WO2019115449A1

WO2019115449A1 - Method and adjustment unit for automatically adjusting a laser beam of a laser processing machine, and laser processing machine comprising the adjustment unit

Info

Publication number: WO2019115449A1
Application number: PCT/EP2018/084144
Authority: WO
Inventors: Murat Cetin Bayram
Original assignee: Messer Cutting Systems Gmbh
Priority date: 2017-12-13
Filing date: 2018-12-10
Publication date: 2019-06-20
Also published as: DE102017129729A1

Abstract

Known methods for automated adjustment of a laser beam of a laser processing machine relative to an outlet opening for the laser beam comprise the method steps of: (a) focusing the laser beam, and (b) setting the position of the laser beam relative to the outlet opening. The aim of the invention is to to provide, from this starting point, a method which can be carried out simply and quickly for automated adjustment of a laser beam which also allows adjustment of the laser beam relative to the outlet opening during the operation of the laser processing. This aim is achieved, according to the invention, in that during processing of a workpiece, the radiation intensity of the radiation emitted by the workpiece is detected by at least three optical sensors, and the radiation intensity values detected by the optical sensors during the processing are used for setting the position of the laser beam according to the method step (b).

Description

Method and adjustment unit for the automated adjustment of a laser beam of a laser processing machine, and laser processing machine with the adjusting unit

Technical background

The present invention relates to a method for the automated adjustment of a laser beam of a laser processing machine relative to an exit opening for the laser beam, comprising the method steps:

(a) focusing the laser beam, and

(b) adjusting the position of the laser beam relative to the exit port.

Furthermore, the present invention relates to an adjusting unit for automated adjustment of a laser beam of a laser processing machine relative to an outlet opening. Finally, the present invention relates to a laser processing machine suitable for carrying out the method, comprising an exit opening for the laser beam, a focusing optics for focusing the laser beam in the direction of the exit opening, and an adjusting unit for automated adjustment of the laser beam relative to the outlet. The term laser processing machine is understood in the context of the invention, a machine with which a workpiece can be processed with a laser beam. Laser processing machines are used for a variety of processing methods, in particular for cutting, joining, cutting, welding, ablation, forming or for marking and labeling; They can be used for machining workpieces made of different materials, for example for machining workpieces made of metal, plastic, etc.

Glass, ceramics, stone or wood. For the purposes of the invention, the term exit opening is understood to mean a spatially limited passage for a laser beam which is delimited by a material which is impermeable to the laser beam. Laser processing machines regularly have an outlet opening for the laser beam. An exit opening of a laser processing machine is a part of the laser processing machine from which the laser beam exits the laser processing machine before it hits the workpiece. If the laser beam is guided in a housing, for example, the outlet opening can be an opening in the housing.

If, as is customary in the case of laser beam cutting of metallic workpieces, the laser beam is guided onto the workpiece together with a process gas via a nozzle for workpiece machining, the outlet opening regularly coincides with the nozzle opening for the process gas. The outlet opening defines an exit plane which the laser beam intersects, ideally with a point or circular cutting surface. The inventive method relates to the adjustment and adjustment of the position of the laser beam and thus the adjustment of the position of the cutting surface of the laser beam with the exit plane. The adjusting unit according to the invention serves to set this position; As a separate component, it can basically be retrofitted into an existing laser processing machine. State of the art

Workpieces, especially those made of metal, can be machined with high quality and precision if laser radiation is used for workpiece machining. For this purpose, laser processing machines are used which generate a laser beam, which is focused by means of focusing optics, before the laser beam exits the laser processing machine via an outlet opening, for example via a nozzle opening, and finally impinges on the workpiece to be machined.

The quality of the machining is influenced by a large number of factors, for example the focus position of the laser beam, the feed rate ability, with which the laser beam and the workpiece are moved relative to each other, or the laser power. In addition, in particular, the position of the laser beam relative to the outlet opening of the laser processing machine has a great influence on the processing quality. It has been found that particularly good results with regard to the machining quality can be achieved if the laser beam is guided as centrally as possible through the outlet opening during machining.

In the opposite case, if the laser beam is not centered relative to the outlet opening, the machined area of the workpiece may have different qualities depending on the processing direction.

To avoid these disadvantages, it is known to laser beam before

Vorzujustieren cutting process, in such a way that it is guided as centrally as possible through the outlet opening. The pre-adjustment of the laser beam can be done manually or automatically. In a known, manual method, an adhesive strip is attached to the outlet nozzle of the laser beam and then briefly delivered a laser beam pulse with low power ("nozzle shot"). This results in the adhesive strip a hole, by means of which the position of the laser beam relative to the nozzle opening, so the position and centering of the laser beam, can be determined. After a corresponding adjustment of the position of the laser beam, this process is repeated until an acceptable result with regard to the mean is achieved. However, this type of adjustment has several disadvantages: the process must firstly be carried out before the machining process and is relatively time-consuming. On the other hand, the reading accuracy is low and, finally, changes that occur during operation of the laser processing machine can not be detected and compensated for in a timely manner. As a result, the processing quality may deteriorate with increasing operating time.

