JP2000227094A - Motor and turbo-molecular pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain optimum of the groove depth of seal grooves or dynamic pressure grooves and guarantee motor performance convenient for high vacuum at using for a turbo-molecular pump, in a motor using a dynamic pressure gas bearing. SOLUTION: In the rotor of a motor, the outer circumferential part is formed out of an inner cylinder, and an outer cylinder is arranged on the outer circumferential side of the rotor. A dynamic pressure gas bearing supporting radial load of the rotor 13 is constituted out of the inner cylinder and the outer cylinder. On the outer circumferential face of the inner cylinder, dynamic pressure grooves 45 and seal grooves 46 are formed, and circumferential grooves 47 are formed on the positions corresponding to the boundaries of the respective grooves 45, 46. The outer cylinder is formed with air feed holes 48 on the positions confronted with the circumferential grooves 47. The groove depth APS of the dynamic pressure groove 45 is in the range of 1-5 times the clearance C of the dynamic pressure gas bearing, the groove depth AGS of the seal groove 46 is in the range of 2-10 times the clearance C, and the groove depth AR of the circumferential groove 47 is in the range of 3-15 times the clearance C, respectively set.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor using a hydrodynamic gas bearing and a turbo molecular pump.

[0002]

2. Description of the Related Art For example, a turbo-molecular pump is used in a semiconductor-related apparatus such as a sputtering apparatus, a CVD apparatus, and an etching apparatus, an electron microscope, a surface analysis apparatus, an environmental test apparatus, and the like to obtain an ultra-high vacuum state. . The turbo-molecular pump generates ultra-high vacuum by rotating a rotating shaft having moving blades to create a molecular flow to exhaust gas. In order to obtain an ultra-high vacuum, it is necessary to rotate the rotating shaft of the motor at high speed, and to smoothly rotate at high speed, it is necessary to employ a bearing suitable for high-speed rotation in the motor.

Heretofore, ball bearings have generally been used as bearings for rotary shafts. However, with a pump that creates an ultra-high vacuum, such as a turbo-molecular pump, the lubricating oil injected into the bearings is vaporized due to the high degree of vacuum, and not only is it not possible to obtain an ultra-high vacuum, but also the lubricating oil A problem arises in that it flows into the vacuum chamber and causes contamination. For this reason, a turbo molecular pump using a non-contact type bearing such as an air bearing or a magnetic bearing has been proposed so as not to use a lubricating oil (Japanese Utility Model Laid-Open No. 63-14894, Japanese Unexamined Patent Publication No. -16389). Conventional turbomolecular pumps cannot be pulled from the atmosphere and require an auxiliary pump. A turbo molecular pump that obtains a high vacuum from the atmosphere can be obtained by configuring a motor with gas bearings.

[0004] For example, a dynamic pressure gas bearing in which a pressure gas film is formed on an outer peripheral surface of a rotating body (rotor) of a motor is used as a bearing structure for supporting a radial load of a rotating shaft. In this case, the cylinder is arranged with a predetermined clearance around the rotating body, and a dynamic pressure groove is formed on the outer peripheral surface of the rotating body. In other words, the dynamic pressure gas bearing includes an outer cylinder (bearing fixed body) fixedly disposed outside with a clearance, and an inner cylinder (bearing rotating body) having a dynamic pressure groove formed on its surface and integrally rotating with the rotating body. Is composed of pairs. Since the inner cylinder and the outer cylinder slide until the rotating body starts to float by the pressure gas film, a wear-resistant ceramic such as alumina or zirconia has been used as a material of the dynamic pressure gas bearing.

[0005] In designing a turbo-molecular pump, when the required pumping speed is determined, design values such as the number of blade stages and the number of revolutions are determined. For example, a small turbo-molecular pump needs to rotate at a high speed of 50,000 to 70,000 rpm. Therefore, it is necessary to set the clearance of the air bearing to about 5 μm or less based on the number of rotations.

[0006]

In a turbo-molecular pump, air is exhausted by the relative rotation of a moving blade and a stationary blade to create an ultra-high vacuum state. Since the projecting end side of the rotating shaft of the motor is evacuated to a predetermined degree of vacuum, the outer peripheral surface of the inner cylinder constituting the dynamic pressure gas bearing is used to seal the negative pressure region of the vacuum side portion and atmospheric pressure. A seal groove is formed. Also,
On the outer peripheral surface of the inner cylinder, a circumferential groove is formed at each boundary between the seal groove and the dynamic pressure groove, and an open hole is formed in the outer cylinder at a portion facing the circumferential groove. The air required when a pressure gas film is formed by the dynamic pressure groove is introduced from this open hole.

