Apparatus and method for determining focal position taking process gas into account

Abstract

The invention relates to a beam analysis device (10) for determining an axial position of a focal point (76) of an energy beam (77) of electromagnetic radiation guided in a laser processing optical system (100). The beam shaping device (12) is configured to receive a sample beam (70) and image at least a part of the sample beam (70) onto a detector (40) to form an intensity distribution (79) on the detector (40). The evaluation device (80) is configured to process an electrical signal (64) from the detector (40) and to determine a geometric parameter from the intensity distribution (79). In order to determine the focal point position more accurately during the processing process, the evaluation device (80) is configured to receive a cutting gas signal (63), determine a correction value taking into account the cutting gas signal (63) and determine the axial position of the focal point (76) of the energy beam (77) taking into account the geometric parameter and the correction value. The invention further relates to a system comprising such a beam analyzing device (10) and a method for determining the axial position of a focal point (76) of an energy beam (77) of electromagnetic radiation guided in a laser processing optical system (100).

Description

[Technical Field]

[0001] The present invention relates to an apparatus and a method for determining the axial position of the focal point of an energy beam of electromagnetic radiation guided in a laser processing optical system. The energy beam may in particular be a laser beam. The laser processing optical system may in particular be a cutting optical system having a cutting gas system. In particular, the present invention provides an apparatus and a method that allow for determining the position of the beam focal point of the processing optical system during an ongoing laser processing process. [Background technology]

[0002] In laser material processing, adjusting and controlling the axial focal position of the laser beam relative to the material being processed or workpiece has a significant impact on the quality of the processing process.

[0003] In the laser cutting process, not only the focal position relative to the workpiece is important, but also the distance between the workpiece and the cutting nozzle, since the flow dynamics of the cutting gas have a significant effect on the outcome of the cutting process. To maintain a defined distance between the workpiece and the cutting nozzle, capacitive distance measurement and control are known in the prior art.

[0004] However, controlling and / or tracking the distance between the cutting nozzle and the workpiece does not simultaneously guarantee a defined axial position of the laser beam focal point relative to the workpiece, since the focal position of the laser processing optics may change independently of the distance or may change unintentionally or uncontrollably.

[0005] Modern laser processing systems often use lasers with high brightness and power, often in the range of several kilowatts. Due to the material properties of the optical elements of laser processing optics, high laser powers can cause the optics to heat up. This generates a radial temperature gradient across the optics, resulting in changes in the optical power of the optics due to the temperature dependence of material parameters such as the refractive index. This phenomenon is called thermal focus shift. This phenomenon is exacerbated by reaction products and particles of various sizes generated during laser material processing. These products and particles can deposit on the processing optics or on the protective glass of the processing optics, resulting in increased absorption. As a result, the protective glass, in particular, often causes undesirable and uncontrollable changes in the beam focus position of the processing optics.

[0006] Furthermore, the laser processing optics may also have a device for adjusting or changing the axial focus position towards the target position. For example, a part of the lens system of the processing optics, in particular the collimator or collimator objective lens, may be arranged to be axially adjustable so that the axial focus position of the optics can also be adjusted or tracked.

[0007] It is therefore desirable, particularly for laser cutting optics, to be able to measure, control and, if necessary, track the axial focus position during an ongoing machining process.

[0008] In the prior art, devices and processing optics are known which split off a part of a laser beam from an optical system and direct the split off beam towards a beam analysis device.

[0009] For example, WO 2021 / 156788 discloses a cutting optical system in which a portion of a focused laser beam is laterally separated by an optical element arranged in front of a cutting nozzle and directed toward a wavefront sensor. The determined wavefront is compared with a reference wavefront. To reduce aberrations, the focal position can be changed by adjustable focusing.

[0010] Furthermore, from DE 10 2011 007 176 A1, a laser processing head is known in which laser radiation reflected back from an inclined optical element, in particular a protective glass, is directed onto a detector, and the focal position is determined from the radiation detected by the detector. A device for varying the focal position also makes it possible to control the focal position.

[0011] German Patent Application No. DE 10 2017 131 224 A1 proposes detecting beam characteristics based on measuring split reflections at at least two positions offset from one another along the propagation direction. Among other things, the focal position can be determined from the determined beam characteristics. Again, split reflections are generated using a protective glass tilted relative to the beam axis.

[0012] It should be noted that in known devices in which beam portions are separated in a focused beam by tilted optical elements, aberrations, such as astigmatism, can occur in the focused beam due to the tilted optical elements, which can have an undesirable effect on the quality of the beam focus.

[0013] For this reason, it has been proposed to first reflect the beam portion partially reflected by the optical element back into the optical system coaxially, and then separate the beam portion from the optical system's beam path by a second separation device located inside the optical system. Thus, the partially reflecting element that generates the back reflection, e.g., a protective glass, is positioned perpendicular to the focused beam so that no aberrations are introduced into the focused beam. Such a device for beam analysis is disclosed, for example, in German Patent Application No. DE 10 2007 053 632.

[0014] Laser cutting processes are known in which the pressure of the process or cutting gas, and additionally or alternatively the axial focus position, is specifically changed during the machining process. For example, JP 3-023091 A discloses using a low-pressure process gas during the drilling process and then supplying a high-pressure process gas during cutting.

[0015] It is therefore known that the influence on the focus position of processing optics is, on the one hand, in particular thermal focus shift, and, on the other hand, movement of the focus position to a target position by adjustable optical elements. Summary of the Invention [Problem to be solved by the invention]

[0016] Another important influence on focus position has not yet been discussed or considered in the prior art.

[0017] Known focus position sensors and methods for determining focus position are inaccurate because they do not take into account the effect of pressurized process gases, particularly cutting gases, on focus position. Therefore, it is a challenge to enable more accurate determination of focus position, especially in the case of cutting optics.

[0018] It is therefore an object of the present invention to advantageously further develop the known focus position sensor and method for determining the focus position, in particular to correct the influence of process gases on the focus position determination, thereby enabling a particularly accurate determination of the focus position.It is also an object of the present invention to provide a particularly robust, accurate, versatile and compact device and method for determining the focus position, which can be used in processing optics and optionally allows the focus position of the processing optics to be controlled. [Means for solving the problem]

[0019] This problem is solved by the features of the independent claims.

[0020] The above problem is solved by a device having the features of claim 1.

[0021] For this purpose, the present invention provides a beam analysis device for determining the axial position of a focal point, the beam analysis device comprising a focal point position sensor and an evaluation device, the focal point being the focal point of an energy beam of electromagnetic radiation guided in laser processing optics, the focus position sensor comprising a beam shaping device and a detector.

[0022] The beam shaping device is configured to receive the sample beam and is also configured to image at least a portion of the sample beam through the beam shaping device onto the detector to form an intensity distribution on the detector.

[0023] The detector comprises a sensor sensitive to optical radiation, having two-dimensional spatial resolution, and configured to convert the intensity distribution incident on the detector into an electrical signal.

[0024] The evaluation device is configured to process the electrical signal of the detector representing the intensity distribution on the detector. The evaluation device is configured to determine a geometric parameter from the intensity distribution. The evaluation device is configured to receive a cutting gas signal representing a pressure of a process gas or cutting gas. The evaluation device is configured to determine a correction value taking into account the cutting gas signal. The evaluation device is further configured to determine the axial position of the focal point of the energy beam taking into account the geometric parameter and the correction value.

[0025] The beam analysis device according to claim 1 has the advantage that focal position changes caused by process gas or cutting gas, in particular under fluctuating and / or high pressures, are compensated for by taking the cutting gas signal into account when determining the focal position, whereby a very accurate and reliable determination of the focal position is achieved during an ongoing machining process.

[0026] Advantageous embodiments are defined by the features set forth in the dependent claims.

[0027] The beam analysis device according to the invention can optionally be further developed by one or more of the features listed below.

[0028] The sample beam may be generated by back-reflection of a portion of the energy beam at an interface of an optical element of the laser processing optics. The optical element may be adjacent to a cavity of a cutting gas unit of the laser processing optics. The sample beam may be separated from the laser processing optics by a separation device. The sample beam may be provided to the beam shaping device of the beam analysis device. The cutting gas signal may represent a current pressure of process gas or cutting gas in the cavity of the cutting gas unit.

[0029] The beam shaping device and the detector may be disposed together in a housing having an opening for introducing the sample beam, the housing being connected to the laser processing optical system, and the sample beam separated by the separating device may be supplied to the beam shaping device.

[0030] In an embodiment of the beam analysis device, the evaluation device may comprise an input unit for the cutting gas signal, an input unit for the electrical signal, a memory unit and a calculation unit.

[0031] The evaluation device may be configured to perform the determination of the correction value taking into account calibration data stored in the memory unit, the calibration data describing the variation of the geometric parameter as a function of the cutting gas signal.

[0032] In another embodiment of the beam analysis device, the evaluation device may be configured to receive a lens position signal representative of an axial position of an axially positionable lens or lens group of the laser processing optics, and the evaluation device may be further configured to determine the axial position of the focal point of the energy beam taking into account the geometric parameters, the correction values ​​and the lens position signal.

[0033] The evaluation device may comprise an input unit for the lens position signal.

[0034] In a further embodiment of the beam analyzing device, the evaluation device may be configured to calculate a focus tracking signal from the determined axial position of the focus of the energy beam, which is the actual focus position, and a focus target position. Furthermore, the evaluation device may be configured to output the focus tracking signal, which may be sent to a positioning device directly or via a higher-level control device. The positioning device may adjust the position of an axially positionable lens of the laser processing optics.

[0035] The evaluation device may comprise an output unit for the focus tracking signal.

[0036] The beam shaping device may comprise an imaging device having at least one optical lens.

[0037] In one possible embodiment of the beam analysis device, the beam shaping device may be configured to image the sample beam onto the detector to form the intensity distribution on the detector, the intensity distribution having a beam spot with a diameter φ. The determination of the geometric parameters by the evaluation device may comprise determining the diameter φ of the beam spot on the detector.

[0038] In another possible embodiment of the beam analysis device, the beam shaping device images the sample beam onto the detector at a mutual separation distance a N1 , a N2 , a NM The evaluation device may further include a lens array for forming the intensity distribution on the detector, the intensity distribution having a plurality of beam spots each having a distance a N1 , a N2 , aNM The determination may include determining at least one of:

[0039] In yet another possible embodiment of the beam analysis device, the beam shaping device may comprise a modulation device for extracting two partial beams from the sample beam. The beam shaping device may be configured to image the two partial beams onto the detector to form the intensity distribution on the detector with two beam spots spaced a apart. In that case, determining the geometrical parameters by the evaluation device may comprise determining the separation a of the beam spots.

[0040] Another embodiment of the beam analysis device is provided, in which the beam shaping device is configured to extract two partial beams from the sample beam at a partial beam extraction surface. The two partial beams are a first partial beam and a second partial beam, and the cross sections of the two partial beams at the partial beam extraction surface are each defined by a subaperture. The subapertures are separated from each other. The centers of the subapertures are separated by a distance k. A first transverse direction is defined by the separation distance k of the subapertures. The term "transverse direction" refers to a direction in a plane perpendicular to the local optical axis. The beam shaping device is further configured to image the two partial beams onto the detector to form the intensity distribution with beam spots on the detector, forming at least one beam spot from the first partial beam and at least one beam spot from the second partial beam. The detector is arranged at a distance s behind the partial beam extraction surface in the propagation paths of the partial beams. The determination of the geometrical parameter by the evaluation device comprises determining a separation distance a between the positions of the two beam spots on the detector along the first lateral direction.

[0041] The beam shaping device may be configured to deflect and / or displace at least one of the at least two partial beams in a second lateral direction to form a separation distance w between the two beam spots on the detector along the second lateral direction, which may be oriented transversely with respect to the first lateral direction.

[0042] That is, the beam shaping device is configured to form the (at least two) partial apertures in the partial beam extraction surface for extracting one partial beam at a time, i.e. the beam shaping device is set such that due to a separation k on the detector (in the first lateral direction in the partial beam extraction surface), the beam spots of one of the at least two partial beams and the beam spots of the other of the at least two partial beams form the separation a on the detector along the first lateral direction on the detector, where the separation a depends, inter alia, on the axial position of the beam focus.

[0043] That is, the beam shaping device is further configured such that, due to the deflection and / or displacement of at least one of the two partial beams, the beam spot of one of the at least two partial beams and the beam spot of the other of the at least two partial beams are offset from each other in the second lateral direction on the detector by a separation distance w. The second lateral direction on the detector is transverse to the first lateral direction on the detector. The separation distance a may, under certain circumstances, be small or even zero. Another separation distance w between the two beam spots on the detector allows the two beam spots to be distinguished even in such cases. For example, even if the separation distance a becomes zero, the beam shaping device can be configured such that the separation distance w is large and the two beam spots only partially overlap (or preferably do not overlap).

[0044] Furthermore, a beam analyzing device is provided, wherein the first lateral direction and the local optical axis between the partial beam extraction surface and the detector are varied by beam folding and / or beam deflection.

[0045] The beam shaping device may be configured to deflect and / or displace the two partial beams relative to one another, in which case the difference in deflection and / or displacement of the two partial beams may be oriented along the second lateral direction to form the separation distance w along the second lateral direction between the two beam spots on the detector.

[0046] The beam shaping device may comprise a beam separator device having at least one partial beam deflecting element that deflects and / or displaces at least a first partial beam of the two partial beams in the second lateral direction to form the separation distance w between the two beam spots on the detector along the second lateral direction.

[0047] Optionally, the beam separator device may comprise at least two partial beam deflection elements for deflecting and / or displacing the two partial beams relative to one another, in which case the difference in deflection and / or displacement of the two partial beams may be oriented along the second lateral direction to form the separation distance w between the two beam spots on the detector along the second lateral direction.

[0048] Optionally, the beam separator device may comprise at least one wedge plate as a partial beam deflection element, which may be arranged in front of or behind one of the sub-apertures in alignment with the beam direction and configured to deflect the partial beam extracted from the sub-aperture by an angular amount in the range of 0.02 degrees to 6 degrees.

[0049] Optionally, the beam separator device may comprise at least one inclined plane-parallel plate or prism as partial beam deflecting element, which may be arranged in front of or behind one of the sub-apertures in alignment with the beam direction and configured to displace the partial beams emerging from the sub-aperture by an amount in the range of 0.05 mm to 3 mm.

[0050] The evaluation device may be further configured to determine a lateral position of the entire intensity distribution on the detector, and may be further configured to calculate a lateral position of the focus of the energy beam from the lateral position of the entire intensity distribution and / or to calculate a change in the lateral position of the focus of the energy beam from a change in the lateral position of the entire intensity distribution.

