Method and apparatus for dynamically positioning a plurality of laser beams on a target plane

Abstract

An apparatus for dynamically positioning a plurality of laser beams (2) on a target plane (5) has at least one dynamic deflection means (3), by means of which the laser beam (2) can be directed onto the target plane (5) and guided across one region of the target plane (5). In this case, the dynamic deflection means (3) comprises an assembly (9) of a plurality of one-axis and / or two-axis microscanners (10) that can be driven independently of one another. The number of microscanners (10) is selected such that each laser beam (2) is directed onto the target plane (5) via a different microscanner (10), and the laser beam (2) is guided to the assembly (9). In this case, the microscanner (10) has a mirror with an elliptical or rectangular mirror shape, and the microscanner (10) is arranged such that in the zero position of the microscanner (10), the major axis of the elliptical or rectangular mirror shape lies in the plane of incidence of the laser beam (2) incident on each microscanner (10).

Description

Technical Field

[0001] The present invention relates to an apparatus for dynamically positioning a plurality of laser beams on a target plane, the apparatus having at least one dynamic deflection means by which the laser beams can be directed onto the target plane and guided across each one region of the target plane. The present invention also relates to a corresponding method that can be implemented using this apparatus.

[0002] In laser material processing, the available laser output of the laser beam source used is often higher than the output that can be effectively utilized for processing with the laser beam. One possibility for efficiently utilizing the available laser output is to split the original laser beam into two or more partial beams having corresponding smaller individual outputs. However, in this case, correct positioning on the target plane, especially on the workpiece to be processed, must be ensured for each partial beam. Fixing the individual partial beams relative to each other only once and moving the workpiece relative to this multi-beam matrix is usually too slow to obtain sufficient process throughput. Therefore, there is a need for a possibility to position the multi-beam matrix very (highly) dynamically on the workpiece without compromising the positioning accuracy of the individual beams. Furthermore, in order to generate an aperiodic patterning in the workpiece, to generate a non-flat machining surface, to machine an edge region, or to dynamically achieve a specific temperature profile as appropriate, it may be necessary to adjust the multi-beam matrix during machining. This adjustment may be related to the number of partial beams, the relative arrangement of the partial beams with respect to each other, the ratio of the movement vectors of the individual beams with respect to each other, and / or the shape of the individual partial beams.

[0003] Prior Art According to the latest laser positioning systems equipped with a mirror rotatable via a galvanometer and a focusing optical system, it is possible to position a laser beam extremely dynamically at a scanning speed of 10 m / s or more at a normal focal length up to 200 mm. These systems can also be used in combination with a multi-beam matrix, but in that case, only the multi-beam matrix as a whole can be positioned or guided. In this case, a plurality of laser beams are directed onto a target plane and guided across the target plane via generally two rotatable or tiltable mirrors arranged one behind the other of the dynamic deflection means. However, these systems cause distortion of the multi-beam matrix depending on the deflection angle, and thus cause positioning errors of the individual beams in the target plane. Such positioning errors reduce the achievable accuracy and / or throughput of the processing process. This is because the available deflection angle of the laser positioning system is significantly limited with a given accuracy.

[0004] From “Highly dynamic positioning of individual laser beams in a multi-beam system for laser surface processing” by O. Hofmann et al., Procedia CIRP 2020; 94: 812-816, it is proposed to optically compensate for the distortion of the multi-beam matrix when a latest laser positioning system for four partial beams is used, which is inserted between the means for generating the multi-beam matrix and the dynamic deflection means. This is a combination of a rotatable parallel plane plate and a focus shifter. However, with this approach, further adjustment of the multi-beam matrix is not possible. Extending this approach to more than four partial beams is already not realistic for space reasons alone.

[0005] Alternatively, it is also possible to use one completely dedicated positioning system for each individual beam. This enables accurate and independent positioning of multiple individual beams, but the cost and required space also become significantly greater, and furthermore, it is not possible to meaningfully scale for a large number of partial beams.

