Apparatus and method for generating multiple grooves

Abstract

A laser processing apparatus (100) for generating a plurality of grooves in a surface (110) includes an optical diffraction device (102) mounted to receive laser radiation (104) and subsequently generate output radiation (106), the output radiation (106) having a plurality of intensity maxima. An actuator device (108) is provided to generate relative motion between the output radiation (106) and the surface (110), each intensity maxima generating one of the plurality of grooves.

Description

[Technical Field]

[0001] The subject matter disclosed herein relates to the field of laser processing of surfaces. [Background technology]

[0002] WO 2018 / 197555 discloses a method and device for producing riblets, which are introduced into a surface, in particular into an already painted and cured surface, by laser interference structuring (DLIP - Direct Laser Interference Patterning). Components with riblets produced in this way enable aircraft, ships and wind power plants to operate with relatively low fluid resistance. Summary of the Invention [Problem to be solved by the invention]

[0003] In view of the above situation, there is a need for techniques that allow for laser processing of surfaces with improved properties. [Means for solving the problem]

[0004] This need is taken into account by the subject matter of the independent claims. Preferred embodiments are set out in the dependent claims.

[0005] According to a first aspect of the subject matter disclosed herein, an apparatus, particularly a laser processing apparatus for creating a plurality of grooves in a surface, is disclosed.

[0006] According to an embodiment of a first aspect, a laser processing apparatus for generating a plurality of grooves in a surface is disclosed, the laser processing apparatus comprising: an optical diffraction device mounted to receive laser radiation and subsequently generate output radiation; and an actuator device for generating relative motion between the output radiation and the surface, the output radiation having a plurality of intensity maxima, each intensity maximum (of the plurality of intensity maxima) generating one of the plurality of grooves.

[0007] According to a second aspect of the presently disclosed subject matter, a method, particularly a method for creating a plurality of grooves in a surface, is disclosed.

[0008] According to an embodiment of a second aspect, a method of generating a plurality of grooves in a surface is disclosed, the method comprising the steps of directing a laser beam towards an optical diffractive device that generates output radiation; directing the output radiation towards a surface; and generating relative motion between the output radiation and the surface, the output radiation having a plurality of intensity maxima, each intensity maximum (of the plurality of intensity maxima) generating one of the plurality of grooves.

[0009] Various aspects and embodiments of the subject matter disclosed herein are based on the idea that laser processing of a surface with improved properties can be provided by generating multiple intensity maxima directly from a laser beam (or laser radiation) with an optical diffraction device (e.g., a diffractive optical element or multiple phase plates) and using each of the multiple intensity maxima to generate one of a plurality of grooves.

[0010] According to an embodiment of the first aspect, the laser processing apparatus is configured to provide the functionality of one or more of the embodiments disclosed herein and / or to provide the functionality required for one or more of the embodiments disclosed herein, particularly the embodiments of the first or second aspect.

[0011] According to an embodiment of the second aspect, the method is configured to provide the functionality of one or more of the embodiments disclosed herein and / or to provide the functionality required for one or more of the embodiments disclosed herein, in particular the embodiments of the first or second aspect.

[0012] Further advantages and features of the subject matter disclosed herein will become apparent from the following illustrative description of a presently preferred embodiment, to which the present disclosure is not limited. The individual figures of the drawings of this application are merely schematic and are not necessarily drawn to scale. Rather, in order to clarify some embodiments of the subject matter disclosed herein, relative dimensions and angles may not be displayed to scale. [Brief explanation of the drawings]

[0013] [Figure 1] 1 illustrates a schematic diagram of a laser processing apparatus according to an embodiment of the subject matter disclosed herein. [Figure 2] 2 shows the surface of the object of FIG. 1 as viewed from line II-II in FIG. [Figure 3] A cross-sectional view of some of the grooves in FIG. 2 taken along line III-III in FIG. [Figure 4] 1 illustrates a laser processing apparatus according to an embodiment of the subject matter disclosed herein. [Figure 5] 1 shows a plan view of a diffractive device according to an embodiment of the subject matter disclosed herein. [Figure 6] 6 shows a cross-sectional view of the optical elements of the diffractive device of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] Exemplary embodiments of the subject matter disclosed herein are described below, for example, with reference to a laser processing apparatus or method. Of course, it should be emphasized that each combination of features of the various aspects, embodiments, and examples is possible. In particular, some embodiments are described with reference to a method, and other embodiments are described with reference to a laser processing apparatus. However, those skilled in the art will infer from the above and below description, claims, and drawings that, unless expressly stated otherwise, features of different aspects, embodiments, and examples can be combined, and such combinations of features are considered to be disclosed by the present application. For example, even features related to a method can be combined with features related to a laser processing apparatus, and vice versa. Furthermore, features of embodiments related to a laser processing apparatus can be combined with corresponding features related to a method. Furthermore, the disclosure of a method, method embodiment, or function is considered to disclose the functionality of one or more components (e.g., optical elements) and / or actuators (e.g., in the form of an actuator device) and a controller configured to perform the method or function that interact with the actuator. Furthermore, the disclosure of a device function is considered to disclose a corresponding method that defines the function without device features.

[0015] Unless otherwise specified, numerical values ​​should be understood to include an extension range of ±5%, i.e., for example, an indication of 100 groove numbers includes, according to one embodiment, groove numbers between the interval (100±5%) = [95, 105], and a percentage of 50% includes, according to one embodiment, a percentage between the interval 50%±5% = [47.5%, 52.5%]. According to another embodiment, numerical values ​​should be understood to include an extension range of ±10%.

