DE102012001609B3 - Laser processing head - Google Patents

Abstract

The invention relates to a laser processing head for machining a workpiece by means of a working laser beam, with a beam shaping optics for collimating a working laser beam emerging from a fiber end of an optical fiber, wherein the fiber end is within a beam forming optical imaging range, a focusing optics for focusing the working laser beam on the workpiece surface or on a relative to the workpiece surface a defined position, and a camera with an adjustable imaging optics arranged in front in the beam path, wherein 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 Strahlformungsoptikabbildungsbereichs on a second sensor area of the camera takes place through a second observation beam via the beam-shaping optical system and the imaging optics.

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 the WO 2011/009594 A1 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 by the focusing lens for the working laser beam. 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. Sci. 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 CO ₂ Laser Welding with Neural Networks in Focus Control System", year 1997.

From the DE 195 163 76 A1 It is known that the imposition of a focal spot oscillation calculates the focus optimum position from the converted amplitude and phase relationship of a photodiode intensity.

The DE 199 254 13 A1 describes a device for determining the focal position of a welding beam.

The DE 9403822 U1 describes a monitoring device for laser radiation in which the entire beam guidance device from the exit of the laser radiation from the laser up to and including the processing optics is monitored for unwanted radiation losses. The monitoring device comprises a beam guiding device with an optical waveguide, one the laser radiation of the beam guiding device focusing on the workpiece processing optics, a laser light from an optically transparent component auskoppelnde measuring device, a measuring signal of the measuring device receiving evaluation, a reference laser output proportional acting reference encoder which acts on the evaluation, and connected to the evaluation, the laser power as a function of reference value related measured values influencing control unit. 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.

The DE 19927803 A1 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.

The DE 10 2007 036 556 A1 describes a method for monitoring the focal position in laser beam processing 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.

The 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.

The 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 the JP 011 22 688 A an automatic focus adjusting 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 EP 2 042 258 A1 describes a laser processing system and a corresponding method. A laser processing system includes a processing laser oscillator, a condensing condenser optical system, and two laser oscillators. A motion adjustment unit adjusts the condenser lens and the laser oscillators to move forwards and backwards in lockstep. An imaging unit images light spots of the laser on the workpiece, and an image processing unit subjects a captured video to image processing and displays an image after processing. A computing unit calculates, in a state in which the lasers are focused on a focus position of the processing laser, the center of gravity positions of the light spots of the respective lasers that are formed on the surface of the workpiece by corresponding movement of the condenser lens. Further, the unit calculates a distance between the centers of gravity. A control unit controls the Motion adaptation unit in such a way that the distance between the centroids is adjusted to zero or almost zero.

The EP 1 716 963 A1 describes an optical arrangement for a remote laser material processing for generating a three-dimensional workspace. For this purpose, a device for remote laser material processing is provided, consisting of a collimator with a first focal length, which collimates the laser beam emerging from an optical fiber. Furthermore, the device comprises a deflection system with at least one rotatably mounted mirror and a drive for the angular adjustment of the mirror. Finally, a focusing lens with a second focal length is provided, which focuses the collimated and deflected by the mirror system laser beam.

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 a beam shaping optical system for shaping or collimating a working laser beam emerging from a fiber end of an optical fiber, wherein the fiber end lies within a beam shaping optical imaging area, a focusing optics for focusing the working laser beam on the workpiece surface or on a 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 beam forming optics imaging area on a second Sensor range of the camera through a second observation beam via the beam shaping optics and the imaging optics he follows.

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 due to a blurred image on the sensor surface.

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 region into the second sensor region 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 passes from the imaging optics through the first beam splitter and after reflection 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 cut area or a molten pool area, spatially separate from an object to be observed within the beam forming optics imaging area, it is particularly advantageous for the reflection apparatus to be tilted to the imaging optics of FIG 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-shaping optical imaging region, it is expedient if the laser processing head is also equipped with a first illumination device whose light is coaxially coupled into the first observation beam path via a second beam splitter between the imaging optics and the first beam splitter, in order to simultaneously illuminate the processing region of the workpiece and the beam-forming optical imaging region.

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 on the second sensor region of the camera can 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 to the images of the first and the second beam path to the camera to separate.

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 a greatly simplified schematic view of a laser processing head according to an embodiment of the invention,

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

3 a greatly simplified schematic view of a laser processing head according to an embodiment of the invention, which is used for example for laser welding,

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

5 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 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.

