Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/04—Automatically aligning, aiming or focusing the laser beam, e.g. using the back-scattered light
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/04—Automatically aligning, aiming or focusing the laser beam, e.g. using the back-scattered light
  • B23K26/042—Automatically aligning the laser beam
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/04—Automatically aligning, aiming or focusing the laser beam, e.g. using the back-scattered light
  • B23K26/042—Automatically aligning the laser beam
  • B23K26/043—Automatically aligning the laser beam along the beam path, i.e. alignment of laser beam axis relative to laser beam apparatus
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/08—Devices involving relative movement between laser beam and workpiece
  • B23K26/0869—Devices involving movement of the laser head in at least one axial direction
  • B23K26/0876—Devices involving movement of the laser head in at least one axial direction in at least two axial directions
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
  • G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means

Definitions

• the present invention relates to a method for determining a point of contact of a focused, pulsed laser beam on an edge of a body, which is preferably formed at an opening of the body, and a laser processing machine with a laser processing nozzle on a laser processing head.
• a laser processing machine with a laser processing nozzle on a laser processing head.
• it is necessary to know as accurately as possible an actual position (XY position) of the laser beam within the laser processing nozzle and a focus position (Z position) of the laser beam relative to a workpiece surface or to align the laser beam, ie the laser beam at a target position relative to the nozzle opening and / or to position relative to the workpiece surface.
• a contact point of the laser beam at an edge of the nozzle opening or the edge of another suitably positioned body can be determined.
• the target position of the laser beam relative to the laser processing nozzle is usually in the center of the nozzle opening. Alignment is normally done manually in the art. For this purpose, an adhesive strip is glued over the nozzle opening and burned a small hole in the adhesive strip with low laser power. The deviation of the beam position from the center of the nozzle is determined with the naked eye and a magnifying glass. Corresponding positioning units with adjustment screws serve to correct the beam position, by means of which the position of the laser beam in a direction perpendicular to the nozzle axis extending X-Y plane of the nozzle opening in the X and Y directions can be changed. This process is inaccurate, time-consuming and due to necessary manual intervention for an automated process sequence unsuitable.
• JP 63108985 A describes a method using the photoacoustic effect.
• the beam diameter varies on a workpiece.
• a small beam diameter on the workpiece results in a high intensity of the generated acoustic signal and vice versa.
• the focal point lies in the plane of the workpiece, then the diameter of the laser spot on the material surface is minimal and the intensity of the photoacoustic signal is maximal. If a maximum intensity is detected during the evaluation of the acoustic signal, then the focal point is in the plane of the workpiece and the focus position is thus determined.
• Object of the present invention is to provide a method and a laser processing machine of the type mentioned, which allow the determination of a contact point of the laser beam at a preferably formed at the opening of a laser machining nozzle or workpiece edge and thus aligning the laser beam in a simple and automatable manner ,
• a method comprising the steps of: a) moving the laser beam relative to the edge in at least one spatial direction, preferably perpendicular to the laser beam axis, until the laser beam sweeps over the edge, b) measuring acoustically when the laser beam is moved by the laser beam Vibrations, and c) determining the point of contact of the laser beam at the edge by evaluating the measured acoustic vibrations.
• the location coordinates of the touch point may subsequently be stored in a memory device which may be e.g. is formed in a control unit, are stored.
• the pulsed laser beam passing through the nozzle opening along a propagation direction (Z direction) substantially corresponding to the direction of the nozzle axis becomes in a plane perpendicular thereto (XY plane) within the opening in the nozzle body or against an edge or within an opening a (test) workpiece until it hits the usually metallic nozzle body or the workpiece and generates an acoustic wave there, which can be received by an acoustic sensor, preferably a microphone.
• an acoustic sensor preferably a microphone.
• the location coordinates of a contact point of the laser beam at the edge are determined. With knowledge of the location coordinates of the starting point before moving the laser beam, the distance of the laser beam is also determined to contact the edge and thus the extent of the beam in the XY plane.