[0016] According to one embodiment, a laser processing apparatus is disclosed that is mounted to generate a plurality of grooves in a surface. According to another embodiment, the laser processing apparatus includes an optical diffraction device mounted to receive laser radiation and subsequently generate output radiation. According to another embodiment, the laser processing apparatus includes an actuator device that generates relative motion between the output radiation and the surface, whereby the output radiation (by removing material from the surface) generates a plurality of grooves in the surface. According to one embodiment, the output radiation has a plurality of intensity maxima, each intensity maxima of the plurality of intensity maxima generating one of the plurality of grooves.

[0017] According to embodiments of the subject matter disclosed herein, the laser processing device has a radiation path mounted to direct the output radiation toward the surface. The radiation path may be, for example, free space through which the output radiation from the diffraction device propagates to the surface. According to other embodiments, the radiation path may include one or more deflection elements, such as mirrors. For example, an actuator device may be mounted to move at least one deflection element, thereby generating relative motion between the output radiation and the surface. According to another embodiment, the actuator device is mounted to move the surface and / or the laser processing device, or a portion thereof.

[0018] According to another embodiment, the radiation path may comprise one or more converging optical elements and / or one or more diverging optical elements, for example optical lenses.

[0019] According to one embodiment, the plurality of intensity maxima are only present along the radiation path within a narrowly limited range of the radiation path of the output radiation. In this case, it is self-evident that the surface is positioned within this range of the radiation path. In other words, according to one embodiment, the surface and the radiation path are positioned relative to each other such that the surface is within the range of the radiation path in which the output radiation has a plurality of intensity maxima.

[0020] Accordingly, according to one embodiment, a method for generating a plurality of grooves in a surface has one or more of the following embodiments: According to one embodiment, the method includes directing laser radiation to an optical diffractive device that generates output radiation having a plurality of intensity maxima; According to another embodiment, the method includes directing the output radiation to a surface; According to another embodiment, the method includes generating relative motion between the output radiation and the surface (e.g., the output radiation is generated during the relative motion); The relative motion between the output radiation and the surface generates a plurality of grooves, where each intensity maximum generates one of the plurality of grooves.

[0021] According to one embodiment, the step of directing the output radiation towards the surface comprises positioning the surface and the output radiation relative to one another such that the surface is within a range of the radiation path within which the output radiation has a plurality of intensity maxima.

[0022] According to one embodiment, the optical element and / or the radiation path and / or the actuator device are mounted such that the grooves generated by the output radiation are parallel grooves.

[0023] According to one embodiment, 80% of the grooves generated by the plurality of intensity maxima have a cross-sectional dimension (e.g., depth) that is about an average value of the cross-sectional dimension and within a tolerance of ±10% of the cross-sectional dimension. According to one embodiment, the average value is the arithmetic mean for the relevant cross-sectional dimensions of the plurality of grooves. According to one embodiment, the cross-sectional dimension may be a groove width or a groove depth.

[0024] According to one embodiment, these grooves in the surface form riblets, i.e. structures that reduce the flow resistance of the surface compared to a smooth surface. In particular with regard to the application, function, shape, dimensions, properties etc. of the riblets, explicit reference is made to WO 2018 / 197555, the entire disclosure of which, in particular the dimensions and applications of the riblets, is hereby incorporated by reference.

[0025] As is typical for riblets, in one embodiment, the grooves each have lateral walls. Thus, the adjacent walls of each two adjacent grooves form two opposite sides of the rib between these two grooves. In other words, in one embodiment, the grooves create ribs on the surface that, with appropriate dimensions, act as riblets (i.e., reduce flow resistance across the entire surface), as described, for example, in the above-cited International Publication No. 2018 / 197555. In one embodiment, the rib sides form an acute angle. In particular, in one embodiment, the ribs are tapered.

[0026] According to one embodiment, the ribs extend substantially parallel to one another, in particular parallel to the flow direction of the flow expected on the surface.

[0027] According to one embodiment, the diffractive device comprises at least one optical element. Insofar as reference is made below to an optical element, it should be understood that according to one embodiment, in the case of two or more optical elements, each of these optical elements may be configured according to one or more of the embodiments disclosed herein.

[0028] According to one embodiment, at least one optical element (e.g., each optical element of the diffractive device) is mounted to generate multiple phase differences between multiple portions of the output radiation. According to another embodiment, at least one optical element is mounted to generate multiple intensity maxima in the output radiation by generating multiple phase differences. It will be appreciated that the phase difference between each two portions of the output radiation will generally be different with respect to another portion of the output radiation.

[0029] For example, in one embodiment, the optical element is a diffractive optical element. For example, in one embodiment, the diffractive optical element has a structure that generates multiple phase differences. In another embodiment, the diffractive device comprises two or more diffractive optical elements. For example, in one embodiment, the diffractive device comprises two or more (diffractive) optical devices (also known as phase masks, for example), which generate phase differences in multiple planes (multi-plane light transformation, MPLC). In another embodiment, the diffractive device is a hologram. Starting from the desired intensity distribution of the output radiation, the diffractive optical element, MPLC element or hologram can be produced by known production methods. The following documents are mentioned here purely by way of example: EP 1 591 805 B1, US 5 073 007 B1.

[0030] In one embodiment, at least one of the at least one optical elements of the diffracting device is configured to generate a plurality of intensity maxima in a cross-section of the output radiation, which cross-section is smaller than the cross-section of the laser radiation incident on the diffracting device. In other words, at least one of the at least one optical elements of the diffracting device is configured to achieve focusing of the laser radiation incident on the diffracting device. For example, in one embodiment, the last optical element (seen in the propagation direction of the laser radiation) of the diffracting device (i.e., the optical element that generates the output radiation) is formed in this manner. In one embodiment, the cross-section (also referred to herein as beam diagonal) is defined by the maximum divergence of the radiation perpendicular to the radiation direction.

