Cleaning system and method for cleaning an optical element in an optical unit of a system for additive manufacturing

Abstract

The present disclosure relates to a cleaning system (1) for cleaning an optical element (27) in an optical unit of a system for the additive manufacturing of three-dimensional workpieces, the cleaning system (1) having: - a compressed air rod (3) which extends in a longitudinal direction (L) and has an end-face compressed air nozzle (25), - a compressed air connection (9) for introducing a blast of compressed air into the compressed air rod (3), and - a positioning device for the compressed air rod (3), wherein the positioning device has a connection piece (11) and a rail guide (5) which extends in the longitudinal direction (L), wherein the connection piece (11) can be connected to the optical unit in a defined position in relation to the optical element (27) at least transverse to the longitudinal direction (L), wherein the compressed air rod (3), guided by the rail guide (5), can be positioned in the longitudinal direction (L) from a retracted connection position region into an extended cleaning position region, wherein the positioning device has a stop (26) which prevents the compressed air rod (3) from being positioned beyond the cleaning position region.

Description

Title: Cleaning system and method for cleaning an optical element in an optical unit of an additive manufacturing system Description

[0001] The present disclosure relates to a cleaning system and method for cleaning an optical element in an optical unit of a system for additive manufacturing of three-dimensional workpieces. In particular, the cleaning system and method disclosed herein can be used to quickly and reliably clean a laser beam entrance disk located deep within a laser fiber connection of an optical unit, which is difficult to access.

[0002] The production of three-dimensional workpieces using additive manufacturing is often referred to as 3D printing. A special form of additive manufacturing is selective laser melting, in which a material to be processed is applied as a raw material in powder form in a thin layer to a base plate. The powdered raw material is melted or sintered selectively, i.e., location-specifically, using laser radiation and, after solidification, forms a layer of the workpiece. Once a workpiece layer is completed, the base plate is lowered by the amount of one layer, and the raw material powder for the next layer is applied, which is then again selectively melted or sintered using laser radiation.

[0003] A system for additive manufacturing using selective laser melting therefore typically has an optical unit with which one or more laser beams can be precisely focused and controlled over the powder bed. Since the laser beam(s) typically selectively scan the entire powder layer, the optical unit of such a system is also referred to as a scanning module. The optical elements within the optical unit must be absolutely clean and precisely positioned and calibrated relative to one another. Therefore, such an optical unit is typically not openable, and the optical elements within are protected as best as possible from external influences.

[0004] If the required laser source is not located within the optical unit, the laser light from an external laser source must be coupled into the optical unit. This is usually done via a laser fiber connector, to which a fiber optic cable is connected in order to couple laser light from an external laser source. A laser beam entrance plate is therefore located within the laser fiber connector of the optical unit. This plate protects the internal optical elements of the optical unit from external influences such as dust or other contaminants. The laser beam entrance plate is also an optical element of the optical unit, as the laser beam passes through it. It should be noted that the energy density of the laser can be very high, so that even the smallest contaminants on the laser beam entrance plate can lead to burns.Burns in an optical element can cause the laser's focus position to shift, resulting in a degraded production quality. Replacing the optical element, however, requires a complete recalibration of the optical unit, which can result in system downtime of several weeks. Since burns can have serious economic consequences, they must be avoided whenever possible. Therefore, it is important to ensure that the exterior of the laser beam entrance disk is as free as possible from dust or other contaminants.

[0005] However, the fact that the laser beam entrance disc is typically 15 cm deep inside the of the laser fiber connection, which offers only a 1.5 cm wide tubular access. The laser beam entrance disk is therefore very difficult to access and correspondingly difficult to clean. It is difficult to determine whether there are any contaminants on the laser beam entrance disk at all. However, this is the subject of another patent application DE 10 2023 1 12 669.5, which had not yet been published on the filing date of this disclosure.

[0006] For the present disclosure, the technical problem is to safely and quickly clean a difficult-to-access optical element in an optical unit of a system for additive manufacturing of three-dimensional workpieces, for example, a laser beam entrance disk located deep in a laser fiber connection. Particularly during the initial installation of an additive manufacturing system or during maintenance and repairs, it is essential that the laser beam entrance disk is exposed to external influences such as dust or other air contaminants.

[0007] This object is achieved by a cleaning system and method according to the independent claims. Preferred embodiments of the inventive solution can be found in the subclaims, the description, and the figures.