In 1 is a highly simplified view of a laser processing apparatus or a laser processing head 10 according to an embodiment of the invention as it is used with laser processing machines or equipment. For machining a workpiece 12 becomes a working laser beam coming from the laser processing machine 14 through a housing 16 of the laser processing head 10 through to the workpiece 12 steered and by means of a focusing optics 18 on the workpiece surface 20 or on a relative to the workpiece surface 20 defined position focused to the workpiece 12 within an editing area 22 of the workpiece 12 to edit. The machining of the workpiece 12 through the laser beam 14 This may be a laser cutting process such as inert gas cutting or flame cutting, but the laser processing head according to the invention is also suitable for a laser welding process or a laser brazing process.

The working laser beam 14 becomes the laser processing head 10 through an optical fiber 24 fed, the fiber end 26 the optical fiber 24 in a fiber holder 28 is held. The at the fiber end 26 the optical fiber 24 within a beamforming optics imaging area 30 from the optical fiber 24 emerging laser beam 14 is by means of a beam shaping optics 32 shaped, passes through a first beam splitter 34 and then hits the focusing optics 18 to work on the workpiece 12 to be focused. For the real implementation of the focusing optics 18 and the beam shaping optics 32 For example, optical lenses or a set of optical lenses are used.

The beam shaping optics 32 should generally be understood as optics, which is suitable to that from the fiber end 26 the optical fiber 24 exiting working laser beam 14 to shape, the working laser beam 14 So after passing through the beam shaping optics 32 continue divergent or convergent and so on the last optics of the laser processing head 10 , so the focusing optics 18 to meet. For the realization of decoupling from the optical fiber 24 the working laser beam 14 and focusing the working laser beam 14 on the workpiece 12 Thus, for example, a retrofocus optic or a telephoto optic can be used. In accordance with the invention, however, preference is given to using the beam-shaping optical system 32 as collimator optics 32 through which the out of the fiber end 26 the optical fiber 24 exiting working laser beam 14 is collimated to a parallel beam to the downstream in the beam direction focusing optics 18 to be guided, since here by moving the focusing optics 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 image quality of the decoupled working laser beam 14 to deteriorate and without the beam diameter on the focusing optics 18 to downsize.

In addition, as will be described in more detail below, simplifies the use of a collimator optics 32 the method for determining the focal position displacements of the focusing lens 18 and the collimator optics 32 because the corresponding focus position shifts of the focusing optics 18 and the collimator optics 32 independently determined and compensated. The focusing optics 18 and the collimator optics 32 can also be composed of several lenses and also constructed as retrofocus optics or telephoto optics. The term beamforming optics used below 32 should therefore preferably as Kollimatoroptik 32 for collimation of the working laser beam 14 be understood. The general term used hereinafter of the beam-forming optical imaging area 30 should preferably be used as Kollimatoroptikabbildungsbereich 30 be understood.

The first beam splitter 34 is so in the beam path 15 the working laser beam 14 between beam shaping optics 32 and focusing optics 18 arranged that a first observation beam path 36 a camera 38 with a previously arranged in the beam path imaging optics 40 in the beam path 15 the working laser beam 14 is coupled. Thus, an illustration of the processing area takes place 22 of the workpiece 12 to a first sensor area 42 the camera 38 through the first observation beam path 36 about the imaging optics 40 and the focusing optics 18 , wherein the first observation beam path 36 through the first beam splitter 34 from the imaging optics 40 coming to the focusing optics 18 is diverted. The workpiece surface 20 of the workpiece 12 can by means of a lighting device (in 1 not shown) with light of wavelength λ _K in contrast to the wavelength λ _{L of} the working laser beam 14 be illuminated. The lighting device may be on an outer side of the laser processing head 10 However, it is also possible, the light coming from the lighting device coaxially into the beam path 15 the working laser beam 14 to couple, as will be explained in more detail in the other embodiments.

