Magnetic fluid seal high vacuum air bearing device and motion stage

Abstract

The application relates to a magnetic fluid sealed high-vacuum air floating device and a moving table, and relates to the field of high-precision movement technology, and is used for solving the problem that the structure of the air floating device is complex and huge due to the increase of the differential air pumping stages. The magnetic fluid sealed high-vacuum air floating device comprises: an air floating cover with an inner cavity; a differential air pumping part arranged in the inner cavity; a planar air float arranged in the differential air pumping part; and a magnetic fluid sealing assembly arranged on the air floating cover and located at the outer periphery of the differential air pumping part. The differential air pumping part is used for reducing the gas diffusion of the planar air float to the edge, a magnetic fluid film with a sealing function is formed on the magnetic fluid sealing assembly, a first contact surface is formed on the magnetic fluid film, a second contact surface is formed on the planar air float, and a to-be-supported part slides on the first contact surface and the second contact surface at the same time. The magnetic fluid sealing assembly is combined with the differential air pumping part, the ability of preventing the gas from diffusing into the vacuum cavity is improved, and the differential air pumping stages are reduced.

Description

Technical Field

[0001] This invention relates to the field of high-precision motion technology, and in particular to a magnetohydrodynamic sealed high-vacuum air levitation device and a motion table. Background Technology

[0002] Air-bearing devices are based on planar air-bearing technology, which uses air as a lubricant in sliding bearings. During normal operation, the two sliding surfaces are completely separated by an air film, with the high-pressure air film between the surfaces supporting the external load. The high-pressure air film offers advantages such as homogenization, low vibration, high motion accuracy, low air viscosity, low friction loss, minimal heat generation and deformation, and long service life. Vacuum air-bearing devices are used in lithography machines, wafer inspection equipment, and semiconductor application equipment as key components for precision transport and positioning. Especially in lithography machines, the workpiece stage is responsible for supporting the wafer movement during exposure. To achieve extremely high motion and positioning accuracy, the workpiece stage and its associated bottom frame structure have very strict requirements for mechanical vibration. Therefore, air-bearing bearings are commonly used as support elements for moving parts between workpieces that undergo relative motion. Air-bearing bearings minimize the coefficient of friction, effectively reducing mechanical vibration caused by friction between workpieces, ensuring high precision, high speed, and high thermal stability of the relative motion of the workpieces.

[0003] In lithography machines, all optical and moving parts are integrated in a high-vacuum environment, and the moving parts must meet the high-vacuum (<10Pa-4Pa) requirements. If ordinary planar air bearings are used, the air supply diffuses through the air film along the surface of the air bearing into the vacuum chamber, disrupting the high-vacuum environment and affecting the normal operation of the lithography machine. If vacuum planar air bearings are used, current vacuum planar air bearings employ a multi-stage differential pumping method, gradually reducing the amount of gas diffusing from the air bearing edge into the vacuum chamber to maintain the vacuum chamber pressure. Typically, a 2-4 stage differential pumping structure is used; if a lower vacuum level is required, the number of pumping stages needs to be increased. Therefore, applying differential pumping methods to high-vacuum chambers requires a high-speed high-vacuum pump set for auxiliary pumping, and the air bearing size will also be large, requiring a relatively large number of vacuum pumps.

[0004] In other words, existing technologies suffer from the problem of complex and bulky structures due to the addition of differential pumping stages within the air flotation device. Summary of the Invention

[0005] This invention provides a magnetohydrodynamic sealed high-vacuum air flotation device and a motion stage to solve the problem of complex and bulky structure caused by adding differential pumping stages inside the air flotation device.

[0006] This invention provides a magnetohydrodynamic (MHD) sealed high-vacuum air flotation device, comprising: an air flotation cap having an inner cavity; a differential suction component disposed within the inner cavity; a planar air flotation component disposed within the differential suction component; and a MHD sealing assembly disposed on the air flotation cap and located on the outer periphery of the differential suction component. The differential suction component is used to reduce gas diffusion from the planar air flotation component to the edge. A magnetohydrodynamic (MHD) film with sealing function is formed on the MHD sealing assembly to prevent gas diffusion into the external vacuum environment. A first contact surface is formed on the MHD film, and a second contact surface is formed on the planar air flotation component. The supported component can slide simultaneously on both the first and second contact surfaces.

