EP4087701A1

EP4087701A1 - Method and device for the controlled machining of a workpiece by means of confocal distance measurement

Info

Publication number: EP4087701A1
Application number: EP20845223.5A
Authority: EP
Inventors: Christoph Dietz; Philipp ROHRMANN
Original assignee: Precitec Optronik GmbH
Current assignee: Precitec Optronik GmbH
Priority date: 2020-01-06
Filing date: 2020-12-21
Publication date: 2022-11-16
Also published as: JP2023509081A; WO2021140396A1; KR20220119398A; CN115003448A

Abstract

The invention describes a method and a device for the controlled machining of a workpiece. According to the described method, a laser light beam is focused at a target point of the workpiece to be machined in order to produce a laser focal point. Furthermore, according to the method, distance measurement data are acquired by means of an optical distance-measuring device in order to determine a distance between the target point of the workpiece to be machined and the laser target optical unit. The method comprises positioning the workpiece to be machined in relation to the laser focal point on the basis of the acquired distance measurement data. The distance-measuring device is designed as an optically confocal distance-measuring device having a measurement light source for producing a measurement light and having a variable-focal-length measurement light optical unit. The method comprises varying the focal length of the variable-focal-length measurement light optical unit over time in order to acquire distance measurement data at different focal length values of the variable-focal-length measurement light optical unit, the laser light reflected by the workpiece and/or the process light produced during machining of the workpiece being detectible.

Description

description

METHOD AND DEVICE FOR THE CONTROLLED PROCESSING OF A

WORKPIECE USING CONFOCAL DISTANCE MEASUREMENT

The present disclosure relates to a method and a device for laser machining a workpiece.

In particular, the present disclosure relates to a method for laser machining of a workpiece while controlling the positioning of the workpiece to be machined for precise laser machining of the workpiece.

Methods are known in which workpieces are machined with a laser beam or laser light beam. Devices for carrying out such methods are also known. For a precise machining of a workpiece with a laser beam, an exact positioning of the workpiece or an exact adjustment of the corresponding

Laser processing devices required, which is only possible to a limited extent with the known methods and with the known devices.

An object of embodiments of the present disclosure is to provide an improved method and an improved device for a controlled

Provide laser processing of workpieces, which is characterized by a high processing precision and a simple design of the device.

To achieve the object, a method for the controlled machining of a workpiece is provided according to a first aspect. The method includes focusing a Laser beam or processing light beam for generating a laser focus point at a target point of the workpiece to be processed by means of laser target optics. A solid-state laser emitting in the near-infrared spectral range, such as a YAG laser or a fiber laser, and a gas laser such as a CO2 laser, for example, can be used to generate the laser beam.

The laser target optics can in particular be designed as focusing and alignment optics which enable targeted alignment and focusing of the laser beam.

The laser target optics can in particular be designed as a laser beam scanner, specifically as a galvo scanner, it being possible for the laser beam to be aligned with electrically controllable mirrors.

The method includes acquiring distance measurement data by means of an optical distance measuring device or an optical sensor to determine a distance between the target point of the workpiece to be processed and the laser target optics, or a fixed reference point or reference plane of the laser target optics.

The method further comprises machining the target point of the workpiece to be machined with the focused laser beam. The processing can in particular laser welding,

Include laser cutting and / or other laser processing.

According to the method, the distance measuring device is designed as an optical-confocal distance measuring device with a focal length variable optics or focal length variable measuring light optics, the method being a temporal one Varying the focal length of the focal length variable measuring light optics for the acquisition of distance measurement data with different focal length values of the focal length variable measuring light optics includes.

By varying the focal length of the focal length variable measuring light optics over time, the focal length of the focal length variable measuring light optics can be varied between a minimum focal length and a maximum focal length in such a way that a desired measuring range is defined. In particular, the measuring range can be defined or established in such a way that also at

Laser processing devices with a large focal length or with a small numerical aperture, the distance between the laser target optics and the target point of the workpiece to be processed can be precisely determined with the optical-confocal sensor. The workpiece can be machined in a controlled and precise manner on the basis of the determined distance measurement data.

The measuring optics with variable focal length also enable distance measurements to be carried out with optical elements that have no or only slight optical dispersion, so that the optical elements provided for the laser beam guidance, which in particular have little or no optical dispersion, are also used for the beam guidance of the measuring light can be.

The method can also include a positioning of the workpiece to be machined with respect to the laser focus point based on the acquired distance measurement data. The positioning of the workpiece to be machined can change the spatial Position and / or the spatial orientation of the workpiece or of the entire laser processing device. Alternatively or additionally, the positioning can include refocusing the laser beam. Thus, if necessary, the workpiece to be machined can be repositioned or the laser can be readjusted so that precise machining of the workpiece to be machined is made possible.

The laser target optics of the laser processing device can form part of the measuring light optics of the distance measuring device. In particular, the measuring light can be coupled to the beam path of the laser light beam in such a way that the measuring light beam runs at least in sections coaxially to the laser light beam.

By using the laser target optics of the laser processing device for the measuring light optics of the distance measuring device, the number of optical components required for carrying out the method can be reduced and the optical structure can thus be simplified. A distance sensor can thus be easily integrated into an already existing laser processing system.

At least some of the method steps can be carried out or repeated at several target locations on the workpiece to be machined. By repeating the

The positioning of the workpiece to be machined can be checked and, if necessary, corrected at several points in the process. In some embodiments, acquiring distance measurement data includes acquiring an intensity of a measurement light reflected back from the workpiece, the distance being determined on the basis of a time profile of the intensity of the measurement light reflected back from the workpiece.

In particular with a controlled temporal variation of the focal length of the focal length variable measuring optics, the points in time of the acquisition of the intensity at certain focal lengths of the focal length variable measuring optics and thus to positions of the measuring light focus point can be assigned, from which conclusions can be drawn about the distance between the laser target optics and the target point. This is because the maximum intensity occurs when the focal plane of the measuring light coincides with the surface of the workpiece or the measuring object to be processed. In such a case, the measuring light spot generated on the surface of the workpiece to be processed is imaged due to the confocal light guidance of the distance measuring device at an aperture or light coupling point arranged on the photodetector side, which also functions as a light exit aperture for the measurement light source, so that a maximum intensity is detected with the photodetector .

A broadband infrared light, in particular near infrared light, can be used as the measuring light. In particular, a near-infrared LED (Light Emitting Diode) with a peak wavelength between 900 nm and 1000 nm, in particular 940 nm and 960 nm, and with a spectral half-width between 40 nm and 60 nm, in particular between 45 nm and 55 nm can be used. Such an LED measuring light has sufficient broadband to avoid or reduce disruptive interference or speckle effects. On the other hand, such an LED measuring light is narrow-banded enough to suppress or keep to a minimum undesired dispersion effects such as chromatic focus shift or focus shift.

In addition, the optical components of the laser processing device, for example mirrors and / or lenses of the laser target optics, which are designed for the near-infrared spectral range, can be used for the distance measurement with a near-infrared measuring light.

The method can furthermore comprise acquiring or detecting laser light. In this case, instead of or in addition to the measuring light, the laser light is detected, which is reflected from the workpiece and guided via the laser target optics and the measuring light optics via the aperture to the detector of the distance measuring device. In this process, the laser focus point is mapped onto the aperture. The focal length of the measuring optics with variable focal length is varied in a controlled manner, and it is detected when the intensity of the laser light transmitted by the diaphragm is at its maximum, ie when the laser focus point is sharply imaged on the diaphragm. In this method, for example, in a first step, the laser can be focused on the workpiece and that focal length of the measuring optics with variable focal length can be determined at which an intensity maximum of the laser light transmitted by the diaphragm occurs. If the focus point of the laser is no longer on the workpiece, but above or below, the position of the image point in the diaphragm plane also changes. So this occurs Intensity maximum at a different focal length of the variable focal length measurement optics. This effect can be used to detect a change in the laser focus position.

