JP2628351B2 - Compound molecular pump - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Industrial application field The present invention relates to an experimental research device such as a particle accelerator, a nuclear fusion experiment, an isotope separation, an analytical measuring device such as an electron microscope and a surface analyzer, and a semiconductor manufacturing vacuum. The present invention relates to a composite molecular pump useful in an industrial vacuum device such as a device in a pressure range from medium vacuum to high vacuum and ultra-high vacuum.

(2) Prior Art Conventionally, as a composite molecular pump of this type, a casing (c) having an intake port (a) and an exhaust port (b) as shown in FIG.
It is known that a turbo molecular pump section (d) and a thread groove pump section (e) are sequentially arranged from the intake port (a) side. (F) is the rotation axis of the rotor (g) of the turbo molecular pump section (d) and the thread groove pump section (e), (h)
Denotes a motor for rotating the shaft (f).

(3) Problems to be solved by the invention According to this conventional composite molecular pump, the suction pressure is 10 ^-1 Pa
The evacuation speed in the above region is insufficiently elongated, and it is difficult to set the maximum allowable pressure of the back pressure capable of maintaining a low suction pressure to a sufficiently high value. I have.

In order to solve this problem, the pumping speed at the inlet of the thread groove pump has a ratio corresponding to the pumping speed at the inlet of the pump, that is, about one-tenth or more, and the maximum allowable height is smaller. The pressure must be high enough. for that purpose,
It is necessary to increase the axial length of the rotor in relation to the cross-sectional area of the thread groove inlet of the thread groove pump section (e), its peripheral speed and the length of the thread groove. That is, the diameter of the rotor (g) is made sufficiently large, the thickness of the outer peripheral portion is increased, the cross-sectional area of the thread groove is increased, the axial dimension is lengthened, and the clearance between the outer periphery of the rotor (g) and the stator is increased. Needs to be sufficiently small.
However, since the thread groove pump portion (e) has a thick outer cylinder portion on the outer peripheral portion, the stress and elongation due to centrifugal force are large and heavy, and the diameter of the rotor (g) is large in a large composite molecular pump. It must be smaller than the rotor outer diameter of the pump section (d). As a result, the number of stages of the turbo molecular pump section (d) increases, resulting in an increase in size, complicated processing and assembly, and a thick cylindrical rotor (g) is heavy and has a large moment of inertia around the rotation axis. Acceleration torque and electric brake torque at the time of stop increase, the motor (h) becomes large, the capacity of the drive power supply also increases, and it has the disadvantage that it is expensive overall, and has a sufficiently high flow rate. Achieving performance also has difficult problems.

SUMMARY OF THE INVENTION An object of the present invention is to solve these problems and to provide a low-cost composite molecular pump which has a large pumping speed in a pressure range from medium vacuum to high vacuum and ultra-high vacuum and is suitable as a large machine.

(4) Means for Solving the Problems In order to achieve this problem, the present invention provides a turbo molecular pump section and a circumferential groove vacuum pump section in a housing having an intake port and an exhaust port sequentially from the intake port side. The circumferential groove vacuum pump section is provided with a notch step formed by notching the periphery of the plurality of rotating disks and an annular concave portion formed in the stator through which the rotating disks are interposed. It is characterized by comprising a ventilation path formed in a peripheral portion of the disc and a communication path communicating between adjacent ventilation paths.

(5) Operation The gas that has flowed into the intake port in the state of molecular flow is transported and compressed in this part by a large number of high-speed rotating blades and stationary blades of the turbo molecular pump section. Then, in the next circumferential groove vacuum pump section, the compressed and moved gas is transported by the molecular drag effect due to gas molecule friction due to the gas molecule friction due to the particularly high-speed rotating peripheral portion of the rotating disk, and the viscous flow from the molecular flow. Compressed exhaust is performed toward the exhaust port at a high exhaust speed.

(6) Embodiment FIGS. 1 to 3 show a first embodiment of the composite molecular pump of the present invention.
Explanation will be given according to FIG.

(1) shows a housing, in which a turbo-molecular pump section (2) is provided at an upper part thereof and a circumferential groove vacuum pump section (3) is provided below the turbo-molecular pump section. The pump section (2) is composed of a number of moving blades (2a) protruding from the outer peripheral surface of the rotor (4) and a number of stationary blades (2b) protruding from the inner peripheral surface of the housing (1). Further, the circumferential groove vacuum pump section (3) is configured as follows.