According to the invention, in addition to the illustration of the processing area 22 of the workpiece 12 to a first sensor area 42 the camera 38 through a first observation beam path 36 another illustration of the beam shaping optics imaging area 30 to a second sensor area 44 the camera 38 through a second observation beam path 46 about the imaging optics 40 and the beam shaping optics 32 , In a very compact embodiment of the invention, this is a reflection device 48 so relative to the first beam splitter 34 arranged that the second observation beam path 46 from the imaging optics 40 first through the first beam splitter 34 passes through, then from the reflection device 48 in the direction of the first beam splitter 34 is reflected back to then from the first beam splitter 34 in the direction of the beam shaping optics 32 to be diverted. Thus, therefore, an image of the beam-forming optical imaging region is taken 30 on the second sensor surface 44 the camera 38 by collimating the collimator lens 32 or by shaping by the beam shaping optics 32 , a reflection on the first beam splitter 34 , a reflection on the reflection device 48 and a focus through the imaging optics 40 , Although it would be conceivable, the at the first beam splitter 34 reflected working laser beam 14 Mapped to an additional camera with its own imaging optics weakened, this solution is very expensive, space consuming and expensive.

In a real implementation, the imaging optics 40 however, 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 out of the fiber end 26 from the optical fiber 24 exiting working laser beam 14 on the second sensor area 44 the camera 38 is to be imaged, it is particularly useful if the reflection device 48 a semitransparent plane plate 50 and a beam incident direction behind the semi-transparent plane plate 50 arranged light absorption element 52 having the semitransparent plane plate 50 a large part of the laser power of the working laser beam 14 transmitted from the light absorption element 52 is recorded. This is the light absorption element 52 ideally formed as a beam trap, which reflects or emits substantially no light. The light absorption element 52 is cooled to dissipate the heat-converted light output accordingly. The transmittance of the semitransparent plane plate 50 is thus on the transmittance of the first beam splitter 34 Tuned that the product of the transmissivity of the first beam splitter 34 and the semitransparent plane plate 50 the working laser beam 14 so weakens that the sensor area of the camera 38 is not destroyed and at the same time a sufficiently high light output on the sensor surface of the camera 38 impinges on the out of the optical fiber 24 within the beamforming optics imaging area 30 exiting working laser beam 14 to be able to depict.

The transmissivity of the first beam splitter 34 lies here for the working laser beam 14 between 95 percent and 99.99 percent, preferably between 99 percent and 99.5 percent, and most preferably 99 percent. Transmissivity of plane-parallel plate 50 is between 95 percent and 99.99 percent, preferably between 98 percent and 99.5 percent and in particular 99 percent. The semitransparent plane plate 50 can with respect to the optical axis of the second observation beam path 46 and to the Sensor surface of the first and second sensor area 42 . 44 be tilted or tilted so that the image of the beam-forming optical imaging area 30 , in particular the image of the fiber end 26 exiting working laser beam 14 , on the second sensor area 44 the camera 38 and the picture of the editing area 22 the workpiece surface 20 of the workpiece 12 , in particular a laser cutting area or a molten bath of a welding area, into separate areas with different positions within the sensor area of the camera 38 he follows. For example, the beamforming optics imaging area becomes 30 in the configured as edge region second sensor area 44 steered to the observation of the editing area 22 of the workpiece 12 in the first sensor area 42 not to bother. Thus, the images of the beamforming optics imaging area are 30 and the editing area 22 easily separated, allowing further image processing of the images on the sensor areas 42 . 44 is relieved.

The beamforming optics imaging area 30 is the area which gives a sharp picture of the out of the fiber end 26 the optical fiber 24 exiting working laser beam 14 through the beam shaping optics 32 for example by means of the imaging optics 40 on the second sensor surface 44 the camera 38 or by means of the focusing optics 18 on the workpiece surface 20 of the workpiece 12 on this sharp is pictured. Thus, therefore, the beamforming optics imaging area is 30 an imaging plane that covers the fiber end 26 the optical fiber 24 contains and usually perpendicular to the optical axis of the beam path 15 the working laser beam 14 lies. When coupling the working laser beam 14 in the case 16 of the laser processing head 10 by means of the fiber holder 28 For example, the beamforming optics imaging area 30 So for example, an upper inner wall of the housing 16 of the laser processing head 10 be. As in the in 1 shown embodiment of the working laser beam 14 even on the second sensor surface 44 In this case, wavelength-dependent effects such as chromatic aberration need not be taken into account.

