Magnetic levitation molecular pump

Abstract

This invention relates to the field of vacuum pumping technology and discloses a magnetic levitation molecular pump, including a rotor, a magnetic bearing assembly, and a drive unit. The magnetic bearing assembly is sleeved on the rotor's shaft and can apply a combined axial force to the shaft. The combined axial force and the component of the rotor's gravity along the shaft's axial direction form a first axial force, which can drive the shaft from a suspended position to a first locked position. The drive unit includes a motor rotor and a motor stator. The motor rotor is sleeved on the shaft, and the motor stator is disposed inside the pump housing and spaced apart from the motor rotor along the shaft's axial direction. The motor stator can apply a second axial force to the shaft through the motor rotor. The direction of the second axial force is opposite to that of the first axial force. The second axial force is greater than the first axial force and drives the shaft back to the suspended position. In the suspended position, the first axial force increases to the same value as the second axial force.

Description

Technical Field

[0001] This invention relates to the field of vacuum pumping technology, specifically to a magnetic levitation molecular pump. Background Technology

[0002] A magnetic levitation molecular pump is a high-vacuum device that operates based on the principle of magnetic levitation. It uses magnetic force to levitate the rotor in the air, fundamentally eliminating the mechanical contact and wear problems inherent in traditional mechanical bearings. This structure not only achieves frictionless operation but also offers significant advantages such as no lubrication required, no oil or gas pollution, low noise, and long lifespan. It is particularly suitable for semiconductor manufacturing processes, scientific research instruments, and other fields requiring extremely clean, oil-free vacuum environments.

[0003] Currently, magnetic levitation molecular pumps are mainly divided into two structural forms: five-axis active magnetic levitation molecular pumps and composite bearing molecular pumps. The five-axis active magnetic levitation molecular pump uses active magnetic bearings to control all five degrees of freedom of the rotor, achieving full levitation support and exhibiting excellent dynamic performance and precise attitude control. However, this approach suffers from problems such as complex system structure, large size, high cost, and significant manufacturing and debugging difficulties, hindering miniaturization.

[0004] In contrast, composite bearing molecular pumps typically use permanent magnet levitation bearings for support at the high vacuum end, while mechanical bearings are used for axial load-bearing. Mechanical bearings are also used near the forestage. This type of structure offers advantages such as compact design, lower cost, and higher reliability. However, because mechanical bearings still require grease or lubricating oil, the risk of oil vapor backflow remains despite various measures, potentially contaminating the high-cleanliness vacuum environment and making it difficult to meet ultra-high cleanliness process requirements. Summary of the Invention

[0005] This invention provides a magnetic levitation molecular pump to solve the problems mentioned above.

[0006] This invention provides a magnetic levitation molecular pump, including a rotor, a magnetic bearing assembly, and a drive unit. The rotor is rotatably disposed within the pump casing of the molecular pump. The rotor includes a rotating shaft. The magnetic bearing assembly is sleeved on the rotating shaft of the rotor and can apply a combined axial force to the rotating shaft. The coupling of the combined axial force and the component of the rotor's gravity along the axial direction of the rotating shaft forms a first axial force. The first axial force can drive the rotating shaft from a suspended position to a first locked position. The drive unit includes a motor rotor and a motor stator. The motor rotor is sleeved on the rotating shaft, and the motor stator is disposed within the pump casing and spaced apart from the motor rotor along the axial direction of the rotating shaft. The motor stator can apply a second axial force to the rotating shaft through the motor rotor. The direction of the second axial force is opposite to that of the first axial force. The second axial force is greater than the first axial force and drives the rotating shaft back to the suspended position. In the suspended position, the first axial force increases to the same value as the second axial force.

[0007] Compared to the aforementioned related technologies (such as composite bearing molecular pumps), this invention does not require an additional mechanical bearing on the rotating shaft for axial support, thus eliminating the need for lubricating grease at the shaft and avoiding grease contamination. Furthermore, in this invention, the drive unit is used to bear the axial magnetic force required for shaft levitation (compared to a five-axis active magnetic levitation pump), effectively simplifying the bearing system structure, thereby reducing the size of the magnetic levitation molecular pump and lowering production costs.

