Method and apparatus for controlled machining of a workpiece by confocal distance measurement - Patents.com

Abstract

The present invention describes a method and apparatus for controlled machining of a workpiece. According to the described method, a laser beam is focused on a target point on the workpiece to be machined to generate a laser focal point. Furthermore, according to the method, distance measurement data is acquired by an optical distance measuring device to determine the distance between the target point on the workpiece to be machined and the laser target optics. The method of the present invention includes positioning the workpiece to be machined relative to the laser focal point based on the acquired distance measurement data. The distance measuring device is designed as an optical confocal distance measuring device having a measurement light source for generating measurement light and a variable focal length measurement light optics. The method includes varying the focal length of the variable focal length measurement optics over time to acquire distance measurement data at different focal length values ​​of the variable focal length measurement optics, whereby the laser light reflected by the workpiece and / or the machining light generated during machining of the workpiece can be detected.

Description

[Technical field]

[0001] The present disclosure relates to methods and apparatus for laser machining of a workpiece. In particular, the present disclosure relates to a method for laser machining a workpiece while controlling the position of the workpiece being machined for precise laser machining of the workpiece. [Background technology]

[0002] Laser beams or methods for machining workpieces with laser beams are known, as are devices for carrying out such methods. In order to accurately machine a workpiece with a laser beam, an accurate positioning of the workpiece or an accurate adjustment of a corresponding laser processing device is required, which is only possible to a limited extent with the known methods and known devices. Summary of the Invention [Problem to be solved by the invention]

[0003] One object of embodiments of the present disclosure is to provide an improved method and an improved apparatus for controlled laser processing of a workpiece, which is characterized by high machining accuracy and simple design of the apparatus. [Means for solving the problem]

[0004] According to a first aspect, to achieve this object, a method for controlled machining of a workpiece is provided, which method comprises focusing a laser beam or machining beam by means of laser targeting optics to generate a laser focus at a target location of the workpiece to be machined. In particular, the laser beam can be generated by a solid-state laser emitting in the near infrared spectral range, such as a YAG laser or a fiber laser, or a gas laser, such as a CO2 laser.

[0005] The laser targeting optics may in particular be configured as focusing and alignment optics, by means of which targeted alignment and focusing of the laser beam can be performed. The laser targeting optics may in particular be configured as a laser beam scanner, in particular as a galvanometer scanner, by means of which alignment of the laser beam can be performed by means of electrically controllable mirrors.

[0006] The method of the present invention includes obtaining distance measurement data with an optical distance measuring device or optical sensor to determine the distance between a target location on the workpiece being machined and the laser targeting optics, or a fixed reference point or surface of the laser targeting optics.

[0007] The method of the present invention further includes machining the target location of the workpiece to be machined with a focused laser beam. The machining may include laser welding, laser cutting, and / or other laser processes, among others.

[0008] According to the method of the present invention, the distance measurement device is configured as an optical confocal distance measurement device equipped with a variable focal length optical system or a variable focal length measurement light optical system, and the method includes varying the focal length of the variable focal length measurement light optical system over time to obtain distance measurement data at multiple different focal length values ​​of the variable focal length measurement light optical system.

[0009] By varying the focal length of the variable focal length measuring light optics over time, the focal length of the variable focal length measuring light optics may be varied between a minimum focal length and a maximum focal length that defines a desired measurement range. In particular, even in the case of laser processing machines with large focal lengths or small numerical apertures, the measurement range can be defined or fixed such that the distance between the laser targeting optics and the target location of the workpiece being machined can be accurately determined with an optical confocal sensor. The measured distance data can be used to machine the workpiece in a controlled and precise manner.

[0010] Since the variable focal length measuring light optical system also makes it possible to perform distance measurements with optical elements that have no or very little light dispersion, optical elements provided for laser beam guidance, in particular optical elements provided for laser beam guidance that have no or very little light dispersion, can also be used for beam guidance of the measuring light.

[0011] The method of the present invention may also include positioning the workpiece to be machined relative to the focal point of the laser based on the acquired distance measurement data. Positioning the workpiece to be machined may include changing the spatial position and / or spatial orientation of the workpiece or the entire laser processing apparatus. Alternatively or additionally, positioning may include refocusing the laser beam. Thus, the workpiece to be machined may be repositioned or the laser realigned as necessary to allow accurate machining of the workpiece to be machined.

[0012] The laser targeting optics of the laser processing device may form part of the measurement optics of the distance measuring device. In particular, the measurement light may be coupled into the optical path of the laser beam in such a way that the measurement beam runs at least partially coaxially with the laser beam.

[0013] By using the laser target optical system of the laser processing device as the measurement optical system of the distance measuring device, the number of optical components required to carry out the method of the present invention can be reduced, and therefore the optical device can be simplified. Therefore, the distance sensor can be easily incorporated into existing laser processing devices in particular.

[0014] At least some of the machining steps may be performed or repeated at several target locations of the workpiece to be machined. By repeating the machining steps at multiple locations, the location of the workpiece to be machined can be rechecked and corrected if necessary.

[0015] In some embodiments, obtaining the distance measurement data includes obtaining an intensity of the measurement light reflected back from the workpiece, and the distance is determined based on a change over time in the intensity of the measurement light reflected back from the workpiece.

[0016] In particular, by controlling the temporal variation of the focal length of the variable focal length measuring light optics, the time point of the intensity detection can be assigned to a specific focal length of the variable focal length measuring light optics and thus to the focal position of the measuring light, from which the distance between the laser targeting optics and the target position can be deduced. This is because an intensity maximum occurs when the focal plane of the measuring light coincides with the surface of the workpiece to be machined or the testing device, respectively. In such a case, the measuring light spot generated on the surface of the workpiece to be machined is imaged by the confocal light guidance of the distance measuring device, which also serves as the light exit aperture of the measuring light source, at an aperture or light coupling point arranged on the light detector side, whereby an intensity maximum is detected by the light detector.

[0017] As the measurement light, broadband infrared light, particularly near-infrared light, can be used. In particular, a near-infrared LED (Light Emitting Diode) with a peak wavelength of 900 nm to 1000 nm, particularly 940 nm to 960 nm, and a spectral half-width of 40 nm to 60 nm, particularly 45 nm to 55 nm, can be used to generate the measurement light. Such an LED measurement light is broadband enough to avoid or reduce disruptive interference or speckle effects. On the other hand, such an LED measurement light is narrowband enough to suppress or keep low undesirable dispersion effects such as chromatic aberration focus shift and focus shift.

[0018] Furthermore, optical components of the laser processing device, for example mirrors and / or lenses of the laser targeting optics configured for the near-infrared spectral region, may be used for distance measurement with near-infrared measurement light.

[0019] The method of the invention may further comprise the acquisition or detection of a laser light. In this case, instead of or in addition to the measuring light, a laser light is detected, which is reflected by the workpiece and directed through the laser targeting optics and the measuring optics through an aperture to a detector of the distance measuring device. In this method, the focus of the laser is imaged on the aperture. The focal length of the variable focal length measuring light optics is varied over time in a controlled manner to detect the moment when the intensity of the laser beam passing through the aperture is maximum, i.e. when the focus of the laser is clearly imaged on the aperture. In this method, for example, in a first step, the laser may be focused on the workpiece and the focal length of the variable focal length measuring light optics at which the maximum intensity of the laser beam passing through the aperture occurs may be measured. When the focus of the laser is not on the workpiece surface but above or below it, the position of the image point in the plane of the aperture also changes. Thus, intensity maxima occur at different focal lengths of the variable focal length measuring light optics. This effect may be used to detect changes in the focus position of the laser.

[0020] In some embodiments, the method of the invention may include detecting both the measurement light and the laser light simultaneously, where both the laser focus and the measurement light spot are imaged onto an aperture, and the portion of the measurement light and the portion of the laser light that passes through the aperture are guided to a detector of the distance measuring device.

