Device for machining a workpiece using a deflectable laser beam

Abstract

Device for workpiece processing by means of a deflectable laser beam, comprising a laser beam source (1) for emitting a laser beam (2), a controllable deflection unit (5) which is designed to deflect the incident laser beam (2) in the xy direction, a focusing lens (6) and a controllable, deformable mirror (3) for focus position correction, wherein the focusing lens (6) is arranged downstream of the deflection unit (5) in the laser beam direction, characterized in that the deflection unit (5) has a deflection mirror (5.1) which is tiltable about two axes and is firmly connected to the focusing lens (6) via a rigid connecting member (7), wherein the deflection mirror (5.1) and the focusing lens (6) are fixed in such a relative position to one another that the laser beam (2) reflected by the deflection mirror (5.1) runs in the direction of an optical axis of the focusing lens (6).

Description

[0001] The invention relates to a device of the type known from DE 44 24 492 A1.

[0002] A variety of devices for laser workpiece processing are known from the prior art. These devices guide a focused laser beam across a workpiece surface. The majority of these devices have a deflection unit, which generally consists either of a mirror that can be tilted about two mutually perpendicular axes or of two mirrors, each tiltable about an axis, with the axes being perpendicular to one another. With such a deflection unit, a focused laser beam incident on it can be deflected in the xy direction in such a way that the laser focus is moved over a large area, depending on the maximum deflection angle.Regardless of whether the means required to focus the laser beam are arranged before or after the deflection unit in the beam path, or whether the deflection unit itself also serves to focus the beam by using concave mirrors instead of merely beam-deflecting plane mirrors, the focal point of a focused laser beam describes a spherical shell-shaped surface when deflected by such a deflection unit. This means that the focus moves with an intended deflection in the xy direction depending on the deflection angle in the z direction.

[0003] To machine a flat workpiece surface or a workpiece surface that is not spherical in shape, it is necessary to shift the focus position with a change in the deflection angle so that the focus point of the workpiece surface is located at every point where the laser beam hits the workpiece surface. For certain applications, it may also be interesting to have the focus point at a defined distance from the workpiece surface instead of on the workpiece surface, for example if effects are not intended on the workpiece surface but rather inside the workpiece. Therefore, when reference is made below to means or measures for focus position correction, this should not only mean a focus position correction on a workpiece surface, but a focus position correction in a desired plane, in a defined position relative to the workpiece surface.

[0004] In order to avoid contamination of optical components, in particular a focusing lens, during processing, a nozzle body can be arranged downstream of a focusing lens through which a laser beam is guided, as disclosed in DE 38 07 471 A1.

[0005] The use of devices for workpiece processing by means of lasers in combination with robot arms is well known from the prior art, e.g. from EP 1 093 881 A2.

[0006] Devices of this type are understood to be materials processing devices that comprise a laser beam source, movable means for controlled beam deflection (deflection unit), focusing means, means for changing the focus position depending on the deflection angle (focus position correction means), and beam deflection means for guiding a laser beam from the laser beam source to the deflection unit. These means can be formed by identical or different elements or assemblies.

[0007] EP 1 228 835 B1 discloses a device comprising all of the aforementioned means. A laser beam source (here, a laser generator) is followed in the beam direction by a beam focusing means (here, a focusing lens), a beam deflection means (here, a fixed mirror), and a deflection unit (here, a mobile mirror). The focusing lens serves as the means for correcting the focus position; it can be moved along its optical axis depending on the deflection angle. The possible range of movement of the laser focus in space is limited by the deflection angle of the mobile mirror.

[0008] DE 100 27 148 A1 discloses a device for machining a workpiece by means of a focusable laser, wherein an adaptive focusing mirror is arranged in front of a gimbal-mounted and two-dimensionally adjustable scanner mirror, which serves as a deflection mirror.

[0009] Another device for machining a workpiece using a focusable laser is disclosed in DE 100 33 846 A1, wherein the deflection mirror is adjusted by three linear motors via a three-point bearing.