• the shape of the laser beam in Z direction can be repeated by repeating several times with reference to the edge and the position of the smallest beam diameter determine. In this way, the focus position of the laser beam is determined relative to the opening of the laser processing nozzle or the workpiece.
• the vibration power increasing at the edge of the edge in an edge is measured as a function of the location and the contact point is set to a predetermined fraction, e.g. 50%, assigned to a maximum vibration power.
• the microphone receives no signal as long as the laser beam passes without contact through the opening or at the edge. Only when the laser beam begins to strike the edge of the opening and thus the edge, with increasing contact ratio, an increase in the signal intensity is observed, which is recognizable as an edge in a characteristic curve in which the acoustic power is applied as a function of location.
• the laser beam is preferably such in the method according to the invention moves to fully sweep the aperture in a first spatial direction, such as the X direction, ie, to strike the nozzle body or workpiece at two opposing points of contact, as evidenced by an increase in the acoustic signal (signal edge).
• the laser beam is preferably moved along a line in the first spatial direction.
• the first spatial direction in which the actual or target position is determined is defined as the line connecting the two points of contact.
• the two contact points in the first spatial direction can be determined on the basis of the measured acoustic signal. From the knowledge of the contact points and the movement path during the movement of the laser beam relative to the opening, an actual position of the laser beam relative to the opening can be determined. Alternatively or additionally, when the contact points are known, a desired position of the laser beam can also be determined, which is usually located in the middle between the two contact points, since usually a centric alignment of the laser beam in the opening is desired. It is understood that in the manner described above, the actual or desired position can be determined not only in the X direction, but also in the Y direction. If the target position in two directions is known, the laser beam can be aligned in the middle of the opening, preferably in the center of the nozzle.
• the laser beam is moved to the desired position after determining the desired position, which preferably lies in the middle between the two contact points.
• the laser beam can thereby be positioned in the center of the nozzle.
• the respective desired position in the two spatial directions of the XY plane can first be determined according to the method described above.
• the desired position in the X-direction is determined and the laser beam is subsequently centered in the X-direction in the opening. Only then is the target position in the Y direction determined and there is a Centering of the laser beam in this direction.
• the determination of the desired position in X direction can be performed to increase the accuracy.
• Direction after moving the laser beam to the target position in the Y direction can be repeated.
• the second direction does not necessarily have to be perpendicular to the first direction. Rather, both directions can for example also have an angle of 120 ° or 60 ° to each other and do not have to coincide with the axes of movement (X or Y) of the laser processing machine.
• either the diameter of the opening, preferably the nozzle opening, or - with known opening diameter - the diameter of the laser beam in the first spatial direction from the respective path of movement of the laser beam from a starting point of the movement can be determined to the opposite points of contact.
• a cross-sectional dimension of the opening is determined from the distance between the two contact points in the first spatial direction and the distance between two further contact points in a second spatial direction.
• the bore diameter can be determined in this way. The method according to the invention thus serves as a plausibility check after a nozzle change, wherein calibration measurements are used to correlate the measured values with the actual diameter.
• the laser processing head moves or preferably arranged in the beam path focusing optics in particular automatically tilted and / or moved transversely to the laser beam and / or at least one arranged in the beam path in front of the nozzle body deflecting particular automated tilted or changed in its radius of curvature.
• the focusing optics is moved in a plane perpendicular to its optical axis.
• the movement of the laser beam can be effected by tilting, for example, the last or penultimate deflecting mirror in front of the focusing optics, or the nozzle body can be displaced while the laser beam is held stationary.
• the radius of curvature of a deflection mirror arranged in front of the focusing optics is preferably changed.
• the vibrations are measured by means of at least one acoustic sensor, preferably a microphone.
• the microphone is aligned so that it receives only possible photoacoustically generated acoustic signals.
• the microphone receives either the structure-borne noise from the nozzle body or the workpiece itself or the acoustic signal from the air.
• a measuring device converts the voltage signal output by the microphone into a digital signal. From the digital signal, the frequency spectrum is calculated (Fourier analysis) and shown as frequency-related power (FFT power).
• FFT power frequency-related power
• the measured oscillations when evaluating the measured oscillations, their properties are compared with characteristics of the pulsed laser beam.