[0051] Also provided is a system comprising the beam analyzing device and laser processing optics for guiding and focusing the energy beam, the laser processing optics including a splitting device for splitting the sample beam, and the beam analyzing device may be connectable to the laser processing optics to receive the split sample beam.

[0052] The above problem is further solved by a method having the features of claim 24.

[0053] For this purpose, the invention also provides a beam analysis method for determining the axial position of a focal point, said focal point being the focal point of an energy beam of electromagnetic radiation guided in a laser processing optics, said method comprising at least the following steps: receiving a separated sample beam from the laser processing optics; imaging at least a portion of the sample beam onto the detector with a beam shaping device to form an intensity distribution on the detector; converting the intensity distribution incident on the detector into an electrical signal by a sensor of the detector that is sensitive to optical radiation and has two-dimensional spatial resolution; processing the electrical signal of the detector representing the intensity distribution on the detector; determining geometric parameters from the intensity distribution; receiving a cut gas signal representative of a process gas or cut gas pressure; determining a correction value in consideration of the cutting gas signal; Determining the axial position of the focal point of the energy beam taking into account the geometric parameters and the correction values.

[0054] The beam analysis method according to the invention can be further developed by one or more of the optional steps listed below.

[0055] A possible beam analysis method may further include the following three steps: generating the sample beam by reflecting a portion of the energy beam back at an interface of an optical element of the laser processing optics, the optical element being adjacent to a cavity of a cutting gas system of the laser processing optics; separating the sample beam from the laser processing optics with a separation device; Providing the separated sample beam to a beam analysis device.

[0056] In a further step, the correction value may be determined taking into account calibration data, which may describe the variation of the geometric parameter as a function of the cutting gas signal.

[0057] Another possible method may further include the following two steps: receiving a lens position signal indicative of an axial position of an axially positionable lens or lens group of the laser processing optics; Determining the axial position of the focal point of the energy beam taking into account the geometric parameters, the correction values ​​and the lens position signal.

[0058] Yet another possible method may further include the following two steps: calculating a focus tracking signal from the determined axial position of the focus of the energy beam, which is an actual focus position, and a focus target position; Providing the focus tracking signal to a positioning device, which adjusts the position of an axially positionable lens or lens group of the laser processing optics.

[0059] The features, embodiments, modifications and advantages described in relation to the device apply mutatis mutandis to the method, and vice versa. [Brief explanation of the drawings]

[0060] [Figure 1] FIG. 1 is a diagram showing an embodiment of a beam analysis device according to the present invention. [Figure 2] FIG. 2 shows the same beam analysis apparatus as shown in FIG. 1 and described above. [Figure 3] FIG. 3 is a diagram schematically showing the beam path after passing through the focusing optics of the processing optics. [Figure 4] FIG. 4 is a diagram showing the beam path after passing through the focusing optical system of the processing optical system, similar to FIG. [Figure 5] FIG. 5 shows the beam analysis device of FIG. 1 in conjunction with the processing optics of FIG. [Figure 6] FIG. 6 shows a beam analysis device in which the evaluation device further comprises an input unit for the lens position signal. [Figure 7] FIG. 7 shows a diagram in which the beam analyzing device further comprises an output unit for a focus tracking signal. [Figure 8]FIG. 8 shows a beam analysis device similar to the device described in FIG. 7, with a first embodiment of a focus position sensor. [Figure 9] FIG. 9 shows a schematic diagram of the intensity distribution with the beam spot on the detector in the case of a beam analysis device according to FIG. 8 with a first embodiment of a focus position sensor. [Figure 10] FIG. 10 shows a beam analysis device having a second embodiment of a focus position sensor. [Figure 11] FIG. 11 shows a further embodiment of a beam analyzing device in combination with the typical processing optics described in FIG. 7, FIG. 8 or FIG. [Figure 12] FIG. 12 shows a beam analyzing device according to the invention having a fourth embodiment of a focal position sensor. [Figure 13] FIG. 13 is an exemplary schematic diagram of the intensity distribution on the detector of a beam analyzing device with a third embodiment of the focus position sensor, i.e. a beam analyzing device as shown in FIG. [Figure 14] FIG. 14 is an exemplary schematic diagram of the intensity distribution on the detector of a beam analyzing device with a fourth embodiment of the focus position sensor, i.e. a beam analyzing device as shown in FIG. [Figure 15] FIG. 15 shows a further embodiment of a beam analyzing device according to the invention, in which the focus position sensor is configured according to the fourth embodiment of the focus position sensor shown in FIG. [Figure 16] FIG. 16 shows the use of the beam analysis apparatus according to the embodiment shown and described in FIG. 15, with a focus position sensor according to a fourth embodiment of the focus position sensor combined with processing optics having an adjustable collimator. [Figure 17] FIG. 17 is a diagram showing a system consisting of a beam analyzing device and a processing optical system, similar to FIG. [Figure 18] FIG. 18 shows the same system as in FIGS. 16 and 17, but consisting of a beam analyzer and processing optics. [Figure 19]FIG. 19 is a diagram illustrating the generation of the two sample beams shown in FIG. [Figure 20] FIG. 20 is a diagram illustrating the generation of two sample beams as shown in FIG. [Figure 21] Figure 21 is a schematic diagram showing the intensity distribution with two beam spot pairs on the detector when the sample beam generated by the two boundary surfaces of the protective glass is imaged onto the detector by a focus position sensor as shown in Figure 18. [Figure 22] Similar to FIG. 21, FIG. 22 is a diagram schematically illustrating an intensity distribution having two beam spot pairs on a detector when a sample beam generated by two boundary surfaces of a protective glass is imaged onto the detector by a focus position sensor such as that shown in FIG. 18. [Figure 23] FIG. 23 shows a diagram illustrating the use of a beam analyzing apparatus according to the embodiment shown and described in FIG. 15, having a focus position sensor according to a fourth embodiment of the focus position sensor coupled to processing optics. DETAILED DESCRIPTION OF THE INVENTION

[0061] FIG. 1 illustrates an embodiment of a beam analysis device 10 according to the present invention. The beam analysis device 10 includes a focus position sensor 13 and an evaluation device 80. The focus position sensor 13 includes a beam shaper 12 and a detector 40. The beam shaper 12 is arranged to receive a sample beam 70 propagating along a local optical axis 11. The beam shaper 12 and the detector 40 are arranged together in a housing having an aperture for introducing the sample beam 70. The sample beam 70 has an intermediate focus 71. The beam shaper 12 images at least a portion of the sample beam 70 onto the detector 40, forming an intensity distribution 79 thereon. The beam shaper 12 may include an optical lens for this purpose, as illustrated by a typical lens shape in the figure. The intensity distribution 79 has at least one specific geometric characteristic, such as the diameter of the beam spots in the intensity distribution 79 and / or the separation distance between two beam spots. The detector 40 includes a radiation-sensitive sensor with two-dimensional spatial resolution that converts the intensity distribution 79 into an electrical signal 64. The evaluation device 80 includes an input unit 84 for the detector signal 64, a memory unit 81, a calculation unit 86, and an input unit 83 for the cutting gas signal 63. The cutting gas signal 63 may have at least two different states or values ​​representing two different pressures of the cutting gas in the cutting gas device. The calculation unit 86 is configured to access data from the input unit 84 for the detector signal 64, data from the memory unit 81, and data from the input unit 83 for the cutting gas signal 63. Using the calculation unit 86, the evaluation device 80 determines geometric parameters from the intensity distribution 79 that represent specific geometric characteristics of the intensity distribution. Thus, the geometric parameters can be, for example, the diameter of a beam spot or the separation distance between two beam spots in the intensity distribution 79. The evaluation device 80 further determines correction values ​​by the calculation unit 86, taking into account the cutting gas signal 63. Finally, the calculation unit 86 determines the axial position of the beam focus by taking into account the geometric parameters and the correction values. The beam focus can be the intermediate focus 71 of the sample beam 70 or the energy beam focus of a processing optics whose focus position is coupled to the position of the intermediate focus 71 .For this purpose, a sample beam 70 is generated in the processing optics by partial reflection from the energy or laser beam and separated from the processing optics. The axially displaced sample beam 70' and a correspondingly displaced intermediate focus 71' are also depicted in the figure by dashed lines. A change in the axial position of the intermediate focus 71 results in a change in the intensity distribution on the detector 40, and thus in the magnitude of the geometric parameters, as a result of imaging by the beam shaping device 12.

[0062] FIG. 2 shows the same beam analyzing device 10 as shown in FIG. 1 and described above. The same reference numerals refer to the same elements and features as in FIG. 1, and therefore reference is made to the relevant descriptions. To better understand how the present invention works, FIG. 2 shows the beam analyzing device 10 used with a processing optical system 100. The optical system of the processing optical system 100 includes a collimator optical system 113, a beam decoupler 115, a focusing optical system 116, and a protective glass 120, arranged along an optical axis 111. An energy beam, specifically a laser beam 77, is supplied to the processing optical system 100 via an optical fiber. The laser beam 77 is emitted from the optical fiber end 110 of the optical cable and collimated by the collimator optical system 113. The collimated laser beam 77 passes through the beam decoupler 115 and is then focused by the focusing optical system 116 to an energy beam focal point 76. At the energy beam focal point 76, a workpiece 150 can be processed, specifically cut. The protective glass 120 is arranged between the focusing optics 116 and the energy beam focus 76. The illustrated processing optics 100 is, in particular, a cutting optics. Accordingly, the processing optics 100 includes a cutting gas device 140. The cutting gas device 140 supplies a process gas or cutting gas 146 to the cutting process, which serves, among other things, to blow away the melt from the cutting gap. For this purpose, the cutting gas device 140 includes a cavity 141 extending from the protective glass 120 to a cutting nozzle 142. The cutting gas 146 is supplied to the cavity 141 via a cutting gas supply 143 and exits the cavity 141 through the bore of the cutting nozzle 142 coaxially with the focused laser beam 77. At the boundary surface 121 of the protective glass 120, in particular the outer boundary surface 121 facing the workpiece 150 and adjacent to the cavity 141 of the cutting gas device 140, a portion of the laser beam 77 is reflected back coaxially into the processing optics 100. The portion of the laser beam 77 that is reflected back forms the sample beam 70. Residual reflection of the anti-reflection coating located on the boundary surface 121 can be used to generate the sample beam 70. Thus, the sample beam 70 is a mirror image of the energy beam 77 with a significantly reduced power and therefore has the mirror geometric properties of the energy beam 77.The sample beam 70 has an intermediate focus 71. The intermediate focus 71 is a mirror image of the energy beam focus 76. This means that a change in the axial focus position 76 results in a proportional change in the mirror image focus or intermediate focus 71 of the sample beam 70. The sample beam 70 is separated from the processing optics 100 by a beam decoupler 115 and exits the processing optics at a certain beam output. The housing of the beam analysis device 10 is coupled to the focus position sensor 13 at this beam output. The beam decoupler 115 can, for example, comprise an inclined partially reflective element. The partially reflective element of the beam decoupler 115 can also be a transparent plane-parallel plate with an anti-reflection coating. The focus position sensor 13 determines the focus position of the sample beam 70, i.e., the focus position of the intermediate focus 71, and from this, the position of the energy beam focus 76 of the laser beam 77 associated therewith is determined. In this embodiment, the cutting gas device 140 includes a gas pressure sensor 62. The gas pressure sensor 62 can be arranged, for example, in a recess in the cavity 141 of the cutting gas device 140. The gas pressure sensor 62 measures the pressure in the cavity 141 and supplies the result of the pressure measurement to the evaluation device 80 as a cutting gas signal 63. For this purpose, the gas pressure sensor 62 is directly connected to the input unit 83 of the evaluation device 80 via a data connection. The gas pressure sensor 62 can also be connected to a higher-level control system, for example a machine control system, and provide the pressure measurement result to the higher-level control system. In this case, the input unit 83 of the evaluation device 80 is connected to the higher-level control system via a data link and receives the cutting gas signal 63 therefrom.

[0063] FIG. 3 shows a schematic diagram of the beam path after passing through the focusing optics 116 of the processing optics 100. In particular, the effect of the pressurized cutting gas 146 on the beam paths of the energy beam 77 and the sample beam 70 is shown. For a detailed description of the cutting gas system 140, see the description of FIG. 2. The cutting gas 146 is supplied to the cavity 141 via the cutting gas supply 143 and exits the cavity 141 through the bore of the cutting nozzle 142 coaxially with the focused laser beam 77. The cutting gas 146 is at high pressure p′ and therefore has an increased refractive index n′. The increased refractive index n within the cavity 141 refracts the laser beam 77, i.e., changes the optical path within the cavity 141, resulting in a shift in the axial focal position 76. The distance between the cover glass 120 and the target focal position 76 is shown as distance L, which roughly corresponds to the length of the beam path traversed by the laser beam within the pressurized cavity 141. Because the refractive index of the pressurized cutting gas is greater than that at normal pressure, the displaced energy beam focal point 76' moves further away from the focusing optics 116. The energy beam focal point 76 moves further away from the focusing optics 116 by an axial amount Δz F . If the protective glass were perfectly rigid, the position of the intermediate focus 71 of the sample beam would not change. However, in reality, all materials have some elasticity, albeit a small one. For this reason, the protective glass 120 under pressure from the cutting gas 146 undergoes a slight deflection, and as a result, the interface 121 has a very slight curvature. This causes the intermediate focus 71 of the sample beam 70 to shift towards the shifted sample beam 70', which has a shifted intermediate focus 71'. Therefore, the intermediate focus 71 is displaced by an axial amount Δz PS The displacement of the intermediate focus point 71 is Δz PS is generally the displacement Δz of the energy beam focus 76 F The displacement Δz F and displacement Δz PS are both approximately proportional to the level of the cutting gas pressure p. The evaluation device 80 of the beam analysis device 10 takes into account the cutting gas signal 63 to determine the two displacements Δz F and Δz PS, and thus the actual position of the energy beam focal point 76 can be determined more accurately.

[0064] FIG. 4, like FIG. 3, shows the beam path after passing through the focusing optics 116 of the processing optics 100. Unlike FIG. 3, FIG. 4 shows a situation in which the cutting gas 146 is supplied under high pressure and, in addition, the temperature T of the protective glass 120 rises above the ambient temperature T0 as a result of low absorption of the energy beam 77 in the protective glass 120, thereby causing a thermal focus shift in the protective glass 120. The thermal focus shift acts to apply a weak refractive power, so that the shifted energy beam focus 76' moves closer to the focusing optics 116 in this example. As a result, the distance between the intermediate focus point 71 and the protective glass also becomes shorter. However, because the sample beam 70 passes through the protective glass 120 a second time after reflecting at the interface 121, the thermal lens effect of the protective glass 120 on the sample beam 70 is approximately twice as large as that on the energy beam 77. This is due to the displacement Δz of the intermediate focus point 71. PS is the displacement Δz of the energy beam focus 76 F means greater than.