[0010] A device described in WO 2007 / 079760 A1 is intended to improve the aforementioned device, in particular by giving the laser focus a larger range of movement in space. For this purpose, the device is designed such that the laser beam, which according to EP 1 228 835 B1 can be deflected about two axes only by means of the deflection unit, can be rotated about two additional axes. This inevitably results in the need to use three deflection elements as a means for beam deflection instead of one deflection element. As a means for beam focusing, one of the deflection elements, all of which are arranged in front of the deflection unit in the beam direction, is designed as an ellipsoidal mirror, while a second deflection element is formed by a deformable mirror as a means for focus position correction.

[0011] DE 44 24 492 A1 discloses a device in which a focusing lens arranged in the beam direction in front of a deflection unit is provided as a means for focusing and a controllable deformable mirror for focus position correction is provided in the beam path in front of the focusing lens.

[0012] The deformable mirror can be controlled via an electronic control and regulating device in such a way that the curvature of the mirror surface is adjusted in dependence on the change in the deflection angle of the deflection unit and thus in dependence on the change in the distance of a focus point unaffected by the deformable mirror from the workpiece surface in the direction of the laser beam axis in such a way that the focus point is shifted along the laser beam axis onto the workpiece surface.

[0013] All of the aforementioned devices have the disadvantage that, due to the early focusing of the laser beam in the beam path, the laser beam impinges on the subsequent optical components with a comparatively smaller beam cross-section and a higher radiance, thus leading to greater thermal stress on these components. The thermal stress is determined not only by the absolute heat input, but in particular by the temperature gradient that arises across the optically effective surface. The varying degrees of heating of the surface result in varying degrees of material expansion and geometric changes in the optically effective surfaces, which leads to an additional, cumulative focus position shift across the affected components. This shift, however, occurs in an uncontrolled manner and therefore cannot be compensated for by a focus position correction that depends on the deflection angle.

[0014] A generic device for correcting the position of a laser beam with a downstream focusing lens is disclosed in US Pat. No. 4,707,596 A. There, the position of a laser beam is adjusted using several deflecting mirrors. However, the system does not have any additional means for correcting the focus position.

[0015] US 2005 / 0247682 A1 discloses a generic device for workpiece processing using a deflectable laser beam, comprising a laser beam source for emitting a laser beam, a controllable deflection unit (second galvano scanner) designed to deflect the incident laser beam in the xy direction using two deflection mirrors, each rotatable about an axis, a focusing lens, and two controllable, deformable mirrors for focus position correction. The focusing lens is arranged downstream of the deflection unit in the laser beam direction.

[0016] The device has the disadvantage that it has two deflecting mirrors, each of which can only rotate around a single axis. This means that the focusing lens, with a rigid connection to one of the mirrors, can only be moved in one of the two directions, the x or y direction.

[0017] The invention is based on the object of creating a generic device in which a focus position shift due to thermal stress on the optically active components is reduced by the action of the laser beam.

[0018] This object is achieved with a device for workpiece processing by means of a deflectable laser beam, which device comprises a laser beam source for emitting a laser beam, a controllable deflection unit which is designed to deflect the incident laser beam in the xy direction, a focusing lens and a controllable, deformable mirror for focus position correction, wherein the focusing lens is arranged downstream of the deflection unit in the laser beam direction and the deflection unit has a deflection mirror which is firmly connected to the focusing lens via a rigid connecting member.

[0019] By arranging the focusing lens behind the deflection unit, the laser beam is guided to the deflection unit as a nearly parallel beam bundle, reducing the radiance of the laser beam when it strikes optically effective components, such as a deflection mirror or the deflection mirror. To further reduce the radiance, a telescope can be arranged downstream of the laser beam source to expand the laser beam. A laser beam source within the meaning of the invention is understood to be a laser, optionally with upstream beam-shaping optics that shapes the laser beam emitted by the laser into a parallel laser beam.

