Laser-processing head and laser-processing machine comprising same

Abstract

A laser processing head comprising a focusing device for focusing a processing laser beam onto a workpiece, the focusing device arranged in a processing beam path, an optical imaging device comprising a detector, wherein the optical imaging device is configured to image observation radiation from a processing region of the workpiece onto the detector along an observation beam path passing through the focusing device, a beam splitter for separating the observation beam path from the processing beam path of the processing laser beam, imaging optics arranged in the observation beam path between the beam splitter and the detector; and a stop arranged between the imaging optics and the detector, wherein the imaging optics produces an image of the stop in the processing beam path of the processing laser beam between the beam splitter and the workpiece.

Claims

1. A laser processing head comprising: a focusing device for focusing a processing laser beam onto a workpiece to be machined, wherein the focusing device is arranged in a processing beam path of the processing laser beam; an optical imaging device comprising a detector, wherein the optical imaging device is configured to image observation radiation from a processing region of the workpiece onto the detector along an observation beam path passing through the focusing device; a beam splitter for separating the observation beam path from the processing beam path; an imaging optics arranged in the observation beam path between the beam splitter and the detector; a stop arranged between the imaging optics and the detector, wherein the stop is spaced apart from the detector, and wherein the imaging optics is configured to produce an image of the stop in the processing beam path of the processing laser beam between the beam splitter and the workpiece; and a further optics arranged between the stop and the detector, the further optics being configured to image the processing region of the workpiece onto the detector.

2. The laser processing head of claim 1, wherein the imaging optics is configured to produce the image of the stop in the processing beam path between the focusing device and the workpiece.

3. The laser processing head of claim 1, wherein the imaging optics is configured to produce the image of the stop in the processing beam path between the beam splitter and the focusing device.

4. The laser processing head of claim 3, wherein the imaging optics is configured to produce the image of the stop in a focal plane of a focusing lens of the focusing device situated between the beam splitter and the focusing lens.

5. The laser processing head of claim 1, wherein the imaging optics is configured to produce the image of the stop within a focusing lens of the focusing device.

6. The laser processing head of claim 1, wherein the stop is displaceable in the observation beam path.

7. The laser processing head of claim 1, wherein an aperture of the stop is movable perpendicular to the observation beam path.

8. The laser processing head of claim 1, wherein the imaging optics comprises a telescope.

9. The laser processing head of claim 8, wherein the telescope is a Kepler telescope.

10. The laser processing head of claim 9, further comprising a second stop arranged in a common focal plane between a first lens and a second lens of the Kepler telescope.

11. The laser processing head of claim 10, wherein the first lens or the second lens, or both the first lens and the second lens of the Kepler telescope in the observation beam path from the beam splitter to the detector are displaceable in the observation beam path.

12. The laser processing head of claim 9, wherein a second stop is displaceable in the observation beam path while coupled to the second lens.

13. The laser processing head of claim 1, further comprising a second optics arranged between the stop and the detector, wherein the second optics is configured to image the processing region of the workpiece onto the detector.

14. A laser processing machine comprising: a laser processing head comprising: a focusing device for focusing a processing laser beam onto a workpiece to be machined, wherein the focusing device is arranged in a processing beam path of the processing laser beam; an optical imaging device comprising a detector, wherein the optical imaging device is configured to image observation radiation from a processing region of the workpiece onto the detector along an observation beam path passing through the focusing device; a beam splitter for separating the observation beam path of the observation radiation from the processing beam path of the processing laser beam; imaging optics arranged in the observation beam path between the beam splitter and the detector; and a stop arranged between the imaging optics and the detector, wherein the stop is spaced apart from the detector, and wherein the imaging optics is configured to produce an image of the stop in the processing beam path of the processing laser beam between the beam splitter and the workpiece, a further optics arranged between the stop and the detector, the further optics being configured to image the processing region of the workpiece onto the detector, and a beam source for producing the processing laser beam.

15. The laser processing head of claim 1, wherein the further optics is a lens.

16. The laser processing machine of claim 14, wherein the further optics is a lens.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic illustration of an example of an embodiment of a laser processing machine having a laser processing head for process observation, wherein the laser processing head has an optical imaging device with a stop that is imaged into a focusing lens.

(2) FIG. 2 is a schematic illustration of another embodiment of a laser processing machine where the stop is imaged into a focal plane of the focusing lens.

(3) FIG. 3 is a schematic illustration of another embodiment of a laser processing machine where the stop is imaged between the focusing lens and a workpiece surface.