[0021] Depending on the distance of the laser focal point from the workpiece surface and the color errors of the optical components, the focal distance at which the measurement light spot is sharply imaged onto the aperture may differ from the focal distance at which the laser focal point is sharply imaged onto the aperture.

[0022] In particular, the method of the present invention may include positioning the workpiece to be machined relative to the focal point of the laser based on a determined difference between the two focal lengths at which either the measurement light spot or the focal point of the laser is clearly imaged into the aperture.

[0023] Varying the focal length of the variable focal length measuring light optics over time may include an adjustment, in particular a periodic adjustment, of the focal length of the variable focal length measuring light optics in order to detect distance measurement data at different focal lengths of the variable focal length measuring light optics. When adjusting the focal length, the focal length range of the variable focal length measuring light optics between a minimum focal length and a maximum focal length is covered, in such a way that the focus of the measuring optics scans the entire measuring range of the light sensor. By periodically adjusting the focal length of the variable focal length measuring light optics, the evaluation of the detected distance measurement data can be synchronized with the temporal variation of the focal length, which makes it easier to clearly and reliably assign the detected measurement data to the determined distance. A distance value or distance, in particular a single distance value or distance to the surface of the measuring piece to be machined, can be determined in one cycle or in one measurement cycle based on the variation of the focal length of the measuring light.

[0024] In some embodiments, the focus of the measurement light is on the surface of the measurement object or workpiece to be machined at two different times within one cycle, so that the reflection from the measurement light point on the surface of the workpiece to be machined is sharply imaged on the fiber end or optical coupling point, which gives rise to a maximum value of the light intensity detected by the photodetector. The distance of the workpiece to be machined can be determined from the time at which the maximum value of the light intensity detected by the photodetector is observed, by a predefined relationship between the cycle time and the focus position of the measurement light, or a relationship that can be determined by calibration measurements.

[0025] The method of the present invention may further comprise performing a calibration measurement to determine the relationship between cycle time and distance. The relationship between cycle time and distance determined by the calibration measurement may improve the reliability and accuracy of the evaluation of the distance measurement data, such that the determined distance may be unambiguously and reliably calculated from the time of intensity maximum in the cycle.

[0026] The calibration measurement may in particular include detection of the reflection of a meniscus lens downstream of the variable focal length optics at different cycle times. The meniscus lens includes a concave and a convex surface. In particular, the meniscus lens may be arranged such that, as the variable focal length optics is adjusted, light reflected back from the concave surface and light reflected back from the convex surface alternately converge at the optical coupling point, each of which results in a measurable intensity peak of the light fed into the optical fiber. The time positions of these peaks within the adjustment cycle correspond to appropriately defined focal lengths of the variable focal length optics, so that the variable focal length optics or the distance measuring device can be accurately calibrated based on the time positions of these intensity peaks or calibration peaks.

[0027] In some embodiments, the calibration measurement involves measuring a two-dimensional grid of lateral positions of the scanner or laser targeting optics. The distance measurement data acquired at the two-dimensional grid can then be used to calibrate the distance measurement device.

[0028] The method of the present invention may further include a calibration measurement to determine the distance at which the laser beam is best focused on the workpiece.

[0029] A machining laser can generate machining light in both the visible and infrared regions when machining a workpiece. In particular, machining light can be generated in a spectral range that is outside the spectral distribution of the laser light during laser machining of a workpiece. The generation of machining light is related to the intensity of the laser light at the irradiation point of the workpiece. When the laser is low powered, machining light is generated only when the workpiece is precisely located in the focal plane of the laser light.

[0030] To determine the focal plane of the laser light, the distance between the focal point of the laser light and the workpiece is varied, which can be done, for example, by adjusting the position of the workpiece or by focusing the laser light using focusing optics.

[0031] The presence or absence of the machining light is recorded by a detector. Detection of the machining light indicates that the laser beam is sufficiently focused on the workpiece surface to generate the machining light. Based on the detected machining light, it can also be determined that the laser beam is optimally focused on the workpiece. In this case, by measuring the distance with the measurement light, a corresponding distance value can be determined.

[0032] In another embodiment, the laser is not operated at a constant power, but instead the power of the laser is varied, in particular the power of the laser is continuously increased from a low value and the critical power at which the machining light first appears can be measured.

[0033] This step may be repeated for different distances between the workpiece and the focal point of the laser. The distance at which the laser beam is as well focused as possible on the workpiece is characterized by the critical power, which has a minimum value.

[0034] The acquisition of distance measurement data may be performed at multiple positions or measurement points at the target location. Arrangement of measurement points at the target location means in the present invention that the measurement points may be arranged at or around the target location. By acquiring distance measurement data at multiple measurement points at the target location, the effect of measurement errors can be reduced by averaging. By acquiring distance measurement data at multiple measurement points, the effect of speckle on the measurement result can also be reduced. This is because the local intensity variations of the light reflected back from the workpiece being machined due to speckle can be averaged out by measuring at multiple measurement points.

[0035] The acquisition of distance measurement data at a number of measurement points may be performed consecutively or sequentially in time, in particular within one measurement cycle. In this way, distance measurement data can be acquired from a number of different measurement points during one measurement cycle, so that an averaged distance can be determined quickly and with little computational effort.

[0036] In some embodiments, distance measurement data is acquired at multiple positions along a scan path at the target location. In particular, the scan path can be selected such that distance measurement data acquired along the scan path can be used to estimate the target distance.

[0037] The scan path may have the shape of a circle surrounding a target location of the workpiece to be machined. In particular, the measurement circle may consist of a path radius corresponding to the laser spot. The distance measurement data acquired along the measurement circle results in a database that can be effectively reduced by averaging to reduce the measurement errors.

[0038] The scan path may have a spiral shape centered on a target location of the workpiece to be machined. In particular, the center of the spiral may coincide with the target location. Due to the spiral scan path, distance measurement data can be acquired from a particularly large surface, so that the averaging effect can be increased and the measurement susceptibility to interference can be reduced.

[0039] In some embodiments, the acquisition of distance measurement data at multiple measurement points is performed substantially simultaneously, in particular within one measurement cycle, and the distance determination is based on physically averaged distance measurement data.

[0040] Physical averaging of the distance measurement data means in particular that the distance determination is not performed separately for each measurement point, e.g. not for forming an average distance value from the determined distances. Physical averaging means that all of the distance measurement data recorded at multiple measurement points of the target position, in particular the intensity measurement data of the measurement light reflected back from the workpiece to be machined, are included in the determination of the distance of the target position, whereby a single distance value is determined for all of the measurement points.

[0041] By physical averaging, all distance measurement data recorded at multiple different measuring points of the target position are evaluated together in one evaluation step, whereby the distance value can be determined in a quick and simple manner.

[0042] The measurement light may be split by at least one multi-hole mask with a plurality of holes, in particular in the form of a confocal aperture, into a plurality of partial measurement light for simultaneous acquisition of distance measurement data at a plurality of measurement points. Thus, with the at least one multi-hole mask, the partial measurement light required for the acquisition of distance measurement data at a plurality of measurement points can be generated in a simple manner.

[0043] The partial measurement light can be detected by a common photodetector. By using a common photodetector for all partial measurement light, the acquisition of distance measurement data from multiple measurement points is simplified. Simultaneously with the acquisition of the partial measurement light by the common photodetector, a physical averaging of the distance measurement data or light intensity is performed. This is because the common photodetector cannot distinguish between light reflected back from different measurement points. In this way, the averaging of the distance measurement data is performed automatically without performing a calculation step.

[0044] According to a second aspect, an apparatus for controlled machining of a workpiece is proposed.

