Method and device for the dynamic positioning of a plurality of laser beams on a target plane

Abstract

A device for the dynamic positioning of a plurality of laser beams (2) on a target plane (5) has at least one dynamic deflection device (3) with which the laser beams (2) can be directed onto the target plane (5) and guided over a respective area of the target plane (5). The dynamic deflection device (3) has an arrangement (9) of a plurality of single-axis and / or dual-axis microscanners (10) which can each be controlled independently of one another. The number of microscanners (10) is selected and the laser beams (2) are guided in the arrangement (9) such that each laser beam (2) is directed onto the target plane (5) via a different microscanner (10). The microscanners (10) have mirrors with an oval or rectangular mirror shape and are arranged such that in a zero position of the microscanner (10), a long axis of the oval or rectangular mirror shape lies in a plane of incidence of the laser beam (2) incident on the respective microscanner (10).

Description

[0001] Method and device for dynamic

[0002] Positioning of multiple laser beams on a

[0003] Target level

[0004] Technical application area

[0005] The present invention relates to a device for dynamically positioning a plurality of laser beams on a target plane, which device has at least one dynamic deflection device with which the laser beams can be directed onto the target plane and guided over a respective region of the target plane. The invention also relates to a corresponding method that can be implemented with the device.

[0006] In laser material processing, the available laser power of the laser beam source used is often higher than the power that can be effectively used for processing with a single laser beam. One option for efficiently using the available laser power is to split the original laser beam into two or more partial beams with correspondingly lower individual power levels. However, the correct positioning of each partial beam on the target plane, particularly on a workpiece to be processed, must be ensured. A one-time, fixed positioning of the individual partial beams relative to one another and movement of the workpiece relative to this multi-beam matrix is ​​usually too slow for sufficient process throughput. A method for highly dynamic positioning of the multi-beam matrix on the workpiece is therefore required without the positioning accuracy of the individual beams suffering.The creation of non-periodic structures in the workpiece, non-planar machining surfaces, the machining of edge areas, or the dynamic, site-specific achievement of specific temperature profiles may also require an adjustment of the multi-beam matrix during machining. This adjustment can relate to the number of partial beams, the arrangement of the partial beams relative to one another, the motion vectors of the individual beams relative to one another, and / or the shape of the individual partial beams.

[0007] State of the art

[0008] Modern laser positioning systems with mirrors that can be rotated via galvanometers and focusing optics enable the highly dynamic positioning of laser beams with scanning speeds of > 10 m / s and typical focal lengths of up to 200 mm. These systems can also be used in combination with multi-beam matrices, but then only allow the positioning or guidance of the multi-beam matrix as a whole. The multiple laser beams are directed onto the target plane and guided across the target plane via two rotatable or tiltable mirrors of a dynamic deflection device that are usually arranged one behind the other. However, depending on the deflection angle, these systems lead to a distortion of the multi-beam matrix and thus to positioning errors of the individual beams in the target plane.These positioning errors reduce the achievable precision of the machining process and / or the throughput, since for a given precision the usable deflection angle of the laser positioning system is severely limited.

[0009] From 0. Hofmann et al., “Highly dynamic positioning of individual laser beams in a multi-beam system for laser surface processing", Procedia CIRP 2020; 94: 812- 816, an optical compensation of the distortion of multi-beam matrices when using modern laser positioning systems for four partial beams is proposed. This is used between the device for generating the multi-beam matrix and the dynamic deflection device. This is a combination of rotatable plane-parallel plates and focus shifters. However, further adjustments of the multi-beam matrix are not possible with this approach. An extension of this approach to more than four partial beams is also not realistic for reasons of space alone.

[0010] Alternatively, a completely separate positioning system could be used for each individual beam. This allows for precise and independent positioning of the individual beams, but also leads to significantly higher costs and increased space requirements, and is not scalable for a large number of partial beams.

[0011] Furthermore, systems for dynamic light and laser beam shaping are known, which enable the generation of almost arbitrary power density distributions in a given target plane. The two key technologies in this area are so-called digital micromirror devices (DMDs) and liquid crystal systems (liquid crystal (LC) or liquid crystal on silicon (LCOS)), as described, for example, in Texas Instruments, Laser Power Handling for DMDs: DLPA027, available from: www. ti . com / lit / wp / dlpa027 / dlpa027.pdf, and in G. Zhu et al., "Thermal and optical performance characteristics of a spatial light modulator with high average power picosecond laser exposure applied to materials processing applications", Procedia CIRP 2018; 74, 594 to 597.

