JP3427950B2 - Molecular drag pump - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molecular drag pump used as a vacuum pump for obtaining a high vacuum or an ultra-high vacuum. [0002] As a vacuum pump for obtaining a high vacuum or an ultra-high vacuum, a molecular drag pump is known.
This molecular drag pump has a rotating cylinder that rotates at a high speed, and a fixed cylinder that is coaxial with the rotating cylinder and is installed with its peripheral surface facing each other, and a thread groove is formed on at least one of the facing surfaces of both cylinders. This is a mechanical pump that obtains a high vacuum or an ultra-high vacuum by giving momentum in the exhaust direction to gas molecules by rotating a rotating cylinder. FIG. 7 is a schematic sectional view of a conventional molecular drag pump. In FIG. 7, a rotating cylinder 1 is attached to a rotating shaft 2 and a motor 40
Is driven to rotate. The rotating shaft 2 is supported by a bearing housing 51 via a bearing 3 and an O-ring 52 installed outside the bearing. On the other hand, the fixed cylinder 50 is installed coaxially with the rotary cylinder 1,
Of the rotary cylinder 1 is opposed to the outer circumferential surface of the rotary cylinder 1 with an interval. A thread groove 53 is formed on at least one of the opposing surfaces of the rotating cylinder 2 and the fixed cylinder 50. The fixed cylinder 50 also serves as a part of the casing 20. When the rotating shaft 2 rotates by driving the motor 40, the rotating cylinder 1 rotates at a high speed with respect to the fixed cylinder 50,
Momentum is given to the gas molecules in the exhaust direction between the opposing surfaces of the two cylinders, and the gas molecules are compressed.
The transfer of gas to 4 takes place. In the conventional molecular drag pump, when the rotating cylinder rotates at a high speed, vibration is generated and noise is generated.
In order to reduce this noise, a bearing or a bearing housing for rotatably supporting the rotating cylinder is supported on a casing (the bearing housing 51 in FIG. 7) by an elastic seal member such as an O-ring. Therefore, the rotating cylinder 1
When vibrating and bending in the radial direction, the elastic seal member such as the O-ring 52 is displaced to absorb the vibration. However, the conventional molecular drag pump has a problem that it is difficult to simultaneously reduce noise and improve compression performance. Generally, in a molecular drag pump, the compression performance per unit length in the axial direction improves as the distance between the opposing surfaces of the rotating cylinder and the fixed cylinder becomes narrower, and as the rotation speed of the rotating cylinder increases, the pumping speed performance increases. Is improved. However, since the conventional molecular drag pump has a structure in which the elastic seal member provided between the bearing and the casing absorbs vibration to reduce noise, the vibration of the rotating cylinder is displaced by the amount of deflection of the elastic seal member. However, the distance between the opposing surfaces of the rotating cylinder and the fixed cylinder changes by the amount of the displacement, and in the case of a large displacement, the two come into contact with each other. When gravity acts in a direction perpendicular to the rotation axis, the rotating cylinder is displaced in the radial direction by the elasticity of the elastic sealing member. Therefore, it is necessary to set the distance d between the rotating cylinder and the fixed cylinder to be sufficiently large so that the opposing surfaces do not come into contact with each other, or to reduce the rotation speed of the rotating cylinder. In addition, the rotating cylinder may be eccentric in the radial direction due to the unevenness of the thickness of the O-ring that absorbs vibration of the rotating cylinder. In order to prevent the rotating cylinder from contacting with the fixed cylinder due to the eccentricity. In addition, it is necessary to make the distance d between the rotating cylinder and the fixed cylinder sufficiently large. Therefore, conventionally, for example, about 0.3 mm to 0.5 mm is used as this interval. Accordingly, an object of the present invention is to solve the above-mentioned problems of the conventional molecular drag pump, and to provide a molecular drag pump having low noise, good compression performance and good exhaust speed performance. According to the present invention, a rotating cylinder and a fixed cylinder are arranged coaxially so that the peripheral surfaces of both cylinders face each other, and a thread groove is formed on at least one of the opposing surfaces of both cylinders. In the formed molecular drag pump, a rotating shaft to which a rotating cylinder is attached is supported by a housing via a bearing, and a fixed cylinder formed integrally with the housing is separated from the housing via an elastic seal member. The above object is achieved by adopting a configuration in which the casing is supported by the casing. In the molecular drag pump of the present invention, a thread groove is formed on at least one of the opposing surfaces, the rotating cylinder and the fixed cylinder are arranged coaxially, and the rotating cylinder is rotated at a high speed to give momentum in the exhaust direction to the gas molecules. It is a vacuum pump that creates a vacuum. The rotating cylinder is attached to the rotating shaft and is supported by the housing via a bearing.The fixed cylinder integrally formed with the housing has a casing via an elastic seal member made of an airtight elastic body or the like. It is supported by.