(4) FIG. 4 is a schematic illustration of another embodiment of a laser processing machine where a further stop is arranged in a focal plane between a first lens and a second lens of a Kepler telescope of the optical imaging device.

(5) In the following description of the drawings, identical reference signs are used for equivalent or functionally equivalent components.

DETAILED DESCRIPTION

(6) FIG. 1 shows an example of a structure of a laser processing head 1 as described herein with a focusing device in the form of a focusing lens 2 that focuses a processing laser beam 3 onto a workpiece 4. In the shown example, the workpiece 4 has a workpiece surface 4a at a distance from the focusing lens 2 that corresponds to the focal length f.sub.1 or the object distance s.sub.1 of the focusing lens 2. The laser processing head 1 moreover has an optical imaging device 5 with a detector 6. Optics 7 in the form of a lens is at the distance of its focal length f.sub.4 or object distance s.sub.4 from the detector 6. Together with the focusing lens 2, the optics 7 image the workpiece surface 4a (the object plane of the optical imaging device 5), onto an image plane or the radiation-sensitive surface 6a of the detector 6.

(7) Observation radiation 8 (e.g., process radiation), which emanates from a processing region 9 of the workpiece 4, is imaged onto the detector 6 along an observation beam path 10 with the aid of the optical imaging device 5. The observation beam path extends along an optical axis which corresponds to the laser beam axis 11 of the processing laser beam 3 in a section between the focusing lens 2 and the workpiece 4. In the processing region 9, the workpiece 4 is pierced by the processing beam 3 in the example shown; however, other processing processes, such as cutting or welding processing, may be performed on the processing region 9. As shown in FIG. 1, the observation beam path 10 extends from the workpiece 4 through a processing nozzle 12 and through the focusing lens 2 in a manner coaxial to the laser beam axis 11 of the processing laser beam 3. The section of the workpiece 4 in the processing region 9 is imaged on the detector 6 is delimited on the edge by the internal contour of the processing nozzle 12.

(8) Within the laser processing head is a beam splitter 13, which can be a wavelength-selective optical element or a beam splitter mirror with a wavelength-selective coating, that separates the observation beam path 10 of the observation radiation 8 from the processing beam path 14 of the processing laser beam 3. In the example shown, the beam splitter 13 reflects the processing laser beam 3 and transmit the observation radiation 8, which has a different wavelength to the processing laser beam 3. In some embodiments, the deflection of the processing laser beam 3 at the beam splitter 13 may be depend on the type of the wavelength-selective coating and can be at an angle other than 90.

(9) The optical imaging device 5 has an imaging optics in the form of a Kepler telescope 16, which has a first lens 16a in the observation beam path 10 from the beam splitter 13 to the detector 6 and a second lens 16b in the observation beam path 10 from the beam splitter 13 to the detector 6. The first lens 16a of the Kepler telescope 16 has focal length f.sub.2 and the second lens 16b of the Kepler telescope 16 with the focal length f.sub.3. The two lenses are arranged at a distance from one another corresponding to the sum of their focal lengths f.sub.2+f.sub.3. The Kepler telescope 16 produces an image 15a in the focusing lens 2 of a stop 15. The distance s.sub.3 between the stop 15 and the second lens 16b corresponds to the focal length f.sub.3 of the second lens 16b and it is matched to the distance s.sub.2 between the first lens 16a and the focusing lens 2 in such a way that the stop 15 is imaged in focus into the focusing lens 2. As may likewise be seen in FIG. 1, the stop 15 is imaged in the focusing lens 2 in a magnified manner due to the Kepler telescope 16.

(10) The image 15a of the stop 15 acts on the imaging of the processing region 9 on the detector 6 by the optical imaging device 5 as if the stop 15 were arranged in the focusing lens 2 in the processing beam path 14 of the processing laser beam 3. The aperture of the image 15a of the stop 15 in this case only has a small, radially interior region of the focusing lens 2, in which the thermal load on the focusing lens 2 is distributed in a uniform or homogeneous manner. Therefore, only object points of the processing region 9, for the imaging of which substantially the same refractive index change of the focusing lens 2 becomes effective, are imaged, and so the thermal lens does not have a substantial effect on the imaging of the processing region 9 on the detector 6.

(11) The laser processing head 1 shown in FIG. 1 is used to carry out a laser processing process for processing the workpiece 4 in a laser processing machine 20. The laser processing machine 20 has a beam source 21 for producing the processing laser beam 3 and further components, not illustrated for simplification, which facilitate the workpiece processing, e.g., the generation of a relative movement between the laser processing head 1 and the workpiece 4. The beam source 21 can be a CO.sub.2 laser source, a solid-state laser source, a diode laser source or a different type of laser source.

