WO2013110467A1 - Laser machining head with focus control - Google Patents

Description

 LASER PROCESSING HEAD WITH FOCUS CONTROL

description

The invention relates to a laser processing head, in particular for controlling and regulating the focal spot position and size in laser material processing, and for visualizing the processing surface, weld pool, process lamps and vapor capillary in laser processing processes.

When machining materials with a laser processing head, laser radiation is focused by means of a lens system or by means of a mirror system. However, a lens system itself heats up during material processing by means of laser light, which also changes the optical properties of the lens system used. This also leads to a change in the focal position of the beam path of the laser light. A change in this focus position relative to the position of the materials to be processed can lead to the desired processing result is not achieved.

From WO 2011/009594 a laser processing head and a method for combining the focus position change in a laser processing head is known in which by means of a camera, a processing area of a workpiece is observed, wherein the observation beam path of the camera is coupled into the beam path of the working laser beam and through the focusing lens for the working laser beam takes place. Thus, with a focus shift of the focusing lens due to heating by the working laser beam, the image of the processing area of the workpiece is blurred to the camera by an imaging optics. By adjusting the imaging optics and corresponding inclusion of the wavelength differences of the observation wavelength and the wavelength of the working laser beam, a Korrekturverstellweg can be calculated to bring the focus of the working laser beam back to the workpiece surface or a defined position. The influence of a heating of the collimator lens associated with a shift of the focal point of the collimator lens is compensated by means of a temperature sensor and a cognitive-technical system. Various monitoring systems are used for process monitoring in laser material processing processes. These are based in part on the detection of process emissions, ie in particular of electromagnetic radiation from the interaction zone between the laser beam and the workpiece by means of photodiodes, other photosensors or imaging sensors, in particular a camera. A camera is integrated for real-time or in-process monitoring usually in the optical system of a laser processing head, z. B. over a coated semi-transparent surface.

Approaches for determining the focus position change relative to the workpiece by means of intensities of individual photodiodes have already been discussed in science.

Thus, a method is known which introduces two optical sensors for different wavelengths in the glass fiber of the supplied laser light. It is attempted to draw a conclusion on the focus position change based on the relative change in the intensities of the two optical sensors to each other, and then compensate for the focus position change. See F. Haran, D. Hand, C. Peters and J. Jones, "Real-time focus control in laser welding", Meas. Sei. Technol., Year: 1996, pages: 1095-1098.

In another known method, the intensity of a wavelength is measured by means of a photodiode during a laser welding process with focus position variation relative to the workpiece. With neural networks, a function has been approximated that corresponds to the output of the photodiode, which was then used to compensate for the focus position. See G. Hui, O. Flemming Ove, "Automatic Optimization of Focal Point Position in C0 ₂ Laser Welding with Neural Networks in Focus Control System", year 1997.

From DE 195 163 76 it is known that by impressing a focal spot oscillation, the focus optimum position is calculated from the converted amplitude and phase relationship of a photodiode intensity.

DE 199 254 13 describes a device for determining the focal position of a welding beam. DE 9403822 Ul describes a monitoring device for laser radiation in which the entire beam guidance device is monitored from the exit of the laser radiation from the laser up to and including the processing optics to undesired radiation losses. The monitoring device comprises a beam guiding device with an optical waveguide, a processing device focusing the laser radiation of the beam guiding device on the workpiece, a measuring device coupling out a laser light from an optically transparent component, an evaluation unit receiving a measuring signal of the measuring device, a reference encoder acting proportionally on the laser output, which acts on the evaluation unit, and a control unit connected to the evaluation unit and influencing the laser power as a function of reference value-related measured values. An optically transparent component of the processing optics is connected to detect the stray radiation to the measuring device and the control unit is able to switch off the laser radiation at a predetermined exceeding or falling below the respective reference value for the laser power.

DE 19927803 AI describes a device for controlling the focus position during laser beam welding. In this case, a device for controlling the focus position in laser beam welding is proposed for use in process monitoring in a control and / or regulating circuit, which comprises a position-sensitive diode, a system for optical imaging and optical filters. The position sensitive diode is connected to an amplifier and / or data processing unit. The determination of the focus position is carried out by detecting the center of gravity of the image of the filtered optical emission of the interaction zone on the position-sensitive diode.

DE 10 2007 036 556 A1 describes a method for monitoring the focus position in laser beam machining processes. In this method, a high-frequency intensity modulation of a working laser beam for machining a workpiece, whereby the process lights due to the laser beam processing, a modulation of the same frequency is impressed. By means of time-resolved measurement of the ratios of the intensity and / or the phase position between the signals of the processing laser beam and the signals of the process illumination, the focal position of the processing laser beam can be determined on the basis of the amplitude Ratio and / or the phase shift or a combination thereof can be determined.

DE 10 2007 039 878 A1 describes a device and a method for focus position stabilization in optics for high-power laser radiation. The device comprises a controller with means for acquiring data and optics in which at least a part of the optical system is movably mounted in the axial direction and driven by a servomotor. The means for acquiring data includes an optical sensor which is suitable either for measuring the instantaneous intensity of the laser beam or for measuring the axial focus position.

DE 10 2009 007 769 A1 describes a laser processing head with integrated sensor device for focus position monitoring. Here, a laser processing head has a focusing lens and a downstream protective glass to focus a processing beam incident on the focusing lens as a parallel beam into a resultant focal point of the focusing lens with a downstream protective glass in which a workpiece is disposed. The focusing lens is preceded in the parallel beam path by a beam splitter which is reflective for a first portion of a laser beam bundle coupled in the laser processing head, the processing beam, transmissive and for a second portion, a measuring beam. In the direction of reflection, a mirror is arranged downstream of the beam splitter in such a way that it reflects the measuring beam at an angle to the optical axis of the focusing lens in order to image it in a focal point conjugate to the receiving surface of a sensor which is connected to an evaluation unit for focus position monitoring.