Therefore, the radial displacement due to the vibration of the rotating cylinder is absorbed by the elastic sealing member via the bearing, the housing, and the fixed cylinder, and the displacement does not affect the distance between the rotating cylinder and the fixed cylinder and reduces the fluctuation. Can be. In an embodiment of the present invention, the cross section of the elastic sealing member provided between the fixed cylinder and the casing is made substantially circular, whereby the vibration of the rotating cylinder can be absorbed to reduce noise. Alternatively, a normal elastic seal member such as an O-ring can be applied. Another embodiment of the present invention is that the cross section of the elastic seal member provided between the fixed cylinder and the casing is rectangular, whereby the vibration of the rotating cylinder can be absorbed and the noise can be reduced, In addition, it is possible to improve the sealing performance of separating the intake port side and the exhaust port side and preventing the backflow of gas. In another embodiment of the present invention, a recess having a rectangular cross section is formed on the opposed surface of the fixed cylinder and the casing, whereby the recess can be installed in the recess regardless of the shape of the elastic seal member. The elastic sealing member can be provided between the fixed cylinder and the casing. In another embodiment of the present invention, a plurality of the elastic seal members are arranged adjacent to each other, whereby a seal that separates an intake port side and an exhaust port side and prevents a backflow of gas is provided. Performance can be improved. Still another embodiment of the present invention is that a fixed cylinder is formed so as to sandwich the rotary cylinder, thereby improving the compression performance per unit length in the axial direction and the exhaust speed performance. According to another embodiment of the present invention, a through hole is formed in the housing and the fixed cylinder so as to communicate with the rotating cylinder, whereby a space surrounded by the casing, the elastic seal member, the housing and the fixed cylinder, the housing and the fixed cylinder are formed. The space between the cylinder and the rotating cylinder is connected to exhaust air from the space surrounded by the casing, the elastic seal member, the housing, and the fixed cylinder, thereby preventing a decrease in the compression ratio due to gas in the space. . In the present invention, when the rotating shaft is rotated, the rotatably supported rotating cylinder rotates, and the gas is exhausted by the relative movement of the opposing surface between the rotating cylinder and the fixed cylinder. When the rotating shaft vibrates and displaces in the radial direction, the displacement displaces the bearing in the radial direction and further displaces the housing in the radial direction. Since the housing and the fixed cylinder are integrally formed, the displacement of the housing also causes the fixed cylinder to be displaced in the radial direction. Since the fixed cylinder is supported by the housing via the elastic seal member, the displacement of the fixed cylinder is absorbed by the elasticity of the elastic seal member. Therefore, the rotating cylinder and the fixed cylinder are connected without interposing the elastic seal member, and the displacement of the interval between the rotating cylinder and the fixed cylinder when the rotating cylinder is displaced in the radial direction is reduced. be able to. The elastic seal member closes the gap between the intake port and the exhaust port, separates them by their airtightness, and serves as a seal for preventing the backflow of gas. The inside of the casing is evacuated. The outside is separated by atmospheric pressure.
