U.S. patent application number 13/381239 was filed with the patent office on 2012-06-07 for vacuum pump and member used for vacuum pump.
This patent application is currently assigned to EDWARDS JAPAN LIMITED. Invention is credited to Yasushi Maejima, Tooru Miwata, Yoshinobu Ohtachi, Tsutomu Takaada.
Application Number | 20120141254 13/381239 |
Document ID | / |
Family ID | 43627641 |
Filed Date | 2012-06-07 |
United States Patent
Application |
20120141254 |
Kind Code |
A1 |
Ohtachi; Yoshinobu ; et
al. |
June 7, 2012 |
VACUUM PUMP AND MEMBER USED FOR VACUUM PUMP
Abstract
To provide a vacuum pump in which possibilities of decreased
exhaust performance and gas leakage at the time of breakage of a
rotor are lessened, in the case where a rotating part closes the
inside opening portion of an exhaust outlet portion to decrease the
height dimension of the vacuum pump, and further a connector lead
wire is installed, easily. An inside opening edge portion of a gas
discharge passage for combining the downstream space of the rotor
with the exhaust outlet portion is caused to take a shape such that
the opening edge portion has no blind portion when a gas exhaust
passage forming member is viewed from at least either of an upper
side or an oblique upper side, or from at least either of an lower
side or an oblique lower side. Furthermore, the inner corner
portion of this opening edge portion is formed into a rounded shape
to reduce stress concentration. Also, a base is provided with a
groove for combining a lead wire installing hole with a hole in the
central part, and further the corners of these parts are formed
into a rounded shape.
Inventors: |
Ohtachi; Yoshinobu; (Chiba,
JP) ; Maejima; Yasushi; (Chiba, JP) ; Takaada;
Tsutomu; (Chiba, JP) ; Miwata; Tooru; (Chiba,
JP) |
Assignee: |
EDWARDS JAPAN LIMITED
Chiba
JP
|
Family ID: |
43627641 |
Appl. No.: |
13/381239 |
Filed: |
May 31, 2010 |
PCT Filed: |
May 31, 2010 |
PCT NO: |
PCT/JP2010/059186 |
371 Date: |
December 28, 2011 |
Current U.S.
Class: |
415/90 |
Current CPC
Class: |
F04D 29/601 20130101;
F04D 19/042 20130101; F04D 29/522 20130101; F04D 27/0292 20130101;
F04D 25/0693 20130101 |
Class at
Publication: |
415/90 |
International
Class: |
F01D 1/36 20060101
F01D001/36 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 28, 2009 |
JP |
2009-198274 |
Claims
1. A vacuum pump comprising: an inlet port; a motor; a rotating
body rotatably driven by the motor; a stator located facing the
rotating body; an outlet port for exhausting a gas that has been
sucked in through the inlet port; and a gas exhaust passage
combining a downstream space of the rotating body with the outlet
port and being formed in a flow channel of the gas, and the
rotating body extending into an inner circumferential side in a
radial direction of the rotating body, of the gas exhaust passage,
wherein no blind portion exists at an opening edge portion of the
gas exhaust passage, of the downstream space side when a as exhaust
passage forming member that forms the gas exhaust passage is viewed
from at least either of an upper side or an oblique upper side, or
from at least either of a lower side or an oblique lower side.
2. The vacuum pump according to claim 1, wherein the gas exhaust
passage forming member is the stator.
3. The vacuum pump according so claim 1, further comprising a
casing that covers an outer circumferential side. of the rotating
body and/or the stator, wherein the gas exhaust passage forming
member is the casing.
4. The vacuum pump according to claim 1, further comprising a
housing or a base member that supports the stator, wherein the gas
exhaust passage forming member is the housing or the base
member.
5. The vacuum pump according to claim 1, further comprising an
outlet port member that forms the outlet port and extends inward
the vacuum pump, wherein the gas exhaust passage forming member is
the outlet port member.