In a motor used for a turbo-molecular pump, higher bearing characteristics and sealing characteristics are required as the number of rotations increases. For example, the depth of the dynamic pressure groove is a factor that determines the natural frequency of the rotating body in the use speed range, and if the natural frequency of the rotating body and the rotation cycle resonate, it may cause vibration, In order to obtain high bearing characteristics, it has become necessary to control the depth of the dynamic pressure grooves. In addition, the quality of the sealing performance by the seal groove depends to some extent on the depth of the groove, and it is necessary to manage to optimize the groove depth of the seal groove in order to obtain a further higher vacuum. Thus, in response to recent demands for further downsizing and higher rotation speed of turbo molecular pumps, the influence of various groove depths in the hydrodynamic gas bearing cannot be ignored.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to optimize the groove depth of a seal groove or a dynamic pressure groove in a motor using a hydrodynamic gas bearing, and to improve the turbocharger performance. An object of the present invention is to provide a motor and a turbo-molecular pump that can guarantee motor performance that is convenient for high vacuum when used in a molecular pump.

[0009]

In order to achieve the above object, according to the first aspect of the present invention, there is provided a rotating body for rotating a rotating shaft, and an armature disposed on an outer peripheral side of the rotating body. A dynamic pressure gas bearing that supports a radial load of the rotating body, and a non-contact type bearing that supports a load of the rotating body in a thrust direction, wherein the dynamic pressure gas bearing has an outer peripheral surface of the rotating body. And a bearing fixed body disposed with a clearance on the outer peripheral side of the bearing rotating body. A seal groove and a dynamic pressure are formed on a surface facing the bearing rotating body and the bearing fixed body. A groove is formed, and the seal groove is set to be deeper than the dynamic pressure groove.

According to a second aspect of the present invention, in the first aspect of the present invention, the seal groove has a groove depth in a range of 2 to 10 times the clearance, and the dynamic pressure groove has a groove depth of 1 to 10 times the clearance. The groove depth is in the range of 5 times.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the clearance is formed at a position corresponding to each boundary between the seal groove and the dynamic pressure groove, and the clearance is opened to the atmosphere. As described above, the circumferential groove facing the open hole provided in the bearing fixing body has a greater groove depth than the seal groove.

According to a fourth aspect of the present invention, in the third aspect, the circumferential groove has a groove depth in a range of 3 to 15 times the clearance. In the invention described in claim 5, in the invention described in claim 3 or 4, the groove depth of the circumferential groove is equal to the groove depth of the seal groove,
It is approximately the sum of the groove depths of the dynamic pressure grooves.

According to a sixth aspect of the present invention, there is provided a turbo molecular pump comprising: the motor according to any one of the first to fifth aspects; and a rotor blade provided on a rotating shaft of the motor.
And a stationary blade necessary for producing a molecular flow by rotating the moving blade.

According to a seventh aspect of the present invention, in the invention of the sixth aspect, a seal groove is provided on a surface of the motor facing the rotor, which is provided so as to cover a part of the motor. Is formed.

In the invention described in claim 8, in the invention described in claim 6 or claim 7, the motor is elastically supported by the housing. (Operation) According to the first aspect of the invention, the rotating shaft is rotated by the rotating body being rotated by the armature. At this time, the radial load of the rotating body is supported by the ceramic dynamic pressure gas bearing, and the load of the rotating body in the thrust direction is supported by the non-contact bearing. A seal groove and a dynamic pressure groove are formed on the surface of the bearing rotating body, and the seal groove is provided deeper than the dynamic pressure groove. For this reason, the sealing performance by the seal groove is enhanced, and the bearing performance by the dynamic pressure groove is enhanced.

According to the second aspect of the present invention, the seal groove is formed in a range of 2 to 10 times the clearance, and the dynamic pressure groove is formed in a range of 1 to 5 times the clearance. For this reason, the sealing performance by the seal groove is enhanced, and the bearing performance by the dynamic pressure groove is enhanced.

According to the third aspect of the present invention, the first aspect is provided.
Alternatively, in addition to the operation of the second aspect, the circumferential groove formed at each boundary between the seal groove and the dynamic pressure groove is provided deeper than the seal groove. Therefore, air is efficiently introduced into the dynamic pressure grooves.

According to the invention described in claim 4, according to claim 3,
In addition to the operation of the invention, the circumferential groove is formed in a range of 3 to 15 times the clearance. Therefore, air is efficiently introduced into the dynamic pressure grooves.

According to the invention set forth in claim 5, according to claim 4,
In addition to the same operation as the invention, the depth of the circumferential groove is substantially the sum of the depth of the seal groove and the depth of the dynamic pressure groove. Therefore, by forming the seal groove and the circumferential groove 2 together and further forming the circumferential groove when forming the dynamic pressure groove,
Three types of grooves having different groove depths can be formed in two groove forming steps.