In some embodiments, the method can include simultaneous detection of both the measurement light and the laser light. Both the laser focus point and the measuring light spot are imaged on the diaphragm and the portions of the measuring light and the laser light transmitted by the diaphragm are directed to the detector of the distance measuring device.

Depending on the distance of the laser focus point from the workpiece surface and the color error of the optical components, the focal length at which the measuring light spot is sharply imaged on the diaphragm can differ from the focal length at which the laser focus point is imaged sharply on the diaphragm.

In particular, the method can include a positioning of the workpiece to be processed with respect to the laser focus point based on the determined difference between those two focal lengths at which either the measuring light spot or the laser focus point are sharply imaged on the diaphragm.

The temporal variation of the focal length of the focal length variable measuring optics can be a tuning, in particular a cyclical tuning, the focal length of the focal length variable measuring optics for the acquisition of the distance measurement data at different focal lengths of the Include variable focal length measurement optics. When tuning the focal length, a focal length range of the measuring optics with variable focal length is covered between a minimum focal length and a maximum focal length, so that the focal point of the measuring optics scans the entire measuring range of the optical sensor. By cyclically tuning the focal length of the focal length-variable measuring optics, the evaluation of the recorded distance measurement data can be synchronized with the temporal variation of the focal length, so that a clear and reliable assignment of the recorded measurement data to the distances to be determined is facilitated.

In particular, one, in particular a single, distance value or distance to the surface of the measuring piece to be processed can be determined in one cycle or in one measuring cycle on the basis of the variation of the focus distance of the measuring light.

In some embodiments, the measurement beam focus is on the surface of the measurement object or the workpiece to be processed at two different times within a cycle, so that the reflection from the measurement light spot on the surface of the workpiece to be processed is sharply imaged onto the fiber end or the light coupling point causes an intensity maximum in the light detected by the photodetector. A relationship between cycle times and positions of the focal point of the measurement light, which is known or can be determined by calibration measurements, can be based on the times at which

Intensity maxima of the light detected by the photodetector are observed, the distance between the workpiece to be processed can be determined. The method can also include performing a calibration measurement to determine a relationship between the cycle time and the interval. The relationship between cycle time and distance determined by the calibration measurement can improve the reliability and accuracy of the evaluation of the distance measurement data, so that the distance to be determined can be calculated unambiguously and reliably from the time of the intensity maximum in a cycle.

The calibration measurement can include the acquisition of reflections from a meniscus lens connected downstream of the focal length variable optics, in particular at different cycle times. The meniscus lens has a concave surface and a convex surface. The meniscus lens can in particular be arranged such that when tuning the focal length variable optics, the light reflected back from the concave surface and the light reflected back from the convex surface alternately at one

Light coupling point is bundled, which in each case causes a measurable intensity peak of the light fed into the optical fiber. The temporal positions of these peaks within a tuning cycle correspond to well-defined focal lengths of the variable focal length optics, so that the variable focal length optic or the distance measuring device can be precisely calibrated on the basis of the temporal positions of these intensity peaks or calibration peaks.

In some embodiments, the calibration measurement includes a measurement of a two-dimensional grid of lateral positions of the scanner or the laser target optics. Distance measurement data recorded on the two-dimensional grid can can then be used to calibrate the distance measuring device.

The method can also include a calibration measurement to determine the distance at which the laser light is focused on the workpiece in the best possible way.

The processing laser can generate process light in the visible as well as in the infrared range when processing the workpiece. In particular, during laser machining of the workpiece, process light can arise in those spectral ranges that are outside the spectral distribution of the laser light. The occurrence of process light is linked to the intensity of the laser light at the irradiated point on the workpiece. If the laser is operated with a low power, process light only occurs when the workpiece is exactly in the focal plane of the laser light.

To determine the focal plane of the laser light, the distance between the laser focus point and the workpiece is varied. This can be done, for example, by positioning the workpiece or by focusing the laser beam by means of focusing optics.

The presence or absence of process light is registered by a detector. The capture bze. Detection of process light allows conclusions to be drawn that the laser beam light is focussed sufficiently well on the workpiece for the formation of the process light. On the basis of the detected process light, it may also be possible to determine that the laser beam light is as best as possible on the Workpiece is in focus. If this is the case, the associated distance value can be determined by measuring the distance through the measuring light.

In an alternative embodiment, the laser is not operated with a constant power, but instead the power of the laser is varied. In particular, the power of the laser can be successively increased starting from a low value and the critical power at which process light occurs for the first time can be determined.

This step can be repeated for different distances between the workpiece and the laser focus point. The distance at which the laser light is focused as well as possible on the workpiece is characterized by the fact that the critical power assumes the smallest value.

The acquisition of the distance measurement data can take place at several points or measuring points at the target point. The arrangement of a measuring point at the target point means in this context that the measuring point can be arranged in, on or around the target point. By recording the distance measurement data at several measuring points at the target point, the susceptibility of the measurements to errors can be reduced by averaging. By recording the distance measurement data at several measuring points, the influence of speckles on the measurement results can also be reduced. This is because the local intensity fluctuations of the light reflected back from the workpiece to be processed, which can be traced back to the speckles, can be determined by measuring at several measuring points. The acquisition of the distance measurement data at a plurality of measurement points can take place sequentially or one after the other, in particular within one measurement cycle. During a measuring cycle, distance measurement data can thus be collected from different measuring points, so that an averaged distance can be determined quickly and with little computational effort.

In some embodiments, the distance measurement data is acquired at several points along a scan path at the target point. The scan path can in particular be selected in such a way that the distance measurement data recorded along the scan path can be used to infer the target point distance.

The scan path can have the shape of a circle surrounding the target point of the workpiece to be machined. In particular, the measuring circle can have a path radius comparable to that of the laser spot. The distance measurement data recorded along the measuring circle result in a database that enables the measurement error to be efficiently reduced by averaging.

The scan path can have the shape of a spiral centered on the target point of the workpiece to be machined. In particular, the center point of the spiral can coincide with the target point. Due to the spiral-shaped scan path, the distance measurement data can be recorded from a particularly large surface, so that the averaging effect is increased and the susceptibility of the measurement to malfunctions can be reduced. In some embodiments, the acquisition of the distance measurement data takes place at a plurality of measuring points essentially simultaneously, in particular within one measurement cycle, the distance being determined on the basis of physically averaged distance measurement data.

The physical averaging of the distance measurement data means in particular that the distance is not determined separately for each measuring point in order, for example, to form an average distance value from the determined distances. The physical averaging means that all of the distance measurement data recorded at the multiple measuring points of the target point, in particular intensity measurement data of the measurement light reflected back from the workpiece to be processed, are included in the determination of the distance to the target point, so that a single distance value is determined for all of the measurement points .

Due to the physical averaging, the entirety of the distance measurement data recorded at the different measurement points of a target point can be evaluated together, in particular in a single evaluation step, so that the distance value can be determined in a quick and simple manner.

The measuring light can be divided into several partial measuring lights for the simultaneous acquisition of the distance measurement data at several measuring points by means of at least one perforated mask with several holes, in particular designed as a confocal diaphragm. The at least one perforated mask can thus be used for the acquisition of the distance measurement data at several measuring points required partial measuring lights can be generated in a simple manner.

The partial measuring lights can be recorded with a common photodetector. The use of the common photodetector for all partial measurement lights simplifies the acquisition of the distance measurement data from the multiple measurement points. Simultaneously with the detection of the partial measuring lights with the common photodetector, the distance measuring data or light intensities are physically averaged. Because the common photo detector does not differentiate between the lights reflected back from the different measuring points. The averaging of the distance measurement data is therefore carried out automatically without having to perform a calculation step.

