U.S. patent application number 13/849719 was filed with the patent office on 2013-10-03 for vacuum evacuation apparatus.
This patent application is currently assigned to EBARA CORPORATION. The applicant listed for this patent is EBARA CORPORATION. Invention is credited to Hiroyuki Kawasaki, Atsushi Oyama, Hiroshi Sobukawa.
Application Number | 20130259712 13/849719 |
Document ID | / |
Family ID | 48039974 |
Filed Date | 2013-10-03 |
United States Patent
Application |
20130259712 |
Kind Code |
A1 |
Kawasaki; Hiroyuki ; et
al. |
October 3, 2013 |
VACUUM EVACUATION APPARATUS
Abstract
The present invention relates to a vacuum evacuation apparatus
which can be mounted in a posture that can freely be selected a
vacuum evacuation apparatus for evacuating a container from an
atmospheric pressure to a high vacuum or less includes a first
vacuum pump for evacuating the container to a high vacuum or less,
and a second vacuum pump for evacuating the container from an
atmospheric pressure to a medium or low vacuum the first vacuum
pump and the second vacuum pump are integrally connected to each
other into an integral unit.
Inventors: |
Kawasaki; Hiroyuki; (Tokyo,
JP) ; Sobukawa; Hiroshi; (Tokyo, JP) ; Oyama;
Atsushi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EBARA CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
EBARA CORPORATION
Tokyo
JP
|
Family ID: |
48039974 |
Appl. No.: |
13/849719 |
Filed: |
March 25, 2013 |
Current U.S.
Class: |
417/201 |
Current CPC
Class: |
F04D 19/046 20130101;
F04C 23/00 20130101; F04D 19/042 20130101; F04B 25/00 20130101;
F04D 25/16 20130101 |
Class at
Publication: |
417/201 |
International
Class: |
F04B 25/00 20060101
F04B025/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 30, 2012 |
JP |
2012-080559 |
Claims
1. A vacuum evacuation apparatus for evacuating a container from an
atmospheric pressure to a high vacuum or less, comprising: a first
vacuum pump for evacuating the container to a high vacuum or less;
and a second vacuum pump for evacuating the container from an
atmospheric pressure to a medium or low vacuum; wherein said first
vacuum pump and said second vacuum pump are integrally connected to
each other into an integral unit.
2. A vacuum evacuation apparatus according to claim 1, wherein said
first vacuum pump has a rotational shaft and said second vacuum
pump has a rotational shaft, and said rotational shaft of said
first vacuum pump and said rotational shaft of said second vacuum
pump have respective axes which are perpendicular to each
other.
3. A vacuum evacuation apparatus according to claim 1, wherein said
first vacuum pump has a rotational shaft and said second vacuum
pump has a rotational shaft, and said rotational shaft of said
first vacuum pump and said rotational shaft of said second vacuum
pump are rotatably supported by one of self-lubricating bearings,
bearings having a semi-solid lubricant or a solid lubricant
therein, gas bearings, and magnetic bearings; and wherein said
rotational shaft of said first vacuum pump and said rotational
shaft of said second vacuum pump are rotatable regardless of
directions in which said first vacuum pump and said vacuum pump are
installed.
4. A vacuum evacuation apparatus according to claim 1, wherein said
first vacuum pump has a bottom component and said second vacuum
pump has a casing, and said bottom component and said casing are
integrally connected to each other, thereby integrally connecting
said first vacuum pump and said second vacuum pump.
5. A vacuum evacuation apparatus according to claim 1, wherein said
first vacuum pump and said second vacuum pump are integrally
connected to each other through a heat insulation member or a small
area of contact.
6. A vacuum evacuation apparatus according to claim 1, wherein said
first vacuum pump and said second vacuum pump are integrally
connected to each other through a vibro-isolating mechanism.
7. A vacuum evacuation apparatus according to claim 1, wherein said
first vacuum pump has an outlet port and said second vacuum pump
has an inlet port, and said outlet port and said inlet port are
interconnected by an evacuation passage component comprising a
vibro-isolating material.
8. A vacuum evacuation apparatus according to claim 1, wherein said
first vacuum pump has an inlet port and said second vacuum pump has
an inlet port, and said inlet port of said first vacuum pump and
said inlet port of said second vacuum pump are interconnected by a
bypass passage for bypassing said first vacuum pump.
9. A vacuum evacuation apparatus according to claim 1, wherein said
first vacuum pump has an outlet port and said second vacuum pump
has an inlet port, and said outlet port and said inlet port are
interconnected by an evacuation passage component incorporating
therein a check valve for preventing a fluid from flowing back from
said second vacuum pump to said first vacuum pump while said first
vacuum pump is in operation.
10. A vacuum evacuation apparatus according to claim 1, further
comprising: a controller for controlling said first vacuum pump and
said second vacuum pump; wherein said controller is integrally
connected to said first vacuum pump or is installed separately from
said first vacuum pump.
11. A vacuum evacuation apparatus according to claim 10, wherein
when each of said first vacuum pump and said second vacuum pump
reaches a rated rotational speed and no gas is introduced into the
container, said controller lowers a voltage applied to a motor of
at least one of said first vacuum pump and said second vacuum pump
and continuously operates said motor at a motor maximum efficient
point.