[0012] DMDs consist of a matrix of approximately 10 m micromirrors that can be tilted into one of two possible positions with high dynamic range. DMDs are typically deployed in such a way that the light from a light source is projected onto the target (e.g., a screen) in one tilted position, and falls into a beam trap in the other tilted position. Each micromirror corresponds to a pixel of the image or video projection and can be switched on and off independently. To change the (apparent) brightness of a pixel, the micromirrors can be resonantly tilted at frequencies well above the flicker fusion frequency of the eye in order to adjust the average brightness of a pixel. However, processes in laser material processing operate on significantly shorter timescales. Direct laser beam shaping with DMDs is possible, but therefore only allows binary intensity levels for each pixel.Since these systems were primarily developed for video projection, they are generally only suitable for laser powers <150 W or significantly lower. Liquid crystal systems use the birefringent property of liquid crystals to locally and continuously adjust the amplitude and / or phase of light. By adjusting the amplitude, a laser beam can be directly shaped and / or split into a multi-beam matrix. However, this process is lossy. Every local reduction in amplitude leads to a loss of the associated light power. Almost loss-free adjustment of the phase of the light is therefore more widespread. By cleverly adjusting the phase, the power density distribution in a plane behind the liquid crystal system can be adjusted almost arbitrarily. Using so-called diffractive phase distributions, multi-beam matrices with almost any beam position can also be realized.However, with diffractive beam splitting, unwanted artifacts in the form of unwanted diffraction orders almost always occur, and these cannot be completely suppressed. With static beam splitting, these can be filtered out, for example, using a mask; with dynamic beam splitting, however, this is not always possible. Liquid crystal systems are currently limited to maximum repetition rates of 120 Hz. Furthermore, determining the phase required for a desired target distribution is not trivial and must be performed for each intermediate distribution or intermediate position when dynamically adapting the power density distribution or multi-beam matrix.

[0013] The DE 10 2020 107 760 Al of fenbart a

[0014] Laser processing device in which an array of micromirror scanners is used for dynamic deflection of the partial beams. US 6515257 B1 uses an array of micromirrors to create through-openings or vias in chips.

[0015] The object of the present invention is to provide a method and a device for the independent dynamic positioning of several laser beams, in particular of individual beams of a multi-beam laser system, on a target plane, with which an independent highly dynamic positioning with high positioning accuracy, preservation of the beam quality and, above all, with little space requirement is made possible.

[0016] Description of the invention

[0017] This object is achieved by the device and the method according to claims 1 and 9. Advantageous embodiments of the device and the method are the subject of the dependent claims or can be found in the following description and the exemplary embodiments.

[0018] The proposed device for the independent dynamic positioning of a plurality of laser beams on a target plane has at least one dynamic deflection device with which the laser beams can be directed onto the target plane and each guided over a region of the target plane, and preferably also a device for generating the laser beams. The plurality of laser beams can, for example, be the partial beams of a multi-beam laser system in which a static optical system splits the laser beam(s) from one or more laser beam sources into the desired number of partial beams. The target plane can, for example, be a workpiece surface of a workpiece to be machined using laser radiation. The laser beams can of course also be generated by a plurality of separate laser beam sources, for example laser diodes, and used in the proposed device without further beam splitting.In the proposed device, the dynamic deflection device has an arrangement of several, preferably two-axis, microscanners, which can each be controlled independently of one another. The number of microscanners is selected and the laser beams in the arrangement are guided in such a way that each laser beam is directed onto the target plane via a different microscanner. The device is characterized in that the microscanners have mirrors with an oval or rectangular mirror shape, each with a long and short axis, and are arranged in such a way that when the microscanners are in a zero position, the long axis of the oval or rectangular mirror shape lies in a plane of incidence of the laser beam incident on the respective microscanner.

[0019] A microscanner is understood in a known manner to be a micro-opto-electro-mechanical system (MOEMS) from the class of micromirror actuators. The scanning movement of an individual mirror in preferably two axes takes place rotationally, with the mirror being continuously tiltable in an angular range in the two axes, which are preferably perpendicular to one another. The lateral dimensions of the mirrors of the individual microscanners are in the millimeter range. In the proposed device, the mirrors of the microscanners preferably have lateral dimensions (length x width) of at least (0.5 + x) mm x 0.5 mm and preferably maximum lateral dimensions of 10 mm x (10 - x) mm (where x > 0). Microscanners of this type can be tilted continuously by > 20 ° around the two tilt axes in a highly dynamic manner. Microscanners with smaller tilt angles can also be used.In resonant mode, sweep frequencies of up to 50 kHz can be achieved. Quasi-static operation of at least one axis of the microscanner is also possible, depending on the desired application.