[0006] Furthermore, systems for dynamically shaping optical and laser beams are known that enable generation of almost any output density distribution in a specified target plane. Two key technologies in this field are the so-called Digital-Micromirror-Devices (DMD) and liquid crystal systems (liquid crystal (LC) or liquid crystal on silicon (LCOS)), and such technologies are described, for example, in Texas Instruments, Laser Power Handling for DMD’s: DLPA027, available from: www.ti.com / lit / wp / dlpa027 / dlpa027.pdf and 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, 594-597.

[0007] The DMD consists of a matrix of micromirrors approximately 10 μm in size, and these micromirrors can be tilted very (highly, extremely) dynamically to one of two possible positions. The DMD is generally used such that light from a light source is projected onto a target (e.g., a screen) at one tilt position and incident on a beam trap at the other tilt position. Each micromirror corresponds to one pixel of an image projection or video projection and can be switched on and off independently. To vary the (apparent) brightness of a pixel, it is possible to resonantly tilt the micromirror at a frequency far exceeding the eye's flicker fusion frequency to adjust (match) the average brightness of the pixel. However, the processes in laser material processing proceed on a much shorter time scale. Thus, direct laser beam shaping using a DMD is possible, but only binary intensity levels are possible for each pixel. Since these systems were developed especially for video projection, they are generally only suitable for laser powers below 150 W or much smaller than that.

[0008] A liquid crystal system utilizes the birefringence 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 involves losses. Each local decrease in amplitude results in a loss of the associated optical output. Therefore, the adjustment of the phase of light, which is almost lossless, is more widespread. By skillfully adjusting the phase, the output density distribution can be adjusted almost arbitrarily on a plane located behind the liquid crystal system. By using a so-called diffractive phase distribution, a multi-beam matrix with almost arbitrary beam positions can also be realized. However, in diffractive beam splitting, almost always, unwanted artifacts in the form of unwanted diffraction orders that cannot be completely suppressed also occur. In the case of static beam splitting, for example, this artifact can be filtered out using a mask, but in the case of dynamic beam splitting, this is not always possible. Furthermore, the liquid crystal system has so far been limited to a refresh rate of up to 120 Hz. Additionally, it is important to specify the phase required for the desired target distribution, and this must be done when dynamically adjusting the output density distribution or the multi-beam matrix for each intermediate distribution or intermediate position.

[0009] German Patent Application Publication No. 102020107760 discloses a laser processing apparatus in which an array of a plurality of micromirror scanners is used to dynamically deflect partial beams. U.S. Patent No. 6515257 utilizes an array of a plurality of micromirrors to generate through openings or vias in chips.

[0010] The object of the present invention is a method and an apparatus for independently and dynamically positioning a plurality of laser beams, in particular the individual beams of a multi-beam laser system, on a target plane, the method and apparatus enabling independent and highly dynamic positioning with high positioning accuracy while maintaining beam quality, in particular with a small required space.

[0011] Disclosure of the Invention The above object is solved by the apparatus according to claim 1 and the method according to claim 9. Advantageous embodiments of the apparatus and the method are the subject of the dependent claims or can be obtained from the following description and examples.

[0012] The proposed device for dynamically positioning multiple laser beams independently on a target plane has at least one dynamic deflection means by which the laser beams can be directed onto the target plane and guided (induced) across one region each of the target plane. The device preferably also has means for generating the laser beams. The multiple laser beams may be, for example, partial beams of a multi-beam laser system in which a static optical system divides one or more laser beams from one or more laser beam sources into a desired number of partial beams. The target plane may be, for example, the workpiece surface of a workpiece to be machined by the laser beams. The laser beams may of course also be generated by a plurality of individual separate laser beam sources, such as laser diodes, and used in the proposed device without further beam splitting. In the proposed device, the dynamic deflection means comprises an assembly of a plurality of, preferably two-axis, microscanners that can be driven independently of each other. In this case, the number of microscanners is selected such that each laser beam is directed onto the target plane via a different microscanner, and the laser beams are guided to the assembly. The device is characterized in that the microscanners have mirrors with an elliptical or rectangular mirror shape each having a major axis and a minor axis, and the microscanners are arranged such that in the zero position (zero pose) of the microscanner, the major axis of the elliptical or rectangular mirror shape lies in the plane of incidence of the laser beam incident on each microscanner.