In order to simplify this process, in particular to increase the reliability of the adjustment and to combine the procedure with the implementation of the method. In order to reduce the time required, DE 11 2010 003 743 B4 proposes a system and a method for the automated adjustment of the focal position of a laser beam. In this method, the laser processing head is positioned above a jet trap before the actual processing operation. For detecting the focus position, two sensors are provided, namely a jet trap sensor arranged in the jet trap on the one hand and a scattered light sensor arranged inside the laser processing head on the other hand. The focus position is adjusted until the intensity signal of the beamfall sensor is as large as possible, and the intensity signal of the scattered light sensor is simultaneously as small as possible. The use of a beam trap for adjusting the laser beam allows a good pre-adjustment of the laser beam before a machining process. However, in particular with a longer workpiece processing time, it has been shown that the position of the laser beam relative to the outlet opening can change during processing, which may be accompanied by an impairment of the processing quality. Even if these changes are detected promptly, a readjustment is usually necessary, for which the machining process must be interrupted. However, a termination of the machining process involves several disadvantages: On the one hand, a readjustment with a jet trap is time-consuming, since the laser machining head first has to be positioned over the jet trap before it can be moved back to the point of processing interruption. On the other hand, after a successful readjustment, the machining process must be continued again at the termination point. The most exact possible positioning of the laser beam at the demolition points is, however, complicated and often a continuation of the processing is accompanied by a reduced processing quality in the demolition area.

Technical task

The invention is therefore based on the object of specifying a method for the automated adjustment of a laser beam of a laser processing machine which can be carried out simply and quickly and which adjusts an adjustment of the laser beam. tively to the exit opening even during operation of the laser processing machine.

Another object of the present invention is to provide a compact and easy-to-manufacture alignment unit for the automated adjustment of a laser beam of a laser processing machine, which enables a simple and rapid adjustment of the laser beam relative to the outlet opening even during operation of the laser processing machine.

Finally, the object of the invention is to provide a laser processing machine with the adjusting unit. General description of the invention

With regard to the method for the automated adjustment of a laser beam of a laser processing machine, the abovementioned object is achieved, starting from a method of the type mentioned above, by detecting the radiation intensity of the radiation emitted by the workpiece with at least three optical sensors during a machining of a workpiece and the radiation intensity values detected by the optical sensors during processing are used to adjust the position of the laser beam according to method step (b).

The basic idea of the method according to the invention is to carry out the adjustment of the laser beam relative to the outlet opening under operating conditions, ie during processing of the workpiece (in-process adjustment), wherein the adjustment of the laser beam relative to the outlet opening from the workpiece during a laser processing process emitted radiation is used. While the laser radiation used for machining the workpiece is narrow-band, the radiation emitted by the workpiece itself comprises radiation components with wavelengths in a relatively broad wavelength range, in particular radiation components in the visible and near-infrared range. It is therefore relatively easy to distinguish the radiation emitted by the workpiece itself from that of the laser beam. The invention The method utilizes the effect that the radiation emitted by the workpiece is always emitted in an undirected manner, that is to say in all directions in space, whereby a uniformly decreasing radiation intensity distribution with a maximum in the region of the current processing point is observed. Since the workpiece has a side facing the laser beam and a side facing away from the laser beam, and higher radiation intensities of the radiation emitted by the workpiece can generally be detected on the side of the workpiece facing the laser beam, it has proven to be advantageous to use the at least three optical sensors to be arranged so that they are associated with the laser beam side facing the workpiece. The radiation intensity of the radiation emitted by the workpiece and its distribution can be easily detected during a machining process; As will be explained in more detail below, it permits conclusions to be drawn, on the one hand, with regard to the current position and position of the laser beam and, on the other hand, with regard to the positional changes to be made in order to optimally adjust the laser beam with respect to the center of the outlet opening. For this purpose, according to the invention, at least three optical sensors are provided with which the radiation intensity of the radiation emitted by the workpiece during processing can be detected. Because according to the invention at least three optical sensors are provided, an adjustment of the laser beam in two spatial directions and thus in the exit plane is possible. The optical sensors according to the invention are designed to detect radiation intensities. The detection of the radiation intensity can take place at selected, individual wavelengths, but also over a wavelength range. It has proven to be favorable if the at least three optical sensors are designed to detect radiation intensities in the same wavelength range or at the same wavelength are. The at least three optical sensors preferably have the same design.

In the simplest case, the sensors are arranged equidistant to the center axis of the outlet opening, that is to say equidistant from the beam path of a fictitious laser beam passing through the actual center of the outlet opening. If the laser beam actually passes through the center of the outlet opening, then those of the optical sensors did not detect radiation intensity values of the radiation emitted by the workpiece or only insignificantly from each other; they are ideally identical. If, on the other hand, the position of the laser beam shifts relative to the center of the outlet opening, then the optical sensors are no longer at the same distance from the point of the workpiece on which the laser beam is focused. This has the consequence that a sensor arranged closer to the focal point of the laser beam detects a higher radiation intensity than a sensor which has a larger distance to the focal point of the laser beam. Based on the radiation intensity values detected by the sensors, it is possible to deduce the current position of the laser beam relative to the outlet opening and its center.