[0031] Unless otherwise stated, the cross-section of the output radiation relates to the cross-section that the output radiation has on the surface. In other words, the cross-section of the output radiation in one embodiment corresponds to the cross-section of the total illumination spot where the output radiation is generated on the surface (i.e., at a specified distance from the diffracting device). Thus, the spot (i.e., the total illumination spot where the output radiation generates on the surface) includes multiple intensity maxima.

[0032] According to one embodiment, at least one further optical element may be arranged between the diffracting device and the surface (i.e. in the radiation path), such as at least one converging and / or at least diverging optical element, such as a lens. For example, the at least one further optical element may have at least one of the following functions: to focus or expand the output radiation, to scale the intensity maxima, to generate the intensity maxima in a desired form if the diffracting device is configured to generate the intensity maxima in a desired form with at least one further optical element, etc. According to one embodiment, the diffracting device is mounted (calculated) to generate the intensity maxima (in particular a spot with the intensity maxima) at a predetermined distance, possibly taking into account the at least one further optical element. According to one embodiment, the surface is arranged at a predetermined distance from the diffracting device.

[0033] In one embodiment, the plurality of intensity maxima (i.e., the plurality of intensity maxima forming each one of the plurality of grooves) includes at least 10 intensity maxima. For example, the plurality of intensity maxima includes at least 50 intensity maxima, or in other embodiments, at least 100, at least 200, at least 500, or at least 1000 intensity maxima. For example, the plurality of intensity maxima includes between 500 and 1500 intensity maxima.

[0034] According to one embodiment, the spacing of the intensity maxima is nominally 40 μm to 160 μm, for example 100 μm. It is clear that if the grooves generate riblets in the surface, the spacing of the intensity maxima is adapted to achieve the desired spacing of the ribs. As explained, the desired spacing of the ribs (and thus the desired spacing of the intensity maxima) can depend, for example, on the flow rate for which the riblets generate the desired reduction in flow resistance. It is clear that the spacing between adjacent grooves of a plurality of grooves may actually deviate from the nominal spacing of the intensity maxima, for example by ±5%. For example, according to one embodiment, for a nominal spacing of the intensity maxima of 100 μm, the spacing between adjacent grooves may be 90 μm to 110 μm.

[0035] In one embodiment, the spot size is between 15 mm and 500 mm, for example between 30 mm and 200 mm. For example, for a 5 kW laser, the spot size may be 120 mm. Furthermore, for example, for a 2 kW laser, the spot size may be 70 mm. In one embodiment, the spot has this spot size in a direction perpendicular to the relative motion.

[0036] According to one embodiment, the spot has a direction of minimum dimension and a direction of maximum dimension, and the maximum dimension dmax, according to one embodiment, is several times the minimum dimension dmin. For example, the maximum dimension dmax is F times the minimum dimension dmin, i.e., dmax = F · dmin, where the factor F, according to one embodiment, is between 5 and 100, e.g., 40 (dmax = 40 · dmin). For example, the minimum dimension can be 3 mm and the maximum dimension can be 120 mm. For example, according to one embodiment, the spot is essentially rectangular or elliptical, having dimensions dmin · dmax, i.e., 3 mm · 120 mm. Because the spot has multiple intensity maxima, the spot size (e.g., of an "essentially rectangular" spot) represents the dimensions (e.g., dmin, dmax) of a rectangle that can be circumscribed around the spot (or around multiple intensity maxima). According to one embodiment, the spot size indicated herein is the maximum dimension dmax of the spot.

[0037] According to one embodiment, the relative movement between the output radiation and the surface is performed in the direction of the smallest dimension. The relatively small minimum dimension thereby allows for a relatively short illumination time of the surface at a given speed of the relative movement. According to one embodiment, the illumination time of the surface by the output radiation is less than 40 ms, for example less than 10 ms. In particular, the illumination time of the surface by the output radiation is less than 2 ms. According to one embodiment, the minimum dimension and the speed of the relative movement are adapted to achieve the indicated illumination time. According to one embodiment, the speed of the relative movement is at least 100 mm / s, for example, in intervals between 100 mm / s and 2 m / s, for example, between 300 mm / s and 1 m / s. For example, the speed of the relative movement is nominally 500 mm / s or more. According to one embodiment, the intensity maxima are periodically arranged, for example, in a periodic array. According to one embodiment, each intensity maximum has a shape that deviates from a circular shape. For example, each intensity maximum of the plurality of intensity maxima has an elongated shape. The shape of the intensity maximum is in this case defined as usual, for example by the shape of lines of equal intensity.

[0038] According to one embodiment, the optical element is mounted to operate in reflection. In other words, the optical element according to one embodiment is a reflective optical element. An optical element operating in reflection allows a reduction in the thermal load of the optical element. In the case of an optical element operating in reflection, the structure generating the phase difference may according to one embodiment be a surface structure.

[0039] According to another embodiment, the optical element has a body made of a metal or semiconductor material. According to one embodiment, the body is made of a metal with high electrical conductivity and / or a metal with high thermal conductivity, such as copper or gold. According to another embodiment, the body is made of a corrosion-resistant metal (i.e., a metal that is resistant to corrosion), such as a suitable metal alloy or a noble metal. According to another embodiment, the body is made of silicon. According to one embodiment, the body is made of a single crystal. In this way, the influence of grain boundaries on the properties of the optical element can be avoided.

[0040] According to another embodiment, the body is at least partially coated with a metal, in particular a corrosion-resistant metal. According to one embodiment, the corrosion-resistant metal is a corrosion-resistant alloy or a noble metal, such as gold. The corrosion-resistant metal allows the optical element to achieve a sustained high reflectivity. For example, the optical element may have a body made of silicon coated with a metal (e.g., gold).