That is, four rotating disks (3) are provided on the outer peripheral surface of the rotor (4).
a) are protrudingly provided, and these rotating disks (3a) are gradually reduced in thickness from the upper side to the lower side, and the peripheral portions of both sides are notched so that the cutting steps (3b) (3b) ), And the cutting steps (3b) (3b) of these rotary disks (3a)
The depth of cut was changed from large to small in the same manner as described above as going from top to bottom. Reference numeral (3c) denotes a stator fixed to the inner surface of the housing (1), and the stator (3c) has an annular shape in which the rotating disk (3a) is interposed at a position corresponding to the rotating disk (3a). Recesses (3d) are formed, and the recesses (3d) and the notch steps (3b) (3b) provide ventilation passages (3e) (3e) on both surfaces of the peripheral portion of each rotating disk (3a). ) Formed.

Here, the distance b between the opposed surfaces of the rotating disk (3a) side and the stator (3c) side in the ventilation path (3e) (3e) of each rotating disk (3a) is, as described above, the notch step (3b) According to the cutting depth of (3b), the size decreases from large to small as going from top to bottom. In each of the recesses (3d), a partition wall (3f) obtained by cutting off a portion through which the peripheral portion of the rotating disk (3a) passes is provided so as to protrude from the stator (3c), and a ventilation path is formed by the partition wall (3f). (3e)
(3e), the ventilation paths (3e) and (3e) of the adjacent rotating disks (3a) and (3a) and the ventilation paths (3e) and (3e) of the upstream rotating disk (3a) in (3e) and (3e) 3e) Ventilation path (3e) (3e) of the other end of partition wall (3f) and downstream rotating disk (3a)
A communication path (3g) communicates with the first end of the partition wall (3f) through a communication path (3g), and further connects the partition wall (3f) and the communication path (3g) from the upstream side to the downstream side as shown in FIGS. The gas molecules from the suction port are sent through the communication path (3g) in the ventilation passages (3e) and (3e) of each rotating disk (3a) while being shifted through the communication port (3g). Compression is performed sequentially to obtain a considerably high compression ratio. As shown in FIGS. 1 and 2, the starting end of the partition wall (3f) of the ventilation path (3e) (3e) of the most upstream rotating disk (3a) is connected to the turbo molecular pump section (2). The other end of the partition (3f) of the ventilation path (3e) (3e) of the most downstream rotating disk (3a) is connected to the intermediate intake port (10) and to the other end of the partition (3f) in FIGS. Exhaust port (9) as shown
Communicated with A pipe connected to the auxiliary vacuum pump is connected to the flange of the exhaust port (9).

The shaft (4a) of the rotor (4) of the pump section (2) (3)
Is an upper bearing (5a) provided above the inner cylinder (1b) projecting upward from the motor housing (1a) below the housing (1).
And an induction motor supported by a lower bearing (5b) provided on a bottom plate (1c) of the motor housing (1a), and an intermediate portion of the shaft (4a) provided in the motor housing (1a).
A rotor (6a) of a high-frequency motor (6) composed of a hysteresis motor or the like is fixed, and a lower end of the shaft (4a) is provided in a lubricating oil tank (7) provided below the bottom plate (1c). The lubricating oil is immersed in the upper bearing through the center hole (4b) of the shaft (4a) and its branch hole (4c) by the high-speed rotation of the shaft (4a) driven by the high-frequency motor (6). (5a). The lower bearing (5b) is supplied with lubricating oil from a groove provided on the inner periphery of the motor housing (1a).

Thus, since the rotor blades (2a) and the rotating disk (3a) of the pump sections (2) and (3) are constituted by an integrated rotor (4), vibrations are small even at high speed rotation and almost no noise is generated. do not do. Incidentally, (8) indicates an intake port.

 Next, the operation of the composite molecular pump of the above embodiment will be described.