[0013] As is well known, a micro scanner should be understood as a micro optoelectromechanical system (MOEMS) from the classification of micro mirror actuators. In this case, preferably, the scanning movement of the individual mirrors in two axes is carried out rotationally, and the mirrors can be continuously tilted within a predetermined angle range in two axes that are preferably perpendicular to each other. The lateral dimension of the mirror of an individual micro scanner is in the millimeter range. Preferably, the mirror of the micro scanner in the proposed device has a lateral dimension (length × width) of at least (0.5 + x) mm × 0.5 mm and preferably has a maximum lateral dimension of 10 mm × (10 - x) mm (where x > 0). Such a micro scanner can be continuously tilted dynamically by more than 20° (extremely, very, highly) about two tilting axes. It is also possible to use a micro scanner with a smaller tilting angle. In this case, a tilting frequency up to 50 kHz can be achieved in a resonant operating mode. A quasi-static operating mode of at least one axis of the micro scanner is also possible depending on the desired application.

[0014] In the device of the present proposal, the microscanners used can be driven individually, so that each laser beam or partial beam can be positioned on the target plane independently of the other laser beams or partial beams. Since the microscanners have small dimensions, the deflection means of the present proposal can be realized in a space-saving manner. In this case, the microscanners are preferably arranged in an array or matrix arrangement consisting of a plurality of rows and columns, either in one plane or in multiple stages. In a preferred embodiment, in this case, the center-to-center distance between the mirrors of the individual microscanners in each row and column is at most twice the length of the extension of the mirrors in that row or column. As a result, based on the reduction in the distance between the individual laser beams or partial beams after passing through the dynamic deflection means, these individual laser beams or partial beams can be focused onto the target plane by a single common focusing optical system if necessary, i.e., for example, by a single lens common to all partial beams.

[0015] By using the present device and the corresponding method, it is possible to generate an arbitrary output density distribution adapted to the process on the target plane based on the possibility of independent positioning of each other. This is especially true for continuous distributions of arbitrary shapes generated by partially overlapping the individual laser beams or partial beams on the target plane. Based on the large dynamics of the microscanners, these output density distributions can be changed or adjusted very quickly during processing, as required when changing, for example, the feed direction, feed speed, local shape of the workpiece to be processed, or the incident angle of the laser beam on the workpiece. By thus adjusting the output density distribution on the target plane extremely (very, highly) dynamically, a constant processing result can be obtained over the entire processing area during laser material processing of the workpiece.

[0016] According to the proposed method in which such dynamic deflection means are utilized to dynamically position a laser beam on a target plane, various different operating modes can be realized, and of course, these various different operating modes can also be arbitrarily combined. Thereby, the laser beam can be positioned in the form of a multi-beam matrix having a fixed beam spacing on the target plane and dynamically guided across the target plane. In this case, the micro scanner is driven such that the laser beam forms a pattern or output density distribution that is guided across at least one region of the target plane without changing. In this case, the laser beam can form a matrix consisting of, for example, a plurality of rows and columns of laser beams, in which adjacent laser beams in each row have a certain distance from each other, and adjacent laser beams in each column have a certain distance from each other. In this case, it is possible to directly compensate for the distortion of the multi-beam matrix caused, for example, by the focusing optical system or by the inclined or curved target plane via the micro scanner. It is also possible to realize, depending on the application, the dynamic and completely independent positioning and movement of partial beams on the target plane. Therefore, these partial beams can be utilized to process one predetermined geometry together independently of each other, that is, in this case, each partial beam processes one section of the entire geometry. Furthermore, the method enables the generation, adjustment (conformity), and positioning of the desired output density distribution on the target plane by arranging and / or overlapping a plurality of partial beams.