[0041] According to one embodiment, the body has a thickness in the range of 1 mm to 200 mm, for example 5 mm to 50 mm. A relatively large thickness can allow a relatively high stiffness of the body and therefore a relatively high precision of the optical element.

[0042] According to another embodiment, the optical element (e.g., the body, or the coating if a coating is disposed on the body) has a first plane with a cross section (e.g., diameter) in the range of 20 mm to 500 mm, for example, a diameter of 70 mm to 200 mm. According to one embodiment, the cross section (e.g., diameter) is defined by the maximum extent of the first plane (e.g., a major surface of the optical element).

[0043] According to one embodiment, the optical element is structured on a first plane, and according to another embodiment, the structured plane is surrounded by an unstructured edge. According to one embodiment, the structured plane of the optical element may be formed by structuring (e.g., engraving, etching, etc.) the body, and the resulting structure of the body is, according to one embodiment, applied to a coating, whereby the coating (if present) has a corresponding structure (i.e., the structured plane of the optical element). According to one embodiment, the width of the unstructured edge is 2% to 20% of the cross section of the first plane. According to one embodiment, the structured plane is completely illuminated by the laser radiation. For this purpose, according to one embodiment, the laser radiation may be expanded accordingly, for example, using a beam expander, for example in the form of a lens group or a DOE.

[0044] According to one embodiment, the laser processing device has a coolant channel for cooling the optical diffraction device (especially for cooling the optical element), in particular a coolant channel for a liquid coolant. For example, the optical element has a hollow portion that forms at least a part of the coolant channel. According to another embodiment, the coolant channel may be formed by a separate component that is thermally coupled to the optical element. According to one embodiment, the coolant channel is arranged on the back side of the body, i.e., on a second plane (e.g., second main surface) of the body that is arranged opposite the structured first plane.

[0045] According to one embodiment, the output radiation forms an angle between 0 and 50 degrees, for example 10 degrees, with respect to the (average) plane normal of the structured (first) plane of the body.

[0046] According to one embodiment, the laser radiation forms an angle between 1 degree and 70 degrees, for example between 45 degrees and 60 degrees, with respect to the plane normal of the structured (first) plane of the optical element.

[0047] According to one embodiment, the angle between the laser radiation (ie the input radiation hitting the diffracting device) and the output radiation is between 20 degrees and 100 degrees, for example 50 degrees.

[0048] According to one embodiment, the optical element (especially the last optical element in the radiation direction of the diffractive optical device) is calculated for a specific arrangement of the optical components and surfaces of the laser processing device (especially for a specific arrangement of the laser radiation, the optical element, and the surface relative to one another). Calculation of the optical element for a specific arrangement of the optical components and surfaces of the laser processing device is particularly advantageous when the diffractive optical device consists of a single diffractive optical element (DOE).

[0049] According to one embodiment, the laser radiation has a diffraction index M of less than 1.5. 2 (M 2 <1.5). According to another embodiment, the laser radiation has a diffraction index M 2 <1.3 or M 2<1.1. The smaller the diffraction index, the more accurately the desired intensity pattern with multiple intensity maxima can be realized.

[0050] According to one embodiment, the laser radiation is that of a CO laser. CO lasers have the advantage that high average powers are available, which also allow for high processing speeds. For example, the average power of the laser radiation is at least 500 watts (W). According to another embodiment, the average power of the laser radiation is at least 1 kilowatt (kW), or according to yet another embodiment, at least 3 kW.

[0051] However, that high average power requires proper configuration of the laser processing apparatus and portions thereof to enable reliable and stable operation of the laser processing apparatus. Embodiments of the subject matter disclosed herein enable reliable and stable operation of the laser processing apparatus at high average power.

[0052] According to one embodiment, the laser processing device comprises a laser source for generating laser radiation, however, according to another embodiment, the laser processing device may be provided to be coupleable to a laser source.

[0053] In summary, the present disclosure specifically encompasses the following embodiments and combinations of embodiments: 1. A laser processing apparatus for producing a plurality of grooves in a surface, the laser processing apparatus comprising: an optical diffraction device mounted to receive the laser radiation and subsequently produce output radiation; an actuator device for generating relative motion between the output radiation and the surface; wherein the output radiation has a plurality of intensity maxima, each intensity maxima generating one of the plurality of grooves.

[0054] 2. A laser processing apparatus as described in embodiment 1, wherein the diffraction device has at least one optical element, and in particular, the at least one optical element is mounted to generate a phase difference between multiple portions of the output radiation.

[0055] 3. A laser processing apparatus as described in embodiment 2, wherein the at least one optical element is mounted to operate in reflection.

[0056] 4. A laser processing apparatus according to embodiment 2 or 3, wherein the at least one optical element has a body made of a metal or semiconductor material.

[0057] 5. A laser processing apparatus as described in embodiment 4, wherein the body is at least partially coated with a metal, in particular a corrosion-resistant metal, such as a corrosion-resistant alloy or a noble metal.

[0058] 6. A laser processing apparatus according to any of the above-mentioned embodiments, wherein the optical element is a diffractive optical element.

[0059] 7. A laser processing apparatus according to any of the above embodiments, wherein the plurality of intensity maxima includes at least 10 intensity maxima, in particular at least 50 intensity maxima or at least 200 intensity maxima.

[0060] 8. Further comprising a radiation path mounted such that the output radiation is directed toward the surface; Relative motion is linear motion, A laser processing apparatus according to any of the above-mentioned embodiments, wherein the diffraction device and / or radiation path is mounted so that each two grooves of the plurality of grooves form a rib between themselves.

[0061] 9. A laser processing apparatus according to any of the above-mentioned embodiments, wherein the laser radiation is CO2 laser radiation.