[0008] According to a first aspect of the present disclosure, a cleaning system is provided for cleaning an optical element in an optical unit of a system for additive manufacturing of three-dimensional workpieces, the cleaning system comprising: a compressed air rod extending in a longitudinal direction with a front-side compressed air nozzle, a compressed air connection for introducing a compressed air blast into the compressed air rod, and a positioning device for the compressed air rod, wherein the positioning device has a connecting piece and a rail guide extending in the longitudinal direction, wherein the connecting piece can be connected to the optical unit in a position defined at least transversely to the longitudinal direction with respect to the optical element, wherein the compressed air rod can be positioned in the longitudinal direction from a retracted connection position area into an extended cleaning position area, guided by the rail guide, wherein the positioning device has a stop which prevents the compressed air rod from being positioned further beyond the cleaning position area.

[0009] The cleaning system according to the invention allows a compressed air nozzle to be positioned quickly and safely close to the optical element when the latter is difficult to access in the optical unit, without striking the optical unit anywhere. As soon as the compressed air rod is positioned in the extended cleaning position area, the front-end compressed air nozzle is close enough to the optical element that a blast of compressed air into and out of the compressed air nozzle creates such a high air velocity on the surface of the optical element that dust or other contaminants on the surface of the optical element are entrained and catapulted out of the optical unit with the blast of compressed air. The stop of the positioning device prevents the front-end compressed air nozzle from coming into contact with the optical element. The length of the compressed air rod is adapted accordingly to the optical unit.The optical element is preferably a laser beam entry disk, which is located in a laser fiber connection of a scanning module of an additive manufacturing system, making it difficult to access. The compressed air nozzle can be configured as a round nozzle, a flat nozzle, or a slotted nozzle with one or more outlet openings. The shape and arrangement of the one or more outlet openings are determined by the user. Outlet openings define the geometry of the compressed air flow. The distance between the compressed air nozzle and the optical element can be selected depending on the type of compressed air nozzle used, ensuring that the compressed air flow is directed at the surface of the optical element to be cleaned as desired.

[0010] Optionally, the compressed air wand can extend through the connection piece in the extended cleaning position. This is useful for optical elements located particularly deep within the optical unit, such as a laser beam entrance disk in a laser fiber connector.

[0011] Optionally, the cleaning system can be designed so that the compressed air wand and the compressed air nozzle do not protrude beyond the connection piece in the retracted connection position area. This is useful to keep the compressed air wand and the front-end compressed air nozzle in a protected position in the retracted connection position area while the cleaning system is connected to the optics unit.

[0012] Optionally, the cleaning system can have a locking device designed to lock the pneumatic rod in the connection position area and / or the cleaning position area. The locking device can be, for example, a locking screw with which the pneumatic rod can be locked at a desired position in the longitudinal direction. Alternatively or additionally, the locking device can be formed by a latching mechanism in which a locking lug engages in a recess. By means of such a latching mechanism, the pneumatic rod can be locked at one or more predetermined latching positions within the cleaning position area and / or the connection position area, and / or in predetermined intermediate positions.

[0013] Optionally, the cleaning system can be equipped with a carriage, with the pneumatic rod attached to the carriage and the carriage sliding longitudinally along the rail guide. This allows for particularly simple and precise longitudinal guidance.

[0014] Optionally, the connection piece can have a slotted sleeve that can be placed over a laser fiber connection of the optical unit with elastic radial expansion to create a tool-free, play-free press fit between the connection piece and the laser fiber connection of the optical unit. It is advantageous to select a plastic with good abrasion resistance to prevent plastic abrasion of the sleeve and ensure that no abraded plastic particles land on the optical element. In this context, it is particularly useful if the slotted sleeve is made of a plastic with a certain degree of elasticity, such as polyoxymethylene (POM). This prevents the cleaning system from leaving scratches on the laser fiber connection.Furthermore, the connection piece clearly defines the positioning of the compressed air rod in a plane perpendicular to the longitudinal direction, so that the compressed air rod is automatically positioned concentrically with the laser fiber connection of the optics unit. This prevents the compressed air rod from hitting the laser fiber connection of the optics unit.

[0015] Optionally, the cleaning system can include at least one air filter, which is connected upstream of the compressed air connection to filter the air before it is introduced into the compressed air wand in the form of a compressed air blast. An air filter in the form of an oil filter can be particularly useful if a compressed air system is connected that may contain oil-containing air. A corresponding oil filter prevents any oil droplets contained in the compressed air from The particles are applied to the optical element by the compressed air blast. Alternatively or additionally, a particle filter in the form of a police filter can be used as an air filter to ensure that particles in the compressed air are not applied to the optical element.