[0045] The apparatus includes a laser source for generating a laser beam for machining or laser processing the workpiece to be machined. In particular, a solid-state laser emitting in the near infrared spectral range, such as a YAG laser or a fiber laser, or a gas laser, for example a CO2 laser, can be used to generate the laser beam.

[0046] The apparatus further comprises laser targeting optics for focusing the laser beam to a laser beam focal point at a target location of the workpiece to be machined. The laser targeting optics can in particular be configured as focusing and alignment optics, which allows for target alignment and focusing of the laser beam. The laser targeting optics may in particular be configured as a laser beam scanner, in particular as a galvanometer scanner, and the alignment of the laser beam may be performed by electrically controlled mirrors.

[0047] The apparatus also includes a distance measuring device for determining a distance between a target position of the workpiece to be machined and the laser targeting optics based on distance measurement data acquired by the distance measuring device, and a positioning device for positioning the workpiece to be machined relative to the laser light focus and / or for refocusing the laser based on the detected distance measurement data.

[0048] The apparatus further includes an evaluation and control configured to evaluate the acquired distance measurement data and to control the placement device based on the acquired distance measurement data.

[0049] The distance measurement device is configured as an optical confocal distance measurement device equipped with a measurement light source for generating measurement light and a variable focal length measurement light optical system, and the variable focal length measurement light optical system is configured to vary the focal length of the variable focal length measurement light optical system over time in order to obtain distance measurement data at multiple different focal length values ​​of the variable focal length measurement light optical system.

[0050] By varying the focal length of the variable focal length measuring light optics over time, the effective measuring range of the distance measuring device can be extended so that in the case of laser processing devices with large focal lengths or small numerical apertures, the distance between the laser targeting optics and the target position on the workpiece being machined can also be accurately measured with the optical confocal sensor.

[0051] Furthermore, since the variable focal length measuring light optical system makes it possible to perform distance measurements with optical elements that have no or little light dispersion, it is also possible to use optical elements required for laser beam guidance, in particular optical elements required for laser beam guidance that have no or little light dispersion, for beam guidance of the measuring light.

[0052] The measurement optics of the distance measuring device may also form at least a part of the laser target optics.

[0053] By using a laser target optical system for the measurement optical system of the distance measuring device, the number of necessary optical components can be reduced, and the structure of the device can be greatly simplified. Therefore, the distance sensor can be easily incorporated into existing laser processing devices.

[0054] The distance measuring device may include a photodetector that detects the intensity of the measuring light reflected back from the workpiece being machined, and may be configured to determine distance based on changes over time in the detected intensity of the measuring light reflected back from the workpiece.

[0055] In particular, by controlled variation in time of the focal length of the variable focal length measuring light optics, the time point of intensity detection can be assigned to a specific focal length of the variable focal length measuring light optics and therefore to a specific distance, from which the distance between the laser targeting optics and the target position can be deduced.

[0056] As the measurement light source, a broadband infrared light source may be used, in particular a light source emitting in the near infrared spectral region. In particular, a near infrared LED with a peak wavelength of about 950 nm and a spectral half width of about 50 nm may be used to generate the measurement light. Such an LED measurement light is broadband enough to avoid or reduce disruptive interference or speckle effects. On the other hand, such an LED measurement light is narrowband enough to suppress or reduce undesirable dispersion effects such as chromatic aberration focus shift.

[0057] The variable focal length measuring light optics may be configured as an adjustable, in particular periodically adjustable, measuring optics. When adjusting the focal length, the focal length range of the variable focal length measuring light optics between the minimum focal length and the maximum focal length is covered, for example ±7 mm, in such a way that the focus of the measuring optics covers the entire measuring range of the light sensor. By periodically adjusting the focal length of the variable focal length measuring light optics, the evaluation can be synchronized with the temporal variation of the focal length, in such a way that the recorded measurement data can be unambiguously and reliably assigned to the determined distance.

[0058] In particular, the variable focal length optics may be arranged in the divergent part of the imaging system of the distance measuring device, that is, in that part of the imaging system of the distance measuring device in which the measurement optics forms a divergent measuring light. In the divergent part of the imaging system, the variable focal length measuring light optics may be arranged in particular in such a way that the effective aperture of the variable focal length optics can be optimally utilized.

[0059] The variable focal length measurement light optics may include a variable focal length lens. With a variable focal length lens, in particular an electrically controllable variable focal length lens, the focal length of the measurement optics can be easily varied. The effective aperture of the variable focal length lens may include a diameter in the range of 1-10 mm, in particular in the range of 2-6 mm. The variable focal length lens can in particular be arranged near the optical coupling point or near the fiber end where the measurement light diverges out.

[0060] In some embodiments, the apparatus of the present invention includes at least one aperture mask having a plurality of apertures for splitting the measurement light into a plurality of partial measurement light, with which distance measurement data can be simultaneously acquired at a plurality of measurement points.

[0061] In one embodiment, the device of the invention comprises an optical fiber with optical coupling points for the ingress and egress of the measurement light, and at least one multi-hole mask is arranged at the optical coupling points. This arrangement of the multi-hole mask is suitable for devices with a fiber coupler, where the optical coupling points are configured both for the egress of the light generated by the measurement light source and for the ingress of the measurement light reflected back from the workpiece to be machined. In this case, the acquisition of distance measurement data at different measurement points can be performed in a simple manner with a single multi-hole mask.

[0062] In particular, the porous mask may be placed directly at the optical coupling point or directly at the end of the optical fiber. By placing the porous mask at the optical coupling point, the porous mask can be used effectively by capturing substantially all of the measurement light leaving the optical coupling point with the porous mask.

[0063] The optical coupling points or ends of the optical fibers and the porous mask can be dimensioned such that the porous mask is essentially totally illuminated, which means that the area of ​​the porous mask can be used particularly efficiently.

[0064] In some embodiments, the apparatus of the present invention includes a first optical fiber having a light output end and a second optical fiber having a light input end, with a first multi-aperture mask disposed at the light output end and a second multi-aperture mask disposed at the light input end. This multi-aperture mask arrangement is suitable for an apparatus with a beam splitter configured to couple measurement light generated by a measurement light source into an imaging system of a distance measuring device and to extract measurement light reflected back from a workpiece to be machined.

[0065] The two multi-hole masks may be arranged such that the holes of the two multi-hole masks are paired and confocal aligned. Due to the paired confocal alignment of the holes of the two multi-hole masks, partial measurement light beams generated by the holes of the first multi-hole mask are bundled with the corresponding holes of the second multi-hole mask, so that light loss through the multi-hole mask can be minimized.

[0066] Instead of using individual optical fibers, a fiber optic bundle may be used to generate multiple partial measurement beams in order to record distance measurement data at different measurement points. Since the fiber optic bundle already provides multiple partial measurement beams, a multi-hole mask is no longer required. A fiber optic bundle for splitting the measurement beam into partial measurement beams can be used both in the inventive device with a fiber coupler and in the inventive device with a beam splitter. By using a fiber optic bundle, the structure and operation of the inventive device can thereby be simplified.

[0067] In some embodiments, the apparatus of the present invention includes a camera configured such that the camera can be used to visually inspect the machining location of the workpiece being machined before, during, and / or after machining.

[0068] In some embodiments, the apparatus of the present invention includes a detector configured to detect the presence of machining light, where the machining light is outside the spectral distribution of the laser light.

