Magnetic suspension molecular pump structure and magnetic suspension molecular pump

Abstract

The invention relates to the technical field of physical fluid equipment, and discloses a magnetic suspension molecular pump structure and a magnetic suspension molecular pump, and the magnetic suspension molecular pump structure comprises a shell and a main shaft. The shell comprises an inner cavity, and the inner wall of the shell is sequentially provided with a dragging-stage stator and a regeneration-stage stator from top to bottom. The main shaft is rotationally arranged in the inner cavity through a bearing assembly, a dragging-stage rotor matched with the dragging-stage stator and a regeneration-stage rotor matched with the regeneration-stage stator are arranged on the main shaft, and the bearing assembly comprises a permanent magnet bearing arranged at the top of the main shaft and a mechanical bearing arranged at the bottom of the main shaft; a permanent magnet matched with the permanent magnet bearing is arranged at the top of the main shaft; and the dragging-stage rotor is a carbon fiber cylinder. Through the structure, friction, heating and load associated with the main shaft can be reduced, the rotating speed of the main shaft is improved to a great extent, and the pumping speed and the limit vacuum degree of the molecular pump are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of physical fluid equipment, and in particular to a magnetic levitation molecular pump structure and a magnetic levitation molecular pump. Background Art

[0002] Molecular pumps are widely used in chemical or physical experimental equipment that requires a vacuum environment, aerospace and industrial industries, etc. As a type of molecular pump, the direct-discharge atmospheric molecular pump can pump the chamber to a high vacuum environment with only one molecular pump, and has been widely used in recent years.

[0003] The ultimate vacuum degree and pumping speed of the molecular pump are closely related to the rotational speed. Due to the friction, load, heating and other problems of the molecular pump's spindle, the spindle's rotational speed is greatly restricted, resulting in the molecular pump's pumping speed and ultimate vacuum degree being unable to be further improved. Summary of the invention

[0004] In view of this, the present invention provides a magnetic levitation molecular pump structure and a magnetic levitation molecular pump to solve the problem that the pumping speed and ultimate vacuum degree of conventional molecular pumps cannot be further improved.

[0005] In a first aspect, the present invention provides a magnetic levitation molecular pump structure, comprising:

[0006] A shell, comprising an inner cavity, wherein the inner wall of the shell is provided with a drag stage stator and a regeneration stage stator in sequence from top to bottom;

[0007] The main shaft is rotatably arranged in the inner cavity through a bearing assembly, and a drag-stage rotor matched with the drag-stage stator and a regeneration-stage rotor matched with the regeneration-stage stator are arranged on the main shaft. The bearing assembly includes a permanent magnet bearing arranged at the top of the main shaft and a mechanical bearing arranged at the bottom of the main shaft, wherein a permanent magnet matched with the permanent magnet bearing is arranged at the top of the main shaft, and the drag-stage rotor is a carbon fiber tube.

[0008] Optionally, a mounting column is provided on the inner wall of the shell, and the mounting column is coaxially arranged with the main shaft. The permanent magnetic bearing is a plurality of first permanent magnetic rings sleeved on the mounting column, and the top of the main shaft has a hole groove. The permanent magnet is a plurality of second permanent magnetic rings installed on the inner wall of the hole groove, and the mounting column partially extends into the hole groove, and the outer wall of the first permanent magnetic ring and the inner wall of the second permanent magnetic ring are gap-matched.

[0009] Optionally, a plurality of the second permanent magnet rings are embedded on the inner wall of the hole groove.

[0010] Optionally, a limiting groove is provided at the end of the mounting column toward the hole groove, the hole groove has a limiting column extending into the limiting groove, and the limiting groove and the limiting column are coaxially arranged with the main shaft.

[0011] Optionally, a top plate connected to the inner wall of the shell is provided on the top of the inner cavity, the mounting column is connected to the top plate, and the top plate has at least one through hole.

[0012] Optionally, the bottom of the shell includes a bearing seat, the mechanical bearing is arranged on the bearing seat, and the bottom of the main shaft has a step that contacts and cooperates with the top of the mechanical bearing.