[0008] Optionally, the magnetic bearing assembly includes a first magnetic bearing and a second magnetic bearing. The first magnetic bearing is sleeved on the outer peripheral surface of the first end of the rotating shaft, and the second magnetic bearing is sleeved on the outer peripheral surface of the second end of the rotating shaft. The drive unit is located between the first magnetic bearing and the second magnetic bearing, so that the driving torque for driving the rotating shaft to rotate is limited between the two support points, thereby enhancing the stability of the rotating shaft rotation.

[0009] Optionally, the first magnetic bearing and the second magnetic bearing apply a third axial force and a fourth axial force to the shaft, respectively. The third axial force and the fourth axial force are coupled to form a combined axial force. The combined axial force is opposite in direction to the component of the rotor's gravity in the axial direction of the shaft, so as to reduce the value of the required second axial force.

[0010] Optionally, the direction of the third axial force is opposite to that of the fourth axial force, and the direction of the third axial force is opposite to that of the component force; wherein, the magnetic force of the first magnetic bearing is higher than that of the second magnetic bearing.

[0011] Optionally, the first end is located on the side of the rotating shaft facing the air inlet of the magnetic levitation molecular pump. The first magnetic bearing includes a first fixed ring and a first rotating ring arranged coaxially. The first rotating ring surrounds the rotating shaft, and the first fixed ring is fixedly connected to the pump housing of the magnetic levitation molecular pump by a mounting bracket. When the rotating shaft reaches the first locking position, the end face of the first fixed ring facing the air inlet protrudes from the first rotating ring.

[0012] Optionally, the second end is located on the side of the rotating shaft away from the air inlet of the magnetic levitation molecular pump. The first magnetic bearing includes a second fixed ring and a second rotating ring arranged coaxially. The second rotating ring is sleeved on the rotating shaft, and the second fixed ring is fixedly connected to the base of the magnetic levitation molecular pump. When the rotating shaft reaches the first locking position, the end face of the second rotating ring facing the air inlet protrudes from the second fixed ring.

[0013] Optionally, in the suspended position, the third axial force applied by the first magnetic bearing is greater than the sum of the fourth axial force and its component applied by the second magnetic bearing.

[0014] Optionally, the magnetic levitation molecular pump also includes a first limiting structure installed in the pump housing, and a first shoulder is formed at the first end of the rotating shaft. The first shoulder can abut against the first limiting structure in the first locking position and be spaced apart from the first limiting structure in the levitated position.

[0015] Optionally, the shaft further includes a second locking position, which is located on one side of the suspension position along the direction of the second axial force, wherein the second axial force applied by the drive unit is greater than zero and less than the limit value that can drive the shaft from the first locking position to the second locking position.

[0016] Optionally, the magnetic levitation molecular pump also includes a second limiting structure installed in the pump housing, and a second shoulder is formed at the second end of the rotating shaft. The second shoulder can abut against the second limiting structure in the second locking position and be spaced apart from the second limiting structure in the levitated position and the first locking position. Attached Figure Description

[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the internal cross-sectional structure of the magnetic levitation molecular pump according to an embodiment of the present invention;

[0019] Figure 2 for Figure 1 A magnified view of local area A;

[0020] Figure 3 for Figure 1 A magnified view of local region B.

[0021] Explanation of reference numerals in the attached figures:

[0022] 1. Rotor; 101. Shaft; 1011. First shoulder; 1012. Second shoulder; 102. Turbine; 103. Air inlet; 2. Magnetic bearing assembly; 201. First magnetic bearing; 2011. First stator ring; 2012. First rotating ring; 202. Second magnetic bearing; 2021. Second stator ring; 2022. Second rotating ring; 3. Drive unit; 301. Motor rotor; 302. Motor stator; 4. First limiting structure; 401 4011 Mounting bracket; 4012 Sleeve; 4013 Connecting plate; 404 First center hole; 405 Clamping component; 406 First lock nut; 407 Second lock nut; 408 First protective bearing; 409 First retaining ring; 500 Second limiting structure; 501 Bearing base; 502 Bottom cover; 503 Second protective bearing; 504 Washer; 505 Second retaining ring; 506 Third lock nut; 507 Second center hole. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Generally, a magnetic levitation molecular pump includes a pump casing, a rotor 1 rotatably disposed within the pump casing, and stationary blades fixedly disposed within the pump casing. The moving blades (such as a turbine 102) on the rotor 1 rotate at high speed relative to the stationary blades, transferring momentum to gas molecules, thereby drawing gas from the pump inlet 103 and achieving vacuuming of the target chamber.