According to the sixth aspect of the present invention, the turbo molecular pump uses the motor according to any one of the first to fifth aspects to rotate the rotor blade. A high degree of vacuum can be achieved by high-speed rotation of the blades.

According to the invention of claim 7, according to claim 6,
In addition to the operation of the invention, a seal groove is formed between the outer peripheral surface of the motor and the inner peripheral surface of the rotor for the rotor blade. Therefore, a higher vacuum can be obtained by the turbo-molecular pump.

According to the invention of claim 8, according to claim 6,
Alternatively, in addition to the function of the invention of claim 7, the motor is elastically supported with respect to the housing, so that a vibration damping action is obtained.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows a turbo-molecular pump. Housing 2 of turbo molecular pump 1
Is constituted by an upper housing 3, a lower housing 4, and an annular support block 5 sandwiched between the two housings 3, 4. The housings 3 and 4 are joined by a plurality of bolts 6 while holding the support block 5 therebetween.

At the tip of the upper housing 3, an air inlet 3 serving as a suction port for air exhausted from a vacuum chamber (not shown) is provided.
a is formed. A plurality of stationary blades 7 are attached to the inner peripheral surface of the upper housing 3 using a support member 8 so as to extend inward. An annular support block 9 is fixed to the lower surface of the support block 5.

A brushless motor (hereinafter simply referred to as a motor) 10 is fitted and fixed to the inner peripheral surfaces of the support blocks 5 and 9 via rubber seal members (O-rings) 11 and 12. The motor 10 is arranged in a state where the protruding end of the rotating shaft 13 is located on the side of the intake port 3a. The rotor 14 is attached by fastening a nut 15 to the tip of the rotating shaft 13. The rotor 14 has a substantially cylindrical shape with a bottom, and a plurality of moving blades 16 extending from the outer peripheral surface thereof are arranged in a state of being inserted into the gap between the respective stationary blades 7.

The rotor 14 rotates relative to the motor casing 17 with a very small clearance from the outer peripheral surface thereof. The space on the upper surface side of the support block 5 is an air intake chamber 18, and the space on the lower surface side of the support block 5 is an exhaust chamber 19. A spiral seal groove 17 a is formed on the upper outer peripheral surface of the motor casing 17 at a position facing the inner peripheral surface of the rotor 14. Also, the motor casing 17
Are formed with a large number of slit holes 17b in a lower portion protruding into the exhaust chamber 19.

When the motor 10 is driven to rotate the rotor 14, the intake port 3 a is provided between the moving blade 16 and the stationary blade 7.
A suction force for drawing air is generated. The drawn air passes through a seal groove 17 a between the rotor 14 and the motor casing 17 and is drawn into the inside of the motor casing 17 from a gap around the rotating shaft 13, and a plurality of air formed at a lower portion of the motor casing 17. Slit hole 1
The gas is exhausted from 7b into the exhaust chamber 19. The air exhausted to the exhaust chamber 19 is supplied to an exhaust port 4 a formed in the lower housing 4.
From the outside. Here, the seal groove 17a functions as a kind of gas seal, and a pressure difference occurs during the passage of air through the seal groove 17a, and the suction port 3
It plays a major role in raising the degree of vacuum of a. The seal groove formed on the surface facing the motor and the rotor for the rotor provided so as to cover a part of the motor is constituted by the seal groove 17a.

An air cooling fan unit 20 is mounted on a side of the lower housing 4. The air-cooling fan unit 20 includes a motor 21 and an air-cooling fan 22, and the rotation of the air-cooling fan 22 directs air to a slit hole 17 b formed below the motor 10.

Next, the structure of the brushless motor 10 will be described. As shown in FIGS. 1 and 2, both ends of the motor casing 17 are closed by substantially annular closing members 23 and 24. The rotating shaft 13 is rotatably supported in a state where the rotating shaft 13 is inserted through insertion holes 23a and 24a formed in the axial centers of the closing members 23 and 24.

As shown in FIG. 2, a rotating body 25 is provided on the rotating shaft 13 so as to be integrally rotatable. The rotating body 25 has a built-in field magnet 26. The field magnet 26 is composed of four permanent magnet pieces, and the permanent magnet pieces are arranged in the circumferential direction around the rotating shaft 13 such that magnetic poles adjacent to each other have different polarities. An inner cylinder 28 is fixed to a pair of bushes 27, 27 holding the field magnet 26 from both sides in the axial direction in a state of being externally fitted. The bush 27 has a function of adjusting the balance of the rotating body 25.

Outer cylinder 29 which houses and arranges inner cylinder 28 inside
Is fixed to the motor casing 17 side so as to be coaxial with the motor 10. The inner cylinder 28 and the outer cylinder 29 form a dynamic pressure gas bearing 30. On the outer peripheral surface of the outer cylinder 29, three armature coils 31 as armatures are arranged at equal intervals in the circumferential direction. The mechanical angle in the circumferential direction of each armature coil 31 is set in a range of approximately 90 ° to 120 °. A cylindrical yoke 32 is provided on the inner peripheral surface of the motor casing 17 so as to be located outside the armature coil 31.
Is provided. The bearing rotating body is constituted by the inner cylinder 28, and the bearing fixed body is constituted by the outer cylinder 29.