From JP 01 1 22 688 A an automatic focus adjustment device for lenses of a laser processing head is described in which the focusing lens is observed by means of an infrared sensor and the temperature measurement is measured in a lateral region and in a central region of the lens, thus calculating a focus shift , The invention has for its object to provide a laser processing head through which a defined focus position can be maintained relative to a workpiece to be machined during a machining process in an effective manner and with little equipment.

This object is achieved by the laser processing head according to claim 1. Advantageous embodiments and modifications of the invention are set forth in the subclaims.

According to the invention, a laser processing head is provided for processing a workpiece by means of a laser beam, with beam shaping optics for forming or collimating a working laser beam emerging from a fiber end of an optical fiber, the fiber end lying within a beam forming optical imaging area, focusing optics for focusing the working laser beam onto the workpiece surface or an image of a processing region of the workpiece on a first sensor area of the camera through a first observation beam via the focusing optics and the imaging optics, and an image of the beamforming optics imaging area on a defined relative to the workpiece surface position, and a camera with an adjustable in the beam path a second sensor area of the camera through a second observation beam path via the beam shaping optics and the imaging optics k takes place.

Thus, a laser processing head is provided, in which on a sensor surface of a camera in a laser processing head, both the processing surface of a workpiece and the fiber end of an optical fiber are imaged, wherein the images of the workpiece surface and the Strahlformungsoptikabbildungsbereichs, in which the fiber end is located in different sensor areas different sensor range locations or by temporal variation of the illumination are temporally separable. The additional observation of the beam-shaping optical imaging region by the process observation camera has the advantage that, for example, a focal point shift of the beam-shaping optical system can be detected on the sensor surface due to a blurred image. In order to be able to calculate a focal shift of the beam shaping optics in the wavelength range of the working laser beam, it is particularly advantageous if the laser processing head according to the invention has an evaluation unit which determines this focal shift by means of an adjustment path of the imaging optics in the direction of the optical axis, which is necessary for a displacement of the focal point sharpen the beamforming optics to recalculate the camera image of the beamforming optics imaging area.

According to the invention, the evaluation unit may further be configured to again sharply adjust the camera image of the processing region of the workpiece by means of an adjustment path of the imaging optics in the direction of the optical axis necessary for refocusing the focal point of the focusing optics, a focus shift of the focusing optics in the wavelength range of the laser processing beam to calculate. Thus, by the evaluation unit of the laser processing head according to the invention both generated by heating lenses of the optical system focus shift of the beam shaping optics and a focus shift of the focusing optics can be detected, whereby a focus shift of the focus of the laser beam relative to the workpiece surface can be completely determined.

For optimum alignment of the camera image generated by the camera with the laser beam striking the workpiece, it is particularly expedient if, furthermore, a first beam splitter or a beam deflector is arranged in the beam path of the working laser beam between beam shaping optics and focusing optics in order to move the first observation beam path of the camera into the beam path of the working laser beam.

In order to superimpose the beam-shaping optical imaging area into the second sensor area of the camera in a particularly simple and effective manner, it is particularly advantageous if a reflection device is arranged relative to the first beam splitter such that the second observation beam path travels from the imaging optical system through the first beam splitter Reflection at the reflection device and the first beam splitter is directed to the beam shaping optics. For a correction of the focus of the working laser beam relative to the working surface of the workpiece, it is particularly useful if the laser processing head according to the invention further comprises an actuator system which is adapted to adjust the position of the laser processing head relative to a processing surface of the workpiece or moving parts of the optical system the calculated focus shift of the focusing optics and / or the beam shaping optics is compensated for in order to focus the working laser beam again on the workpiece surface or on a position defined relative to the workpiece surface.

The reflection device according to the invention may in this case be a semitransparent plane plate, it being particularly expedient if a light absorption element is arranged in the direction behind the semitransparent plane plate in order to image a larger part of the laser energy of the working laser beam in the case of imaging the working laser beam emerging from the fiber end onto the second sensor region absorb.

In order to enable an object to be observed to be imaged within the processing surface of the workpiece, such as a cutting area or a molten pool area, spatially separated from an object to be observed within the beam forming optical imaging area, it is particularly advantageous if the reflecting device is so tilted Imaging optics of the camera is provided that the images take place on the first and the second sensor area of the camera in different sensor areas of the camera and they are thus separable.

However, in the case of an additional illumination of the beam-shaping optical imaging region, it is also conceivable and particularly advantageous if the reflection device is provided tilted to the imaging optics of the camera, that the images on the first and the second sensor area of the camera in different sensor areas of the camera done and this thus separable are.

For illuminating the beam-forming optical imaging region, it is expedient if the laser processing head is further equipped with a first illumination device whose light is coaxial with the first observation beam path via a second radiation element. It is coupled between the imaging optics and the first beam splitter to simultaneously illuminate the processing area of the workpiece and the beam-forming optical imaging area.

However, it is also conceivable to equip the laser processing head with a second illumination device for uniform illumination of the beam shaping optical imaging region.

Instead of a lighting device for uniform illumination of the beam shaping optical imaging region, however, a light-emitting device for imaging the emitted light of the light-emitting device onto the second sensor region of the camera may also be expediently arranged in the beam-shaping optical imaging region next to the fiber end.