• the characteristics of the measured vibrations, in particular frequency and phase are in this case compared with the pulse duration, pulse frequency and phase of the pulsed laser beam in order to exclude erroneous measurements (for example noise from drives).
• the moving and measuring takes place under Protective gas.
• a protective gas flow can be generated, being used as a protective gas, for example nitrogen.
• the protective gas allows the performance of the measurement even at high laser powers, in particular work, so that the effects of thermal changes of optical elements in the beam path in front of the nozzle can be detected and in particular deviations of the beam position can be detected by the optical axis.
• the measured vibrations are generated by a preferably plate-shaped body (workpiece) arranged in the beam path after a nozzle body.
• a preferably plate-shaped body workpiece
• the laser beam is shifted in the X-Y plane of the nozzle opening and hits the edge of the nozzle opening, less laser power is available on the plate-shaped body. This leads to a reduction in the intensity of the acoustic signal generated in the body. It is understood that in this case the photoacoustic signal generated in the nozzle body has to be shielded in order to be able to measure only the signal resulting from the plate-shaped body with the acoustic sensor.
• the distance between the focal point of the laser beam and the plate-shaped body along the propagation direction of the laser beam is varied to determine a focus position of the laser beam, ie the distance between the focal point and workpiece plane, as is basically known from JP 63108985 A.
• the focus diameter on the plate-shaped body varies. In principle, a small focus diameter on the body results in a high intensity of the generated acoustic signal and vice versa. If the focal point lies in the plane of the body, then the diameter of the laser spot on the material surface is minimal and the intensity of the photoacoustic signal is maximal.
• the focal point is in the plane of the plate-shaped body and the focal position is thus determined.
• the focus position determined in this way can be compared with a predetermined target focal position, which is usually chosen such that the focal point in the Working plane or work piece level. If the predetermined desired focus position and the focus position determined on the basis of the measurement deviate from one another, then the focus position can be corrected by means of the measurement results.
• Focusing optics for the laser beam and / or the plate-shaped body can be moved in the propagation direction of the laser beam. Alternatively or additionally, the entire laser processing head is moved in the Z direction while the plate-shaped body rests. However, it is preferred if an adaptive deflecting mirror is adjusted in the beam path in front of the nozzle body. Such an adaptive deflection mirror is e.g. lapped by water at its back. Due to the different water pressure the degree of curvature of the mirror and thus the focus are changed.
• the material of the plate-shaped body is selected such that it absorbs more laser power than the material of the nozzle body. If a material, for example a ceramic, which absorbs more energy than the generally metallic material of the nozzle body is used for the plate-shaped body, the acoustic signal is amplified and the measurement can be carried out with lower laser powers, so that the nozzle body is hit with low power and thereby spared.
• the method according to the invention allows both a centering of the laser beam in a laser processing nozzle as well as the determination and adjustment of the focus position of the laser beam with respect to the laser processing nozzle or a (test) workpiece.
• the method makes it possible to perform both the centering and the focus position adjustment only with the aid of the laser processing nozzle as a measurement object when the acoustic signal is generated directly at the edge of the nozzle opening. In this way, a separate body does not necessarily have to be introduced into the beam path for the measurement.
• the invention is also realized in a laser processing machine with a laser processing nozzle on a laser processing head, through the opening of which a pulsed, focused laser beam passes, the laser beam and the laser beam Opening are relative to each other in at least a first spatial direction perpendicular to the laser beam axis movable until the laser beam sweeps over an edge of a body, which is preferably formed at an opening of the body, at least one acoustic sensor, preferably a microphone, for measuring during the movement of the laser beam photoacoustically generated acoustic vibrations, and an evaluation device, which is designed to determine a point of contact of the laser beam at the edge by evaluating the measured vibrations.
• the laser processing machine further comprises a preferably automated movement device for tilting and / or displacement of a focusing lens arranged in the beam path in front of the nozzle body transversely to the laser beam.
• the displacement can be done for example by means of stepper motors, whereby at the same time information about the movement path is provided.