[0020] Because the microscanners used in the proposed device can be controlled separately, each laser beam or partial beam can be positioned independently of the others on the target plane. The microscanners are small in size, so that the proposed deflection device can be implemented in a space-saving manner. The microscanners are preferably arranged in an array or matrix-like arrangement comprising several rows and columns in one plane or in several stages. In a preferred embodiment, the center-to-center distances of the mirrors of the individual microscanners in each row and column are at most twice the extent of the mirrors in this row or column. Due to the resulting small distance between the individual laser beams or partial beams after passing through the dynamic deflection device, these can, if required, be equipped with a common focusing optics, for example.a single lens common to all partial beams, into the target plane.

[0021] Due to the independent positioning capabilities, any process-adapted power density distributions can be generated in the target plane using the device and the associated method. This particularly applies to coherent distributions of any shape, which are generated by partially overlapping the individual laser beams or partial beams in the target plane. Due to the high dynamics of the microscanners, these power density distributions can be changed or adapted very quickly during processing, as is necessary, for example, when the feed direction, feed rate, local shape of a workpiece to be machined, or the angle of incidence of the laser beams on the workpiece change.Through such a highly dynamic adjustment of the power density distribution in the target plane, consistent processing results can be achieved over the entire processing area during laser material processing of a workpiece.

[0022] With the proposed method, in which such a dynamic deflection device is used for the dynamic positioning of the laser beams on the target plane, different operating modes can be implemented, which of course can also be combined as desired. The laser beams can be positioned in the target plane in the form of a multi-beam matrix with fixed beam spacings and guided dynamically over the target plane. The microscanners are controlled in such a way that the laser beams in the target plane form a pattern or a power density distribution which is guided without change over at least one area of ​​the target plane. The laser beams can, for example, form a matrix of columns and rows of laser beams in which neighboring laser beams in each row and neighboring laser beams in each column have a constant distance from one another. Distortions of the multi-beam matrix, e.g.Misalignments caused by the focusing optics or tilted or curved target planes can be compensated for directly using the microscanners. Depending on the application, dynamic and completely independent positioning and movement of the partial beams in the target plane can also be achieved. This allows the partial beams to be used to process a given geometry together, independently of one another: Each partial beam processes a section of the overall geometry. Furthermore, the process enables targeted generation, adjustment, and positioning of power density distributions in the target plane by arranging and / or overlapping the partial beams.

[0023] Preferably, the device for generating the laser beams—as an optional component of the proposed device—is configured to emit at least four laser beams, which are directed onto the target plane via the dynamic deflection device. The device can be scaled as required, i.e., the number of generated and deflected laser beams can be easily increased by appropriately configuring the device for generating the laser beams and enlarging the array of microscanners.

[0024] In an advantageous embodiment, in which the individual laser beams represent partial beams generated from a laser beam source with a suitable beam splitting device, an optical device for parallelizing—and, if necessary, collimating—the laser beams is preferably located between the beam splitting device and the dynamic deflection device so that they impinge on the array of microscanners at the same angle. Typically, diffractive beam splitting devices do not initially generate parallel partial beams.

[0025] In the proposed device and the proposed method, the mirrors of the microscanners have an oval shape in one alternative, whereby the microscanners are oriented such that the long axis of the oval shape lies in the plane of incidence of the respective laser beams when the microscanners are in the zero position (i.e. when the mirrors are not deflected). This allows the microscanners to be placed closer to one another perpendicular to the plane of incidence than would be the case with circular or square mirrors. Instead of the oval shape, a correspondingly rectangular shape - with pointed or rounded edges - with a greater length than width can be used. The proposed device and the associated method enable the highly dynamic, independent and scalable positioning of several laser beams or partial beams of a multi-beam system.The device is cost-effective compared to solutions with multiple separate laser positioning systems, as microscanners are already cheaper than galvanometer-based 2D deflection devices. Furthermore, the proposed device and the associated method can in many cases be operated with just a single focusing optic, i.e. an optical lens or lens combination common to all laser beams or partial beams. Furthermore, there is an analytical and often even linear relationship between the deflection angles of the respective micromirror and the beam position in the target plane. This means that the required deflection angles can be calculated directly from the desired beam positions. Time-consuming optimization for all possible combinations of individual beam positions, as is the case with diffractive approaches, is therefore not necessary with the present invention.The proposed device allows significantly shorter switching times compared to known liquid crystal systems.