In order to eliminate interfering radiation, as occurs, for example, during operation of the laser processing head, it is expedient if the laser processing head according to the invention has an optical bandpass filter which is arranged in front of the camera in the observation beam path, the transmission wavelength of the optical bandpass filter being limited to the emission wavelength of the first and / or or second lighting device and / or the lighting device is tuned.

For a simple separation of the images of the workpiece area and the beam shaping optical imaging area, for example by means of a lock-in method, it is particularly advantageous if the second lighting device or the lighting device is varied in its intensity relative to the illuminance of the workpiece in time to the images to separate the first and the second beam path to the camera.

According to the invention, the laser processing head is particularly suitable to be used for laser welding or laser cutting.

The invention will be explained in more detail with reference to the drawings. Show it: 1 shows a greatly simplified schematic view of a laser processing head according to an embodiment of the invention,

2 shows a greatly simplified schematic view of a laser processing head according to the invention, which is used for laser cutting,

FIG. 3 shows a greatly simplified schematic view of a laser processing head according to one exemplary embodiment of the invention, which is used, for example, for laser welding,

4 shows a greatly simplified schematic view of a laser processing head according to a further exemplary embodiment of the invention, which is used for example for laser welding,

Figure 5 is a greatly simplified schematic view of a laser processing head according to yet another embodiment of the invention, which is used for example for laser welding, and

6 shows a greatly simplified schematic view of a laser processing head according to the invention with an external illumination device.

In the various figures of the drawings, corresponding components are provided with the same reference numerals.

FIG. 1 shows a greatly simplified view of a laser processing apparatus or a laser processing head 10 according to an exemplary embodiment of the invention, as used with laser processing machines or systems. For processing a workpiece 12, a working laser beam 14 coming from the laser processing machine is directed through a housing 16 of the laser processing head 10 onto the workpiece 12 and focused by means of focusing optics 18 onto the workpiece surface 20 or onto a position defined relative to the workpiece surface 20 12 within a processing area 22 of the workpiece 12 to edit. The machining of the workpiece 12 by the laser beam 14 can in this case be a laser cutting However, the laser processing head according to the invention can also be used for a laser welding method or a laser soldering method.

The working laser beam 14 is supplied to the laser processing head 10 through an optical fiber 24, wherein the fiber end 26 of the optical fiber 24 is held in a fiber holder 28. The laser beam 14 emerging from the optical fiber 24 at the fiber end 26 of the optical fiber 24 within a beam forming optical imaging region 30 is formed by beam shaping optics 32, passes through a first beam splitter 34 and then impinges on the focusing optics 18 to focus on the workpiece 12. For the real implementation of the focusing optics 18 and the beam shaping optics 32 optical lenses or a set of optical lenses are used in each case.

The beam shaping optics 32 should generally be understood as optics suitable for forming the working laser beam 14 emerging from the fiber end 26 of the optical fiber 24, ie the working laser beam 14 may continue to divergent or converge after passing through the beam shaping optics 32 and thus also to the last optics of the laser processing head 10, so the focusing optics 18 meet. For the realization of the Auskoppeins from the optical fiber 24 of the working laser beam 14 and the focusing of the working laser beam 14 on the workpiece 12 so, for example, a retrofocus optics or a telephoto optics can be used. According to the invention, however, it is preferable to use the beam shaping optics 32 as collimator optics 32 through which the working laser beam 14 emerging from the fiber end 26 of the optical fiber 24 is collimated in order to be guided as a parallel beam bundle to the focusing optics 18 located downstream in the beam direction, since the beam displacement Focusing lens 18 or focusing lens, the focus position of the working laser beam 14 relative to the workpiece to be machined 12 can be changed without too much deteriorate the image quality of the decoupled working laser beam 14 and without reducing the beam diameter on the focusing lens 18.

Moreover, as will be described in more detail below, the use of collimator optics 32 simplifies the method for determining the focus position shift. tions of the focusing lens 18 and the collimator optics 32, since the corresponding focus position displacements of the focusing optics 18 and the collimator optics 32 can be determined and compensated independently of each other. The focusing optics 18 and the collimator optics 32 can moreover be composed of a plurality of lenses and also constructed as retrofocus optics or telephoto optics. The term beam shaping optics 32 used below is therefore to be understood as a collimator optics 32 for collimating the working laser beam 14. The general term of the beam-forming optical imaging region 30 used in the following is intended to be understood as a collimator optical imaging region 30.

The first beam splitter 34 is arranged in the beam path 15 of the working laser beam 14 between beam shaping optics 32 and focusing optics 18 such that a first observation beam path 36 of a camera 38 is coupled with an imaging optics 40 arranged in front of it in the beam path into the beam path 15 of the working laser beam 14. Thus, the processing region 22 of the workpiece 12 is imaged onto a first sensor region 42 of the camera 38 through the first observation beam path 36 via the imaging optics 40 and the focusing optics 18, the first observation beam path 36 coming from the imaging optics 40 through the first beam splitter 34 onto the focusing optics 18 is deflected. The workpiece surface 20 of the workpiece 12 can be illuminated by means of a lighting device (not shown in FIG. 1) with light of the wavelength λκ in contrast to the wavelength of the working laser beam 14. However, it is also possible for the light coming from the illumination device to coaxially couple into the beam path 15 of the working laser beam 14, as will be explained in more detail in the further embodiments.