6. The vacuum pump according to any one of claims 1 to 5, wherein
an inner corner portion of the opening edge portion has a rounded
inner corner shape that reduces stress concentration.
7. A vacuum pump comprising: an inlet port.; a motor; a rotating
body rotatably driven by the motor; a stator located facing the
rotating body; and an outlet port for exhausting a gas that has
been sucked in through the inlet port; and a gas exhaust passage
combining a downstream space of the rotating body with the outlet
port is formed in a flow channel of the gas, and the rotating body
extends into an inner circumferential side in a radial direction of
the rotating body, of the gas exhaust passage, wherein an inner
corner portion of an opening edge portion of the gas exhaust
passage, of the downstream space side has a rounded inner corner
shape that reduces stress concentration.
8. The vacuum pump according to any one of claims 1 to 7, further
comprising a connector for connecting a controller that controls
the rotation of the rotating body, wherein the housing or the base
member has a nearly coaxial hole that is nearly coaxial with a
rotation center axis of the rotating body, a conductor wire
insertion hole into which a conductor wire that connects the
connector and the motor is inserted, and a groove that combines the
nearly coaxial hole with the conductor wire insertion hole.
9. A vacuum pump comprising: an inlet port; a motor; a rotating
body rotatably driven by the motor; a stator located facing the
rotating body; a housing or a base member supporting the stator;
and a connector for connecting a controller that controls the
rotation of the rotating body; wherein the housing or the base
member has a nearly coaxial hole that is nearly coaxial with a
rotation center axis of the rotating body, a conductor wire
insertion hole into which a conductor wire that connects the
connector and the motor is inserted, and a groove that combines the
nearly coaxial hole with the conductor wire insertion hole.
10. The vacuum pump according to claim 8 or 9, wherein an edge of
at least one from the nearly coaxial hole, the conductor wire
insertion hole, and the groove has a rounded outer corner shape
such that damage of the conductor wire caused by contact with the
edge is reduced.
11. The vacuum pump according to any one of claims 8 to 10, wherein
an outer circumferential end of the groove in the radial direction
of the rotating body is positioned further toward the outer
circumferential side than an inner circumferential end of the
conductor wire insertion hole.
12. A member for use in a vacuum pump comprising: an inlet port; a
motor; a rotating body rotatably driven by the motor; a stator
located facing the rotating body; and an outlet port for exhausting
a gas that has been sucked in through the inlet port; and a gas
exhaust passage combining a downstream space of the rotating body
with the outlet port and being formed in a flow channel of the gas,
wherein no blind portion exists at an opening edge portion of the
gas exhaust passage, of the downstream space side when the member
is viewed from at least either of an upper side or an oblique upper
side, or from at least either of a lower side or an oblique lower
side.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a vacuum pump such as a
turbomolecular pump performing gas evacuation from a vacuum
container such as a process chamber used in a semiconductor
fabrication apparatus. More particularly, the present invention
relates to a technique for improving the evacuation performance
that decreases depending on the arrangement positions of an outlet
port and a connector, and for reducing the size of a vacuum
pump.
[0003] 2. Description of the Related Art
[0004] A multiple-stage blade pump in which a rotary blade section
and a cylindrical threaded section are combined is widely used as a
large-flow-rate pump such as a turbomolecular pump.
[0005] FIG. 9 illustrates an example of such a multiple-stage blade
pump. This multiple-stage blade pump 200 is constituted by a
tubular casing 20 having, formed in the upper portion thereof, an
inlet port 10 for sucking in the gas from a chamber that is not
shown in the figure, a plurality of rotary blades 32 that are
provided at a rotating body 30 inside the casing 20, fixed blades
40 provided alternately with the rotary blades 32, a thread groove
spacer 45 and a rotary blade cylindrical portion 50 constituting a
spiral groove portion 80 where evacuation is performed by drag
action, a disk-shaped base 70 covering the lower portion of the
casing 20, an outlet port 90 for evacuating the gas evacuated from
the upstream side where the inlet port is located to the outside on
the downstream side, a connector 100 that is electrically connected
to an externally located controller for controlling the pump, and a
rear lid 110 that covers the bottom portion.