[0007] In one embodiment, the differential suction device is provided with a receiving cavity and at least one differential groove, the at least one differential groove being arranged in a ring around the outer periphery of the receiving cavity, and the differential suction device is also provided with a first suction hole communicating with at least one differential groove.

[0008] In one embodiment, the differential extraction component is provided with a plurality of differential slots, which are arranged sequentially along the central axis d away from the accommodating cavity. In two adjacent differential slots, the differential slot closer to the central axis d is located inside the other differential slot.

[0009] In one embodiment, the differential air extraction component is provided with a third air extraction hole, one end of which is connected to the accommodating cavity, and the other end of which is connected to a second air extraction hole provided on the air flotation cap.

[0010] In one embodiment, the magnetofluid sealing assembly includes: a magnetofluid cap sleeved on the outer periphery of a differential pump and located on an air flotation cap; a magnetic assembly disposed within the magnetofluid cap; and an injection line, one end of which communicates with the interior of the magnetic assembly and the other end of which extends out from the air flotation cap, the injection line being used to supply magnetofluid to the magnetic assembly, the magnetic assembly being capable of converting the magnetofluid into a magnetofluid membrane.

[0011] In one embodiment, the magnetic fluid sealing assembly further includes a first magnetic stop and a second magnetic steel stop, both of which are disposed within the magnetic fluid sealing cover for mounting magnetic components.

[0012] In one embodiment, the magnetic component includes: a plurality of annular magnetic strips disposed between two adjacent annular magnetic strips along a path away from the magnetofluid cap; wherein, the annular pole piece is provided with a toothed end near the end of the member to be supported, and the magnetofluid membrane is located at the toothed end of the toothed strip.

[0013] In one implementation, the tooth width of the rack is twice the height of the magnetofluid film.

[0014] In one embodiment, the first upper surface of the differential air extraction component, the second upper surface of the planar air flotation component, and the third upper surface of the magnetohydrodynamic sealing assembly are coplanar.

[0015] In one embodiment, the flatness of the first upper surface, the second upper surface, and the third upper surface is no greater than 2 μm.

[0016] In one embodiment, the air flotation cap includes: an air flotation cap body; a magnetohydrodynamic adjustment seat disposed on the air flotation cap body for supporting the magnetohydrodynamic sealing assembly; and a differential support seat disposed within the air flotation cap body for supporting a differential air extraction component; wherein the magnetohydrodynamic adjustment seat and the differential support seat cooperate to make the first upper surface and the third upper surface coplanar.

[0017] The present invention also provides a motion platform under which at least one of the above-mentioned magnetohydrodynamic sealed high vacuum air levitation devices are disposed.

[0018] Compared with existing technologies, the advantages of this invention lie in the provision of a magnetic fluid sealing assembly. This assembly generates a magnetic fluid membrane with sealing function, preventing gas from diffusing from the gap between the supported component and the air-float cap into the external vacuum environment. This reduces the number of differential pumping stages in the differential pumping unit. Specifically, by combining the magnetic fluid sealing assembly with the differential pumping unit, the ability to prevent gas diffusion into the vacuum chamber is effectively improved, while simultaneously reducing the number of differential pumping stages. This avoids the structural complexity and bulkiness caused by the need for additional differential pumping stages in existing air-float devices. Furthermore, it reduces the volume of the magnetic fluid-sealed high-vacuum air-float device and simplifies the number of its components, resulting in a compact structure, fewer pumping stages, and a low vacuum leakage rate. Attached Figure Description

[0019] The invention will now be described in more detail with reference to embodiments and the accompanying drawings.