12. A vacuum evacuation apparatus according to claim 10, wherein
said controller is capable of controlling the pressure in the
container at a target pressure level by individually controlling
respective rotational speeds of said first vacuum pump and said
second vacuum pump depending on flow rates of the gas evacuated
therefrom.
13. A vacuum evacuation apparatus according to claim 1, wherein
said first vacuum pump comprises a turbomolecular pump, and said
second vacuum pump comprises a dry vacuum pump.
14. A vacuum evacuation apparatus according to claim 1, wherein
said second vacuum pump comprises a dry vacuum pump having a pair
of pump rotors with respective magnet rotors mounted thereon, said
magnet rotors have equal numbers of magnetic poles and are disposed
so that their different magnetic poles are magnetically attracted
to each other, and currents supplied to a multiphase armature
including an iron core and a plurality of windings disposed
radially outwardly of at least one of said magnet rotors are
switched to actuate said at least one of said magnet rotors for
thereby rotating said pump rotors in opposite directions in
synchronism with each other.
15. A vacuum evacuation apparatus according to claim 1, wherein one
of said first vacuum pump and said second vacuum pump comprises a
single vacuum pump and the other of said first vacuum pump and said
second vacuum pump comprises either a single vacuum pump or a
plurality of vacuum pumps.
16. A vacuum evacuation apparatus according to claim 15, wherein
said first vacuum pump and said second vacuum pump are integrally
connected to each other by at least one evacuation passage.
17. A vacuum evacuation apparatus according to claim 1, wherein the
ratio of an axial dimension of said second vacuum pump and an axial
dimension, which is assumed to be 1, of said first vacuum pump is
in a range from 1 to 0.6, and the ratio of a volume of said second
vacuum pump and a volume, which is assumed to be 1, of said first
vacuum pump is in a range from 0.3 to 0.5.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This document claims priority to Japanese Patent Application
No. 2012-080559, filed on Mar. 30, 2012, the entire contents of
which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a vacuum evacuation
apparatus which is capable of compressing a gas from an ultrahigh
vacuum to an atmospheric pressure, and more particularly to a
vacuum evacuation apparatus which can be mounted in a posture that
can freely be selected.
[0004] 2. Description of the Related Art
[0005] Conventionally, in a semiconductor fabrication apparatus or
the like, a combination of a turbomolecular pump and a dry vacuum
pump has been used for evacuating a gas in a chamber to create a
clean ultrahigh vacuum in the chamber. The turbomolecular pump
serves to evacuate the chamber to an ultrahigh vacuum range, and
the dry vacuum pump serves to evacuate the chamber in a range from
an atmospheric pressure to a medium vacuum. The turbomolecular pump
and the dry vacuum pump are driven by respective power supplies and
individually controlled in operation.
[0006] The turbomolecular pump and the dry vacuum pump are thus
used as vacuum pumps in different vacuum ranges. When a
turbomolecular pump is used, it is necessary to initially use a dry
vacuum pump to evacuate the chamber to a rough vacuum range, i.e.,
a medium vacuum range, in which the turbomolecular pump can be used
to further evacuate the chamber. Therefore, it is essential to
install the dry vacuum pump as a roughing vacuum pump in order to
use the turbomolecular pump.
[0007] As one advanced concept of the turbomolecular pump, an
atmospheric pressure-evacuation-type turbomolecular pump which can
evacuate the chamber from an atmospheric pressure range has been
proposed. However, such turbomolecular pump has not yet been fully
developed into a practically feasible product on account of various
problems about requirements for mechanical strength of a rotor that
needs to rotate at ultrahigh speeds, radiation of the heat of a
compressed gas produced at the time of evacuation from an
atmospheric pressure range to an ultrahigh vacuum range, the
structure of a motor that needs large torques and ultrahigh-speed
rotation, and a driving power supply source.
[0008] Heretofore, in order to create an ultrahigh vacuum, it has
been the general practice to use a positive displacement vacuum
pump such as an oil rotary pump, a roots dry pump, or a screw dry
pump which is capable of creating a vacuum in the range from
several Torr to 10.sup.-2 Torr, and a kinetic vacuum pump
(turbomolecular pump) or an entrapment vacuum pump (cryopump),
disposed upstream of the positive displacement vacuum pump, for
creating an ultrahigh vacuum (see Japanese laid-open patent
publication Nos. 11-40094, 2000-131476 and 2002-147386).
Specifically, two vacuum pumps are connected in series with each
other for creating an ultrahigh vacuum. The positive displacement
vacuum pump is mostly installed or placed on an installation
surface such as a ground surface, and the kinetic vacuum pump or
the entrapment vacuum pump is installed in the vicinity of a vacuum
container (vacuum chamber) to be evaluated to an ultrahigh vacuum
or is directly connected to the vacuum container (vacuum chamber).
The vacuum pump that is installed in the vicinity of the vacuum
container or is directly connected to the vacuum container is
referred to as a first vacuum pump, and the vacuum pump that is
installed or placed on the installation surface such as a ground
surface is referred to as a second vacuum pump. The second vacuum
pump is not installed in the vicinity of the vacuum container
because of its vibrations or noise or because it uses oil, but is
installed at a remote location, e.g., at a downstairs installation
site. Therefore, the second vacuum pump is connected to the first
vacuum pump by a long vacuum piping. As a result, the second vacuum
pump needs to have evacuation capacity in view of the conductance
of the vacuum piping, i.e., to have larger capacity as required by
the conductance of the vacuum piping.