[0025] Currently, existing magnetic levitation molecular pumps mainly fall into two categories. The first category is the five-axis active magnetic levitation molecular pump, which typically consists of two radial active magnetic bearings and one axial active magnetic bearing assembly. Each degree of freedom of this type of pump is controlled by an active magnetic bearing, enabling complete oil-free levitation and superior performance. However, its significant drawbacks are system complexity, large size, high cost, and difficulty in manufacturing and debugging.

[0026] The second type is the composite bearing molecular pump (or semi-magnetic levitation molecular pump). This type of pump typically uses a permanent magnet bearing in the high-vacuum section (upper part) and a mechanical bearing (such as a ceramic ball bearing) in the forestage section (lower part). While this structure is relatively compact and low-cost, its key drawback is that the lower mechanical bearing still requires lubricating grease. Due to the physical structure, the lubricating grease remains connected to the vacuum chamber, making trace amounts of lubricating grease contamination unavoidable and posing a risk of oil vapor backflow contamination.

[0027] Understandably, in permanent magnet bearings, the rotor is supported by a non-contact suspension using magnetic force. This type of bearing not only provides load-bearing capacity in the axial direction but also creates stable magnetic confinement in the radial direction. When the rotor of the permanent magnet bearing shifts relative to the stator in the radial or axial direction, the magnetic field distribution between them changes with the displacement, causing the magnetic field lines to tend to close again and generate a corresponding restoring force. For radial shift, the magnetic field imbalance generates a magnetic force pointing towards the axis in the radial direction, causing the rotor to return to the center position, and the radial force is very small in a steady state. For axial shift, the change in magnetic flux density similarly generates an axial restoring force pointing towards the equilibrium position, pushing the rotor back to the set magnetic levitation gap.

[0028] To address this, the rotor 1 of the magnetic levitation molecular pump in this embodiment includes a rotating shaft 101. Furthermore, the magnetic levitation molecular pump also includes a magnetic bearing assembly 2 and a drive unit 3. The magnetic bearing assembly 2 is sleeved on the rotating shaft 101 and can apply a combined axial force and radial constraint to the rotating shaft 101 to achieve levitation support for the rotating shaft 101.

[0029] Because the rotor 1 has its own weight, this gravity has a component force along the axial direction of the rotating shaft 101. The combined axial force applied by the magnetic bearing assembly 2 couples with this gravity component force to form a first axial force. That is, the first axial force is the resultant force of the gravity component force and the combined axial force. Furthermore, this first axial force can drive the rotating shaft 101 from the suspended position (i.e., the rotating shaft 101 is suspended in the pump casing without contacting other components) to the first locked position. It can be understood that in the suspended position, the first axial force is not zero, so the rotating shaft 101 will move along the direction of the first axial force and eventually stop at the first locked position.

[0030] At this time, the motor rotor 301 of the drive unit 3 is sleeved on the rotating shaft 101, and the motor stator 302 is disposed inside the pump housing, with the motor rotor 301 and the motor stator 302 spaced apart along the axial direction of the rotating shaft 101. When the motor stator 302 receives current, it can apply a driving force to the motor rotor 301 to rotate the rotating shaft 101 and a second axial force along the axial direction of the rotating shaft 101.

[0031] The second axial force is opposite in direction to the first axial force and is greater than the first axial force, thereby forming a force difference on the rotating shaft 101 toward the suspended position, and thus the rotating shaft 101 moves toward the suspended position under the action of the force difference.