In a preferred modification of the method according to the invention, it is therefore provided that the radiation intensity of the radiation emitted by the workpiece is detected with at least three optical sensors which are arranged equidistantly to the central axis of the outlet opening, the laser beam then being adjusted centrally to the outlet opening, if the radiation intensity values respectively recorded by the at least three optical sensors deviate from the mean value of the radiation intensity values detected by the optical sensors by at least a predefined percentage tolerance value. An equidistant arrangement of the at least three optical sensors makes possible a particularly simple evaluation of the radiation intensity values detected by the optical sensors, since in this case a direct comparison of the radiation intensity values detected by the at least three sensors can be made. In practice, however, give way to one

Passage of the laser through the center of the outlet opening of the optical

Sensors recorded radiation intensities within certain limits. One reason for these deviations are, for example, measurement errors, as they can basically occur with each measurement. The laser beam is therefore preferably considered to be aligned in the middle of the outlet opening if the radiation intensity values detected by the optical sensors are at most a predetermined percentage tolerance value from one another or value of the radiation intensity values recorded by the at least three optical sensors. The percentage tolerance value to be set depends on a variety of factors, for example the desired machining accuracy, the nozzle diameter or the laser power. Alternatively, however, it is also possible to arrange the sensors arbitrarily with respect to the laser beam, but then the position of the sensors in the evaluation of the radiation intensities detected by them must be taken into account, for example by a computational correction. This can be done, for example, via an evaluation or correction unit to which the radiation intensity values determined by the optical sensors are present as an input signal.

The radiation intensity values detected by the at least three optical sensors are used as the basis for the adjustment by adjusting the position of the laser beam relative to the outlet opening on the basis of the radiation intensity values. In the simplest case of equidistantly arranged optical sensors, the adjustment is achieved, for example, when all the optical sensors detect the same radiation intensity value within a predetermined fluctuation range. In this case, the end point of the adjustment can be made without specifying a desired value. Alternatively, however, it is also possible to prescribe a desired value, in particular if, for example, additional empirically determined correction factors are to be taken into account during the adjustment. In this case, the position can be adjusted by comparing each radiation intensity value currently detected by an optical sensor (actual value of the sensor) with the desired value specified for the respective sensor and setting it to the respective desired value. The accuracy or the resolution of the position determination of

Laser beam and the subsequent adjustment can be increased if a larger number of optical sensors is used, so by four or more sensors are provided. Alternatively, it is also possible to increase the accuracy or resolution by using groups of optical sensors of different types. Here it has in particular as proven favorable when the radiation intensity of the radiation emitted by the workpiece is simultaneously detected by a first sensor group having at least three optical sensors of a first type and a second sensor group having at least three optical sensors of a second type during processing of a workpiece , The optical sensors of the first and second sensor groups differ, for example, in their design, if they are designed to detect different wavelengths or wavelength ranges of the radiation emitted by the workpiece.

Due to the fact that the adjustment method according to the invention can also be carried out during the operation of a laser processing machine (in-process adjustment), there are several advantages: The advantage of an in-process adjustment is on the one hand that even during A processing possible adjustment a consistent quality machining can be achieved even with a longer processing time and on the other hand, the total processing time can be reduced, as a complex readjustment, for example using a jet trap, and the most accurate positioning of the laser beam at resumption The processing at the place of processing interruption can be omitted. This contributes to efficient and thus cost-effective processing. At the same time, the method according to the invention can also be used for monitoring the laser processing process, since it is also possible to detect deviations from predetermined radiation intensity values. An additional sensor for process monitoring can therefore be dispensed with.

Advantageously, the method can be used for separating or marking metallic workpieces, since the inventive method is accompanied by a high processing accuracy. In particular, when separating metalli shear workpieces, there is the problem that it can lead to cut surface injuries or burrs in the region of the cut surfaces in the case of poor centering of the laser beam with respect to the outlet opening. In the worst case, gross deviations of the centering, it is even possible that the cut due to the lack of centering of the laser beam tearing even during the cutting process.

It has proved to be advantageous if, for adjusting the position of the laser beam relative to the outlet opening in accordance with method step b), the radiation intensity values detected by the optical sensors in the wavelength range from 800 nm to 1400 nm are used.

To detect the radiation emitted by the workpiece, it is possible to use optical sensors which are sensitive over a more or less large wavelength range. However, the adjustment accuracy can be increased if, for setting the position of the laser beam, only certain radiation intensity values are used, which were determined for a specific wavelength range or those at a specific wavelength. Which wavelength range or which wavelength appears the most suitable is basically independent of the laser wavelength and essentially depends on which material the workpiece is manufactured from. In the machining of metallic workpieces, in particular of steel, stainless steel, aluminum, brass or copper, good results are obtained with regard to the alignment accuracy, if the radiation intensity values determined in the wavelength range from 800 nm to 1,400 nm are used to set the position of the laser beam. The wavelength range from 900 nm to 1250 nm has proved particularly suitable. This can be achieved, for example, by using either special optical sensors that are sensitive only in a certain wavelength range, preferably the above-mentioned wavelength range, or that a filter is arranged in the beam path in front of a sensitive sensor over a relatively large wavelength range for radiation of certain wavelengths, preferably only for wavelengths in the above-mentioned wavelength ranges, is permeable.

It has proved to be particularly favorable when, for adjusting the position of the laser beam relative to the outlet opening according to method step b), that of the optical sensors in the wavelength range from 800 nm to 1000 nm and in Wavelength range from 1,100 nm to 1,400 nm recorded radiation intensity values are used. The fact that the wavelength range of 1000 nm to 1100 nm is not detected, the method is particularly suitable for the adjustment of an Ytterbium fiber laser with an emission wavelength of 1060 nm. The detection of two separate wavelength ranges can be carried out both with separate sensors and with a single sensor, for example by arranging a filter which absorbs optical radiation having wavelengths in the wavelength range from 1000 nm to 1100 nm by the single sensor. Advantageously, the irradiation intensity of the radiation emitted by the workpiece is detected by the at least three optical sensors after they have passed through the outlet opening.