[0016] Optionally, the compressed air wand can be moved back and forth longitudinally within the cleaning position range during the compressed air blast and / or between multiple compressed air blasts. This is particularly useful for varying the point of impact of the compressed air blast on the optical element and achieving a contactless brushing effect with the compressed air blast. The stop of the positioning system prevents the compressed air nozzle from hitting the optical element, allowing an operator to safely move the compressed air wand back and forth. The positioning system can provide multiple predetermined locking positions in which the compressed air wand can be moved or locked within the cleaning position range. This enables reproducible back and forth movement. There can be multiple cleaning position ranges in which the compressed air wand can be moved back and forth.

[0017] Optionally, the connection piece can have a through-hole, wherein the through-hole has an inner diameter that is larger than the outer diameter of the compressed air rod. This preferably results in an annular air outlet around the compressed air rod within the through-hole, which is large enough to discharge the compressed air blast, but small enough so that the air velocity through the air outlet opening is high enough to expel any contaminant particles. A through-hole that is too large would also be disadvantageous in that new dust particles could fall back into the laser fiber connection. This is particularly problematic if the laser fiber connection is directed vertically. It has been found that an inner diameter of the through hole that is approximately 1.5 to 2.5 times the outer diameter of the pneumatic rod is useful.

[0018] Alternatively or in addition to the through-hole, at least one outlet opening can be provided on the connection piece through which contaminants blown off the optical element can be removed. An extraction device can be connected to such an outlet opening, for example, for active extraction. Passive extraction through the overpressure generated by the compressed air blast from the outlet opening is also conceivable. A check valve could be arranged at the outlet opening to prevent dust from entering from the outside through the outlet opening.

[0019] Optionally, the cleaning system can include a suction device designed to extract the contamination particles ejected from the through-hole by the pressure surge. This prevents the ejected contamination particles from landing on the optical element again.

[0020] To prevent new dust particles from being sucked in from the environment and into the optical system, it can optionally be provided that the extraction flow generated by the extraction device has a lower extraction power than the compressed air blast introduced by the compressed air nozzle. Furthermore, it can be provided that an extraction flow is only generated during the compressed air blast.

[0021] It is conceivable that the extraction device is designed in such a way that an extraction flow is generated near the compressed air nozzle and near the optical element. Thus, the contaminant particles that are not thrown out of the through-hole by the pressure surge, are sucked off directly at the point of turbulence near the optical element.

[0022] Optionally, the connection piece can have a sleeve base surface that runs annularly around the through-opening and is designed to rest circumferentially on a front-side annular surface of a laser fiber connection of the optical unit. This is particularly advantageous for closing off the laser fiber connection, so that the through-opening is the only air outlet for the compressed air blast, so that the air velocity is sufficiently high to expel the contaminant particles. To ensure that the connection piece fits correctly on the laser fiber connection of the optical unit, it is advisable to design the axial length of the sleeve of the connection piece smaller than the axial length of the laser fiber connection, so that the connection piece can rest flatly with the sleeve base surface on the front-side annular surface of the laser fiber connection when the cleaning system is installed.To check that the connection piece is correctly placed on the laser fiber connection of the optical unit, a viewing window and / or a spirit level can be provided on the connection piece.

[0023] Optionally, the cleaning system can include an inspection unit for inspecting the optical element, wherein the inspection unit can be positioned in a defined inspection position relative to the optical element using the positioning device. The positioning device can thus be used to alternately position the compressed air wand for cleaning and the inspection unit for inspecting the optical element. The optical element can be inspected before cleaning to determine whether it requires cleaning at all, and / or after cleaning to determine whether it requires further cleaning. The inspection unit from DE 10 2023 1 12 669. 5 can be used here, for example. The inspection unit can, for example, have a camera and lighting. To simplify and accelerate the transition between cleaning and inspection, the positioning device could have a turret system with which either the compressed air nozzle or the inspection unit can be positioned without having to remove the positioning device from the optical unit for the change.

[0024] According to a second aspect of the present disclosure, a cleaning method is provided for cleaning an optical element in an optical unit of a system for additive manufacturing of three-dimensional workpieces. The cleaning method comprises the following steps: Placing a connection piece of a cleaning system described above onto a laser fiber connection of the optical unit, with the compressed air rod positioned in the retracted connection position area, Positioning the compressed air wand in the extended cleaning position area, and Introducing a burst of compressed air into the compressed air rod.