[0009] Vacuum pumps having a single rotational shaft which can
compress a gas from an ultrahigh vacuum to an atmospheric pressure
are disclosed in the following documents:
[0010] 1) Japanese laid-open patent publication No. 60-204997:
[0011] The disclosed vacuum pump is a kinetic vacuum pump, which
includes a helical screw pump section and a centrifugal pump
section, for compressing a gas from an ultrahigh vacuum to an
atmospheric pressure. Since turbine blades and centrifugal blades
are mounted in series on one rotational shaft, the centrifugal
blades which are located at an atmospheric pressure side have a
poor evacuation efficiency in the atmospheric pressure range, and
thus the vacuum pump requires large driving power.
[0012] 2) Japanese patent No. 2680156:
[0013] The disclosed vacuum pump is a kinetic vacuum pump, which
includes a centrifugal compression pump stage and a circumferential
flow compression pump stage, for compressing a gas from an
ultrahigh vacuum to an atmospheric pressure. Since centrifugal
blades and vortex flow blades are mounted in series on one
rotational shaft, the vortex flow blades which are located at an
atmospheric pressure side have a poor evacuation efficiency in the
atmospheric pressure range, and thus the vacuum pump requires large
driving power.
[0014] The problems of the related art in which a single vacuum
pump can compress a gas from an ultrahigh vacuum to an atmospheric
pressure are summarized as follows: The use of blades having
different evacuation principles provided on the same rotational
shaft causes a problem of limitations of evacuation performance,
and the use of kinetic vacuum pump section having a poor evacuation
efficiency in an atmospheric pressure range causes a problem of
increased driving power.
SUMMARY OF THE INVENTION
[0015] As described above, in a vacuum evacuation apparatus having
two vacuum pumps connected in series, i.e., a positive displacement
vacuum pump and a kinetic vacuum pump which can compress a gas from
an ultrahigh vacuum to an atmospheric pressure, because the
positive displacement vacuum pump has a good evacuation efficiency
in an atmospheric pressure range, a highly efficient evacuation
system can be realized. However, the displacement vacuum pump
cannot be installed in the vicinity of a vacuum container (vacuum
chamber) because of its vibrations, heat generated when a gas is
compressed to an atmospheric pressure, and the like.
[0016] Further, a single vacuum pump which is capable of
compressing a gas from an ultrahigh vacuum to an atmospheric
pressure has a problem of limitations of evacuation performance and
a problem of increased driving power.
[0017] The present invention has been made in view of the above
drawbacks. It is therefore an object of the present invention to
provide a vacuum evacuation apparatus which is capable of
compressing a gas from an ultrahigh vacuum to an atmospheric
pressure, simplifying an evacuation system and reducing a driving
power for higher efficiency, and can be installed in any desired
directions in the vicinity of a vacuum container or directly on the
vacuum container.
[0018] In order to achieve the above object, according to a first
aspect of the present invention, there is provided a vacuum
evacuation apparatus for evacuating a container from an atmospheric
pressure to a high vacuum or less, comprising: a first vacuum pump
for evacuating the container to a high vacuum or less; and a second
vacuum pump for evacuating the container from an atmospheric
pressure to a medium or low vacuum; wherein the first vacuum pump
and the second vacuum pump are integrally connected to each other
into an integral unit.
[0019] Here, the high vacuum means a pressure range from 0.1 to
10.sup.-5 Pa. The medium vacuum means a pressure range from 100 to
0.1 Pa. The low vacuum means a pressure range from a pressure lower
than the atmospheric pressure to 100 Pa. Further, an ultrahigh
vacuum means a pressure range from 10.sup.-5 to 10.sup.-8 Pa. An
extrahigh vacuum means a pressure lower than 10.sup.-8 Pa. A vacuum
that can be created on the earth is about 10.sup.-10 Pa at
present.
[0020] According to the present invention, the first vacuum pump
and the second vacuum pump are integrally connected to each other,
and hence it is possible for the user to evacuate a gas in a
container to an ultrahigh vacuum by a single pump system. Since the
first vacuum pump for evacuating a gas in the container to a high
vacuum or less and the second vacuum pump for evacuating the gas in
the container from an atmospheric pressure to a medium or low
vacuum are combined with each other, it is possible for the
respective pumps to consume appropriate amounts of power
respectively in the medium vacuum range and the ultrahigh vacuum
range. Therefore, there is provided a pump system that does not
essentially operate in a low evacuation efficiency state, i.e., a
state where evacuation in the ultrahigh vacuum range is performed
by a single pump comprising a positive vacuum pump or a state where
evacuation in the atmospheric pressure range is performed by a
single pump comprising a kinetic vacuum pump.
[0021] The expression "the first vacuum pump and the second vacuum
pump are integrally connected to each other into an integral unit"
means that the first vacuum pump and the second vacuum pump are
coupled and integrated into a physically single pump unit. In this
case, a controller for controlling the whole pumps in the vacuum
evacuation apparatus may be mounted on the pump unit or may be
installed in the vicinity of the pump unit. In the case where the
first vacuum pump and the second vacuum pump are coupled and
integrated, the first vacuum pump and the second vacuum pump may be
directly coupled or a coupling member may be provided between the
first vacuum pump and the second vacuum pump.