[0020] The deflection unit consists of a single mirror, which allows it to be connected to a focusing lens via a fixed connection, allowing the focusing lens to move along with the deflection movement of the deflection mirror. The deflection mirror and the focusing lens are fixed relative to each other in such a way that a laser beam reflected by the deflection mirror travels in the direction of the optical axis of the focusing lens.

[0021] In order to deflect the laser beam in the xy direction with only one deflection mirror, the deflection mirror must be able to tilt around two axes.

[0022] The deflection mirror is advantageously mounted on a gimbal and connected to two rotary drives that can be controlled separately. Alternatively, the deflection mirror can advantageously be connected via a three-point bearing to three linear drives, which can also be controlled separately.

[0023] Advantageously, at least one plane mirror for beam deflection is present between the deformable mirror and the deflecting mirror, which can be tilted about an axis.

[0024] Advantageously, the laser beam source and the deformable mirror are arranged rigidly relative to one another in a robot base to which a multi-jointed robot arm is attached. In this robot base, the laser beam is guided via the plane mirrors arranged in the joints, and the deflection unit is located at the free end of the multi-jointed robot arm. The deformable mirror and the control system required for it are heavier than simple plane mirrors, which is why its arrangement in the robot base, where its weight does not have to be moved with the robot arm, is advantageous. The laser beam reflected by the deformable mirror is weakly convergent and changes its convergence angle depending on the deformation of its surface, which changes with the change in the deflection angle.

[0025] However, the convergence is so small that the laser beam is nearly parallel along the beam path up to the deflection unit, and the cross-section of the laser beam is almost identical when it strikes the plane mirrors and the deflection mirror. The number of joints, and thus the number of deflection mirrors, determines the degrees of freedom with which the free end of the multi-joint robot arm can move in space. The focus of the laser beam can thus execute a compound movement, determined by the movement of the multi-joint robot arm and the deflection unit.

[0026] Compared to devices of the same type, a workpiece can be machined more precisely with a device according to the invention, since the laser focus can be guided precisely to the workpiece.

[0027] It is advantageous to have a nozzle located behind the focusing lens in the direction of the laser beam and fixed to it. A shielding gas can be supplied through the nozzle in the direction of the laser beam striking the workpiece, or exhaust gases and particles can be extracted. Particles moving from the workpiece toward the focusing lens are largely deflected by the outer surface of the nozzle, thus preventing contamination of the focusing lens.

[0028] The device is explained in more detail below using the drawing as an example.

[0029] They show: Fig. 1 a schematic diagram of a device Fig. 2a a first embodiment of a deflection unit Fig. 2b a second embodiment of a deflection unit

[0030] Like generic devices, a device according to the invention serves to process a workpiece with a laser beam 2, wherein the device is designed such that the focus of the laser beam 2 can be guided in a defined plane to the workpiece, which can be the workpiece surface.

[0031] A device according to the invention according to Fig. 1 comprises a laser beam source 1 which emits a laser beam 2 and, arranged one after the other in the beam path in the direction of radiation: a controllable, deformable mirror 3, for example four deflecting mirrors 4, a deflection unit 5 and a focusing lens 6 which is firmly connected to the deflection unit 5 via a rigid connecting member 7.

[0032] From an optical perspective, the arrangement of the focusing lens 6 in the beam path behind the deflection unit 5 has the effect that all previous components in the beam path are exposed to a virtually identical beam cross-section of the laser beam 2 and are therefore subject to a lower thermal load compared to the arrangement of the focusing lens 6 at an earlier point in the beam path. In the illustrated embodiment, the deflection mirrors 4 are each rotatable about an axis, thus increasing the range of motion of the laser beam 2 across the workpiece.

[0033] However, the device can also comprise no, fewer, or more deflection mirrors 4, which serve only to couple the laser beam 2 reflected by the deformable mirror 3 into the deflection unit 5. However, the optical advantage of a device according to the invention is hardly effective here, since apart from the deflection mirror 5.1, no further optical component follows the deflection unit 5, which would need to be protected from excessive thermal stress.