[0017] Preferably, the means for generating a laser beam (as an optional component of the device of the present proposal) is configured to emit at least four laser beams directed onto a target plane via dynamic deflection means. In this case, the device can be arbitrarily scaled, that is, by appropriately configuring the means for generating the laser beam and correspondingly expanding an array consisting of a plurality of microscanners, the number of laser beams generated and deflected can be easily increased.

[0018] In an advantageous embodiment where each laser beam is a partial beam generated from one laser beam source by appropriate beam splitting means, in order for these partial beams to hit the array of microscanners at the same angle, between the beam splitting means and the dynamic deflection means, preferably optical means for parallelizing the laser beam (and also for collimating if necessary) are provided. Typically, diffractive beam splitting means do not generate partial beams that are parallel to each other.

[0019] In the device and method of the present proposal, the mirrors of the microscanners alternatively have an elliptical shape, and the microscanners are oriented such that the major axis of the elliptical shape is located in the incident plane of each laser beam in the zero position of the microscanner (i.e., the state where the mirror has not been displaced). Thereby, the microscanners can be arranged closer to each other in a direction perpendicular to the incident plane than in the case of circular or square mirrors. Instead of the elliptical shape, it is similarly possible to utilize a corresponding rectangular shape where the length is greater than the width (with sharp or rounded edges).

[0020] The apparatus and corresponding method of this proposal enable extremely dynamic and independently scalable positioning of multiple laser beams or partial beams in a multi-beam system. Since microscanners are now already less expensive than 2D deflection means based on galvanometers, the present apparatus is cost-effective compared to solutions using multiple individual separate laser positioning systems. Furthermore, the apparatus and corresponding method of this proposal can often operate using only a single focusing optical system, i.e., using only one optical lens or combination lens common to all laser beams or partial beams. Moreover, there is an analytical, and in many cases even a linear, relationship between the deflection angle of each micromirror and the beam position in the target plane. Therefore, the required deflection angle can be calculated directly from the desired beam position. That is, the time-consuming optimization for all possible combinations from individual beam positions, as in the case of the diffractive approach, is not necessary in the case of the present invention. The apparatus of this proposal enables significantly shorter switching times compared to known liquid crystal systems.

[0021] Furthermore, by illuminating the individual micromirror scanners with a defined target, heating or damage to the electronic devices provided under or between the mirrors is avoided. Furthermore, in order to further increase the available laser output, the micromirror scanners can be provided with the latest reflective coatings. In contrast, in the case of DMDs, the individual mirrors are made of polished metal, generally aluminum, and thus achieve only a reflectivity of about 90%, which significantly reduces the available laser output. Therefore, the apparatus and corresponding method of this proposal also enable dynamic laser beam shaping at laser powers far exceeding the damage thresholds of beam shaping elements such as DMDs or liquid crystal systems.

[0022] In the following, the apparatus and corresponding method of this proposal will be explained in more detail again, based on examples and in connection with the drawings.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

[0024] Embodiments for Carrying Out the Invention An example of the principle structure of the proposed apparatus is shown in FIG. 1. This apparatus has (optional) means 1 for generating a plurality of laser beams 2, dynamic deflection means 3 for dynamically deflecting the laser beams two-dimensionally, and (if necessary) focusing optics 4. By the dynamic deflection means 3, the laser beams 2 are directed onto the target plane 5, and the laser beams 2 are guided across this target plane, which in this example is the surface of the illustrated substrate 6, for example the surface of the workpiece to be processed. The focusing optics are used, if necessary, for focusing the laser beams onto the target plane.