[0065] Figure 5 shows the beam analysis device 10 of Figure 1 in conjunction with the processing optics 100 of Figure 2. Figure 5 shows schematically how the beam patterns of the laser beam 77 and the sample beam 70 change when cutting gas 146 is supplied under high pressure p. In particular, this results in a different intensity distribution 79 on the detector 40 of the focus position sensor 13.

[0066] 6 shows a beam analyzing device 10 in which the evaluation device 80 further comprises an input unit 85 for a lens position signal 65. Otherwise, the beam analyzing device 10 corresponds to the devices shown in FIGS. 1, 2 and 5. Therefore, reference is made to the corresponding descriptions. In this example, the processing optics 100 includes a collimator optic or collimator lens 113 that can be adjusted axially by a positioning device 105 in order to adjust the position of the energy beam focus 76 towards the target. Since the imaging characteristics of the entire optical system of the processing optics 100 may vary slightly depending on the position of the collimator, taking the lens position signal 65 into account when determining the focus position by the evaluation device 80 improves the accuracy of the determined focus position.

[0067] FIG. 7 shows the case where the beam analyzing device 10 further comprises an output unit 87 for a focus tracking signal 67. Otherwise, the beam analyzing device 10 corresponds to the device shown in FIG. 6. In this embodiment, the evaluation device 80 is configured to calculate the focus tracking signal 67 from the determined axial position of the focus 76 of the energy beam 77 as the actual focus position and a predetermined target focus position. The target focus position may be a predetermined focus position or a focus position determined under optimal conditions. The focus tracking signal 67 is transmitted directly or via a higher-level control device, e.g., a machine control device, to the positioning device 105, which can adjust the position of an axially positionable lens of the laser processing optics 100, in this case the collimator optics 113. In this way, the accuracy of the focus position determination is improved, thereby achieving particularly precise control of the focus position of the energy beam focus 76.

[0068] 8 shows a beam analysis device 10 similar to the device described in FIG. 7 with a first embodiment of a focus position sensor 13. In the first embodiment of the focus position sensor 13, the beam shaping device 12 comprises an imaging device 50 with an optical lens 51. As a result of imaging by the lens 51, the intensity distribution 79 on the detector has a beam spot 91, the diameter φ of which is determined as a geometric parameter by an evaluation device 80.

[0069] 9 shows a schematic representation of an intensity distribution 79 with a beam spot 91 on the detector 40 in the case of a beam analysis device 10 according to FIG. 8 with a first embodiment of a focus position sensor 13. The beam spot 91 has a diameter φ. If the axial focus position of the energy beam focus 76 changes, the altered beam spot 91′ has an altered diameter φ′, in this example an increased diameter.

[0070] FIG. 10 shows a beam analyzing device 10 with a second embodiment of the focus position sensor 13. An example of the use of the beam analyzing device 10 on a typical processing optical system 100 is also shown here, the configuration of which corresponds to the processing optical system 100 shown in FIG. 7. Therefore, for a description of the processing optical system 100, please refer to the descriptions of FIGS. 2 and 7. In this second embodiment, the focus position sensor 13 includes a lens array 56 having a plurality of individual lens elements 57 arranged side by side in a plane. The beam shaping device 12 can optionally include an imaging device 50 having an optical lens 51. Each of the individual lens elements 57 illuminated by the sample beam 70 images a small aperture portion of the sample beam 70 onto the detector 40. As a result, the individual lens elements 57 are spaced apart from each other by a distance a N1 ~a NM An intensity distribution 79 having a plurality of beam spots with a separation distance a N1 ~a NM varies as a function of the axial position of the intermediate focus 71 and therefore with the axial position of the energy beam focus 76. In this example, the evaluation device 80 uses the beam spot separation a as a geometric parameter for determining the axial focus position. N1 ~a NMUse one or more of the following.

[0071] FIG. 11 shows a further embodiment of the beam analyzing device 10, which is combined with the exemplary processing optics 100 described in FIG. 7, 8, or 10. The beam analyzing device 10 shown here comprises a third embodiment of the focus position sensor 13. In the third embodiment of the focus position sensor 13, the beam shaping device 12 comprises an imaging device 50 with an optical lens 51 and a modulation device 20 with a blocking zone 25 and two transmission zones 23, 24. Two partial beams 73, 74 are extracted from the sample beam 70 by the modulation device 20. For this purpose, the modulation device 20 has two transmission zones 23, 24. The partial beams 73, 74 extracted from the sample beam 70 by the imaging device 50 are imaged onto the detector 40 to form an intensity distribution 79 with two beam spots 93, 94. The partial beam 73 separated from the transmission zone 23 forms the beam spot 93 on the detector 40. Correspondingly, a beam spot 94 on the detector 40 is formed by the partial beams 74 extracted from the transmission zone 24. The separation distance a between the beam spots 93, 94 depends on the axial position of the intermediate focus 71 of the sample beam 70 and thus on the axial position of the energy beam focus 76 of the laser beam 77. The axial position of the beam focus 71 and therefore of the energy beam focus 76 can therefore be determined from the magnitude of the separation distance a. Thus, in the third embodiment of the focus position sensor 13, the evaluation device 80 determines the separation distance a between the beam spots 93, 94 as a geometric parameter from the intensity distribution 79, and from there, the focus position 76 is determined, taking into account the cutting gas signal 63.

[0072] FIG. 12 shows a beam analyzing device 10 according to the present invention with a fourth embodiment of a focus position sensor 13. The fourth embodiment of the focus position sensor 13 includes all the elements of the third embodiment of the focus position sensor 13 shown in FIG. 11 and additionally includes a beam separator device 52. In the fourth embodiment, the beam shaping device 12 of the beam analyzing device 10 comprises an imaging device 50 with an optical lens 51, a modulation device 20, and a beam separator device 52. The beam separator device 52 includes at least one partial beam deflection element 53, 54. In the embodiment shown here, the beam separator device 52 includes two partial beam deflection elements 53, 54. The modulation device 20 functions to extract two partial beams 73, 74 from the sample beam 70 at the partial beam extraction surface 19. For this purpose, the modulation device 20 has at least two mutually delimited transmission zones 23, 24 and at least one blocking zone 25. The blocking zone 25 completely surrounds the transmission zones 23, 24 in each case and separates them from each other. In the region of the transmission zones 23, 24, the radiation beam propagates further to the detector 40, while in the region of the blocking zone 25, the radiation beam is prevented from propagating to the detector. The edges of the transmission zones 23, 24 thus define two sub-apertures 33, 34. These sub-apertures define the cross sections of the partial beams 73, 74 formed at the partial beam extraction surface 19. The centers of the sub-apertures 33, 34 are separated by a distance k. The distance k, i.e., the imaginary shortest connecting line of the centers of the sub-apertures 33, 34, defines a first transverse direction 31. The first transverse direction 31 is oriented perpendicular to the local optical axis 11. In FIG. 12, the local optical axis 11 is associated with the z-coordinate axis, and the first transverse direction 31 is aligned in the plane of the drawing, for example, parallel to the y-coordinate axis. The modulator 20 modulates the intensity distribution of the sample beam 70, thereby forming a shaped sample beam having two partial beams 73, 74. The modulator 20 may, for example, be a double-aperture diaphragm having two apertures, which represent the transmission zones 23, 24. The partial beams 73, 74 of the shaped sample beam are imaged onto the detector 40 by the imaging device 50.The detector 40 has a sensor in the sensor plane 39 that is sensitive to optical radiation and has a two-dimensional spatial resolution that converts the intensity distribution 79 on the detector 40 into an electrical signal. The detector signal 64 formed in this way is supplied to the evaluation device 80 via an input unit 84 and processed by the evaluation device 80, in particular by a calculation unit 86 of the evaluation device 80. By imaging the sample beam shaped by the imaging device 50 onto the detector 40, beam spots 93, 94 are formed in the intensity distribution 79 on the detector 40 for each of the partial beams 73, 74 of the shaped sample beam. The two beam spots 93, 94 have a separation distance a on the detector 40 in the first transverse direction 31. The separation distance a depends, inter alia, on the separation distance k of the subapertures 33, 34, the distance s between the partial beam extraction surface 19 and the sensor plane 39, and the axial position of the intermediate focus 71. The axial position of the intermediate focus 71, and thus of the energy beam focus 76 of the processing optics 100 (not shown in FIG. 12 ), can thus be determined from the separation distance a. At least one of the partial beams 73, 74 is deflected or displaced along a second transverse direction 37 oriented transversely to the first transverse direction 31, so that the evaluation device 80 can unambiguously assign the beam spots 93, 94 and thus distinguish between positive and negative, i.e., forward and backward, displacements of the intermediate focus 71. The second transverse direction 37 is, for example, oriented perpendicular to the first transverse direction 31. Like the first transverse direction 31, the second transverse direction 37 is oriented perpendicular to the local optical axis 11. In the embodiment of FIG. 12 , for example, the second transverse direction 37 is oriented perpendicular to the plane of the drawing and therefore cannot be shown in FIG. 12 . 12, both partial beams 73, 74 are deflected along the second transverse direction 37. For this purpose, the beam shaping device 12 has in this example a beam separator device 52 which comprises two wedge plates as partial beam deflecting elements 53, 54. In each case, one of the wedge plates 53, 54 is aligned in the beam direction behind one of the transmission zones 23, 24.In the illustrated example, both partial beams are deflected by approximately the same amount along the second transverse direction 37, i.e., out of the plane of the drawing, but in opposite directions. The deflection direction is determined by the orientation of the wedge angles of the wedge plates. For example, partial beam 73 can be deflected by wedge plate 53 by an angular amount ranging from 0.02 degrees to 6 degrees, while partial beam 74 can be deflected by wedge plate 54 by the same angular amount in the opposite direction. As a result of the deflection and propagation to detector 40, beam spots 93, 94 have a separation distance w between them in the second transverse direction 37. The separation distance w between beam spots 93, 94 is not shown in FIG. 12 because the separation distance w is perpendicular to the plane of the drawing. To illustrate this deflection out of the plane of FIG. 12, please refer to FIG. 14, described below. FIG. 14 shows an intensity distribution 79 with two beam spots 93, 94 on detector 40. In this fourth exemplary embodiment of the focus position sensor 13, the first lateral separation distance a is a geometric parameter that allows the evaluation device 80 to determine the axial focus position of the sample beam 70 and thus the focus position of the energy beam of the processing optics. For this purpose, the evaluation device 80 comprises at least an input unit 84 for the detector signal 64, a memory unit 81 for storing, for example, calibration data, a calculation unit 86, and an input unit 83 for the cutting gas signal 63. The calculation unit 86 determines the axial focus position by taking into account the geometric parameters and a correction value determined by taking into account the cutting gas signal 63. The cutting gas signal 63 represents the pressure level of the cutting gas. To better illustrate the operating mode, FIG. 12 shows the sample beam 70 with the intermediate focus 71 in dashed lines and both the axially displaced sample beam 70′ with the displaced intermediate focus 71′ and the correspondingly displaced partial beams 73′ and 74′ in solid lines. Shifted beam spots 93', 94' having a spacing a' that varies in the first lateral direction 31 result from the shifted sample beam 70'.

[0073] FIG. 13 shows an exemplary schematic diagram of the intensity distribution on the detector 40 of a beam analyzing device 10 having a focus position sensor 13 according to a third embodiment of the focus position sensor, i.e., the beam analyzing device 10 shown in FIG. 11. The intensity distribution on the detector 40 is composed of beam spots 93 and 94 that are focused or nearly focused by imaging by the imaging device 50. The beam spots 93 and 94 have a separation distance a between them. The separation distance a changes when the axial position of the intermediate focus point 71 changes. FIG. 13 also shows, by way of example, beam spots 93′ and 94′ corresponding to changed axial focus positions. At the changed focus position, the changed beam spots 93′ and 94′ have a separation distance a′, which in this example is greater than the separation distance a for the original focus position. It can be seen that the positions of the beam spots 93 and 94 or the beam spots 93′ and 94′ change along a direction that is on the same imaginary line for both beam spots 93 and 94. Therefore, when the separation distance a is zero, the beam spots 93, 94 overlap each other. When the separation distance a is negative, the beam spots 93, 94 exchange their relative positions. Therefore, the evaluation device 80 cannot reliably identify which beam spot is generated by which partial beam or from which transmission zone. Due to this uncertainty, the focus position sensor 13 according to the third exemplary embodiment can only be used with a limited detection range for the axial focus position.

[0074] FIG. 14 shows an exemplary schematic diagram of the intensity distribution on the detector 40 of a beam analyzing device 10 having a focus position sensor 13 according to a fourth embodiment of the focus position sensor, i.e., the beam analyzing device 10 as shown in FIG. 12. The intensity distribution on the detector 40 is composed of beam spots 93, 94 generated by partial beams 73, 74 extracted from the sample beam 70 by the modulation device 20. The beam spots 93, 94 have a separation distance a in the first transverse direction 31. The separation distance a is zero in the illustrated exemplary distribution of beam spots, but can have any value. The separation distance a changes as the axial position of the intermediate focus 71 changes. Due to the deflection of the partial beams 73, 74 by the beam separator device 52, the beam spots 93, 94 have a separation distance w in the second transverse direction 37. The separation distance w does not change when the axial position of the intermediate focus 71 changes. FIG. 14 also exemplarily shows beam spots 93′ and 94′ corresponding to varied axial focus positions. At varied focus positions, the varied beam spots 93′, 94′ have a separation distance a′. It can be seen that the positions of the beam spots 93, 94 or the beam spots 93′, 94′ vary along the same direction, i.e., along the first transverse direction 31, but each beam spot lies on its own imaginary line, and in the second transverse direction 37, the two imaginary lines are offset parallel to each other by an amount w. Thus, even when the separation distance a=0, the beam spots 93, 94 are spatially separated from each other. The evaluation device 80 can therefore always reliably identify which beam spot was generated by which partial beam or extracted from which transmission zone. The focus position sensor 13 according to the fourth exemplary embodiment is therefore suitable for a significantly larger detection range relative to the axial focus position than the focus position sensor according to the third exemplary embodiment. This advantage of the fourth embodiment of the focus position sensor 13 is achieved by the beam separator device 52 .

