COOLING FOR GALVOMIERS IN LASER MATERIAL PROCESSING

Abstract

A system for cooling a mirror (1), comprising: a. a rotatable mirror (1) which is attached to an axis of rotation and which has at least one gas channel inside the rotatable mirror (1) behind a reflecting surface (2) with an inlet channel (5) and at least one outlet (9); and b. a static supply (10) for a gas which has an outlet channel (15) which is connected via a gap (12) and thus without contact to the inlet channel (5) of the gas channel inside the rotatable mirror (1) for the supply of a gas.

Description

Field of invention The present disclosure relates generally to a cooling system for galvo mirrors in laser material processing. Brief description of the state of the art Laser processing systems comprise a variety of optical elements. In certain laser material processing applications, so-called galvo mirrors are successfully used to deflect the laser beam. A galvo mirror is a mirror with a highly reflective coating, connected via an axis to a galvanometer drive, allowing the mirror to be moved to deflect a laser beam. One problem with using galvo mirrors is their thermal insulation. An increase in the temperature of the galvo mirrors can result in a limitation in the throughput of laser material processing operations. Galvo mirrors made of glass are known from the prior art, allowing a small fraction of the laser light to pass through that is not reflected by the highly reflective thin-film coating. Galvo mirrors made of materials with good thermal conductivity, such as aluminum, are also known, thus flattening thermal gradients and minimizing the resulting deformation. Galvo mirrors are also manufactured from special lightweight materials such as beryllium or silicon carbide to reduce their moment of inertia. The moment of inertia of all these galvo mirrors known from the prior art can be further reduced by special mechanical bracing on the back side. German patent application DE 43 31 856 A1 discloses a deflecting mirror whose rear surface is equipped with recesses to increase the cooling area. The device according to DE 43 31 856 A1 provides a cooling plate on the side facing away from the deflecting mirror. This cooling plate is equipped on its side facing away from the deflecting mirror with an externally sealed, annular chamber, which is connected via a feed bore to a cooling gas source (not shown). Cooling bores extend from the chamber towards the rear surface 5a of the deflecting mirror 5. The published German patent DE 199 55 574 B4 relates to a mass-optimized mirror for laser processing and a method for cooling the mass-optimized mirrors during laser processing. It is preferably used in laser processing, particularly for beam-shaping laser mirrors for two- and three-dimensional laser surface processing of semi-finished or finished products made of any materials and material combinations, for example, as scanner mirrors (e.g., ablation, drilling, cutting, welding, hardening, coating, etc.). According to the invention, the mass-optimized mirror has a thickness reduced to the absolute minimum necessary, and the resulting loss of self-cooling is compensated for by at least one additional cooling device coupled to the mirror.According to the invention, the method for cooling the mass-optimized mirrors provides that the mass-optimized mirror is cooled during the laser processing process in such a way that an expanding gas is blown via a nozzle precisely onto the point on the mirror surface (reaction surface) where the laser beam directly hits, without affecting the laser beam itself. The published German part DE 689 07 713 T2 of the granted European patent EP 0 383 942 B1 discloses two reflecting mirrors, which are parallel to each other and arranged at a predetermined angle to an incident beam, and which are each attached to rotatable waveguide elements. On the back of the mirror holders are an inlet for cooling air, an air baffle section, and an air outlet opening. Since the reflecting mirrors are cooled by air and the air baffle section is provided, sufficient cooling is achieved. The amount of heat that needs to be dissipated by a galvo mirror is relatively small. For example, the reflectivity of the highly reflective coating is typically > 99.5%, so that less than 50 W needs to be dissipated at an average laser power of 10 kW. The axis of a galvo mirror is unsuitable for efficient cooling, as it would only cool a small area of ​​the mirror, and the motor shaft has only a small contact area with the mirror, allowing for very limited and likely only localized heat dissipation. While air cooling can theoretically dissipate power up to 100 W, simply cooling the back of a galvo mirror with an airflow is insufficient. Another problem with cooling a galvo mirror arises from the fact that the mirror is moved, and therefore a device for cooling the mirror must be adapted to the movement of the mirror. The technical object of the present invention is therefore to provide efficient cooling for a galvo mirror. Summary of the invention The present invention provides a system for cooling a mirror, comprising a rotatable mirror which is attached to an axis of rotation and which has at least one gas channel inside the rotatable mirror behind a reflective surface, with an inlet channel and at least one outlet; and a static gas supply which has an outlet channel which is connected via a gap and thus without contact to the inlet channel of the gas channel inside the rotatable mirror for supplying a gas. In a further embodiment of the system according to the invention, it is provided that the static feed is arranged axially, radially or parallel to the axis of rotation of the rotatable mirror. Another aspect of the invention provides that the rotatable mirror has a cylindrical surface on the side opposite the reflecting surface, which surrounds the axis of rotation, around which a corresponding cylindrical recess of the feed with the outlet channel is arranged. Furthermore, the static feed of a system according to the invention can have a hose connection on the side opposite the cylindrical recess. In a further embodiment of the system according to the invention, the inlet channel of the mirror can be arranged transversely to the axis of rotation. It is also planned that the rotating mirror will be made of lightweight materials, including beryllium, aluminum, and silicon carbide. Furthermore, the rotatable mirror of a system according to the invention can have support structures on the back side facing the reflective surface, in which at least one outlet is arranged. In another embodiment, at least one outlet is arranged laterally to the reflecting surface. In a system according to the present disclosure, the distance between the cylindrical surface on the back of the rotatable mirror and the cylindrical recess of the static feed can be less than 1 mm. An embodiment is also provided in which the distance is less than 0.1 mm. In a further embodiment of a system according to the present invention, the mirror can rotate in the cylindrical recess of the feeder. Another aspect of the present disclosure relates to a method for cooling a mirror, comprising the steps of: a. arranging a static gas supply on a rotatable mirror, which has at least one gas channel inside the rotatable mirror behind the reflecting surface of the rotatable mirror, the gas channel having an inlet channel, the static supply having an outlet channel which is connected to the inlet channel of the gas channel inside the rotatable mirror via a gap and thus without contact; b. introducing a gas via the static