Each armature coil 3 is provided on the outer peripheral surface of the outer cylinder 29.
Three magnetic sensors (Hall elements) 3 at positions corresponding to 1
3 are provided. The three armature coils 31 and the respective magnetic sensors 33 are connected to a plurality of connector pins 34 (only one is shown in FIG. 2) inserted into the closing member 24. The connector pins 34 are electrically connected to an external control circuit (not shown). Then, the rotation speed detection signal obtained by the magnetic sensor 33 detecting the magnetic pole of the permanent magnet piece constituting the field magnet 26 is:
The feedback of the current flowing through each armature coil 31 is fed back to control the rotating shaft 13 at a constant speed.

Near the front and rear ends in the axial direction of the rotating body 25,
A pair of magnetic bearings 37 and 38 as non-contact type bearings are provided. The rotating shaft 1 includes a pair of magnetic bearings 37 and 38.
3 is supported in the thrust direction. The pair of magnetic bearings 37 and 38 include permanent magnets 39 and 40 fixed to both ends of the rotating body 25 and permanent magnets 41 and 42 fixed to the closing members 23 and 24, respectively. A pair of permanent magnets 39 and 41 forming the magnetic bearing 37 and a pair of permanent magnets 40 and 42 forming the magnetic bearing 38 are arranged such that opposing surfaces of the pair have the same polarity. A repulsive force acts between the two. Permanent magnet 39-4
The material 2 is a neodymium magnet or a samarium magnet.

On the other hand, the inner cylinder 2 constituting the dynamic pressure gas bearing 30
8 and the outer cylinder 29 are both made of a ceramic sintered material.
The inner cylinder 28 and the outer cylinder 29 are arranged so that their axes coincide with each other, and a predetermined bearing clearance C (see FIG. 3) is set between the two. Initial bearing clearance C
Is determined from design values such as the exhaust speed and the number of revolutions of the turbo-molecular pump 1. When the turbo molecular pump 1 is used at 60,000 to 90,000 rpm as in this example, it is set to, for example, C = 10 μm or less. In this embodiment, C = about 5 μm is employed.

The inner cylinder 28 is made of silicon carbide, and the outer cylinder 28 is made of alumina. The coefficient of thermal expansion of silicon carbide is 3 to 4 × 10 ⁻⁶ / ° C., and the coefficient of thermal expansion of alumina is 7 to 8 × 10 ⁻⁶ / ° C. That is, the ceramic material of the outer cylinder 29 has a larger coefficient of thermal expansion than the ceramic material of the inner cylinder 28.

As shown in FIG. 3, two air bearing bands 43 and one gas seal band 44 are formed on the outer peripheral surface of the inner cylinder 28. In the air bearing band 43, a plurality of herringbone-shaped dynamic pressure grooves 45 are formed at equal intervals in the circumferential direction. The gas seal band 44 is adjacent to the two air bearing bands 43 on the rotor 14 side, and has a spiral seal groove 46 formed on the surface thereof. Also, the inner cylinder 28
Are formed at the boundary between the two air bearing bands 43 and the gas seal band 44 on the outer peripheral surface of the. In this example, the groove depth of each of the grooves 45 to 47 is individually adapted, and the seal groove 46 has a deeper groove depth than the dynamic pressure groove 45, and of the three types of grooves, the circumferential groove 47 has Groove depth is the deepest. The conditions for matching the groove depths of the grooves 45 to 47 will be described later.

As shown in FIGS. 2 and 3, an air supply hole 48 as an open hole is formed in the outer cylinder 29 at a position facing each circumferential groove 47.
Are formed. When the motor 10 is driven, air is introduced into the clearance between the inner peripheral surface of the outer cylinder 29 and the outer peripheral surface of the inner cylinder 28 through the air supply holes 48 by the dynamic pressure grooves 45. When the rotating body 25 rotates in a predetermined direction, the introduction of air into the clearance between the inner cylinder 28 and the outer cylinder 29 is promoted by the action of the dynamic pressure groove 45, and the pressure gas flows into the center of the width of the air bearing band 43. A film is formed, and the radial load of the rotating shaft 13 is supported. Note that the inner peripheral surface of the outer cylinder 28 is polished so as to have a peripheral surface having excellent contact slidability.