[0025] Optionally, the compressed air wand can protrude through the connection piece in the extended cleaning position area.

[0026] Optionally, the cleaning procedure can be carried out in such a way that the compressed air rod does not protrude beyond the connection piece with the compressed air nozzle in the retracted connection position area.

[0027] Optionally, a locking device can be released before the compressed air wand is positioned from the connection position area to the cleaning position area.

[0028] Optionally, the air can be filtered by at least one upstream air filter before it is introduced into the compressed air wand in the form of a compressed air blast.

[0029] Optionally, the compressed air wand can be moved back and forth longitudinally in the cleaning position area during the compressed air blast and / or between several compressed air blasts.

[0030] Optionally, the cleaning process may further comprise the following steps: Positioning an inspection unit in a defined inspection position with respect to the optical element by means of the positioning device, and Inspecting the optical element using the inspection unit. The positioning device can therefore be used either to position the compressed air rod for cleaning or to position the inspection unit for inspecting the optical element. The optical element can be inspected before cleaning, i.e., positioning the compressed air rod and initiating the compressed air blast, to determine whether it requires cleaning at all, and / or after cleaning, i.e., positioning the compressed air rod and initiating the compressed air blast, to determine whether it requires further cleaning. Cleaning, i.e., positioning the compressed air rod and initiating the compressed air blast, and checking, i.e., positioning an inspection unit and inspecting the optical element, can be repeated alternately as often as necessary. The inspection unit from DE 102023 1 12 669.5, for example, can be used here.

[0031] The present disclosure is explained in more detail below with reference to the accompanying drawings. Fig. 1 is a perspective view of an embodiment of a cleaning system disclosed herein mounted on a laser fiber connector with the pneumatic wand in the retracted connector position region; Fig. 2 is a perspective view of the embodiment according to Fig. 1 , wherein the compressed air rod is in the extended cleaning position area; and Fig. 3 is a longitudinal sectional view of the embodiment according to Fig. 2.

[0032] Fig. 1 shows an embodiment of the cleaning system 1 according to the invention, which can be used for cleaning an optical element 27 in an optical unit of a system for additive manufacturing of three-dimensional workpieces. Only one laser fiber connection 21 of the optical unit is shown in Fig. 1. The additive manufacturing system is not shown.

[0033] The cleaning system 1 has a compressed air rod 3 extending in a longitudinal direction L. The compressed air rod 3 is attached to an end of the compressed air rod 3 arranged at the top in Fig. 1 by means of a carriage 7 which slides on a rail guide 5. The rail guide 5 also extends in the longitudinal direction L, so that the carriage 7 can be moved and positioned in the longitudinal direction L. The carriage 7 has a compressed air connection 9 for introducing a burst of compressed air into the compressed air rod 3. At an end of the compressed air rod 3 shown at the bottom in Fig. 1 there is a front-end compressed air nozzle 25 from which a burst of compressed air introduced into the compressed air rod 3 through the compressed air connection 9 emerges.

[0034] At one end of the rail guide 5 arranged at the bottom in Fig. 1, a connecting piece 11 is attached, which can be connected to the laser fiber connection 21 of the optical unit in a position defined at least transversely to the longitudinal direction L with respect to the optical element 27 to be cleaned. The connecting piece 11 here has a cover plate 13 and a slotted sleeve 15. The cover plate 13 extends in a plane xy perpendicular to the longitudinal direction L. For better orientation in the figures, a right-handed Cartesian coordinate system is shown in which the z-axis runs parallel to the longitudinal direction L and the x-axis and the y-axis span the plane xy perpendicular to the longitudinal direction L. The sleeve 15 of the connecting piece 11 extends coaxially to the compressed air rod 3 from the cover plate 13 of the connecting piece 11 downwards.The sleeve 15 has an axial slot 17 so that the sleeve 15 can be placed onto the laser fiber connection 21 of the optical unit with elastic radial expansion to form a tool-free, detachable and play-free press fit between the connection piece 11 and the laser fiber connection 21. The connection piece 11, i.e. the cover plate 13 with the sleeve 15, are preferably made of a plastic, for example polyoxymethylene (POM). The compressed air rod 3, the rail guide 5 and the carriage 7 are preferably made of metal and have stainless steel surfaces that can be ultrasonically cleaned, for example, in an isopropanol bath. A locking device 19 in the form of a locking screw on the carriage 7 serves to lock the compressed air rod 3 in a desired position in the longitudinal direction L.