According to the invention, in addition to imaging the processing region 22 of the workpiece 12 onto a first sensor region 42 of the camera 38 through a first observation beam path 36, a further image of the beam shaping optical image region 30 is applied to a second sensor region 44 of the camera 38 through a second observation beam path 46 via the imaging optics 40 and the beam shaping optics 32. In a very compact embodiment of the invention, a reflection device 48 is for this purpose arranged relative to the first beam splitter 34, that the second observation beam path 46 from the imaging optical system 40 first passes through the first beam splitter 34, then reflected by the reflection device 48 in the direction of the first beam splitter 34 back to then from the first beam splitter 34 in the direction of Beam shaping optics 32 to be deflected. Thus, an imaging of the beam-shaping optical imaging region 30 onto the second sensor surface 44 of the camera 38 takes place by collimation of the collimator lens 32 or shaping by the beam-shaping optical system 32, reflection at the first beam splitter 34, reflection at the reflection device 48 and focusing the imaging optics 40. Although it would also be conceivable to attenuate the reflected at the first beam splitter 34 working laser beam 14 attenuated to an additional camera with its own imaging optics, this solution is very expensive, space consuming and expensive.

In a real implementation, the imaging optics 40 may be only one lens in this case, but it is also possible to use an optical lens set. A mirror system is also possible, for. An off-axis paraboloid. Although this creates aberrations, but these could be compensated by software in image processing. In the event that the emerging from the fiber end 26 of the optical fiber 24 working laser beam 14 is to be imaged on the second sensor portion 44 of the camera 38, it is particularly useful if the reflection device 48, a semi-transparent plane plate 50 and a beam incident direction behind the semi-transparent plane plate The semi-transparent planar plate 50 transmits a majority of the laser power of the working laser beam 14 received by the light absorption element 52. For this purpose, the light absorption element 52 is ideally designed as a beam trap, which reflects or emits substantially no light. The light-absorbing element 52 is cooled to dissipate the heat-converted light output accordingly. The transmittance of the semitransparent plane plate 50 is matched to the transmittance of the first beam splitter 34 that the product of the transmissivity of the first beam splitter 34 and the semi-transparent plane plate 50 so weakens the working laser beam 14 that the sensor portion of the camera 38 is not destroyed and simultaneously sufficiently high light output on the sensor surface of the camera 38 impinges to be able to image the emerging from the optical fiber 24 within the Strahlformungsoptikabbil- training area 30 working laser beam 14.

The transmissivity of the first beam splitter 34 is for the working laser beam 14 between 95 percent and 99.99 percent, preferably between 99 percent and 99.5 percent and in particular 99 percent. The transmissivity of the plane-parallel plate 50 is between 95 percent and 99.99 percent, preferably between 98 percent and 99.5 percent and most preferably 99 percent. The semitransparent plane plate 50 may be inclined or tilted with regard to the optical axis of the second observation beam path 46 and to the sensor surface of the first and second sensor regions 42, 44, so that the image of the beam shaping optical imaging region 30, in particular the image of the working laser beam 14 emerging from the fiber end 26, on the second sensor area 44 of the camera 38 and the image of the processing area 22 of the workpiece surface 20 of the workpiece 12, in particular a laser cutting area or a molten pool of a welding area, into separate areas with different position within the sensor surface of the camera 38. Thus, for example, the beam-shaping optical imaging region 30 is directed into the second sensor region 44 designed as an edge region in order not to disturb the observation of the machining region 22 of the workpiece 12 in the first sensor region 42. Thus, the images of the beam shaping optics imaging area 30 and the processing area 22 are easily separated, thereby facilitating further image processing of the images on the sensor areas 42, 44.

The beamforming optics imaging region 30 is the region that results in a sharp image of the working laser beam emerging from the fiber end 26 of the optical fiber 24

14 by the beam-shaping optical system 32, for example by means of the imaging optics 40 on the second sensor surface 44 of the camera 38 or by means of the focusing lens 18 on the workpiece surface 20 of the workpiece 12 is shown in focus on this. Thus, therefore, the beamforming optics imaging portion 30 is an imaging plane containing the fiber end 26 of the optical fiber 24, and typically perpendicular to the optical axis of the beam path

15 of the working laser beam 14 is located. When the working laser beam 14 is coupled into the housing 16 of the laser processing head 10 by means of the fiber holder 28, the beam-forming optical imaging region 30 can therefore, for example, have an upper inner wall of the housing. be 16 of the laser processing head 10. Since, in the exemplary embodiment shown in FIG. 1, the working laser beam 14 itself is imaged onto the second sensor surface 44, wavelength-dependent effects such as chromatic aberration need not be taken into account here.

The laser processing head 10 according to the invention has an actuator system by means of which the position of the laser processing head 10 relative to the processing surface 22 of the workpiece 12 or moving parts of the optical system 18, 32 can be adjusted so that a focus shift of the working laser beam 14 relative to the workpiece surface 20 is compensated or compensated can be. In the case of a constant distance of the laser processing head 10 to the surface 22 of the workpiece 12, a focal point shift Δζπ of the focusing optical system 18 at the wavelength of the working laser beam 14 X _L and a focal point shift ΔZf 2 is decisive for a focus shift of the working laser beam 14 relative to the workpiece surface 20 beam shaping optics 32 at the wavelength X _L of the working laser beam 14. for this purpose, one first actuator 54 to linear displacement of the laser processing head 10 relative to the workpiece surface 20 of the workpiece 12 to an adjustment Δζ _1? a second actuator 56 for the linear displacement of the focusing optics 18 in the direction of the beam path 15 of the working laser beam 14 by an adjustment Δζ ₂ and a third actuator 58 for linear displacement of the beam shaping optics 32 along the beam path 15 of the working laser beam 14 by an adjustment Δζ _{3 be} provided. In order to be able to image an image of the workpiece surface 20 or of the beam-shaping optical imaging region 30 on the first sensor region 42 or second sensor region 44 of the camera 38, a fourth actuator 60 is furthermore provided in order to surround the imaging optical system 40 along the observation beam path 36, 46 Correction adjustment path Adu linear shift.