According to a second aspect, a device for the controlled machining of a workpiece is proposed.

The device comprises a laser light source for generating a laser light beam for processing or laser processing the workpiece to be processed. In particular, a solid-state laser emitting in the near-infrared spectral range, such as a YAG laser or a fiber laser, and a gas laser, for example a CO2 laser, can be used to generate the laser beam.

The device further comprises laser aiming optics for focusing the laser light beam to one

Laser light focus point at a target point of the workpiece to be machined. The laser aiming optics can in particular be designed as focusing and alignment optics that enable targeted alignment and focusing of the laser beam enables. The laser target optics can in particular be designed as a laser beam scanner, specifically as a galvo scanner, wherein the alignment of the laser beam can take place by means of electrically controlled mirrors.

The device also comprises a distance measuring device for determining a distance between the target point of the workpiece to be machined and the laser target optics based on distance measurement data acquired by the distance measuring device and a positioning device for positioning the workpiece to be machined with respect to the laser light focus point and / or refocusing the laser based on the acquired distance measuring data .

The device further comprises an evaluation control unit which is designed to evaluate the acquired distance measurement data and to control the positioning device based on the acquired distance measurement data.

The distance measuring device is designed as an optical-confocal distance measuring device with a measuring light source for generating a measuring light and with a focal length variable measuring light optics in such a way that the focal length of the focal length variable measuring light optics can be varied over time in order to acquire the distance measuring data at different focal length values of the focal length variable measuring light optics.

By varying the focal length of the measuring light optics with variable focal length over time, an enlargement of an effective measuring range of the distance measuring device can be achieved, so that at Laser processing devices with a large focal length or with a small numerical aperture, the distance between the laser target optics and the target point of the workpiece to be processed can be precisely determined with the optical-confocal sensor.

The measuring optics with variable focal length also make it possible to carry out distance measurements with optical elements with no or little optical dispersion, so that the optical elements required for the laser beam guidance, which in particular have little or no optical dispersion, are also used for the beam guidance of the measuring light can be.

The measuring light optics of the distance measuring device can comprise at least a part of the laser targeting optics.

By using the laser target optics for the measuring light optics of the distance measuring device, the number of optical components required can be reduced or the structure of the device can be significantly simplified. In this way, a distance sensor can also be easily integrated into an existing laser processing system.

The distance measuring device can comprise a photodetector for detecting an intensity of a measuring light reflected back from the workpiece to be machined and can be designed such that the distance can be determined based on a time profile of the detected intensity of the measuring light reflected back from the workpiece. In particular with a controlled temporal variation of the focal length of the focal length variable measuring optics, the times of the acquisition of the intensity can be assigned to certain focal lengths of the focal length variable measuring optics and thus to certain distances, from which conclusions can be drawn about the distance between the laser target optics and the target point.

A broadband infrared light source, in particular a light source emitting in the near infrared spectral range, can be used as the measuring light source. In particular, a near-infrared LED with a peak wavelength of approx. 950 nm and a spectral half-width of approx. 50 nm can be used to generate the measurement light. Such an LED measuring light has sufficient broadband to avoid or reduce disruptive interference or speckle effects. On the other hand, such an LED measuring light is narrow enough to suppress or minimize undesired dispersion effects such as chromatic focus shifts.

The measuring optics with variable focal length can be designed as tunable, in particular cyclically tunable, measuring optics. When tuning the focal length, a focal length range of the variable focal length measuring optics is covered between a minimum focal length and a maximum focal length, so that the focal point of the measuring optics covers the entire measuring range of the optical sensor, for example +/- 7 mm. As a result of the cyclical tuning of the focal length of the measuring optics with variable focal length, the evaluation can be synchronized with the temporal variation of the focal length in such a way that a clear and reliable assignment of the recorded measurement data is made possible for the distances to be determined.

The focal length variable optics can in particular be arranged in a diverging part of an imaging system of the distance measuring device. As a diverging part, a part of the imaging system becomes the

Distance measuring device referred to in which the measuring light optics forms a diverging measuring beam. In the diverging part of the imaging system, the measuring optics with variable focal length can in particular be positioned in such a way that the free aperture of the variable focal length optics can be optimally used.

The measuring optics with variable focal length can comprise a variable focal length lens. With a focal length variable lens, in particular with an electrically controllable focal length variable lens, the focal length of the measuring optics can be varied in a simple manner. The free aperture of the variable focal length lens can have a diameter in the range between 1 and 10 mm, in particular between 2 and 6 mm. The focal length variable lens can in particular be arranged in the vicinity of a light coupling point or in the vicinity of a fiber end from which the measuring light emerges in a divergent manner.

In some embodiments, the device comprises at least one shadow mask with a plurality of holes for dividing the measuring light into a plurality of partial measuring lights. With the partial measuring lights, the distance measuring data can be recorded at several measuring points at the same time. In one embodiment, the device comprises an optical fiber with a light coupling point for coupling the measurement light in and out, the at least one perforated mask being arranged at the light coupling point. This arrangement of the shadow mask is suitable for the devices with a fiber coupler, the light coupling point being designed both for coupling out the light generated by the measuring light source and for coupling in the measuring light reflected back from the workpiece to be processed. The acquisition of the distance measurement data at different measuring points can in this case be done in a simple manner with a single perforated mask.

In particular, the perforated mask can be placed directly on the light coupling point or on the end of the optical fiber. The arrangement of the perforated mask at the light coupling point enables efficient use of the perforated mask in that essentially all of the measurement light emerging from the light coupling point is captured by the perforated mask.

The light coupling point or the end of the optical fiber and the perforated mask can be dimensioned such that the perforated mask is essentially completely illuminated. The area of the shadow mask can thus be used particularly efficiently.

In some embodiments, the device has a first light fiber with a light exit end and a second light fiber with a light entry end, a first perforated mask being arranged at the light exit end and a second perforated mask being arranged at the light entry end. This arrangement of the shadow masks is suitable for the devices with a beam splitter, which is used to couple the from the Measuring light source generated measuring light in the imaging system of the distance measuring device and designed for coupling out the measuring light reflected back from the workpiece to be machined.

The two perforated masks can be positioned in such a way that the holes of the two perforated masks are aligned confocally to one another in pairs. Due to the paired confocal alignment of the holes of the two shadow masks, the partial measuring light beams generated by the holes of the first shadow mask are bundled in the corresponding holes of the second shadow mask, so that the light losses caused by the shadow masks can be minimized.

Instead of individual optical fibers, optical fiber bundles can be used to generate a large number of the partial measuring lights for recording the distance measuring data at different measuring points. The fiber optic bundles already supply a large number of the partial measuring lights so that the shadow masks are no longer required. The optical fiber bundles for dividing the measuring light into partial measuring lights can be used both in the device with the fiber coupler and in the device with the beam splitter. The use of the optical fiber bundles thus simplifies the construction and handling of the device.

In some embodiments, the device has a camera which is designed such that the processing point of the workpiece to be processed can be visually checked with the aid of the camera before, during and / or after processing. In some embodiments, the device has a detector which is designed such that the presence of process light can be detected, the process light lying outside the spectral distribution of the laser light.

The exemplary embodiments are explained in more detail below with reference to the drawings, in which the same reference numbers are used to designate the same or comparable components.

Fig. 1 shows schematically a device for the controlled machining of a workpiece according to an embodiment,

Fig. 2 shows a shadow mask according to an embodiment,

Fig. 3 shows a shadow mask according to another embodiment,

4 shows a schematic side view of a meniscus lens according to an embodiment,

FIG. 5 shows a schematic plan view of the meniscus lens of FIG. 4,

6 shows schematically a possible beam path in a section of the distance measuring device according to an exemplary embodiment,

FIG. 7 schematically shows another possible beam path in the section according to FIG. 6, FIG. 8 schematically shows a further possible beam path in the section according to FIG. 6,

9 shows a time course of the intensity of a light reflected back by a meniscus lens,

Fig. 10 shows schematically a device for the controlled machining of a workpiece according to another embodiment,

11 shows a flow diagram of a method for the controlled machining of a workpiece according to an exemplary embodiment, and FIGS

12 shows schematically a device for the controlled machining of a workpiece according to a further exemplary embodiment.