The laser processing head according to the invention 10 has an actuator system, by which the position of the laser processing head 10 relative to the editing 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 can be compensated or compensated. Decisive for a focus shift of the focus of the working laser beam 14 relative to the workpiece surface 20 is here in the case of a constant distance of the laser processing head 10 to the surface 22 of the workpiece 12 a focus shift Δz _{f1 of} the focusing optics 18 at the wavelength of the working laser beam 14 λ _L and a focus shift Δz _{f2 of} the beam shaping optics 32 at the wavelength λ _{L of} the working laser beam 14 , For this purpose, a first actuator 54 for linear displacement of the laser processing head 10 relative to the workpiece surface 20 of the workpiece 12 by an adjustment Δz ₁ , a second actuator 56 for linear displacement of the focusing optics 18 in the direction of the beam path 15 the working laser beam 14 by an adjustment Δz ₂ and a third actuator 58 for linear displacement of the beam shaping optics 32 along the beam path 15 the working laser beam 14 be provided by an adjustment .DELTA.z ₃ . To get an illustration of the workpiece surface 20 or the beamforming optics imaging area 30 on the first sensor area 42 or second sensor area 44 the camera 38 to be able to map sharply is also a fourth actuator 60 provided to the imaging optics 40 along the observation beam path 36 . 46 to linearly shift a correction displacement Δd _kl . By means of the laser processing head according to the invention 10 can a focus position compensation of the focus position of the working laser beam 14 relative to the workpiece surface 20 at a heating of the beam shaping optics 32 and / or the focusing optics 18 be performed as described below.

The laser processing head according to the invention 10 or the laser processing device according to the invention 10 with a laser processing head has an evaluation unit 62 on which image data from the camera 38 processed, the fourth actuator 60 the imaging optics 40 controls and reads out the actuating position to by driving the first, second or third actuator 54 . 56 . 58 to be able to perform a focus position compensation. Here is the evaluation unit 62 formed on the one hand, by means of a displacement Δd _{kl of} the imaging optics 40 in the direction of the optical axis, which is necessary for a displacement .DELTA.z _{f2 of} the focal point of the beam-shaping optical system 32 the camera image of the beamforming optics imaging area 30 to focus again, the focus shift Δz _{f2 of} the beam shaping optics 32 in the wavelength range λ _{L of} the working laser beam 14 to calculate. Furthermore, the evaluation unit 62 adapted to, by means of a displacement Δd _{kl of} the imaging optics 40 in the direction of the optical axis, which is necessary for a displacement .DELTA.z _{f1 of} the focal point of the focusing optics 18 the camera image of the editing area 22 of the workpiece 12 to focus again, a focus shift Δz _{f1 of} the focusing optics 18 in the wavelength range λ _{L of} the working laser beam 14 to calculate. Once both focus shifts the beam shaping optics 32 Δz _f2 and the focusing optics 18 Δz _{f1 are} known, by means of the actuators 54 . 56 and 58 the working laser beam 14 back to the workpiece surface 20 or on a relative to the workpiece surface 20 be focused defined location.

To achieve this, the optical system of the laser processing head 10 initially set in an initial state so that the laser beam 14 through the beam shaping optics 32 is optimally collimated and as a parallel beam in the direction of the focusing optics 18 running. This initial state can be adjusted by the imaging optics 40 is moved to a predetermined position, in which the collimated laser beam 14 sharp on the second sensor surface 44 the camera 38 is shown. The focusing lens 18 is through the second actuator 56 also moved to a predetermined position in which the focus of the focusing lens 18 a predetermined distance to the bottom of the laser processing head 10 having. The imaging optics 40 becomes after the collimation of the working laser beam 14 adjusted so that a sharp picture of the workpiece surface 20 of the workpiece to be machined 12 takes place at the illumination wavelength λ _K.

When machining the workpiece 12 by means of the laser processing head 10 Due to the incomplete transmissivity of the optical system, heating of the focusing optics occurs 18 and the beam shaping optics 32 , associated with a due to the heating of the lenses of the focusing optics 18 and the beam shaping optics 32 changed refractive power and an associated focal shift .DELTA.z _{f1 of} the focusing optics 18 and Δz _{f2 of} the beam shaping optics 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 becomes that of the first sensor area 42 the camera 38 recorded camera image of the workpiece surface 20 blurred. By adjusting the optical system, in particular by passing through the imaging optics 40 by a Korrekturverstellweg Δd _kl by means of the fourth actuator 60 becomes the camera image of the workpiece surface 20 by controlling the evaluation unit 62 focused again and the required Korrekturverstellweg Δd _kl stored. By inclusion of the imaging ratio of imaging optics 40 and focusing optics 18 and by incorporating the focusing differences due to the different wavelengths of the observation system λ _K and the processing laser light wavelength λ _{L used} due to the chromatic aberration or other wavelength-dependent effects can by sharply places the camera image of the workpiece surface 20 and determining the correction displacement Δd _kl the focus shift Δz _{f1 of} the focusing optics 18 in the wavelength range λ _{L of} the working laser beam 14 be determined.