By means of the laser processing head 10 according to the invention, a focus position compensation of the focus position of the working laser beam 14 relative to the workpiece surface 20 can be performed with heating of the beam shaping optics 32 and / or the focusing optics 18, as will be described below. The laser processing head 10 according to the invention or the laser processing apparatus 10 according to the invention with a laser processing head has an evaluation unit 62 which processes image data from the camera 38, drives the fourth actuator 60 of the imaging optics 40 and reads out its actuating position to control the first, second or third Actuators 54, 56, 58 to be able to perform a focus position compensation. In this case, the evaluation unit 62 is designed, on the one hand, to set the camera image of the beam shaping optical imaging area 30 again sharply by means of an adjustment path Δdki of the imaging optics 40 in the direction of the optical axis, which is necessary for sharply adjusting the camera image of the beam shaping optical imaging area 30, the focus shift ΔZf2 of the beam shaping optics 32 in the wavelength range λ _\ _ of the working laser beam 14 to calculate. Furthermore, the evaluation unit 62 is configured to adjust the camera image of the processing region 22 of the workpiece 12 again by means of a displacement path Δd _k i of the imaging optics 40 in the direction of the optical axis, which is necessary for a displacement Δζπ of the focus of the focusing optics 18 Focus shift Δζπ the focusing optics 18 in the wavelength range λι to calculate the working laser beam 14. Once both focus shifts of the beam shaping optics _ß 32 AEZ nd of the focusing optics 18 Az are known, by means of the Aktu- atoren 54, 56 and 58 of the working laser beam 14 is focused again on the workpiece surface 20, or to a defined relative to the workpiece surface 20 position.

In order to achieve this, the optical system of the laser processing head 10 is initially adjusted in an initial state such that the laser beam 14 is optimally collimated by the beam shaping optics 32 and runs in the direction of the focusing optics 18 as a parallel beam. This initial state can be set by moving the imaging optics 40 into a predetermined position, in which the collimated laser beam 14 is sharply imaged onto the second sensor surface 44 of the camera 38. The focusing lens 18 is also driven by the second actuator 56 to a predetermined position, in which the focal point of the focusing lens 18 has a predetermined distance from the bottom of the laser processing head 10. The imaging optics 40 is set after the collimation of the working laser beam 14 so that a sharp image of the workpiece surface 20 of the workpiece to be machined 12 takes place at the illumination wavelength λ. During processing of the workpiece 12 by means of the laser processing head 10, due to the incomplete transmissivity of the optical system, the focusing optics 18 and the beam shaping optics 32 are heated, combined with a refractive power which has changed due to the heating of the lenses of the focusing optics 18 and the beam shaping optics 32 associated focus shift Δζπ the focusing optics 18 and ÄZf2 the beam-forming optical system 32. Thus, on the one hand shifts the focus of the working laser beam 14 relative to the workpiece surface 20, associated with a generally deteriorated work result. Simultaneously with the shift of the focal point of the working laser beam 14, the camera image of the workpiece surface 20 picked up by the first sensor region 42 of the camera 38 is blurred. By adjusting the optical system, in particular by passing through the imaging optics 40 by a correction displacement Aki by means of the fourth actuator 60, the camera image of the workpiece surface 20 is again focused by control of the evaluation unit 62 and stores the required correction displacement Aki. By incorporating the imaging ratio of imaging optics 40 and focusing optics 18 and by including the focusing differences due to the different wavelengths of the observation system λκ and the processing laser wavelength XL used due to the chromatic aberration or other wavelength-dependent effects can by sharpening the camera image of the workpiece surface 20 and determining the Korrekturverstellwegs Ädki the focus shift ÄZfi the focusing optics 18 in the wavelength range λ! ^ Ε8 working laser beam 14 are determined.

After detecting the focus shift Δζπ of the focusing optical system 18, the imaging optical system 40 is set to the preset position of the above-described initial state for collimating the working laser beam 14, and then sharply imaging the working laser beam 14 and the beam forming optical imaging section 30 by adjusting the imaging optical system 40 by a correction displacement value Δdki the second sensor region 42 to produce. Since, in the exemplary embodiment shown in FIG. 1, the working laser beam 14 is imaged directly onto the second sensor surface 42, In this case, no wavelength effects due to chromatic aberration are taken into account.

The invention includes all common methods for focusing and image definition, some important should be explicitly mentioned:

m g Variance: Squared difference of the image values around the mean with subsequent summation. For an image i (x, z) and S as the number of pixels, this can be calculated as follows:

mg

as well as

A high variance or wide histogram means good contrast.

Sum Modulus Difference (SMD): measure based on image gradients,

and its amount

SMD is determined with

SMD = -YVV ,. ^: with sharp pictures the difference from picture point x to x +1 is very big. Signal Power (SL): The maximum of

so wie die schneller zu berechnende Fast-Fourier-Transformation wird unter Verwendung von

gives the best image state, also applies to the Liao modified threshold value method. Fourier Analysis: The Discrete Fourier Transform

like the faster-to-calculate fast Fourier transform, using

Determines rows and columns. In the defocal image, the high frequency range, calculated by summing the power spectra, decreases significantly compared to the focal image.

der Fourierspektren dar und steht im Zusammenhang mit hohen Frequenzen. Durch Operatoridentität und Formelerweiterung kann diese in den Zeitbereich umgeformt werden. Die darin enthaltenen einzelnen Komponenten müssen durch Approximationen der 2. Ableitung bestimmt werden wodurch wir Laplace operator or Laplace focus function: represents the second statistical moment,

the Fourier spectra and is associated with high frequencies. Through operator identity and formula expansion, this can be transformed into the time domain. The individual components contained in it must be determined by approximations of the second derivative, whereby we

+ y)+ *(* ^~ y)+ Kx,y + 1) + x,y - 1) - 4i(x,y)] erhalten und direkt bestimmen können. L

+ y) + * (* ^~ y) + Kx, y + 1) + x, y - 1) - 4i (x, y)] receive and determine directly.