• the movement device is mounted in a laser processing head or on an adjustment station of the laser processing machine, in which the laser processing head for determining a Istoder target position of the laser beam in the opening and / or a focal position and for moving the laser beam to the desired position and / or Adjustment of focus position can be spent.
• the laser processing head for determining a Istoder target position of the laser beam in the opening and / or a focal position and for moving the laser beam to the desired position and / or Adjustment of focus position can be spent.
• stepper motors are mounted directly to the laser processing head instead of the usual adjustment screws in the former case, so that an automated alignment of the laser beam relative to the nozzle edge can be achieved.
• the stepper motors are coupled to adjusting spindles in the adjustment station at an adjustment position into which the laser processing head can be moved to adjust the beam position.
• the laser processing machine further comprises a preferably plate-shaped body, which is arranged in the beam path after the nozzle body and which preferably has an edge formed in particular on an opening of the plate-shaped body.
• the material of the body can be chosen to absorb more laser radiation than the material of the nozzle body, so that the measurement can be performed at lower beam powers, whereby the nozzle body is spared.
• the body may have an opening or edge, so that the focal position of the laser beam with respect to this opening or edge can be adjusted.
• the laser processing machine further comprises a beam trap for protecting the acoustic sensor from stray light.
• the jet trap is placed at a suitable distance from the edge of the opening below the nozzle body in the beam path and absorbs the laser beam, whereby the acoustic sensor is protected from destruction by the laser radiation.
• the acoustic sensor is positioned offset in a spatial direction to the laser beam axis outside the beam path and aligned at an angle to the laser beam axis or to the plate-shaped body. In this way, the contribution of noise, which is not caused by the photoacoustic effect, is reduced.
• the positioning of the acoustic sensor not only serves to mask out interference noise by targeted alignment to the nozzle or the plate-shaped body, but also has a decisive influence on the measured intensity. At certain positions / angles of the optical sensor, significantly larger maxima are measured at constant laser power than at other positions / angles. More intense maxima in the characteristic allow a higher accuracy in the determination of the contact points, because in this case the edges of the characteristic curve are steeper.
• FIG. 1 is a schematic representation of an embodiment of a laser processing machine according to the invention
• FIGS. 2a, b are schematic representations of a section through a
• FIGS. 3a-c are schematic representations of the movement of a laser beam from a starting position to a first side of an edge of an opening
• FIGS. 4a-c are schematic illustrations of the movement of the laser beam of FIGS. 3a-c to an opposite side of the edge of the opening
• Fig. 5 is a schematic representation of a waveform of the acoustic
• Fig. 6 is a schematic representation of an opening of a laser processing nozzle in a plan view with nominal positions of the laser beam between points of contact of the opening.
• Fig. 1 shows a laser processing machine 1 with a plurality of optical elements 2.1 to 2.5 having optics for beam guidance for a laser beam 3 to a laser processing head 4 for machining a (not shown) workpiece.
• the laser processing head 4 For moving the laser processing head 4 along a working table 5 defining a working table in a first spatial direction X of an XYZ coordinate system, the laser processing head 4 is attached to a carriage 6 movable in the first spatial direction X, as indicated by a double arrow.
• the laser processing head 4 can continue to be moved in a second spatial direction Y in the working plane 5 by moving along of the carriage 6 is moved, as is also indicated by a double arrow.
• the laser processing head 4 can be moved in both spatial directions X, Y over the entire working plane 5 of the machining table and edited on this positioned workpiece. Furthermore, the laser processing head 4 can be moved to an adjustment position on the edge of the processing table 5, where an adjustment station 7 is provided, on which the laser processing head 4 can be adjusted, as described in more detail below.
• the pulsed laser beam 3 is guided starting from a laser source, not shown, via a first mirror 2.1 onto a compensating element 8, which has two further mirrors 2.2 and 2.3 and which is displaceable in the first spatial direction X, as indicated by a further double arrow.
• the beam path of the laser beam 3 in the laser processing machine 1 can be kept constant.