[0032] Furthermore, as the rotating shaft 101 moves from the first locked position to the suspended position, the relative displacement inside the magnetic bearing assembly 2 changes, causing the first axial force to gradually increase until it balances with the second axial force. At this point, the rotating shaft 101 reaches the suspended position and is stably suspended inside the pump casing.

[0033] Therefore, compared to the aforementioned related technologies (such as composite bearing molecular pumps), this embodiment does not require an additional mechanical bearing on the rotating shaft 101 for axial support, thus eliminating the need for lubricating grease at the rotating shaft 101 and avoiding grease contamination. Simultaneously, in this embodiment, the drive unit 3 is used to bear the axial magnetic force required for the levitation of the rotating shaft 101. (Compared to a five-axis active magnetic levitation pump), this effectively simplifies the bearing system structure, thereby reducing the size of the magnetic levitation molecular pump and lowering production costs.

[0034] The aforementioned combined axial force is the resultant force of the forces applied by the magnetic bearing assembly 2 along the axial direction of the rotating shaft 101. In this embodiment, both the first magnetic bearing 201 and the second magnetic bearing 202 can be permanent magnet bearings.

[0035] Understandably, according to Enshao's theorem, a purely permanent magnet structure cannot simultaneously achieve static stability in all degrees of freedom. In other words, relying solely on permanent magnet bearings makes it difficult to achieve stable levitation of the rotor of a magnetic levitation molecular pump across all degrees of freedom. Therefore, this embodiment, based on a permanent magnet, introduces an active force in the axial direction of the rotating shaft 101 through the drive unit 3, thereby overcoming the theoretical limitations of static stability in a purely permanent magnet system and achieving stable levitation of the rotating shaft 101.

[0036] In this technical field, axial flux motors offer advantages such as high torque density, compact structure, and excellent heat dissipation. Compared to traditional radial flux motors, using axial flux motors can significantly reduce the overall size of magnetic levitation molecular pumps, and they are more suitable for magnetic levitation molecular pump systems requiring high dynamic response.

[0037] Axial flux motors are typically driven using vector control (FOC) algorithms, and their stator current can be decomposed into direct-axis current (Id) and quadrature-axis current (Iq). The direct-axis current mainly generates axial magnetic force between the rotor and stator of the axial flux motor, while the quadrature-axis current is used to provide torque output to drive the rotor of the axial flux motor to rotate relative to the stator.

[0038] In traditional magnetic levitation molecular pump designs, to avoid the additional axial magnetic force from the direct-axis current affecting levitation stability, Id is typically controlled to zero. However, this embodiment breaks through this traditional control strategy. By setting the direct-axis current Id to a fixed non-zero value, the axial flux motor can generate an axial electromagnetic force in the axial direction while providing driving torque, i.e., the aforementioned second axial force. Therefore, this embodiment can precisely control the axial position and operating state of the shaft 101 in the magnetic levitation molecular pump by adjusting only a single variable, Id, thereby significantly simplifying the control structure. Simultaneously, it enables the shaft 101 to float stably within the magnetic levitation molecular pump.

[0039] Therefore, this embodiment does not require an independent axial active magnetic bearing like traditional five-axis active magnetic levitation pumps, and also avoids the complex control logic or structure in related technologies, thereby simplifying the overall structure of the magnetic levitation molecular pump, reducing its size, and significantly reducing the complexity of the control system and production costs.

[0040] In one embodiment, reference Figure 1The magnetic bearing assembly 2 includes a first magnetic bearing 201 and a second magnetic bearing 202. The first magnetic bearing 201 is sleeved on the outer peripheral surface of the first end of the rotating shaft 101, and the second magnetic bearing 202 is sleeved on the outer peripheral surface of the second end of the rotating shaft 101, thereby subjecting both ends of the rotating shaft 101 to radial constraint. At this time, the drive unit 3 is located between the first magnetic bearing 201 and the second magnetic bearing 202, limiting the driving torque for rotating the rotating shaft 101 to the two support points, thus enhancing the stability of the rotating shaft 101.

[0041] In one embodiment, the first magnetic bearing 201 and the second magnetic bearing 202 apply a third axial force and a fourth axial force to the rotating shaft 101, respectively, and the third axial force and the fourth axial force are coupled to form the combined axial force. That is, the aforementioned combined axial force is the resultant force of the third axial force and the fourth axial force.