If the optical sensors are arranged behind the exit opening, viewed from the workpiece, only a portion of the radiation emitted by the workpiece is detected by the optical sensors, namely the part which is emitted in the direction of the exit opening. As a result, it is primarily radiation portions which are emitted by the workpiece at a certain near range around the processing point of the laser beam that are detected. Since the differences in the radiation intensities in the vicinity of the processing point of the laser beam are particularly pronounced, the above-described arrangement of the optical sensors contributes to the accuracy of the position detection improves and, consequently, the Justiergenauigkeit is increased. The outlet opening acts as an aperture, so that the light transmission is reduced to the optical sensors and only a limited proportion of radiation emitted by the workpiece radiation has to be detected by the optical sensors and taken into account in the adjustment of the laser beam. This opens up possibilities in two respects: On the one hand, by suitable choice of the outlet opening and its size, the radiation fraction detectable by the optical sensors can be adapted to the physical properties of the optical sensors and, on the other hand, the radiation emitted by the workpiece can be adjusted by the limitation of the radiation component through the outlet opening and the use of inexpensive sensors allows.

In an advantageous embodiment of the method according to the invention, a pilot beam is used for pre-adjustment of the laser beam, the radiation of the pilot beam reflected by the workpiece being detected by the at least three optical sensors, and the intensity values of the reflected radiation detected by the optical sensors for presetting the position of the laser beam are used relative to the outlet opening.

The inventive method for automated laser beam adjustment relates primarily to the in-process adjustment of the laser beam. However, it is also advantageous when using the method according to the invention if, prior to workpiece machining, a pre-adjustment of the laser beam is first carried out. This has the advantage that processing can begin immediately. With regard to the pre-adjustment can be made either known methods, as described for example in DE 11 2010 003 743 B4, or, if the workpiece to be machined has a reflective surface, the pre-adjustment can alternatively with a pilot beam and the already existing at least three optical sensors are performed. A reflective surface is understood to be a surface whose surface roughness (mean roughness R _a ) is less than the wavelength of the pilot beam. The use of the pilot beam for pre-adjustment has the advantage that the optical sensors already provided according to the invention can also be used for pre-adjustment, so that a simple and cost-effective method is obtained which simultaneously involves a low outlay on equipment.

For the purposes of the invention, a pilot beam is understood to mean a laser beam with low energy, preferably below 5 mW, which is guided in such a way that it is focused on the workpiece through the outlet opening instead of the laser beam. Particularly good results with regard to the accuracy of the pre-adjustment are achieved if the laser beam and pilot beam are at least partially coincidental. Focused on the workpiece using the same optics. The wavelength of the pilot beam is chosen so that it can be detected by the already existing at least three optical sensors. Preferably, the pilot beam has a wavelength in the visible spectral range, in particular in the wavelength range of 635 nm to 750 nm. Since the energy of the pilot beam is too low to machine the workpiece, the pilot beam is reflected at the workpiece, the reflected radiation from the optical sensors is detected. The intensity values of the reflected radiation detected by the optical sensors are used analogously to the radiation intensity values described above for in-process adjustment for detecting and adjusting the position of the pilot beam and thus also of the laser beam relative to the outlet opening.

In addition, it is also conceivable that the pilot beam is guided parallel to the beam path of the laser beam through a separate pilot beam opening. In this case, however, the point at which the pilot beam hits the workpiece does not necessarily coincide exactly with the point at which the laser beam strikes the workpiece. In order nevertheless to be able to perform a pre-adjustment, it would therefore be necessary to provide either separate optical sensors for the pilot beam or a mathematical correction of the results determined by means of the pilot beam. With regard to the adjusting unit, the abovementioned technical problem is solved according to the invention by an adjusting unit of the type mentioned in the introduction in that the adjusting unit has at least three optical sensors for detecting the radiation emitted by the workpiece during machining of a workpiece wherein the adjusting unit is designed such that the radiation intensities detected by the at least three optical sensors during processing are taken into account by the adjusting unit when adjusting the position of the laser beam relative to the outlet opening.

The adjusting unit according to the invention can be used for in-process adjustment of the laser beam of a laser processing machine and has at least three optical sensors, with which the sensors can be adjusted during a laser processing process. This radiation emitted by the workpiece, in particular its intensity, can be detected. As already explained above, the radiation intensities detected by the optical sensors permit conclusions, on the one hand, with regard to the current position and position of the laser beam relative to an outlet opening and, on the other hand, with regard to possible changes in position in order to optimally position the laser beam with respect to the center of the outlet opening to adjust. The detection of the radiation intensity can take place at selected, individual wavelengths, but also over a wavelength range. It has proved to be advantageous if the at least three optical sensors are designed to detect radiation intensity in the same wavelength range or at the same wavelength. The at least three optical sensors preferably have the same design.

Furthermore, the adjusting unit is designed such that it takes into account the radiation intensity values detected by the at least three optical sensors when adjusting a laser beam. For this purpose, the adjusting unit preferably has an evaluation unit with a computer, at which the radiation intensities determined by the optical sensors are present as an input signal and which calculates and outputs an output signal on the basis of which the setting of the position the laser beam can be made relative to the outlet opening. It has proved favorable if the evaluation unit is designed in such a way that, based on the radiation intensity values detected by the sensors, the current position of the laser beam relative to the outlet opening and its center can first be determined. Given the specification of upper and lower limits for the position of the laser beam, the processing process can first be monitored by means of the optical sensors. If the upper and / or lower limits are exceeded or fallen below, necessary position changes can be calculated by the evaluation unit in order to adjust the position of the laser beam relative to the outlet opening.