• the laser beam 3 After the laser beam 3 has been deflected by means of two further arranged in the carriage 6 mirrors 2.4 and 2.5 from the first spatial direction X in the second spatial direction Y, the laser beam 3 enters the laser processing head 4, where he with the aid of a first and second deflecting mirror 9.1 , 9.2 is deflected from the second spatial direction Y in a third spatial direction Z.
• the second deflection mirror 9.2 is designed here as an adaptive mirror, i. it can change its shape to finally form the laser beam 3.
• the laser beam 3 passes through a focusing optics 10 for focusing the laser beam 3 onto a focal point F in the working plane 5 of a laser processing nozzle 11, as shown in detail in a sectional view of the laser processing head 4 in FIG.
• the laser processing nozzle 11 has a metallic nozzle body 12 in which a nozzle bore 13 is provided with a circular opening 14, through the center of which in Fig. 2a, b, the laser beam axis 15 extends.
• a microphone 16 is arranged as an acoustic sensor such that this offset by the method of the laser processing head 4 in the adjustment position in the first spatial direction X to the laser beam axis 15 outside the beam path to the nozzle body 12 and below Angle ⁇ of 30 ° to Laser beam axis 15 is aligned.
• the laser beam 3 is absorbed by a beam trap 17.
• a blanket gas stream (not shown) of nitrogen.
• the laser beam 3 In order to position the laser beam 3 at a desired position in the center of the nozzle, which coincides with the position of the laser beam axis 15 in the nozzle center at the circular opening 14, it is necessary first to set a desired position in the first spatial direction X (in the following short: X-direction). to determine.
• the laser beam 3 is moved from the starting position shown in Fig. 3a along the positive X direction by the focusing optics 10 shown in Fig. 2 is moved in the X direction.
• the laser beam 3 first touches the edge of the opening 14, cf. Fig. 3b, to then be further moved in the X direction until it hits completely on the nozzle body 12, see. Fig. 3c.
• the laser beam 3 is first moved back along the negative X direction to the starting position, which is shown in Fig. 4a, first to touch the edge of the nozzle opening 14 (Fig. 4b) before the laser beam 3 completely on the nozzle body 12 hits (Fig. 4c).
• Figs. 3a-c and Figs. 4a-c of this movement of the laser beam 3 thus passes completely over the nozzle opening 12 in the X direction and strikes an edge 20 of the opening 14 on two opposite sides.
• the pulsed laser beam 3 strikes the metallic nozzle body 12 (see Fig. 3b, c and Fig. 4b, c) during the movement described above, it triggers a photoacoustic wave there.
• the pulsed laser beam 3 thus triggers an acoustic signal with a frequency which corresponds to its pulse frequency.
• the acoustic signal is in the audible range and can be detected by the microphone 16, wherein an increase in the laser frequency due to the inertia leads, as expected, to a reduction of the signal intensity.
• the gas pressure of the air is also changed directly by the heating due to the laser irradiation. These pressure fluctuations are usually too weak or the ambient noise too strong to be measured with conventional microphones.
• the movement of the laser beam in the X direction to determine the points of contact of the opening 14, between which a desired position can be determined are measured during the movement of the laser beam with the microphone 16 and converted by this into an analog voltage signal acoustic oscillations an evaluation unit 18 of the laser processing machine 1 (see Fig. 1) converted into a digital signal.
• the frequency spectrum is calculated from the digital signal (Fourier analysis) and displayed as frequency-related power (Fast Fourier Transformation, FFT power). Frequency and phase of the digital signal are compared here with the pulse frequency and the phase of the laser pulses of the laser beam 3 in order to rule out incorrect measurements (eg noise from drives).
• a generated in the evaluation trace 19, in which the frequency-related, i. is measured at the pulse rate measured power P over the location along the X direction is shown in Fig. 5.
• the maximum sound intensity of the acoustic signal is measured at a number of measuring points and displayed as frequency-related power.
• the microphone 16 does not receive a signal as long as the laser beam 3 passes through the opening 12 without contact. Only when the laser beam 3 begins to strip the edge 20 of the opening 14, an increase in the signal intensity is observed with increasing contact ratio, which can be seen as flanks 19a, 19b in the measurement curve 19.