1 shows schematically a device for the controlled machining of a workpiece according to an exemplary embodiment. The device 1 comprises a laser light source 2 for generating a laser light beam 3 for processing the workpiece 4 to be processed. Furthermore, the device 1 comprises a laser target optics 5 for aiming or for the targeted focusing of the laser light beam 3 to a focal point F at a target point 6 of the workpiece to be processed Workpiece 4.

The device 1 comprises a distance measuring device 7 for determining a distance between the target point 6 of the workpiece 4 to be processed and the laser target optics 5. The distance measuring device 7 is designed as an optical-confocal distance measuring device and comprises a Measuring light source 8 for generating a measuring light and a photodetector 9 for detecting a measuring light reflected back from the workpiece 4. In this exemplary embodiment, the distance measuring device 7 has a distance measuring range H of +/- 7 mm around a zero plane 0.

The measuring light source 8 is connected to a first optical fiber 10 at a first connection point 11 of a fiber coupler 12 in the form of a Y-coupler. The photodetector 9 is connected to a second optical fiber 13 at a second connection point 14 of the fiber coupler 12. At a third connection point 15 of the fiber coupler 12, a third optical fiber 16 is connected with a first end, the second end of the third optical fiber 16 being designed as a light coupling point 17 for coupling the measurement light in and out. In this exemplary embodiment, the first optical fiber 10, the second optical fiber 13 and the third optical fiber 16 are designed as multi-mode fibers which are capable of transmitting broadband light in the near-infrared spectral range.

The light coupling point 17 is followed by a collimation lens 18, a focal length variable lens 19 being arranged between the light coupling point 17 and the collimation lens 18. The light coupling point 17 is designed in such a way that the measuring light emerges from the light coupling point 17 in a divergent manner, so that a diverging measuring light beam results in the area between the light coupling point 17 and the collimation lens 18. In this exemplary embodiment, the variable focal length lens 19 is an electrically controllable variable focal length lens EL-03-10 from Optotune. Arranged in the beam path of the laser light beam 3 is a first deflection plate 30 for coupling in and for coupling out the measuring light into the beam path of the laser light beam 3 or into the laser target optics 5. The deflection plate 30 can be designed in such a way that the measuring light can propagate in the beam path of the laser light beam coaxially to the laser light beam 3, in particular along an optical axis A common to the measuring light and the laser light beam.

The device 1 also has a second deflection plate 31 which is positioned in the beam path of the laser light beam between the first deflection plate 30 and the laser target optics 5. A camera 32 is optically coupled to the laser target optics 5 via a second collimation lens 33 and the second deflection plate 31 in such a way that the processing point of the workpiece to be processed can be visually checked with the aid of the camera 32. The deflection plates 30 and 31 are designed as plates which are transparent or partially transparent to the laser light, so that the beam path of the laser light beam is not or only slightly disturbed by the deflection plates 30 and 31.

In some embodiments, the light for the camera 32 is branched off with the deflector 31 between the laser 2 and the deflector 30. By branching off the camera light between the laser and the deflection plate 30, the distance measurement by the deflection plate 31 for the branching off of the camera light is not impaired. In the arrangement shown in FIG. 1, the laser light beam 3 is coupled through the deflection plate 30 or deflection plate 31 and thus transmissively into the laser target optics 5. In alternative embodiments, the laser light beam 3 is coupled into the laser target optics 5 in a reflective manner or by means of a laser beam mirror.

In particular, the laser beam can be coupled reflective into the optical system of the device 1 laterally or perpendicular to the common optical axis A. In such an arrangement, for example, the laser 2 would be arranged instead of the camera 32 and the collimation lens 33, and a laser beam mirror would be arranged instead of the deflection plate 31. A laser beam mirror which is at least partially permeable to the measurement light can be used as the laser beam mirror. Other configurations of the light beam path are also possible in which the principles described here can be implemented. In a non-limiting embodiment, the measuring light is coupled coaxially or along the common optical axis A into the beam path of the laser beam.

In some embodiments of the laser target optics 5, the focusing lens 50 is connected downstream of the mirror pair 51, so that the laser beam 3 is first aligned by the mirror pair 51 before the aligned laser beam 3 can be focused on the target point by the focusing lens 50.

The device 1 according to the exemplary embodiment in FIG. 1 also has an evaluation control unit 40. The evaluation control unit 40 comprises an evaluation unit 41 for evaluating the detected distance measurement data, a lens control unit 42 for controlling the focal length of the Variable focal length lens 19 and one

Positioning control unit 43 for positioning the workpiece to be machined with respect to the laser focus point. The evaluation unit 41 is connected to an output of the photodetector 9 via a signal line 44. The lens control unit 42 is connected to a control connection of the variable focal length lens 19 via a lens control line 45. The positioning unit 43 is connected via a positioning control line 46 to a positioner 47 for positioning the workpiece 4 to be machined.

In this exemplary embodiment, a YAG laser is used as the laser light source, which generates optical radiation in the wavelength range between 1030 nm and 1070 nm.

Other solid-state lasers, in particular those emitting in the near-infrared spectral range, or gas lasers, for example CO2 lasers, can also be used as the laser light source.

The lasers emitting in the near-infrared spectral range are well suited for material processing. This is because these lasers are able to provide the power in the kW range and the high power densities of the optical radiation required for material processing. The device 1 further comprises a laser power control, which is designed to control the power of the laser 2, and a laser focusing control with controllable focusing optics, which are arranged in the beam path of the laser and are designed to control the laser focusing. The laser power control and laser focusing control are not shown in FIG. 1 to simplify the illustration. In this exemplary embodiment, a broadband near-infrared LED with a peak wavelength of approx. 950 nm and a spectral half-width of approx. 50 nm is used as the measurement light source. Such an LED measuring light has sufficient broadband to avoid or reduce disruptive interference or speckle effects. On the other hand, such an LED measuring light is narrow enough to suppress or minimize undesired dispersion effects such as chromatic focus shift.

In the embodiment of FIG. 1, the laser target optics 5 or the scanner comprises a focusing lens 50 and a controllable pair of mirrors 51 for aligning the focused radiation to the target point 6 of the workpiece 4 to be processed and, if necessary, for moving the focused laser beam over a processing field of the workpiece 4 to be machined. The pair of mirrors 51 can in particular be designed as a pair of galvo mirrors which can be controlled electrically in a simple manner.

The focusing lens 50 has a focal length of approximately 180 mm. The diameter of the laser beam 3 before it enters the laser target optics 5 is approximately 10 mm. The laser target optics 5 is dimensioned in such a way that the laser beam 3 can process a processing area of approximately 80 mm × 80 mm.

In some embodiments, the laser aiming optics 5 are designed as telecentric laser aiming optics. The telecentric design of the laser target optics enables the workpiece to be machined to be machined with the laser beam at different distances from the device. The positioner 47 can in particular be designed for positioning and / or orientation of the workpiece 4 to be machined with respect to the laser beam focus point and can in particular comprise one or more actuators with one or more control signals from the

Positioning control unit 46 for positioning or orienting the workpiece 4 to be machined can be controlled. The possibility of orienting the workpiece is symbolically represented in FIG. 1 by means of coordinate axes.