[0025] In this device, the generation of a plurality of laser beams may be carried out by using a plurality of lasers, for example semiconductor lasers, or may also be carried out by using only one (or more) lasers, and the laser beam(s) of this (or these) laser(s) is / are split into a plurality of partial beams via beam splitting means. Fig. 2 shows an example in this regard. In this example, means 1 for generating a plurality of laser beams is formed by a laser not shown in this drawing and a subsequent beam splitter 7, and by this beam splitter 7, the laser beam 13 of the laser is split into a desired number of partial beams 2. This beam splitter 7 is a static optical system in this example, for example a diffractive optical element as shown in Fig. 2, or a mask as shown in Fig. 3. Instead of this, a dynamically adjustable (adaptive) beam splitter (for example, LCOS) is also possible. According to such a dynamically adjustable (adaptive) beam splitter, for example, individual beams can be switched on and off with a much smaller dynamics than that of the deflection means. In the case of the diffractive optical element in Fig. 2, the generated partial beams 2 do not extend parallel, and are appropriately directed parallel via optical means 8 and directed onto the dynamic deflection means 3. This dynamic deflection means 3 is formed by a micro scanner matrix 9 as shown in Figs. 2 and 3 in the device proposed herein. In this case, each partial beam 2 preferably hits the center of one of the micro scanners 10 of the micro scanner 10, or the center of a mirror that can be continuously tilted two-dimensionally of the micro scanner 10. The plane of the drawing represents the incident plane in Figs. 2 and 3. The micro mirrors of the micro scanner 10 have a rectangular shape in these examples, and the major axis of this rectangular shape is located in this incident plane. In that case, the micro mirror has a shorter extension length in the direction perpendicular to the plane of the drawing. The illustrations in Figs. 2 and 3 are only schematic, and therefore, the slight spacing between the micro scanners 10 is not shown. In this case, the individual micro scanners can be driven independently of each other.Downstream of the micro scanner matrix 9, additional optical elements can be arranged, for example, to focus the multi-beam matrix onto the target plane 5. In FIGS. 2 and 3, a single common focusing optical system 4 is shown for this purpose.

[0026] When using a mask 11 for beam splitting as schematically shown in FIG. 3, generally, means for collimating the individual partial beams 2 can be omitted. This is because the individual partial beams 2 already extend parallel to each other. For this purpose, the laser beam 13 from the laser beam source is appropriately widened and correspondingly collimated before hitting the mask 11 as shown by the beam shape of the laser beam 13 in FIG. 3.

[0027] In the proposed device and the corresponding method, by using the individual micro scanners 10, each partial beam 2 can be positioned and moved very (extremely) dynamically in the target plane 5 independently of the other partial beams 2. In this case, the number of generated partial beams 2 is not limited to the number shown in the drawings. FIGS. 2 and 3 show three or four partial beams in the plane of the drawing, but in the case of a rectangular matrix with the same number of mirrors in each row and column, actually nine or sixteen partial beams are generated in space respectively. This number can be arbitrarily scaled by increasing the number of micro scanners 10 in the micro scanner matrix 9 if more partial beams are correspondingly generated. It is of course also possible to generate partial beams for a non-rectangular matrix.

[0028] The device can operate in various different operating modes, and these various different operating modes can also be arbitrarily combined. Figure 4 very schematically shows three operating modes in this regard, and in these operating modes, the laser spots 12 generated on the target plane 5 and the exemplary movement directions of these laser spots 12 are shown. In the first drawing of this figure, the dynamic positioning of a multi-beam matrix consisting of four partial beams with a fixed beam spacing in the target plane is carried out. In this case, for example, the distortion of the multi-beam matrix caused by the focusing optical system or by the inclined or curved workpiece surface can be compensated while moving this multi-beam matrix as indicated by the arrows in the target plane.

[0029] In the central drawing of this figure, an operating mode is shown in which the individual partial beams or laser spots 12 are dynamically positioned completely independently of each other and are moved in the target plane. Also in this case, the movement is exemplarily shown by the arrows. Therefore, a plurality of mutually independent partial beams can be used to machine a predetermined geometry together, and in this case, each partial beam is utilized to machine one section of the entire geometry.

[0030] As schematically shown in the right drawing of this figure, it is also possible to carry out the targeted generation, adjustment (adaptation), and positioning of the output density distribution in the target plane by arranging and / or overlapping the partial beams or the laser spots 12 of the partial beams in the target plane 5. In that case, the output density distribution generated by arranging or partially overlapping the laser spots 12 of a plurality of laser beams in the target plane, for example, to achieve a specific temperature profile, can be moved across the target plane, for example, in the direction indicated by the arrows, and in some cases, it can also be corrected while moving.