[0026] The targeted illumination of the individual microscanner mirrors also prevents heating or damage to the electronics beneath or between the mirrors. In addition, the microscanner mirrors can be provided with modern reflective coatings to further increase the usable laser power. In contrast, the individual mirrors in DMDs are made of polished metal, usually aluminum, and thus only achieve reflection factors of around 90%, which significantly reduces the usable laser power. The proposed device and the associated method therefore also enable dynamic laser beam shaping at laser powers that significantly exceed the damage threshold of beam-shaping elements such as DMDs or liquid crystal systems.

[0027] Short description of the drawings

[0028] The proposed device and the associated method are explained in more detail below using exemplary embodiments in conjunction with the drawings. Herein:

[0029] Fig. 1 is a schematic representation of the basic structure of an embodiment of the proposed device;

[0030] Fig. 2 shows an example of the generation of several laser beams in the proposed device via a beam splitter;

[0031] Fig. 3 shows an example of the generation of multiple laser beams in the proposed device via a mask; and

[0032] Fig. 4 shows three examples of the positioning and movement of the laser beams in a target plane using the proposed method.

[0033] Ways to implement the invention

[0034] An example of the basic structure of the proposed device is shown in Figure 1. The device has an (optional) device 1 for generating a plurality of laser beams 2, a dynamic deflection device 3 for the dynamic two-dimensional deflection of the laser beams and - if required - a focusing optics 4. With the dynamic deflection device 3, the laser beams 2 are directed onto the target plane 5 and guided over this target plane, which in the present example represents the surface of the substrate 6 shown, for example a workpiece to be machined. The focusing optics are used to focus the laser beams onto the target plane if necessary.

[0035] The generation of a plurality of laser beams can take place in the present device either by using a plurality of lasers, for example semiconductor lasers, or by using just one (or more) lasers, the laser beam of which is split into a plurality of partial beams by a beam splitting device. Figure 2 shows an example in which the device 1 for generating a plurality of laser beams is formed by a laser (not shown in this illustration) and a subsequent beam splitter 7, which splits the laser beam 13 of the laser into the desired number of partial beams 2. In the present example, this beam splitter 7 is a static optical system, for example a diffractive optical element as in Figure 2 or a mask as in Figure 3. Alternatively, a dynamically adjustable beam splitter (e.g. LOOS) is also possible, by means of which, for example,with significantly lower dynamics than the deflection device, individual beams can be switched on and off. In the case of the diffractive optical element in Figure 2, the partial beams 2 generated do not run parallel and are suitably aligned in parallel via an optical device 8 and directed onto the dynamic deflection device 3. In the proposed device, this dynamic deflection device 3 is formed by a microscanner matrix 9, as indicated in Figures 2 and 3. Each partial beam 2 preferably strikes the center of one of the microscanners 10 or its two-dimensionally continuously tiltable mirror. The plane of the page represents the plane of incidence in Figures 2 and 3. In these examples, the micromirrors of the microscanners 10 have a rectangular shape whose long axis lies in this plane of incidence. In the direction perpendicular to the plane of the page, the micromirrors then have a smaller extent.The representation in Figures 2 and 3 is only schematic, so the short distances between the microscanners 10 are not shown. The individual microscanners can be controlled independently of one another. Further optical elements, for example, for focusing the multi-beam matrix into the target plane 5, can be arranged downstream of the microscanner matrix 9. A common focusing optics 4 is indicated for this purpose in Figures 2 and 3.

[0036] When using a mask 11 for beam splitting, as schematically shown in Figure 3, a device for parallelizing the individual partial beams 2 can generally be dispensed with, since they already run parallel to one another. For this purpose, the laser beam 13 from the laser beam source is suitably widened and collimated before striking the mask 11, as indicated in Figure 3 by the beam shape of the laser beam 13.

[0037] With the help of the individual microscanners 10, in the proposed device and the associated method, each partial beam 2 can be positioned and moved highly dynamically in the target plane 5 independently of the other partial beams 2. The number of partial beams 2 generated is not limited to the number shown in the figures. Figures 2 and 3 show 3 and 4 partial beams in the page plane, but in the case of a rectangular matrix with the same number of mirrors in each row and column, they actually generate nine and sixteen partial beams in space, respectively. This number can be scaled as required by increasing the number of microscanners 10 in the microscanner matrix 9 to generate a larger number of partial beams. The generation of partial beams for a non-rectangular matrix is ​​of course also possible.

[0038] The device can be operated in different operating modes, which can also be combined as desired. Figure 4 shows three operating modes in a highly schematic manner, in which the laser spots 12 generated on the target plane 5 and their exemplary direction of movement are indicated. In the first representation in this figure, a dynamic positioning of a multi-beam matrix consisting of four partial beams with fixed beam spacings in the target plane takes place. Distortions of the multi-beam matrix, e.g. due to the focusing optics or tilted or curved workpiece surfaces, can also be compensated for during the movement of this multi-beam matrix in the target plane, indicated by the arrows.