In some embodiments, as in the example shown in FIG. 1, the device 1 has a perforated mask 60 or diaphragm which is arranged in the beam path of the distance measuring device 7. The perforated mask 60 has several holes 61, which can be clearly seen below in FIGS. 2 and 3. The perforated mask 60 is positioned between the light coupling point 17 and the variable focal length lens 19 in such a way that the measuring light is divided by the perforated mask 60 into several parts for the simultaneous acquisition of the distance measurement data at several points on the surface of the workpiece 4 to be machined. In the one shown in Fig.

1, the perforated mask is placed directly on the fiber end functioning as the light coupling point 17, so that the fiber end also serves as a holder for the perforated mask 60.

In some exemplary embodiments, the optical fiber, at the end of which the shadow mask is placed, has a diameter that is sufficient to illuminate the shadow mask 60 essentially completely and to capture the light reflected back through essentially all of the holes 61 of the shadow mask 60. In some exemplary embodiments, instead of the fiber 16 with the perforated mask 60, a fiber bundle is used which, similar to the fiber 16 in FIG. 1, is coupled with a fiber coupler.

In some embodiments, as in the example shown in FIG. 1, the device 1 for the controlled machining of a workpiece has a meniscus lens 80 which is positioned between the focal length variable lens 19 and the collimation lens 18.

The meniscus lens 80 has a substantially spherical concave surface 81 and a substantially spherical convex surface 82. The concave surface 81 or the concave side of the meniscus lens 80 faces the focal length adjustable lens 19 and the convex surface 82 or the convex side of the meniscus lens 80 faces the collimation lens 18. In the exemplary embodiment shown, the meniscus lens 80 has a circular hole 83 in the center.

During operation of the device 1, part of the light generated in the measuring light source 8 is guided through the first optical fiber 10, via the fiber coupler 12 and via the third optical fiber 16 to the light coupling point 17. The measuring light emerges diverging from the light coupling point 17, after which the measuring light passes through the variable focal length lens 19 and the collimation lens 18 and is coupled into the beam path of the laser light beam 3 by the deflection plate 30. The measuring light coupled into the beam path of the laser light beam 3 can then pass through the laser target optics 5 pass through to the workpiece 4 to be processed.

When the measuring light hits the workpiece 4, part of the measuring light can be reflected back and reach the third optical fiber 16 via the laser target optics 5, the collimation lens 18, the variable focal length lens 19 and the light coupling point 17. A part of the measurement light is branched off at the fiber coupler 12 via the second fiber 13 to the photodetector 9. The photodetector 9 supplies a measurement signal via the signal line 44 to the evaluation unit 41 for evaluation. The evaluation unit 41 is designed to evaluate a time profile of the intensity of the light detected by the photodetector 9. The evaluation unit 41 is also designed to derive distances between the target point of the workpiece to be processed and the laser target optics from the time profile of the intensity.

The variable focal length lens 19 can in particular be controlled cyclically in such a way that the refractive power of the variable focal length lens is tuned by, for example, +/- 13 diopters, the focal point of the measuring light being shifted by approx. +/- 7 mm along the optical axis. At two different points in time within a cycle, the measuring beam focus is on the surface of the measuring object or the workpiece to be processed, so that the reflection from the measuring light spot on the surface of the workpiece to be processed is sharply imaged onto the fiber end or light coupling point 17, which is an intensity maximum caused by the light detected by the photodetector. A relationship between cycle times and positions of the focal point of the measurement light, which is known or can be determined by calibration measurements, can be used to determine the distance of the workpiece to be processed based on the times at which intensity maxima of the light detected by the photodetector are observed.

In particular, the calibration measurement to determine the relationship between the cycle time point and the distance between the surface of the workpiece to be machined can be carried out in advance or before the laser machining. The calibration measurement can take place via a two-dimensional grid of lateral positions of the scanner or the laser target optics. On the basis of the determined relationship, the distance of the surface or the distance between the laser target optics 5 and the target point 6 of the workpiece to be processed can then be determined from the point in time of the intensity maximum in one cycle.

The cyclical variation or modulation of the focal length of the variable focal length lens 19 is symbolically represented in FIG. 1 by a jagged curve in the lens control unit 42. The relationship between the cycles of the focal length variation of the focal length variable lens 19 and the occurrence of the intensity maxima is illustrated schematically in Fig. 1 by dashed lines which extend between the sawtooth curve of the lens control unit 42 and an intensity curve shown in the evaluation unit 41 with the time coordinate t.

The measurement light divided by the perforated mask 60 enables the distance measurement data to be recorded at several at the same time Points on the surface of the workpiece 4 to be machined. In particular, the measurement light reflected back by the workpiece also passes through the holes 61 of the perforated mask 60 via the coupling point 17 into the fiber 16, so that it can be detected with the photodetector 9. The light intensity detected by the photodetector 9 corresponds to the total intensity of the light collected via all the holes 61 of the perforated mask 60 and reflected back from all the measuring points, so that a physical averaging of the intensity differences between the light reflected back from different points takes place due to the optical arrangement. The physical averaging of the different holes 61 of the perforated mask 60 detected light intensities can considerably simplify the evaluation of the measurement data, since the distance determination does not have to be carried out individually for each point. Rather, the distance can already be determined on the basis of the physically averaged distance measurement data, in particular intensity data, for all of the locations generated by the perforated mask 60.

Due to the arrangement of the meniscus lens 80, the light reflected back from the surfaces 81 and 82 of the meniscus lens 80 can reach the fiber 16 via the light coupling point 17 and be detected by the photodetector 9.

In particular, if the light rays emerging from the variable focal length lens 19 strike one of the two surfaces 81 and 82 of the meniscus lens 80 perpendicularly, a maximum proportion of the light from the corresponding surface 81 or 82 of the meniscus lens 80 is returned to the focal length variable lens 19 back into the Fiber 16 reflects. Such a beam configuration can thus be based on a corresponding intensity peaks of the light reflected back are recognized, each of the two surfaces 81 and 82 of the meniscus lens 80 being responsible for its own intensity peak.

In some exemplary embodiments, the meniscus lens is dimensioned in such a way that the peaks occur at the beginning or at the end of a repeated time cycle during the tuning of the focal length variable lens 19. The position of each of the two peaks always corresponds to a constant value of the focal length of the variable focal length lens 19 and therefore constantly to the same distance. Under the influence of temperature changes, in particular the relationship between the course of time and the distance value can change. The tunable lens has a significant influence, so that the association between the control value and the focal length of the variable focal length lens 19 can change in the event of temperature fluctuations. Since the intensity peaks caused by the meniscus lens 80 each occur with the same focal length of the variable focal length lens 19, the variable focal length lens 19 or the relationship between the time course and distance can be precisely calibrated on the basis of these peaks. This is because, in contrast to the variable focal length lens 19, the meniscus lens 80 has a negligible temperature dependency.

The beams of the measuring light pass through the circular hole 83 in the center of the meniscus lens 80 undisturbed through the meniscus lens, so that only the edge beams can be reflected back by the meniscus lens 80. By choosing the lens surface or the hole size, the intensity of the reflections can be adjusted so that the intensity of the light reflected back from the meniscus lens 80 is high enough to serve as a calibration signal, but also not so high that the measurement signal or the intensity signal of the measurement light reflected back from the object to be processed is overshadowed by the reflections of the meniscus lens. In some embodiments, the hole 83 is dimensioned so that the majority of the measurement light passes through the hole 83 of the meniscus lens 80 without being reflected.

In some embodiments, the meniscus lens 80 is followed by a diaphragm which is configured to allow the inner beam part of the measuring light to pass through and which cut off the outer beam part of the measuring light. Thus, in particular the rays influenced by the meniscus lens 80 can be excluded from the measurement.