The following describes the conditions for matching the groove depths of the three types of grooves 45 to 47. FIG. 4 is a graph showing the relationship between the groove depth of the seal groove 46 and the inlet pressure (Pa). The suction port pressure indicates a degree of vacuum of an outer portion (a right portion in FIG. 3) of the seal groove 46 serving as an air intake port. The desired value of the inlet pressure to obtain the set vacuum degree (ultra high vacuum) at the inlet 3a is 10 ² (Pa) or less. That is, since the inside of the seal groove 46 is opened to the atmosphere, it is desired that the seal groove 46 secures a pressure reducing effect of 10 ² (Pa) or less. As can be seen from the graph, the sealing performance of the seal groove 46 depends on the groove depth. And, the seal groove depth is 2 with respect to the clearance C.
It can be seen that the target sealing performance can be obtained in the range of 10 to 10 times. Based on this data, in the present example, the groove depth of the seal groove 46 is set to be in a range of 2 to 10 times the clearance C.
The value is set in a range of up to 8 times.

FIG. 5 shows the groove depth of the dynamic pressure groove 45 and the rotating body 2.
5 is a graph showing the relationship between the characteristic frequency of No. 5 and the natural frequency. The natural frequency of the rotating body 25 is affected by the groove depth of the dynamic pressure groove 45.
Since the rotation speed of the motor 10 is about 60,000 to 90,000 rpm, the rotation cycle of the rotating body 25 is about
It becomes 1,000 to 1,500 Hz. It is necessary that the natural frequency of the rotating body 25 does not resonate with the rotation cycle.

As can be seen from the graph, the natural frequency decreases as the groove depth of the dynamic pressure groove 45 increases.
When the groove depth is 1 to 5 times the clearance C, the natural frequency deviates from the used rotation cycle. When the groove depth is 6 times the clearance C, the natural frequency is significantly reduced. When the groove depth exceeds 5 times the clearance C, the natural frequency is around the operating speed (operating rotation cycle of about 1,000 to 1,500 Hz). It comes to have. For this reason, the groove depth is 5 times the clearance C.
If it exceeds twice, the rotation shaft 13 tends to swing due to resonance, and it is difficult to obtain stable rotation. The groove depth of the dynamic pressure groove 45 is preferably in a range of 1 to 5 times the clearance C.

The depth of the circumferential groove 47 is determined by the air supply hole 48.
In order to facilitate the smooth introduction of air into the clearance by the action of the dynamic pressure groove 45, it is preferable to set the value to more than twice the groove depth of the dynamic pressure groove 45. Each of the grooves 45 to 47 is formed by, for example, a sand blast method. Each groove 45-47
In this example, the following method is used in order to form with a small number of steps at different fitting groove depths. The area where the seal groove 46 is formed is protected by a mask, and the dynamic pressure groove 45 and the circumferential groove 47 are engraved to an appropriate groove depth of the dynamic pressure groove 45 (1 to 5 times the clearance C). Next, the formation area of the dynamic pressure groove 45 is protected by a mask,
And the circumferential groove 47 are engraved to an appropriate groove depth of the seal groove 46 (2 to 10 times the clearance C). As a result of these two steps,
The circumferential groove 47 is formed to have a groove depth (3 to 15 times the clearance C) which is the sum of the groove depth of the dynamic pressure groove 45 and the groove depth of the seal groove 46. The groove depth of the circumferential groove 47 is preferably larger than twice the groove depth of the dynamic pressure groove 45. However, in consideration of the simplicity of manufacture, the groove depth is preferably 3 to 15 times the clearance C. 4
It is preferable that the sum is the sum of the groove depth of No. 5 and the groove depth of the seal groove 46.

As described above, the appropriate value of the groove depth of each of the grooves 45 to 47 is set to A _PS ,
When A _GS , A _R , and clearance are C, the following is obtained. Groove depth A _PS = 1-5 × C of dynamic pressure groove 45, seal groove 4
6 groove depth A _GS = 2 to 10 × C, circumferential groove 47 groove depth A
_R = 3 to 15 × C, and especially A _GS = 4 to 8 × C is effective. It is preferable that the relationship A _R = A _PS + A _GS is established. It should be noted that satisfying the above-described conditions in the clearance range of 10 μm or less required for the small-sized turbo-molecular pump 1 is an appropriate value of the groove depth of each of the grooves 45 to 47.

Next, the operation of the above-configured device will be described. When the drive of the motor 10 is started and the rotor 14 rotates, air is drawn in from the intake port 3 a by the relative rotation of the moving blade 16 and the stationary blade 7. The drawn air passes through a seal groove 17 a in a gap between the motor casing 17 and the rotor 14, and
7 to the clearance through the seal groove 46 inside. The air that has reached the clearance is supplied from the air supply hole 48 to the chamber 36.
And is exhausted from the chamber 36 to the outside of the motor casing 17 through the slit hole 17b.