(12) In the shown example, the second lens 16b of the Kepler telescope 16 is displaceable along the observation beam path 10, more precisely along the optical axis 11, by an actuator (not shown here), as indicated in FIG. 1 by a double-headed arrow. In the case of a change in focal length of the focusing lens 2, caused for thermal reasons, or in the case of a change of the distance 51 between the workpiece 4 and the focusing lens 2 of the laser processing head 1, there is a change in the position of the intermediate image of the processing region 9 which is produced without such a thermal lens or load in a common focal plane 17 between the two lenses 16a, 16b of the Kepler telescope 16. By displacing the second lens 16b of the Kepler telescope 16, the intermediate image once again lies in the focal plane 17 of the second lens 16b and the beam is collimated downstream of the lens 16b and passes through the stop 15 in collimated fashion. Additionally, the stop 15 may likewise be arranged in a displaceable manner in the observation beam path 10 to correct the error in the position of the virtual stop 15a, which arises from the change in focal length of the focusing lens 2 caused by thermal reasons.

(13) A laser processing head 1, which likewise facilitates an improved process observation, is illustrated in FIG. 2. The laser processing head 1 shown in FIG. 2 differs from the laser processing head 1 shown in FIG. 1 by virtue of the imaging optics (e.g., Kepler telescope 16) imaging the stop 15 not into the focusing lens 2, but into the processing beam path 14 of the processing laser beam 3 between the focusing lens 2 and the beam splitter 13. Specifically, the image 15a is imaged onto the (image-side) focal plane 18 of the focusing lens 2 as shown, with the object-side and image-side focal lengths f.sub.1 of the focusing lens coinciding. Both the processing laser beam 3 and the observation radiation 8 are collimated between the beam splitter 13 and the focusing lens 2. When arranging the image 15a of the stop 15 in the focal plane 18 of the focusing lens 2, the object plane or the workpiece surface 4a is imaged in a telecentric manner on the detector 6 by the optical imaging device 5, if the focusing lens 2 is not loaded or only slightly loaded thermally.

(14) An intermediate image of the workpiece surface 4a (the object plane) that contains the processing region 9 is produced by the focusing lens 2 in the focal plane 18 thereof that faces away from the workpiece 4. The image 15a of the stop 15 is produced in the focal plane 18. Changes in the object distance s.sub.1, (in the distance between the workpiece surface 4a and the focusing lens 2), do not affect the imaging in this case since the magnification does not change with the object distance in the case of telecentric imaging so that the imaged region of the workpiece surface 4a containing the processing region 9 remains unchanged.

(15) To compensate for the influence of the focal length change of the focusing lens 2 in the case of a thermal load on the imaging of the workpiece surface 4a or of the processing region 9, the stop 15 is arranged in the observation beam path 14 in such a way that the Kepler telescope 16 images the stop at a position in the observation beam path 10 which lies between the focal plane 18 of the thermally unloaded focusing lens 2 and the focusing lens 2 itself. The thermal load on the focusing lens 2 leads to a shortened focal length f.sub.1 compared to the focal length f.sub.1 in the thermally unloaded state; this length can be determined by computation, depending on the strength of the laser power. Therefore, if the laser power is known, the position of the stop 15 in the observation beam path 10 can be selected such that the image 15a of the stop 15 lies in the focal plane (not shown here), displaced in the direction of the focusing lens 2, of the thermally loaded focusing lens 2 with a shortened focal length f.sub.1, and so there is telecentric imaging of the processing region 9 or the workpiece surface 4a onto the detector 6, even during the laser processing. To maintain the image 15a of the stop 15 in the focal plane 18 of the focusing lens 2, the stop 15 and either the Kepler telescope 16 or at least one of the telescope lenses 16a, 16b optionally may be displaced with the aid of one or more actuators (not shown here) in the observation beam path 10.

(16) On the basis of a model of the focal length f.sub.1, f.sub.1 of the focusing lens 2 that depends on the laser power of the processing laser beam 3, a control device 22 of the laser processing machine 20 can always set the displacement path of the stop 15 and of the Kepler telescope 16 or of the first telescope lens 16a or the second telescope lens 16b in such a way that the image 15a of the stop 15 is imaged in the focal plane 18 of the focusing lens 2, the focal plane varying in terms of its position along the beam axis 11 of the processing laser beam 3. Displaceability of the stop 15 is not necessary if the errors in the positioning of the virtual stop 15a as a result of the thermally induced change in focal length of the focusing lens 2 are small.