[0006] The rotating body 30 is contactless supported and position
controlled by magnetic levitation implemented by radial bearings
34, 36 and a thrust bearing 38. The rotating body 30 is rotatably
driven at a high speed by a drive motor 60. When the rotating body
30 rotates at a high speed, the rotary blades 32 provided at the
rotating body 30 simultaneously rotate at a high speed such that
these rotary blades 32 interact with the alternately disposed
stator blades 40, whereby evacuation is performed.
[0007] Turbomolecular pumps generally have a back pressure
dependence, that is, the pump performance is affected by the
pressure on the back pressure side (outlet port side). Accordingly,
in a multiple-stage blade pump, a low pressure is maintained on the
inlet port side and the back pressure is increased, thereby
improving the pump performance, by enlarging the diameter of the
spiral groove portion 80 and increasing the axial length of the
spiral groove portion 80.
[0008] However, multiple-stage blade pumps should be designed with
consideration for restrictive conditions relating to the
installation thereof. In particular, where the length of the spiral
groove portion 80 is increased, the axial length of the pump itself
is also increased causing problems in installation.
[0009] Japanese Patent Application Publication No. 2008-163857
discloses a technique for preventing the reduction of the opening
area of outlet port inside the pump and the degradation of exhaust
performance caused by the extension of the spiral groove portion.
Thus, when the rotary section of the pump blocks a opening portion
of the outlet port inside the pump, the exhaust performance is
degraded because the reduction of the opening decreases the
conductance and prevents the flow of gas into the outlet port.
[0010] Accordingly, with the aforementioned technique, a U-shaped
groove for which the radial direction from the inner side serves as
a depth direction is provided with respect to a cylindrical hole
connecting the spiral groove portion with the outlet port provided
in the base or thread groove spacer. The reduction in the opening
area of outlet port is thereby prevented. As a result, the exhaust
performance of the pump is improved.
[0011] However, where a U-shaped groove is provided from the inside
with respect to the cylindrical, hole leading to the outlet port
according to the technique described in Japanese Patent Application
Publication No. 2008-163857, special cutting tools and settings are
required during turning and the machining is difficult. Further,
even if the machining is successful, significant time and efforts
are required therefor and the production cost rises.
[0012] Further, where the housing is manufactured by casting, since
the concave groove exists on the inner side, the cast housing is
difficult to remove from the mold, the mold structure becomes
complex, and the casting cost rises significantly.
[0013] In addition, where the spiral rotor is broken during
rotation, the broken pieces thereof collide with the spiral stator
and a force acts on the spiral stator or on the housing via the
spiral stator. In this case, stress concentration occurs in the
corners of the formed groove, thereby creating weak points in terms
of the pump strength and reducing the strength of the pump
itself.
[0014] Further, in a dry etching apparatus, which is one of
semiconductor fabrication apparatuses, where the pressure of
process gas that has taken part in a reaction inside the chamber
increases, the increase in temperature over the normal temperature
results in a phase transition from a gaseous state to a solid
state. For this property, when a multiple-stage blade pump is used
for evacuating a dry etching apparatus, the solidified reaction
products of the process gas are deposited on the spiral groove
portion where The gas pressure rises, thereby degrading the exhaust
performance of the pump. For this reason, the reaction products
that have deposited on the interior portions of the pump should be
removed periodically. However, a cleaning agent or a removal tool
is difficult to insert into the U-shaped groove and therefore the
removal operation becomes difficult.