[0069] Embodiments will now be described in more detail with reference to the drawings, in which like reference numerals are used to refer to like or similar components. [Brief description of the drawings]

[0070] [Figure 1] FIG. 1 illustrates a schematic diagram of an apparatus for controlled machining of a workpiece according to one embodiment; [Diagram 2] FIG. 2 illustrates a porous mask according to one embodiment. [Diagram 3] FIG. 13 illustrates a porous mask according to another embodiment. [Figure 4] FIG. 2 is a schematic side view of a meniscus lens according to one embodiment. [Diagram 5] FIG. 5 is a schematic plan view of the meniscus lens of FIG. 4. [Figure 6]2A and 2B are schematic diagrams illustrating possible optical paths in a portion of a distance measuring device according to an embodiment; [Figure 7] 7A-7D show schematic diagrams of alternative light paths that may occur in the section according to FIG. 6; [Figure 8] 7A-7D show schematic diagrams of alternative light paths that may occur in the section according to FIG. 6; [Figure 9] FIG. 13 is a diagram showing the change over time in the intensity of light reflected back from a meniscus lens. [Figure 10] 2 shows a schematic diagram of an apparatus for controlled machining of a workpiece according to another embodiment; [Figure 11] FIG. 1 is a flow diagram of a method for controlled machining of a workpiece according to one embodiment. [Figure 12] 4 shows a schematic diagram of an apparatus for controlled machining of a workpiece according to a further embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0071] 1 shows diagrammatically an apparatus for controlled machining of a workpiece according to one embodiment. The apparatus 1 comprises a laser source 2 for generating a laser beam 3 for machining a workpiece 4 to be machined. Furthermore, the apparatus 1 comprises laser targeting optics 5 for directing or selectively focusing the laser beam 3 to a focal point F at a target location 6 of the workpiece 4 to be machined.

[0072] The apparatus 1 comprises a distance measuring device 7 for determining the distance between a target position 6 on a workpiece 4 to be machined and laser targeting optics 5. The distance measuring device 7 is configured as an optical confocal distance measuring device and comprises a measurement light source 8 for generating measurement light and a photodetector 9 for detecting the measurement light reflected back from the workpiece 4. In the present embodiment, the distance measuring device 7 has a distance measuring range H of ±7 mm centred on the zero plane O.

[0073] The measurement light source 8 is connected to the 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 the second optical fiber 13 at a second connection point 14 of the fiber coupler 12. A first end of a third optical fiber 16 is connected to a third connection point 15 of the fiber coupler 12, and a second end of the third optical fiber 16 is formed as an optical coupling point 17 for the entrance and exit of the measurement light. In this embodiment, the first optical fiber 10, the second optical fiber 13 and the third optical fiber 16 are formed as multimode fibers capable of transmitting broadband light in the near infrared spectral range.

[0074] A collimating lens 18 is disposed downstream of the optical coupling point 17, and a variable focal length lens 19 is provided between the optical coupling point 17 and the collimating lens 18. The optical coupling point 17 is configured such that the measurement light diverges from the optical coupling point 17, thereby generating a divergent measurement light beam in the region between the optical coupling point 17 and the collimating lens 18. In this embodiment, the variable focal length lens 19 is an EL-03-10 from OptOtune, which is an electrically controllable variable focal length lens.

[0075] A first deflection plate 30 is arranged in the optical path of the laser beam 3 for coupling and decoupling the measurement light into and from the optical path of the laser beam 3 and into the laser targeting optics 5. The deflection plate 30 may be configured in such a way that the measurement light can propagate in the optical path of the laser beam coaxially with the laser beam 3, in particular along a common optical axis A of the measurement light and the laser beam.

[0076] The device 1 further comprises a second deflection plate 31, which is arranged in the optical path of the laser beam between the first deflection plate 30 and the laser targeting optics 5. The camera 32 is optically coupled to the laser targeting optics 5 via a second collimating lens 33 and the second deflection plate 31, such that the machining position of the workpiece to be machined can be visually inspected by means of the camera 32. The deflection plates 30, 31 are configured as transparent or partially transparent plates for the laser beam, such that the optical path of the laser beam is not disturbed or is disturbed only slightly by the deflection plates 30, 31.

[0077] In some embodiments, the light for the camera 32 is split by a deflector 31 between the laser 2 and the deflector 30. By splitting the light for the camera between the laser and the deflector 30, the distance measurement is not affected by the deflector 31 for splitting the light for the camera.

[0078] 1, the laser beam 3 is coupled by deflector plate 30 or deflector plate 31, respectively, and passes transparently to the laser targeting optics 5. In another embodiment, the laser beam 3 is coupled to the laser targeting optics 5 by reflection or by a laser beam mirror.

[0079] In particular, the laser beam may be coupled into the optical system of the device 1 by reflection, either laterally or perpendicularly to the common optical axis A. In the case of such an arrangement, for example, the camera 32 and the collimating lens 33 are replaced by a laser 2, and the deflection plate 31 is replaced by a laser beam mirror. As a laser beam mirror, a laser beam mirror at least partially transparent for the measurement light may be used. Other configurations of the beam path are also possible, in which the principles described herein can be realized. In a non-limiting embodiment, the measurement light is coupled into the beam path of the laser beam coaxially or along the common optical axis A.

[0080] In some embodiments of the laser targeting optics 5, a focusing lens 50 is positioned downstream of the pair of mirrors 51 such that the laser beam 3 is first aligned by the pair of mirrors 51 and then the aligned laser beam 3 can be focused by the focusing lens 50 at the target position.

[0081] The device 1 according to the embodiment of Fig. 1 also comprises an evaluation control 40. The evaluation control 40 comprises an evaluation unit 41 for evaluating the detected distance measurement data, a lens control 42 for controlling the focal length of the variable focal length lens 19 and a position control 43 for positioning the workpiece to be machined relative to the focus of the laser. The evaluation unit 41 is connected to the output of the photodetector 9 via a signal line 44. The lens control 42 is connected to the control port of the variable focal length lens 19 via a lens control line 45. The position control 43 is connected to a positioner 47 for positioning the workpiece 4 to be machined via a position control line 46.

[0082] The laser source used in this embodiment is a YAG laser generating optical radiation in the wavelength range of 1030 nm to 1070 nm. Other solid-state lasers, in particular lasers emitting in the near infrared spectral region, and gas lasers, such as CO2 lasers, may also be used as laser sources. Lasers emitting in the near infrared spectral region are suitable for material machining because they are capable of providing the kW range power and high power density of optical radiation required for material machining. The device 1 further includes a laser output control unit configured to control the output of the laser 2 and a laser focus control unit including a controllable focusing optics arranged in the optical path of the laser and configured to control the laser focus. In FIG. 1, for the sake of simplicity, the laser output control unit and the laser focus control unit are not shown.

[0083] The measurement light source used in this embodiment is a broadband near-infrared LED with a peak wavelength of about 950 nm and a spectral half-width of about 50 nm. Such an LED measurement light is broadband enough to avoid or reduce disruptive interference or speckle effects, while being narrowband enough to prevent or reduce the occurrence of undesirable dispersion effects such as chromatic aberration focus shift.

[0084] In the embodiment of Figure 1, the laser targeting optics 5 or scanner comprises a focusing lens 50 for directing the focused radiation to a target location 6 of the workpiece 4 to be machined and, if necessary, for moving together with the focused laser beam in the machining area of ​​the workpiece 4 to be machined, and a controllable pair of mirrors 51. The pair of mirrors 51 can in particular be configured as a pair of galvanometer mirrors which can be electrically controlled in a simple manner.

[0085] The focusing lens 50 has a focal length of about 180 mm. The diameter of the laser beam 3 before entering the laser targeting optics 5 is about 10 mm. The laser targeting optics 5 are dimensioned such that the laser beam 3 can machine a machining area of ​​approximately 80 mm x 80 mm.

[0086] In some embodiments, the laser targeting optics 5 are configured as telecentric laser targeting optics. The telecentric configuration of the laser targeting optics allows for machining of the workpiece at various distances from the device with the laser beam.