[0062] 10. A laser processing apparatus according to any of the previous embodiments, wherein the average power of the laser radiation is at least 500 W, in particular at least 1 kW.

[0063] 11. A laser processing apparatus according to any of the preceding embodiments, further comprising a laser source for generating laser radiation.

[0064] 12. A laser processing apparatus according to any of the previous embodiments, further comprising a coolant channel for cooling the optical diffraction device, in particular a coolant channel for a liquid coolant.

[0065] 13. A method for generating a plurality of grooves in a surface, the method comprising: directing the laser radiation onto an optical diffraction device that produces output radiation; directing output radiation onto a surface; generating relative motion between the output radiation and the surface; wherein the output radiation has a plurality of intensity maxima, each intensity maxima generating one of the plurality of grooves.

[0066] 14. The method of embodiment 13, wherein generating the output radiation comprises reflecting the laser radiation off an optical diffraction device.

[0067] 15. The method of embodiment 13 or 14, wherein the plurality of intensity maxima comprises at least 10 intensity maxima.

[0068] 16. Use of a laser processing device according to any one of claims 1 to 12 or a method according to any one of claims 13 to 15 for producing a plurality of parallel ribs, in particular riblets, on a surface.

[0069] Embodiments of the subject matter disclosed herein allow for free shape selection of the grooves or ribs between the grooves (within the unit cell, e.g., tapered tips of the ribs, flat groove bottoms), whereas conventional interference machining only allows for ribs and grooves that are at least partially sinusoidally shaped.

[0070] Furthermore, embodiments of the subject matter disclosed herein allow for precise demarcation of the spots that the output radiation generates on the surface, especially in a direction transverse to the processing direction. This can allow for improved juxtaposition of processing tracks of different spots in a direction transverse to the processing direction. In contrast, in the case of conventional interference with Gaussian radiation, a Gaussian-like envelope exists. This envelope may be shaped into (or approximated to) a rectangular function using a diffracting device, according to one embodiment.

[0071] The generation of multiple intensity maxima in the output radiation by a diffractive optical device (according to one embodiment, by a single optical element, particularly a single diffractive optical element) allows for significant simplification compared to conventional interference structuring (particularly involving beam splitting and subsequent recombination of the split beams), since, according to embodiments of the subject matter disclosed herein, beam forming (shaping of the spot envelope) and the formation of intensity maxima are achieved with fewer optical elements (e.g., just a single optical element). In particular, the formation of multiple intensity maxima according to embodiments of the subject matter disclosed herein, in contrast to conventional interference structuring, is not based on the generation of path differences by a single optical element positioned at a defined distance from one another. This results in greater stability in industrial environments, particularly since fewer optical elements need to be held in defined positions relative to one another.

[0072] Detailed Description Exemplary embodiments of the subject matter disclosed herein are described below with reference to the drawings. It should be noted that in different figures, similar or identical elements or components are partially labeled with the same reference numerals or with reference numerals that differ only in the first digit. Features or components that are the same or at least functionally the same as corresponding features or components in another figure will only be described in detail when they first appear in the following text, and this description will not be repeated when these features and components (or corresponding reference numerals) appear later. The above definitions also apply, according to one embodiment, to the following embodiments, and vice versa. Furthermore, the features and embodiments described above can be combined with the features and embodiments described below.

[0073] FIG. 1 illustrates a schematic diagram of a laser processing apparatus 100 according to an embodiment of the subject matter disclosed herein.

[0074] According to one embodiment, the laser processing apparatus 100 comprises an optical diffraction device 102 mounted to receive laser radiation 104 and subsequently generate output radiation 106. According to one embodiment, the laser radiation 104 forms an angle 103 of 1 to 70 degrees, e.g., 30 or 45 degrees, with respect to an average plane normal of the diffraction device 102. According to one embodiment, the direction of the plane normal is averaged with respect to an active plane (e.g., a structured plane) of the diffraction device 102, and in particular with respect to an outer active plane of the diffraction device 102 illuminated by the laser radiation 104 (e.g., if the diffraction device 102 has more than one active plane). Therefore, the plane normal is also referred to herein as an average plane normal. According to one embodiment, the output radiation 106 forms an angle 105 of 0 to 70 degrees, e.g., 30 or 45 degrees, with respect to the average plane normal.

[0075] The laser processing apparatus 100 further includes an actuator device 108 for generating relative movement between the output radiation 106 and the surface 110 of the object 112. In one embodiment, the actuator device 108 is stationary, as shown at 114. In another embodiment, the processing component 116 is coupled to the actuator device 108 via a carrier 118. In one embodiment, the actuator device 108 and / or the carrier 118 are formed by a robot arm. In one embodiment, the actuator device 108 and / or the carrier 118 may stand on a movable lift platform (not shown in FIG. 1 ) for rough positioning. This may be advantageous, especially for large objects, such as aircraft parts. In one embodiment, the lift platform may have at least one actuator for moving the lift platform. In one embodiment, the at least one actuator for moving the lift platform may be part of the actuator device 108. Using the actuator device 108, the processing component 116 can be moved relative to the object 112 or the surface 110 of the object 112, causing the output radiation 106 to move relative to the surface. According to another embodiment, the object 112 may be intended to be movably arranged using an actuator device in addition to or instead of the actuator device 108 .

[0076] A sensor arrangement 119 may be provided to maintain a predetermined spacing range between the diffracting device 102 and the surface 110 and / or to maintain a predetermined orientation range (swivel range) between the diffracting device 102 and the surface 110. According to one embodiment, the sensor arrangement comprises one or more sensors, such as at least one of a position sensor, a distance sensor, etc.