[0015] Furthermore, when the reaction products are removed, it is
necessary to confirm visually that all of the reaction products
have been removed. Since the process as in the dry etching
apparatus is typically highly corrosive, it is also necessary to
verify visually after the removal whether corrosion is present on
the gas flow channel surface of the housing or spiral stator and
whether the surface film such as a plated film provided for
corrosion protection has peeled off from the surface, and where
such defects are present, they should be repaired. Where portions
of the gas flow channel surface cannot be visually inspected, the
residues of corrosion products or corrosion can remain unnoticed on
such portions and the vacuum pump is restarted in the unrepaired
state. Another problem is that when the corrosion advances, the
strength of the spiral stator or housing decreases and the
abovementioned rotor fracture occurs, the spiral stator and housing
can be fractured and the gas can leak therethrough. With the
U-shaped groove, such as that of the conventional technique, the
portion that cannot be visually inspected can be reduced in size by
decreasing the groove depth. However, the problem arising in this
case is that because the groove is shallow, a sufficient opening
area cannot be ensured.
[0016] Another problem is associated with a connector. A
turbomolecular pump has a connector serving to connect the pump to
a controller for power supply to the motor or magnetic bearings or
input/output of signals. The pump structure is such that the hole
for passing the connector wiring is completely isolated from the
exhaust flow channel. Such a structure is used because if the
exhaust flow channel and the hole are connected and gas flows to
the connector, the exhaust performance is degraded or the connector
is corroded. In some cases, it can result in accidents and cause
significant problems for the pump.
[0017] Further, when the height position of the lower end of the
spiral groove portion is below the height position of the hole for
connector wiring, the opening area of the hole for connector wiring
should be reduced and the operation of passing the wiring from the
motor or magnetic bearings to the connector becomes complex.
Accordingly, the problem. associated with the connector is similar
to that relating to the outlet port. Namely, the increase in the
spiral groove portion length requires the vacuum pump height to be
increased.
[0018] Such a problem relating to the connector is not taken into
account in the above-described conventional technique.
SUMMARY OF THE INVENTION
[0019] It is the first object of the present invention to provide a
vacuum pump in which the decrease in exhaust performance occurring
when the spiral groove portion is extended or positioned further
below inside the pump with the object of reducing the size of the
vacuum pump can be prevented.
[0020] It is the second object of the present invention to provide
a vacuum pump in which the operability of connector wiring that
decreases when the spiral groove portion is extended or positioned
further below inside the pump with the object of reducing the size
of the vacuum pump can be improved.
[0021] The invention described in claim 1 provides a vacuum pump
which includes an inlet port, a motor, a rotating body rotatably
driven by the motor, a stator located facing the rotating body, and
an outlet port for exhausting a gas that has been sucked in through
the inlet port, and a gas exhaust passage combining a downstream
space of the rotating body with the outlet port is formed in a flow
channel of the gas, and the rotating body extends into en inner
circumferential side in a radial direction of the rotating body, of
the gas exhaust passage, wherein no blind portion exists at an
opening edge portion of the gas exhaust passage, of the downstream
space side when a gas exhaust passage forming member that forms the
gas exhaust passage is viewed from at least either of an upper side
or an oblique upper side, or from at least either of a lower side
or an oblique lower side.
[0022] The invention described in claim 2 provides the vacuum pump
according to claim 1, wherein the gas exhaust passage forming
member is the stator.
[0023] The invention described in claim 3 provides the vacuum pump
according to claim 1, further including a casing that covers an
outer circumferential side of the rotating body and/or the stator,
wherein the gas exhaust passage forming member is the casing.
[0024] The invention described in claim 4 provides the vacuum pump
according no claim 1, further including a housing or a base member
that supports the stator, wherein the gas exhaust passage forming
member is the housing or the base member.
[0025] The invention described in claim 5 provides the vacuum pump
according to claim 1, further including an outlet port member that
forms the outlet port and extends inward the vacuum pump, wherein
the gas exhaust passage forming member is the outlet port
member.
[0026] The invention described in claim 6 provides the vacuum. pump
according to any one of claims 1 to 5, wherein an inner corner
portion of the opening edge portion has a rounded inner corner
shape that reduces stress concentration.