[0022] In a preferred aspect of the present invention, the first
vacuum pump has a rotational shaft and the second vacuum pump has a
rotational shaft, and the rotational shaft of the first vacuum pump
and the rotational shaft of the second vacuum pump have respective
axes which are perpendicular to each other.
[0023] When the first vacuum pump and the second vacuum pump are in
operation, they produce vibrations in substantially the same
directions, i.e., their vibrational energies are intensive in
substantially the same directions. Specifically, the first vacuum
pump and the second vacuum pump produce vibrations due to
unbalanced rotating bodies in the radial directions of their
rotational shafts. If the rotational shaft of the second vacuum
pump and the rotational shafts of the first vacuum pump in the
unitized vacuum evacuation apparatus according to the present
invention are disposed parallel to each other, then it is possible
for the second vacuum pump and the first vacuum pump to
simultaneously produce rotary vibrations in the radial directions
perpendicular to the axes of the rotational shafts, causing
resonant vibrations and causing impairment of pump mechanical
components. If such radial vibrations are generated, they tend to
be added to each other and the added vibrations are transmitted as
excessive vibrations to the vacuum container side. According to the
present invention, the axes of the rotational shafts of the first
vacuum pump and the axis of the rotational shaft of the second
vacuum pump extend perpendicularly to each other, thereby
minimizing radial vibrations generated by the rotational shaft of
the first vacuum pump that is attached to the vacuum container.
[0024] In a preferred aspect of the present invention, the first
vacuum pump has a rotational shaft and the second vacuum pump has a
rotational shaft, and the rotational shaft of the first vacuum pump
and the rotational shaft of the second vacuum pump are rotatably
supported by one of self-lubricating bearings, bearings having a
semi-solid lubricant or a solid lubricant therein, gas bearings,
and magnetic bearings; and wherein the rotational shaft of the
first vacuum pump and the rotational shaft of the second vacuum
pump are rotatable regardless of directions in which the first
vacuum pump and the vacuum pump are installed.
[0025] According to the present invention, the bearings that
support the rotational shaft of the first vacuum pump and the
bearings that support the rotational shafts of the second vacuum
pump may comprise rolling bearings made of a self-lubricating
material or including grease in roller races, self-lubricating
journal bearings, or non-contact bearings such as gas bearings or
magnetic bearings. These bearings allow the rotational shafts to
rotate in stable conditions regardless of mounting directions of
the vacuum evacuation apparatus. Since the vacuum evacuation
apparatus according to the present invention has an appearance as a
single pump unit, the user does not usually think that it contains
the first vacuum pump and the second vacuum pump combined together.
The dry vacuum pumps used generally for a second vacuum pump uses
low-viscosity lubricating oil such as mineral oil to lubricate the
bearings, and hence has certain limitations on the mounting
directions thereof. On the other hand, the turbomolecular pump has
its rotational shaft rotatably supported by ball bearings that are
lubricated mainly by grease, or non-contact bearings, so that the
turbomolecular pump is free of limitations with respect to
directions in which it is mounted. The dry vacuum pump according to
the present invention uses the bearings which can support the
rotational shafts without using low-viscosity lubricating oil such
as mineral oil, and thus does not pose limitations on the mounting
directions of the pump unit.
[0026] In a preferred aspect of the present invention, the first
vacuum pump has a bottom component and the second vacuum pump has a
casing, and the bottom component and the casing are integrally
connected to each other, thereby integrally connecting the first
vacuum pump and the second vacuum pump.
[0027] According to the present invention, the bottom component of
the first vacuum pump and the pump casing of the second vacuum pump
are integrated into a common part, and an evacuation passage is
provided in the common part to allow the first vacuum pump and the
second vacuum pump to communicate with each other. Thus, the number
of parts used is reduced and hence the cost thereof is reduced, and
the overall unit takes up a reduced volume. By incorporating the
evacuation path of the two pumps into the common part, the
evacuation path of the two pumps can be shortened to increase the
conductance of the pump unit, and the volume of the second vacuum
pump can be reduced. Then, the cost of the entire pump unit can be
further reduced and the volume taken up by the entire pump unit can
be reduced. Furthermore, since the bottom component and the pump
casing are integrated, thermal conductivity of the two pumps can be
improved. The second vacuum pump which compresses a gas up to the
atmospheric pressure consumes more electric power and generates
more heat than the first vacuum pump at the ultrahigh vacuum side.
If the second vacuum pump is cooled by cooling water, the increased
thermal conductivity between the two pumps allows only a cooling
mechanism incorporated in the first vacuum pump to cool the two
pumps efficiently (to radiate heat from the two pumps
efficiently).
[0028] In a preferred aspect of the present invention, the first
vacuum pump and the second vacuum pump are integrally connected to
each other through a heat insulation member or a small area of
contact.
[0029] If the second vacuum pump is not cooled by cooling water,
then in order to lower the thermal conductivity between the
fastening surfaces of the first vacuum pump and the second vacuum
pump, it is effective to combine a thermal insulation with the
fastening portion or to reduce the cross-sectional area of a
contacting region of the fastening portion, or both to combine a
thermal insulation with the fastening portion and to reduce the
cross-sectional area of a contacting region of the fastening
portion. If the second vacuum pump is not cooled by cooling water,
then it is forcedly air-cooled. The second vacuum pump which
compresses a gas up to the atmospheric pressure consumes more
electric power and generates more heat than the first vacuum pump.