Focus Point or Object Tracking Focusing: Feature points are pixels with a prominent environment so that they can be rediscovered in a different image of the same image sequence. As a result, movement tendencies can be detected in image sequences and the focus can thus work in the right direction. In addition, it is possible to create a focus window for the focusing function by means of object recognition algorithms in known image sequences and thus to enable optimum focus adjustment of the target object. Many methods can be used for this purpose, but it is the Harris corner detector, the division of the image into specific sub-sizes, image gradient and threshold calculation, sum of square difference, fuzzy logic for autofocus, support vector classification, main components analysis and so on. be used.

In the method according to the invention, in a setting process of the system, first of all a sharply imaged reference image is taken from the processing region 22 or the beamforming optical imaging region 26 to reference the image sharpness compared to a later captured camera image when the respective focus positions of the focusing optics 18 or the beamforming optics 32 have served to serve. This can be created during or before a machining process.

FIG. 2 shows a greatly simplified schematic view of a laser processing head 10 which is used for laser cutting a workpiece 12. The laser processing head 10 shown in Figure 2 corresponds to the embodiment shown in Figure 1, wherein only one nozzle 64 is provided for blowing out the molten workpiece material. Since the luminous intensity of the process light coming from the workpiece 12 is relatively small compared to a laser welding process, the embodiment of the laser processing head 10 shown in FIG. 1, in which no filter devices have to be provided for the camera 38, is particularly well suited. FIG. 3 shows a further exemplary embodiment of a laser processing head 10 according to the present invention schematically and greatly simplified. The laser processing head 10 from FIG. 3 differs from the laser processing head 10 shown in FIG. 1 in that a pattern element 66 is provided in the beam shaping optical imaging region 30, which is imaged onto the second sensor region 44 of the camera 38, by a focal point displacement Δθ of the beam shaping optics 32 by adjusting the imaging optics 40 to determine a Korrekturverstellwert Äd _k i can. The pattern member 66 may be a structure embossed in the inner wall of the housing 16 in the vicinity of the fiber holder 28, but it is also possible to print a structure either on the inner wall or to provide a sticker including the pattern member 66.

The illumination of the pattern element 66 is effected by a first illumination device 68 whose light is first collimated or shaped by means of optics 70 and then coaxially coupled into the first observation beam path 36 via a second beam splitter 72 between the imaging optics 40 and the first beam splitter 34 in order to simultaneously Processing area 22 of the workpiece 12 and the Strahlformungsoptikabbil- training area 30, in which the pattern element 66 is arranged to illuminate. When attaching the pattern element 66, care must be taken that it is arranged in the beam-forming optical imaging region 30 or at a defined distance in the direction of the optical axis to the fiber end 26 of the optical fiber 24 from which the working laser beam 14 exits.

Since, in the embodiment of the laser processing head 10 shown in FIG. 3, the observation of both the workpiece surface 20 and the beam shaping optical imaging region 30 with the pattern element 66 takes place under illumination with the same wavelength .lambda..sub.k, the calculation of the focal point shift .DELTA.Zf2 of the beamforming optical system 32 must take place a Korrekturverstellwegs Ädu the imaging optics 40 for focusing a camera image of the camera 38 now also in the beam shaping optics 32, the chromatic aberration due to the different to the illumination wavelength λκ working laser beam wavelength are taken into account. The chromatic aberration is, however, in a particularly preferred manner according to the invention by a corresponding offset or displacement of the pattern member 66 in the direction of the beam path 15 of the working laser beam 14 to the position of the fiber end 26 of the optical fiber 24, from which the working laser beam 14 exits, compensated or compensated. Here, the pattern element 66 is arranged so that at a sharp imaging of the pattern element 66 on the second sensor surface 44 at the illumination wavelength λκ simultaneously complete collimation of emerging from the fiber end 26 working laser beam 14 by the beam shaping optical system 32 at the wavelength X _{L of} the working laser beam 14 ,

In the case of the laser processing head 10 shown in FIG. 3, the reflection device 48 is preferably a plane-parallel plate with a high reflection rate, the highest possible light intensity of the illumination by the first illumination device 68 on the pattern element 66 and a subsequent high-light image of the pattern element 66 on the second Sensor surface 44 of the camera 38 to reach. In front of the camera 38 between the second beam splitter 72 and the imaging optics 40, an optical bandpass filter 74 is further provided, which is tuned to the illumination wavelength λ of the first illumination device 68 in order to block out interfering radiation from the region of the workpiece 12. The laser processing head 10 shown in FIG. 3 is particularly suitable for use in a laser welding process because, due to the process emissions of the generated weld pool in the processing area 22 of the workpiece 12, illumination of the workpiece 12 with a predetermined illumination wavelength λ _k associated with observation at the illumination wavelength λ tuned bandpass filter 74 is particularly advantageous.

FIG. 4 greatly simplifies and diagrammatically illustrates another exemplary embodiment of a laser processing head 10, wherein the laser processing head 10 of FIG. 4 differs from the laser processing head 10 shown in FIG. 3 in that a second illumination device 76 is provided in addition to the first illumination device 68 the pattern element 66 evenly illuminates. This second illumination device 76 can be provided if illumination of the pattern element 66 by the first illumination device 68 has insufficient intensity. can be done. Moreover, it is conceivable to mount the first illumination device 68 on an outer side of the laser processing head 10, as shown for example in FIG. The illumination by means of the second illumination device 76 preferably takes place in the same wavelength range λκ as that of the first illumination device 68 and is also tuned to the transmission wavelength of the optical bandpass filter 74.