[0042] It is understood that the aforementioned second axial force is positively correlated with the value of the direct-axis current Id. Therefore, the aforementioned combined axial force can be designed to be opposite in direction to the component of the rotor 1's gravity along the axial direction of the shaft 101. In this case, the amplitude of the first axial force is only the difference between the two. Correspondingly, the second axial force only needs to be greater than this difference to drive the shaft 101 to move towards the suspended position. Compared to the case where the combined axial force and the component force are in the same direction, this embodiment can significantly reduce the required amplitude of the second axial force, thereby reducing the control range and power consumption of the direct-axis current Id.

[0043] Furthermore, the third axial force and the fourth axial force can be in opposite directions. The third axial force is in the opposite direction to the component force, and the magnetic force of the first magnetic bearing 201 is higher than that of the second magnetic bearing 202, making the third axial force greater than the fourth axial force. Therefore, the direction of the combined axial force is consistent with the third axial force and opposite to the direction of the component force. Alternatively, in this embodiment, the third axial force and the fourth axial force can be set to be in the same direction and both opposite to the component force, which also achieves the purpose of the combined axial force being opposite to the gravitational component force.

[0044] Specifically, since the turbine 102, moving blades, and other components in the magnetic levitation molecular pump need to be installed on the shaft 101 near the pump body inlet, the center of gravity of the rotor 1 is shifted upwards (closer to the first end). This requires applying a large radial constraint to the outer circumferential surface of the shaft 101 facing the inlet (i.e., the first end).

[0045] Therefore, in this embodiment, the magnetic force of the first magnetic bearing 201 is greater than that of the second magnetic bearing 202. This allows for a reasonable distribution of magnetic force while providing stronger radial support at the higher center of gravity position (the first end), ensuring the smooth operation of the rotating shaft 101. In this embodiment, the first magnetic bearing 201 and the second magnetic bearing 202 can have different magnetic forces by adjusting the number of magnetic rings contained in the first magnetic bearing 201 and the second magnetic bearing 202, or by adjusting the magnetic strength of a single magnetic ring.

[0046] Furthermore, in the suspended position, the third axial force applied by the first magnetic bearing 201 is greater than the sum of the fourth axial force applied by the second magnetic bearing 202 and the component force, thereby giving the first end of the rotating shaft 101 a larger radial constraint when it is in the suspended position.

[0047] In one embodiment, the first end is located on the side of the rotating shaft 101 facing the air inlet 103 of the magnetic levitation molecular pump. The first magnetic bearing 201 includes a first fixed ring 2011 and a first rotating ring 2012 coaxially arranged. The first rotating ring 2012 surrounds the rotating shaft 101, and the first fixed ring 2011 is fixedly connected to the pump housing of the magnetic levitation molecular pump by a mounting bracket 401. In the first locked position, the end face of the first fixed ring 2011 facing the air inlet 103 protrudes from the first rotating ring 2012. That is, when the rotating shaft 101 reaches the first locked position, the first fixed ring 2011 can magnetically attract the first rotating ring 2012, generating a third axial force opposite to the direction of the component force.

[0048] In one embodiment, reference Figure 3 The second end is located on the side of the rotating shaft 101 away from the air inlet 103 of the magnetic levitation molecular pump. The first magnetic bearing 201 includes a second fixed ring 2021 and a second rotating ring 2022 coaxially arranged. The second rotating ring 2022 is sleeved on the rotating shaft 101. The second fixed ring 2021 is fixedly connected to the base of the magnetic levitation molecular pump. The end face of the second rotating ring 2022 facing the air inlet 103 protrudes from the second fixed ring 2021, so that the end face of the second rotating ring 2022 facing the air inlet 103 protrudes from the end face of the second fixed ring 2021 on the same side. This allows the second fixed ring 2021 to magnetically attract the second rotating ring 2022 and generate a fourth axial force in the same direction as the component force.