If the second vacuum pump is forcedly air-cooled, its exhaust heat
performance is much lower than the cooling water. If the thermal
conductivity between the two pumps is high, the heat may be
transferred from the second vacuum pump to the first vacuum pump,
possibly impairing the normal operation of the first vacuum pump.
Therefore, by providing the heat insulation member at the
connecting portion of the two pumps or making the contact area of
the connecting portion small, the thermal conductivity between the
two pumps is lowered to minimize the heat transfer from the second
vacuum pump to the first vacuum pump.
[0030] In a preferred aspect of the present invention, the first
vacuum pump and the second vacuum pump are integrally connected to
each other through a vibro-isolating mechanism.
[0031] The second vacuum pump which compresses a gas up to the
atmospheric pressure vibrates to an extent greater than the first
vacuum pump. If vibrations of the vacuum evacuation apparatus of
the present invention which integrates the first vacuum pump and
the second vacuum pump are large, the vacuum evacuation apparatus
cannot be installed in the vicinity of the vacuum container.
Therefore, the vibro-isolating mechanism for isolating vibrations
from the second vacuum pump is provided at the connecting portion
of the first vacuum pump and the second vacuum pump, and thus any
vibrations that are transmitted from the second vacuum pump to the
first vacuum pump can be reduced. The vibro-isolating mechanism may
comprise a vibro-isolating rubber (natural rubber, nitrile rubber,
silicone rubber, fluoro rubber, etc.) which has a Young's modulus
equal to or smaller than 1000 KPa (1000 to 10 KPa) and an Asker C
hardness level equal to or smaller than 50 (50 to 4), or may
comprise a spring.
[0032] In a preferred aspect of the present invention, the first
vacuum pump has an outlet port and the second vacuum pump has an
inlet port, and the outlet port and the inlet port are
interconnected by an evacuation passage component comprising a
vibro-isolating material.
[0033] If the evacuation passage component is made of a highly
rigid material or has a highly rigid structure, then it may
transmit vibrations from the second vacuum pump to the first vacuum
pump. Since the evacuation passage component is made of a
vibro-isolating material, it can minimize vibrations transmitted
from the second vacuum pump to the first vacuum pump. The
vibro-isolating material may be a rubber material (natural rubber,
nitrile rubber, silicone rubber, fluoro rubber, etc.) which has a
Young's modulus equal to or smaller than 1000 KPa (1000 to 10 KPa)
and an Asker C hardness level equal to or smaller than 50 (50 to
4), and may be in the shape of a tube or a block.
[0034] In a preferred aspect of the present invention, the first
vacuum pump has an inlet port and the second vacuum pump has an
inlet port, and the inlet port of the first vacuum pump and the
inlet port of the second vacuum pump are interconnected by a bypass
passage for bypassing the first vacuum pump.
[0035] According to the present invention, the bypass pipe which
interconnects the inlet port of the first vacuum pump and the inlet
of the second vacuum pump is provided. The bypass pipe serves to
directly discharge a gas from the inlet port of the first vacuum
pump into the inlet of the second vacuum pump, thereby bypassing
the first vacuum pump. Consequently, even when the vacuum in the
vacuum container breaks, a sudden load buildup can be prevented
from being exerted on the first vacuum pump, and hence the rotating
body of the first vacuum pump can be protected against damage.
[0036] In a preferred aspect of the present invention, the first
vacuum pump has an outlet port and the second vacuum pump has an
inlet port, and the outlet port and the inlet port are
interconnected by an evacuation passage component incorporating
therein a check valve for preventing a fluid from flowing back from
the second vacuum pump to the first vacuum pump while the first
vacuum pump is in operation.
[0037] According to the present invention, the first vacuum pump
and the second vacuum pump are integrally connected together into
an integral pump unit including the evacuation passage component
therein. Therefore, the pressure conditions for the evacuation
passage component are known. When one of the first and second
vacuum pumps fails to operate, e.g., when the second vacuum pump
becomes faulty in operation, the back pressure of the first vacuum
pump increases suddenly. By providing the check valve which
automatically closes under the differential pressure in the
evacuation passage component, the pressure at the exhaust side of
the first vacuum pump can be prevented from abruptly rising.
[0038] In a preferred aspect of the present invention, further
comprising a controller for controlling the first vacuum pump and
the second vacuum pump wherein the controller is integrally
connected to the first vacuum pump or is installed separately from
the first vacuum pump.
[0039] In a preferred aspect of the present invention, when each of
the first vacuum pump and the second vacuum pump reaches a rated
rotational speed and no gas is introduced into the container, the
controller lowers a voltage applied to a motor of at least one of
the first vacuum pump and the second vacuum pump and continuously
operates the motor at a motor maximum efficient point.
[0040] In a preferred aspect of the present invention, the
controller is capable of controlling the pressure in the container
at a target pressure level by individually controlling respective
rotational speeds of the first vacuum pump and the second vacuum
pump depending on flow rates of the gas evacuated therefrom.
[0041] With the first vacuum pump and the second vacuum pump that
are integrally connected into an integral unit, passage pipes
combined with the integral unit and having given diameters and
lengths remain unchanged or constant. In the event of changes in
the rotational speeds of the first vacuum pump and the second
vacuum pump, the flow rate and the pressure change with
regularity.