(17) FIG. 3 shows a laser processing machine 20 having a laser processing head 1, in which the imaging optics in the form of the Kepler telescope 16 produces an image 15a of the stop 15 between the focusing lens 2 and the workpiece surface 4a in the processing beam path 14 of the processing laser beam 3. By this imaging it is possible to correct an object plane or workpiece plane 4a that is not perpendicular to the beam axis 10 of the processing laser beam 3 since the object points of the processing region 9 at the workpiece surface 4a lying further to the outside are imaged by a lens region of the focusing lens 2 lying further to the inside in the case where the image 15a of the stop 15 is positioned between the workpiece 4 and the focusing lens 2.

(18) In the example shown in FIG. 4, the stop 15 is imaged into the focusing lens 2. In contrast to the laser processing head 1 shown in FIG. 1, the Kepler telescope 16 of the optical imaging device 5 has a further stop 19 (near field stop) in a focal plane 17 of the Kepler telescope 16 between the first lens 16a and the second lens 16b. The further stop 19 serves to reduce the influence of parasitic stray radiation on the imaging. Reflected radiation components from optical elements in the processing beam path 14 of the processing laser beam 3, e.g., from the surfaces of the focusing lens 2 which are not reflected at a parallel angle to the chief ray of the observation radiation 8, are masked by the further stop 19 and do not reach the detector 6.

(19) In the laser processing head 1 shown in FIG. 4, the further stop 19 and the second lens 16b are coupled to one another and displaceable in the observation beam path 10, and can be displaced without changing their relative spacing along the optical axis 11 of the observation beam path 10. An actuator, which is indicated by a double-headed arrow in FIG. 4, may serve for the common displacement of the further stop 19 and the second lens 16b. In a manner analogous to the example shown in FIG. 1, in the example shown in FIG. 4, by displacing the unit made of second lens 16b and further stop 19, the further stop 19 can be arranged exactly in the intermediate image in the focal plane 17 of the Kepler telescope 16 that has been displaced along the optical axis 11 in the case of a thermally induced change in the focal length f.sub.1 of the focusing lens 2 or in the case of a change in the object distance s.sub.1.

(20) Moreover, in the laser processing head 1 shown in FIG. 4, the stop 15 is perpendicular to the observation beam path 10, or to the optical axis 11 thereof, (displaceable in the plane of the stop) in the observation beam path 10. By displacing the stop 15, it is possible to set the portion of the focusing lens 4 by which the imaging of the processing region 9 on the detector 6 is effectuated. In this way, it is possible to change the observation direction or the observation angle. The stop 15 may alternatively or additionally be rotated about an axis of rotation extending parallel to the optical axis 11, as a result of which it is likewise possible to adjust the position of an aperture of the stop 15 in the stop plane.

(21) The accuracy of the process observation during the laser material processing (for example during laser cutting or laser welding) is thus improved. Additionally, the process observation can be flexibly adapted to the process conditions where necessary. It is understood that the imaging optics 16 need not necessarily be embodied as a Kepler telescope and it may also have reflecting optical elements in addition to transmitting optical elements or, where necessary, it may consist of reflecting optical elements only. Additionally, the beam splitter 13 is not necessarily embodied as a wavelength-selective optical element but may be embodied, for example, as a geometric beam splitter, e.g. in the form of a scraper mirror or the like. The focusing device need not necessarily consist of a focusing lens but may, for example, have a lens group for focusing the processing laser beam 3 or contain, or consist of, reflecting optical elements. It is understood that the examples explained further above apply analogously in the case of a focusing device in the form of a lens group, wherein the focal length f.sub.1 of the focusing lens 2 is replaced by the overall focal length of the lens group for the observations above. Additionally, the lenses 16a, 16b of the imaging optics 16 naturally may be embodied as lens groups, wherein the respective focal lengths f.sub.2 and f.sub.3 of the lenses 16a, 16b are replaced by the overall focal length of the respective lens group for the observations made above. The control of the displacement of the lenses 16a, 16b of the imaging optics 16, the control of the displacement or movement of the stop 15 and, optionally, of the further stop 19 is effectuated by the control device 22 of the laser processing machine 20. To this end, the control device 22 can, where necessary, resort to information about the thermally induced focal length change in the focusing lens 2.

Other Embodiments

(22) It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.