supply into the inlet channel of the at least one gas channel inside the rotatable mirror; and c. expelling the gas via at least one outlet of the at least one gas channel inside the rotatable mirror. The method according to the invention can further include the step of rotating the rotatable mirror during the introduction and discharge of the gas. Furthermore, air can be used as the gas in a method according to the invention, wherein the gas can be at room temperature. In one embodiment of the method according to the invention, the gas can be discharged laterally from the rotatable mirror. Another aspect of the invention relates to the use of the system as previously described in a laser processing head. Further aspects, features, and advantages of the present invention will readily become apparent from the following detailed description, which simply presents preferred embodiments and implementations. The present invention can also be realized in other and different embodiments, and its various details can be modified in various obvious aspects without departing from the teaching and scope of the present invention. Accordingly, the drawings and descriptions are to be regarded as illustrative and not as limiting. Additional problems and advantages of the invention are partly set forth in the following description and partly become apparent from the description or can be deduced from the embodiment of the invention. Brief description of the characters The invention is described in more detail below with reference to the figures. It is obvious to those skilled in the art that these are only possible, exemplary embodiments, without limiting the invention to the embodiments shown, wherein: Fig. 1 shows a top view of a system of the present disclosure for cooling a galvo mirror. Fig. 2 shows a perspective view of a system of the present disclosure for cooling a galvo mirror. Fig. 3 shows a schematic representation of a system with a static axis for introducing a gas for cooling into a rotatable mirror. Detailed description of the invention The previously formulated problem of the invention is solved by the features of the independent claims. The dependent claims cover further specific embodiments of the invention. The present disclosure relates to a cooling system for a mirror, in particular a galvo mirror, to dissipate heat from the mirror. The proposed solution consists of introducing a gas into the area behind the mirror. The gas is introduced either through the axis of rotation of the mirror or into an opening transverse to the axis of the mirror by means of a feeder. The technical advantage of the proposed solution lies in the use of a static feed for the movable mirror. This allows a single stationary component to supply the gas to the interior of the movable mirror without increasing the mirror's moment of inertia. The gas can flow laterally towards the reflecting surface of the mirror or through an outlet between the feed and the mirror. The mirror is designed with a cylindrical surface on its back side, surrounding the axis of rotation. The feed has a corresponding cylindrical protrusion in which the cylindrical surface of the mirror is positioned at a distance. For efficient heat dissipation, the distance between the mirror and the feed should be as small as possible, for example, less than 1 mm, so that the gas flows into the cooling channel in the mirror and does not escape through the gap between the mirror and the feed.A small gap between the outlet of the supply and the inlet of the mirror allows the gas to be efficiently introduced into the mirror's channel. With an axial inlet (Fig. 3), this small gap is necessary for efficient heat dissipation because otherwise the gas would not flow across the hot surface. The cooling element is located at the axis of rotation, so adding cylindrical mirror material around the axis of rotation to improve heat transfer has no significant effect on the mirror's moment of inertia. To improve the gas transfer from the feed to the mirror, the gap between the feed and the mirror can be further reduced to less than 0.1 mm. As long as the distance between the feed and the mirror is smaller than the diameter of the radial channels, sealing is not required. Additional radial gas channels can be arranged inside the mirror to transport the gas laterally outwards. This can be advantageous if the thermal conductivity of the mirror material is insufficient. These channels can be located within the mirror itself or inside reinforcing structures on the back side of the highly reflective surface. In another embodiment, the gas is directed straight into the axis of rotation and thus enters the feed channel of the mirror. Fig. 1 shows a top view of a system according to the present disclosure with a mirror 1 which can be moved about the shaft 7. On the back side of the reflective side 2 of the mirror 1, a cylindrical surface 6 is arranged, in which the inlet channel 5 is located. The feeder 10 has a cylindrical recess 16 which, with a gap, surrounds the cylindrical surface 6 of the mirror 1. The outlet channel 15 is arranged in the cylindrical recess. According to the invention, the channels extend in a tangential direction, i.e., as shown in Fig. 1, along the gap. The inlet channels 5 and 15 must still overlap when the mirror rotates, but inlet channel 5 must be completely covered by the feeder 10 during rotation, which is why an axial and tangential / angular extension of the channels 5 and 15 and the feeder 10 is provided. A mounting 13 for a hose 20 can be arranged on the rear of the feeder. The gas is supplied via the hose 20. The gas can be air, which does not need to be cooled due to the hot mirror, since using excessively cool air carries the risk of condensation on the mirror. The system according to the invention can, for example, be used with air at room temperature. Fig. 2 shows a perspective view of the system components, with the feeder 10 positioned away from the back of the mirror 1 to allow a view of the inlet 8 of the inlet channel 5 (not visible). Outlets 9 of the discharge channels 4, located inside the mirror, are visible on the side of the mirror 1. A mounting 13 for a hose 20, through which the gas is supplied, is located on the back of the feeder 10. Fig. 3 shows an embodiment in which the mirror 1 is connected to a galvanometer 30 via a shaft 7. The mirror 1 and shaft are rotated by the galvanometer 30. The feed 10 is statically arranged, and the gas is supplied via inlet channel 5. The gap 12 between the feed 10 and the inlet channel 5 ensures efficient cooling, with the gas exiting the mirror substrate via outlet 9. Further aspects, features, and advantages of the present invention will readily become apparent from the following detailed description, which simply presents preferred embodiments and implementations. The present invention can also be implemented in other and different embodiments, and its various details can be modified in various obvious aspects without departing from the teaching and scope of the present invention.Accordingly, the drawings and descriptions are to be regarded as illustrative and not as limiting. Additional tasks and advantages of the invention are partly set out in the following description and partly become apparent from the description or can be deduced from the embodiment of the invention. Reference sign 1 Mirror 2 Reflective surface 3 Feed channel mirror 4 Discharge channel 5 Inlet channel 6 Cylindrical surface 7 Shaft 8 Inlet 9 Outlet 10 Feed 11 Outlet 12 Gap 13 Hose attachment 15 Outlet channel 16 Cylindrical recess 20 Hose 30 Galvanometer