[0042] Usually, the evacuation rate of a pump is controlled by
adjusting the opening area of the suction side with a control valve
or the like. According to the present invention, however, the
pressure in the vacuum container to be evacuated is controlled by
controlling at least one of the rotational speed of the first
vacuum pump and the rotational speed of the second vacuum pump,
rather than by adjusting the opening (opening area) of a valve
disposed between the vacuum container and the pump. In this manner,
the evacuation rate of each of the vacuum pumps is adjusted to
adjust the overall evacuation rate of the pump system as the vacuum
evacuation apparatus. In other words, the pressure in the vacuum
container can be controlled by the single pump system without the
need for a control valve other than the vacuum pumps.
[0043] In a preferred aspect of the present invention, wherein the
first vacuum pump comprises a turbomolecular pump, and the second
vacuum pump comprises a dry vacuum pump.
[0044] In a preferred aspect of the present invention, the second
vacuum pump comprises a dry vacuum pump having a pair of pump
rotors with respective magnet rotors mounted thereon, the magnet
rotors have equal numbers of magnetic poles and are disposed so
that their different magnetic poles are magnetically attracted to
each other, and currents supplied to a multiphase armature
including an iron core and a plurality of windings disposed
radially outwardly of at least one of the magnet rotors are
switched to actuate the at least one of the magnet rotors for
thereby rotating the pump rotors in opposite directions in
synchronism with each other.
[0045] According to the present invention, the dual-shaft pump
rotors can be rotated synchronously in the opposite directions by a
simple structural motor having permanent magnets and windings for
rotating the permanent magnets. Therefore, any timing gears for
synchronizing the dual-shaft pump rotors are not required, and
oil-free, low vibrations and low noise can be realized. If
lubricating oil is used to lubricate the bearings and timing gears,
the lubricating oil leaks out when the pump is tilted, and hence
mounting posture of the pump is limited. However, the oil-free pump
according to the present invention can be mounted in a posture that
can freely be selected, and does not produce significant vibrations
and noise caused by contact of the timing gears.
[0046] Since the dry vacuum pump having the above structure is used
as the second vacuum pump, any vibrations that are transmitted from
the second vacuum pump to the first vacuum pump can be suppressed,
and thus the second vacuum pump can be integrally coupled to the
first vacuum pump. When the first vacuum pump and the second vacuum
pump are integrally coupled to each other, the second vacuum pump
can be mounted at a freely selectable posture. Furthermore, when
the integral unit of the first vacuum pump and the second vacuum
pump is attached to an object to be evacuated, e.g., a vacuum
container (vacuum chamber), the integral unit can be mounted at a
freely selectable posture.
[0047] In a preferred aspect of the present invention, one of the
first vacuum pump and the second vacuum pump comprises a single
vacuum pump and the other of the first vacuum pump and the second
vacuum pump comprises either a single vacuum pump or a plurality of
vacuum pumps.
[0048] In a preferred aspect of the present invention, the first
vacuum pump and the second vacuum pump are integrally connected to
each other by at least one evacuation passage.
[0049] According to the present invention, since the plural second
vacuum pumps are integrally connected to the single first vacuum
pump, it is possible to construct a roughening pump system having
an evacuation capacity which matches the evacuation capacity of the
first vacuum pump. Since the plural second vacuum pumps can be
controlled in parallel for controlling the pressure in the vacuum
container, the pressure in the vacuum container can be controlled
more appropriately. Further, even if one of the second vacuum pumps
fails to operate, the other second vacuum pump can back up the
first vacuum pump. Therefore, even if one of the second vacuum
pumps shuts down, a situation where the first vacuum pump shuts
down to cause a quick pressure buildup in the vacuum container can
be avoided.
[0050] A plurality of the first vacuum pumps may be integrally
connected to a single second vacuum pump. With this arrangement,
the rotor of each of the first vacuum pumps can be reduced in size.
Two or three vacuum pumps that are integrally connected to each
other can be controlled by a single controller.
[0051] In a preferred aspect of the present invention, the ratio of
an axial dimension of the second vacuum pump and an axial
dimension, which is assumed to be 1, of the first vacuum pump is in
a range from 1 to 0.6, and the ratio of a volume of the second
vacuum pump and a volume, which is assumed to be 1, of the first
vacuum pump is in a range from 0.3 to 0.5.
[0052] Since the second vacuum pump can be smaller in size than the
first vacuum pump, there is no limitation on the mounting posture
when the second vacuum pump is mounted on the first vacuum
pump.
[0053] By using the combination of the above dimension and volume
ratios for the first vacuum pump and the second vacuum pump, it is
possible to integrally connect a plurality of second vacuum pumps
to the first vacuum pump which has an evacuation capacity that is
several times greater than each of the second vacuum pumps.
[0054] The present invention offers the following advantages:
[0055] (1) By integrating a first vacuum pump for evacuating the
container to a high vacuum or less and a second vacuum pump for
evacuating the container from an atmospheric pressure to a medium
or low vacuum, ultrahigh vacuum evacuation can be performed by a
single pump system. Further, by a combination of the first vacuum
pump for evacuating the container to a high vacuum or less and the
second vacuum pump for evacuating the container from an atmospheric
pressure to a medium or low vacuum, the pumps can evacuate the
container respectively to the medium vacuum range and the ultrahigh
vacuum range by appropriate respective consumed power, and the
consumed power of the whole system can be reduced.