[0087] The positioner 47 may in particular be configured for positioning and / or orienting the workpiece 4 to be machined relative to the focal point of the laser beam and may in particular include one or more actuators which can be controlled with one or more control signals from the position control 46 for positioning or orienting the workpiece 4 to be machined. The possible orientations of the workpiece are symbolically indicated in Fig. 1 by coordinate axes.

[0088] In some embodiments, such as the example shown in Fig. 1, the device 1 includes a multi-hole mask 60 or aperture arranged in the optical path of the distance measuring device 7. The multi-hole mask 60 includes a number of holes 61, which can be clearly seen below in Figs. 2 and 3. The multi-hole mask 60 is arranged between the optical coupling point 17 and the variable focal length lens 19, such that the measurement light is split into a number of parts by the multi-hole mask 60 in order to simultaneously obtain distance measurement data at a number of positions on the surface of the workpiece 4 to be machined. In the embodiment shown in Fig. 1, the multi-hole mask is arranged directly on the end of the fiber acting as the optical coupling point 17, such that the end of the fiber also serves as a holder for the multi-hole mask 60.

[0089] In some embodiments, the optical fiber at the end of which the porous mask is disposed has a diameter sufficient to illuminate substantially the entire porous mask 60 and capture the light reflected back by substantially all of the holes 61 in the porous mask 60.

[0090] In some embodiments, the fiber 16 with the porous mask 60 is replaced with a fiber bundle that is coupled to a fiber coupler in a manner similar to the fiber 16 of FIG.

[0091] In some embodiments, such as the example shown in FIG. 1, the apparatus 1 for controlled machining of a workpiece includes a meniscus lens 80 disposed between the variable focal length lens 19 and the collimating lens 18.

[0092] The meniscus lens 80 includes a substantially spherical concave surface 81 and a substantially spherical convex surface 82. The concave surface 81 or concave side of the meniscus lens 80 faces the variable focal length lens 19, and the convex surface 82 or convex side of the meniscus lens 80 faces the collimating lens 18. In the illustrated embodiment, the meniscus lens 80 includes a circular hole 83 in its center.

[0093] In operation of the device 1, a portion of the light generated by the measurement light source 8 is guided through the first optical fiber 10, through the fiber coupler 12, and through the third optical fiber 16 to the optical coupling point 17. After diverging from the optical coupling point 17, the measurement light passes through the variable focal length lens 19 and the collimating lens 18, and is coupled into the optical path of the laser beam 3 by the deflection plate 30. The measurement light coupled into the optical path of the laser beam 3 can then pass through the laser targeting optics 5 to reach the workpiece 4 to be machined.

[0094] When the measurement light reaches the workpiece 4, a part of the measurement light may be reflected back and travels through the laser targeting optics 5, the collimating lens 18, the variable focal length lens 19 and the optical coupling point 17 to the third optical fiber 16. This causes a part of the measurement light to be diverted by the fiber coupler 12 through the second fiber 13 to the photodetector 9. The photodetector 9 supplies a measurement signal via a signal line 44 to an evaluation unit 41 for evaluation. The evaluation unit 41 is configured to evaluate the change over time in the intensity of the light detected by the photodetector 9. The evaluation unit 41 is also configured to derive from the change over time in intensity the distance between the target position of the workpiece to be machined and the laser targeting optics.

[0095] In particular, the variable focal length lens 19 may be controlled cyclically such that the refractive power of the variable focal length lens is adjusted, for example, by ±13 diopters, thereby moving the focus of the measurement light along the optical axis by approximately ±7 mm. At two different times within the cycle, the focus of the measurement light is at the surface of the object to be measured or the workpiece to be machined, so that the reflection from the measurement light point on the surface of the workpiece to be machined is sharply imaged at the fiber end or optical coupling point 17, resulting in a maximum value of the light intensity detected by the photodetector.

[0096] The distance of the workpiece to be machined may be determined based on the time at which a maximum value of the intensity of the light detected by the photodetector is observed, according to a predetermined relationship between the cycle time and the focal position of the measurement light, or a relationship that may be determined by a calibration measurement.

[0097] In particular, a calibration measurement defining the relationship between the time point in the cycle time and the distance of the surface of the workpiece to be machined may be performed in advance or before performing the laser processing. The calibration measurement may be performed via a scanner or a two-dimensional grid of lateral positions of the laser targeting optics. Using the determined relationship, the surface distance or the distance between the laser targeting optics 5 and the target position 6 of the workpiece to be machined can then be determined from the time point of the maximum intensity in the cycle.

[0098] The periodic variation or adjustment of the focal length of the variable focal length lens 19 is shown diagrammatically in Fig. 1 by the sawtooth curve of the lens control 42. The relationship between the cycles of the focal length variation of the variable focal length lens 19 and the occurrence of intensity maxima is shown diagrammatically in Fig. 1 by the dashed line extending between the sawtooth curve of the lens control 42 and the intensity curve at the time coordinate t shown in the evaluation unit 41.

[0099] The measurement light split by the multi-hole mask 60 allows the simultaneous acquisition of distance measurement data at multiple locations on the surface of the workpiece 4 to be machined. In particular, the measurement light reflected back from the workpiece also passes through the holes 61 of the multi-hole mask 60 and reaches the fiber 16 via the coupling point 17 so that it can be detected by the photodetector 9. The light intensity detected by the photodetector 9 corresponds to the total intensity of the light reflected back from all measurement points collected through all holes 61 of the multi-hole mask 60, whereby a physical averaging of the intensity differences between the light reflected back from the different points due to the optical arrangement is performed. The physical averaging of the different light intensities detected by the different holes 61 of the multi-hole mask 60 can considerably simplify the evaluation of the measurement data, since a distance measurement does not have to be performed for each location individually. To be more precise, the distance can be sufficiently determined using the distance measurement data, in particular the intensity data, physically averaged for all locations provided by the multi-hole mask 60.

[0100] Due to the configuration of the meniscus lens 80 , light reflected back from the surfaces 81 , 82 of the meniscus lens 80 may enter the fiber 16 via the optical coupling point 17 and be detected by the photodetector 9 .

[0101] In particular, when a light beam leaving the variable focal length lens 19 strikes one of the two surfaces 81, 82 of the meniscus lens 80 perpendicularly, a maximum percentage of the light from the corresponding surface 81 or 82 of the meniscus lens 80 is reflected back through the variable focal length lens 19 into the fiber 16. Thus, such a beam configuration can be detected by a corresponding intensity peak in the reflected back light, with each of the two surfaces 81, 82 of the meniscus lens 80 contributing its own intensity peak.

[0102] In some embodiments, the meniscus lens is dimensioned such that a peak occurs at the beginning and end of each repetitive time cycle during the adjustment of the variable focal length 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 corresponds to the same distance. The relationship between the age and distance values ​​may change, especially due to the effect of temperature changes. Adjustable lenses are highly sensitive, so that the relationship between the control value and the focal length of the variable focal length lens 19 may change under temperature changes. Since the multiple intensity peaks of the meniscus lens 80 each occur at the same focal length of the variable focal length lens 19, the variable focal length lens 19 or the relationship between age and distance can be precisely calibrated based on these peaks. This is because, in contrast to the variable focal length lens 19, the meniscus lens 80 has negligible temperature dependence.

[0103] Through a circular hole 83 in the center of the meniscus lens 80, the measurement light beam passes through the meniscus lens undisturbed, so that only the edge beam can be reflected back by the meniscus lens 80. By selecting the lens area or the hole size, respectively, the intensity of the reflection can be adjusted so that the intensity of the light reflected back from the meniscus lens 80 is high enough to act as a calibration signal, but not so high that the measurement signal or intensity signal, respectively, of the measurement light reflected back from the object to be machined is overshadowed by the meniscus lens reflection. In some embodiments, the hole 83 is dimensioned such that a large portion of the measurement light passes through the hole 83 of the meniscus lens 80 unreflected.