In some embodiments, the meniscus lens 80 does not have a hole, the meniscus lens 80 having a coating on at least one of the two surfaces 81, 82. The thickness or the reflectivity of the coating can be selected so that the measurement signal is not overshadowed by the reflection components of the meniscus lens. In some exemplary embodiments, the meniscus lens 80 has an anti-reflection coating, the reflection portion of which in the wavelength range of the measuring light is less than 4%.

In some embodiments, the meniscus lens 80 has both the circular hole 83 and the coating, wherein the dimensions of the circular hole 83 and the thickness of the coating can be selected so that a sufficiently strong calibration signal is achieved, without overshadowing the measurement signal or impairing it too much.

Fig. 2 shows a shadow mask according to an embodiment.

The perforated mask 60 in FIG. 2 is designed in the form of an essentially rectangular screen and has a plurality of circular holes 61. In this exemplary embodiment, the circular holes 61 are distributed essentially uniformly over the entire surface of the screen in a hexagonal grid. The distribution of the holes 61 in a hexagonal grid enables a high density of the holes, so that the measurement light can be divided through the perforated mask into many parts for recording the distance measurement data at many measurement points. At the same time, for a given density, the distance between adjacent holes is maximum when a hexagonal grid is selected, so that crosstalk between the holes is minimal.

3 shows a shadow mask according to another exemplary embodiment.

The perforated mask 60 of FIG. 3 is designed in a manner similar to the perforated mask 60 of FIG. 2 in the form of an essentially rectangular screen and has a plurality of holes 61. In contrast to the perforated mask 60 of FIG. 2, the holes 61 of the perforated mask of FIG. 3 are rectangular and are distributed in a checkerboard pattern essentially uniformly over the entire surface of the screen.

The degree of filling of the shadow masks 60 shown in FIGS. 2 and 3 is preferably between 30% and 70%, in particular about 50%, so that about 50% of the light incident on the shadow masks passes through the shadow masks.

As an alternative to the embodiments shown in FIGS. 2 and 3, the perforated mask can also be designed to be essentially circular. A circular shadow mask is particularly well suited for being precisely placed on the end of an optical fiber with a circular cross section.

4 shows a schematic side view of a meniscus lens according to an exemplary embodiment.

As can be clearly seen in the view of FIG. 4, the meniscus lens 80 has an essentially spherical concave surface 81 and an essentially spherical convex surface 82. In the one shown

In the exemplary embodiment, the meniscus lens 80 has a circular hole 83 in the center.

FIG. 5 shows a schematic plan view of the meniscus lens from FIG. 4.

In the top view of FIG. 5, the circular hole 83 of the meniscus lens 80 can be seen particularly well. As already mentioned above in the description of FIG. 1, the meniscus lens 80 can be designed differently.

In particular, at least one of the two surfaces 81,

82 have a coating. Furthermore, the

Dimensioning of the circular hole 83 and / or the thickness or the reflectivity of the coating can be selected so that the back reflections on the surfaces 81, 82 of the Meniscus lens result in 80 calibration peaks of sufficient intensity without overshadowing the measurement signal or impairing the distance measurement.

6 schematically shows a possible beam path in a section of the distance measuring device according to an exemplary embodiment.

The section shown in FIG. 6 comprises the focal length variable lens 19, the meniscus lens 19 and the coupling point 17 of the optical fiber 13 according to FIG. 1.

The long arrows pointing away from the coupling point 17 represent the measuring light beam emerging from the light coupling point 17, which is radiated through the variable focal length lens 19 and also partly through the meniscus lens 80. The arrows directed from the meniscus lens 80 back to the light coupling point 17 illustrate the rays reflected from the concave surface 81 or from the convex surface 82. Due to the essentially spherical curvature of the surfaces 81 and 82, the rays reflected back are bundled to the respective focal point.

In the case shown in FIG. 6, the light reflected from the concave surface 81 of the meniscus lens 80 is bundled at the light exit surface of the light coupling point 17, while the focal point of the light reflected back from the convex surface 82 of the meniscus lens 80 is above the light entry surface or light coupling point 17 lies. The beam path shown can occur in particular at a specific focal length of the variable focal length lens 19. FIG. 7 schematically shows another possible beam path in the section according to FIG. 6.

The beam path in FIG. 7 essentially corresponds to the beam path shown in FIG. 6. In contrast to the case shown in FIG. 6, the focal length variable lens 19 has a different value of the focal length, so that neither of the two beams reflected back is bundled at the light coupling point 17.

FIG. 8 schematically shows a further possible beam path in the section according to FIG. 6.

The beam path shown in Fig. 8 corresponds to a focal length of the variable focal length lens 19 when the light reflected back from the convex surface 82 of the meniscus lens 80 is bundled at the light exit surface of the light coupling point 17, while the focus point of the light reflected back from the concave surface 81 of the meniscus lens 80 below which lies from the light entry surface or light coupling point 17.

The possible beam configurations of the measuring light shown in FIGS. 6, 7 and 8 illustrate the mode of operation of the meniscus lens 80. If, for example, the variable focal length lens 19 is cyclically tuned, the focal length will periodically run through all values between a minimum focal length and a maximum focal length, and the The beam configuration shown in FIGS. 6, 7 and 8 occur periodically. The beam path shown in Fig. 7 or a similar if none of the Beams reflected back by the meniscus lens 80 are bundled at the light coupling point 17, can occur with a large number of settings of the focal length variable lens 19. The beam configuration shown in FIGS. 6 and 8, on the other hand, can only occur with very specific values of the focal length of the variable focal length lens 19. Due to the bundling of the light reflected back from the surfaces 81 and 82 of the meniscus lens 80 at the light coupling point 17 of the optical fiber 13, a larger proportion of the light reflected back from the meniscus lens 80 is coupled into the light coupling point in the beam configurations shown in FIGS An increase in the coupled-in amount of light can be detected by a corresponding increase in the light intensity detected by the photodetector. The corresponding intensity peaks can be detected with a photodetector, for example with the photodetector 9 in the arrangement according to FIG. 1, and used as calibration peaks for calibrating the distance measuring device 7. In particular, based on the temporal position of the respective intensity peak, conclusions can be drawn about the corresponding focal length of the variable focal length lens 19 or the corresponding measuring distance of the distance measuring device 7.

The section shown in FIGS. 6, 7 and 8 does not have a perforated mask 60. The above remarks on FIGS. 6, 7 and 8 regarding the mode of operation of the meniscus lens 60 also apply accordingly if a perforated mask 60 is used to split the measurement light into several parts and to record the distance measurement data from different points, for example between the coupling point 17 and the Focal length variable lens 19 could be arranged. 9 shows a time profile of the intensity of a light reflected back from a meniscus lens.

In particular, FIG. 9 shows a time dependence of the measured light intensity in the arrangement shown in FIGS. 6, 7 and 8, the intensity of the portion of the light reflected back from the meniscus lens 80 and the workpiece 4 to be machined being measured during a tuning cycle that is coupled into the optical fiber 16 becomes. A tuning cycle here corresponds to a curve from a minimum to a maximum control value or vice versa. The time t and the intensity I are shown in arbitrary units in FIG. At certain time values, the time dependency of the intensity I (t) has distinct intensity peaks or calibration peaks. In particular, the curve I (t) has a left sharp peak (a), a right sharp peak (c) and a somewhat broader central peak (m). The left sharp peak (a) corresponds to the beam configuration shown in FIG. 6 when the reflection from the concave surface 81 of the meniscus lens 80 is bundled at the light coupling point 17 of the optical fiber 16 and thus enters the optical fiber 16 in a bundled manner. The beam configuration shown in FIG. 7 occurs between the two peaks (a) and (c) when the light coupling point 17 lies between the two focal points of the light reflected back from the concave surface 81 and from the convex surface 82 of the meniscus lens 80. In this case, neither the reflection from the concave surface 81 nor the reflection from the convex surface 82 can be correctly coupled into the optical fiber 16. In this interval the peak (m) occurs, which of the to be processed Workpiece 4 is reflected light and allows the determination of the distance of the workpiece 4 (measurement peak). The right peak (c) corresponds to the beam configuration shown in FIG. 8 when the reflection from the convex surface 82 of the meniscus lens at the light coupling point 17 reaches the light fiber 16 in a bundled manner. In particular, the sharp peaks (a) and (c) at the beginning and at the end of the cycle shown each have a well-defined time position so that they can serve as the basis for a precise calibration of the distance measuring device. Using the characteristic course of the intensity curve, peaks (a) and (c) can easily be identified and assigned to the respective beam configuration.