The optical sensors are preferably arranged in the adjusting unit such that the adjusting unit can be installed in a laser processing machine, in such a way that the optical sensors are arranged equidistant from the center axis of the outlet opening. Alternatively, however, it is also possible for the sensors in the adjusting unit to be arranged as desired when the adjusting unit is designed such that the actual position of the sensors relative to the laser beam to be adjusted can be determined and determined by the adjusting unit can be considered in the evaluation of the radiation intensities detected by them, for example, by a computational correction by means of the evaluation unit.

The accuracy or the resolution of the position determination of the laser beam and the subsequent adjustment can be increased if a larger number of optical sensors is provided. If at least three optical sensors are provided, an adjustment in two spatial directions and thus in the exit plane is possible. The accuracy or resolution of the position determination and adjustment can be further increased by four or more sensors are provided. Alternatively, it is also possible to increase the accuracy or resolution by using groups of optical sensors of different types. In this case, it has proved particularly advantageous for the adjustment unit for detecting the radiation emitted by the workpiece to have a first sensor group with at least three optical sensors of a first type and a second sensor group with at least three optical sensors second construction, wherein the adjusting unit is configured such that it takes into account the radiation intensity values detected by the first sensor group and / or the radiation intensity values detected by the second sensor group for adjusting the position of the laser beam relative to the outlet opening. The consideration of the radiation intensity values of two sensor groups contributes to a high adjustment accuracy. The optical sensors of the first and second sensor groups differ in their design, for example, when they are designed to detect different wavelengths or wavelength ranges of the radiation emitted by the workpiece. It has proved to be advantageous if the at least three optical sensors are designed to detect optical radiation in the wavelength range of visible light and / or near-infrared radiation.

It has been shown that a good adjustment accuracy can be achieved if the optical sensors are designed to detect optical radiation in the wavelength range of the visible and near-infrared light. Radiation in the wavelength range of visible light or those with wavelengths in the near-infrared range is emitted by many workpiece materials during their processing with a laser beam. Moreover, radiation in this wavelength range is easily distinguishable from the laser beam emission of many commonly used laser beam sources. Preferably, the at least three optical sensors are each sensitive in a wavelength range from 800 nm to 1,400 nm.

Advantageously, at least five optical sensors are provided for detecting the radiation emitted by the workpiece during machining of a workpiece.

If a plurality of optical sensors are provided for detecting the radiation emitted by the workpiece, then the sensors differ in their position relative to the feed direction. If, for example, four optical sensors are arranged offset by 90 ° relative to one another around the central axis of the outlet opening, a distinction can be made between an optical sensor which precedes the machining process in the feed direction, two laterally arranged optical sensors and an optical sensor tracking the machining process. It has now been shown that at feed speeds of more than 800 mm / min, in particular, a sensor tracking the feed direction detects a signal, albeit usually slightly higher, than a sensor preceded in the feed direction or the two laterally arranged sensors sensors. However, too high a radiation intensity value detected by the tracking optical sensor can contribute to a misalignment of the laser beam relative to the outlet opening. Are at least five optical Provided sensors at feed speeds of more than 800 mm / min in the evaluation, the signal of the tracked in the feed direction led optical sensor can be disregarded without this an impairment of the alignment accuracy purchase must be taken because four sensors are still available for adjustment stand.

In a preferred embodiment of the adjusting unit according to the invention, an optical filter is arranged in the beam path in front of the at least three optical sensors, which filters out the wavelength of the laser beam.

An optical filter, which selects incident optical radiation by the wavelength in which it filters out the wavelength of the machining laser beam, contributes to the fact that radiation components, which are not needed in the adjustment of the laser beam and can even disturb, eliminated as effectively as possible - the. This contributes to achieving a high adjustment accuracy.

In this context, it has proved to be advantageous if the optical sensors are arranged in the beam path after a partially transmissive mirror on which the optical filter is applied.

A partially transmissive mirror is a mirror which is permeable to some of the optical radiation incident on it and which reflects the other part. The use of a semitransparent mirror has advantages in particular when the optical sensor is arranged downstream of the partially transmissive mirror, so that the proportion of the radiation impinging on the optical sensor is reduced. If the optical sensor is mounted behind a semitransparent mirror, the optical filter can be easily applied to the partially transmissive mirror. A partially transparent mirror with a coating applied thereon is easy and inexpensive to manufacture. In addition, a coated semitransparent mirror requires only a small space and thus contributes to a compact adjustment unit. It has proven useful if the optical sensors are photodiodes or CCD chips, and if an optical filter is applied as a coating to the photodiodes or the CCD chips.

The optical filter can be applied directly to the optical sensors, for example to a photodiode or a CCD chip. A coated photodiode or a coated CCD chip can be manufactured easily and inexpensively; they also require little more space than their uncoated embodiment.

With regard to the laser processing machine, the abovementioned technical object is achieved on the basis of a laser processing machine of the type mentioned at the outset by providing an adjusting unit-as described above-for automated adjustment of the laser beam relative to the outlet opening.

The laser processing machine according to the invention is designed for in-process adjustment of the laser beam relative to the outlet opening. It can be used in particular for cutting and marking workpieces made of metal. The laser processing machine has an adjustment unit, which detects the intensity of the radiation emitted by the workpiece during processing. Based on the detected radiation intensities, it is possible to determine the current position and position of the laser beam as well as position changes that have to be made in order to optimally adjust the laser beam with respect to the center of the outlet opening. With regard to the adjusting unit and its configuration, reference is made to the above statements.