[0104] In some embodiments, an aperture is disposed downstream of the meniscus lens 80 and configured to pass an inner beam portion of the measurement light and block an outer beam portion of the measurement light, in this way, specifically, beams affected by the meniscus lens 80 may be excluded from the measurement.

[0105] In some embodiments, the meniscus lens 80 does not have a hole but comprises a coating on at least one of the two surfaces 81, 82. The thickness or reflectivity of the coating, respectively, can be selected such that the measurement signal is not obscured by the reflected component of the meniscus lens. In some embodiments, the meniscus lens 80 comprises an anti-reflection coating such that its reflected component is less than 4% in the wavelength range of the measurement light.

[0106] In some embodiments, the meniscus lens 80 includes both a circular hole 83 and a coating, and the dimensions of the circular hole 83 and the thickness of the coating can be selected to obtain a sufficiently strong calibration signal without obscuring or unduly affecting the measurement signal.

[0107] FIG. 2 illustrates a porous mask according to one embodiment.

[0108] The multi-hole mask 60 of Fig. 2 is in the form of a substantially rectangular opening and includes a number of circular holes 61. In this embodiment, the circular holes 61 are substantially evenly distributed over the entire opening in a hexagonal lattice. The distribution of the holes 61 in a hexagonal lattice allows a high density of holes, so that the measurement light can be divided into many parts by the multi-hole mask in order to obtain distance measurement data at many measurement points. At the same time, for a certain density, the distance between adjacent holes is maximized when a hexagonal lattice is selected, and therefore the crosstalk between the holes is minimized.

[0109] FIG. 3 shows a porous mask according to another embodiment.

[0110] The porous mask 60 of Figure 3 includes a plurality of holes 61 in the form of substantially rectangular openings and is similar to the porous mask 60 of Figure 2. In contrast to the porous mask 60 of Figure 2, the holes 61 of the porous mask of Figure 3 are rectangular and substantially evenly distributed over the entire opening in a checkerboard pattern.

[0111] The filling degree of the porous mask 60 illustrated in FIGS. 2 and 3 is preferably 30% to 70%, and in particular about 50% so that about 50% of the light striking the porous mask passes through the porous mask.

[0112] Alternatively to the embodiment illustrated in Figures 2 and 3, the porous mask may also be essentially circular, which is particularly well suited for precise placement on the end of an optical fiber having a circular cross section.

[0113] FIG. 4 is a schematic side view of a meniscus lens according to one embodiment.

[0114] 4, the meniscus lens 80 includes a substantially spherical concave surface 81 and a substantially spherical convex surface 82. In the illustrated embodiment, the meniscus lens 80 includes a circular hole 83 in the center.

[0115] FIG. 5 shows a schematic plan view of the meniscus lens of FIG.

[0116] In the plan view of Fig. 5 the circular hole 83 of the meniscus lens 80 can be particularly well seen. As already mentioned above in the description of Fig. 1, the meniscus lens 80 may have different shapes. In particular, at least one of the two surfaces 81, 82 may comprise a coating. Furthermore, the dimensions of the circular hole 83 and / or the thickness or reflectivity of the coating can be selected such that the return reflections at the surfaces 81, 82 of the meniscus lens 80 generate a calibration peak of sufficient intensity without obscuring the measurement signal or impairing the distance measurement.

[0117] FIG. 6 shows a schematic representation of possible optical paths in a part of a distance measuring device according to an embodiment.

[0118] The portion illustrated in FIG. 6 includes the variable focal length lens 19, meniscus lens 80, and coupling point 17 of optical fiber 13 illustrated in FIG.

[0119] The long arrows pointing away from the optical coupling point 17 represent measurement rays emerging from the optical coupling point 17, which rays are emitted through the variable focal length lens 19 and partially through the meniscus lens 80. The arrows pointing back from the meniscus lens 80 to the optical coupling point 17 show rays reflected from the concave or convex surfaces 81 and 82, respectively. The essentially spherical curvature of the surfaces 81, 82 causes the reflected rays to converge at their respective focal points.

[0120] 6, light reflected from the concave surface 81 of the meniscus lens 80 is focused onto the light emitting surface of the optical coupling point 17, while light reflected back from the convex surface 82 of the meniscus lens 80 is focused onto the light receiving surface or upstream of the optical coupling point 17. The illustrated optical path may occur at certain focal lengths of the variable focal length lens 19, among others.

[0121] FIG. 7 shows diagrammatically another possible light path in the section according to FIG.

[0122] The optical paths in Figure 7 basically correspond to those illustrated in Figure 6. In contrast to the case illustrated in Figure 6, the variable focal length lens 19 has different focal length values ​​such that neither of the two reflected back beams meets at the optical coupling point 17.

[0123] FIG. 8 shows diagrammatically another possible light path in the section according to FIG.

[0124] The optical path shown in FIG. 8 corresponds to the 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 focused at the light emitting surface of the optical coupling point 17, while the focus of the light reflected back from the concave surface 81 of the meniscus lens 80 is downstream of the light accepting surface or optical coupling point 17.

[0125] The possible beam configurations of the measurement light shown in Figures 6, 7 and 8 illustrate the operation of the meniscus lens 80. For example, if the variable focal length lens 19 is adjusted periodically, the focal length will cycle periodically through all values ​​between the minimum focal length and the maximum focal length, and the beam configurations shown in Figures 6, 7 and 8 may occur periodically. The beam configuration shown in Figure 7 or a similar beam configuration, where none of the beams reflected back by the meniscus lens 80 are focused at the optical coupling point 17, may occur at various settings of the variable focal length lens 19. In contrast, the beam configurations illustrated in Figures 6 and 8 may only occur at very specific values ​​of the focal length of the variable focal length lens 19. Due to the fact that the light reflected back from the surfaces 81, 82 of the meniscus lens 80 is focused at the optical coupling point 17 of the optical fiber 13, a larger proportion of the light reflected back from the meniscus lens 80 is coupled to the optical coupling point in the beam configurations shown in Figures 6 and 8 than would otherwise be the case. This increase in the amount of coupled light can be detected by a corresponding increase in the intensity of the light detected by a photodetector. The corresponding intensity peaks may be detected by a photodetector, for example the photodetector 9 in the arrangement according to Fig. 1, and used as calibration peaks for calibrating the distance measuring device 7. In particular, the position in time of each intensity peak may be used to estimate the corresponding focal length of the variable focal length lens 19 or the corresponding measured distance of the distance measuring device 7.

[0126] The parts shown in Figures 6, 7 and 8 do not have a multi-aperture mask 60. The above explanations in Figures 6, 7 and 8 regarding the operation of the meniscus lens 80 also apply accordingly when a multi-aperture mask 60 is used to split the measurement light into several parts and obtain distance measurement data from different positions, and the multi-aperture mask 60 can be placed, for example, between the coupling point 17 and the variable focal length lens 19.

[0127] FIG. 9 is a diagram showing the change over time in the intensity of light reflected back from a meniscus lens.