[0020] Figure 1 This is a schematic diagram of the three-dimensional structure of the magnetohydrodynamic sealed high vacuum air levitation device in an embodiment of the present invention;

[0021] Figure 2 for Figure 1 Main sectional view of the medium magnetohydrodynamic sealed high vacuum air flotation device (showing the air flotation cover and the holes opened thereon);

[0022] Figure 3 for Figure 1 Main sectional view of the magnetohydrodynamic (MHD) high vacuum air-float device (showing the specific structure of the MHD sealing assembly and the assembly relationship between the vacuum chamber and the MHD high vacuum air-float device);

[0023] Figure 4 for Figure 1A schematic diagram showing the assembly relationship between the central motion platform, the differential air extraction component, and the planar air flotation system (showing the specific structure of the differential air extraction component);

[0024] Figure 5 for Figure 1 A schematic diagram of the planar distribution of the annular pole shoe bars, planar air flotation, and differential tank (top view);

[0025] Figure 6 This is a three-dimensional structural diagram of a magnetohydrodynamic sealed high vacuum air levitation device in another embodiment of the present invention (showing the motion table).

[0026] Figure label:

[0027] 10. Air flotation cap; 11. Air flotation cap body; 12. Magnetofluid adjustment seat; 13. Differential support seat; 14. Inner cavity; 15. Second evacuation port; 16. Cap base; 17. Injection port; 20. Differential evacuation component; 21. Receptacle; 22. Differential groove; 23. First evacuation port; 24. Third evacuation port; 25. Air flotation supply port; 30. Magnetofluid sealing assembly; 31. Magnetofluid cap; 32. First magnetic steel block; 33. Second magnetic steel block; 34. Magnetic assembly; 341. Annular magnetic steel strip; 342. Annular pole shoe strip; 3421. Rack; 40. Motion table; 41. Motion table base; 42. Motion table sliding block; 50. Planar air flotation; 100. Vacuum chamber; 200. Magnetofluid-sealed high-vacuum air flotation device. Detailed Implementation

[0028] The invention will now be further described with reference to the accompanying drawings.

[0029] like Figures 1 to 3 As shown, the present invention provides a magnetohydrodynamic (MHD) sealed high-vacuum air flotation device 200, which includes an air flotation cap 10, a differential suction component 20, a planar air flotation component 50, and a magnetohydrodynamic (MHD) sealing assembly 30. The air flotation cap 10 has an inner cavity 14; the differential suction component 20 is disposed within the inner cavity 14; the planar air flotation component 50 is disposed within the differential suction component 20; the MHD sealing assembly 30 is disposed on the air flotation cap 10 and located on the outer periphery of the differential suction component 20; the differential suction component 20 is used to reduce gas diffusion from the planar air flotation component 50 to the edge; a magnetohydrodynamic (MHD) film with sealing function can be formed on the MHD sealing assembly 30 to prevent gas diffusion into the external vacuum environment; a first contact surface is formed on the MHD film; a second contact surface is formed on the planar air flotation component 50; the supported component can slide simultaneously on the first and second contact surfaces.

[0030] In the above configuration, a magnetic fluid sealing assembly 30 is provided. The magnetic fluid membrane generated by the magnetic fluid sealing assembly 30, which has a sealing function, prevents gas from diffusing from the gap between the support component and the air-float cover 10 into the external vacuum environment. This reduces the number of differential pumping stages in the differential pumping component 20. Specifically, by combining the magnetic fluid sealing assembly 30 with the differential pumping component 20, the ability to prevent gas diffusion into the vacuum chamber is effectively improved, while also reducing the number of differential pumping stages. This avoids the structural complexity and bulkiness caused by the need to add differential pumping stages to the differential pumping component 20 of existing air-float devices. Furthermore, it reduces the volume of the magnetic fluid-sealed high-vacuum air-float device 200 and simplifies the number of its components, resulting in a compact structure, fewer pumping stages, and a low vacuum leakage rate.

[0031] It should be noted that the magnetohydrodynamic sealed high-vacuum air levitation device 200 of this invention provides a method and means for realizing a precision motion control console in high vacuum. Existing technologies typically employ non-contact high-precision motion control mechanisms, specifically magnetic levitation and air levitation. Magnetic levitation has stringent control requirements and is difficult to manage thermally, while air levitation has a simple structure and is easy to control. The magnetohydrodynamic sealed high-vacuum air levitation device 200 of this invention, combined with vacuum technology, can be used in high-vacuum systems to meet the needs of photolithography and semiconductor systems. The planar air levitation 50 in this application can be an air bearing.