[0034] From a mechanical point of view, the arrangement of the focusing lens 6 as the last optical component has the advantage that a nozzle 8 can be attached to it or to its mount, which nozzle 8 envelops the beam path after the focusing lens 6.

[0035] For example, during welding, a shielding gas can be advantageously supplied to the processing site via nozzle 8 to support laser processing. Alternatively, gases generated during cutting can be extracted. In either case, the final component, in this case the focusing lens 6, can be largely protected from contamination caused by workpiece processing.

[0036] A device according to the invention thus combines the advantages of conventional devices in which the laser beam is moved via a deflection unit with the advantages of a laser head with a nozzle guided by a robot arm. Conventional devices with deflection units enable very high processing speeds within a limited working area, but the supply of shielding gas or the extraction of gases generated during processing are not possible using simple means.

[0037] Devices with a laser head guided by a robot arm can be used for larger work areas and a nozzle that can be mounted on the laser head offers the advantages mentioned, but the processing speed is limited by the inertia of the robot arm.

[0038] In principle, the deformable mirror 3 can be arranged instead of each of the deflecting mirrors 4, but this has the disadvantage that its mass, which is greater than that of a simple deflecting mirror 4, which can be a thin plane mirror, must be moved along.

[0039] The deflection unit 5 comprises only one deflection mirror 5.1, which can be tilted about two axes.

[0040] In a first embodiment, the deflection mirror 5.1, or the mount in which the deflection mirror 5.1 is mounted, is to be mounted in a gimbal with two pivot axes. The two pivot axes are connected to separately controllable drives.

[0041] In a second embodiment, the deflection mirror 5.1 is connected to a separately controllable linear drive via three joints provided on its circumference or the circumference of a mount in which the deflection mirror 5.1 is mounted.

[0042] The device can advantageously be designed as a robot with a fixed robot base to which a multi-joint robot arm is attached and at whose free end the deflection unit with the focusing lens 6 and a nozzle 8 firmly connected to it is arranged. List of reference symbols 1 laser beam source 2 laser beam 3 deformable mirrors 4 deflecting mirrors 5 Deflection unit 5.1 Deflecting mirror 6 Focusing lens 7 connecting link 8 nozzle

Claims

[1] Device for workpiece machining by means of a deflectable laser beam, comprising a laser beam source (1) for emitting a laser beam (2), a controllable deflection unit (5) which is designed to deflect the incident laser beam (2) in the xy direction, a focusing lens (6) and a controllable, deformable mirror (3) for focus position correction, wherein the focusing lens (6) is arranged downstream of the deflection unit (5) in the laser beam direction, characterized by that the deflection unit (5) has a deflection mirror (5.1) which can be tilted about two axes and is firmly connected to the focusing lens (6) via a rigid connecting member (7), wherein the deflection mirror (5.1) and the focusing lens (6) are fixed in such a relative position to one another that the laser beam (2) reflected by the deflection mirror (5.1) runs in the direction of an optical axis of the focusing lens (6). [2] Device according to claim 1, characterized bythat a nozzle (8) is arranged behind the focusing lens (6) in the laser beam direction and is fixed to the latter. [3] Device according to claim 1, characterized by that the deflection mirror (5.1) is mounted in a gimbal suspension and is connected to two rotary drives. [4] Device according to claim 1, characterized by that the deflection mirror (5.1) is connected to three linear drives via a three-point bearing. [5] Device according to claim 1, characterized by that between the deformable mirror (3) and the deflection mirror (5.1) there is at least one deflection mirror (4) which can be tilted about an axis. [6] Device according to claim 5, characterized by , that the laser beam source (1) and the deformable mirror (3) are arranged rigidly relative to one another in or on a robot base to which a multi-joint robot arm is attached, in which the laser beam (2) is guided via the deflection mirrors (4) arranged in the joints and the deflection unit (5) is located at the free end of the multi-joint robot arm.

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