[0027] The invention described in claim 7 provides a vacuum pump
which includes an inlet port, a motor, a rotating body rotatably
driven by the motor, a stator located facing the rotating body, and
an outlet port for exhausting a gas that has been sucked in through
the inlet port, and a gas exhaust passage combining a downstream
space of the rotation body with the outlet port is formed in a flow
channel of the gas, and the rotating body extends into an inner
circumferential side in a radial direction of the rotating body, of
the gas exhaust passage, wherein an inner corner portion of an
opening edge portion of the gas exhaust passage, of the downstream
space side has a rounded inner corner shape that reduces stress
concentration.
[0028] The effect of reducing stress concentration can be obtained
even when the rounding size of the rounded inner corner portion is
0.1 mm. Even greater effect can be obtained when the rounding size
is further increased.
[0029] The invention described in claim 8 provides the vacuum pump
according to any one of claims 1 to 7, further including a
connector for connecting a controller that controls the rotation of
the rotating body, wherein the housing or the base member has a
nearly coaxial hole that is nearly coaxial with a rotation center
axis of the rotating body, a conductor wire insertion hole into
which a conductor wire that connects the connector and the motor is
inserted, and a groove that combines the nearly coaxial hole with
the conductor wire insertion hole.
[0030] The controller may be directly connected to the connector or
may be connected by a cable.
[0031] The invention described in claim 9 provides a vacuum pump
which includes an inlet port, a motor, a rotating body rotatably
driven by the motor, a stator located facing the rotating body, a
housing or a base member supporting the stator, and a connector for
connecting a controller that controls the rotation of the rotating
body, wherein the housing or the base member has a nearly coaxial
hole that is nearly coaxial with a rotation center axis of the
rotating body, a conductor wire insertion hole into which a
conductor wire that connects the connector and the motor is
inserted, and a groove that combines the nearly coaxial hole with
the conductor wire insertion hole.
[0032] The invention described in claim 10 provides the vacuum pump
according to claim 8 or 9, wherein an edge of at least one from the
nearly coaxial hole, the conductor wire insertion hole, and the
groove has a rounded outer corner shape such that damage of the
conductor wire caused by contact with the edge is reduced.
[0033] The invention described in claim 11 provides the vacuum pump
according to any one of claims 8 to 10, wherein an outer
circumferential end of the groove in the radial direction of the
rotating body is positioned further toward the outer
circumferential side than an inner circumferential end of the
conductor wire insertion hole.
[0034] The invention described in claim 12 provides a member for
use in a vacuum pump which includes an inlet port, a motor, a
rotating body rotatably driven by the motor, a stator located
facing the rotating body, and an outlet port for exhausting a gas
that has been sucked in through the inlet port, and a gas exhaust
passage combining a downstream space of the rotating body with the
outlet port is formed in a flow channel of the gas, wherein no
blind portion exists at an opening edge portion of the gas exhaust
passage, of the downstream space side when the member is viewed
from at least either of an upper side or an oblique upper side, or
from at least either of a lower side or an oblique lower side.
[0035] Examples of the aforementioned member include the stator,
casing, housing, base member, and outlet port member extending
inward of the vacuum pump, which constitute the vacuum pump.
[0036] In accordance with the present invention, the decrease in
exhaust performance of the vacuum pump occurring when the spiral
groove portion of the pump is extended or positioned further below
inside the pump can be prevented.
[0037] Further, in accordance with the present invention, the
degradation of wiring operability that decreases when the spiral
groove portion is extended or positioned further below inside the
pump can be reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 is a vertical sectional view illustrating a
multiple-stage blade pump in which an outlet port is provided in a
thread groove spacer according to the first embodiment;
[0039] FIG. 2 is vertical sectional view illustrating a
multiple-stage blade pump in which an outlet port is provided in a
base according to the first embodiment;
[0040] FIG. 3 illustrates the first embodiment relating to the case
in which the outlet port is provided in the thread groove
spacer;
[0041] FIG. 4 illustrates the first embodiment relating to the case
in which the outlet port is provided in the base;
[0042] FIG. 5 relates to an example in which a cylindrical hole is
formed as a gas evacuation passage in the thread groove. spacer and
illustrates the blind portions;
[0043] FIG. 6 illustrates how the thread groove spacer is viewed
directly from a lower side and an oblique lower side;
[0044] FIG. 7 illustrates how the base is viewed directly from an
upper side and an oblique upper side;
[0045] FIG. 8 illustrates the second embodiment; and
[0046] FIG. 9 is a vertical sectional view illustrating an example
of the conventional multiple-stage blade pump.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0047] The preferred embodiment of the vacuum pump in accordance
with the present invention will be explained below in greater
detail with reference to FIGS. 1 to 8.