[0056] (2) Since the second vacuum pump as an auxiliary pump can be
integrally coupled to the first vacuum pump, the installation space
(footprint) of the auxiliary pump can be reduced.
[0057] (3) When the first vacuum pump and the second vacuum pump
are integrally coupled to each other, the second vacuum pump can be
mounted at a freely selectable posture. Furthermore, when the
integral unit of the first vacuum pump and the second vacuum pump
is attached to an object to be evacuated, e.g., a vacuum container
(vacuum chamber), the integral unit can be mounted at a freely
selectable posture.
[0058] (4) The pressure in the vacuum container to be evacuated is
controlled by controlling at least one of the rotational speed of
the first vacuum pump and the rotational speed of the second vacuum
pump, rather than by adjusting the opening (opening area) of a
valve disposed between the vacuum container and the pump.
Therefore, the evacuation rate of each of the vacuum pumps is
adjusted to adjust the overall evacuation rate of the pump system.
In other words, the pressure in the vacuum container can be
controlled by the single pump system without the need for a control
valve or the like.
[0059] The above and other objects, features, and advantages of the
present invention will become more apparent from the following
description when taken in conjunction with the accompanying
drawings in which preferred embodiments of the present invention
are shown by way of illustrative example.
BRIEF DESCRIPTION OF THE DRAWINGS
[0060] FIG. 1A is a front elevational view, partly in cross
section, of a vacuum evacuation apparatus according to a first
aspect of the present invention;
[0061] FIG. 1B is a side elevational view, partly in cross section,
of the vacuum evacuation apparatus shown in FIG. 1A;
[0062] FIG. 1C is a bottom view, partly in cross section, of the
vacuum evacuation apparatus shown in FIG. 1A;
[0063] FIG. 2 is a schematic cross-sectional view showing
structural details of a first vacuum pump of the vacuum evacuation
apparatus shown in FIG. 1A;
[0064] FIG. 3 is a schematic cross-sectional view showing
structural details of a second vacuum pump of the vacuum evacuation
apparatus shown in FIG. 1A;
[0065] FIG. 4 is a cross-sectional view taken along line IV-IV of
FIG. 3;
[0066] FIG. 5A is a front elevational view, partly in cross
section, of the vacuum evacuation apparatus with the second vacuum
pump being installed at another posture;
[0067] FIG. 5B is a side elevational view, partly in cross section,
of the vacuum evacuation apparatus shown in FIG. 5A;
[0068] FIG. 5C is a bottom view, partly in cross section, of the
vacuum evacuation apparatus shown in FIG. 5A;
[0069] FIGS. 6A and 6B are front elevational views of the vacuum
evacuation apparatus with a controller mounted on the first vacuum
pump in different positions;
[0070] FIGS. 7A and 7B are schematic cross-sectional views showing
a vacuum evacuation apparatus in which a bottom component of the
first vacuum pump and a pump casing of the second vacuum pump are
integrally joined to each other;
[0071] FIG. 8 is a schematic front elevational view, partly in
cross section, of a vacuum evacuation apparatus in which a
vibro-isolating mechanism is provided between the first vacuum pump
and the second vacuum pump
[0072] FIG. 9 is a schematic front elevational view, partly in
cross section, of a vacuum evacuation apparatus in which a
fastening component for fastening the first vacuum pump and the
second vacuum pump is combined with a vibro-isolating
mechanism;
[0073] FIG. 10A is a cross-sectional view of the structure of a
fastening assembly comprising the fastening component and
vibro-isolating bushings shown in FIG. 9;
[0074] FIG. 10B is a bottom view of the fastening assembly shown in
FIG. 10A;
[0075] FIG. 10C is an exploded perspective view of one of the
vibro-isolating bushings shown in FIG. 10A;
[0076] FIGS. 11A and 11B are front elevational views of a pump unit
(vacuum evacuation apparatus) having a first vacuum pump and a
second vacuum pump that are integrally mounted on a vacuum
container (vacuum chamber);
[0077] FIG. 12A is a front elevational view, partly in cross
section, of a vacuum evacuation apparatus with a second vacuum pump
mounted on a side surface of a first vacuum pump;
[0078] FIG. 12B is a bottom view of the vacuum evacuation apparatus
with the second vacuum pump mounted on the side surface of the
first vacuum pump;
[0079] FIGS. 13A and 13B are a front elevational view, partly in
cross section, and a bottom view of a vacuum evacuation apparatus
with a second vacuum pump mounted on a side surface of a first
vacuum pump, the first vacuum pump and the second vacuum pump being
fastened to each other by a fastening component combined with a
vibro-isolating mechanism;
[0080] FIG. 13C is a cross-sectional view showing structural
details of a fastening assembly of the vacuum evacuation apparatus
shown in FIGS. 13A and 13B;
[0081] FIG. 14 is a schematic front elevational view of a vacuum
evacuation apparatus including a first vacuum pump, a second vacuum
pump, and a check valve disposed in a evacuation passage component
which interconnects an outlet port of the first vacuum pump and an
inlet port of the second vacuum pump;
[0082] FIG. 15 is a schematic front elevational view of a vacuum
evacuation apparatus including a first vacuum pump, a second vacuum
pump, and a bypass pipe interconnecting an inlet port of the first
vacuum pump and an inlet port of the second vacuum pump for
bypassing the first vacuum pump;
[0083] FIG. 16 is a set of graphs showing comparison results in