When the rotor (4) is rotating at a high speed by driving the high frequency motor (6), the gas flowing into the intake port (8) is in a molecular flow or an intermediate flow state close thereto, and the gas molecules are in a turbo molecular pump section. The moving blade (2a) collides with the rotating blade (2a) of (2), and moves by the action of the moving blade (2a) and the stationary blade (2b) protruding from the housing (1). Momentum is given downward in a direction parallel to the circumferential direction and the axis (4a), and is compressed and moved downward by the rotation of the stacked moving blades (2a) and stationary blades (2b). During acceleration at the time of starting, the molecular pump unit (2) has a large windage due to the presence of a gas having a high density in the pump and a large acceleration torque with respect to the moment of inertia of the rotor (4). The current is automatically limited so that the current does not become excessive, and the number of rotations is controlled.

The compressed and moved gas passes through the intermediate suction port (10) and forms the peripheral portion of the rotating disk (3a) of the circumferential groove vacuum pump section (3) integrally formed with the rotor (4) at the highest rotational speed. The transport effect occurs due to the molecular drag effect due to the gas molecule friction at this time on both sides of the notch step (3b) (3b), and the ventilation path (3e) of each rotating disk (3a) passes through the communication path (3g). (3e) is sequentially transported as indicated by the arrow in FIG. 2, and a large compression ratio is realized as a whole by evacuating in the pressure region where the molecular flow is in a viscous flow, and the auxiliary vacuum pump is used from the exhaust port (9). Compressed to atmospheric pressure.

Here, according to the experiment of the inventor, according to the circumferential groove vacuum pump 1
A compression ratio of 10 times can be obtained in the viscous flow region from the molecular flow only by the stage, and a compression ratio of 10 ⁴ or more can be easily achieved by the four-stage configuration as in this embodiment. In addition, in the above-described conventional composite molecular pump, the relationship between the inlet pressure and the exhaust speed for nitrogen gas (N ₂ ) is as shown by the solid line graph in FIG.
The relationship between the outlet pressure and the compression ratio for nitrogen gas (N ₂ ) and hydrogen gas (H ₂ ) is as shown by the solid line graph in FIG. 12, which is indicated by the broken line with respect to the performance of the conventional composite molecular pump shown by these solid lines. The performance of the composite molecular pump of the present invention can be equal or better.

In addition, since the ventilation passages (3e) and (3e) of each rotating disk (3a) are directly communicated with the communication passage (3g), no special communication conduit is required, and the casing (1) is not required. The space in the parentheses can be used effectively, and the axial length of the circumferential groove vacuum pump (3) is
Compared to the axial length assuming a thread groove vacuum pump part having the same performance, it is only required to be about one-third shorter, the rotor (4) is lightweight, and the moment of inertia of rotation is much smaller. .

In the first embodiment, the circumferential groove vacuum pump section (3)
Is shown with four rotating disks (3a), but the number of rotating disks (3a) may be one to three or five or more depending on the required compression ratio.

Next, FIGS. 13 to 16 show a second embodiment of the circumferential groove vacuum pump section, in which the rotary disks (3a) are used.
The distance b between the opposed surfaces of the rotating disk (3a) and the stator (3c) in the ventilation passages (3e) and (3e) is gradually reduced from the start end to the end. Thus the first
When the rotating disk (3a) is rotated at a high speed as in the embodiment, the gas in the ventilation passages (3e) and (3e) becomes high in pressure from the start end to the end, and the mean free path λ of the gas becomes small. Accordingly, as described above, the distance b between the facing surfaces of the ventilation passages (3e) and (3e) becomes gradually smaller as described above, so that the ratio b / of the depth b of the groove to the mean free path λ of the gas molecules is obtained. λ is kept close to the optimum value, the transport effect is further increased, and the exhaust compression performance is improved.

FIG. 17 shows a third embodiment of a circumferential groove vacuum pump unit. In this embodiment, the thickness of the cutting steps (3b) and (3b) at the periphery of each rotary disk (3a) is shown. As the thickness is gradually reduced toward the outside, these cutting steps (3b) (3
The distance b between the inner surface of the concave portion (3d) and the inner surface of the concave portion (3d) is set so that the distance becomes smaller as the concave portion (3d) faces outward so that the distance b becomes equal at any position in the radial direction. Since the thickness of the cutting steps (3b) and (3b) at the periphery of the rotating disk (3a) becomes gradually smaller as going outward, Even if the rotating disk (3a) rotates at a high speed, the maximum value of the centrifugal stress acting on the center of the rotating disk (3a) becomes small, so that the rotating disk (3a) is not required to have considerable strength, and The material of the plate (3a) may be engineering plastic, ceramics, or a casting, and a large machine can be easily manufactured.