On the other hand, when the motor 10 is driven, air is introduced into the clearance from each air supply hole 48 by the action of the dynamic pressure groove 45, and a high-pressure air pool is formed at the center of the width of the air bearing band 43, and the pressure gas A film is formed. For this reason, the rotating body 25 floats from the inner peripheral surface of the outer cylinder 29 when the rotation speed exceeds about 5,000 rpm. The radial load of the rotating shaft 13 is supported by a dynamic pressure gas bearing 30 that forms a pressure gas film between the rotating body 25 and the outer cylinder 29. At this time, the groove depth of the circumferential groove 47 is adjusted to A _R = 3 to 15 × C, and the supply of air from the air supply hole 48 to the clearance proceeds smoothly. The pressure gas film quickly reaches a predetermined pressure.

The groove depth of the dynamic pressure groove 45 is A _PS = 1 to 5
XC, the natural frequency of the rotating body 25 is about 60,000 to 90,000 rpm.
Since it is out of the range of 1,000 to 1,500 Hz, the rotating body 25
Does not cause resonance. Therefore, good bearing characteristics are obtained, and the rotating shaft 13 stably rotates at the used rotation speed.

Further, if the groove depth of the seal groove 46 is A _GS = 2
Since the pressure is adjusted to 10 × C, the pressure at the outside of the intake port is secured to a degree of vacuum of 10 ² Pa or less. Especially A _GS
In this embodiment adopting = 4 to 8 × C, the suction port pressure of the seal groove 46 is secured to a degree of vacuum of 10 Pa or less.

Further, the pressure at the inlet of the seal groove 17a is ensured to a higher degree of vacuum (about 1 Pa or less). And
The degree of vacuum is further reduced by the suction pressure due to the relative rotation of the moving blade 16 and the stationary blade 7, and the degree of vacuum at the intake port 3a is determined. As described above, since each seal portion formed by the seal groove 46 and the seal groove 17a plays a role in increasing the degree of vacuum, the degree of vacuum obtained by the turbo molecular pump 1 can be further increased.

During the high-speed rotation of the motor 10, the inner cylinder 28 and the outer cylinder 29 generate heat due to viscous friction of air. The blast from the air cooling fan unit 20 hits the outer cylinder 29 via the slit hole 17b, whereby the dynamic pressure gas bearing 30 is air-cooled. At this time, a temperature difference occurs between the outer cylinder 29 and the inner cylinder 28, but the thermal expansion coefficient of the inner cylinder 28 made of silicon carbide (3 to 4 ×
10 ⁻⁶ / ° C.) is smaller than the thermal expansion coefficient (7 to 8 × 10 ⁻⁶ / ° C.) of the outer cylinder 29 made of alumina. For this reason, even if the clearance C required for the small turbo molecular pump 1 is as small as 5 μm or less based on design values such as the exhaust speed and the number of revolutions, the clearance is secured in the usage range.

As described in detail above, according to the present embodiment,
The following effects can be obtained. (1) The seal groove 46 is adapted to be deeper than the dynamic pressure groove 45, the seal groove 46 has a groove depth of A _GS = 2 to 10 × C, and the dynamic pressure groove 45 has a groove depth of A _PS = 1 to 5 × C. Therefore, high sealing performance can be obtained by the seal groove 46, and high bearing performance can be obtained by the dynamic pressure groove 45, which can stably support the radial load of the rotating body 25 without vibration due to resonance.

(2) Set the depth of the seal groove 46 to A _GS = 2.
By conforming to 10 × C, the suction port pressure of the seal groove 46 is secured to a degree of vacuum of 10 ² pa or less, so that the ability of the turbo-molecular pump 1 to obtain an ultra-high vacuum can be enhanced. In particular, since the groove depth of the seal groove 46 is adapted to A _GS = 4 to 8 × C and the pressure at the inlet of the seal groove 46 is maintained at a vacuum degree of 10 pa or less, the performance of the turbo-molecular pump 1 is reduced. Can be further enhanced.

(3) The circumferential groove 47 has the deepest groove depth,
Since the groove depth is adjusted to the range of A _R = 3 to 15 × C, the supply amount of air introduced into the dynamic pressure groove 45 is sufficiently increased, and the pressure of the high pressure capable of stably supporting the rotating shaft 13 is increased. A gas film can be formed. Therefore, the bearing performance of the dynamic pressure gas bearing 30 can be improved.

(4) The groove depth of the circumferential groove 47 is
(A _R = A _PS + A _GS ), so that three types of grooves 45 to 47 having different groove depths are formed in two groove forming steps. be able to.

(5) By forming a seal groove 17a on the upper outer peripheral surface of the motor casing 17, a gap between the motor casing 17 and the rotor 14 is used as a seal portion, and the seal groove 1a is formed.
Since the degree of vacuum is further increased by 7a, it contributes to further increasing the performance of the turbo-molecular pump 1.