[0032] Specifically, such as Figure 4 and Figure 5 As shown, in one embodiment, the differential suction component 20 is provided with a receiving cavity 21 and at least one differential groove 22. The at least one differential groove 22 is arranged in a ring around the outer periphery of the receiving cavity 21. The differential suction component 20 is also provided with a first suction hole 23 communicating with at least one differential groove 22. The air flotation cap 10 is provided with a second suction hole 15. One end of the second suction hole 15 is connected to the first suction hole 23, and the other end of the second suction hole 15 is connected to an external suction device.

[0033] Specifically, such as Figure 4 and Figure 5 As shown, in one embodiment, the differential extraction component 20 is provided with three differential slots 22. The three differential slots 22 are arranged sequentially along the central axis d away from the accommodating cavity 21. In two adjacent differential slots 22, the differential slot 22 closer to the central axis d is located inside the other differential slot 22.

[0034] Specifically, such as Figure 2 and Figure 4 As shown, in one embodiment, the differential air extraction component 20 is provided with a third air extraction hole 24. One end of the third air extraction hole 24 is connected to the accommodating cavity 21, and the other end is connected to the second air extraction hole 15 provided on the air flotation cap 10.

[0035] In the above configuration, the differential groove 22, the first extraction port 23, the third extraction port 24, and the accommodating cavity 21 define a four-stage differential extraction channel. The four-stage differential extraction function can be achieved using an external extraction device, thereby reducing the gas diffusion from the planar air flotation 50 to the edges.

[0036] Specifically, such as Figures 1 to 3 As shown, in one embodiment, the first upper surface of the differential suction component 20, the second upper surface of the planar air flotation 50, and the third upper surface of the magnetohydrodynamic sealing assembly 30 are coplanar. This ensures that the component to be supported can be placed on the same plane, thereby ensuring the subsequent movement accuracy of the component to be supported.

[0037] Specifically, in one embodiment, the flatness of the plane shared by the first upper surface of the differential air extraction component 20, the second upper surface of the planar air flotation 50, and the third upper surface of the magnetohydrodynamic sealing assembly 30 is within 2 μm.

[0038] It should be noted that the differential suction component 20 in this application can reduce the pressure of the planar air float 50 to meet the magnetic fluid sealing differential pressure requirements of the magnetic fluid sealing assembly 30. Simultaneously, the differential suction component 20 provides support for the planar air float 50, and the load on the supported component must be considered. The differential suction component 20 includes a differential groove 22, annular suction holes (first suction hole 23 and third suction hole 24), and an air float supply hole 25. The planar air float 50 is fixed to the bottom of the differential suction component 20. The structural design of the differential suction component 20 is consistent with that of the planar air float; for example, if the planar air float is a cylindrical disk structure, the differential suction component is designed as a cylindrical disk structure with a differential suction groove on the disk. The pump is connected to the vacuum chamber exhaust pump (with an external suction device connected) through the annular suction holes, gradually reducing the inflation pressure of the planar air float 50 from 0.4 MPa to 8000 Pa in the air float sealing chamber, thereby meeting the magnetic fluid sealing differential pressure requirements.

[0039] Specifically, such as Figure 5 As shown, in one embodiment, the differential groove 22 is a rectangular annular groove.

[0040] Specifically, such as Figure 3 As shown, in one embodiment, the magnetic fluid sealing assembly 30 includes a magnetic fluid cap 31, a magnetic component 34, and a liquid injection line. The magnetic fluid cap 31 is fitted onto the outer periphery of the differential pump 20 and is located on the air flotation cap 10. The magnetic component 34 is disposed within the magnetic fluid cap 31. One end of the liquid injection line communicates with the interior of the magnetic component 34, and the other end extends out of the air flotation cap 10. The liquid injection line is used to supply magnetic fluid to the magnetic component 34, which is capable of converting the magnetic fluid into a magnetic fluid membrane.