[0048] FIGS. 1 and 2 are vertical sectional views illustrating the
configuration of the multiple-stage blade pump using the present
invention.
[0049] FIG. 1 illustrates an example where an outlet port is
provided in a thread groove spacer 45 serving as a stator. FIG. 2
illustrates an example where an outlet port is provided in a base
70 serving as a base member. In the explanation of FIGS. 1 to 8,
the members identical to those in FIG. 9 that illustrates the
conventional example will be assigned with same reference
numerals.
[0050] The first embodiment relates to a technique for improving
the exhaust performance of a vacuum pump that has decreased because
a rotary blade cylindrical portion 50 serving as a rotating body or
a thread groove spacer 45 covers the opening of a cylindrical hole
45a or 70a serving as a gas exhaust passage combining an outlet
port 90 with a downstream space S of the rotary blade cylindrical
portion 50 on the space S side.
[0051] In this embodiment, a thread groove spacer 45 serving as a
gas exhaust passage forming member in the configuration shown in
FIG. 1 and the base 70 serving as a gas exhaust passage forming
member in the configuration shown in FIG. 2 form the cylindrical
hole 45a or 70a as shown in FIGS. 3B and 4B. The opening edge
portion 130 of the cylindrical hole 45a on the space S side in the
thread groove spacer 45 is formed. such that no blind portion
exists at the opening edge portion. 130 when the thread groove
spacer 45 is viewed from at least either of the lower side or the
oblique lower side.
[0052] The opening edge portion 130 of the cylindrical hole 70a on
the space S side in the base 70 is formed such that no blind
portion exists at the opening edge portion 130 when the base 70 is
viewed from at least either of the upper side or the oblique upper
side.
[0053] FIG. 5 is an explanatory drawing illustrating the blind.
portions in the case where the cylindrical hole 45a is formed as
the gas exhaust passage in the thread groove, spacer 45. In FIG. 5,
because the cross-hatched portion exists, blind portions exist at
the opening edge portion 130 when the thread groove spacer 45 is
viewed from at least either of the lower side or the oblique lower
side. By contrast, in the present embodiment, in the cylindrical
hole 45a formed by the thread groove spacer 45, the opening edge
portion 130 is formed such that no blind portion exists at the
opening edge portion 130 when the thread groove spacer 45 is viewed
from at least either of the lower side or the oblique lower side.
When the thread groove spacer 45 is viewed from at least either of
the lower side or the oblique, lower side, the field of view such
as the cross-hatched portion in FIG. 5 is not blocked. Therefore,
the entire opening edge portion 130 can be seen. In accordance with
the present invention, no blind portion exists in such a state.
[0054] Meanwhile, in the cylindrical hole 70a formed by the base
70, the opening edge portion. 130 is formed such that no blind
portion exists at the opening edge portion 130 when she base 70 is
viewed from at least either of the upper side or the oblique upper
side. When the base 70 is viewed from at least either of the upper
side or the oblique upper side, the field of view such as the
cross-hatched portion in FIG. 5 is not blocked. Therefore, the
entire opening edge portion 130 can be seen.
[0055] The definition of the "upper side", "oblique upper side",
"lower side", and "oblique lower side" will be explained below.