In the embodiment in which the cross section of the elastic seal member provided between the fixed cylinder and the casing is substantially circular, noise can be reduced by absorbing the vibration of the rotating cylinder, and an O-ring or the like is easily available. An elastic seal member can be applied. Further, in the embodiment in which the cross section of the elastic seal member provided between the fixed cylinder and the casing is rectangular, the vibration of the rotating cylinder can be absorbed to reduce noise, and
It is possible to improve the sealing performance of separating the intake port side and the exhaust port side and preventing the backflow of gas. Further, in the embodiment in which a concave portion having a rectangular cross section is formed on the opposed surface of the fixed cylinder and the casing, the elastic seal member can be installed regardless of whether the cross section is substantially circular or rectangular. Further, in the embodiment in which a plurality of elastic seal members are arranged adjacent to each other, the elastic seal members are additionally provided, and the performance of preventing the backflow of the gas from the exhaust port side to the intake port side is improved. Further, in the embodiment in which the fixed cylinder is formed so as to sandwich the rotating cylinder, the area of the facing surface between the rotating cylinder and the fixed cylinder increases, and the compression performance and the exhaust speed performance per unit length in the axial direction are improved. improves. Further, in the embodiment in which the housing and the fixed cylinder are formed with a through-hole communicating with the rotating cylinder, in the space surrounded by the casing, the elastic seal member, the housing, and the fixed cylinder, the space interposed between the housing, the fixed cylinder, and the rotating cylinder through the through-hole. The compression ratio can be prevented from lowering due to leakage of gas remaining in the space. An embodiment of the present invention will be described below in detail with reference to the drawings. (Configuration of the First Embodiment of the Present Invention) The configuration of the first embodiment of the present invention will be described with reference to FIG. In FIG.
The molecular drag pump according to the present invention includes a rotary cylinder 1, a fixed cylinder 10, and a casing 20 that accommodates the two cylinders therein to form a pump body. The rotating cylinder 1 is attached to one end of a rotating shaft 2, and the rotating shaft 2 is
It is rotated at high speed by driving. Motor 4
0 is a motor rotor 41 attached to the other end of the rotating shaft 2
And a motor tester 42 fixed to the base 26 on the casing 20 side. The rotating shaft 2 is rotatably supported at its outer periphery by a housing 11 via a bearing 3 such as a ball bearing. The bearing 3
The rotating shaft 2 can be supported at two places on the rotating cylinder 1 side and the motor 40 side of the rotating shaft 2.
Is supported by attaching an outer peripheral surface opposite to the rotating shaft 2 to a bearing housing 15 formed along the axial direction of the rotating shaft. Therefore, the rotating cylinder 1 is rotatably supported by the housing 11. Further, a fixed cylinder 10 is formed integrally with the housing 11 so as to surround the outside of the rotary cylinder 1 at an outer peripheral position of the rotary cylinder 1. In the embodiment shown in FIG.
A screw groove 12 is spirally formed on a surface of the fixed cylinder 10 facing the rotary cylinder 1. The diameter of the fixed cylinder 10 and the rotating cylinder 1 and the depth of the groove are set so that a gap D is formed between the convex portion of the inner peripheral surface of the fixed cylinder 10 and the outer peripheral surface of the rotating cylinder 1. I have. An opening 14 is formed in a part of the housing 11. The screw groove 12 is formed on the fixed cylinder 10 side in FIG.
It can also be formed on the side. Rotating cylinder 1 and fixed cylinder 10
A casing 20 is provided on the outside of the casing so as to surround both cylindrical portions. One end of the casing 20 forms an inlet flange 21 to open an inner diameter portion to form an inlet 22, and the other end of the casing 20 forms a base 26 to house the motor 40, Exhaust port flange 23
And the open portion is used as the exhaust port 24. A ring-shaped elastic seal member 30 is provided between the fixed cylinder 10 and the casing 20.