[0041] Specifically, such as Figure 3As shown, in one embodiment, the magnetic fluid sealing assembly 30 further includes a first magnetic steel block 32 and a second magnetic steel block 33, both of which are disposed inside the magnetic fluid sealing cover 31 for mounting magnetic components.

[0042] Furthermore, such as Figure 3 As shown, in one embodiment, the magnetic fluid sealing assembly 30 includes a magnetic fluid cap 31, a first magnetic stop 32, a second magnetic stop 33, a magnetic component 34, and an injection line. The magnetic fluid cap 31 is sleeved on the outer periphery of the differential pump 20 and is located on the air flotation cap 10; the first magnetic stop 32 is disposed inside the magnetic fluid cap 31; the second magnetic stop 33 is disposed inside the magnetic fluid cap 31 and is closer to the central axis of the magnetic fluid cap 31 than the first magnetic stop 32; the magnetic component 34 is disposed inside the magnetic fluid cap 31 and is located between the first magnetic stop 32 and the second magnetic stop 33; one end of the injection line communicates with the interior of the magnetic component 34, and the other end of the injection line extends out from the air flotation cap 10. The injection line is used to provide magnetic fluid to the magnetic component 34, which is capable of converting the magnetic fluid into a magnetic fluid membrane.

[0043] Of course, in alternative embodiments not shown in the accompanying drawings, only the first magnet stop 32 may be provided, and the second magnet stop 33 may not be provided.

[0044] Specifically, such as Figure 3 and Figure 5 As shown, in one embodiment, the magnetic component 34 includes a plurality of annular magnetic strips 341 and annular pole piece strips 342. The plurality of annular magnetic strips 341 are sequentially arranged along a direction away from the central axis of the magnetic fluid cap 31; the annular pole piece strips 342 are disposed between two adjacent annular magnetic strips 341; a toothed rack 3421 is provided at one end of the annular pole piece strip 342 near the member to be supported, and the magnetic fluid membrane is located at the toothed end of the toothed rack 3421.

[0045] Specifically, such as Figure 5 As shown, in one embodiment, the magnetic component 34 includes four annular magnetic strips 341.

[0046] Specifically, such as Figure 5 As shown, in one embodiment, the annular magnet strip 341 is a rectangular ring.

[0047] Specifically, in one embodiment, the tooth width of the rack 3421 is twice the height of the magnetofluid film.

[0048] It should be noted that the magnetohydrodynamic (MHD) sealing assembly 30 is suitable for sealing residual gas in differential pumping under high vacuum conditions. The MHD sealing assembly 30 isolates the high vacuum from the air-floating cap cavity through multi-stage MHD rings (annular pole shoe strips 342), and the MHD rings provide a non-contact fluid seal, suitable for non-contact support. Compared to traditional MHD seals, this structure allows for planar movement of the MHD seal. The MHD sealing assembly 30 forms a cubic annular structure, integrated with the air-floating cap 10 to form a cuboid encapsulation cavity. The upper surface is the MHD sealing surface (third upper surface) and the air-floating film surface (second upper surface). The MHD cap 31 is the main structural component of the MHD sealing assembly 30, possessing sufficient strength to fix the annular magnetic strips 341, annular pole shoe strips 342, and magnetic stops (including first and second magnetic stops), while also preventing the leakage of the MHD film liquid. It is mostly made of non-magnetic stainless steel.

[0049] The main function of the magnetic steel stop is to isolate the magnetic steel from the magnetic fluid seal 31, and it is mostly made of non-magnetic material. The annular magnetic steel strip 341 is made of permanent magnet material N52, and the strength of the closed-loop magnetic field it forms has a significant impact on the sealing pressure difference of the magnetic fluid. When using the annular magnetic steel strip 341, it is important to avoid overheating and demagnetizing, which would lead to a decrease in the sealing pressure difference. The annular pole shoe strip 342 is arranged alternately with the annular magnetic steel strip 341. The closed-loop magnetic field formed by the annular magnetic steel strip 341 has a good magnetizing effect on the annular pole shoe strip 342, which is conducive to the adsorption of magnetic fluid by the end teeth of the rack 3421 of the annular pole shoe strip 342, thereby forming a good seal.