After determining the focus shift Δz _{f1 of} the focusing optics 18 becomes the imaging optics 40 in the preset position of the above-described initial state for collimating the working laser beam 14 adjusted to then by adjusting the imaging optics 40 by a Korrekturverstellwert .DELTA.d _kl a sharp image of the working laser beam 14 and the beamforming optics imaging area 30 on the second sensor area 42 to create. Since at the in 1 shown embodiment of the working laser beam 14 directly on the second sensor surface 42 In this case, no wavelength effects due to chromatic aberration need to be considered.

The invention includes all common methods for focussing or sharpening, some important should be explicitly mentioned:
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:

A high variance or wide histogram means good contrast.

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

bei scharfen Bildern ist der Unterschied von Bildpunkt x zu x + 1 sehr groß.SMD is determined with

with sharp images, the difference from pixel x to x + 1 is very large.

ergibt den besten Bildzustand, gilt auch für die nach Liao veränderte Schwellwertmethode.Signal Power (SL): The maximum of

gives the best image state, also applies to the Liao modified threshold value method.

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

Zeilen und Spaltenweise ermittelt. Im defokalen Bild nimmt der hohe Frequenzbereich, zu berechnen durch aufsummieren der Leistungsspektren, gegenüber dem fokalen Bild signifikant ab.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

erhalten und direkt bestimmen können.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

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, but it should be the Harris corner detector, the division of the image into certain sub-sizes, image gradient and threshold calculation, Sum of Square Difference, fuzzy logic for autofocusing, support vector classification, main component analysis and more.

In the method according to the invention, in a setting process of the system, first of all a sharply reproduced reference image is obtained from the processing area 22 or the beamforming optics imaging area 26 taken as a reference for the sharpness compared to a later recorded camera image when the corresponding focus positions of the focusing optics 18 or the beam shaping optics 32 have moved to serve. This can be created during or before a machining process.

In 2 is a highly simplified schematic view of a laser processing head 10 shown which for laser cutting a workpiece 12 is used. The in 2 shown laser processing head 10 corresponds to the in 1 shown embodiment, wherein only one nozzle 64 is provided for blowing out the molten workpiece material. Because the luminous intensity of the workpiece 12 is relatively low compared to a laser welding process, this is suitable in 1 shown embodiment of the laser processing head 10 in which no filter devices for the camera 38 must be provided, especially good.

In 3 is another embodiment of a laser processing head 10 shown schematically and greatly simplified according to the present invention. The laser processing head 10 out 3 is different from the one in 1 shown laser processing head 10 in that in the beam-shaping optics imaging area 30 next to the fiber end 26 a pattern element 66 is provided, which on the second sensor area 44 the camera 38 is imaged to a focus shift Δz _{f2 of} the beam shaping optics 32 by adjusting the imaging optics 40 in order to be able to determine a correction adjustment value Δd _kl . The pattern element 66 can one in the inner wall of the housing 16 near the fiber holder 28 However, it is also possible to print a structure either on the inner wall or a pattern element 66 to provide the inclusion of stickers.

The lighting of the pattern element 66 is done by a first lighting device 68 whose light is initially by means of an optic 70 is collimated or formed, and then 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 simultaneously to the editing area 22 of the workpiece 12 and the beamforming optics imaging area 30 in which the pattern element 66 is arranged to illuminate. When attaching the pattern element 66 Care should be taken to ensure that this is in the beamforming optics imaging area 30 or at a defined distance in the direction of the optical axis to the fiber end 26 the optical fiber 24 from which the working laser beam 14 exit, is arranged.