The elastic sealing member 30 is formed of a material such as rubber having elasticity and airtightness, and generates a restoring force to deform and return to an original shape when receiving a pressure, and to return to an original shape when the pressure is removed. Is to be restored. The elastic seal member 30 was installed at a position opposite to the elastic seal member holding portion 13 on the inner peripheral surface of the casing 20 and the concave elastic seal member holding portion 13 formed on the outer peripheral surface of the fixed cylinder 10. This is performed by the concave elastic seal member holding portion 25. The installation positions of the elastic seal member holding portions 13 and 25 can be near substantially both ends of the bearing housing 15. (Operation of the First Embodiment of the Present Invention) Next, the operation of the first embodiment of the present invention will be described. The rotating cylinder 1 is rotated by a rotating shaft 2 that is rotated by driving a motor 40. At this time, the rotating shaft 2 is supported by the bearing housing 15 and the housing 11 via the bearing 3. When the rotating cylinder 1 rotates, relative movement occurs between the opposing surfaces of the outer peripheral surface of the rotating cylinder 1 and the inner peripheral surface of the fixed cylinder 10, and gas is supplied to a screw formed on at least one of the two opposing surfaces. The gas is compressed by the groove 12 and moves from the intake port 22 to the exhaust port 24. The gas compressed through the thread groove 12 is exhausted from the exhaust port 24 through the opening 14 of the housing 11. When vibration occurs in the rotating shaft 2 and the rotating cylinder 1, the rotating shaft 2 and the rotating cylinder 1 are displaced in the radial direction. At this time, in the embodiment of the present invention, when the rotating shaft 2 is displaced in the radial direction, the bearing 3 is also displaced in the same direction, and the bearing housing 15 is also displaced in the same direction. Further, since the housing 11 in which the bearing housing 15 is formed is formed integrally with the fixed cylinder 10, the fixed cylinder 10 is also displaced in the same direction. The displacement direction of the fixed cylinder 10 and the rotating cylinder 1
Of the bearing 3 and the housing 11
Since the amount of deformation such as is negligible, the amount of displacement can be treated as substantially the same. Therefore, when vibration occurs in the rotating shaft 2 and the rotating cylinder 1, the rotating cylinder 1 and the fixed cylinder 10 are displaced synchronously while the distance D between the rotating cylinder 1 and the fixed cylinder 10 is kept substantially constant. become. On the other hand, since the elastic seal member 30 is provided between the fixed cylinder 10 and the casing 20, when the fixed cylinder 10 is displaced, the elastic seal member 30 is fixed to the fixed casing 20.
And the fixed cylinder 10 which is displaced and compressed and deformed. When the elastic seal member 30 is deformed, the vibration of the rotating shaft 2 and the rotating cylinder 1 is absorbed. According to the above configuration, the relative displacement between the rotating cylinder and the fixed cylinder is reduced even when the vibration of the rotating portion occurs, and even when gravity acts in a direction perpendicular to the rotation axis, Since the relative displacement of the rotating cylinder in the radial direction is small, the relative distance D between the rotating cylinder and the fixed cylinder can be, for example, about 0.1 mm to 0.2 mm. Further, the elastic seal member 30 is provided at the intake port 1.