[0050] Specifically, the annular pole piece 342 is made of a material with high magnetic permeability, and the pole piece adopts a multi-stage design structure, typically thirteen stages. This device has a differential pumping structure, designed as a four-stage structure, reducing the size and complexity of the device. A single pole piece can withstand a pressure of 0.02 MPa. The magnetofluid membrane is formed by the adsorption of magnetofluid by four annular pole pieces 342, creating a four-stage magnetofluid sealing ring.

[0051] It should be noted that the main component of the magnetofluid membrane is magnetofluid, and for high vacuum applications, a grease-based magnetofluid is used with a saturated vapor pressure of less than 10 Pa - 6 Pa. Magnetofluid seals suffer from sliding losses due to translational magnetofluid, necessitating an auxiliary fluid injection structure. Generally, the amount of magnetofluid is six times that of a fourth-stage magnetic ring. The magnetofluid sealing assembly 30 is designed to meet the requirements of 10⁻⁵ Pa high vacuum applications. Using a magnetically conductive material on the contact surface of the supported component can effectively improve the sealing effect and service life.

[0052] Specifically, such as Figure 2As shown, in one embodiment, the air-floating cap 10 includes an air-floating cap body 11, a magnetofluid adjustment seat 12, and a differential support seat 13. The magnetofluid adjustment seat 12 is disposed on the air-floating cap body 11 to support the magnetofluid sealing assembly 30; the differential support seat 13 is disposed within the air-floating cap body 11 to support the differential air extraction component 20; the magnetofluid adjustment seat 12 and the differential support seat 13 cooperate to make the first upper surface and the third upper surface coplanar.

[0053] like Figure 1 As shown, the present invention also provides a motion platform 40 (the aforementioned support member), under which a set of the aforementioned magnetohydrodynamic sealed high vacuum air levitation device 200 is provided to maintain its balanced movement.

[0054] Of course, attached to this application Figure 6 In the alternative embodiment shown, multiple sets of the aforementioned magnetohydrodynamic sealed high-vacuum air levitation devices 200 can be arranged under the motion stage 40 to maintain its balanced movement. The motion stage 40 includes a motion stage base 41 and motion stage sliding blocks 42 slidably disposed thereon. The motion stage base 41 is mounted on four sets of magnetohydrodynamic sealed high-vacuum air levitation devices 200.

[0055] It should be noted that the air-floating cover 10 mainly serves as a support and auxiliary device interface connection. The air-floating cover 10 is required to be designed according to the preload weight and undergo strength verification. It supports the air-floating plane 50 and is fixed to the base of the vacuum chamber 100. The air-floating cover 10 includes an air-floating cover body 11, a cover base 16, a magnetohydrodynamic adjustment seat 12, and a differential support seat 13. The cover base 16 is fixed to the wall of the vacuum chamber and mainly bears the load transmitted by the moving stage. The magnetohydrodynamic adjustment seat 12 and the differential support seat 13 are adjusted to ensure that the third upper surface and the second upper surface are coplanar, and the coplanarity is maintained within 3μm. The coplanar adjustment uses a standard plane as a reference plane. The two planes to be adjusted are attached to the standard plane, and with the fixed support fixture, a sealed space is formed with the standard plane. The sealed space is evacuated, and the fixed support is adjusted appropriately to ensure that after vacuum adsorption, the fixed support is pre-tightened to the two planes to achieve the coplanarity requirement. The air is then vented and the coplanar adjustment is completed.

[0056] Specifically, the air flotation cap 10 is designed with a liquid injection hole 17 to replenish the fluid loss due to the motion of the magnetic fluid sealing plane. An independent flexible tube is connected to the inside of the magnetic fluid sealing assembly 30 to compensate for the fluid loss. The air flotation cap is also designed with an air extraction hole (second air extraction hole 15) for pre-extraction of leaked gas from the differential air extraction component 20, maintaining the pressure in the air flotation cap sealing space at less than 8000 Pa. The air flotation cap 10 is also designed with an inflation hole and an air flotation supply hole 25 for supplying air to the planar air flotation 50. The liquid injection hole 17 and the inflation hole on the air flotation cap 10 are isolated from the inner cavity of the cap and injected through separate pipelines.