[0077] In one embodiment, the object 112 is, for example, a part of an aircraft, such as a wing or a fuselage of the aircraft. In another embodiment, the object 112 may be, for example, a rotor blade of a wind power plant. In one embodiment, the object 112 is fixedly arranged (as shown at 114), for example, on a carrier (not shown in FIG. 1 ).

[0078] According to one embodiment, the laser processing apparatus 100 comprises a laser emitting device 120 that emits laser radiation 104. According to one embodiment, a laser source that generates the laser radiation is arranged within the laser emitting device 120. According to another embodiment, the laser source is arranged external to the laser emitting device 120. In particular, for embodiments in which the laser processing apparatus 100, or a portion of the laser processing apparatus 100, is moved relative to the surface 110 by an actuator device 108, as shown in FIG. 1 for example, it may be expedient (e.g., for weight reasons) to arrange the laser source external to the laser processing apparatus.

[0079] According to one embodiment, the laser processing apparatus further includes a cooling device 124 that supplies a coolant 128 to the optical diffraction device 102 or the coolant passage 126 .

[0080] Additionally, in one embodiment, the laser processing apparatus 100 includes a controller 122 that controls other components of the laser processing apparatus, such as the laser emitting device 120, the cooling device 124, and / or the actuator device 108. The control of the other components by the controller 122, in one embodiment, is via a signal communication link 130 between the other components and the controller 122, as shown in FIG. 1 , for example. In one embodiment, the controller 122 is signal communication coupled (indicated at 130) with the sensor device 119. In another embodiment, the controller 122 is adapted to control one or more components of the laser processing apparatus 100 in response to a sensor signal 123 from the sensor device 119. In one embodiment, the control of the components of the laser processing apparatus (particularly the control of the other components, more particularly the control of the actuator device) may be adapted to maintain a spacing between the diffracting device 102 and the surface 110 within a predetermined spacing range and / or an orientation between the diffracting device 102 and the surface 110 within a predetermined orientation range. In one embodiment, the laser processing apparatus is solely a passive device. In this case, the signalling connection to the control device may be omitted.

[0081] According to one embodiment, processing component 116 includes one or more of the following components: laser emitting device 120, control device 122, cooling device 124, optical diffraction device 102, and sensor device 119. For example, processing component 116 may include all of these components as shown, for example, in FIG. 1 , schematically indicated by dashed lines at 116.

[0082] In one embodiment, the output radiation has multiple intensity maxima (not shown in FIG. 1 ), and a cross section 132 of the output radiation 106, and in particular the overall cross section of the multiple intensity maxima, is smaller than a cross section 134 of the laser radiation 104 incident on the optical diffracting device 102. For example, in one embodiment, the optical diffracting device 102 acts to focus, thereby reducing the cross section of the laser radiation 104 from the cross section 134 of the laser radiation 104 at the diffracting device 102 to the cross section 132 of the output radiation 106 at the surface 110. In one embodiment, the cross section 132 is also referred to as the spot size of the output radiation 106. In one embodiment, interference occurs within the output radiation 106, thereby forming the multiple intensity maxima.

[0083] It is noted that, in addition to output radiation 106 having multiple intensity maxima, diffracting device 102 may also generate other radiation that is not used for processing surface 110. This unused radiation (not shown in FIG. 1 ) may be blocked, for example, by an appropriate shield, from emitting from laser processing device 100 or processing component 116.

[0084] FIG. 2 shows the surface 110 of the object 112 of FIG. 1 as viewed from line II-II in FIG.

[0085] According to one embodiment, output radiation 106 has multiple intensity maxima, some of which are shown at 136 in Figure 2. Due to relative motion between the surface and output radiation 106, shown at 138 in Figure 2, intensity maxima 136 create multiple parallel grooves in the surface, some of which are shown at 140 in Figure 2. The shown direction 138 is the direction of motion of output radiation 106 over surface 110.

[0086] According to one embodiment, the shape of the intensity maxima deviates from a circle. In particular, according to one embodiment, the intensity maxima have a first extent 143 along a first direction 142, along which the intensity maxima are arranged next to one another according to one embodiment, the first extent being smaller than a second extent 144 in a second direction 146, which is arranged perpendicular to the first direction 142. According to one embodiment, the relative movement 138 between the output radiation 106 and the surface 110 is performed along the second direction 146, as shown in, for example, FIG. 2 .

[0087] According to one embodiment, the plurality of intensity maxima form or are formed by a spot of output radiation. According to one embodiment, the spot has a minimum extent in the second direction 146 (i.e., the longitudinal direction of the groove 140) and a maximum extent in a direction perpendicular thereto (along the first direction 142). The greater the maximum extent of the spot in the first direction (the direction perpendicular to the longitudinal direction of the groove 140), the more grooves the spot can produce for a given groove width. The more grooves a single spot can produce, the higher the planar processing speed of the laser processing apparatus 100 can be.

[0088] FIG. 3 shows a portion of the plurality of grooves 140 of FIG. 2 in cross section taken along line III-III in FIG.

[0089] In one embodiment, grooves 140 are sized and spaced such that ribs 150 remain between grooves 140. Ribs 150 are thus formed from material 148 that forms surface 110 and that is removed within grooves 140 upon irradiation with output radiation 106. In one embodiment, material 148 is a coating (e.g., paint) disposed on a base portion 152 of object 112, as shown in FIG.

[0090] FIG. 4 illustrates a laser processing apparatus 200 according to an embodiment of the subject matter disclosed herein.