[0049] In this embodiment, the distance between the same-side end faces of the first fixed ring 2011 and the first rotating ring 2012, as well as the distance between the same-side end faces of the second fixed ring 2021 and the second rotating ring 2022, is approximately 0.1mm to 0.5mm.

[0050] Understandably, as the rotating shaft 101 moves from the first locked position toward the suspended position, the distance between the first fixed ring 2011 and the first rotating ring 2012 gradually increases, resulting in an increase in the third axial force. Since the magnetic force of the first magnetic bearing 201 is greater than that of the second magnetic bearing 202, the increase in the third axial force is much greater than the decrease in the fourth axial force. In other words, the overall axial force gradually increases.

[0051] In this embodiment, if the first bearing and the second bearing are made of repulsive magnetic rings, the first rotating ring 2012 is closer to the air inlet 103 than the first fixed ring 2011, causing the first fixed ring 2011 to exert a magnetic repulsive force on the first rotating ring 2012, thereby generating a third axial force. Similarly, the positional relationship between the second fixed ring 2021 and the first rotating ring 2012 changes accordingly.

[0052] In one embodiment, reference Figure 1 and Figure 2 The magnetic levitation molecular pump further includes a first limiting structure 4 installed inside the pump housing. A first shoulder 1011 is formed at the first end of the rotating shaft 101. The first shoulder 1011 can abut against the first limiting structure 4 in the first locking position and be spaced apart from the first limiting structure 4 in the levitation position to form the aforementioned first locking position.

[0053] In one embodiment, the rotating shaft 101 further includes a second locking position, which is located on one side of the suspended position along the direction of the second axial force, wherein the second axial force applied by the driving unit 3 is greater than zero and less than the limit value that can drive the rotating shaft 101 from the first locking position to the second locking position.

[0054] In one embodiment, the magnetic levitation molecular pump further includes a second limiting structure 5 installed in the pump housing, and a second shoulder 1012 is formed at the second end of the rotating shaft 101. The second shoulder 1012 is able to abut against the second limiting structure 5 in the second locking position and be spaced apart from the second limiting structure 5 in the levitation position and the first locking position.

[0055] Based on this, this embodiment can measure the numerical range of Id. Specifically:

[0056] (1) Start the pump body and set the control strategy to Id=0 initially. At this time, the rotor 1 moves from the suspended position to the first locked position under the action of the third axial force.

[0057] (2) With Id=0, accelerate the molecular pump to the rated speed.

[0058] (3) While maintaining a stable rotational speed, gradually increase the value of Id.

[0059] (4) Monitor the position of rotor 1. When the shaft 101 moves to the second locking position, record the current value Id_down at this time. It should be noted that the axial force generated by this current value is the limit value mentioned above.

[0060] (5) The Id rating is usually set to about half of Id_down (e.g., 50%-60%) as the set point for balanced suspension.

[0061] In this embodiment, the impact sound emitted when the rotating shaft 101 contacts the second limiting structure 5 can be used to determine whether the rotating shaft 101 is in the second locking position; or the position of the rotating shaft 101 can be monitored by installing an axial displacement sensor in the pump body for precise control.

[0062] In one embodiment, reference Figure 1 The first limiting structure 4 includes a mounting bracket 401, which is installed inside the pump housing. The mounting bracket 401 has a first central hole 402, and a protective bearing is installed in the first central hole 402. The first end includes a first section and a second section with decreasing diameter along the direction of the third axial force.

[0063] The diameter of the first segment is larger than the inner ring diameter of the protective bearing, while the diameter of the second segment is smaller than the inner ring diameter of the first protective bearing 404. Therefore, the portion where the first and second segments connect forms the aforementioned first shoulder 1011. It should be noted that the difference between the diameter of the second segment and the inner ring diameter of the first protective bearing 404 is smaller than the interval between the first fixed ring 2011 and the first rotating ring 2012, so that the first protective bearing 404 can apply radial constraint to the rotating shaft 101 when it deviates during rotation.

[0064] The second segment is inserted into the first protective bearing 404.