(6) The motor 10 is connected to the rubber sealing member 1
Since a support structure is provided for elastically supporting the housing 2 via the first and second members 12, vibration of the motor 10 can be hardly transmitted to the housing 2.

It should be noted that the embodiment is not limited to the above, but can be carried out in the following manner. It is also possible to implement a configuration in which the groove depths of the dynamic pressure groove 45 and the seal groove 46 are matched and the groove depth of the circumferential groove 47 is not matched. Even if the groove depth of the dynamic pressure groove 45 and the groove depth of the seal groove 46 are simply adjusted, high sealing performance and bearing performance can be obtained.

The groove depth of the circumferential groove 47 is not limited to the sum of the respective groove depths of the dynamic pressure groove 45 and the seal groove 46. If the groove depth of the circumferential groove 47 exceeds twice the groove depth of the dynamic pressure groove 45, sufficient air can be supplied to the clearance, and a high pressure gas film can be formed by the dynamic pressure groove 45. .

At least one of the dynamic pressure groove and the seal groove may be formed on the inner peripheral surface of the outer cylinder. When a seal groove is formed between the motor 10 and the rotor 14, the seal groove may be formed on the inner peripheral surface of the rotor 14 instead of the outer peripheral surface of the motor casing 17.
In short, the seal groove is formed in the motor casing 17.
Any one of the surfaces facing the rotor 14 is sufficient.

It is not always necessary to provide a seal groove between the motor 10 and the rotor 14. ○ If the inner cylinder and the outer cylinder are ceramics, it is preferable from the viewpoint of wear resistance and heat resistance. Anything can be used, such as ceramic oxide, ceramic carbide, ceramic nitride. Also,
As long as the clearance between the dynamic pressure gas bearings (inner cylinder and outer cylinder) is ensured in the usage range, the coefficient of thermal expansion of the material need not be particularly considered. The materials of the inner cylinder and the outer cylinder may be the same or different, and for example, ceramics such as silicon carbide, silicon nitride, alumina, zirconia, mullite, zircon, boron nitride, and aluminum nitride can be used.

The material of the dynamic pressure gas bearing is not limited to ceramic. At least one of the inner cylinder and the outer cylinder may be made of plastic as long as necessary wear resistance and heat resistance can be obtained.

The non-contact type bearing for supporting the load in the thrust direction of the rotating shaft is not limited to the magnetic bearing. An air bearing may be used. ○ The motor is not limited to use for turbo molecular pumps. For example, a motor may be used for the compressor. In this case, the seal grooves 17a, 46 in the rotation direction
The direction of the spiral is reversed.

The technical ideas other than the claims grasped from the embodiment and other examples are described below. (1) In claim 1, the depth of the seal groove is in a range of 2 to 10 times the clearance. In this case, the sealing performance is improved by adapting the groove depth of the seal groove.

(2) In the technical idea of claims 2 to 5 and (1), the depth of the seal groove is in a range of 4 to 8 times the clearance. In this case, the sealing performance by the seal groove can be effectively improved.

(3) In claim 1, the depth of the dynamic pressure groove is in a range of 1 to 5 times the clearance. In this case, the bearing performance is enhanced by adapting the groove depth of the dynamic pressure groove. (4) In claim 3, the groove depth of the circumferential groove is set to be greater than twice the groove depth of the dynamic pressure groove instead of being deeper than the groove depth of the seal groove. Also in this case, the bearing performance can be similarly enhanced.

(5) Claims 1-8 and (1)-
In any of the technical ideas described in (4), the dynamic pressure gas bearing is a ceramic dynamic pressure gas bearing. In this case, since it is made of ceramic, wear resistance and heat resistance are guaranteed.

[0065]

As described above in detail, according to the first aspect of the present invention, the groove depth of the seal groove and the dynamic pressure groove provided on the opposing surface of the bearing rotating body and the bearing fixed body is reduced. Since the seal groove is deeper than the dynamic pressure groove, the sealing performance by the seal groove,
And the bearing performance by the dynamic pressure groove can be enhanced.

According to the second aspect of the present invention, the seal groove is formed to have a clearance between 2 and 1 of the clearance between the bearing fixed body and the bearing rotating body.
Since the range is set to 0 times and the dynamic pressure groove is adapted to a range of 1 to 5 times the clearance, the sealing performance by the seal groove and the bearing performance by the dynamic pressure groove can be effectively improved.

According to the invention described in claim 3, according to claim 1
Or, in addition to the effect of the invention of claim 2, the groove depth of the circumferential groove formed at a position corresponding to each boundary between the seal groove and the dynamic pressure groove,
Since it is deeper than the seal groove, air can be sufficiently supplied to the dynamic pressure groove to promote the formation of a pressure gas film, which contributes to further improving bearing performance.