It has proved to be advantageous if the outlet opening has an opening width and the laser beam in the plane of the outlet opening has a maximum laser beam diameter, and if the ratio of the maximum laser beam diameter to the opening width is less than 0.7, preferably Range is between 0.5 and 0.25. The ratio of the laser beam diameter to the opening width of the Austrittsöff opening has influence on the alignment accuracy. The following applies: the larger the opening width, the more radiation can pass through the outlet opening and be subsequently detected, that is to say the greater are the detected radiation intensity values. Since the laser beam can have different diameters in the exit plane as a function of the focal position, the diameter which the laser beam can take up to a maximum in the exit plane is subsequently turned off. This diameter is referred to herein as the maximum laser beam diameter. At a ratio of the maximum laser beam diameter to the opening width of less than 0.7, at least 50% of the area of the exit plane is available for detecting the radiation emitted by the workpiece. Preferably, the ratio of the maximum laser beam diameter to the opening width is less than 0.5. If the ratio of the maximum laser beam diameter to the opening width is less than 0.5, more than 75% of the surface of the exit plane is available for detecting the radiation emitted by the workpiece. The detected signal is an intense radiation intensity signal, which contributes to the most accurate possible adjustment. If the ratio of the maximum laser beam diameter to the opening width is less than 0.25, more than 93% of the surface of the exit plane is available for detecting the radiation emitted by the workpiece. A further reduction of the ratio of maximum laser beam diameter to the opening width therefore hardly contributes to an improvement in the alignment accuracy.

EXEMPLARY EMBODIMENT The invention will be described in more detail below on the basis of exemplary embodiments and drawings. It shows in a schematic representation:

FIG. 1 shows an embodiment of a laser processing head of a laser cutting machine according to the invention, positioned above a workpiece surface, with an alignment unit in longitudinal section, FIG. 2 shows a cutting nozzle of a laser cutting machine according to the invention, positioned above a workpiece surface, and the radiation path of the laser radiation and the radiation emitted by the workpiece, when the laser beam is non-centered relative to the outlet opening;

FIG. 3 shows the cutting nozzle positioned above the workpiece surface according to FIG

FIG. 2 and the beam path of the laser radiation and the radiation emitted by the workpiece at a laser beam centered relative to the outlet opening, FIG. 4 shows a first embodiment of an adjustment unit according to the invention with twelve sensors, and

Figure 5 shows a second embodiment of an adjusting unit according to the invention with five sensors.

FIG. 1 shows, in a schematic representation, an embodiment of a laser cutting machine to which the reference numeral 100 as a whole is assigned. The laser cutting machine 100 is suitable for cutting a metallic workpiece 108 with a thickness of up to 25 mm and comprises a laser beam source 111 for generating a laser beam 101, a laser processing head 110 with a process gas inlet 105 and a focusing optics 104 for focusing the laser beam. serstrahls 101 in the direction of the cutting nozzle outlet opening 106 or in the direction of the workpiece 108, and an adjusting unit 112, which allows an automated adjustment of the laser beam 101 relative to the outlet opening 106.

The laser beam source 111 is a CO2 laser; the wavelength of the laser beam 101 generated by the laser beam source 111 is 10.6 μm. For deflecting the laser beam 101 in the direction of the workpiece 108, a mirror 102 is provided. The laser beam 101 is finally focused by the focusing unit 104 so that the diameter of the laser beam 101 seen in the plane of the outlet opening 106 is a maximum of 2 mm. The outlet opening 106 has an opening wide of 3 mm. The ratio of the maximum diameter of the laser beam 101 in the plane of the exit opening 106 to the opening width is 0.67 adjustment unit 112 comprises three optical sensors 103a, 103b in the form of photodiodes designed to detect infrared radiation in the wavelength range of 800 nm to 1250 nm (In Figure 1, one of the three optical sensors is not shown). Applied to the two optical sensors 103a, 103b is a coating (not shown) which acts as a filter, which absorbs radiation in the wavelength range of the laser beam 101 generated by the laser beam source 111, for radiation in the abovementioned wavelength range from 800 nm to 1250 but permeable. The optical sensors 103a, 103b are designed to detect radiation intensities.

During the processing of the workpiece 108 with the laser beam 101, an energy input into the workpiece 108 occurs locally, as a result of which the workpiece 108 itself emits radiation 107. The spectrum of the radiation 107 emitted by the workpiece 108 depends primarily on the material from which the workpiece 108 is manufactured. Workpieces made of metal as a rule emit radiation in the wavelength range from 800 nm to 1,400 nm. The two optical sensors 103a, 103b are arranged parallel to the beam path of the laser beam 101 and equidistant from a center axis extending through the center of the outlet opening 106 such that they detect the radiation 107 emitted by the workpiece 108 during processing, provided that it passes through the exit opening 106 of the cutting nozzle. At the evaluation unit 113 of the adjusting unit 112, the radiation intensities detected by the optical sensors 103a, 103b are present as an input signal. The evaluation unit 113 has a computing unit (not shown) which uses the input signals to determine the position of the laser beam

101 calculated relative to the outlet opening 106. In addition, the computing unit calculates from the input signals how the position of the laser beam 101 needs to be changed so that the laser beam 101 passes through the center of the output port. Based on this, the evaluation unit 112 outputs an output signal to an actuator (not shown), which converts the calculated position changes. In an alternative embodiment of the laser cutting machine 100 (not shown), the mirror 102 is a partially transmissive mirror onto which a filter layer is applied, which absorbs the wavelength of the laser beam 101. In addition, three optical sensors in the form of CCD chips are provided, which are arranged in the beam path of the radiation emitted by the workpiece following the partially transmissive mirror in a plane perpendicular to the beam direction of the laser beam 101. Alternatively, it is of course also possible to use an uncoated, partially transparent mirror instead of the partially transmissive mirror provided with the filter layer and to apply the filter layer therefor to the CCD chips (likewise not shown).