[0035] The cover plate 13 of the connecting piece 11 has a through-opening 23, which runs coaxially to the sleeve 15 in the longitudinal direction L through the cover plate 13. The sleeve 15, the through-opening 23, the laser fiber connection 21 and the compressed air rod 3 are thus arranged coaxially. As a result, the compressed air rod 3, when displaced along the longitudinal direction L with the front-side compressed air nozzle 25, can move through the through-opening 23 into the sleeve 15 and beyond downwards into extend into the laser fiber connection 21. If the sleeve 15 is placed precisely on the laser fiber connection 21 as shown, the compressed air rod 3 can extend into the laser fiber connection 21 without contact, so that the front-side compressed air nozzle 25 can be safely placed deep into the laser fiber connection 21.

[0036] In Fig. 1, the carriage 7 is in a maximum upper position, in which the compressed air rod 3 is located in a retracted connection position range. In this position of the compressed air rod 3, the cleaning system 1 can preferably be attached to the laser fiber connection 21. The compressed air nozzle 25 is retracted so far that when the sleeve 15 is placed on the laser fiber connection 21, no contact is possible between the compressed air nozzle 25 and the laser fiber connection 21. As soon as the sleeve 15 of the connection piece 11 is placed on the laser fiber connection 21, the compressed air rod 3 only has one translational degree of freedom of movement, namely along the longitudinal direction L, provided the locking screw 19 is loosened.

[0037] In Fig. 2, the pneumatic rod 3 is located in an extended cleaning position, with the carriage 7 in a lower position. A stop 26 in the form of a rubber stopper, located on the underside of the carriage 7, rests against the cover plate 13 and prevents the pneumatic rod 3 from being moved further downward. Alternatively, the stop can be formed by a latching mechanism, in which a locking lug engages a recess.

[0038] Fig. 3 shows the operation of the cleaning system 1 mounted on a laser fiber connection 21 while the compressed air rod 3 is in the extended cleaning position. In the cleaning position shown, the compressed air nozzle 25 is close to a laser beam entry disk 27, which here represents the optical element of the optical unit to be cleaned. If a compressed air blast is now applied via the compressed air connection 9 is introduced into the compressed air rod 3, the compressed air exits the compressed air nozzle 25 at high speed and hits the top side of the laser beam entry disk 27 to be cleaned at high speed. As a result, dust particles or other contaminants are entrained by the compressed air and pushed upwards past the compressed air rod 3. The through-opening 23 in the cover plate 13 is selected to be large enough that the compressed air can exit at high speed and as little dust as possible can penetrate from the outside into the laser fiber connection 21. For this purpose, an underside of the cover plate 13 forms a sleeve base surface 29 which runs annularly around the through-opening 23 and rests circumferentially on an end-face annular surface 31 of the laser fiber connection 21 of the optics unit. As a result, the compressed air can only escape upwards through the through-opening 23.

[0039] To achieve a non-contact brushing effect on the laser beam entry disk 27, the carriage 7 is moved up and down a short distance within the cleaning position range during a pressure pulse and / or between multiple pressure pulses, so that the compressed air pulse exiting the compressed air nozzle 25 impacts different points on the surface of the laser beam entry disk 27. Once cleaning has been performed, the cleaning system 1 can be removed and checked with an inspection system to determine whether the laser beam entry disk 27 has been successfully cleaned. If this is not the case, the cleaning process can be repeated.

[0040] List of reference symbols: 1 cleaning system 3 compressed air rods 5 Rail guide 7 sleds 9 Compressed air connection 1 1 connecting piece 13 Cover plate 15 Sleeve 17 Slot 19 Locking device / locking screw 21 Laser fiber connection 23 Passage opening 25 Compressed air nozzle 26 Stop 27 Optical element / laser beam entrance disc 29 Case base area 31 frontal ring surface of the laser fiber connection L longitudinal direction

Claims

Claims 1. A cleaning system (1) for cleaning an optical element (27) in an optical unit of a system for additive manufacturing of three-dimensional workpieces, the cleaning system (1) comprising: a compressed air rod (3) extending in a longitudinal direction (L) with a front-end compressed air nozzle (25), a compressed air connection (9) for introducing a compressed air blast into the compressed air rod (3), and a positioning device for the compressed air rod (3), the positioning device comprising a connecting piece (11) and a rail guide (5) extending in the longitudinal direction (L), the connecting piece (11) being connectable to the optical unit in a position defined at least transversely to the longitudinal direction (L) with respect to the optical element (27), the compressed air rod (3) being guided by the rail guide (5) in the longitudinal direction (L) and being positionable from a retracted connection position range into an extended cleaning position range.wherein the positioning device has a stop (26) which prevents the pneumatic rod (3) from being moved further beyond the cleaning position range., 2. Cleaning system (1) according to claim 1, wherein the compressed air rod (3) projects through the connecting piece (11) in the extended cleaning position area.