[0039] The middle section of the figure shows an operating mode in which the individual partial beams or laser spots 12 are dynamically and completely independently positioned and moved within the target plane. The movement is again indicated by the arrows. This allows the partial beams to work together, independently of one another, on a given geometry, with each partial beam being used to process a portion of the overall geometry.

[0040] A targeted generation, adjustment, and positioning of power density distributions in the target plane can also be achieved by arranging and / or overlapping the partial beams or their laser spots 12 in the target plane 5, as is schematically indicated in the right-hand illustration of the figure. The power density distribution generated there by arranging or partially overlapping the laser spots 12 of a plurality of laser beams, for example to achieve specific temperature profiles, can then be moved across the target plane, for example, in the direction indicated by the arrow, and if necessary, also modified during the movement. List of reference symbols

[0041] I Device for generating multiple laser beams 2 laser or partial beams

[0042] 3 dynamic deflection device

[0043] 4 Focusing optics

[0044] 5 Target level

[0045] 6 Substrate 7 Beam splitter

[0046] 8 optical device for parallelization

[0047] 9 Microscanner matrix

[0048] 10 micro scanners

[0049] II Mask 12 Laser Spot

[0050] 13 Laser beam

Claims

Patent claims Device for dynamically positioning several laser beams (2) on a target plane (5) which has at least one dynamic deflection device (3) with which the laser beams (2) can be directed onto the target plane (5) and guided over a respective region of the target plane (5), wherein the dynamic deflection device (3) has an arrangement (9) of several single- and / or two-axis microscanners (10), which can each be controlled independently of one another, wherein the number of microscanners (10) is selected and the laser beams (2) are guided in the arrangement in such a way that each laser beam (2) is directed onto the target plane (5) via a different microscanner (10), characterized in that the microscanners (10) have mirrors with an oval or rectangular mirror shape and are arranged in such a way that, in a zero position of the microscanners (10), a long axis of the oval or rectangular mirror shape lies in a plane of incidence of the laser beam (2) incident on the respective microscanner (10).Device according to claim 1, characterized in that the device comprises a device (1) for. Generation of the laser beams (2). Device according to claim 2, characterized in that the device (1) for generating the laser beams is designed such that it emits at least four laser beams (2) which are directed onto the target plane (5) via the dynamic deflection device (3). Device according to one of claims 1 to 3, characterized in that the microscanners (10) are arranged in an array- or matrix-like arrangement comprising a plurality of rows and columns such that the center-to-center distances of the mirrors of the individual microscanners in each row and column are at most twice the extent of the mirrors in this row or column. Device according to claim 2 or one of claims 3 or 4 in conjunction with claim 2, characterized in that the device (1) for generating the laser beams is formed from a plurality of laser beam sources arranged next to one another.Device according to claim 2 or one of claims 3 or 4 in conjunction with claim 2, characterized in that the device (1) for generating the laser beams comprises one or more laser beam sources and one or more beam splitting devices. devices (7, 11). Device according to claim 2 or one of claims 3 to 6 in conjunction with claim 2, characterized in that an optical device (8) for parallelizing the laser beams (2) is arranged between the device (1) for generating the laser beams and the dynamic deflection device (3). Device according to one of claims 1 to 7, characterized in that a focusing optic (4) common to all laser beams (2) is arranged between the dynamic deflection device (3) and the target plane (5). Method for dynamically positioning a plurality of laser beams (2) on a target plane (5), in which the laser beams (2) are directed onto the target plane with the dynamic deflection device (3) according to one or more of the preceding claims. (5), wherein the number of microscanners (10) is selected and the laser beams (2) are guided over the dynamic deflection device in such a way that each laser beam (2) is directed onto the target plane (5) via a different microscanner (10). Method according to claim 9, characterized in that the microscanners (10) are controlled in such a way, that the laser beams (2) in the target plane (5) form a pattern or a power density distribution which is guided without change over at least one region of the target plane (5). Method according to claim 10, characterized in that the laser beams (2) in the target plane (5) form a matrix of columns and rows of laser beams, in which adjacent laser beams in each row and adjacent laser beams in each column are the same distance from one another. Method according to claim 9, characterized in that the microscanners (10) are controlled such that the laser beams (2) are guided over the target plane (5) completely independently of one another. Method according to claim 9, characterized in that the microscanners (10) are controlled such that the laser beams (2) in the target plane (5) form a pattern or a power density distribution which changes according to a specification while the laser beams (2) are guided over the target plane.

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