The gap formed between the casing 20 and the fixed cylinder 10 between the zero and the exhaust port 24 is closed to prevent the backflow of gas from the exhaust port 24 side to the intake port 10 side. Generally, the relationship between the relative radial distance between the rotating cylinder and the fixed cylinder and the compression ratio per unit length in the axial direction is such that the smaller the distance, the higher the compression ratio and the higher the exhaust speed. Therefore, according to the molecular drag pump of the present invention, the relative radial distance between the rotating cylinder and the fixed cylinder is reduced from about 0.3 mm to 0.5 mm in the related art to about 0.1 mm to 0.1 mm. By reducing the width to about 2 mm, a high compression ratio and a high pumping speed can be obtained. For example, the diameter of the rotating cylinder is 150 mm, the height of the rotating cylinder is 60 mm, the depth of the screw groove is 3.2 mm, the width of the screw groove is 8 mm, the inclination angle of the screw groove is 15 °, and the number of the screw grooves is 12 When a molecular drag pump having a rotation speed of 35,000 rpm is configured and operated under the condition of an exhaust port pressure of 37 (Pa) and a flow rate of 667 (PaL / s), the distance between the rotating cylinder and the fixed cylinder is reduced. A compression ratio as shown in FIG. 2A and a pumping speed as shown in FIG. 2B can be obtained. In FIG. 2, black circles indicate the case of hydrogen gas,
Open circles indicate nitrogen gas, and indicate that the smaller the radial distance between the rotating cylinder and the fixed cylinder, the larger the compression ratio and the exhaust speed can be. In addition, since the possibility of contact between the rotating cylinder and the fixed cylinder is reduced, high-speed rotation is possible, and noise due to vibration can be reduced. Further, the number of members for preventing noise can be reduced, so that the molecular drag pump can be reduced in size. (Structure and Operation of the Second and Third Embodiments of the Present Invention) FIGS. 3A and 3B are diagrams for explaining the second and third embodiments of the present invention. The embodiment shown in FIG. 3A differs from the first embodiment in the shape of the elastic seal member 31, and the embodiment shown in FIG. Since the embodiment is different from the first embodiment and the other configuration is the same as that of the first embodiment, only the configuration of the different part will be described here, and the description of the other configuration will be omitted. . In the second embodiment, as shown in FIG. 3A, the cross-sectional shape of the elastic seal member 31 is formed in a rectangular shape. The elastic seal member 31 having a rectangular cross section is fitted between the rotary cylinder and the fixed cylinder by fitting the same into the rectangular recesses formed in the rotary cylinder and the fixed cylinder. Can be. According to this elastic seal member 31, since the cross-sectional shape is rectangular, the gap between the elastic seal member 31 and the rectangular concave portion on the cylindrical side is reduced, and the effect of preventing gas leakage can be improved. In the third embodiment, as shown in FIG. 3B, a plurality of elastic seal members 32 and 33 are arranged adjacent to each other. A plurality of (two are shown in the figure) elastic seal members 32 and 33 can be arranged in the plurality of recesses formed by the above-described method. The plurality of elastic seal members 32,
By arranging 33, the effect of preventing gas leakage can be improved. By adjoining a plurality of elastic seal members, the elastic seal members can be separated from each other to prevent vibration of the rotating cylinder which is generated with the elastic seal members serving as fulcrums. (Structure and operation of the fourth embodiment of the present invention)
FIG. 4 is a diagram for explaining a fourth embodiment of the present invention. The embodiment shown in FIG. 4 differs from the first embodiment in the configuration of a part of the fixed cylinder, and the other configuration is the same as the first embodiment. Will be described only, and the description of other configurations will be omitted. In the fourth embodiment, a through-hole 18 communicating with the rotating cylinder is formed in the fixed cylinder 10. The through hole 18 is provided between the casing 20 and the elastic seal member 30.
And a space surrounded by the housing and the fixed cylinder 10 and a space interposed between the housing and the fixed cylinder 10 and the rotating cylinder 1 to exhaust air from the space surrounded by the casing, the elastic seal member, the housing and the fixed cylinder. In addition, it is possible to prevent a reduction in the compression ratio due to gas remaining in the space. When the molecular drag pump is constructed under the atmospheric pressure, the space surrounded by the casing 20, the elastic seal member 30, the housing and the fixed cylinder 10 is hermetically sealed at the atmospheric pressure by these members. It is caused by If this residual gas leaks during driving of the molecular drag pump, the compression ratio will decrease. In the fourth embodiment, the residual gas is exhausted through the through hole 18 to remove the residual gas and prevent the compression ratio from lowering. By setting the position of the through-hole 18 in the rotary cylinder 1 so that the pressure ratio between the inlet and the through-hole and the pressure ratio between the through-hole and the outlet are equal, uniform compression and exhaust can be performed. it can. (Structure and operation of the fifth embodiment of the present invention)
FIG. 5 is a diagram for explaining a fifth embodiment of the present invention. The embodiment shown in FIG. 5 differs from the first embodiment in a part of the configuration of the fixed cylinder, and the other configuration is the same as the first embodiment. Will be described only, and the description of other configurations will be omitted. In the fixed cylinder of the fifth embodiment, the second fixed cylinder 16 is disposed inside the rotary cylinder 1 and a thread groove is formed on a surface facing the rotary cylinder 1.