According to the invention set forth in claim 4, according to claim 3,
In addition to the effects of the invention, the groove depth of the circumferential groove is adapted to be in a range of 3 to 15 times the clearance, so that air can be efficiently introduced into the dynamic pressure groove, contributing to further enhancing bearing performance. .

According to the invention set forth in claim 5, according to claim 4,
In addition to the same effects as the invention, the depth of the circumferential groove is substantially the sum of the depth of the seal groove and the depth of the dynamic pressure groove, so that the seal groove and the circumferential groove are formed together, Further, by forming the dynamic pressure groove and the circumferential groove together, three types of grooves having different groove depths can be formed in two groove forming steps.

According to the sixth aspect of the present invention, the turbo molecular pump uses the motor according to any one of the first to fifth aspects to rotate the rotor blade. A high degree of vacuum can be achieved by stable high-speed rotation of the blades.

According to the invention of claim 7, according to claim 6,
In addition to the effects of the invention described above, a seal groove is also formed between the motor and the rotor for the moving blade, so that a higher vacuum can be obtained by the turbo-molecular pump.

According to the invention of claim 8, according to claim 6,
Alternatively, in addition to the effect of the seventh aspect, the motor is elastically supported by the housing, so that a vibration-proof effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a turbo molecular pump according to one embodiment.

FIG. 2 is a side sectional view showing a brushless motor.

FIG. 3 is a side view showing the outer peripheral surface of the rotating body.

FIG. 4 is a graph showing a relationship between a seal groove depth and an intake port pressure.

FIG. 5 is a graph showing a relationship between a dynamic pressure groove depth and a natural frequency of a rotating body.

[Explanation of symbols]

Reference numeral 1: turbo molecular pump, 2: housing, 7: stationary blade, 1
0: brushless motor as motor, 11, 12: seal member, 13: rotating shaft, 14: rotor, 16: rotor blade,
DESCRIPTION OF SYMBOLS 17 ... Motor casing, 17a ... Seal groove, 25 ... Rotating body, 28 ... Inner cylinder as a bearing rotating body, 29 ... Outer cylinder as a bearing fixed body, 30 ... Dynamic pressure gas bearing, 31 ... Armature as an armature Coil, 37, 38: Magnetic bearing as non-contact type bearing, 43: Air bearing band, 44: Gas seal band,
45 ... dynamic pressure groove, 46 ... seal groove, 47 ... circumferential groove, 48 ...
Air supply holes as open holes.

 ──────────────────────────────────────────────────続 き Continued from the front page F term (reference) 3H031 DA02 EA02 EA07 EA08 FA04 FA13 FA14 FA15 FA16 FA32 FA36 FA39 3J011 AA04 BA02 CA01 CA03 3J102 AA01 CA21 DA02 DA07 5H607 AA06 AA12 BB01 CC01 CC05 DD01 DD02 DD03 DD08 GG06 GG06 GG06 GG06 GG06 HH01 JK19

Claims (8)

[Claims] A rotating body for rotating a rotating shaft; an armature disposed on an outer peripheral side of the rotating body; a dynamic pressure gas bearing for supporting a radial load of the rotating body; A non-contact type bearing that supports a load in the thrust direction, wherein the dynamic pressure gas bearing is provided with a bearing rotating body forming an outer peripheral surface of the rotating body and a clearance provided on an outer peripheral side of the bearing rotating body. A seal groove and a dynamic pressure groove are formed on opposing surfaces of the bearing rotating body and the bearing fixed body, and the seal groove has a groove depth set to be deeper than the dynamic pressure groove. Motor. 2. The method according to claim 1, wherein the seal groove has a groove depth in a range of 2 to 10 times the clearance, and the dynamic pressure groove has a groove depth in a range of 1 to 5 times the clearance. Item 2. The motor according to Item 1. 3. A circumferential groove formed at a position corresponding to each boundary between the seal groove and the dynamic pressure groove and facing an opening provided in the bearing fixing body so as to open the clearance to the atmosphere. 3. The motor according to claim 1, wherein the groove depth is greater than the seal groove. 4. The motor according to claim 3, wherein the circumferential groove has a groove depth in a range of 3 to 15 times the clearance. 5. The groove depth of the circumferential groove is substantially the sum of the groove depth of the seal groove and the groove depth of the dynamic pressure groove. A motor according to claim 1. 6. The motor according to any one of claims 1 to 5, a moving blade provided on a rotation shaft of the motor, and a molecular flow necessary for generating a molecular flow by rotation of the moving blade. A turbo-molecular pump including a stationary blade. 7. The turbo-molecule according to claim 6, wherein a seal groove is formed on a surface facing the motor and a rotor for rotor provided to cover a part of the motor. pump. 8. The turbo-molecular pump according to claim 6, wherein the motor is elastically supported by a housing.