Claims

A system for cooling a mirror (1), comprising: a. a rotatable mirror (1) which is attached to an axis of rotation and which has at least one gas channel inside the rotatable mirror (1) behind a reflecting surface (2) with an inlet channel (5) and at least one outlet (9); and b. a static supply (10) for a gas which has an outlet channel (15) which is connected via a gap (12) and thus without contact to the inlet channel (5) of the gas channel inside the rotatable mirror (1) for the supply of a gas. The system according to claim 1, wherein the static feed (10) is arranged axially, radially or parallel to the axis of rotation of the rotatable mirror (1). The system according to claim 1 or 2, wherein the rotatable mirror (1) has a cylindrical surface (6) on the side opposite the reflecting surface (2), which surrounds the axis of rotation around which a corresponding cylindrical recess (16) of the static feed (10) with the outlet channel (15) is arranged. The system according to claim 3, wherein the static feed (10) has a hose connection (13) on the side opposite the cylindrical recess (16). The system according to one of claims 1 to 4, wherein the inlet channel (5) of the rotatable mirror (1) is arranged transversely to the axis of rotation. The system according to any one of claims 1 to 5, wherein the rotatable mirror (1) is made of lightweight materials comprising beryllium, aluminium, silicon carbide. The system according to claim 6, wherein the rotatable mirror (1) has support structures on the back side facing the reflecting surface (2) in which the at least one outlet (9) is arranged. The system according to one of claims 5 or 6, wherein at least one outlet (9) is arranged laterally to the reflecting surface (2). The system according to one of claims 3 to 7, wherein the distance between the cylindrical surface (6) on the back of the rotatable mirror (1) and the cylindrical recess (16) of the static feed (10) is less than 1 mm. The system according to claim 9, wherein the distance is less than 0.1 mm. The system according to one of claims 3 to 10, wherein the rotatable mirror (1) rotates in the cylindrical recess (16) of the static feeder (10). A method for cooling a rotatable mirror (1), comprising the steps: a. Arranging a static gas supply (10) on a rotatable mirror (1), which has at least one gas channel inside the rotatable mirror (1) behind a reflective surface (2) of the rotatable mirror (1) with an inlet channel (5), wherein the static gas supply has an outlet channel (15) which is connected to the inlet channel (5) of the gas channel inside the rotatable mirror (1) via a gap (12) and thus without contact; b. Introducing a gas via the static gas supply (10) into the inlet channel (5) of the at least one gas channel inside the rotatable mirror (1); and c. Discharging the gas from the interior of the rotatable mirror (1) via at least one outlet (9) of the at least one gas channel. The method according to claim 12, wherein the rotatable mirror (1) rotates during the introduction and discharge of the gas. The method according to one of claims 12 or 13, wherein the gas is air. The method according to any one of claims 12 to 14, wherein the gas is at room temperature. The method according to one of claims 12 to 15, wherein the gas is discharged laterally from the rotatable mirror (1). The use of the system according to any one of claims 1 to 11 in a laser processing head.

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