3. Cleaning system (1) according to claim 1 or 2, wherein the compressed air rod (3) does not protrude beyond the connection piece (11) with the compressed air nozzle (25) in the retracted connection position area.

4. Cleaning system (1) according to one of the preceding claims, further comprising a locking device (19) which is designed to lock the compressed air rod (3) in the connection position area and / or the cleaning position area.

5. Cleaning system (1) according to one of the preceding claims, further comprising a carriage (7), wherein the compressed air rod (3) is attached to the carriage (7) and the carriage (7) is slidably guided in the longitudinal direction (L) along the rail guide (5).

6. Cleaning system (1) according to one of the preceding claims, wherein the connecting piece (11) has a slotted sleeve (15) which can be placed onto a laser fiber connection (21) of the optical unit with elastic radial expansion in order to form a tool-free, play-free press fit between the connecting piece (11) and the laser fiber connection (21) of the optical unit.

7. Cleaning system (1) according to one of the preceding claims, further comprising at least one air filter, wherein the at least one air filter is connected upstream of the compressed air connection (9) in order to filter compressed air before it is introduced into the compressed air rod (3) in the form of the compressed air blast.

8. Cleaning system (1) according to one of the preceding claims, wherein the compressed air rod (3) is movable back and forth in the longitudinal direction (L) during the compressed air blast and / or between several compressed air blasts in the cleaning position area.

9. Cleaning system (1) according to one of the preceding claims, wherein the connecting piece (11) has a through-opening (23), the through-opening (23) having an inner diameter which is larger than an outer diameter of the compressed air rod (3).

10. Cleaning system (1) according to claim 9, wherein the connecting piece (11) has a sleeve bottom surface (29) which runs annularly around the through-opening (23) and is designed to rest annularly on an end-face annular surface (31) of a laser fiber connection (21) of the optical unit. 1 1. Cleaning system (1) according to one of the preceding claims, further comprising an inspection unit for inspecting the optical element (27), wherein the inspection unit can be positioned in a defined inspection position with respect to the optical element (27) by means of the positioning device.

12. A cleaning method for cleaning an optical element (27) in an optical unit of a system for additive manufacturing of three-dimensional workpieces, the cleaning method comprising: Placing a connection piece (11) of a cleaning system (1) according to one of the preceding claims onto a laser fiber connection (21) of the optical unit, wherein the compressed air rod (3) is positioned in the retracted connection position area, Positioning the compressed air rod (3) in the extended cleaning position area, and Introducing a burst of compressed air into the compressed air rod (3).

13. Cleaning method according to claim 12, wherein the compressed air rod (3) projects through the connecting piece (11) in the extended cleaning position area.

14. Cleaning method according to claim 12 or 13, wherein the compressed air rod (3) does not protrude beyond the connecting piece (11) with the compressed air nozzle (25) in the retracted connection position area.

15. Cleaning method according to one of claims 12 to 14, wherein a locking device (19) is released before the compressed air rod (3) is positioned from the connection position area into the cleaning position area.

16. Cleaning method according to one of claims 12 to 15, wherein compressed air is filtered by means of at least one upstream air filter before it is introduced into the compressed air rod (3) in the form of the compressed air blast.

17. Cleaning method according to one of claims 12 to 16, wherein the compressed air rod (3) is moved back and forth in the longitudinal direction during the compressed air burst and / or between several compressed air bursts in the cleaning position area.

18. Cleaning method according to one of claims 12 to 17, wherein contaminant particles blown off the optical element by means of the compressed air blast are sucked off by means of a suction device.

19. A cleaning method according to any one of claims 12 to 18, further comprising the steps of: Positioning an inspection unit in a defined inspection position with respect to the optical element (27) by means of the positioning device, and Inspecting the optical element (27) using the inspection unit.

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