FIG. 5 shows a greatly simplified schematic view of a laser processing head 10 according to yet another exemplary embodiment of the invention. The laser processing head 10 shown in FIG. 5 differs from the laser processing head 10 shown in FIG. 4 in that, instead of the pattern element 66 and the second illumination device 76, a lighting device 78 is arranged in the beam shaping optical imaging region 30 next to the fiber end 26, the emitted light of the lighting device 78 the second sensor region 44 of the camera 38 is imaged in order to be able to determine a focus shift AZQ of the beam shaping optical system 32 by adjusting the imaging optical system 40 by a correction displacement path Adki. The lighting device 78, like the pattern element 66, may be offset in the direction of the optical axis of the beam shaping optics 32 to the fiber end 26, so that a chromatic aberration with respect to the emission light wavelength λκ of the lighting device 78 and the wavelength X _{L of} the working laser beam 14 is compensated by the beam shaping optics 32 in that the working laser beam 14 is collimated by the beam shaping optical system 32 when a sharp imaging at the observation wavelength λ _κ of the light emitted by the lighting device 78 takes place on the second sensor surface 44.

FIG. 6 shows a greatly simplified schematic view of a laser processing head 10 in which the first illumination device 68 is attached to an outer side of the housing 16.

It should be emphasized that the embodiments of the laser processing head 10 shown in Figures 1 to 5 are freely combinable with respect to the components shown, so the embodiments shown in Figures 1 to 6 show only particularly advantageous embodiments and are not designed to limit the invention - the. Although the embodiment shown in Figure 2 shows a laser cutting head 10, this laser processing head 10 can also be used for laser welding. Likewise, the embodiments of the laser processing heads 10 shown in FIGS. 3 to 6 are suitable for use in a laser cutting process. Moreover, as shown in FIG. 3, the first illumination device 68 may be used in the laser processing head 10 shown in FIG. 2 to illuminate the workpiece surface. Furthermore, the first illumination device 68 shown in FIG. 6 can likewise be used to illuminate the workpiece in the case of the laser processing head 10 shown in FIGS. 1 and 2.

As a light source for the first illumination device 68 is due to the high intensity, a laser light source, which may be a semiconductor laser diode. For this purpose, AlGalnP laser diodes with multi-quantum-well structures can be used, which have a radiation maximum in a wavelength range between 635nm and 670nm. For example, a laser diode with a radiation wavelength of 658 nm and a radiation power of 60 milliwatts can be used.

As a light source of the second lighting device 76 and / or the lighting device 78, for example, a semiconductor light emitting diode or an LED can be used, which is provided with an optical resonator, whereby the spontaneous emission of the light emitting diode is amplified by the optical resonator. These so-called RC-LEDs (resonant cavity light emitting diodes) have, in contrast to normal semiconductor light-emitting diodes, a strongly narrowed emission spectrum with a half width or FWHM (filling width of half maximum) of about 5 to 1 onm. When using a laser diode as the first illumination device 68, it is advantageous if, due to the use of a similar material system, the emission characteristic of the second illumination device 76 or the illumination device 78 is matched to the emission characteristic of the first illumination device 68.

In order to minimize a speckle effect due to illumination by a laser diode in the first illumination device 68, either the coherence of the laser light can be resolved or by rapid temporal variation of the speckle interferences. be reduced within the integration time of the eye, the speckle contrast. Here, for example, the laser light of the first illumination device 68 may be passed through a rotating diffuser (not shown). As a diffuser, for example, a glass plate with a rough surface is suitable.

The preferred emission wavelength of the light of the first illumination device 68 is in a wavelength range between 630 nm and 670 nm, with an intensity maximum at 640 nm, for example, being expedient. The radiation emerging from the fiber end can also be viewed directly, this can be in addition to the laser radiation and the radiation of the pump wavelength.

The bandpass filter 74 arranged in front of the camera 38, which is, for example, a CMOS or CCD camera, has a wavelength transmission range which points to the at least local emission maxima of the light of the first illumination device 68 and / or the light of the second illumination device 76 and / or the light of the lighting device 78 is adjusted. Here, the half width or FWHM (fill width at half maximum) of the wavelength passage range of the filter 74 is to be selected such that the maxima of the first and second illumination devices 68, 76 and / or the illumination device 78 are within the passband of the optical bandpass filter. In this case, the half-width is preferably less than 100 nm, particularly preferably less than 50 nm and in particular less than 20 nm. The optical bandpass filter 78 is preferably a Fabry-Perot filter or a Fabry-Perot etalon, this type of filter transmitting electromagnetic waves of a certain frequency range and extinguishing the remaining frequency components by interference. With regard to the half-value width of the optical bandpass filter 78, it is advantageous if this region is as narrow as possible in order to produce the least possible disruption of the camera image by process lights during operation of the laser processing head 10, which by machining the workpiece 12 by means of the working laser beam 14th produced by melting the workpiece material. In this case, the camera 38 can use an HDR method to increase the dynamics of the recorded camera images. Furthermore, it is inventively preferred if the emitted light of the second illumination device 76 or the lighting device 78 is varied in its intensity relative to the illuminance, for example by the first illumination device 68 of the workpiece 12 in time to lock images by means of a lock-in process - Mung optics imaging area 30 and the workpiece surface 20 to the sensor area 42, 44 of the camera 38 to be able to separate. In this case, the images of the workpiece surface 20 and the beam-forming optical imaging region 30 can be made to the same local sensor region because the images can be separated due to the temporal variance.