The method according to the invention for the automated adjustment of a laser beam 101 of a laser processing machine 100 relative to an outlet opening 106 for the laser beam 101 will be explained in greater detail below with reference to FIG.

Before starting a machining of the workpiece 108, a pre-adjustment is carried out first. Here, instead of the laser beam 101, a pilot beam with a wavelength of 730 nm and a power of 4.5 mW is generated and focused by means of the focusing unit 104 through the outlet opening 106 onto the workpiece 108. The energy of the laser radiation of the pilot beam is so small that the workpiece 108 can not be processed with the pilot beam. Consequently, no radiation emitted by the workpiece 108 itself also arises. However, the pilot beam is reflected at the workpiece surface, so that the reflected pilot beam radiation is detected by the two optical sensors 103a, 103b. Since the optical sensors 103a, 103b are arranged equidistantly to the center axis of the outlet opening 106 in FIG. 1, the desired pre-adjustment is achieved when the intensity values of the reflected radiation detected by the two optical sensors 103a, 103b are no more than 0.5% radiation intensity values differ.

During the processing, a laser beam 101 is initially generated by means of the laser beam source 11 1. The laser beam 101 is deflected by a mirror 102 in the direction of the workpiece 108. By means of the focusing unit 104, the laser beam 101 focused on the workpiece 108, in such a way that the laser beam 101 first passes through the exit opening 106 of the cutting nozzle before it hits the workpiece 108. By machining the workpiece 108 with the laser beam 101, the workpiece 108 undirectedly emits radiation 107 having wavelengths in a wide wavelength range, in particular in the wavelength range of 800 nm to 1400 nm. The radiation 107 emitted by the workpiece 108 finally becomes with the three optical sensors 103a .

103b recorded. The optical sensors 103a, 103b are photodiodes designed to detect radiation intensities at a measurement wavelength of 1200 nm. As a function of time, radiation intensity values which are subsequently used for adjusting the position of the laser beam 101 relative to the outlet opening 106 are detected by the optical sensors 103a, 103b. In particular, the current position of the laser beam 101 relative to the center of the outlet opening 106 can be determined from the detected radiation intensity values. In addition, it can be calculated on the basis of the detected radiation intensity values as to how the position of the laser beam 101 relative to the outlet opening 106 is to be changed in order to adjust the laser beam 101 centrally to the outlet opening 106. Finally, the position of the laser beam 101 relative to the outlet opening 106 is adjusted by means of a suitable actuator. The adjustment / adjustment of the position of the laser beam 101 relative to the exit opening 106 takes place in an iterative method. Since the optical sensors 103a, 103b are arranged equidistantly to the center axis of the exit opening 106 in FIG. 1, the desired adjustment of the laser beam 101 relative to the exit opening 106 is achieved when the radiation intensity values detected by the three optical sensors 103a, 103b by a maximum of 0.5%. In an alternative method, it is also possible to refer the radiation intensity values detected by the optical sensors 103a, 103b to the mean value of the radiation intensity values detected by all the optical sensors 103a, 103b. In this case, it is preferable to use the arithmetic mean. The desired adjustment is achieved if none of the radiation intensity values recorded by the optical sensors exceeds by more than 0.3% (percentage tol- value) deviates from the arithmetic mean value of the radiation intensity values detected by the optical sensors.

Figures 2 and 3 show a cutting nozzle 210 of a laser cutting machine positioned over a steel workpiece 108. Furthermore, a laser beam 211 is shown, which is focused on the workpiece 108 through the outlet opening 106. Finally, on the side facing away from the workpiece 108 of the cutting nozzle 210 three sensors are arranged, which are designed to detect the emitted radiation from the workpiece 200 200. Of the three sensors, only two sensors S1 and S2 are shown to simplify the illustration. FIG. 2 illustrates the case that the beam path of the laser beam 211 does not run centered to the outlet opening 106. The processing of the workpiece 108 with the laser beam 211 results in an energy input into the workpiece 108. As a result, the workpiece 108 emits non-directionally radiation 200 in a wavelength range from 800 nm to 1,400 nm, among other things. If one considers the boundary rays 201, 202 of the radiation emitted by the workpiece with critical angles ai, a ₂ , it is shown that in the case of a maladjustment the sensors S1, S2 detect radiation intensity values deviating from each other. Here, the sensor S1 detects a lower radiation intensity than the sensor S2.

In contrast, FIG. 3 illustrates the case in which the beam path of the laser beam 211 is centered with respect to the outlet opening 106. If one observes the boundary rays 201, 202 of the radiation emitted by the workpiece with the critical angles a, it can be seen that in the case of an adjusted laser beam 211, the sensor S1 and the sensor S2 theoretically detect the same radiation intensity.