[0057] It should be noted that the motion table 40 is a preload component of the air flotation device. The design of the air flotation device must meet the load capacity of the workpiece table, that is, the plane bearing capacity must be greater than twice the load capacity. The sliding surface of the motion table 40 and the air flotation device should have a surface roughness less than the air flotation height, which is one-tenth of the air flotation height, based on the air flotation film formation height.

[0058] In this application, the magnetohydrodynamic sealed high-vacuum air levitation device 200 is applied to a high-vacuum system. Using a motion stage 40 as the load, it assists in vacuuming, gas filling, and detection components, enabling non-contact two-degree-of-freedom movement of the motion stage 40 while simultaneously providing good vibration damping. The specific implementation steps are as follows:

[0059] The first step is to level the air flotation device. By using leveling fixtures, the coplanarity of the second upper surface, the first upper surface, and the third upper surface is adjusted, and the flatness is controlled within 2 μm.

[0060] The second step is to fix the air flotation device on the bottom plate of the vacuum chamber, connect the air flotation device's air extraction pipeline, air filling pipeline, and magnetic fluid injection pipeline, and then load the motion table onto the sliding plane of the air flotation device.

[0061] The third step involves simultaneously evacuating the main cavity of the motion stage and the sealing cavity of the air flotation device. Once the pressure difference between the vacuum levels in the main cavity and the sealing cavity is less than 1000 Pa, the magnetic fluid is injected into the toothed grooves of the annular pole shoe of the magnetic fluid sealing assembly to form a magnetic fluid sealing film.

[0062] The fourth step is to activate the differential pumping and the planar air flotation inflation. The inflation source pressure is 0.4 MPa. The air flotation device supports and floats the load. By adjusting the flow rate of the differential pumping valve, the vacuum inside the air flotation device's sealing chamber is maintained at 8000 Pa to meet the high vacuum sealing conditions of the magnetohydrodynamic pressure difference.

[0063] Fifth step: The main chamber of the motion stage is opened to evacuate to a high vacuum of 10⁻⁵ Pa. The air flotation device is normally maintained at 5000 Pa. The air flotation device and the motion stage share the same coarse vacuum pump, and only the flow rate of the air extraction valve needs to be controlled.

[0064] Step six: With the support of the air flotation device, the motion stage can slide in the X and Y directions. The optimal sliding speed is controlled within 30 mm / s. During the motion of the motion stage, the main cavity maintains a high vacuum state.

[0065] Step 7: Stopping the air flotation device. First, stop the air supply to the planar air flotation device, and the moving platform descends onto the plane of the air flotation device. Then, stop the vacuuming and release air simultaneously from the main chamber of the moving platform and the sealing chamber of the air flotation device.

[0066] As described in the specific embodiments above, the magnetic fluid sealing assembly utilizes a magnetic fluid membrane with sealing function generated by the assembly to prevent gas from diffusing from the gap between the supported component and the air-float cover into the external vacuum environment. This reduces the number of differential pumping stages in the differential pumping component. Specifically, by combining the magnetic fluid sealing assembly with the differential pumping component, the ability to prevent gas diffusion into the vacuum chamber is effectively improved, while also reducing the number of differential pumping stages. This avoids the structural complexity and bulkiness caused by the need to add differential pumping stages in the differential pumping components of existing air-float devices. Furthermore, it reduces the volume of the magnetic fluid-sealed high-vacuum air-float device 200 and simplifies the number of its components, resulting in a compact structure, fewer pumping stages, and a low vacuum leakage rate.