FIG. 6 shows the thread groove spacer 45 and. FIG. 7 shows the base
70. As shown in FIGS. 6 and 7, when these components are assembled
in the multiple-stage blade pump, the inlet port is on the upper
side and the pump bottom is on the lower side. Thus, the C side of
the center line C-C' is taken as the upper side and the C side is
taken as the lower side. Further, the C side of a straight line
forming an angle .alpha. less than 90 degrees with the center line
C-C' is taken as the oblique upper side and the C' side meeting
such a requirement is taken as the oblique lower side. The absence
of a blind portion at the opening edge portion 130 when the thread
groove spacer 45 is viewed from at least either of the lower side
or the oblique lower side means that any portion of the opening
edge portion 130 is included in at least either of the visible
portion of the opening edge portion 130 when it is viewed from the
lower side or the visible portion of the opening edge portion 130
when it is viewed from the oblique lower side. The absence of a
blind portion at the opening edge portion 130 when the base 70 is
viewed from at least either of the upper side or the oblique upper
side means that any portion of the opening edge portion 130 is
included in at least either of the visible portion of the opening
edge portion 130 when it is viewed from the upper side or the
visible portion of the opening edge portion 130 when it is viewed
from the oblique upper side.
[0056] The outer side of the outlet port 90 is connected by a pipe
to an auxiliary pump having the usual suction power.
[0057] In the above-described related art, a U-shaped groove is
formed in the opening edge portion 130 of the cylindrical hole
combining the outlet port 90 with the downstream space S of the
rotary blade cylindrical portion 50, the groove being formed on the
space S side of the cylindrical hole. FIGS. 3A and 4A illustrate an
example in which the conventional U-shaped groove is formed with
the conventional technique, the inner corner portion of the opening
edge portion 130 does not have the rounded inner corner shape such
as shown in these figures.
[0058] Cylindrical shapes and cavities thereof are usually machined
by turning, and when a groove is bored in the direction
perpendicular to the center axial line of the cylinder in the inner
wall of the cavity portion, the cutting cannot be performed to the
necessary depth or the cutting process becomes complex and the
production cost rises due to the restrictions such as a machinable
range of the cutting tool (bite). However, with the shape of the
opening edge portion 130 of the present embodiment, cutting may be
performed so as to bore a hole that becomes coaxial with the
cylindrical outer circumferential surface in the center axial line
direction of the cylinder and therefore the machining in the
turning process is facilitated.
[0059] Furthermore, when the thread groove spacer 45 or base 70 is
cast, since no concave groove exists on the inner wall of the
hollow portion, the mold structure does not become complex and the
cast article can be easily removed from the mold, thereby making it
possible to reduce the casting cost.
[0060] Further, with the present embodiment, the operation of
removing the deposited reaction products, verifying the presence of
corrosion on the thread groove spacer 45 or base 70, and repairing
the corrosion are not complex. Therefore, the residual amount of
reaction products and leak caused by poor repair of corrosion can
be reduced.
[0061] Further, since the cross-hatched portions shown in FIGS. 3A
and 4A do not exist, the rotary blade cylindrical portion 50 can be
moved further down or the vacuum pump height can be further
reduced.
[0062] As a variation example of the first embodiment, a structure
is considered in which the inner corner portion of the opening edge
portion 130 of the cylindrical hole 45a on the space S side is
rounded as shown in FIG. 3B, and stress concentration is reduced.
In a vacuum pump, in particular a turbomolecular pump, the rotary
blade 32 and the rotary blade cylindrical portion 50 rotate at a
high speed during operation and a large centrifugal force acts
thereupon. Where the material strength decreases due to corrosion
or temperature increase caused by friction with the gas or the
like, the resistance to the centrifugal force decreases and the
pump is fractured. Where the rotary blade cylindrical portion 50 is
fractured in high-speed rotation, the rotary blade cylindrical
portion is often split into 3 to 4 sections and these split
cylindrical sections collide with the thread groove spacer 45. As a
result a force is applied to the thread groove spacer 45 and to the
base 70 via the thread groove spacer 45. The rotary blade 32 and
rotary blade cylindrical portion 50 usually rotate as a speed equal
to or higher than 10,000 rpm, and where they are fractured the
rotation energy thereof is released. Therefore, the force acting
upon the thread groove spacer 45 or base 70 becomes very strong.