[0091] In one embodiment, the laser processing apparatus 200 includes a cooling device 124 for cooling the diffraction device 102. In one embodiment, the cooling device 124 is located external to the processing component 116, as shown in FIG. 4, for example. In another embodiment, the laser processing apparatus includes a coolant line 127 through which a coolant 128 for the diffraction device 102 can be delivered. In one embodiment, the laser processing apparatus 200 includes a heat exchanger 160 (e.g., a heat sink) having a coolant flow path 126, in thermal contact with the diffraction device 102 (as shown in FIG. 4, for example) for carrying heat away from the diffraction device 102 using the coolant 128. In one embodiment, the warmed coolant 128 is returned to the cooling device 124 to cool and recondition the coolant for the diffraction device.

[0092] According to one embodiment, the laser processing apparatus 200 comprises a laser source 162, which generates laser radiation 104 and supplies it to the laser emitting device 120 via a suitable optical waveguide 164, from which the laser radiation 104 is emitted to the diffraction device 102, as shown, for example, in FIG. 4 . According to one embodiment, the optical waveguide 164 comprises an optical waveguide and / or a suitable mirror device that supplies the laser radiation 104 to the laser emitting device 120. For example, in the case of high power laser radiation 104 and / or high requirements regarding maintaining the coherence of the radiation, a mirror device may be preferable compared to an optical waveguide. According to one embodiment, the laser source 162 is arranged external to the processing component 116, as shown, for example, in FIG. 4 .

[0093] According to one embodiment, the laser processing apparatus 200 includes one or more additional optical elements 166, such as a focusing optical element 166 at the location shown by the dashed lines in FIG. 4 to focus the output radiation 106 onto a surface (not shown in FIG. 4) and / or a diverging optical element 167 to expand the laser radiation 104 to a desired cross-section 134 (see FIG. 1).

[0094] 4 is an example of an optical element in radiation path 169 between diffracting device 102 and the surface on which the grooves are generated. For example, optical element 166 can contribute to radiation path 169 being mounted to direct output radiation 106 towards the surface.

[0095] For example, the at least one optical element 166 (which optical element is also referred to herein as another optical element) may be a mirror of a scanner that moves the output radiation across the surface. In this case, the actuator device would include the at least one actuator of the scanner. According to another embodiment, directing the output radiation 106 towards the surface is performed solely by the diffractive device 102. In other words, according to one embodiment, the radiation path 169 does not include any optical elements, such as mirrors, lenses, etc.

[0096] According to one embodiment, the laser processing apparatus 200 further includes a control device 122 that is coupled in signal communication with components of the laser processing apparatus 200 (some components are illustratively designated 130 in FIG. 4 ).

[0097] According to one embodiment, the laser processing apparatus 200 includes an actuator device 108 and a carrier 118. According to one embodiment, the actuator device 108 and the carrier 118 form at least a portion of a robot arm. According to one embodiment, connection paths between components external to the laser processing apparatus 200 (e.g., the cooling device 124, the laser source 162, and the control device 122) and movable components of the laser processing apparatus (e.g., the laser emitting device 120, the diffraction device 102, and any other optical elements 166, 167, particularly components of the processing component 116) are guided by the carrier 118 and / or the actuator device 108 (e.g., at least a portion of a robot arm), as shown, for example, schematically in FIG. 4 .

[0098] The moving mass (i.e., the mass that must be moved by the actuator device 108) can be reduced by providing external components, such as the external components 122, 124, 162. An external component, according to one embodiment, is a component that is located externally relative to the processing component 116. The external component may be located (fixed), for example, at the base of the robot arm or at a portion of the robot arm that is located adjacent the base of the robot arm (e.g., a "lower" portion of the robot arm).

[0099] In general, it should be emphasized that while the arrangement of some components of the laser processing apparatus described herein may be preferred for particular applications, within the scope of this disclosure, the components of the laser processing apparatus may be located in any suitable location. For example, according to one embodiment, the diffraction device 102 may be located remotely from the processing component 116, such as on a robotic arm or as an external component.

[0100] FIG. 5 shows a top view of a diffractive device 102 according to an embodiment of the subject matter disclosed herein.

[0101] According to one embodiment, the diffractive device 102 comprises a diffractive optical element 168 (hereinafter also referred to as optical element for short). According to one embodiment, the diffractive optical element 168 comprises a first plane 172, which comprises an unstructured portion 174 and a structured portion 176. According to one embodiment, the unstructured portion 174 extends around the structured portion 176 (thus forming an unstructured edge in one embodiment), as shown, for example, in FIG. 5 . According to one embodiment, the diffractive optical element has at least one of a geometrical optical function, such as a focusing function, a beam steering function, etc., in addition to generating multiple (relative) intensity maxima.

[0102] FIG. 6 shows in cross section an optical element 168 of the diffractive device 102 of FIG.

[0103] According to one embodiment, at least the structured portion 176 of the first plane 172 is formed from a metal, e.g., a coating 178. According to one embodiment, the optical element 168 has a body 170 and a coating 178 on the body 170. According to one embodiment, the body 170 is a structured silicon wafer, and the surface structure 180 of the optical element 168 according to one embodiment is defined by the structure of the silicon wafer. It is noted that the surface structure 180 in FIG. 6 merely exemplarily and schematically illustrates the structured plane 176 of the optical element 168 and its opposing plane 182, but does not necessarily represent the actual structuring of the optical element 168 of the diffractive device 102 according to embodiments of the subject matter disclosed herein. According to one embodiment, the opposing plane 182 is formed by a flat plane, e.g., a flat plane of the body 170, as shown in FIG. 6 . The flat opposing plane 182 can improve thermal contact with a heat exchanger, e.g., a heat sink. The distance between the structured plane 176 and the opposing plane 182, according to one embodiment, defines the thickness of the optical element 168. According to one embodiment, the thickness of the optical element 168 is averaged across the structured plane 176 (average thickness of the optical element). According to one embodiment, the layer thickness of the coating 178 is less than 10% of the thickness of the body 170. Thus, according to one embodiment, the body 170 essentially defines the thickness of the optical element 168.