[0067] Although the invention has been described with reference to preferred embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of the invention. In particular, the technical features mentioned in the various embodiments can be combined in any manner as long as there is no structural conflict. The invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A magnetohydrodynamic sealed high vacuum air levitation device, characterized in that, include: Air-float cap with an inner cavity; as well as A differential extraction device is disposed within the inner cavity; as well as Planar air flotation is installed inside the differential air extraction component; as well as A magnetohydrodynamic sealing assembly is disposed on the air flotation cap and located on the outer periphery of the differential pumping unit; The differential pumping component is used to reduce the gas that diffuses from the planar air float to the edge. The magnetic fluid sealing assembly can form a magnetic fluid membrane with sealing function to prevent the gas from diffusing into the external vacuum environment. A first contact surface is formed on the magnetic fluid membrane, and a second contact surface is formed on the planar air float. The support member can slide on the first contact surface and the second contact surface simultaneously.

2. The magnetohydrodynamic sealed high vacuum air levitation device according to claim 1, characterized in that, The differential suction component is provided with a receiving cavity and at least one differential groove. The at least one differential groove is arranged in a ring around the outer periphery of the receiving cavity. The differential suction component is also provided with a first suction hole communicating with the at least one differential groove.

3. The magnetohydrodynamic sealed high vacuum air levitation device according to claim 2, characterized in that, The differential extraction component is provided with a plurality of differential slots, which are arranged sequentially along the central axis d away from the accommodating cavity. In two adjacent differential slots, the differential slot closer to the central axis d is located inside the other differential slot.

4. The magnetohydrodynamic sealed high vacuum air levitation device according to claim 2, characterized in that, The differential air extraction component is provided with a third air extraction hole. One end of the third air extraction hole is connected to the accommodating cavity, and the other end is connected to the second air extraction hole provided on the air flotation cover.

5. The magnetohydrodynamic sealed high vacuum air levitation device according to claim 1, characterized in that, The magnetohydrodynamic sealing assembly includes: A magnetohydrodynamic (MHD) cap, fitted around the outer periphery of the differential pump and positioned on the air flotation cap; and Magnetic components, disposed within the magnetofluid cap; and The liquid injection line has one end connected to the interior of the magnetic component and the other end extending out from the air flotation cap. The liquid injection line is used to provide magnetic fluid to the magnetic component, and the magnetic component is able to convert the magnetic fluid into the magnetic fluid membrane.

6. The magnetohydrodynamic sealed high vacuum air levitation device according to claim 5, characterized in that, The magnetic fluid sealing assembly further includes a first magnetic stop and a second magnetic steel stop, both of which are disposed within the magnetic fluid sealing cover for mounting the magnetic assembly.

7. The magnetohydrodynamic sealed high vacuum air levitation device according to claim 5, characterized in that, The magnetic component includes: Multiple annular magnetic strips are sequentially arranged along a direction away from the central axis of the magnetohydrodynamic seal; and An annular pole piece is disposed between two adjacent annular magnet pieces; The annular pole shoe bar has a toothed end near the end of the member to be supported, and the magnetofluid membrane is located at the toothed end of the toothed bar.

8. The magnetohydrodynamic sealed high vacuum air levitation device according to claim 7, characterized in that, The tooth width of the rack is twice the height of the magnetofluid film.

9. The magnetohydrodynamic sealed high vacuum air levitation device according to claim 1, characterized in that, The first upper surface of the differential air extraction component, the second upper surface of the planar air float, and the third upper surface of the magnetohydrodynamic sealing assembly are coplanar.

10. The magnetohydrodynamic sealed high vacuum air levitation device according to claim 9, characterized in that, The flatness of the first, second, and third upper surfaces is no greater than 2 μm.

11. The magnetohydrodynamic sealed high vacuum air levitation device according to claim 9, characterized in that, The air flotation cap includes: Air flotation capping body; and A magnetofluid regulating seat, disposed on the air-float cap body, is used to support the magnetofluid sealing assembly; and A differential support base is disposed within the air flotation cap body to support the differential air extraction component; The magnetic fluid adjustment seat and the differential support seat cooperate to make the first upper surface and the third upper surface coplanar.

12. A motion table, characterized in that, It is provided with at least one set of magnetohydrodynamic sealed high vacuum air levitation device as described in any one of claims 1 to 11.

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