[0065] In one embodiment, the mounting bracket 401 includes a sleeve 4011 and a plurality of connecting plates 4012. The first central hole 402 is formed inside the sleeve 4011. The sleeve 4011 is coaxially arranged with the rotating shaft 101. The plurality of connecting plates 4012 are distributed circumferentially around the sleeve 4011 and connected to the sleeve 4011. The plurality of connecting plates 4012 are connected to the inner side surface of the pump housing.

[0066] Among them, reference Figure 1 A clamping member 403 is installed on the sleeve 4011, which is used to fit the first stator onto the outer circumferential surface of the sleeve 4011. The first rotor 1 is looped around the outer circumferential surface of the first stator and fixed on the turbine 102.

[0067] In one embodiment, the clamping member 403 includes a first locking nut 4031 and a second locking nut 4032. Both the first locking nut 4031 and the second locking nut 4032 are threadedly connected to the outer circumferential surface of the sleeve 4011 and are spaced apart along the axial direction of the sleeve 4011, with the first stator clamped and fixed between them. To achieve a slight position adjustment, an elastic washer 504 can be provided between the second locking nut 4032 and the first stator. When the first locking nut 4031 is screwed out to increase the axial distance between it and the second locking nut 4032, the elastic washer 504, under the action of restoring deformation, can push the first stator outward, thereby achieving a slight position adjustment of the first stator relative to the first rotor 1. It should be clarified that "screwing out" of the first lock nut 4031 here only refers to adjusting the distance between the first lock nut 4031 and the second lock nut 4032, and does not mean removing the first lock nut 4031 from the sleeve 4011, but rather providing the necessary elastic recovery space for the elastic washer 504.

[0068] In one embodiment, reference Figure 1 The first protective bearing 404 can be fixed inside the sleeve 4011 by the first retaining ring 405. Of course, any other suitable fixing method can also be used, which will not be elaborated on here.

[0069] In one embodiment, reference Figure 1 and Figure 3 The second limiting structure 5 includes a bearing base 501, a second central hole 507 is provided in the bearing base 501, a second protective bearing 503 is provided in the second central hole 507, and the protective bearing is fixed in the second central hole 507 by a second retaining ring 505.

[0070] Similarly, the second end has a third and a fourth segment with decreasing diameters along the direction of the force component. The second rotating shaft 101 is sleeved on the fourth segment, and its end face facing the air inlet 103 abuts against the annular surface at the connection between the third and fourth segments. A third locking nut 506 is sleeved on the third segment, which is used to clamp the second rotating ring 2022 between the third locking nut 506 and the annular surface. The second shoulder 1012 is formed on the end face of the third locking nut 506 facing away from the air inlet 103.

[0071] The fourth segment is inserted into the second protective bearing 503. The gap between the inner ring of the second protective bearing 503 and the fourth segment is smaller than the gap between the second fixed ring 2021 and the second rotating ring 2022.

[0072] In one embodiment, the second limiting structure 5 further includes a bottom cover 502, the second central hole 507 penetrating the bearing base 501, and the bottom cover 502 blocking one end of the second central hole 507 away from the fourth segment. Furthermore, referring to... Figure 3The second retaining ring 505 abuts against the corresponding surface of the bottom cover 502.

[0073] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A magnetic levitation molecular pump, characterized in that, include: Rotor (1), which is rotatably disposed in the pump housing of the molecular pump, the rotor (1) including a rotating shaft (101). A magnetic bearing assembly (2) is sleeved on the rotating shaft (101) and can apply a combined axial force to the rotating shaft (101). The combined axial force and the component of the weight of the rotor (1) in the axial direction of the rotating shaft (101) are coupled to form a first axial force. The first axial force can drive the rotating shaft (101) to move from the suspended position to the first locked position. The drive unit (3) includes a motor rotor (301) and a motor stator (302). The motor rotor (301) is sleeved on the rotating shaft (101), and the motor stator (302) is disposed in the pump housing and spaced apart from the motor rotor (301). The motor stator (302) can apply a second axial force to the rotating shaft (101) through the motor rotor (301). Wherein, the direction of the second axial force is opposite to that of the first axial force, the second axial force is greater than the first axial force and drives the rotating shaft (101) to return to the floating position, and at the floating position, the first axial force increases to the same value as the second axial force; The rotating shaft (101) further includes a second locking position, which is located on one side of the suspension position along the direction of the second axial force. Wherein, the second axial force applied by the drive unit (3) is greater than zero and less than the limit value that can drive the rotating shaft (101) from the first locking position to the second locking position; the drive unit includes a stator current, the stator current includes a direct axis current (Id), wherein the direct axis current (Id) is initially set to Id=0, after the rotor moves to the first locking position, the molecular pump is accelerated to the rated speed, and then the direct axis current (Id) is increased until the rotating shaft moves to the second locking position, and the current value of the direct axis current (Id) at this time is obtained as Id_down, the rated value of the direct axis current (Id) is set to 50%-60% of Id_down as the set point for balanced suspension.

2. The magnetic levitation molecular pump according to claim 1, characterized in that, The magnetic bearing assembly (2) includes a first magnetic bearing (201) and a second magnetic bearing (202). The first magnetic bearing (201) is sleeved on the outer peripheral surface of the first end of the rotating shaft (101), and the second magnetic bearing (202) is sleeved on the outer peripheral surface of the second end of the rotating shaft (101). The drive unit (3) is located between the first magnetic bearing (201) and the second magnetic bearing (202).

3. The magnetic levitation molecular pump according to claim 2, characterized in that, The first magnetic bearing (201) and the second magnetic bearing (202) apply a third axial force and a fourth axial force to the rotating shaft (101) respectively. The third axial force and the fourth axial force are coupled to form the combined axial force. The combined axial force is opposite in direction to the component of the rotor (1)'s gravity in the axial direction of the rotating shaft (101).

4. The magnetic levitation molecular pump according to claim 3, characterized in that, The direction of the third axial force is opposite to that of the fourth axial force, and the direction of the third axial force is opposite to that of the component force; The magnetic force generated by the first magnetic bearing (201) is higher than that of the second magnetic bearing (202).

5. The magnetic levitation molecular pump according to claim 4, characterized in that, The first end is located on the side of the rotating shaft (101) facing the air inlet (103) of the magnetic levitation molecular pump. The first magnetic bearing (201) includes a first fixed ring (2011) and a first rotating ring (2012) arranged coaxially. The first rotating ring (2012) surrounds the rotating shaft (101). The first fixed ring (2011) is fixedly connected to the pump casing of the magnetic levitation molecular pump by a mounting bracket (401). When the rotating shaft (101) reaches the first locking position, the end face of the first fixed ring (2011) facing the air inlet (103) protrudes from the first rotating ring (2012).

6. The magnetic levitation molecular pump according to claim 4, characterized in that, The second end is located on the side of the rotating shaft (101) away from the air inlet (103) of the magnetic levitation molecular pump. The second magnetic bearing (202) includes a second fixed ring (2021) and a second rotating ring (2022) arranged coaxially. The second rotating ring (2022) is sleeved on the rotating shaft (101), and the second fixed ring (2021) is fixedly connected to the base of the magnetic levitation molecular pump. When the rotating shaft (101) reaches the first locking position, the end face of the second rotating ring (2022) facing the air inlet (103) protrudes from the second fixed ring (2021).

7. The magnetic levitation molecular pump according to claim 4, characterized in that, When in the suspended position, the third axial force applied by the first magnetic bearing (201) is greater than the resultant force of the fourth axial force applied by the second magnetic bearing (202) and the component force.

8. The magnetic levitation molecular pump according to claim 7, characterized in that, The magnetic levitation molecular pump also includes a first limiting structure (4) installed in the pump housing. A first shoulder (1011) is formed at the first end of the rotating shaft (101). The first shoulder (1011) can abut against the first limiting structure (4) in the first locking position and be spaced apart from the first limiting structure (4) in the levitation position.

9. The magnetic levitation molecular pump according to claim 1, characterized in that, The magnetic levitation molecular pump also includes a second limiting structure (5) installed in the pump housing. A second shoulder (1012) is formed at the second end of the rotating shaft (101). The second shoulder (1012) can abut against the second limiting structure (5) in the second locking position and be spaced apart from the second limiting structure (5) in the levitation position and the first locking position.

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