[0075] FIG. 15 shows a further embodiment of the beam analyzing device 10 according to the present invention, in which the focus position sensor 13 is configured according to the fourth embodiment of the focus position sensor 13 shown in FIG. 12 . For a description of the components and operation mode of the focus position sensor, please refer to the description of FIG. 12 . The embodiment of the beam analyzing device 10 shown here differs from the embodiment of FIG. 12 by additional components in the evaluation device 80. Therefore, the evaluation device 80 of the beam analyzing device 10 shown here further comprises an input unit 85 for the lens position signal 65. This input unit 85 is intended for use with processing optics having an adjustable lens unit for adjusting the axial focus position. Such an adjustable lens unit is, for example, an adjustable collimator 113 as shown in FIGS. 6 to 8 , 10 , and 11 . Since the imaging characteristics of the entire optical system of the processing optics 100 can slightly change depending on the position of the adjustable lens unit, taking the lens position signal 65 into account when determining the focus position by the evaluation device 80 improves the accuracy of the focus position determination. Furthermore, the evaluation device 80 of the beam analyzing device 10 shown here also has an output unit 87 for the focus tracking signal 67. In this embodiment, the evaluation device 80 is configured to calculate the focus tracking signal 67 from the determined axial position of the focus 76 of the energy beam 77 as the actual focus position and a predetermined target focus position. The focus tracking signal 67 is intended to control an adjustable lens unit of the processing optics, thereby allowing the axial focus position of the optics to be adjusted. Therefore, the embodiment of the beam analyzing device 10 shown here is suitable for and intended for controlling the focus position of the energy beam focus of a laser processing optics.

[0076] Figure 16 shows the use of the beam analyzing device 10 according to the embodiment shown and described in Figure 15, with a focus position sensor 13 according to a fourth embodiment of the focus position sensor combined with processing optics 100 having an adjustable collimator 113. For a description of the processing optics 100, please refer to the description of Figures 2 and 7. The shown system consisting of the beam analyzing device 10 and the processing optics 100 allows for fast and accurate control of the focus position during the processing process.

[0077] FIG. 17 shows the same system as FIG. 16 , consisting of the beam analyzer 10 and the processing optical system 100. FIG. 17 shows a modified beam path compared to FIG. 16 . In FIG. 17 , the position of the energy beam focus 76′ has shifted upward toward the optical system compared to the original position 76 of the energy beam focus. For ease of comparison, the position 76 is shown as a dashed beam path. This is a typical situation that can occur as a result of thermal focus shift during the processing process in the processing optical system 100. The sample beam 70′ generated by reflection at the lower protective glass interface 121 has an intermediate focus 71′, whose position has also shifted relative to the original position 71 of the intermediate focus. As a result of the mirror image of the energy beam focus 76′, the intermediate focus 71′ is shifted downward. The modified sample beam 70′ is separated from the processing optical system 100 and irradiated to the beam analyzer 10. The altered partial beams 73′, 74′ are extracted from the altered sample beam 70′ by the modulation device 20 and imaged onto the detector 40 by the imaging device 50. In the intensity distribution on the detector, the resulting beam spots 93′, 94′ have an altered separation distance a′ in the first transverse direction 31. This altered separation distance a′ is determined as a geometric parameter by the evaluation device 80. The evaluation device 80 also determines a correction value using the current cutting gas signal 63 and determines an altered focal position 76′ using the separation distance a′ and the correction value. By comparison with the original or previously determined focal position 76, the evaluation device 80 can calculate a focus tracking signal 67 and send it to the positioning device 105 for the adjustable collimator 113. Based on the focus tracking signal 67, the collimator 113 is adjusted by the positioning device 105 so that the altered focal position 76′ again corresponds to the original or target focal position 76.

[0078] 16 and 17, but consisting of a beam analyzing device 10 and processing optics 100. As already explained in the other examples above, the first sample beam 70 or the modified sample beam 70′ with an intermediate focus 71′ is generated by partial reflection of the laser beam 77 at the outer boundary surface 121 of the protective glass 120. FIG. 18 further shows a situation in which the second sample beam 170 or the modified second sample beam 170′ with an intermediate focus 171′ is generated by partial reflection of the laser beam 77 at the second inner boundary surface 122 of the protective glass 120. Like the first sample beam 70′, the second sample beam 170′ is split off and fed to the beam analyzing device 10 with the focus position sensor 13. As shown here, a focus position sensor 13 according to the fourth embodiment shown and described in detail in FIGS. 12 and 15 is preferably used. Here, two partial beams 73′, 74′, 173′, 174′ are generated from each sample beam 70′, 170′ by the modulation device 20 of the beam shaping device 12. Each partial beam 73′, 74′, 173′, 174′ generates a beam spot 93′, 94′, 193′, 194′ on the detector 40. Here, the beam spot 93′ and the beam spot 94′ formed by imaging the sample beam 70′ form a first beam spot pair, and the further beam spot 193′ and the beam spot 194′ formed by imaging the second sample beam 170′ form a second beam spot pair. The beam spots 93′, 94′ of the first beam spot pair have a separation distance a′ in the first transverse direction 31, and the beam spots 193′, 194′ of the second beam spot pair have a separation distance b′ in the first transverse direction 31. Both pairs of beam spots can be evaluated by the evaluation device 80 and the separation distance a and b or the separation distance a' and b' can be determined. The evaluation device 80 is therefore configured to identify a corresponding number of beam spots in the intensity distribution 79 on the detector 40.The advantage of evaluating the beam spots for both sample beams 70, 170 is that for the first pair of beam spots 93, 94, the sample beam 70 passes through the protective glass twice, thereby obtaining focus position information that includes the thermal shift of the protective glass; and for the second pair of beam spots 193, 194, the second sample beam 170 is generated by the second boundary surface, the inner boundary surface 122, of the protective glass 120 and therefore does not pass through the protective glass 120, thereby obtaining focus position information that does not include the thermal shift of the protective glass. In this way, the evaluation device 80 can distinguish the focus shift caused by the protective glass 120 from other focus shift components of the entire processing optical system 100. In particular, this allows the evaluation device 80 to determine the focus shift of the protective glass 120 in isolation and to issue a warning signal if the focus shift of the protective glass 120 increases significantly (which usually indicates heavy contamination of the protective glass). This can be used to automatically indicate that the protective glass needs to be replaced.

[0079] 19 and 20 illustrate the generation of the two sample beams 70, 170 shown in FIG. 18. One of them is generated by partial reflection at the outer boundary surface 121 of the protective glass 120, and the other is generated by partial reflection of the laser beam 77 at the second boundary surface 122 of the protective glass. Here, a somewhat more detailed partial view of the lower region of the processing optics around the protective glass 120 is shown. FIG. 19 particularly illustrates the beam path of the laser beam 77 when the protective glass 120 has a significantly elevated temperature T' due to absorption of the laser radiation caused by contamination, thereby generating a thermal focus shift. The focused laser beam 77 is further refracted and more strongly focused by thermally induced refractive forces in the protective glass 120, resulting in a shift of the energy beam focus 76' upward, i.e., toward the optics. The beam path without the thermal focus shift and the original energy beam focus 76 are shown by dashed lines for comparison. The position of the energy beam focus is determined by the amount Δz FAlso, the intermediate focus 71′ of the sample beam 70′ produced by reflection at the lower interface 121 shifts by an amount Δz PS The shift amount of the intermediate focus point 71' is Δz PS is the shift amount Δz of the energy beam focus 76' F , which is approximately twice as large as the original intermediate focus 171. This is because the sample beam 70' passes through the protective glass twice, once before reflection and once after reflection, and therefore the thermally induced refractive power of the protective glass 120 acts on the sample beam 70' twice. In contrast, the second sample beam 170' generated by reflection at the second interface 122 does not pass through the protective glass at all, and as a result, the position of the intermediate focus 171' of the second sample beam 170' approximately corresponds to the original intermediate focus 171. Therefore, if the shift of the energy beam focus 76 is caused only by the thermal focus shift of the protective glass, the shift amount Δz of the intermediate focus of the second sample beam PS2 19, FIG. 20 shows a situation in which the thermal focal shift occurs primarily in the focusing optics 116. In this case, the shift amount Δz of the energy beam focal point 76′ is F , the shift amount Δz of the intermediate focus point 71′ of the sample beam 70′ PS , and the shift amount Δz of the intermediate focus point 171′ of the second sample beam 170′ PS2 The magnitudes of are approximately equal.

[0080] Figure 21 shows schematically the intensity distribution 79 with two beam spot pairs 93, 94 and a beam spot pair 193, 194 on the detector 40 when the sample beams 70, 170 generated by the two interface surfaces 121, 122 of the protective glass 120 are imaged onto the detector 40 by the focus position sensor 13 as shown in Figure 18. In other respects, Figure 21 corresponds to the situation shown in Figure 14. Therefore, for further details, please refer to the description of Figure 14.

[0081] 22, similar to FIG. 21, shows a schematic intensity distribution 79 on the detector 40, including two beam spot pairs 93, 94 and 193, 194, when the sample beams 70, 170 generated by the two boundary surfaces 121, 122 of the protective glass 120 are imaged onto the detector 40 by the focus position sensor 13 shown in FIG. 18. FIG. 22 shows a situation in which the beam spots 93, 193 and the beam spots 94, 194 generated by the two sample beams 70, 170 are not completely spatially separated from each other. This situation can occur when a very thin protective glass 120 is used. The second sample beam 170 generated by reflection at the second (inner or upper) boundary surface 122 of the protective glass 120 differs only slightly in its axial position from the first sample beam 70 generated by reflection at the outer boundary surface 121 of the protective glass 120. As a result, the intermediate focus 71 of the sample beam 70 and the intermediate focus 171 of the sample beam 170 also have a small axial separation. In this situation, the evaluation device 80 can be configured to determine an average separation m in the first transverse direction 31 between a first average position obtained from the beam spots 93 and 193 and a second average position obtained from the beam spots 94 and 194. The two beam spots 93 and 193 are therefore considered to be a common first beam spot. Similarly, the beam spots 94 and 194 are considered to be a common second beam spot. The average separation m determined in this way is identical to the average value m from the separation distances a and b, where a is the separation distance in the first transverse direction 31 between the beam spots 93 and 94 formed by the first sample beam 70, and b is the separation distance in the first transverse direction 31 between the beam spots 193 and 194 formed by the second sample beam 170. In such a situation, this average separation distance m may alternatively be used by the evaluation device 80 as the geometric parameter for determining the focus position.As the focal position changes, the positions of the modified beam spots 93', 94', 193', 194' change, and therefore the average separation m' in the first lateral direction 31 changes accordingly.

[0082] FIG. 23 shows the use of the beam analyzing device 10 according to the embodiment shown and described in FIG. 15, with a focus position sensor 13 according to a fourth embodiment of the focus position sensor coupled to a processing optical system 200. The processing optical system 200 is essentially identical in components to the processing optical system 100 already described in FIGS. 2 and 7. However, unlike the processing optical system 100, the processing optical system 200 further comprises a second protective glass 125 and a cutting gas device 140, which further comprises a pressure equalization connection 145. The pressure equalization connection 145 is a pneumatic connection, e.g., a simple open passage, connecting the cavity 141 to the intermediate region between the outer protective glass 120 and the second protective glass 125. The pressure equalization connection 145 ensures that the same pressure is always present in the intermediate region between the outer protective glass 120 and the second protective glass 125 as in the cavity 141. As a result, no pressure difference occurs in the outer protective glass 120. Therefore, the protective glass 120 does not sag even under high cutting gas pressure. This has the advantage that, while the second protective glass 125 must be designed to withstand pressure, a thinner and therefore less expensive protective glass can be used for the outer protective glass 120 as a wear part. Because the second protective glass 125 is protected from contamination by the outer protective glass 120, the thicker second protective glass 125 never or only rarely needs to be replaced. Because the outer protective glass does not sag, the intermediate focus 71 of the sample beam 70 does not shift when the cutting gas pressure changes. Nevertheless, a correction depending on the cutting gas pressure p is necessary when determining the focus position because the refractive index increases with pressurized cutting gas, which shifts the energy beam focus 76.

[0083] In laser processing processes, particularly laser cutting, the axial focus position of the laser beam can be changed by process gases, particularly cutting gases, which is not recognized by conventional focus position sensors and can result in inaccurate or even erroneous measurements of the focus position. The present invention solves this problem.

[0084] The beam analysis device 10 according to the present invention comprises a beam shaping device 12, a detector 40, and an evaluation device 80. The beam shaping device 12 is configured to receive the sample beam 70. For this purpose, the beam shaping device is coupled, for example, to a beam output of a separation device of a processing optics 100. The processing optics 100 focuses an energy beam 77, in particular a laser beam 77, at a focal point 76. By means of the separation device, the sample beam 70 is separated in the beam path of the processing optics 100 and sent to the beam shaping device 12. The beam shaping device 12 and the detector 40 form a focus position sensor 13 and are preferably arranged together in a housing that can be attached to the processing optics 100. The evaluation device 80 comprises at least one input unit 84 for the detector signal 64, an input unit 83 for the cutting gas signal 63, a memory unit 81 for calibration data and / or other parameters, and a calculation unit 86 for determining the corrected focus position.

[0085] The axial focus position 76 in a laser cutting system is primarily determined by the imaging system of the processing optics 100. Deviations from the nominal focus position are primarily caused by the following effects: Lens systems, e.g., movement of collimators; Thermal focus shift in one or more optical elements of the optical system, in particular in the protective glass; and The pressure of the cutting gas in the cutting gas unit.

[0086] Thermal focus shift is a phenomenon that also depends on contamination of the optical system, especially the protective glass, and therefore typically increases with increasing operating time. Because the magnitude of this effect is uncertain and changes over time, accurate tracking of the axial focus position can only be achieved using a focus position sensor that allows continuous determination of the focus position during the machining process.

[0087] For this purpose, it is particularly advantageous to perform beam sampling or generation of the sample beam 70 at the last optical interface 121 of the optical system for determining the focus position, for example, at the surface of the protective glass 120 facing the processing process or workpiece 150. A portion of the laser beam 77 is reflected at this interface 121. This generates the sample beam 70, which consequently has a mirror image 71 of the laser beam focus 76. This mirror image of the laser beam focus 76 is therefore the intermediate focus 71 of the sample beam 70. This means that a change in the axial focus position 76 results in a proportional change in the mirror image focus or intermediate focus 71 of the sample beam 70. For example, the sample beam 70 is separated from the processing optical system 100 by a beam decoupler 115 and guided to the focus position sensor 13. The beam decoupler 115 can, for example, comprise an inclined partially reflecting element. The focal position sensor 13 is used to determine the change in the focal position of the sample beam 70, i.e. the focal position of the intermediate focus 71, and a proportional change in the focal position 76 of the laser beam 77 is determined from this.

[0088] Therefore, the focus position sensor 13 can detect all changes in focus position caused by the optics of the processing optics 100. However, the focus position sensor 13 cannot detect changes caused by sources external to the optics, including, among others, the cutting gas 146 supplied to the process under pressure.

[0089] During laser cutting, cutting gas 146 is supplied to the cutting process by a cutting gas unit 140, which functions, among other things, to blow the melt out of the cutting gap. To this end, the cutting gas unit 140 has a cavity 141 extending from the protective glass 120 to the cutting nozzle 142. The cutting gas 146 is supplied to the cavity 141 via a cutting gas supply 143 and exits the cavity 141 through the bore of the cutting nozzle 142 coaxially with the focused laser beam 77. The cutting gas 146 is at high pressure p' and therefore has an increased refractive index n'. Any increase in the refractive index n within the cavity 141 (even if only slightly) causes the laser beam 77 to be refracted, i.e., the optical path within the cavity 141 changes, resulting in a shift in the axial focal position 76.

[0090] This change in the focal position cannot be detected by the focal position sensor 13 because, in principle of operation, the sample beam 70 does not pass through the cavity 141 of the cutting gas device 140 .

[0091] However, the change in focal spot position 76 caused by cutting gas 146 can certainly be appreciable, as the following numerical example shows.

[0092] The following typical parameters are assumed: the distance L travelled by the laser beam 77 within the cutting gas device 140 is L=100 mm, and the cutting gas 146 is nitrogen at a pressure of p′=20 bar.

[0093] The refractive index of nitrogen at normal pressure and room temperature is n0 = 1.00028.

[0094] The refractive index of a gas as a function of pressure p and temperature T is given by the following equation: n-1=(n0-1)(p / p0)(T0 / T) ···(1)

[0095] At a pressure of p'=20 bar, this gives n'=1.0056 for nitrogen. The change in back focal length Δz, i.e. the axial focal position 76 of the laser beam 77, is given by: Δz=L(n´-1) / n´ (2)

[0096] Therefore, the change in focal position in this example is Δz=0.56 mm.

[0097] The numerical values ​​are approximately the same when ordinary compressed air is used as the cutting gas instead of nitrogen.

[0098] However, the high pressure of the cutting gas 146 has an additional effect: it causes a very slight deflection of the protective glass 120, so that the interface 121, where the sample beam 70 is generated by partial reflection, is no longer flat. As a result, the mirror image focus 71 of the sample beam 70 also shifts slightly.

[0099] This shift can also be calculated and is shown below by a typical numerical example.

[0100] For this purpose, a thickness d = 5 mm and a diameter 2R PG The protective glass 120 is assumed to be made of quartz glass with a thickness of 30 mm. The elastic modulus E of the protective glass material is also required for the calculation. For quartz glass, E = 72500 N / mm 2 The deflection w at the center of a circular plate hinged at its edges is calculated according to the following formula: w=0.696pR PG 4 / (Ed 3 ) ···(3) The radius of curvature R of the plate, i.e., the protective glass 120, is C is obtained from the following formula: R C =(w 2 +R PG 2 ) / 2w≒R PG 2 / 2w ···(4)

[0101] For the given example values, the radius of curvature R for the two protective glass surfaces 121, 122 isC =14.4m.

[0102] This is because the protective glass 120 under pressure from the cutting gas 146 is -f Refl =R C This means that the sample beam 70 acts like a very weakly convexly curved mirror with a focal length of 200 mm. If the distance of the laser beam focus 76 to the protective glass 120 is L=100 mm, then the axial displacement of the mirror image beam focus 71 in the sample beam 70 is Δz=L 2 / f Refl =-1.4mm.

[0103] In the selected numerical example, the focus position sensor will therefore detect an apparent axial focus position shift of 1.4 mm, whereas the true axial focus position shift is 0.56 mm. In this numerical example, the focus position sensor will therefore overestimate the change in focus position by a factor of 1.4 / 0.56=2.5. The magnitude of this factor can therefore be determined directly or calculated from the parameters of the cover glass, the cutting device, and the pressure of the cutting gas. The value of this factor can also be obtained from a previous calibration.

[0104] While the parameters of the cover glass and cutting device are constant for a given processing optics, the pressure of the cutting gas can be variable. Both the change in the position of the energy beam focus 76 due to the refractive index n of the cutting gas and the change in the position of the intermediate focus 71 in the sample beam 70 are approximately proportional to the magnitude of the cutting gas pressure p, at least for small changes.

[0105] In particular, the current cutting gas pressure p therefore determines the current deviation between the change in position of the energy beam focus 76 and the change in the position of the intermediate focus 71 in the reflected sample beam 70 detected by the focus position sensor. In order to correct this deviation which the focus position measurement value, which is determined primarily by the evaluation device 80 from data from the focus position sensor 13, may have and to distinguish it from changes in focus position resulting from other causes such as collimator adjustments or thermal focus shifts, the evaluation device 80 requires information on whether the cutting gas 146 is switched on and / or information representing the level of the cutting gas pressure p.

[0106] Therefore, the evaluation device 80 of the beam analysis device 10 according to the present invention comprises an input unit 83 for the cutting gas signal 63, a memory unit 81 for calibration data and / or other parameters, and a calculation unit 86 for determining the corrected focus position.

[0107] The input unit 83 for the cutting gas signal 63 can be, for example, a physical interface for an electric line, or a virtual interface in a computer program, or a wireless interface for wireless transmission of data.

[0108] In a particularly simple example embodiment, the cutting gas signal 63 may be a binary signal whose two states represent different pressures. For example, in a first state, no cutting gas 146 is supplied (the cutting gas is switched off), and in a second state, the cutting gas 146 is supplied at a predetermined pressure (the cutting gas is switched on). The binary signal may represent two different predefined pressures of the supplied cutting gas 146, for example a low pressure p1 for a drilling process and a high pressure p2 for a cutting process. In each case, the pressures to which the values ​​of the signal 63 respectively correspond are stored in the memory unit 81 as a calibration.

[0109] The cutting gas signal 63 may be an analog or digital signal proportional to the cutting gas pressure. Using the current cutting gas signal 63, the calculation unit 86 can determine a correction value according to a proportionality coefficient stored in the memory unit 81 or calibrated, and thus determine a corrected focus position.

[0110] The values ​​of various parameters required for the calculations of the calculation unit 86 are preferably stored in the memory unit 81. The parameters may be proportionality coefficients and / or constants determined through a calibration process. The calibration data may describe, for example, the change in the geometric parameters as a function of the gas pressure signal. The parameters may be various characteristic values ​​of the optical system, the cutting device, and the protective glass, such as the magnification of the optical system, the focal length of the collimating optics and the focusing optics, the refractive index of the cutting gas, the transmission length of the cavity of the cutting device, the radius or diameter of the protective glass, the thickness of the protective glass, the elastic modulus of the protective glass, and / or other parameters as needed. From the above data, one or more proportionality coefficients and / or constants required for the calculations can be determined or adjusted, for example, when using protective glass of a different thickness when replacing the protective glass. For this purpose, the memory unit may have an interface or port for inputting or updating one or more parameters.

[0111] Alternatively or additionally, correction values ​​for at least one state of the cutting gas signal 63 or for at least one value indicative of the magnitude of the cutting gas signal 63 may be stored in the memory unit 81, which correction values ​​are used by the calculation unit 86 to correct the focus position determined by the focus position sensor 13. The one or more correction values ​​may be determined in advance in a calibration cycle. The correction value required in each case may be linked to the value or state of the cutting gas signal 63 via a look-up table. If intermediate values ​​are required, the calculation unit 86 may perform interpolation between the values ​​of the look-up table.

[0112] The cutting gas signal 63 may correspond, for example, to the state of a switching valve that switches the cutting gas on or off or that sets different pressures of the cutting gas 146 .

[0113] The cutting gas signal 63 may be a pressure setting or target signal from a higher level system control, in which case a controllable valve may be used to set the required pressure according to the setting.

[0114] The cutting gas signal 63 may be a measured value of the gas pressure sensor 62 or may be provided by the gas pressure sensor 62. The measured value of the gas pressure sensor 62 can be sent directly to an input unit 83 of the evaluation device 80 via a data connection. Alternatively, the gas pressure sensor 62 may be connected to a higher-level system control, which sends the cutting gas signal 63 to the evaluation unit 80 or to the input unit 83 of the evaluation unit 80 via a data connection.

[0115] The gas pressure sensor 62 may be arranged inside the cutting gas device 140. For this purpose, the gas pressure sensor 62 may be arranged, for example, in a recess in the cavity 141.

[0116] The gas pressure sensor 62 may also be coupled to the cavity 141 of the cutting gas system 140 via a pneumatic connection.

[0117] The gas pressure sensor 62 may be located anywhere in the cutting gas supply 143 or may be pressure connected to the supply of cutting gas.

[0118] The focus position sensor 13 comprises a beam shaper 12 and a detector 40. The beam shaper 12 is positioned to receive a sample beam 70 and image the sample beam 70 onto the detector 40, thereby producing an intensity distribution 79 on the detector 40. The detector 40 includes a radiation-sensitive sensor with two-dimensional spatial resolution that converts the intensity distribution 79 into an electrical signal 64.

[0119] The evaluation device 80 processes the detector signal 64. For this purpose, the evaluation device 80 comprises an input unit 84 for receiving the detector signal 64. The input unit 84 for the detector signal 64 can be, for example, a physical interface for an electric line, or a virtual interface in a computer program, or a wireless interface for wireless transmission of detector data.

[0120] The evaluation device 80 is configured to determine geometric parameters from the detector signal 64 representing the intensity distribution 79. The geometric parameters describe certain geometric properties of the intensity distribution 79. The geometric parameters may describe the geometric values ​​of basic features of the intensity distribution 79. The geometric parameters may therefore be values ​​that can be assigned units of length such as mm (millimeters) or μm (micrometers), or may be values ​​that can be assigned units of length such as mm (millimeters) or μm (micrometers). 2 (square millimeter) or μm 2 (square micrometers). This geometric parameter can be, for example, the diameter φ of the beam spot 91 of the intensity distribution 79, or the separation distance a between two beam spots 93, 94 of the intensity distribution 79, or any other equivalent geometric parameter of the intensity distribution 79. The geometric parameters will be described in more detail in the individual embodiments below.

[0121] Since the intermediate focus 71 is a mirror image focus of the energy beam focus 76, the magnitude of the geometric parameter directly depends on the axial position of the intermediate focus 71 of the sample beam 70 and therefore on the axial position of the energy beam focus 76 of the laser beam 70. The evaluation device 80 determines the axial position of the energy beam focus 76 from the geometric parameter taking into account the cutting gas signal 63. For this purpose, the evaluation device 80 comprises a calculation unit 86 and a memory unit 81.

[0122] Determining the position of the energy beam focal point 76 or determining the change in position can proceed in the manner described below.

[0123] The evaluation device 80 first determines, by means of the calculation unit 86 , from the detector signal 64 a first uncorrected geometrical parameter, for example the separation a between the two beam spots 93 , 94 .

[0124] From this separation distance a, a corrected geometric parameter is calculated taking into account the cutting gas signal 63 or taking into account the pressure p related to the value of the cutting gas signal 63, i.e. in this case the corrected separation distance a corr is determined, for example, according to the following formula: a corr =a+p[c1+c2(a)] (5)

[0125] The term p[c1+c2(a)] therefore constitutes the correction value for the geometric parameter in this calculation formula.

[0126] where c1 is a constant parameter and c2 is a function that depends on the uncorrected geometric parameters, for example, a simple linear form c2(a)=c2'a. The parameters c1 and c2 or c2' may be stored in a memory unit 81. The parameters c1 and c2 or c2' may have been determined in a calibration process performed beforehand. The parameters c2 or c2' may be zero. In an embodiment intended for use with processing optics having an adjustable collimator, the parameters c1 and c2 or c2' may be determined by the collimator setting z Coll individually or both, so that the following equation can be used, for example, to correct for geometric parameters: a corr =a+p[c1+c2(a)+c K (z Coll )] ···(6)

[0127] In a linear approximation, the geometric parameters can be corrected using the following equation: where c1, c2', c K ´ is a constant coefficient. a corr =a+p(c1+c2´a+cK ´z Coll ) ···(7)

[0128] Finally, the corrected geometric parameters or the corrected separation distance a corr axial focus position z of the energy beam focus 76 using F or change in axial position Δz F =z F -z0 is calculated, for example, according to the following formula: Δz F =ga corr -z0···(8)

[0129] The parameter z0 can be the starting position of the focus position, or the nominal position, or the zero position, or the previous focus position determined in the previous step.

[0130] Corrected geometric parameter a corr as a function of the focal position z F In order to express as accurately as possible, the focal position z F The function for calculating the corrected geometric parameters a corr In particular, the function may have quadratic terms such as: Δz F =g1a corr +g2a corr 2 -z0···(9)

[0131] The parameter g, or the parameters g1 and g2, may be constant coefficients stored in the memory unit 81. If the processing optical system 100 includes a device for adjusting the energy beam focus 76, for example, with an axially adjustable collimator 113, the parameter g or the parameters g1 and g2 may be determined by the collimator optical system position z Coll A function g=g(z Coll ) This means that the function g or the function g1 and / or the function g2 may be z CollFor example, the equation used to determine the focus position can be expressed as: Δz F =(g 10 +g 11 z Coll +g 12 z Coll 2 )a corr +(g 20 +g 21 z Coll +g 22 z Coll 2 )a corr 2 -z0···(10)

[0132] Parameter g 10 , g 11 , g 12 , g 20 , g 21 , g 22 is a constant coefficient that may even have a value of zero depending on the overall system layout.

[0133] Of course, the various units and modules of the evaluation device 80 do not have to be designed as separate units. All modules of the evaluation device 80 can be designed as functional units of a digital information processing device, such as a microcomputer. Individual or all modules of the evaluation device 80 can be realized as computer programs that run on a conventional microcomputer or personal computer. An embodiment is provided in which the evaluation device 80 is integrated into a housing in which the focus position sensor 13 is also arranged. An embodiment is also provided in which the evaluation device 80 is not integrated into the housing of the focus position sensor 13.

[0134] A beam analysis method is also provided that further determines the focal position, taking into account an offset that depends on the thickness of the protective glass 120 .

[0135] In a further possible beam analysis method, the calibration data can be adjusted depending on the thickness of the protective glass 120 .

[0136] Furthermore, a beam analysis method is provided in which calibration data is determined by determining geometric parameters for at least two different cutting gas pressure settings at low laser power before the start of actual laser processing, particularly after replacing the protective glass 120.

[0137] Which variables are used as geometric parameters determined by the evaluation device 80 from the intensity distribution 79 on the detector 40 depends on the embodiment of the focus position sensor 13. The focus position sensor 13 comprises at least the beam shaping device 12 and the detector 40.

[0138] First embodiment of the focus position sensor

[0139] A first embodiment of the focus position sensor 13 of the beam analysis device 10 is shown in FIGS. 8 and 9. In a first possible embodiment of the focus position sensor 13, the beam shaping device 12 includes an imaging device 50 with an optical lens 51. The imaging device 50 images the sample beam 70 onto the detector 40. In the first embodiment of the focus position sensor, for example, the entire sample beam 70 received by the beam shaping device 12 is focused onto the detector 40, where a beam spot 91 with a diameter φ is formed. As a result, an image of the intermediate focus 71 of the sample beam 70 is generated near the detector 40. The distance of the image of the intermediate focus 71 depends on the axial position of the intermediate focus 71 and is therefore also linked to the axial position of the energy beam focus 76 of the laser beam 77 from which the sample beam is generated. Depending on the distance of the image of the intermediate focus 71 to the detector 40, the diameter φ of the beam spot 91 on the detector 40 varies. The diameter φ is smallest when the image of the intermediate focus 71 is located exactly in the plane of the detector 40. The greater the distance between the image of the intermediate focus 71 and the detector 40, the larger the diameter φ of the beam spot 91. As a result, the axial position of the beam focus 71, and therefore of the energy beam focus 76, can be determined from the size of the diameter φ. In this first embodiment of the focus position sensor 13, the diameter φ of the beam spot 91 on the detector 40 is therefore a geometric parameter determined by the evaluation device 80 from the intensity distribution 79 comprising the beam spot 91.

[0140] Second embodiment of the focus position sensor

[0141] A second embodiment of the focus position sensor 13 of the beam analysis device 10 is shown in FIG. 10. In a second possible embodiment of the focus position sensor 13, the beam shaping device 12 comprises a lens array 56. The beam shaping device 12 may further comprise an imaging device 50 for initially collimating the sample beam 70. The lens array 56 comprises a plurality of lens elements 57, also called lenslets 57, arranged side by side in a plane. Each of the individual lens elements 57 images a portion of the sample beam 70 onto the detector 40, resulting in an intensity distribution 79 with a plurality of beam spots on the detector 40. The detector 40 is arranged at a distance from the lens array 56 that corresponds to the focal length of the individual lens elements 57 of the lens array 56. In this second exemplary embodiment, the lens array 56 and the detector 40 form a so-called wavefront sensor, the operation mode of which is known from the prior art and therefore need not be described in more detail here. The separation a of the individual beam spots from each other is N1 ~a NM From this, the wavefront of the sample beam 70 can be reconstructed, from which the axial position of the beam focus 71 and therefore the axial position of the energy beam focus 76 can be determined. Thus, in this second embodiment of the focus position sensor 13, the mutual separation a of the beam spots N1 ~a NM One or more of these constitute geometric parameters determined by an evaluation device 80 from an intensity distribution 79 having a plurality of beam spots.

[0142] Third embodiment of the focus position sensor

[0143] A third embodiment of the focus position sensor 13 of the beam analysis device 10 is shown in Figures 11 and 13. In this third possible embodiment of the focus position sensor 13, the beam shaping device 12 comprises an imaging device 50 with an optical lens 51 and a modulation device 20 with a blocking zone 25 and two transmission zones 23, 24. By means of the modulation device 20, two partial beams 73, 74 are extracted from the sample beam 70. For this purpose, the modulation device 20 has two transmission zones 23, 24, which are, for example, circular openings of a double-aperture diaphragm. By means of the imaging device 50, the partial beams 73, 74 extracted from the sample beam 70 are imaged onto the detector 40 to form an intensity distribution 79 with two beam spots 93, 94. To ensure that the two beam spots 93, 94 on the detector are laterally separated from one another, the distance between the imaging device 50 and the detector 40 and the focal length of the imaging device 50 are selected so that the image of the intermediate focus 71 is preferably not formed in the plane of the detector 40, but rather in front of or behind the detector 40 in the beam direction. As a result, the two beam spots 93, 94 have a separation distance a, the size of which depends on the axial position of the intermediate focus 71 of the sample beam 70 and thus on the axial position of the energy beam focus 76 of the laser beam 77. The axial position of the beam focus 71 and thus the axial position of the energy beam focus 76 can therefore be determined from the size of the separation distance a. In this third embodiment of the focus position sensor 13, the separation distance a of the beam spots 93, 94 on the detector 40 therefore constitutes a geometric parameter that is determined by the evaluation device 80 from the intensity distribution 79 comprising the beam spots 93, 94.

[0144] Fourth embodiment of the focus position sensor

[0145] A fourth embodiment of the focus position sensor 13 of the beam analysis device 10 is shown in Figures 12 and 14 to 17. In the fourth preferred embodiment of the focus position sensor 13, the beam shaping device 12 comprises an imaging device 50 with an optical lens 51, a modulation device 20 and a beam separator device 52 with at least one partial beam deflection element 53, 54.

[0146] In a fourth embodiment of the focus position sensor 13, the beam shaping device 12 is configured to extract at least two partial beams 73, 74 from the sample beam 70 at the partial beam extraction surface 19. The cross-section of each partial beam 73, 74 at the partial beam extraction surface 19 is defined by a respective sub-aperture 33, 34. In other words, the beam shaping device 12 is configured to form at least two sub-apertures 33, 34 at the partial beam extraction surface 19 to extract each partial beam 73, 74. The sub-apertures 33, 34 are separated from each other, i.e., the edges of the sub-apertures 33, 34 do not touch each other. The lateral positions of the sub-apertures 33, 34 are defined by their respective centers. Here, the term "lateral direction" refers to a direction in a plane perpendicular to the local optical axis 11. The centers of the sub-apertures 33, 34 are separated by a separation distance k. Furthermore, a first lateral direction 31 is defined by the separation distance k between the sub-apertures 33, 34. That is, an imaginary connecting line joining the centers of the two sub-apertures 33, 34 defines a first transverse direction 31. The first transverse direction 31 lies in a plane perpendicular to the local optical axis 11. Since the local optical axis 11 in the beam path is always aligned with the z-axis of the local coordinate system, the first transverse direction 31 lies in the xy-plane.

[0147] The partial beam extraction of the beam shaping device is realized, for example, as a modulation device 20 configured with at least two transmission zones 23, 24 and at least one blocking zone 25. In each case, one of the transmission zones 23, 24 constitutes one of the two sub-apertures 33, 34. The transmission zones 23, 24 are characterized in that the transmittance of radiation therein is substantially greater than that of the blocking zone 25. The transmittance here should be understood to be with respect to the intended propagation direction of the partial beams 73, 74 extracted in this way. In particular, the radiation transmittance (or reflectance) in the transmission zones 23, 24 is at least twice as great as that in the blocking zone 25. Preferably, the radiation transmittance (or reflectance) in the blocking zone 25 is less than one-tenth of that in the transmission zones 23, 24. Particularly preferably, the radiation transmittance (or reflectance) in the blocking zone 25 is more than 100 times smaller than the radiation transmittance (or reflectance) in the transparent zones 23, 24.

[0148] The sub-apertures 33, 34 have a width b at the partial beam extraction surface 19 along the first transverse direction 31. The width b of the sub-apertures 33, 34 is at most equal to half the separation distance k between the centers of the sub-apertures 33, 34. This results in an area, e.g., a blocking zone 25, between the sub-apertures 33, 34, whose width is at least as wide as the width b of the sub-apertures 33, 34. In other words, the separation distance k between the centers of the sub-apertures 33, 34 is at least twice the width b of the sub-apertures 33, 34.

[0149] The beam shaping device 12 is further configured to shape the intensity distribution 79 on the detector 40, which has at least two beam spots 93, 94, form at least one beam spot 93, 94 from each of the two partial beams 73, 74, image the at least two partial beams 73, 74 on the detector 40, and deflect and / or displace at least one of the at least two partial beams 73, 74 in the second lateral direction 37. Each of the two partial beams 73, 74 forms at least one associated beam spot 93, 94 on the detector 40. By deflecting and / or displacing at least one of the partial beams 73, 74 in the second lateral direction 37, a separation distance w is formed along the second lateral direction 37 between the positions of the two beam spots 93, 94 on the detector 40. Preferably, the positions of the two beam spots 93, 94 are defined by the centers and / or centroids of the intensity distributions of the beam spots 93, 94 on the detector 40. The second transverse direction 37 is oriented transversely to the first transverse direction 31. The second transverse direction 37 lies in a plane perpendicular to the local optical axis 11. Thus, like the first transverse direction 31, the second transverse direction 37 lies in a plane perpendicular to the local optical axis 11, i.e., in the xy plane. The second transverse direction 37 is, for example, aligned at an angle in the range of 30 degrees to 150 degrees with respect to the first transverse direction 31. In particular, the second transverse direction 37 may be aligned (at least substantially) perpendicular to the first transverse direction 31.

[0150] By the beam shaping device 12 deflecting and / or displacing a first of the at least two partial beams 73, 74 in the second transverse direction 37 and / or deflecting and / or displacing both partial beams 73, 74 in different directions in the second transverse direction 37, a beam spot 93 of a first of the at least two partial beams and a beam spot 94 of a second of the at least two partial beams are offset from each other along the second transverse direction 37 by a separation distance w in the intensity distribution 79 (at the detector 40 and therefore). The separation distance w is transverse to a separation distance a of these beam spots 93, 94 along the first transverse direction 31 in the intensity distribution 79 (at the detector 40). The separation distance a is caused only by the separation distance k in the first transverse direction 31.

[0151] That is, the beam spot 93 caused by the first partial beam of the at least two partial beams in the intensity distribution at the detector 40 and the beam spot 94 caused by the second partial beam of the at least two partial beams in the intensity distribution at the detector are further offset in the intensity distribution by an offset amount w along the second transverse direction 37 in addition to the separation distance a along the first transverse direction 31.

[0152] The detector 40 comprises a sensor that is sensitive to optical radiation, has two-dimensional spatial resolution, and is configured to convert the intensity distribution 79 incident on the detector 40 into an electrical signal. The detector 40 may be a CCD camera or a CMOS camera or an equivalent device. The sensor that is sensitive to optical radiation and has two-dimensional spatial resolution is typically a pixel-based semiconductor sensor. The detector 40 is arranged in the propagation paths of the partial beams 73, 74 at a distance s behind the partial beam extraction surface 19.

[0153] The evaluation device 80 is configured to process the electrical signal 64 of the detector 40, which represents an intensity distribution 79 on the detector 40. The evaluation device 80 is configured to determine a geometric parameter from the intensity distribution 79. In the fourth embodiment of the focus position sensor 13 shown here, the geometric parameter preferably corresponds to the separation distance a along the first transverse direction 31 between the positions of the two beam spots 93, 94 on the detector 40. More precisely, the evaluation device 80 is configured to determine the difference in the positions of the two beam spots 93, 94 in the first transverse direction 31. The difference in the positions of the two beam spots 93, 94 in the first transverse direction 31 is the separation distance a. Preferably, the position of each beam spot 93, 94 is defined by the center point and / or the center of gravity of the intensity distribution of the respective beam spot 93, 94 on the detector 40.

[0154] The magnitude of the separation distance a between the beam spots 93, 94 in the first transverse direction 31 depends on the axial position of the intermediate focus 71 of the sample beam 70 and therefore on the axial position of the energy beam focus 76 of the laser beam 77. The axial position of the beam focus 71 and therefore of the energy beam focus 76 can therefore be determined from the magnitude of the separation distance a along the first transverse direction 31. In this fourth embodiment of the focus position sensor 13, the separation distance a between the beam spots 93, 94 formed in the first transverse direction 31 on the detector 40 therefore constitutes a geometric parameter that is determined by the evaluation device 80 from the intensity distribution 79 comprising the beam spots 93, 94.

[0155] The focus position sensor 13 is used to determine the axial position of the energy beam focus 76. In this regard, the formula given below for calculating the position of the intermediate focus point 71 from the separation distance a first constitutes an intermediate result. In the final determination of the position of the energy beam focus 76, the imaging of the sample beam 70 by the focusing optics 116 of the processing optics 100 still needs to be taken into account, since the separation of the sample beam 70 by the beam decoupler 115 usually occurs in the collimated region between the focusing optics 116 and the collimator optics 113 in the processing optics 100.

[0156] The basic relationship between the position of the energy beam focus 76 and the intermediate focus 71 of the sample beam 70 has already been described above. In the simplest case, when the refraction of the sample beam 70 by the focusing optics 116 can be ignored, the intermediate focus 71 is a mirror image of the energy beam focus 76, so that changes in the position of the intermediate focus 71 are opposite in direction and equal in magnitude to changes in the position of the energy beam focus 76. When the intermediate focus 71 is close to the focusing optics 116 or in exactly the same plane as the focusing optics 116, the refraction of the sample beam 70 by the focusing optics 116 can be ignored. In many typical embodiments of processing optics, particularly cutting optics, the protective glass 120 is often located approximately midway between the focusing optics 116 and the energy beam focus 76, so that the intermediate focus 71 is relatively close to the focusing optics 116. Furthermore, the refraction of the sample beam 70 by the focusing optics 116 is already included in the proportionality constants and constants generated during calibration as a result of the calibration of the focus position sensor 13 and therefore does not need to be taken into account in the evaluation algorithm.

[0157] Thus, the formulas given below as examples for calculating the position of the intermediate focus 71 can also be used in an equivalent mathematical construction for calculating the position of the energy beam focus 76. This may result in slightly different proportionality coefficients and constants.

[0158] As the axial position of the sample beam intermediate focus 71 changes, the separation a between the beam spots 93, 94 on the detector 40 changes along the first lateral direction 31. This means that the separation a is a function of the z position of the intermediate focus 71, and therefore the z position of the energy beam focus 76. This functional relationship is influenced and / or defined by the following geometric variables: a is the separation distance along the first lateral direction 31 between the beam spot 93 and the beam spot 94 on the detector 40; a' is the separation distance along the first lateral direction between the beam spot 93' and the beam spot 94' on the detector 40 when the beam focus position is changed; Δa is the change in the difference between the positions of the beam spots 93, 94 in the first lateral direction 31, Δa=a′−a; k is the separation distance between the centers of the sub-apertures 33, 34 in the partial beam extraction surface 19, and an imaginary connecting line connecting the centers of the sub-apertures 33, 34 defines a first transverse direction 31; z PS is the distance between the axial position of the intermediate focus 71 of the sample beam 70 and the partial beam extraction surface 19; z PS ′ is the distance between the axial position of the displaced intermediate focus 71′ and the partial beam extraction surface 19; Δz PS is the change in the axial intermediate focus position, and Δz PS =z PS ´-z PS is; s is the distance between the partial beam extraction surface 19 and the sensor surface 39 of the detector 40; d is the distance from the position of the imaging device 50, more precisely from the main plane of the imaging device 50, to the partial beam extraction surface 19;

[0159] By applying the intersecting lines theorem and known imaging formulas, the following functional relationship is obtained for the focus position sensor of the beam analysis device 10: Δz PS =Δac3 / (c4+Δac5) (11)

[0160] The symbols c3, c4, and c5 in the equation are coefficients introduced to simplify the expression of the equation.

[0161] If the modulator 20 is placed after the imaging device 50, the coefficients c3, c4, and c5 are as follows: c3=[z PS (fd)+d 2 ] 2 ···(12) c4=f 2 ks ···(13) c5=(fd)[z PS (fd)+d 2 ] ···(14)

[0162] The coefficients c3, c4, and c5 can be determined by setting at least three different known axial positions of the intermediate focus 71 or energy beam focus 76 and determining the corresponding change Δa in the separation distance a. The coefficients thus determined can be stored as calibration data in the evaluation device 80, which can then be used to calculate the change Δz in focus position for any change Δa in separation distance. F can be calculated by the evaluation device 80.

[0163] Alternatively or additionally, the coefficients may be calculated directly from the geometric distances of the configurations using the formulas above and stored in the evaluation unit 80 .

[0164] All axial distances, i.e. z PS Note that , d, f, s are distances along the optical axis 11. Therefore, when the beam is deflected, the distance z PS , d, f, s may be constructed from the respective distances along the local optical axis 11. Note also that if the beam is partially guided by an optical material, such as when the beam is guided by a beam splitter cube, the corresponding partial distances must be corrected by a factor that depends on the refractive index of the optical material.

[0165] In an embodiment of the beam analyzing device 10 having a modulator 20 behind the imaging device 50, i.e. behind at least one optical lens 51 in the beam direction, there is a special case of particular interest, in which the distance d from the main plane of the imaging device 50 to the partial beam extraction surface 19 is equal to the focal length f of the imaging device 50. In other words, the partial beam extraction surface 19 is arranged at the image-side focus of the imaging device 50. In the case of such an embodiment of the beam analyzing device 10, the coefficients of the functional relationship are as follows: c3=f 4 ···(15) c4=f 2 ks ···(16) c5=0 (17)

[0166] This is because the change Δa in the separation distance a between the beam spots 93 and 94 corresponds to the change Δz in the axial intermediate focus position. PS This results in a particularly simple functional relationship which has the special feature of being exactly proportional to Δz PS =Δaf 2 / (ks) ···(18)

[0167] This linear relationship simplifies the calibration of the device and achieves a high level of accuracy when determining the focus position.

[0168] In this case, the focal position change Δz F When calculating the intermediate focus point 71(z PS ) or energy beam focus 76 (z F It is particularly advantageous that the absolute z position of the

[0169] This feature or arrangement can be advantageously realized in embodiments where there is a distance between the imaging device 50 and the modulation device 20, for example when the modulation device 20 is arranged in a folded beam path.

[0170] To achieve the highest possible accuracy in determining the positions of the beam spots 93, 94 on the detector 40, it is advantageous if the width b of the subapertures 33, 34 is small compared to their separation distance k. In this case, the beam spots 93, 94 on the detector 40 are relatively small over a wide range of axial positions of the beam focus 71, and the possible influence of the intensity distribution within the beam spots 93, 94 on determining their positions is small or can be completely ignored. On the other hand, the subapertures should not be too small, because otherwise the beam spots 93, 94 may be broadened by diffraction, and diffraction structures may occur outside the beam spots 93, 94. Therefore, the separation distance k is preferably at least 2.5 times and at most 25 times the width b of the subapertures 33, 34. Particularly preferably, the separation distance k is at least 3 times and at most 12 times the width b of the subapertures 33, 34. Most preferably, the separation distance k is at least 4 times and at most 7 times the width b of the subapertures 33, 34. Preferably, the sub-openings 33, 34 have a simple geometric shape, such as a circle or an ellipse. However, the sub-openings 33, 34 may also have a square, rectangle, rhombus, hexagon, octagon, trapezoid, or similar shape. In the case of a circular sub-opening 33, 34, the width b corresponds to the diameter of the sub-opening 33, 34.

[0171] In further embodiments of the invention, the beam shaping device 12 can also be configured to extract more than two partial beams. For this purpose, more than two, for example three or four, mutually separated partial apertures can be arranged in the partial beam extraction surface 19. All the partial apertures can be distributed along the first transverse direction 31. Additional sub-apertures relative to the two partial apertures 33, 34 can also be arranged in a transverse direction different from the two partial apertures 33, 34 in the partial beam extraction surface 19.

[0172] Preferably, the beam shaping device 12 comprises a beam separator device 52 for deflecting and / or displacing a first partial beam of the at least two partial beams 73 , 74 in the second lateral direction 37 .

[0173] In a further embodiment, the beam separator device 52 is further configured to deflect and / or displace both partial beams 73, 74 in different directions, the difference in the deflection directions being set along the second transverse direction 37.

[0174] In an example embodiment of the fourth focus position sensor 13, the beam shaping device 12 of the beam analyzing device 10 comprises a modulation device 20, an imaging device 50 having at least one optical lens 51, and a beam separator device 52. These three devices 20, 50, 52 can be realized as separate devices. However, two or all of the three devices 20, 50, 52 may also be realized as a single device. For example, the modulation device 20 can be realized as a double-aperture diaphragm. The imaging device 50 can be designed, for example, as a single converging lens 51. However, it is also possible to provide the modulation device 20 as a masking device, for example by partial blackening, directly on or in the optical lens 51. In this latter example, the modulation device 20 and the imaging device 50 are realized as an integrated device. In keeping with this example, the optical lens 51 can also be designed as an aspherical freeform lens, in which the lens surfaces within the sub-apertures 33, 34 have an additional slope for deflecting the partial beams 73, 74 in the second lateral direction 37. In such an example embodiment of the beam shaping device 12, all devices 20, 50, 52 are realized as a single device.

[0175] The first transverse direction 31 can be defined locally: it is (at least essentially) perpendicular to the local optical axis 11. In particular, it can be defined as a direction in a plane perpendicular to the local optical axis 11, along which the at least two partial beams 73, 74 are spaced apart in this plane due only to the separation distance k between the sub-apertures 33, 34.

[0176] The second transverse direction 37 can be locally defined. In any case, it is (at least substantially) perpendicular to the optical axis 11 and transverse to the (local) first transverse direction 31. The second transverse direction 37 is changed globally once or several times, for example by beam folding and / or beam deflection.

[0177] The beam direction can be defined locally, or the beam direction can be changed globally, for example, by beam folding and / or beam deflection. The local beam direction may be defined, for example, by the direction of the local Poynting vector of the sample beam 70.

[0178] In the propagation direction of the emitted light downstream of the partial beam extraction surface 19, the local beam direction of the partial beams 73, 74 can be defined by the direction of the local Poynting vector of the respective partial beam 73, 74.

[0179] In the propagation direction of the radiation downstream of the partial beam extraction surface 19, the local (overall) beam direction can be defined by the average of the local Poynting vectors of at least two partial beams 73, 74. The magnitudes of the Poynting vectors of these partial beams can be normalized before averaging. Alternatively, the local (overall) beam direction can be defined by the Poynting vector of a virtual path of the sample beam without extraction of the partial beams.

[0180] The local optical axis 11 is defined, for example, by the intended local overall beam direction during operation.

[0181] In a further embodiment of the invention, the beam analyzing device 10 is configured to identify a plurality of beam spots 93, 94, 193, 194 in the intensity distribution 79 on the detector 40 and to determine their mutual separation in a first lateral direction. For this purpose, the beam analyzing device 10 preferably comprises a focus position sensor 13 according to the fourth exemplary embodiment. This means that the focus position sensor 13 in this further embodiment is preferably equipped with a modulation device 20 for extracting preferably two partial beams from the sample beam. When a plurality of axially superimposed sample beams 70, 170 are irradiated onto the beam analyzing device 10, the modulation device 20 forms beam spot pairs 93, 94 and beam spot pairs 193, 194 from each sample beam 70, 170 in the intensity distribution 79 on the detector 40. In particular, the beam analysis device 10 can be configured to identify a first pair of beam spots 93, 94 in the intensity distribution 79, which are formed from the first sample beam 70 by the modulation device 20, and further to identify a second pair of beam spots 193, 194, which are formed from the second sample beam 170 by the modulation device 20. The evaluation device 80 is configured to determine a first separation distance a between the beam spots 93, 94 in the first transverse direction 31, which are formed by the separation of partial beams from the first sample beam 70, and to determine a second separation distance b between the beam spots 193, 194 in the first transverse direction 31, which are formed by the separation of partial beams from the second sample beam 170. The separation distance a is, for example, a geometric parameter, and the separation distance b is, in this case, a second geometric parameter. Both geometric parameters, i.e. both separation distances a, b, are corrected in the above-described manner with a term that depends on the cutting gas signal 63 or the cutting gas pressure p. To determine the focus position, the evaluation device 80 preferably calculates two corrected geometric parameters a corr , b corr Determine the average value from m korr =(a corr +b corr ) / 2 ···(19)

[0182] The focus position is determined according to the above formula. Δz F =g(z Coll )m korr -z0···(20)

[0183] This embodiment of the invention is particularly suitable for use in a processing optics 100 in which a first sample beam 70 is generated by reflection at a first boundary surface of the protective glass, for example the outer boundary surface 121 of the protective glass 120, and a second sample beam 170 is generated by reflection at a second boundary surface of the protective glass, for example the inner boundary surface 122 of the protective glass 120, and both sample beams 70, 170 are separated from the processing optics 100 by a beam decoupler 115 and enter the beam analysis device 10. Surprisingly, in such an arrangement, the thermal focal shift of the entire processing optics as well as the thermal focal shift of only the protective glass, which has approximately the same sensitivity, can be calculated by the average value m or m consisting of the two separation distances a and b between the beam spots 93, 94 and the beam spots 193, 194. korr Therefore, to determine the focal position, the average value m or m korr is particularly advantageous because the accuracy of the focus position determination does not depend on the position at which the thermal focus shift occurs, and therefore the focus position determination overall is particularly accurate and reliable.

[0184] The evaluation device 80 may also be configured to calculate an average value m from the first separation distance a and the second separation distance b according to the formula m=(a+b) / 2 and use this average value m as a geometric parameter for determining the focus position. In this case, after calculating the average value m from the separation distance a and the separation distance b, the geometric parameter is corrected using a term that depends on the cutting gas signal 63 or the cutting gas pressure p.

[0185] Alternatively or in addition to determining the average value m from the two separation distances a and b between the beam spots 93, 94 and the beam spots 193, 194, the evaluation device 80 can be configured to determine a first average position from the beam spots 93 and 193, determine a second average position from the beam spots 94 and 194, and calculate the distance m in the first lateral direction 31 between the first and second average positions. Here, the beam spots 93 and 193 for the first average position are formed by partial beams extracted from the two sample beams 70 and 170 by the first transmission zone 23 of the modulation device 20, and the beam spots 94 and 194 for the second average position are formed by two partial beams extracted from the sample beams 70 and 170 by the second transmission zone 24 of the modulation device 20. Of course, this determination of the distance m from the average position results in the same average value m as can be determined from the two separation distances a and b between the beam spots 93, 94 and 193, 194. Therefore, the distance m determined in this manner can also be used as a geometric parameter for determining the focal position. The advantage of this alternative determination of the value m as a geometric parameter is that the beam spots 93, 193 and the beam spots 94, 194 do not need to be spatially separated from each other for the determination of the average position. In other words, in this type of evaluation, the beam spots 93, 193 may partially or completely overlap. The beam spots 94, 194 may also overlap. Partial overlap of the beam spots can occur, for example, when the axial distance from the intermediate focus 71 of the first sample beam 70 to the intermediate focus 171 of the second sample beam 170 is relatively small. Therefore, this type of evaluation is particularly advantageous when used with processing optics having thin protective glass. Thin protective glass, for example, typically has a thickness of 1.5 mm, whereas protective glass, particularly if suitable for higher cutting gas pressures, typically has a thickness of more than 3 mm.

[0186] In yet another embodiment of the present invention, the evaluation device 80 may be configured to determine a separation distance c between the beam spots 93 and 193 extracted from the two sample beams 70 and 170 by the first transmission zone 23 of the modulation device 20, and also a substantially equal separation distance c between the beam spots 94 and 194 extracted from the two sample beams 70 and 170 by the second transmission zone 24 of the modulation device 20. Figure 21 shows the separation distance c together with other geometric relationships between the positions of the beam spots 93, 94, 193, and 194. The separation distance c can be determined by the evaluation device 80, in particular, by calculating the difference between the two separation distances a and b between the beam spots 93 and 94 and between the beam spots 193 and 194 according to the formula c = (ab) / 2. The value of this parameter c is directly related to the axial distance between the intermediate focus 71 of the first sample beam 70 and the intermediate focus 171 of the second sample beam 170, i.e., the axial focal distance between the two sample beams 70, 170. This axial focal distance depends on the thickness of the protective glass, on the one hand, and on the thermal focal shift within the protective glass, on the other hand. This axial focal distance, and therefore the parameter c, is largely independent of other influences. Therefore, the parameter c is particularly suitable for determining the level of the thermal focal shift of the protective glass alone. Therefore, the evaluation device 80 may be configured to output a signal if a predetermined value for the parameter c is exceeded (which indicates that a predetermined thermal shift of the protective glass has been exceeded). Such a signal can be used, in particular, to indicate the need to replace a contaminated protective glass.

[0187] The beam analysis device 10 according to the present invention can also be advantageously used for a processing optical system 200 in which two protective glasses 120, 125 are arranged one behind the other in the beam direction, and a pressure equalization connection 145 is provided between the cavity 141 and the intermediate region between the two protective glasses in the cutting gas device 140, so that no pressure difference acts on the outer protective glass 120. Such a configuration of the processing optical system 200 is shown in FIG. 23. Therefore, the outer protective glass 120 facing the processing process does not need to be pressure-resistant, and therefore a thinner, and therefore less expensive, protective glass can be used as a wear part. This type of arrangement with two protective glasses 120, 125 and a pressure equalization connection 145 results in no deflection of the outer protective glass 120 due to the cutting gas pressure p. Therefore, no displacement of the intermediate focus 71 of the sample beam 70 occurs due to deflection of the protective glass. Nevertheless, when determining the focal position, a correction that depends on the cutting gas pressure p is necessary, since pressurizing the cutting gas increases the refractive index, which in turn shifts the energy beam focal point 76. Therefore, by taking the cutting gas into account, the beam analysis device 10 according to the invention allows a particularly accurate determination of the focal position, even in the case of processing optics without deflection of the outer protective glass.

[0188] An advantage of the present invention is that changes in the focus position caused by the process gas or cutting gas, especially under fluctuating and / or high pressures, are corrected by taking the cutting gas signal into account when determining the focus position, thereby achieving a very accurate and reliable determination of the focus position during an ongoing machining process.

[0189] A further advantage of the present invention, particularly in relation to the focus position sensor 13 according to the fourth embodiment of the focus position sensor, is that the measurement principle of the beam analysis device 10 is based on determining the positions of the beam spots 93, 94 on the detector 40, which are separated from one another. The positions of the beam spots can be determined, for example, by calculating the centroids of the associated intensity distributions, i.e., the first moments of the intensity distributions. The determination of their positions and their separation distance is largely independent of the constant signal background height, which may be caused, for example, by scattered light and / or sensor noise. As a result, the measurement principle is less prone to errors than other methods based on determining, for example, the beam diameter, i.e., the second moment of the intensity distribution, and its changes, because the determination of the second moment is relatively sensitive to changes in the background height.

[0190] Another important advantage of the present invention is that the determination of the axial position of the beam focus is not affected by variations in the beam quality of the laser beam or the sample beam.

[0191] The determination of the change in axial position of the beam focus can be made in near real time, i.e., the determination requires only a fraction of the typical time constant of the focus position change caused by thermal focus shift. Thus, the present invention can also provide signals for controlling a laser material processing process during the laser processing process. The processing process can be controlled, for example, by continuously readjusting or correcting the axial focus position of the processing optics.

[0192] A beam of electromagnetic radiation having a wavelength in the range of 0.1 μm to 10 μm, particularly preferably in the range of 0.3 μm to 3 μm, in particular in the range of 0.3 μm to 1.5 μm, is preferably considered as an energy beam within the meaning of the present disclosure.

[0193] For the purposes of the present invention, laser radiation is preferably electromagnetic radiation in the range from 0.3 μm to 1.5 μm and has a power of at least 1 mW, particularly preferably a power of at least 100 W. [Explanation of symbols]

[0194] 10...Beam analysis device 11...Optical axis, local optical axis 12...Beam forming device 13...Focus position sensor 19…Partial beam extraction surface 20...Modulator 23, 24...Transmission zone 25...Blocked Zone 31...First horizontal direction 33, 34...partial opening 37...Second horizontal 39...Sensor surface 40...Detector 49...Position of imaging device, principal plane of imaging device 50...imaging device 51...Optical lens 52...Beam separator device 53, 54...partial beam deflection elements, such as wedge plates, prisms, or plane-parallel plates 56...Lens array 57...Individual lens elements, lenslets 62...Gas pressure sensor 63...Disconnect gas signal (data connection) 64...Detector signal (data connection) 65...Lens position signal (data connection) 67...Focus tracking signal (data connection) 70...Sample beam 71...Focus of sample beam (intermediate focal point) 73, 74...Partial beam 76...Energy beam focus 77...Energy beam or laser beam 79...Intensity distribution on the detector 80...Evaluation device 81...Memory unit 83...Cutting gas signal input unit 84...Detector signal input unit 85...Lens position signal input unit 86...Computational unit 87...Focus tracking signal output unit 91...Single beam spot 93, 94...Beam spot 100, 200...Laser processing optical system 105... Positioning device 110...Optical fiber end 111...optical axis 113...Collimator 114...Separation device 115...Beam decoupler 116…Focusing optical system 120...Optical element, for example, protective glass 121...Outer boundary surface of optical element 122...second boundary surface of optical element 125...Second protective glass 140...Cutting gas device 141...Cutting gas device cavity 142...Outlet opening of cutting gas device 143...Cutting gas supply unit 145...Pressure equalization connection 146...Cutting gas 150...Workpiece 170...Second sample beam 171...Focus of second sample beam (second intermediate focusing point) 173, 174...other partial beams 193, 194...other beam spots

Claims

1. A beam analysis device (10) for determining the axial position of a focal point (76) of an energy beam (77) of electromagnetic radiation guided in a laser processing optical system (100), the beam analysis device comprising a focal point position sensor (13) and an evaluation device (80), The focus position sensor (13) comprises a beam shaping device (12) and a detector (40); The beam shaping device (12) receiving the sample beam (70); imaging at least a portion of the sample beam (70) onto the detector (40) by the beam shaping device (12) to form an intensity distribution (79) on the detector (40); It is configured as follows: The detector (40) a sensor that is sensitive to optical radiation and has two-dimensional spatial resolution and is configured to convert the intensity distribution (79) incident on the detector (40) into an electrical signal (64); The evaluation device (80) processing the electrical signal (64) of the detector (40) representative of the intensity distribution (79) on the detector (40); determining geometric parameters from said intensity distribution (79); receiving a cutting gas signal (63) indicative of the pressure of the process gas or cutting gas; determining a correction value taking into account the cutting gas signal (63); determining the axial position of the focal point (76) of the energy beam (77) taking into account the geometric parameters and the correction values; It is configured as follows: Beam analysis equipment.

2. 2. The beam analysis device (10) according to claim 1, the sample beam (70) is generated by back-reflection of a portion of the energy beam (77) at an interface (121) of an optical element (120) of the laser processing optical system (100); The optical element (120) is adjacent to a cavity (141) of a cutting gas device (140) of the laser processing optical system (100); The sample beam (70) is separated from the laser processing optics (100) by a beam decoupler (115) and supplied to the beam shaping device (12) of the beam analysis device (10); the cutting gas signal (63) represents the current pressure of the process gas or cutting gas (146) in the cavity (141) of the cutting gas device (140); Beam analysis equipment.

3. 3. The beam analysis device (10) according to claim 2, the beam shaping device (12) and the detector (40) are disposed together in a housing having an opening for introducing the sample beam (70); The housing is connected to the laser processing optical system (100), and the sample beam (70) separated by the beam decoupler (115) is supplied to the beam shaping device. Beam analysis equipment.

4. 2. The beam analysis device (10) according to claim 1, the evaluation device (80) comprises an input unit (83) for the cutting gas signal (63), an input unit (84) for the electrical signal (64), a memory unit (81) and a calculation unit (86), Beam analysis equipment.

5. 5. The beam analysis device (10) according to claim 4, the evaluation device (80) is configured to carry out the determination of the correction values ​​taking into account calibration data stored in the memory unit (81), the calibration data describing the variation of the geometric parameters as a function of the cutting gas signal (63); Beam analysis equipment.

6. 2. The beam analysis device (10) according to claim 1, The evaluation device (80) receiving a lens position signal (65) representing the axial position of an axially positionable lens or lens group of the laser processing optical system (100); determining the axial position of the focal point (76) of the energy beam (77) taking into account the geometric parameters, the correction values ​​and the lens position signal (65); It is configured as follows: Beam analysis equipment.

7. 7. A beam analysis device (10) according to claim 6, the evaluation device (80) comprises an input unit (85) for the lens position signal (65), Beam analysis equipment.

8. 2. The beam analysis device (10) according to claim 1, The evaluation device (80) calculating a focus tracking signal (67) from the determined axial position of the focus (76) of the energy beam (77), which is the actual focus position, and a focus target position; outputting the focus tracking signal (67); It is configured as follows: The focus tracking signal (67) is sent directly or via a higher-level control device to a positioning device (105), which adjusts the position of an axially positionable lens of the laser processing optical system (100). Beam analysis equipment.

9. A beam analysis device (10) according to claim 8, the evaluation device (80) comprises an output unit (87) for the focus tracking signal (67), Beam analysis equipment.

10. 2. The beam analysis device (10) according to claim 1, the beam shaping device (12) comprises an imaging device (50) having at least one optical lens (51); Beam analysis equipment.

11. 2. The beam analysis device (10) according to claim 1, the beam shaping device (12) is configured to image the sample beam (70) onto the detector (40) to form the intensity distribution (79) on the detector (40) having a beam spot (91) with a diameter (φ); determining the geometrical parameters by the evaluation device (80) includes determining the diameter (φ) of the beam spot (91) on the detector (40); Beam analysis equipment.

12. 2. The beam analysis device (10) according to claim 1, The beam shaping device (12) images the sample beam (70) onto the detector (40) at a separation distance (a Ｎ１ , a Ｎ２ , ...a ＮＭ a lens array (56) for forming the intensity distribution (79) on the detector (40) having a plurality of beam spots having a plurality of beam spots, The determination of the geometrical parameters by the evaluation device (80) is based on the separation distance (a) of the beam spots from each other. Ｎ１ , a Ｎ２ , ...a ＮＭ ) determining at least one of Beam analysis equipment.

13. 2. The beam analysis device (10) according to claim 1, The beam shaping device (12) a modulation device (20) for extracting two partial beams (73, 74) from the sample beam (70), the beam shaping device is configured to image the two partial beams (73, 74) onto the detector (40) to form the intensity distribution (79) on the detector (40) having beam spots (93, 94) spaced apart by a distance (a); determining the geometric parameters by the evaluation device (80) includes determining the separation distance (a) of the beam spots (93, 94); Beam analysis equipment.

14. 2. The beam analysis device (10) according to claim 1, the beam shaping device (12) is configured to extract two partial beams (73, 74) from the sample beam (70) at a partial beam extraction plane (19); the two partial beams (73, 74) are a first partial beam (73) and a second partial beam (74), the cross sections of the two partial beams (73, 74) at the partial beam extraction surface (19) are defined by partial apertures (33, 34), respectively; the sub-openings (33, 34) are spaced apart from one another, and the centers of the sub-openings (33, 34) are spaced apart by a separation distance (k); a first lateral direction (31) defined by the separation distance (k) between the partial openings (33, 34); The term "lateral" refers to a direction in a plane perpendicular to the local optical axis (11), the beam shaping device is further configured to image the two partial beams (73, 74) onto the detector (40) to form the intensity distribution (79) with beam spots (93, 94) on the detector (40), forming at least one beam spot (93) from the first partial beam (73) and at least one beam spot (94) from the second partial beam (74); the detector (40) is arranged at a distance (s) behind the partial beam extraction surface (19) in the propagation path of the partial beams (73, 74), determining the geometrical parameters by the evaluation device (80) includes determining a separation distance (a) between the positions of the two beam spots (93, 94) on the detector (40) along the first lateral direction (31); Beam analysis equipment.

15. A beam analysis device (10) according to claim 14, the beam shaping device (12) is configured to deflect and / or displace at least one of the at least two partial beams (73, 74) in a second lateral direction (37) to form a separation distance (w) along the second lateral direction (37) between the two beam spots (93, 94) on the detector (40); The second transverse direction (37) is oriented transversely to the first transverse direction (31); Beam analysis equipment.

16. A beam analysis device (10) according to claim 14, the first lateral direction (31) and the local optical axis (11) between the partial beam extraction surface (19) and the detector (40) are changed by beam folding and / or beam deflection, Beam analysis equipment.

17. A beam analysis device (10) according to claim 15, the beam shaping device (12) is configured to deflect and / or displace the two partial beams (73, 74) relative to one another, the difference in deflection and / or displacement of the two partial beams (73, 74) is oriented along the second transverse direction (37) so as to form the separation distance (w) along the second transverse direction (37) between the two beam spots (93, 94) on the detector (40). Beam analysis equipment.

18. A beam analysis device (10) according to claim 15, the beam shaping device (12) comprises a beam separator device (52) having at least one partial beam deflecting element (53, 54) for deflecting and / or displacing at least a first partial beam of the two partial beams (73, 74) in the second lateral direction (37) to form the separation distance (w) between the two beam spots (93, 94) on the detector (40) along the second lateral direction (37). Beam analysis equipment.

19. A beam analysis device (10) according to claim 18, the beam separator device (52) comprises at least two partial beam deflection elements (53, 54) for deflecting and / or displacing the two partial beams (73, 74) relative to one another, the difference in deflection and / or displacement of the two partial beams (73, 74) is oriented along the second transverse direction (37) so as to form the separation distance (w) along the second transverse direction (37) between the two beam spots (93, 94) on the detector (40). Beam analysis equipment.

20. A beam analysis device (10) according to claim 18, the beam separator device (52) comprises at least one wedge plate (53, 54) as a partial beam deflection element, the at least one wedge plate being arranged in front of or behind one of the sub-apertures (33, 34) in alignment with the beam direction and configured to deflect the partial beam (73, 74) extracted from the sub-aperture (33, 34) by an angular amount ranging from 0.02 degrees to 6 degrees; Beam analysis equipment.

21. A beam analysis device (10) according to claim 18, the beam separator device (52) comprises at least one inclined plane-parallel plate (53, 54) or prism as a partial beam deflection element, the at least one inclined plane-parallel plate or prism being arranged in front of or behind one of the sub-apertures (33, 34) in alignment with the beam direction and configured to displace the partial beams (73, 74) emerging from the sub-aperture (33, 34) by an amount in the range of 0.05 mm to 3 mm; Beam analysis equipment.

22. A system comprising the beam analysis device (10) according to any one of claims 1 to 21 and laser processing optics (100) for guiding and focusing the energy beam (77), The laser processing optical system (100) includes a beam decoupler (115) for separating the sample beam (70); The beam analysis device (10) is connectable to the laser processing optics (100) to receive the separated sample beam (70). system.

23. 1. A method for determining the axial position of a focal point (76) of an energy beam (77) of electromagnetic radiation guided in a laser processing optical system (100), the method comprising: receiving a sample beam (70) separated from the laser processing optics (100); imaging at least a portion of the sample beam (70) onto a detector (40) by a beam shaping device (12) to form an intensity distribution (79) on the detector (40); converting the intensity distribution (79) incident on the detector (40) into an electrical signal (64) by a sensor of the detector (40) that is sensitive to optical radiation and has two-dimensional spatial resolution; processing the electrical signal (64) of the detector (40) representative of the intensity distribution (79) on the detector (40); determining geometric parameters from said intensity distribution (79); receiving a cutting gas signal (63) representative of a pressure of a process or cutting gas (146); determining a correction value taking into account the cutting gas signal; determining the axial position of the focal point (76) of the energy beam (77) taking into account the geometric parameters and the correction values; having method.

24. 24. The method of claim 23, further comprising: generating the sample beam (70) by reflecting a portion of the energy beam (77) back at an interface (121) of an optical element (120) of the laser processing optical system (100), the optical element (120) being adjacent to a cavity (141) of a cutting gas device (140) of the laser processing optical system (100); separating the sample beam (70) from the laser processing optics (100) by a beam decoupler (115); providing the separated sample beam (70) to a beam analysis device (10); further comprising method.

25. 25. The method of claim 23 or 24, wherein the method comprises: determining said correction value taking into account calibration data; the calibration data describing the variation of the geometric parameters as a function of the cutting gas signal (63); method.

26. 25. The method of claim 23 or 24, wherein the method comprises: receiving a lens position signal (65) representing the axial position of an axially positionable lens or lens group of the laser processing optical system (100); determining the axial position of the focal point (76) of the energy beam (77) taking into account the geometric parameters, the correction values ​​and the lens position signal (65); further comprising method.

27. 25. The method of claim 23 or 24, wherein the method comprises: calculating a focus tracking signal (67) from the determined axial position of the focal point (76) of the energy beam (77), which is the actual focus position, and a focus target position; providing the focus tracking signal (67) to a positioning device (105), which adjusts the position of an axially positionable lens or lens group of the laser processing optical system (100); further comprising method.

Images