FIGS. 18 to 21 show a fourth embodiment of a circumferential groove vacuum pump unit. In this embodiment, the intermediate intake port is provided in the ventilation passages (3e) and (3e) of each rotating disk (3a). (10) Two communication passages (3g) and two exhaust ports (9) are provided at intervals of 180 degrees, and the partition (3f) is also two
Since gas molecules are compressed and exhausted in two substantially semicircular ventilation passages (3e) and (3e) separated by the partition walls (3f) and (3f), the exhaust speed is substantially the same. Double. In this embodiment, an example is shown in which the ventilation path (3e) (3e) is divided into two places by two partition walls (3f). May be divided into three or more places.

(7) Effects of the Invention According to the present invention, as described above, the turbo molecular pump section and the circumferential groove vacuum pump section are sequentially arranged from the intake port side in the housing having the intake port and the exhaust port, and The gas is compressed and transferred once in the turbo-molecular pump unit, and then the gas is efficiently transported by molecular drag due to gas molecule friction due to the particularly high-speed rotating peripheral portion of the rotating disk in the circumferential groove vacuum pump unit. At the same time, it is possible to take a large dimension in the radial direction of the intake port to the ventilation path of the first-stage rotating disk which determines the pumping speed of the circumferential groove vacuum pump section, thus obtaining a large pumping speed. By increasing the number of rotating disks in the circumferential groove vacuum pump section, a large compression ratio can be obtained, enabling efficient exhaust compression in a pressure range from medium vacuum to ultra-high vacuum. The axial length of the peripheral groove vacuum pump part is shorter than that of the same performance, the rotor is lightweight and the moment of inertia is small, so high processing accuracy is not required and it can be obtained at low cost and is preferable in performance. This has the effect that a large machine can be obtained.

[Brief description of the drawings]

1 is an overall sectional view of a first embodiment of a composite molecular pump according to the present invention, FIG. 2 is a sectional view taken along line II of FIG. 1, and FIG. 3 is a sectional view taken along line II-II of FIG. Fig. 4 is III-III in Fig. 2.
5 is a sectional view taken along the line IV-IV in FIG. 2, and FIG.
The drawing is a sectional view taken along the line VV of FIG. 2, and FIG.
8 is a sectional view taken along line VII-VII of FIG. 8, FIG. 9 is a sectional view taken along line VIII-VIII of FIG. 2, and FIG. 10 is a line IX-IX of FIG. FIG. 11 is a graph showing the relationship between the intake port pressure and the exhaust speed, FIG. 12 is a graph showing the relationship between the exhaust port pressure and the compression ratio, and FIG. 13 is a diagram showing the circumferential groove vacuum pump section. 2
FIG. 14 is a partial sectional view taken along line II of FIG. 13; FIG. 15 is a partial sectional view taken along line II-II of FIG. 13;
16 is a sectional view of a part taken along the line III-III of FIG. 13, FIG. 17 is a partial sectional view of a third embodiment of the circumferential groove vacuum pump section, and FIG.
FIG. 19 is a plan view of a fourth embodiment of a circumferential groove vacuum pump section, FIG. 19 is a cross-sectional view of a part taken along the line II of FIG. 18, and FIG. FIG. 21 is a sectional view of a part of FIG.
FIG. 22 is a cross-sectional view of a part of a conventional composite molecular pump taken along a line II. (1) ... Housing (2) ... Turbo molecular pump section (3) ... Circumferential groove vacuum pump section (8) ... Intake port (9) ... Exhaust port

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shoji Iguchi 7-775, Hotocho, Sakai-shi, Osaka Inside Sakai Plant of Osaka Vacuum Equipment Co., Ltd. (56) References JP-A-63-85287 (JP, A)

Claims (1)

(57) [Claims] 1. A turbo molecular pump section and a circumferential groove vacuum pump section are sequentially arranged from a suction port side in a housing having an inlet port and an exhaust port, and the circumferential groove vacuum pump section includes a plurality of rotating pumps. Adjacent to the ventilation passages formed in the periphery of each of the rotating disks by a notch step formed by cutting out the periphery of the disks and an annular recess formed in the stator through which the rotating disks are interposed. A composite molecular pump comprising: a communication path communicating between the ventilation paths.