[0013] Optionally, the drag stage stator is a cylinder arranged on the inner wall of the shell, the outer wall and the inner wall of the cylinder are provided with spiral grooves, the carbon fiber cylinder includes a first rotating cylinder and a second rotating cylinder, the first rotating cylinder cooperates with the spiral groove of the outer wall of the cylinder, the second rotating cylinder cooperates with the spiral groove of the inner wall of the cylinder, and the cylinder, the first rotating cylinder and the second rotating cylinder are coaxially arranged with the main shaft.

[0014] Optionally, the regeneration stage stator includes a plurality of concentric grooves of different radial sizes arranged on the shell, and the side walls of the concentric grooves between the head end and the tail end are provided with notches. The regeneration stage rotor is a rotor disk, and the rotor disk has a plurality of annular blade assemblies of different radial sizes. The plurality of annular blade assemblies extend into corresponding concentric grooves, respectively. The concentric grooves at the head end are connected to the drag stage stator through a first channel, and the concentric grooves at the tail end are connected to the discharge pipe arranged on the shell through a second channel.

[0015] Optionally, the notches on the side walls of two adjacent concentric grooves are staggered.

[0016] In a second aspect, the present invention provides a magnetic levitation molecular pump, comprising the magnetic levitation molecular pump structure described above, and also comprising a motor, wherein the motor is arranged at the periphery of the main shaft, and a permanent magnet sheet cooperating with the motor is arranged on the main shaft.

[0017] Beneficial effects:

[0018] The magnetic levitation molecular pump structure provided by the present invention comprises: a housing and a main shaft. The housing comprises an inner cavity, and a drag stage stator and a regeneration stage stator are sequentially arranged on the inner wall of the housing from top to bottom. The main shaft is rotatably arranged in the inner cavity through a bearing assembly, and a drag stage rotor matched with the drag stage stator and a regeneration stage rotor matched with the regeneration stage stator are arranged on the main shaft, and the bearing assembly comprises a permanent magnetic bearing arranged at the top of the main shaft and a mechanical bearing arranged at the bottom of the main shaft, wherein a permanent magnet matched with the permanent magnetic bearing is arranged at the top of the main shaft, and the drag stage rotor is a carbon fiber tube.

[0019] During operation, the main shaft drives the drag-stage rotor and the regeneration-stage rotor to rotate. The drag-stage rotor cooperates with the drag-stage stator to draw gas molecules into the inner cavity and move along the drag-stage stator to the regeneration-stage stator. The regeneration-stage rotor cooperates with the regeneration-stage stator to continue to drive the gas molecules to flow until they are discharged from the downstream exhaust pipe. The above-mentioned multi-stage structure can be used to evacuate the corresponding chamber to a high vacuum environment. The bearing assembly includes a permanent magnetic bearing and a mechanical bearing. The permanent magnetic bearing cooperates with the permanent magnet to reduce the friction at the top of the main shaft, thereby reducing the heat generated by friction, thereby increasing the rotation speed of the main shaft. Since the total weight of the main shaft and the multi-stage rotor arranged on the main shaft is large, the mechanical bearing can support the bottom of the main shaft to ensure the stability of the rotation of the main shaft and the multi-stage rotor. At the same time, compared with the traditional one-piece drag-stage rotor, the drag-stage rotor of the present application is a carbon fiber tube, which greatly reduces the weight of the multi-stage rotor, reduces the load of the main shaft, further increases the rotation speed of the main shaft, and can also reduce power consumption. The above structure can reduce the friction, heat and load associated with the main shaft, greatly improve the rotation speed of the main shaft, and improve the pumping speed and ultimate vacuum degree of the molecular pump. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 A schematic cross-sectional view of a magnetic levitation molecular pump structure according to an embodiment of the present invention;

[0022] Figure 2 for Figure 1 A local enlarged schematic diagram of the middle A;

[0023] Figure 3 for Figure 1 A partial enlarged schematic diagram of point B in the middle;

[0024] Figure 4 A schematic diagram of the structure of a top plate according to an embodiment of the present invention;

[0025] Figure 5 Schematic diagram of the structure of the regeneration stage stator according to an embodiment of the present invention.

[0026] Description of reference numerals:

[0027] 1. Shell; 11. Mounting column; 111. Limiting groove; 12. Top plate; 121. Through hole; 13. First channel; 14. Second channel; 15. Exhaust pipe; 16. Bearing seat; 2. Driving stage stator; 21. Spiral groove; 3. Regeneration stage stator; 31. Concentric groove; 311. Notch; 4. Main shaft; 41. Hole groove; 42. Limiting column; 43. Step; 44. Bearing lock nut; 5. Driving stage rotor; 51. First rotating drum; 52. Second rotating drum; 6. Regeneration stage rotor; 61. Annular blade assembly; 7. Permanent magnetic bearing; 71. First permanent magnetic ring; 8. Permanent magnet; 81. Second permanent magnetic ring; 9. Mechanical bearing; 101. Motor; 102. Permanent magnetic sheet. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0029] like Figure 1 As shown, in an embodiment of the present application, a magnetic levitation molecular pump structure is provided, including: a housing 1 and a main shaft 4.

[0030] The shell 1 comprises an inner cavity, and a drag stage stator 2 and a regeneration stage stator 3 are arranged on the inner wall of the shell 1 in sequence from top to bottom.

[0031] The main shaft 4 is rotatably arranged in the inner cavity through the bearing assembly, and the main shaft 4 is provided with a drag-stage rotor 5 matched with the drag-stage stator 2, and a regeneration-stage rotor 6 matched with the regeneration-stage stator 3. The top of the inner cavity of the shell 1 has a suction port, and the suction port can be connected to an external device. The shell 1 also has a discharge pipe 15 connected to the regeneration-stage stator 3. When the main shaft 4 rotates, the drag-stage rotor 5 and the regeneration-stage rotor 6 rotate synchronously, thereby driving the external gas molecules to flow unidirectionally along the suction port, the drag-stage stator 2 and the regeneration-stage stator 3 until the gas molecules are discharged from the discharge pipe 15, thereby realizing multi-stage treatment of the gas molecules.

[0032] The bearing assembly includes a permanent magnetic bearing 7 arranged at the top of the main shaft 4 and a mechanical bearing 9 arranged at the bottom of the main shaft 4, wherein a permanent magnet 8 cooperating with the permanent magnetic bearing 7 is arranged at the top of the main shaft 4, and the permanent magnetic bearing 7 and the mechanical bearing 9 are used together to support the rotation of the main shaft 4, and the permanent magnetic bearing 7 and the permanent magnet 8 repel each other, so that the top of the main shaft 4 does not need to contact with the permanent magnetic bearing 7, and no friction is generated, thereby reducing the heat generated by friction, and the mechanical bearing 9 has sufficient supporting strength to support the heavy main shaft 4 and the multi-stage rotor arranged on the main shaft 4. The drag stage rotor 5 is a carbon fiber cylinder, which can be used to cooperate with the drag stage stator 2. Compared with the traditional drag stage rotor, the setting of the carbon fiber cylinder can greatly reduce the weight of the drag stage rotor 5, thereby reducing the total weight of the main shaft 4 and the multi-stage rotor.

[0033] During operation, the main shaft 4 drives the drag-stage rotor 5 and the regeneration-stage rotor 6 to rotate. The drag-stage rotor 5 cooperates with the drag-stage stator 2 to draw gas molecules into the inner cavity and move along the drag-stage stator 2 to the regeneration-stage stator 3. The regeneration-stage rotor 6 cooperates with the regeneration-stage stator 3 to continue to drive the gas molecules to flow until they are discharged from the downstream exhaust pipe 15. The above-mentioned multi-stage structure can be used to evacuate the corresponding chamber to a high vacuum environment. The permanent magnetic bearing 7 cooperates with the permanent magnet 8 to reduce the friction at the top of the main shaft 4, thereby reducing the heat generated by friction, thereby increasing the rotation speed of the main shaft 4. At the same time, there is no need to set a separate lubrication oil circuit on the top of the main shaft 4, simplifying the structure. Since the total weight of the main shaft 4 and the multi-stage rotors arranged on the main shaft 4 is relatively large, the mechanical bearing 9 can stably support the bottom of the main shaft 4 to ensure the stability of the rotation of the main shaft 4 and the multi-stage rotors.

[0034] Compared with the traditional one-piece drag stage rotor 5, the drag stage rotor 5 of the present application is a carbon fiber tube, which greatly reduces the weight of the multi-stage rotor, reduces the load of the main shaft 4, further increases the rotation speed of the main shaft 4, and can also reduce power consumption. In addition, it can also reduce the extremely high requirements for processing accuracy during the drag stage rotor processing.

[0035] The above structure can reduce the friction, heat and load associated with the main shaft 4, greatly increase the rotation speed of the main shaft 4, and improve the pumping speed and ultimate vacuum degree of the molecular pump.

[0036] like Figure 1 and Figure 2As shown, in this embodiment, the inner wall of the shell 1 is provided with a mounting column 11, the mounting column 11 is coaxially arranged with the main shaft 4, the permanent magnetic bearing 7 is a plurality of first permanent magnetic rings 71 sleeved on the mounting column 11, the top of the main shaft 4 has a hole groove 41, the permanent magnet 8 is a plurality of second permanent magnetic rings 81 installed on the inner wall of the hole groove 41, the mounting column 11 partially extends into the hole groove 41, the outer wall of the first permanent magnetic ring 71 and the inner wall of the second permanent magnetic ring 81 are gap-matched, for example, five first permanent magnetic rings 71 can be provided, and five corresponding permanent magnetic rings 71 can be provided. The second permanent magnet ring 81, the five first permanent magnet rings 71 are closely arranged and fixedly connected to the outer wall of the mounting column 11 through the inner wall, the five second permanent magnet rings 81 are closely arranged and fixedly connected to the inner wall of the hole groove 41 through the outer wall, the first permanent magnet ring 71 and the second permanent magnet ring 81 repel each other and there is a very small gap between them, so that the mounting column 11 can axially support the main shaft 4 through multiple first permanent magnet rings 71, and at the same time, it will not cause friction on the top of the main shaft 4, reducing the heat generated by friction. Traditional bearings need to be supplemented with lubricating oil. In contrast, through the cooperation of permanent magnetic bearings 7 and permanent magnets 8, there is no need to set up a separate oil circuit, which simplifies the structure.

[0037] like Figure 2 As shown, in the present embodiment, a plurality of second permanent magnet rings 81 are embedded on the inner wall of the hole groove 41. The inner wall of the hole groove 41 has an annular step groove, into which the plurality of second permanent magnet rings 81 can be embedded, thereby reducing the difficulty of installing the plurality of second permanent magnet rings 81 and reducing the risk of the plurality of second permanent magnet rings 81 falling off, thereby avoiding failure of the permanent magnet bearing 7.

[0038] like Figure 2 As shown, in this embodiment, a limiting groove 111 is provided at the end of the mounting column 11 toward the hole groove 41, and the hole groove 41 has a limiting column 42 extending into the limiting groove 111, and the limiting groove 111 and the limiting column 42 are coaxially arranged with the main shaft 4. The cooperation of the limiting column 42 and the limiting groove 111 can prevent the permanent magnetic bearing 7 from failing and causing the main shaft 4 to shake.

[0039] like Figure 1 and Figure 3 As shown, in this embodiment, a top plate 12 connected to the inner wall of the shell 1 is provided on the top of the inner cavity, and a mounting column 11 is connected to the top plate 12. The mounting column 11 is cylindrical in shape, and the top plate 12 has at least one through hole 121. For example, the top plate 12 has three through holes 121, and the three through holes 121 are evenly arranged along the circumference of the top plate 12. The shape of the through hole 121 can be fan-shaped, and external gas molecules can enter the inner cavity of the shell 1 from the through hole 121. The mounting column 11 is connected to the top plate 12 and extends along the axial direction of the main shaft 4 to cooperate with the main shaft 4.

[0040] like Figure 1As described above, in this embodiment, the bottom of the shell 1 includes a bearing seat 16, a mechanical bearing 9 is arranged on the bearing seat 16, the bottom of the main shaft 4 has a step 43 that contacts and cooperates with the top of the mechanical bearing 9, and a bearing lock nut 44 can also be arranged at the bottom of the main shaft, and the mechanical bearing 9 is located between the step 43 and the bearing lock nut 44, thereby stably supporting the main shaft 4.

[0041] like Figure 1 and Figure 2 As shown, in this embodiment, the drag stage stator 2 is a cylinder arranged on the inner wall of the shell 1, and the outer wall and the inner wall of the cylinder are provided with a spiral groove 21. The carbon fiber cylinder includes a first rotating cylinder 51 and a second rotating cylinder 52. The first rotating cylinder 51 cooperates with the spiral groove 21 of the outer wall of the cylinder, and the second rotating cylinder 52 cooperates with the spiral groove 21 of the inner wall of the cylinder. The cylinder, the first rotating cylinder 51 and the second rotating cylinder 52 are coaxially arranged with the main shaft 4. The rotation of the first rotating cylinder 51 and the second rotating cylinder 52 can drive the gas molecules to move from the spiral groove 21 of the inner wall of the cylinder to the spiral groove of the outer wall of the cylinder until they move to the first channel 13.

[0042] like Figure 1 , Figure 4 and Figure 5 As shown, in this embodiment, the regeneration stage stator 3 includes a plurality of concentric grooves 31 of different radial sizes arranged on the shell 1, and the side walls of the concentric grooves 31 between the head end and the tail end are provided with notches 311. The regeneration stage rotor 6 is a rotor disk, and the rotor disk has a plurality of annular blade assemblies 61 of different radial sizes. The annular blade assembly 61 is composed of a plurality of blades, and the plurality of annular blade assemblies 61 extend into the corresponding concentric grooves 31 respectively. The concentric groove 31 located at the head end is connected with the drag stage stator 2 through the first channel 13, and the concentric groove 31 located at the tail end is connected with the discharge pipe 15 arranged on the shell 1 through the second channel 14.

[0043] For example Figure 4 and Figure 5As shown, the regeneration stage stator 3 includes 6 concentric grooves 31, the position of the concentric groove 31 close to the edge position is defined as the head end, and the position of the concentric groove 31 close to the main shaft 4 is defined as the end. The size of the concentric groove 31 gradually decreases from the head end to the end, and the size of the corresponding annular blade assembly 61 also gradually decreases. The first channel 13 is connected to the concentric groove 31 located at the head end. When the rotor disk rotates, the multiple annular blade assemblies 61 rotate synchronously. The multiple annular blade assemblies 61 rotate at high speed in the corresponding concentric grooves 31, which produces a huge stirring effect on the gas, thereby generating a series of vortices. The gas molecules enter the concentric groove 31 at the head end from the first channel 13, and then enter the next concentric groove 31 through the corresponding notch 311 in turn. By analogy, after the gas molecules enter the concentric groove 31 at the end, they will enter the exhaust pipe 15 through the second channel 14, and the gas molecules will be discharged from the exhaust pipe 15.

[0044] like Figure 2 In this embodiment, the notches 311 on the side walls of two adjacent concentric grooves 31 are staggered to facilitate one-way cutoff of the gas flow direction.

[0045] In the second aspect, the present invention provides a magnetic levitation molecular pump, including the above-mentioned magnetic levitation molecular pump structure, and also including a motor 101, the motor 101 is arranged on the periphery of the main shaft 4, and the main shaft 4 is provided with a permanent magnet piece 102 that cooperates with the motor 101. The stator in the motor 101 controls the rotation of the main shaft 4 through electromagnetic induction between the stator and the permanent magnet piece 102, thereby driving the multi-stage rotor to rotate.

[0046] The structure of the magnetic levitation molecular pump in this embodiment is completely the same as the structure of the magnetic levitation molecular pump in the above text, and will not be described again here.