Since at the in 3 shown embodiment of the laser processing head 10 now the observation of both the workpiece surface 20 as well as the beamforming optics imaging area 30 with the pattern element 66 under illumination with the same wavelength λ _K , must be in the calculation of the focus shift Δz _{f2 of} the beam shaping optics 32 due to a correction displacement Δd _{kl of} the imaging optics 40 to focus a camera image of the camera 38 now also with the beam shaping optics 32 the chromatic aberration due to the different to the illumination wavelength λ _K working laser beam wavelength λ _{L 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 element 66 in the direction of the beam path 15 the working laser beam 14 to the position of the fiber end 26 the optical fiber 24 from which the working laser beam 14 exit, compensated or balanced. Here is the pattern element 66 arranged so that when a sharp picture of the pattern element 66 on the second sensor surface 44 at the illumination wavelength λ _K at the same time a complete collimation of the fiber from the end 26 exiting working laser beam 14 through the beam shaping optics 32 at the wavelength λ _{L of} the working laser beam 14 he follows.

The reflection device 48 is at the in 3 shown laser processing head 10 preferably a plane-parallel plate with a high reflection rate, in order to maximize the light intensity of the illumination by the first illumination device 68 on the pattern element 66 and a following as bright as possible image of the pattern element 66 on the second sensor surface 44 the camera 38 to reach. In front of the camera 38 between second beam splitter 72 and imaging optics 40 is further an optical bandpass filter 74 provided, which on the illumination wavelength λ _{K of} the first lighting device 68 is tuned to disturbing radiation from the area of the workpiece 12 hide. The in 3 shown laser processing head 10 is particularly suitable for use in a laser welding process, because of the process emissions of the generated weld pool in the machining area 22 of the workpiece 12 an illumination of the workpiece 12 with a predetermined illumination wavelength λ connected to an observation by means of a tuned to the illumination wavelength λ _K bandpass filter 74 is particularly advantageous.

In 4 is another embodiment of a laser processing head 10 greatly simplified and shown schematically, with the laser processing head 10 out 4 from the in 3 shown laser processing head 10 It differs in that in addition to the first lighting device 68 a second lighting device 76 is provided, which is the pattern element 66 evenly illuminates. This second lighting device 76 can be provided if a lighting of the pattern element 66 by the first lighting device 68 can not be done with sufficient intensity. In addition, it is conceivable the first lighting device 68 on an outside of the laser processing head 10 to install, such as in 6 is shown. The lighting by means of the second lighting device 76 is preferably in the same wavelength range λ _K as that of the first lighting device 68 and is also on the pass wavelength of the optical bandpass filter 74 Voted.

In 5 is a highly simplified schematic view of a laser processing head 10 shown according to yet another embodiment of the invention. The in 5 shown laser processing head 10 is different from the one in 4 shown laser processing head 10 in that instead of the pattern element 66 and the second lighting device 76 a lighting device 78 in the beamforming optics imaging area 30 next to the fiber end 26 is arranged, wherein the emitted light of the lighting device 78 on the second sensor area 44 the camera 38 is imaged to a focus shift Δz _{f2 of} the beam shaping optics 32 by adjusting the imaging optics 40 in order to be able to determine a correction displacement Δd _kl . The lighting device 78 can be like the pattern element 66 so in the direction of the optical axis of the beam shaping optics 32 to the fiber end 26 be offset that a chromatic aberration with respect to the emission light wavelength λ _{K of} the lighting device 78 and the wavelength λ _{L of} the working laser beam 14 from the beam shaping optics 32 so balanced that the working laser beam 14 from the beam shaping optics 32 is collimated when a sharp image at the observation wavelength λ _K of the lighting device 78 emitted light on the second sensor surface 44 he follows.

In 6 is a highly simplified schematic view of a laser processing head 10 shown in which the first lighting device 68 on an outside of the housing 16 is appropriate.

It should be emphasized that the in the 1 to 5 shown embodiments of the laser processing head 10 are freely combinable with respect to the components shown in the 1 to 6 Thus, embodiments shown only show particularly advantageous embodiments and should not be construed limiting the invention. Although that in 2 embodiment shown a laser cutting head 10 shows, this laser processing head 10 also be used for laser welding. In the same way are in the 3 to 6 shown embodiments of the laser processing heads 10 suitable for use in a laser cutting process. In addition, the first lighting device 68 , as in 3 shown at the in 2 shown laser processing head 10 be used to illuminate the workpiece surface. Furthermore, the in 6 shown first lighting device 68 be used in the same way to illuminate the workpiece in which in the 1 and 2 shown laser processing head 10 to be used.