• the degree of steepness of the flanks 19, 19b depends inter alia on the position (angle, distance) of the microphone 16 relative to the opening 14. If the complete beam diameter strikes the nozzle body 12, the signal intensity of the measuring curve 19 is reduced on further deflection. As a result, a defined maximum M1, M2 is formed on each flank 19a, 19b.
• the focusing optics 10 has been moved in the X direction over the entire possible adjustment range of ⁇ 2 mm, whereby the laser beam 3 has been moved in this direction, as shown in Fig. 5 by overlapping beam cross sections.
• the laser power was 1.5 kW and the pulse frequency of the laser beam 3 was 500 Hz.
• Measurements of the acoustic signal were carried out at intervals of 90 .mu.m.
• the course of the measuring curve 19 shows an increase as soon as the Laser beam 3, the edge 20 of the opening 14 contacts, which is also shown in Fig. 5.
• a location is determined on both measuring edges 19a, 19b at which the relative intensity with respect to the respective maximum M1, M2 has the same fraction, which in the present case is 50%.
• the so determined locations are identified with a first and a second, opposite in the X direction Berckentician B1, B2 of the opening 14, see. Fig. 6a.
• a target position S1 for the centering of the laser beam 3 in the center of the nozzle is determined as the center of these contact points B1, B2 in the X direction.
• the actual position of the laser beam 3 relative to the opening 14 can be determined.
• the laser beam 3 is moved to this and the measuring process shown above is repeated in the second spatial direction Y (in the following short: Y-direction).
• a third and a fourth contact point B3, B4 of the opening 14 are determined and a second setpoint position S2 is determined at the midpoint between the third and fourth contact point B3, B4, cf. Fig. 6b.
• the laser beam 3 has been moved to the second target position S2, this is ideally positioned in the center of the opening 14.
• the distance between the first and second contact points B1, B2 available for the determination of the first setpoint value S1 is quite small, so that the determination of the first setpoint value may not have been carried out with sufficient precision.
• the above-described measurement may be performed one more time in the X direction, whereby a fifth and sixth touch points B5, B6 are detected. Due to the larger distance between the fifth and sixth contact point B5, B6, a third target position S3 can be determined, which is more accurate than the first target position S1 in the X direction.
• the diameter of the circular opening 12 can also be determined from the determined contact points B1 to B6 However, this additionally requires a calibration which determines which portion of the maximum frequency-related power the diameter can be most accurately determined. Such a determination of the nozzle diameter can serve as a plausibility check during a change of the laser processing nozzle 11.
• the position of the laser beam focus point is determined and adjusted relative to the laser processing nozzle. For this purpose, starting from a starting point SP in the XY plane whose coordinates are stored in the control unit, a contact point (B1 to B6) of the laser beam 3 at the nozzle opening is determined as described above. For this purpose, as shown in Fig. 3a, the laser beam 3 is moved from the starting point SP along the positive X or Y direction by shifting the focusing optics 10 shown in Figs. 2a, b in the X or Y direction , During the movement, the laser beam 3 first touches the edge 20 of the opening 14, cf. Fig.
• the coordinates of the determined Bermmddlings are also stored in the control unit. From the stored coordinates, the distance from the starting point SP to the impact of the laser beam on the nozzle opening and, therefrom, the extent of the laser beam in the XY plane can be determined. If the measurement is repeated from the starting point in the negative X or Y direction, the diameter of the laser beam is determined in this way with a known diameter of the nozzle opening. Subsequently, the focal point of the laser beam in the Z direction is shifted by changing the radius of curvature of the adaptive deflection mirror 9.2 and the measurement is carried out again.
• the Z setting in which the smallest dimension or the smallest diameter of the beam is measured, indicates that the focal point of the laser beam lies exactly in the XY plane of the nozzle opening. Subsequently, the focal point is defined in a plane below the nozzle opening, usually exactly in the working plane 5, moved.
• the determination of the focus position does not have to be carried out with the aid of the nozzle body, but can also be carried out analogously on a (test) workpiece that is located in the working plane 5 and a has defined edge or a square or round opening, which is "touched" by the laser beam.
• the use of the laser processing nozzle as a measurement object offers the advantage that no additional workpiece has to be introduced into the beam path.
• the focusing lens 10 shown in Fig. 2 is shifted in the X and Y directions. This movement takes place by means of stepper motors (not shown, indicated by a double arrow B), whereby information about the movement path is simultaneously provided.
• the stepper motors are coupled to adjusting spindles in the adjustment station 7 of FIG. 1, in which the laser processing head 4 must travel to adjust the beam position.
• the deflection of the laser beam by tilting the last or penultimate deflection mirror 9.1, 9.2 in front of the focusing optics 10 take place.
• this can also be attached directly to the nozzle body 12 itself to receive its structure-borne sound.
• the provision of an adjustment station can be dispensed with, i. the adjustment can in principle be made at any location in the working level 5, since all the necessary components in the laser processing head 4 are attached to the evaluation device 18.
• the measurements can also be made by measuring the acoustic vibrations emitted by a plate-shaped body 21 shown in FIG. 2 a instead of the acoustic vibrations generated by the nozzle body 12, onto which the laser beam 3 below the nozzle body 12 incident.
• a piezoelectric sensor 16 ' is provided, which is arranged on the side of the body 21 remote from the nozzle body 12, so that the body 21 shields the acoustic vibrations emitted by the nozzle body 12.
• the laser beam 3 When moving the laser beam 3 in the XY plane of the nozzle opening 14, as soon as it impinges on the edge 20 of the opening 14, less laser power is available on the plate-shaped body 21, resulting in a reduction in intensity of the in the plate-shaped body 21 by the laser beam. 3 generated acoustic signal leads.
• the laser beam 3 is displaced outwards until it is shielded, for example, halfway through the nozzle body 12 and thus the intensity of the signal emanating from the plate-shaped body 21 has likewise fallen to 50% of the maximum value.
• such materials for example ceramics, can be used, which absorb more energy than the usually metallic material of the nozzle body 12. In this way, the measurement can be performed with lower laser powers to the nozzle body 12 conserve.
• the focus position FL of the laser beam 3 can also be checked in addition.
• the focal point F of the laser beam 3 is adjusted by means of the focusing optics 10 and the adaptive deflection mirror 9.2 in such a way that it lies at the desired focus position FL in the working plane 5.
• the optical elements arranged in the beam path of the laser beam 3 heat up, as a result of which the focal point F can move away from the desired focus position FL.
• the focal point F is displaced along the third spatial direction Z (in the following: Z-direction), for example by adjusting the adaptive deflection mirror 9.2.
• a small focus diameter on the plate-shaped body 21 results in a high intensity of the generated acoustic signal and vice versa.
• the focal point F the focus diameter on the plate-shaped body 21 is varied. If the focal point F lies in the plane of the plate-shaped body 21, the diameter of the laser spot on the body 21 is minimal and the intensity of the photoacoustic signal is maximal. If the maximum detected at a different location than at the target focus position FL along the Z direction, the focal point F must be moved along the Z direction, which can be done for example by suitable adjustment of the adaptive mirror 9.2. Alternatively, in determining the nozzle center and the focus position, as shown in Fig.
• the plate-shaped body 21 a region of continuous material which is larger than the nozzle opening 13, and a uniform edge 22 which at a square or circular opening 23 in the plate-shaped body 21 is formed.
• the focus position FL of the laser beam 3 can also be determined as described above by "touching" the edge 22 of the opening 23 of the plate-shaped body 21 at different focus settings. This method also makes it possible to determine not only the position of the focal point but also the shape of the laser beam in the area of the focal point (beam caustic).
• the beam position of the laser beam 3 can be determined within the opening 14, 23 and the laser beam 3 are centered in this, both of which can be automated.
• the focus position can be checked and, if necessary, corrected. It should be understood that the method described above is not limited to use in laser processing machines, but can also be used to advantage in other equipment in which the position of a laser beam in any aperture is to be determined and adjusted, in particular centered.

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• 2007
  • 2007-06-27 DE DE102007029787A patent/DE102007029787B3/de active Active
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