[0128] In particular, Fig. 9 shows the time dependence of the measured light intensity for the arrangement shown in Figs. 6, 7 and 8, where the intensity of the portion of the light reflected back by the meniscus lens 80 and the workpiece 4 to be machined and coupled into the optical fiber 16 is measured during an adjustment cycle, which corresponds to a progression from a minimum operating value to a maximum operating value or vice versa. The time t and the intensity I are shown in Fig. 9 in arbitrary units. For a certain value of time, the time dependence of the intensity I(t) shows a clear intensity or calibration peak. In particular, the curve I(t) includes a sharp peak on the left (a), a sharp peak on the right (c) and a slightly broader intermediate peak (m). The sharp peak on the left (a) corresponds to the light beam configuration shown in Fig. 6, when the reflection from the concave surface 81 of the meniscus lens 80 is focused at the optical coupling point 17 of the optical fiber 16 and is thereby focused into the optical fiber 16. Between the two peaks (a) and (c), the beam configuration shown in FIG. 7 occurs when the optical coupling point 17 is between the two foci of the light reflected back from the concave surface 81 and the light reflected back from the convex surface 82 of the meniscus lens 80. In this case, neither the reflected light from the concave surface 81 nor the reflected light from the convex surface 82 can be properly coupled into the optical fiber 16. In this section, a peak (m) occurs caused by the reflected light from the workpiece 4 to be machined, and the distance of the workpiece 4 can be determined (measurement peak). The right peak (c) corresponds to the beam configuration shown in FIG. 8, when the reflected light from the convex surface 82 of the meniscus lens enters the optical fiber 16 in a bundle at the optical coupling point 17. In particular, the sharp peaks (a) and (c) at the beginning and end of the depicted period, respectively, have a well-defined time position, so that they can be the basis for an accurate calibration of the distance measuring device. Based on the characteristic course of the intensity curves, the peaks (a) and (c) can be easily identified and assigned to the respective beam configuration.

[0129] FIG. 10 shows a schematic diagram of an apparatus for controlled machining of a workpiece according to another embodiment. The apparatus 1 of FIG. 10 basically corresponds to the apparatus 1 shown in FIG. 1, but instead of the fiber coupler, it includes a beam splitter 90 configured to couple the measurement light through a light output end 91 of a first optical fiber 10 and to extract the measurement light reflected back from the workpiece 4 to be machined. The measurement light extracted through the beam splitter 90 can be coupled into a light input end 92 of a second optical fiber 13 to be detected by a photodetector. The light output end 91 of the first optical fiber 10 and the light input end 92 of the second optical fiber 13 are set to be confocal to each other. The use of a beam splitter makes it possible to avoid disturbing light scattering effects that occur in fiber couplers. In some embodiments, the beam splitter 90 is configured as a beam splitter cube. Beam splitter cubes are robust and have low scattering losses.

[0130] In some embodiments, the apparatus 1 with the beam splitter 90 includes at least one porous mask. In the example shown in Fig. 10, the apparatus 1 includes two substantially identically formed porous masks 60, one porous mask 60 connected downstream of the light output end 91 of the first optical fiber 10 and the second porous mask 60 connected upstream of the light input end 92 of the second optical fiber 13. The porous masks 60 are disposed directly at the fiber ends of the first and second optical fibers 10, 13.

[0131] The porous mask 60 may be similar to the porous masks shown in Figures 1, 2 and 3 and described above. The porous masks 60 are positioned and adjusted such that the holes 61 (not shown) of the two porous masks 60 are aligned confocal to each other.

[0132] FIG. 11 is a flow diagram of a method for controlled machining of a workpiece according to one embodiment.

[0133] The method 100 for controlled machining of a workpiece includes several steps, which may be performed in different orders and repeated as necessary, and may be performed, for example, by the apparatus of FIG.

[0134] In step 110, the laser beam is focused so as to generate a laser focus at a target location of the workpiece to be machined. The focusing of the laser beam may in particular be performed using laser targeting optics, in order to focus the laser beam at a target location of the workpiece to be machined. The focusing of the laser beam in step 110 may in particular be performed with low laser power, so that no or only little material machining of the workpiece 4 to be machined takes place. The laser beam may be focused by an auxiliary laser, for example a HeNe laser, the light of which is coupled into the optical path of the laser beam collinearly with the laser beam, for example by a deflector plate. As the laser targeting optics or scanner, a galvanometer scanner with two pivotable galvanometer mirrors may be used.

[0135] In step 120, optical distance measurement data is obtained by an optical distance measurement device for determining the distance between a target position of the machined workpiece and the laser targeting optics or a reference point or surface of the laser targeting optics. The distance measurement device can be configured as an optical confocal distance measurement device with a measurement light source for generating measurement light, particularly broadband measurement light in the near infrared spectral range, and a variable focal length measurement light optics, particularly a variable focal length lens, and the method includes varying the focal length of the variable focal length measurement light optics over time to obtain distance measurement data at different focal length values ​​of the variable focal length measurement light optics.

[0136] Obtaining the distance measurement data may in particular include obtaining the intensity of the measurement light reflected back from the workpiece being machined, whereby the distance is determined based on the intensity, in particular based on the change over time in the intensity of the measurement light reflected back from the workpiece.

[0137] In step 130, the workpiece to be machined is positioned relative to the focal point of the laser based on the acquired distance measurement data. In some embodiments, instead of or in addition to positioning the workpiece to be machined, the laser is refocused.

[0138] In step 140, a target location on the workpiece to be machined is machined using a focused laser beam.

[0139] In some embodiments, varying the focal length of the variable focal length measurement light optical system over time includes adjusting, in particular periodically adjusting, the focal length of the variable focal length measurement light optical system to obtain distance measurement data at different focal lengths of the variable focal length measurement light optical system.

[0140] The variation of the focal length of the variable focal length measuring optical system can in particular be performed by means of a variable focal length optical element, in particular a variable focal length lens.

[0141] A measurement cycle may typically last 25 milliseconds. During the measurement cycle, the focal power of the variable focal length lens may be adjusted, for example, in a range of ±13 diopters, and the focus of the measurement light may be moved approximately ±7 mm in the axial direction or along the optical axis of the measurement optics.

[0142] Due to the known relationship between cycle time and focal position, the distance of the workpiece that is machined can be determined using the intensity maximum.

[0143] To determine the relationship between cycle time and distance, in some embodiments a calibration measurement is performed, particularly prior to laser processing.

[0144] Figure 12 shows diagrammatically an apparatus for controlled machining of a workpiece according to a further embodiment. The apparatus 1 of Figure 12 essentially corresponds to the apparatus shown in Figure 10, but additionally comprises a light detector 161 by means of which machining light resulting from machining of the workpiece with the laser 2 can be detected.

[0145] 12 further includes an optical filter 162 having wavelength-dependent reflectivity configured to reflect machining light in a particular spectral range while not reflecting laser light, and further configured to transmit substantially all of the measurement light such that the measurement is not affected by the filter.

[0146] When machining a workpiece, machining light generated by laser 2 passes through laser targeting optics 5 and measurement optics to reach optical filter 162, where it is reflected and directed to beam splitter 90, which then reflects and directs the machining light to receiver 161. Due to the reflective properties of optical filter 162, the laser light reflected or scattered by workpiece 4 and returning to optical filter 162 through laser targeting optics 5 is not directed to photodetector 161.

[0147] The machining light is detected when determining the distance at which the laser light is best focused on the workpiece. When the light source 8 for the measurement light is turned off, this ensures that neither the measurement light nor the laser light is detected by the photodetector 161 and thus erroneously taken as machining light.

[0148] In some embodiments, the photodetector 161 only checks for the presence or absence of machining light, and does not provide positional information about where the machining light originates, so the machining light does not need to be focused onto the photodetector 161. This makes for an easy structural implementation, since the exact location of the photodetector 161 is not important, and so there is no need to adjust the photodetector 161.

[0149] 12, the porous mask 60 may also be provided with a partially reflecting layer so as to act as a reflective filter that reflects only the machining light and not the laser light and the measurement light. In this embodiment, therefore, an additional component in the form of the filter 162 can be omitted.

[0150] In some embodiments, the machining light is detected by photodetector 9. In this embodiment, optical filter 162 transmits both machining light and measurement light, but not laser light. When measurement light source 8 is turned off, photodetector 9 can thus be used to detect the machining light.