When such a force is received, large stresses are generated in the
thread groove spacer 45 and base 70. In the case of the
conventional U-shaped groove, stress concentration occurs in the
inner corner portions of the groove and cracks can initiate from
the stress concentration zones. The cracks can cause fracture and
destruction of the thread groove spacer 45 or base 70 that can
result in the gas leaking to the outside of the pump. This gas leak
adversely affects the environment. When the inner corner portion of
the opening edge portion 130 of the cylindrical hole 45a or 70a on
the spacer S side is machined to a rounded shape, as in the present
embodiment, the stress concentration can be reduced. As a result,
the strength of the pump itself can be increased and the
probability of gas leak can be reduced. Further, in the present
embodiment, only one inner corner portion exists, by contrast with
the conventional U-shaped groove having two inner corner portions
and the number of stress concentration zones is small. Therefore,
the probability of gas leak can be further reduced.
[0063] The inner corner portions of the conventional U-shaped
groove may be also rounded as shown in FIGS. 3A and 4A.
[0064] The second embodiment in which the problems associated with
the connector are resolved will be explained below.
[0065] FIG. 8 is the view of the base 70 taken from the rear lid
110. As shown in the figure, a structure is obtained in which when
the connector wiring hole 120 serving as a conductor wire.
insertion hole is drilled in the base 70 from the outer
circumferential side, the drilling is performed to die outer
circumferential side in the radial direction of the rotary blade
cylindrical portion 50 and a groove 102 is provided from the bottom
surface of the base 70 so as to combine die connector wiring hole
120 with the hole 101 that is nearly coaxial with the rotation
center axial line of the rotary blade cylindrical portion 50.
[0066] In the present embodiment, as shown in FIG. 8, the connector
wiring hole 120 is drilled as far as the outer circumferential side
of the rotary blade cylindrical portion 50, rather than linearly to
the hole 101 in order to avoid interference of the connector wiring
hole 120 with the rotary blade cylindrical portion 50 or with the
space S for the gas flow channel located therebelow. Where the
connector wiring hole 120 interferes and is combined with the space
S for the gas flow channel, the gas flows into the connector wiring
hole 120 and the connector is corroded.
[0067] Further, as shown in FIG. 8, the outer corners formed in the
connector wiring hole 120 and groove 102 can have the rounded outer
corner shape. In such a case, a structure can be obtained in which
the connector 100 and the conductor wire connected to the motor or
magnetic bearings are unlikely to be damaged.
[0068] Further, the end o of she groove 102 on the outer
circumferential side of the pump is located on the outside of the
end i of the connector wiring hole 120 on the inner circumferential
side of the pump. This is done so because by increasing the
distance "L" between the two ends "o" and "i", it is possible to
ensure a larger pass-through area from the groove 102 to the
connector 100.
[0069] According to this embodiment, where the depth of the groove
102 is reduced within a range in which the minimum pass-through
area necessary for the wiring of the conductor wire can be ensured,
the rotary blade cylindrical portion 50 or the space S for the gas
flow channel located therebelow can be disposed at a lower level.
Since the wiring of the conductor wire to the connector 100 is also
performed by the groove of the shape obtained by cutting the wall
below the inner circumferential portion of the connector wiring
hole 120, the wiring connection is facilitated. Consequently, the
production time of the pump can be reduced.
[0070] As a result, the rotary blade cylindrical portion 50 and the
space S for the gas flow channel located therebelow can be enlarged
in length to reach the lower level or disposed at the lower level
without interfering with the connector wiring hole. 120. In
addition, the connector 100 can be provided at a height greater
than that in the conventional pump. As a result, the vacuum pump
can be reduced in height.
[0071] Further, with the above-described embodiment, the machined
shape of the base 70 can be simplified and the production cost
thereof can be reduced, without changing significantly the
structure of the conventional pump.
* * * * *