Thus, the rotating cylinder 1 is sandwiched between the two fixed cylinders and the screw grooves. With this configuration, the gas from the intake port 22 is first supplied to the rotating cylinder 1 and the fixed cylinder 10.
And then the rotating cylinder 1 and the second stationary cylinder 1
After being further compressed by 6, it goes to the exhaust port 24 through the opening 14, so that a good compression ratio can be obtained. (Structure and Operation of the Sixth and Seventh Embodiments of the Present Invention) FIGS. 6A and 6B are diagrams for explaining the sixth and seventh embodiments of the present invention. The sixth and seventh embodiments are different from the first embodiment in the configuration of a part of the rotating cylinder and the fixed cylinder, and the other configurations are the same as the first embodiment. Only the configuration of the part to be performed will be described, and description of the other configuration will be omitted. In the sixth embodiment, a screw groove is formed on the surface of the rotating cylinder 1 facing the fixed cylinder 10, and gas is compressed in a gap between the rotating cylinder 1 and the fixed cylinder 10. It is. In the seventh embodiment, screw grooves are formed on both surfaces on the rotating cylinder 1 side, and a fixed cylinder and a second fixed cylinder 17 are provided so as to sandwich the rotating cylinder 1. Note that no thread groove is formed in the second fixed cylinder 17. According to the sixth and seventh embodiments, the same effect as in the first embodiment or the fifth embodiment can be obtained by the configuration in which the thread groove is formed on the rotating cylinder side. As described above, according to the present invention,
It is possible to provide a molecular drag pump having low noise and excellent compression performance and pumping speed performance.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view illustrating a configuration of a first exemplary embodiment of the present invention. FIG. 2 is a diagram showing a relationship between a cylinder interval, a compression ratio, and an exhaust speed. FIG. 3 is a diagram for explaining a second and a third embodiment of the present invention. FIG. 4 is a diagram for explaining a fourth embodiment of the present invention. FIG. 5 is a diagram for explaining a fifth embodiment of the present invention. FIG. 6 is a diagram for explaining sixth and seventh embodiments of the present invention. FIG. 7 is a schematic sectional view of a conventional molecular drag pump. DESCRIPTION OF SYMBOLS 1 ... Rotating cylinder, 2 ... Rotating shaft, 3 ... Bearing, 10 ... Fixed cylinder, 11 ... Housing, 12 ... Screw groove, 13,25 ... Elastic seal member holding part, 14 ... Opening, 15 ... Bearing housing, 16, 17: second fixed cylinder, 18: through hole, 2
0: casing, 21: intake port flange, 22: intake port, 23: exhaust port flange, 24: exhaust port, 26: base, 30, 31, 32: elastic seal member, 40: motor.

Claims (1)

(57) [Claims 1] A rotating cylinder and a fixed cylinder are coaxially arranged so that the peripheral surfaces of both cylinders face each other, and a thread groove is formed on at least one of the opposing surfaces of both cylinders. In the molecular drag pump, the rotating cylinder is attached to a rotating shaft supported by a housing via a bearing, and the fixed cylinder is formed integrally with the housing, and a casing separate from the housing via an elastic seal member. A molecular drag pump, characterized in that it is supported by: