image may be focused or the lens 9 may be controlled for adjusting the focal length on the basis of contrast values in the image. In this case, the focal length of the lens 52 effectively determined therefrom itself may be used to determine the distance and this value may then be used, for example, to control a motor-adjustable part of the collimating optics 17 of the laser beam 4.

[0071] In summary, the control 10 may be configured to adjust a focal position of the laser beam 4 by adjusting the collimating optics 17 and/or the focusing optics 18 based on the measurement value, the measured distance value, the contrast value or the distance value.

[0072] FIG. 2 is a schematic view of a laser machining head 1 according to another embodiment. Specifically, the laser machining head 1 differs from that of FIG. 1 in that the distance measuring device 13 is implemented as an OCT device 13a. The OCT device 13a may be arranged behind the image acquisition device 5, for example. A beam path of the OCT device 13a may be coupled into the beam path 8 of the image acquisition device 5 via a deflection mirror 25. The OCT device 13a is configured to acquire the distance 7 between the workpiece surface 3 and the laser machining head 1 by means of optical coherence tomography.

[0073] While the laser machining head 1 is shown as a fixed optics head in FIG. 2, the laser machining head 1 may be a scanner laser machining head. In this case, the laser machining head 1 may include a scanning device 2 instead of the deflection mirror 22, for example as shown in FIG. 4.

[0074] FIG. 3 is a schematic view of a laser machining head 1 according to a another embodiment, wherein a scanning device 2 for directing the laser beam 4 at different positions on the workpiece surface 3 is additionally provided. For this purpose, the scanning device 2 includes, for example, two mirrors 20 that are movable, in particular rotatable and/or pivotable about different axes, so that the laser beam 4 can be guided over the workpiece surface 3 in two dimensions along a predetermined path. The other features of the embodiment of FIG. 3 are essentially the same as those of the embodiment of FIG. 1.

[0075] FIG. 4 is a schematic view of a laser machining head 1 according to another embodiment, wherein a scanning device 2 is provided as in FIG. 3. The laser machining head 1 of FIG. 4 differs from the laser machining head shown in FIG. 3 only in that the distance measuring device 13 is implemented as an OCT device 13a.

[0076] FIG. 5 schematically shows a method 100 according to an embodiment for machining a workpiece by means of a laser beam 4 by a laser machining head 1 with an image acquisition device 5 that includes an objective with a lens 9 that has an adjustable focal length. The method 100 includes: acquiring 110 a measurement value from or on the workpiece surface, adjusting 120 the focal length of the lens 9, e.g. a liquid lens, based on the acquired measured value, and acquiring 130 an image of the workpiece surface 3 by means of the image acquisition device 5, such as a gray image camera. The focal length of the lens 9 may be set, changed and/or adjusted by means of an actuator 14, for example.

[0077] In an example of a method 100 according to the present invention, the workpiece and/or the laser machining head may first be positioned. Then in step 110, for example by means of an OCT measuring device, a distance measurement may be carried out to acquire a measured distance value at a predetermined position of the workpiece, e.g. at the position of a marking or a specific feature on the workpiece surface 3. Based on the acquired measured distance value, the focal length of the lens 9 may be adjusted (step 120). In other words, the predetermined position on the work surface 3 may be brought into focus by adjusting the focal length of the lens 9. The image of the workpiece surface acquired in step 130 may be evaluated, e.g. by image processing, in order to determine a machining position of the laser beam 4 on the workpiece surface 3. Furthermore, the method 100 may include the step of directing the laser beam 4, e.g. by means of the scanning device 2, at the specific machining position.

[0078] In another example of a method 100 according to the present invention, the workpiece and/or the laser machining head may first be positioned. The image acquisition device 5 may then carry out (gray) image sharpening, e.g. via an autofocus function. For this purpose, for example, a contrast value of the workpiece surface 3 may be acquired by the image acquisition device 5 or the control 10 and the focal length of the lens 9 may be adjusted accordingly (step 120) in order to put the workpiece surface into focus. The image of the workpiece surface acquired in step may can in turn be evaluated, e.g. by image processing, in order to determine a machining position of the laser beam 4 on the workpiece surface 3. Furthermore, the method 100 may comprise the step of directing the laser beam 4, e.g. by means of the scanning device 2, at the specific machining position. Alternatively or additionally, the method may comprise: determining a distance value from the contrast value and, if necessary, the set focal length of the lens 9, and adjusting the focal position of the laser beam 4 based on the distance value, e.g. by displacing at least part of the focusing optics and/or the collimating optics by means of an actuator (not shown).

[0079] By using a lens with an adjustable or variable focal length, such as a liquid lens, in a lens for an image acquisition device of a laser machining head, in particular a scanner machining head, a sharp gray image can be achieved in each machining level. In addition, it is possible to set up a system with higher dynamics than with manual or motorized adjustment. The structure can also be made more compact and less expensive.

LIST OF REFERENCE SYMBOLS

[0080] 1 laser machining head [0081] 2 scanning device [0082] 3 workpiece surface [0083] 4 laser beam [0084] 41 beam path of the laser beam [0085] 5 image acquisition device [0086] 51 sensor [0087] 6 housing [0088] 7 distance between workpiece surface and laser machining head [0089] 8 imaging beam path or beam path of the image acquisition device [0090] 9 lens with adjustable focal length [0091] 10 control [0092] 12 light guide [0093] 13 distance measuring device [0094] 13a OCT measuring device [0095] 14 actuator [0096] 15 dichroic minor [0097] 16 deflection minor [0098] 16 beam splitter or dichroic minor [0099] 52 lens [0100] 17 collimating optics [0101] 18 focusing optics [0102] 19 exit opening [0103] 21 movable (rotatable/pivotable) mirror [0104] 22 deflection minor [0105] 25 deflection minor [0106] 100 method for machining a workpiece using a laser beam [0107] 110 acquiring a measurement value [0108] 120 adjusting the focal length of the lens based on the acquired measurement value [0109] 130 acquiring an image of the workpiece surface by means an image acquisition device with the adjusted focal length [0110] z focal length change [0111] h height h of machining on the workpiece surface relative to an arbitrary reference point, preferably in the z-direction [0112] FL focal position of the imaging beam path