FIG. 4 shows an embodiment of an adjusting unit according to the invention, to which the reference numeral 400 as a whole is assigned. The adjusting unit 400 comprises an evaluation unit 401, an opening 402 through which a laser beam to be adjusted can be guided, and three sensor groups 403, 404, 405 each with four identically constructed sensors which are offset by 90 ° about the opening 402 are arranged. The output signals of the individual sensors of the sensor groups 403, 404, 405 are applied to the evaluation unit 401 as an input signal. The sensor groups 403, 404, 405 differed as follows:

The sensor group 403 comprises four identically constructed sensors which are designed to detect wavelengths in the range from 600 nm to 900 nm. The sensor group 404 comprises four identically constructed sensors which are designed to detect wavelengths in the range of 1,000 nm to 1,200 nm. Because the sensors of the sensor groups 403 and 404 differ in the wavelength ranges that can be detected with them, it is possible to select, for example, depending on the laser used or the workpiece to be machined, which radiation components are to be detected in which wavelength ranges. In this case, it is possible to detect radiation in the wavelength range from 600 nm to 900 nm and / or radiation in the wavelength range from 1000 nm to 1200 nm. This contributes to the fact that the adjustment unit can be used flexibly.

The sensor group 405, like the sensor group 404, comprises four identically constructed sensors which are designed to detect wavelengths in the range from 1,000 nm to 1,200 nm. The sensors of the sensor group 405, however, have an approximately 10-fold higher sensitivity than the sensors of the sensor group 404. The advantage of the simultaneous use of sensor groups, which differ in the sensor sensitivities, is that the same adjusting unit for focusing different laser beams can be used, for example, to focus a working laser beam and a pilot laser beam. In this way, a flexibly usable adjustment unit is obtained.

FIG. 5 shows an embodiment of an adjusting unit according to the invention, to which the reference numeral 500 is assigned overall. The adjusting unit 500 comprises a suitable for performing a laser beam to be adjusted opening 501, and five identical optical sensors 503-507, which around the opening 501 to

72 ° offset from one another. If, for example, the adjusting unit 500 is moved relative to a workpiece at a feed rate of more than 800 mm / min in the feed direction 502, in particular the sensor tracked in the feed direction of the machining, here the sensor 503, regularly detects a higher one Radiation intensity signal than the others in Vorschubrich- 502 seen laterally arranged sensors, here the sensors 504-507. The adjustment unit 500 is therefore designed so that the radiation intensity signal of the sensor tracked in the feed direction 502, which is the signal of the sensor 503 in the present example, is disregarded and only the signals of the four remaining sensors are taken into account for the adjustment , This counteracts a misalignment caused by an increased radiation intensity signal of a sensor tracked in the feed direction.

Claims

claims

1. A method for the automated adjustment of a laser beam of a laser processing machine relative to an exit opening for the laser beam, comprising the method steps:

(a) focusing the laser beam, and

(b) adjusting the position of the laser beam relative to the outlet opening, characterized in that during a machining of a workpiece, the radiation intensity of the radiation emitted by the workpiece is detected by at least three optical sensors, and the radiation intensity values detected by the optical sensors during the Processing for adjusting the position of the laser beam according to method step (b) can be used.

2. The method according to claim 1, characterized in that for adjusting the position of the laser beam relative to the outlet opening according to process step b) the radiation intensity values recorded by the optical sensors in the wavelength range from 800 nm to 1400 nm are used.

3. The method of claim 1 or 2, characterized in that is detected by the at least three optical sensors, the radiation intensity of the radiation emitted by the workpiece after their passage through the outlet opening.

4. Method according to claim 1, characterized in that a pilot beam is used for pre-adjustment of the laser beam, wherein the radiation reflected by the workpiece is detected by the at least three optical sensors, and the intensity values of the reflected radiation detected by the optical sensors be used for presetting the position of the laser beam relative to the outlet opening.

5. adjusting unit for the automated adjustment of a laser beam of a laser machining machine relative to an exit opening for the laser beam, characterized in that the adjusting unit has at least three optical sensors for detecting the radiation emitted by the workpiece during machining of a workpiece, wherein the adjusting unit is designed in such a way that the radiation intensities detected by the at least three optical sensors during processing are taken into account by the adjusting unit when adjusting the position of the laser beam relative to the outlet opening.

6. Adjustment unit according to claim 5, characterized in that the at least three optical sensors are designed for detecting optical radiation in the wavelength range of visible light and / or near-infrared radiation.

7. adjusting unit according to claim 5 or 6, characterized in that

at least five optical sensors are provided for detecting the radiation emitted by the workpiece during a machining of a workpiece.

8. Adjustment unit according to one of the preceding claims 5 to 7, characterized in that in the beam path in front of the at least three optical sensors, an optical filter is arranged, which filters out the wavelength of the processing laser.

9. Adjusting unit according to claim 8, characterized in that the optical sensors are arranged in the beam path after a partially transparent mirror, on which the optical filter is applied.

10. Adjustment unit according to claim 9, characterized in that the optical sensors are photodiodes or CCD chips, and that an optic filter is applied as a coating to the photodiodes or the CCD chips.

11. Laser processing machine, comprising an outlet opening for the laser beam and a focusing optics for focusing the laser beam in the direction of the outlet opening, characterized in that an adjusting unit according to one of the preceding claims 5 to 10 for the automatic adjustment of the laser beam relative is provided to the outlet opening.

12. Laser processing machine according to claim 11, characterized in that the outlet opening has an opening width and the laser beam in the plane of the outlet opening seen a maximum laser beam diameter, and that the ratio of the maximum laser beam diameter to the opening width is less than 0.7, preferably ranges between 0.5 and 0.25.