10 schematically shows a device for the controlled machining of a workpiece according to another exemplary embodiment. The device 1 of FIG. 10 essentially corresponds to the device 1 shown in FIG. 1, whereby instead of a fiber coupler it comprises a beam splitter 90 which is used to couple the measuring light via a light exit end 91 of a first optical fiber 10 and to decouple the one to be processed Workpiece 4 is formed back-reflected measuring light. The measuring light coupled out by the beam splitter 90 can be coupled into a light entry end 92 of a second fiber 13 in order to be detected by the photodetector. The light exit end 91 of the first optical fiber 10 and the light entry end 92 of the second optical fiber 13 are set up confocally to one another. By using the beam splitter, the disruptive scattered light effects that occur in the fiber couplers can be avoided. In some embodiments, the beam splitter 90 is as Beam splitter cube formed. The beam splitter cubes are robust and have low scattering losses.

In some exemplary embodiments, the device 1 with the beam splitter 90 has at least one perforated mask.

In the example shown in FIG. 10, the device 1 has two essentially identically designed perforated masks 60, one perforated mask 60 being connected downstream of the light exit end 91 of the first fiber 10 and the second perforated mask 60 being connected upstream of the light entry end 92 of the second light fiber 13. The perforated masks 60 are arranged directly on the fiber ends of the first and second optical fibers 10, 13.

The perforated masks 60 can be designed in a manner similar to the perforated masks shown in FIGS. 1, 2 and 3 and described above. The shadow masks 60 are arranged and aligned in such a way that the holes 61 (not shown) of the two shadow masks 60 are confocally aligned with one another.

11 shows a flow diagram of a method for the controlled machining of a workpiece according to an exemplary embodiment.

The method 100 for the controlled machining of a workpiece comprises several steps, which can also be carried out in different sequences and possibly also repeatedly. The method can be carried out, for example, by means of a device according to FIG. 1 or 2. In a step 110, a laser light beam for generating a laser focus point is focused on a target point of the workpiece to be machined. The focusing of the laser light beam can in particular take place with the laser target optics in order to focus the laser beam in a targeted manner at the target point of the workpiece to be processed. The focusing of the laser light beam in step 110 can in particular take place at a low laser power, so that in step 110 no or only slight material processing of the workpiece 4 to be processed takes place. The laser light beam can also be focused by means of an auxiliary laser, for example a HeNe laser, the beam of which is coupled into the beam path of the laser light beam collinear to the laser beam, for example with a deflection plate. A galvo scanner with two swiveling galvo mirrors can be used as laser target optics or scanner.

In a step 120, optical distance measurement data are acquired by means of an optical distance measurement device for determining a distance between the target point of the workpiece to be processed and the laser target optics or a reference point or a reference plane of the laser target optics. The distance measuring device can be designed as an optical-confocal distance measuring device with a measuring light source for generating a measuring light, in particular a broadband measuring light in the near-infrared spectral range, and with a focal length variable measuring light optics, in particular a focal length variable lens, the method varying the focal length of the focal length variable over time Measurement light optics for capturing distance measurement data at different focal length values of the focal length variable measurement light optics. The acquisition of distance measurement data can include, in particular, the acquisition of an intensity of a measurement light reflected back from the workpiece to be machined, so that the distance is determined on the basis of the intensity, in particular on the basis of a time profile of the intensity of a measurement light reflected back from the workpiece.

In a step 130, the workpiece to be machined is positioned with respect to the laser focus point based on the acquired distance measurement data. In some embodiments, the laser is refocused as an alternative or in addition to the positioning of the workpiece to be processed.

In a step 140, the target point of the workpiece to be machined is machined with the focused laser beam.

In some embodiments, varying the focal length of the focal length variable measuring optics over time includes tuning, in particular cyclical tuning, of the focal length of the focal length variable measuring optics to acquire the distance measurement data at different focal lengths of the focal length variable measuring optics.

The focal length variation of the focal length variable measuring optics can in particular take place with the aid of a focal length variable optical element, in particular a focal length variable lens.

A measuring cycle can typically last 25 ms. During the measurement cycle, the power of the variable focal length lens can, for example, be in the range of +/- 13 diopters be tuned, wherein the focus point of the measuring light can be shifted axially or along the optical axis of the measuring light optics by approximately +/- 7 mm.

Given a known relationship between cycle times and positions of the focal point, the distance between the workpiece to be machined can be determined on the basis of the intensity maxima.

To determine the relationship between cycle times and intervals, in some embodiments a calibration measurement is carried out, in particular in advance of the laser processing.

12 shows schematically a device for the controlled machining of a workpiece according to a further exemplary embodiment. The device 1 in FIG. 12 essentially corresponds to the device shown in FIG. 10, it additionally having a photodetector 161 with which the process light can be detected, which is produced by processing the workpiece with the laser 2.

Furthermore, the device 1 according to FIG. 12 comprises an optical filter 162 with a wavelength-dependent reflectivity, which is designed such that process light is reflected in a specific spectral range, with laser light not being reflected. In addition, the optical filter 162 is designed in such a way that the measurement light is essentially completely transmitted so that the measurement is not impaired by the filter. The process light generated by the laser 2 when machining the workpiece reaches the optical filter 162 via the laser target optics 5 and the measuring light optics, is reflected by this and directed to the beam splitter 90, reflected by this in turn and directed to the photodetector 161. Due to the reflection properties of the optical filter 162, laser light that is reflected or scattered by the workpiece 4 and reaches the optical filter 162 via the laser targeting optics 5 is not conducted to the photodetector 161.

When determining the distance at which the laser light is optimally focused on the workpiece, the process light is detected. If the light source 8 for the measuring light is switched off, this ensures that the photodetector 161 detects neither measuring light nor laser light and is incorrectly interpreted as process light.

In some embodiments, the photodetector 161 only checks the presence or absence of process light, but does not provide any location information about the location of the origin of the process light. For this reason, the process light need not be focused on the photodetector 161. This in turn facilitates the structural implementation, since the photodetector 161 does not have to be adjusted because its exact position is not critical.

As an alternative to the embodiment shown in FIG. 12, the perforated mask 60 can be provided with a partially reflective layer so that the perforated mask 60 acts as a reflection filter that only reflects the process light, but not the laser light and the measurement light. In this embodiment an additional component in the form of the filter 162 is thus saved.

In some embodiments, the detection of the process light takes place via the photodetector 9. In this embodiment, the optical filter 162 is designed in such a way that both process light and the measurement light are transmitted, but the laser light is not transmitted. When the measuring light source 8 is switched off, the photodetector 9 can thus be used to detect process light.

Although at least one exemplary embodiment has been shown in the foregoing description, various changes and modifications can be made. The embodiments mentioned are only examples and are not intended to limit the scope, applicability or configuration of the present disclosure in any way. Rather, the preceding description provides the person skilled in the art with a plan for implementing at least one exemplary embodiment, it being possible to make numerous changes in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of protection of the appended claims and their legal equivalents .