As a light source for the first lighting device 68 is suitable due to the high intensity of a laser light source, which may be a semiconductor laser diode. For this purpose, AlGaInP laser diodes with multi-quantum-well structures can be used, which have a radiation maximum in a wavelength range between 635 nm and 670 nm. 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 full width of half maximum (FWHM) of about 5 to 10 nm. When using a laser diode as the first lighting device 68 In this case, it is advantageous if, due to the use of a similar material system, the emission characteristic of the second illumination device 76 or the lighting device 78 to the emission characteristic of the first illumination device 68 is agreed.

For minimizing a speckle effect due to illumination by a laser diode in the first lighting device 68 Either the coherence of the laser light can be resolved or reduced by rapid temporal variation of speckle interference within the integration time of the eye's speckle contrast. In this case, for example, the laser light of the first lighting device 68 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 lies in a wavelength range between 630 nm and 670 nm, wherein, for example, an intensity maximum at 640 nm is expedient. The radiation emerging from the fiber end can also be viewed directly, which can rub the laser radiation and the radiation of the pump wavelength.

The front of the camera 38 , which is for example a CMOS or CCD camera, arranged bandpass filters 74 has a wavelength transmission range that is responsive 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 full width at half maximum (FWHM) of the wavelength passband of the filter is FWHM 74 to choose so that just the maxima of the first and second lighting device 68 . 76 and / or the lighting device 78 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 transmits electromagnetic waves of a certain frequency range and extinguishes the remaining frequency components by interference. Regarding the half width of the optical bandpass filter 78 it is advantageous if this area is as narrow as possible in order to operate the laser processing head 10 To generate the least possible disturbance of the camera image by process lights, which by the machining of the workpiece 12 by means of the working laser beam 14 produced by melting the workpiece material. The camera 38 can use an HDR method to increase the dynamics of the recorded camera images.

Furthermore, it is preferred according to the invention if the emitted light of the second illumination device 76 or the lighting device 78 in their intensity relative to the illuminance, for example by the first illumination device 68 of the workpiece 12 is varied over time to lock-in the images of the beamforming optics imaging area 30 and the workpiece surface 20 on the sensor area 42 . 44 the camera 38 to be able to disconnect. In this case, the images of the workpiece surface 20 and the beamforming optics imaging area 30 be done on the same local sensor area, since the images can be separated due to the temporal variance.

By the laser processing head according to the invention 10 Thus, 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, which in a simple manner by using only a process observation sensor such as a camera simultaneously determines a focus shift of the focusing optics and the beam shaping optics and relatively by an actuator system a focus shift of the working laser beam can be compensated for the workpiece surface.

Claims (15)