[0104] According to one embodiment, the plane forming the surface structure 180 may or can be curved, and in another embodiment may be flat. In other words, the starting plane prior to creating the surface structure 180 may be curved, or according to other embodiments, may be flat. For example, the geometrical optical function of the optical element 168 may be achievable by the curvature of the starting plane.

[0105] According to one embodiment, the diffractive device 102 consists of a single diffractive optical element 168, for example a diffractive optical element such as that shown with reference to FIGS.

[0106] It should be noted that the components (e.g., controllers, laser processing devices, laser emitting devices, cooling devices, actuator devices, objects, etc.) disclosed herein are not limited to the definitive entities as described in some embodiments. Rather, the subject matter disclosed herein can be implemented in a variety of ways while still providing the specific functionality disclosed.

[0107] It should be noted that each entity (e.g., device, element, feature, and method step) disclosed herein is not limited to the definitive entity as described in some embodiments. Rather, the subject matter described herein may be provided in various ways, with various granularities at the device level or method level, while still providing the indicated functionality. It should also be noted that, according to an embodiment, a separate entity may be provided for each of the functions disclosed herein. According to another embodiment, one entity may be configured to provide two or more functions described herein. According to yet another embodiment, two or more entities may be configured to together provide one function described herein.

[0108] It should be noted that the embodiments in the drawings described herein are merely a limited selection of possible implementation variations of the subject matter disclosed herein. Therefore, the features of the individual embodiments can be combined with each other in an appropriate manner, so that those skilled in the art can regard multiple different embodiments as disclosed in accordance with the implementation variations explicitly stated herein. Furthermore, it should be noted that concepts such as "ein" or "eines" do not exclude multiple. Concepts such as "including" or "having" do not exclude other features or method steps. The concepts "having" or "including" encompass both the meanings of "comprising, inter alia," and "consisting of," respectively.

[0109] Furthermore, it should be noted that the exemplary laser processing apparatus and exemplary surfaces in the drawings illustrate certain combinations of multiple embodiments of the subject matter disclosed herein, and that other combinations of each of the embodiments are similarly possible and are considered to be disclosed by this application.

[0110] Advantageous combinations of embodiments of the subject matter disclosed herein can be summarized as follows: A laser processing apparatus for generating a plurality of grooves in a surface includes an optical diffraction device mounted to receive laser radiation and subsequently generate output radiation, the output radiation having a plurality of intensity maxima, and an actuator device is provided for generating relative motion between the output radiation and the surface, each intensity maxima generating one of the plurality of grooves.

Claims

1. 1. A laser processing apparatus for creating a plurality of grooves in a surface, the laser processing apparatus comprising: an optical diffraction device mounted to receive laser radiation and subsequently produce output radiation, the laser radiation being CO2 laser radiation, the optical diffraction device comprising at least one optical element; a radiation path mounted such that the output radiation is directed toward the surface; an actuator device for generating relative motion between said output radiation and said surface; the output radiation having a plurality of intensity maxima, each intensity maxima generating one of the plurality of grooves; the at least one optical element is mounted to create a phase difference between portions of the output radiation, and by creating the phase differences, create the plurality of intensity maxima in the output radiation, the plurality of intensity maxima being created by interference of the output radiation; the at least one optical element is mounted to operate in reflection; the at least one optical element has a body made of a metal or semiconductor material; Laser processing equipment.

2. the body being at least partially coated with metal; the body being at least partially coated with a corrosion-resistant metal; the body is at least partially coated with a corrosion-resistant alloy; or The laser processing device of claim 1 , wherein the body is at least partially coated with a noble metal.

3. The laser processing apparatus according to claim 1 or 2, wherein the plurality of intensity maxima includes at least 10 intensity maxima.

4. The laser processing apparatus according to claim 1 or 2, wherein the plurality of intensity maxima includes at least 50 intensity maxima or at least 200 intensity maxima.

5. the relative motion is linear motion; 5. The laser processing apparatus according to claim 1, wherein at least one of the optical diffraction device and the radiation path is mounted so that two grooves of the plurality of grooves form a rib between themselves.

6. 6. The laser processing apparatus according to claim 1, wherein the average power of the laser radiation is one of at least 500 W and at least 1 kW.

7. The laser processing apparatus of claim 1 , further comprising a laser source for generating the laser radiation.

8. The laser processing apparatus of claim 1 , further comprising one of a coolant flow path for cooling the optical diffraction device and a coolant flow path for a liquid coolant for cooling the optical diffraction device.

9. A laser processing apparatus described in any one of claims 1 to 7, wherein at least one optical element is a diffractive optical element.

10. 1. A method for creating a plurality of grooves in a surface, the method comprising: directing laser radiation onto an optical diffraction device that produces output radiation, the laser radiation being CO2 laser radiation, the optical diffraction device comprising at least one optical element; directing the output radiation through a radiation path onto the surface; generating relative motion between the output radiation and the surface; the output radiation having a plurality of intensity maxima, each intensity maxima generating one of a plurality of grooves; generating the output radiation includes reflecting laser radiation off the optical diffractive device, and the at least one optical element has a body made of a metal or semiconductor material; the at least one optical element is mounted to create a phase difference between portions of the output radiation, and to create the plurality of intensity maxima in the output radiation by creating the plurality of phase differences, the plurality of intensity maxima being created by interference of the output radiation. A method for generating multiple grooves in a surface.

11. 11. Use of the laser processing apparatus according to any one of claims 1 to 9 or the method according to claim 10 for producing a plurality of parallel ribs or a plurality of riblets on the surface.

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