List of reference symbols

1 device

2 lasers

3 laser light beam

4 workpiece

5 laser target optics

6 target point

7 Distance measuring device

8 measuring light source

9 photo detector

10 first optical fiber

11 first junction

12 fiber couplers

13 second light fiber

14 second junction

15 third junction

16 third light fiber

17 light coupling point

18 collimation lens

19 variable focal length lens

30 baffle

31 deflector plate

32 camera

33 collimation lens

40 Evaluation control unit

41 Evaluation unit

42 lens control unit 43 Positioning Control Unit

44 signal line

45 Lens control line

46 Positioning Control Line

47 Positioning

50 focus lens

51 pair of mirrors

60 shadow mask

61 holes

80 meniscus lens

81 concave surface

82 convex surface

83 circular hole

90 beamsplitters

91 End of the first optical fiber

92 end of the second optical fiber

100 procedures

110 Focus

120 Acquiring Distance Measurement Data

130 Positioning

140 Edit

161 photo detector

162 optical filter

A optical axis

F focus point H measuring range

0 zero level t time coordinates X, y z space coordinates

Claims

Expectations

1. A method for the controlled machining of a workpiece, comprising:

- Focussing a laser light beam (3) to generate a laser focus point (F) at a target point (6) of the workpiece (4) to be processed by means of laser target optics (5),

- Acquisition of distance measurement data by means of an optical distance measurement device (7) to determine a distance between the target point (6) of the workpiece (4) to be machined and the laser target optics (5), and

- Processing of the target point (6) of the workpiece (4) to be processed with the focused laser light beam (3), characterized in that the distance measuring device (7) as an optical-confocal distance measuring device with a measuring light source (8) for generating a measuring light and with a Measuring light optics (19) with variable focal length are formed, the method comprising a temporal variation of the focal length of the variable focal length measuring light optics (19) for the acquisition of distance measurement data at different focal length values of the variable focal length measuring light optics (19), and wherein the laser light reflected from the workpiece (4) and / or the process light generated during machining of the workpiece (4) is detected.

2. The method according to claim 1, wherein the distance between the laser focus point (F) and the workpiece (4) is varied and the presence of process light is registered as a function of the distance between the laser focus point (F) and the workpiece (4), the distance being determined by means of the distance measuring device (7).

3. The method according to any one of claims 1 or 2, wherein the power of the laser light beam (3) is varied and a critical power is determined at which process light occurs for the first time.

4. The method according to claim 3, wherein the power of the laser light beam (3) is varied for different distances between the workpiece (4) and the laser focus point (F) and the critical power at which it occurs for the first time is determined for each distance comes from process light.

5. The method according to any one of the preceding claims, wherein the method further comprises a positioning of the workpiece (4) to be machined with respect to the laser focus point (F) based on the detected distance measurement data.

6. The method according to any one of the preceding claims, wherein the acquisition of distance measurement data comprises an acquisition of an intensity of a measuring light reflected back from the workpiece (4) to be machined, and wherein the distance is based on a time profile of the intensity of the workpiece (4) to be machined back-reflected measuring light is determined.

7. The method according to any one of the preceding claims, wherein the temporal variation of the focal length of the focal length variable measuring light optics (19) a tuning, in particular a cyclic tuning, the focal length of the focal length variable measuring light optics (19) to acquire the distance measurement data at different focal lengths of the focal length variable measuring light optics (19) includes.

8. The method according to claim 7, wherein the method further comprises performing a calibration measurement to determine a relationship between cycle time and distance, wherein the calibration measurement comprises detecting reflections of a meniscus lens (80) connected downstream of the focal length variable measuring light optics (19).

9. The method according to any one of the preceding claims, wherein the acquisition of the distance measurement data takes place at several measuring points at the target point (6).

10. The method according to claim 9, wherein the acquisition of the distance measurement data at a plurality of measuring points takes place sequentially within a measuring cycle, the measuring points being arranged along a scan path at the target point (6).

11. The method according to claim 10, wherein the scan path has the shape of a circle surrounding the target location (6) of the workpiece (4) or a spiral centered on the target location (6) of the workpiece (4) to be machined.

12. The method according to claim 9, wherein the acquisition of the distance measurement data takes place essentially simultaneously at a plurality of measuring points, and wherein the determination of the distance takes place on the basis of physically averaged distance measurement data.

13. The method according to claim 12, wherein the measuring light is divided by means of at least one perforated mask (60) with several holes (61) into several partial measuring lights for the simultaneous acquisition of the distance measurement data at several measuring points.

14. The method according to claim 13, wherein the partial measurement lights are detected simultaneously with a common photodetector.

15. Apparatus for the controlled machining of a workpiece, comprising:

- a laser light source (2) for generating a laser light beam (3) for processing the workpiece (4) to be processed,

- a laser target optics (5) for focusing the laser light beam (3) to a laser light focus point (F) at a target point (6) of the workpiece (4) to be processed,

- a distance measuring device (7) for determining a distance between the target point (6) of the workpiece (4) to be machined and the laser target optics (5) on the basis of the distance measurement data recorded by the distance measuring device (7), - A positioning device (47) for positioning the workpiece to be machined with respect to the laser light focus point (F), and

- An evaluation control unit (40) which is designed to evaluate the recorded distance measurement data and to control the positioning device (47) based on the recorded distance measurement data, characterized in that the distance measurement device (7) is an optical-confocal distance measurement device with a measurement light source ( 8) is designed for generating a measuring light and with a focal length variable measuring light optics in such a way that the focal length of the focal length variable measuring light optics can be varied over time in order to record the distance measurement data at different focal length values of the focal length variable measuring light optics, whereby the laser light and / or or the process light generated during machining of the workpiece (4) can be detected.

16. The device according to claim 15, wherein the measuring light optics of the distance measuring device (7) comprise the laser target optics (5).

17. The device according to claim 15 or 16, wherein the distance measuring device (7) comprises a photodetector (9) for detecting an intensity of a measuring light reflected back from the workpiece (4) to be machined and is designed such that the distance is based on a temporal course of the detected Intensity of that Workpiece (4) reflected back measuring light can be determined.

18. Device according to one of claims 15 to 17, which has a second detector, in particular a further photodetector (161), which is designed such that the presence of process light can be detected.

19. The device according to claim 18, wherein the device comprises an optical filter (162) with a wavelength-dependent reflectivity which is designed such that process light is reflected in a specific spectral range while the measurement light is essentially completely transmitted.

20. Device according to one of claims 15 to 17, wherein the measuring light source (8) can be switched on and off and the photodetector (9) is set up to detect the presence of process light while the measuring light source is switched off.

21. Device according to one of claims 15 to 20, wherein the measuring light source (8) is designed as a broadband infrared light source, in particular near infrared light source.

22. Device according to one of claims 15 to 21, wherein the focal length of the focal length variable measuring light optics (19) is tunable, in particular cyclically tunable.

23. Device according to one of claims 15 to 22, wherein the focal length variable measuring light optics (19) is arranged in a diverging part of an imaging system of the distance measuring device (7)

24. Device according to one of claims 15 to 23, wherein the focal length variable measuring light optics (19) comprises a focal length variable lens (19).

25. Device according to one of claims 15 to 24, wherein the device (1) has at least one perforated mask (60) with several holes (61) for dividing the measuring light into several partial measuring lights.

26. The device according to claim 25, wherein the device (1) comprises an optical fiber (16) with a light coupling point (17) for coupling the measuring light in and out, and wherein the at least one perforated mask (60) is arranged at the light coupling point (17) .

27. The device according to claim 26, wherein the perforated mask (60) is provided with a partially reflective layer so that the perforated mask 60 acts as a reflection filter that only reflects the process light, but not the laser light and the measurement light.

28. Device according to one of claims 26 or 27, wherein the device has a first light fiber (10) with a light exit end (91) and a second light fiber (13) with a light entry end (92), and wherein a first shadow mask (60) the light exit end (91) and a second shadow mask (60) is arranged at the light entry end (92).