By fiction, contemporary laser processing head 10 so a laser welding head or laser cutting head or a laser processing head is provided for further processing options of a workpiece by means of a laser in which in a simple manner by using only a process observation sensor such as a camera simultaneously determined a focus shift of the focusing optics and the beam shaping optics and by a Actuator system, a focus shift of the working laser beam relative to the workpiece surface can be compensated.

Claims

claims A laser processing head (10) for processing a workpiece (12) by means of a working laser beam (14), comprising:  beam shaping optics (32) for shaping a working laser beam (14) emerging from a fiber end (26) of an optical fiber (24), the fiber end (26) being within a beam forming optical imaging region (30);  a focusing optics (18) for focusing the working laser beam (14) on the workpiece surface (20) or on a relative to the workpiece surface (20) defined position; and  a camera (38) with an adjustable imaging optics (40) arranged in front of it in the beam path (36, 46), wherein an image of a processing region (22) of the workpiece (12) on a first sensor region (42) of the camera (38) by a first An observation beam path (36) via the focusing optics (18) and the imaging optics (40), and an image of the beam-forming optics imaging area (30) on a second sensor area (42) of the camera (38) through a second observation beam path (46) via the beam-shaping optics (32). and the imaging optics (40) takes place. 2. Laser processing head (10) according to claim 1, further comprising an evaluation unit (62) which is adapted by means of an adjustment path (Adi _d ) of the imaging optics (40) in the direction of the optical axis, which is necessary for a displacement of the Focal point (λZf2) of the beam-shaping optical system (32) to sharpen the camera image of the beam-forming optical imaging area (30), to calculate the focal shift (ΔZβ) of the beam-shaping optical system (32) in the wavelength range ( _L ) of the working laser beam (14). 3. Laser processing head (10) according to claim 1 or 2, wherein the evaluation unit (62) is further adapted by means of a displacement path (Ad ^) of the imaging optics (40) in the direction of the optical axis, which is necessary for a displacement of the Focal point (Δζπ) of the focusing optics (18), the camera image of the processing area (22) of the workpiece (12) again set sharply, a focus shift (Δζη) of the focal point kussieroptik (18) in the wavelength range k _L ) of the laser processing beam (14) to calculate. 4. Laser processing head (10) according to claim 1, 2 or 3, further comprising a in the beam path (15) of the working laser beam (14) between the beam shaping optical system (32) and focusing optics (18) arranged first beam splitter (34) or beam deflector for coupling the first observation beam path (36) of the camera in the beam path (15) of the working laser beam (14). 5. The laser processing head (10) according to claim 4, further comprising a reflection device (48) which is arranged relative to the first beam splitter (34) such that the second observation beam path (46) from the imaging optics (40) through the first beam splitter (34). passes therethrough and, after reflection at the reflecting device (48) and the first beam splitter (34) to the beam-shaping optical system (32) is directed. The laser processing head (10) of any of claims 2 to 5, further comprising an actuator system (54, 56, 58) adapted to adjust the position of the laser processing head (10) relative to a processing surface (20) of the workpiece (12) to adapt moving parts of the optical system (18, 32) in such a way that the calculated focus shift (Δζη, λZf2) of the focusing optics (18) and / or the beam shaping optics (32) is compensated to bring the working laser beam (14) back onto the workpiece surface (20) or to focus on a relative to the workpiece surface (20) defined position. 7. Laser processing head (10) according to any one of the preceding claims, characterized in that the reflection device (48) comprises a semitransparent flat plate (50) and arranged in the direction behind the beam incidence light absorption element (52). 8. Laser processing head (10) according to any one of the preceding claims, characterized in that the reflection device (48) tilted to the imaging optics (40) of the camera (38) is provided that the images on the first (42) and the second (44) Sensor region of the camera (38) take place in different sensor regions of the camera (38) and these are thus separable. 9. laser processing head (10) according to any one of the preceding claims, characterized in that in the beam-forming optical imaging region (30) adjacent to the fiber end (26) a pattern element (66) for imaging on the second sensor region (44) of the camera (38) is arranged. 10. The laser processing head (10) according to claim 4 and one of the preceding claims, further comprising a first illumination device (68), the light coaxially in the first observation beam path (36) via a second beam splitter (72) between imaging optics (40) and first beam splitter ( 34) is coupled to simultaneously illuminate the processing area (22) of the workpiece (12) and the beam-forming optical imaging area (30). 11. The laser processing head (10) according to any one of the preceding claims, further comprising a second illumination device (76) for uniform illumination of the beam forming optical imaging region (30). 12. Laser processing head (10) according to one of the preceding claims, characterized in that in the beam-forming optical imaging region (30) adjacent to the fiber end (26) a lighting device (78) for imaging the emitted light of the lighting device (78) on the second sensor region (44) Camera (38) is arranged. 13. The laser processing head (10) according to any one of claims 10 to 12, further comprising an optical bandpass filter (74) disposed in the observation beam path (36, 46) in front of the camera (38), wherein the transmission wavelength of the optical bandpass filter (74) the emission wavelength of the first (68) and / or second (76) lighting device and / or the lighting device (78) is tuned. 14. Laser processing head (10) according to one of claims 10 to 13, characterized in that the second illumination device (76) or the lighting device (78) is varied in time relative to the illuminance of the workpiece (12), to separate the images of the first (36) and second (46) beam path to the camera (38). 15. Laser processing head (10) according to any one of the preceding claims, characterized in that it is suitable for laser welding or laser cutting.