[0151] In the above description, at least one exemplary embodiment has been shown, but various modifications and variations are possible. The above embodiment is merely an example, and is in no way intended to limit the scope, applicability, or configuration of the present disclosure. Rather, the above description provides a person skilled in the art with a scheme for implementing at least one exemplary embodiment, and numerous changes in the function and arrangement of elements described in the exemplary embodiment can be made without departing from the scope of protection of the claims and their legal equivalents. [Explanation of symbols]

[0152] 1 device 2. Laser 3. Laser beam 4 Workpiece 5 Laser targeting optics 6 Target position 7 Distance measuring devices 8 Measurement light source 9. Photodetector 10 First Optical Fiber 11 First connection point 12 Fiber Coupler 13 Second Optical Fiber 14 Second Connection Point 15 Third Connection Point 16 The third optical fiber 17 Optical coupling section 18 Collimating Lens 19 Variable focal length lens 30 Deflection plate 31 Deflection plate 32 Camera 33 Collimating Lens 40 Evaluation control section 41 Evaluation Department 42 Lens control unit 43 Position control section 44 Signal Line 45 Lens control line 46 Position control line 47 Positioner 50 Focusing Lens 51 Pair of Mirrors 60 Multi-hole mask 61 holes 80 Meniscus Lens 81 Concave 82 Convex 83 Circular Hole 90 Beam splitter 91 End of the first optical fiber 92 End of second optical fiber 100 ways 110 Focusing 120 Acquiring distance measurement data 130 Positioning 140 Machining 161 Photodetector 162 Optical Filters A optical axis F focus H Measurement range O Zero Plane T Time coordinate X, Y, Z spatial coordinates

Claims

1. 1. A method for controlled machining of a workpiece, comprising: - focusing the laser beam (3) by means of laser targeting optics (5) to produce a laser focal point (F) at a target location (6) of the workpiece (4) to be machined; - acquiring distance measurement data by means of an optical distance measuring device (7) in order to determine the distance between the target location (6) of the workpiece (4) to be machined and the laser targeting optics (5); - machining the target location (6) of the workpiece (4) to be machined with the focused laser beam (3); the distance measuring device (7) is configured as an optical confocal distance measuring device with a measurement light source (8) for generating measurement light and a variable focal length measuring light optical system (19), the method comprising varying a focal length of the variable focal length measuring light optical system (19) over time to obtain distance measurement data at different focal length values ​​of the variable focal length measuring light optical system (19), the laser beam (3) reflected by the workpiece (4) and / or machining light generated during machining of the workpiece (4) is detected, characterized in that the variable focal length measuring light optical system (19) comprises a variable focal length lens (19).

2. 2. The method according to claim 1, wherein the distance between the focus (F) of the laser and the workpiece (4) is varied and the presence of machining light is registered in association with the distance between the focus (F) of the laser and the workpiece (4), the distance being determined by the distance measuring device (7).

3. 3. The method according to claim 1 or 2, wherein the power of the laser beam (3) is varied to determine a critical power at which machining light first occurs.

4. 4. The method according to claim 3, further comprising changing the power of the laser beam (3) for different distances between the workpiece (4) and the focal point (F) of the laser, and determining for each distance the critical power at which machining light first occurs.

5. The method according to any of the preceding claims, further comprising positioning the workpiece (4) to be machined relative to a focal point (F) of the laser based on the acquired distance measurement data.

6. 6. The method according to claim 1, wherein obtaining the distance measurement data comprises detecting an intensity of measurement light reflected back from the workpiece (4) being machined, and the distance is determined based on a change over time in the intensity of the measurement light reflected back from the workpiece (4) being machined.

7. 7. The method according to claim 1, wherein varying the focal length of the variable focal length measuring light optical system (19) over time comprises adjusting, in particular periodically adjusting, the focal length of the variable focal length measuring light optical system (19) in order to obtain the distance measurement data at a plurality of different focal lengths of the variable focal length measuring light optical system (19).

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

9. The method according to any of the preceding claims, wherein the acquisition of distance measurement data is performed at a plurality of measurement points at the target location (6).

10. 10. The method according to claim 9, wherein the acquisition of distance measurement data at a plurality of measurement points is performed consecutively within one measurement cycle, the measurement points being arranged along a scan path at the target location (6).

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

12. 10. The method of claim 9, wherein the acquisition of the distance measurement data at a plurality of measurement points is performed substantially simultaneously, and the determination of the distance is based on the distance measurement data at the plurality of measurement points physically averaged.

13. 13. The method according to claim 12, wherein the measurement light is split into a plurality of partial measurement light by at least one aperture mask (60) having a plurality of holes (61) for simultaneous acquisition of the distance measurement data at a plurality of measurement points.

14. The method of claim 13 , wherein the partial measurement light is detected simultaneously on a shared photodetector.

15. 1. An apparatus for controlled machining of a workpiece, comprising: - a laser source (2) for generating a laser beam (3) for machining said workpiece (4) to be machined; - laser targeting optics (5) for focusing said laser beam (3) onto a laser beam focus (F) at a target location (6) of said workpiece (4) to be machined; a distance measuring device (7) for determining the distance between the target location (6) of the workpiece (4) to be machined and the laser targeting optics (5) based on distance measurement data acquired by said distance measuring device (7); - a positioning device (47) for positioning the workpiece to be machined relative to the laser light focus (F); an evaluation and control unit (40) configured to evaluate the acquired distance measurement data and to control the placement device (47) on the basis of the acquired distance measurement data; the distance measuring device (7) is configured as an optical confocal distance measuring device with a measurement light source (8) for generating measurement light and a variable focal length measuring light optics, the variable focal length measuring light optics being capable of varying a focal length of the variable focal length measuring light optics over time in order to obtain the distance measurement data at different focal length values ​​of the variable focal length measuring light optics, the laser beam (3) reflected by the workpiece (4) and / or machining light generated during machining of the workpiece (4) being detectable, characterized in that the variable focal length measuring light optics (19) comprises a variable focal length lens (19).

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

17. 17. Apparatus according to claim 15 or 16, wherein the distance measuring device (7) comprises a photodetector (9) for detecting the intensity of measuring light reflected back from the workpiece (4) to be machined, and is configured so that the distance can be determined based on the change over time in the detected intensity of the measuring light reflected back from the workpiece (4).

18. 18. Apparatus according to any of claims 15 to 17, comprising a second detector, in particular a further light detector (161), said second detector being configured such that the presence of machining light can be detected.

19. 20. The apparatus of claim 18, further comprising an optical filter (162) having wavelength-dependent reflectivity configured to reflect machining light within a particular spectral range while transmitting substantially all of the measurement light.

20. 18. The apparatus of claim 17, wherein the measurement light source (8) can be turned on and off, and the light detector (9) is configured to detect the presence of machining light while the measurement light source is off.

21. 21. Apparatus according to any one of claims 15 to 20, wherein the measurement light source (8) is configured as a broadband infrared light source, in particular as a near infrared light source.

22. 22. Apparatus according to any of claims 15 to 21, wherein the focal length of the variable focal length measuring light optics (19) is adjustable, in particular periodically adjustable.

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

24. 24. Apparatus according to any of claims 15 to 23, wherein the apparatus (1) comprises at least one aperture mask (60) having a plurality of apertures (61) for splitting the measurement light into a plurality of partial measurement light.

25. The apparatus (1) according to claim 24, wherein the apparatus (1) comprises an optical fiber (16) having an optical coupling point (17) for the measurement light to enter and exit, and the at least one porous mask (60) is arranged at the optical coupling point (17).

26. 26. The apparatus of claim 25, wherein the porous mask (60) comprises a partially reflective layer to act as a reflective filter that reflects only the machining light and not the laser light and the measurement light.

27. The apparatus of claim 25 or 26, comprising a first optical fiber (10) having a light exit end (91) and a second optical fiber (13) having a light input end (92), a first porous mask (60) being disposed at the light exit end (91) and a second porous mask (60) being disposed at the light input end (92).

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