Laser processing head ( 10 ) for machining a workpiece ( 12 ) by means of a working laser beam ( 14 ), with - a beam shaping optics ( 32 ) for forming a fiber end ( 26 ) an optical fiber ( 24 ) exiting working laser beam ( 14 ), wherein the fiber end ( 26 ) within a beamforming optics imaging area (FIG. 30 ) lies; - 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 location; and - a camera ( 38 ) with one in front in the beam path ( 36 . 46 ) arranged adjustable imaging optics ( 40 ), where an image of a processing area ( 22 ) of the workpiece ( 12 ) to a first sensor area ( 42 ) the camera ( 38 ) by a first observation beam path ( 36 ) via the focusing optics ( 18 ) and the imaging optics ( 40 ), and an image of the beamforming optics imaging area (FIG. 30 ) on a second Sensor area ( 44 ) the camera ( 38 ) by a second observation beam path ( 46 ) via the beam shaping optics ( 32 ) and the imaging optics ( 40 ) he follows. Laser processing head ( 10 ) according to claim 1, further comprising an evaluation unit ( 62 ), which is designed, by means of an adjustment path (Δd _kl ) of the imaging optics ( 40 ) in the direction of the optical axis, which is necessary for a shift of the focal point (.DELTA.z _f2 ) of the beam-shaping optical system ( 32 ) the camera image of the beamforming optics imaging area ( 30 ), the focus shift (Δz _f2 ) of the beam shaping optics ( 32 ) in the wavelength range (λ _L ) of the working laser beam ( 14 ) to calculate. Laser processing head ( 10 ) according to claim 1 or 2, wherein the evaluation unit ( 62 ) is further adapted, by means of an adjustment path (Δd _kl ) of the imaging optics ( 40 ) in the direction of the optical axis, which is necessary for a shift of the focal point (.DELTA.z _f1 ) of the focusing optics ( 18 ) the camera image of the editing area ( 22 ) of the workpiece ( 12 ) focus again, a focus shift (Δz _f1 ) of the focusing optics ( 18 ) in the wavelength range (λ _L ) of the laser processing beam ( 14 ) to calculate. Laser processing head ( 10 ) according to claim 1, 2 or 3, further comprising one in the beam path ( 15 ) of the working laser beam ( 14 ) between beam shaping optics ( 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 ). Laser processing head ( 10 ) according to claim 4, further comprising a reflection device ( 48 ), which are relative to the first beam splitter ( 34 ) is arranged such that the second observation beam path ( 46 ) of the imaging optics ( 40 ) through the first beam splitter ( 34 ) and after reflection at the reflection device ( 48 ) and the first beam splitter ( 34 ) to the beam shaping optics ( 32 ) is directed. Laser processing head ( 10 ) according to one of claims 2 to 5, further comprising an actuator system ( 54 . 56 . 58 ), which is adapted to the position of the laser processing head ( 10 ) relative to a processing surface ( 20 ) of the workpiece ( 12 ) or moving parts of the optical system ( 18 . 32 ) so that the calculated focus shift (Δz _f1 , Δz _f2 ) of the focusing optics ( 18 ) and / or the beam shaping optics ( 32 ) is compensated to the working laser beam ( 14 ) back to the workpiece surface ( 20 ) or on a relative to the workpiece surface ( 20 ) defined position to focus. Laser processing head ( 10 ) according to one of the preceding claims, characterized in that the reflection device ( 48 ) a semitransparent plane plate ( 50 ) and a light absorption element arranged behind it in the direction of jet incidence ( 52 ). Laser processing head ( 10 ) according to one of the preceding claims, characterized in that the reflection device ( 48 ) so tilted to imaging optics ( 40 ) the camera ( 38 ), that the figures at the first ( 42 ) and the second ( 44 ) Sensor area of the camera ( 38 ) in different sensor areas of the camera ( 38 ) and these are thus separable. Laser processing head ( 10 ) according to one of the preceding claims, characterized in that in the beam-forming optical imaging region ( 30 ) next to the fiber end ( 26 ) a pattern element ( 66 ) for imaging onto the second sensor area ( 44 ) the camera ( 38 ) is arranged. Laser processing head ( 10 ) according to claim 4 and one of the preceding claims, further comprising a first lighting device ( 68 ) whose light is coaxial with the first observation beam path ( 36 ) via a second beam splitter ( 72 ) between imaging optics ( 40 ) and first beam splitter ( 34 ) is simultaneously coupled to the processing area ( 22 ) of the workpiece ( 12 ) as well as the beamforming optics imaging area ( 30 ) to illuminate. Laser processing head ( 10 ) according to claim 10, further comprising a second illumination device ( 76 ) for uniform illumination of the beam shaping optics imaging area (FIG. 30 ). Laser processing head ( 10 ) according to one of the preceding claims, characterized in that in the beam-forming optical imaging region ( 30 ) next to the fiber end ( 26 ) a lighting device ( 78 ) for imaging the emitted light of the lighting device ( 78 ) to the second sensor area ( 44 ) the camera ( 38 ) is arranged. Laser processing head ( 10 ) according to one of claims 10 to 12, further comprising an optical bandpass filter ( 74 ), which in the observation beam path ( 36 . 46 ) in front of the camera ( 38 ), wherein the transmission wavelength of the optical bandpass filter ( 74 ) to the emission wavelength of the first ( 68 ) and / or second ( 76 ) Lighting device and / or the lighting device ( 78 ) is tuned. Laser processing head ( 10 ) according to one of claims 10 to 13, characterized in that the second lighting device ( 76 ) or the lighting device ( 78 ) in intensity relative to the illuminance of the workpiece ( 12 ) is varied over time to the illustrations of the first ( 36 ) and the second ( 46 ) Beam path to the camera ( 38 ) to separate. Laser processing head ( 10 ) according to one of the preceding claims, characterized in that it is suitable for laser welding or laser cutting.

Images