[0047] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A magnetic levitation molecular pump structure, characterized in that: include: A shell (1) comprises an inner cavity, and a drag stage stator (2) and a regeneration stage stator (3) are arranged on the inner wall of the shell (1) in order from top to bottom; A main shaft (4) is rotatably arranged in the inner cavity via a bearing assembly, a drag-stage rotor (5) matched with the drag-stage stator (2) and a regeneration-stage rotor (6) matched with the regeneration-stage stator (3) are arranged on the main shaft (4), and the bearing assembly comprises a permanent magnetic bearing (7) arranged at the top of the main shaft (4) and a mechanical bearing (9) arranged at the bottom of the main shaft (4), wherein a permanent magnet (8) matched with the permanent magnetic bearing (7) is arranged at the top of the main shaft (4), and the drag-stage rotor (5) is a carbon fiber tube.

2. The magnetic levitation molecular pump structure according to claim 1, characterized in that: The inner wall of the shell (1) is provided with a mounting column (11), the mounting column (11) is coaxially arranged with the main shaft (4), the permanent magnetic bearing (7) is a plurality of first permanent magnetic rings (71) sleeved on the mounting column (11), the top of the main shaft (4) has a hole groove (41), the permanent magnet (8) is a plurality of second permanent magnetic rings (81) mounted on the inner wall of the hole groove (41), the mounting column (11) partially extends into the hole groove (41), and the outer wall of the first permanent magnetic ring (71) is gap-matched with the inner wall of the second permanent magnetic ring (81).

3. The magnetic levitation molecular pump structure according to claim 2, characterized in that: A plurality of the second permanent magnetic rings (81) are embedded on the inner wall of the hole groove (41).

4. The magnetic levitation molecular pump structure according to claim 2, characterized in that: The mounting column (11) is provided with a limiting groove (111) at the end portion facing the hole groove (41); the hole groove (41) has a limiting column (42) extending into the limiting groove (111); the limiting groove (111) and the limiting column (42) are coaxially arranged with the main shaft (4).

5. The magnetic levitation molecular pump structure according to claim 2, characterized in that: A top plate (12) connected to the inner wall of the shell (1) is arranged at the top of the inner cavity, the mounting column (11) is connected to the top plate (12), and the top plate (12) has at least one through hole (121).

6. The magnetic levitation molecular pump structure according to claim 1, characterized in that: The bottom of the housing (1) comprises a bearing seat (16), the bearing seat (16) is provided with the mechanical bearing (9), and the bottom of the main shaft (4) has a step (43) that contacts and cooperates with the top of the mechanical bearing (9).

7. The magnetic levitation molecular pump structure according to any one of claims 1 to 6, characterized in that: The drag stage stator (2) is a cylinder arranged on the inner wall of the shell (1), and the outer wall and the inner wall of the cylinder are provided with spiral grooves (21). The carbon fiber cylinder comprises a first rotating cylinder (51) and a second rotating cylinder (52), and the first rotating cylinder (51) cooperates with the spiral groove (21) on the outer wall of the cylinder, and the second rotating cylinder (52) cooperates with the spiral groove (21) on the inner wall of the cylinder. The cylinder, the first rotating cylinder (51) and the second rotating cylinder (52) are coaxially arranged with the main shaft (4).

8. The magnetic levitation molecular pump structure according to any one of claims 1 to 6, characterized in that: The regeneration stage stator (3) comprises a plurality of concentric grooves (31) of different radial sizes arranged on the housing (1), and the side walls of the concentric grooves (31) between the head end and the tail end are each provided with a notch (311). The regeneration stage rotor (6) is a rotor disk, and the rotor disk has a plurality of annular blade assemblies (61) of different radial sizes. The plurality of annular blade assemblies (61) extend into corresponding concentric grooves (31), respectively. The concentric grooves (31) at the head end are connected to the drag stage stator (2) through a first channel (13), and the concentric grooves (31) at the tail end are connected to a discharge pipe (15) arranged on the housing (1) through a second channel (14).

9. The magnetic levitation molecular pump structure according to claim 8, characterized in that: The notches (311) on the side walls of two adjacent concentric grooves (31) are staggered.

10. A magnetic levitation molecular pump, characterized in that: The magnetic levitation molecular pump structure comprises the structure as claimed in any one of claims 1 to 9, and further comprises a motor (101), wherein the motor (101) is arranged on the periphery of the main shaft (4), and a permanent magnet sheet (102) cooperating with the motor (101) is arranged on the main shaft (4).

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