Explanation of Reference Signs

[0031] 1 Means for generating a plurality of laser beams 2 Laser beam or sub - beam 3 Dynamic deflection means 4 Focusing optical system 5 Target plane 6 Substrate 7 Beam splitter 8 Optical means for parallelization 9 Micro - scanner matrix 10 Micro - scanner 11 Mask 12 Laser spot 13 Laser beam

Claims

1. An apparatus for dynamically positioning a plurality of laser beams (2) on a target plane (5), said apparatus having at least one dynamic deflection means (3) by means of which the laser beam (2) can be directed onto the target plane (5) and the laser beam (2) can be guided across one region of the target plane (5), said dynamic deflection means (3) comprising an assembly (9) of a plurality of single-axis and / or two-axis microscanners (10) which are each independently drivable, the number of microscanners (10) being selected such that each laser beam (2) is directed onto the target plane (5) via a different microscanner (10), and the laser beam (2) being guided to the assembly, wherein in the apparatus, the microscanner (10) has a mirror with an elliptical or rectangular mirror shape, and the microscanner (10) is arranged such that in the zero position of the microscanner (10), the major axis of the elliptical or rectangular mirror shape lies in the plane of incidence of the laser beam (2) incident on each respective microscanner (10). Apparatus, characterized in that.

2. said apparatus having means (1) for generating the laser beam (2). Apparatus according to claim 1, characterized in that.

3. The means (1) for generating the laser beam is configured to emit at least four laser beams (2) directed onto the target plane (5) via the dynamic deflection means (3). Apparatus according to claim 2, characterized in that.

4. The microscanners (10) are arranged in an array or matrix arrangement consisting of a plurality of rows and columns, and the center-to-center distance between the mirrors of the individual microscanners in each row and column is arranged to be at most twice the extension length of the mirror in that row or column. Apparatus according to any one of claims 1 to 3, characterized in that.

5. The means (1) for generating the laser beam is formed from a plurality of laser beam sources arranged adjacent to each other. Apparatus according to claim 2, or claim 3 or 4 which cites claim 2, characterized in that.

6. The means (1) for generating the laser beam has one or more laser beam sources and one or more beam splitting means (7, 11). The device according to claim 2, or claim 3 or 4 which cites claim 2.

7. An optical means (8) for collimating the laser beam (2) is arranged between the means (1) for generating the laser beam and the dynamic deflection means (3). The device according to claim 2, or any one of claims 3 to 6 which cites claim 2.

8. One focusing optical system (4) common to all the laser beams (2) is arranged between the dynamic deflection means (3) and the target plane (5). The device according to any one of claims 1 to 7.

9. A method for dynamically positioning a plurality of laser beams (2) on a target plane (5), wherein the laser beam (2) is directed onto the target plane (5) by the dynamic deflection means (3) according to any one or more of claims 1 to 8, the number of the microscanners (10) is selected such that each laser beam (2) is directed onto the target plane (5) via a different microscanner (10), and the laser beam (2) is guided through the dynamic deflection means. Method.

10. The microscanner (10) is driven such that the laser beam (2) forms a pattern or an output density distribution that is guided without change over at least one region of the target plane (5) on the target plane (5). The method according to claim 9, characterized in that.

11. The laser beam (2) forms a matrix consisting of columns and rows of a plurality of laser beams on the target plane (5), in the matrix, adjacent laser beams in each row have the same interval from each other, and adjacent laser beams in each column have the same interval from each other. The method according to claim 10, characterized in that.

12. The microscanner (10) is driven such that the plurality of laser beams (2) are guided completely independently of each other over the target plane (5). The method according to claim 9, characterized in that.

13. While the laser beam (2) is being guided across the target plane, the micro scanner (10) is driven so that the laser beam (2) forms a pattern or output density distribution on the target plane (5) that changes according to a preset. Method according to claim 9, characterized in that.

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