which the rotational speeds of first and second vacuum pumps were
changed to adjust the pressure in a vacuum container in a pump
rotational speed control process which was performed on a vacuum
evacuation apparatus according to the present invention and a
vacuum evacuation apparatus according to the related art, in the
case of the first vacuum pump comprising a turbomolecular pump and
the second vacuum pump comprising a dry pump;
[0084] FIG. 17 is a schematic front elevational view, partly in
cross section, of a vacuum evacuation apparatus according to an
embodiment of the present invention which includes a single first
vacuum pump and a plurality of second vacuum pumps integrally
connected to the first vacuum pump;
[0085] FIG. 18 is a schematic front elevational view, partly in
cross section, of a vacuum evacuation apparatus according to an
embodiment of the present invention which includes a single first
vacuum pump and a plurality of second vacuum pumps integrally
connected to the first vacuum pump by inlet and outlet
passages;
[0086] FIG. 19 is a schematic front elevational view, partly in
cross section, of a vacuum evacuation apparatus according to an
embodiment of the present invention which includes a plurality of
first vacuum pumps and a single second vacuum pump integrally
connected to the first vacuum pumps by inlet and outlet
passages;
[0087] FIG. 20 is a block diagram of a control circuit for
controlling a vacuum evacuation apparatus including two first
vacuum pumps and a single second vacuum pump which are integrally
connected;
[0088] FIG. 21 is a graph showing how the rotational speeds of a
single first vacuum pump and two second vacuum pumps were changed
to adjust the pressure in a vacuum container in a pump rotational
speed control process which was performed on a vacuum evacuation
apparatus according to the present invention, in the case of the
first vacuum pump comprising a turbomolecular pump and the two
second vacuum pumps comprising a dry pump;
[0089] FIG. 22 is a cross-sectional view of a turbomolecular pump
for use in a vacuum evacuation apparatus according to the present
invention;
[0090] FIG. 23 is a cross-sectional view of another turbomolecular
pump for use in a vacuum evacuation apparatus according to the
present invention;
[0091] FIG. 24 is a cross-sectional view of still another
turbomolecular pump for use in a vacuum evacuation apparatus
according to the present invention; and
[0092] FIG. 25 is a cross-sectional view of yet another
turbomolecular pump for use in a vacuum evacuation apparatus
according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0093] A vacuum evacuation apparatus according to preferred
embodiments of the present invention will be described in detail
below with reference to FIGS. 1A through 25. Identical or
corresponding parts are denoted by identical or corresponding
reference characters throughout views.
[0094] FIGS. 1A, 1B and 1C are views showing a vacuum evacuation
apparatus according to a first aspect of the present invention,
FIG. 1A is a front elevation view, partly in cross section, FIG. 1B
is a side elevational view, partly in cross section, and FIG. 1C is
a bottom view, partly in cross section.
[0095] As shown in FIGS. 1A, 1B and 1C, according to an embodiment
of the present invention, a vacuum evacuation apparatus is
configured to evacuate a vacuum container (vacuum chamber) from an
atmospheric pressure to an ultrahigh vacuum range. The vacuum
evacuation apparatus comprises a first vacuum pump 1 capable of
evacuating the container to a high vacuum or less and a second
vacuum pump 2 capable of evacuating the container to a pressure
ranging from an atmospheric pressure to a medium or low vacuum. The
first vacuum pump 1 and the second vacuum pump 2 are unitized as an
integral apparatus. Specifically, the first vacuum pump 1 and the
second vacuum pump 2 are coupled together into an integral unit.
The first vacuum pump 1 comprises a turbomolecular pump, and the
second vacuum pump 2 comprises a dry vacuum pump. An outlet port of
the first vacuum pump 1 and an inlet port of the second vacuum pump
2 are interconnected by an evacuation passage component 3.
[0096] For evacuating a gas in a certain container from an
atmospheric pressure range to an ultrahigh vacuum range, normally,
a positive displacement pump (e.g., dry pump) as a second vacuum
pump is initially used to evacuate the container to a medium vacuum
range, and then a turbomolecular pump as a first vacuum pump is
activated to evacuate the container to an ultrahigh vacuum range,
thus performing evacuation operation. According to the conventional
method, the second vacuum pump (e.g., dry pump) for evacuating the
container to a medium vacuum and the first vacuum pump (e.g.,
turbomolecular pump) for evacuating the container to an ultrahigh
vacuum range are separately prepared, and connected together by a
piping, thus constructing an evacuating system which is capable of
performing a series of evacuation. However, in this method,
depending on the length and diameter of the piping used to
interconnect the dry pump and the turbomolecular pump, even though
the container to be evacuated remains unchanged, the evacuation
time and power required for evacuation tend to vary, and even the
pumps themselves may need to be changed. Consequently, special
engineering expertise is often required in evacuating equipment
planning.
[0097] According to the present invention, the first vacuum pump 1
comprising a turbomolecular pump and the second vacuum pump 2
comprising a dry vacuum pump are integrated and unitized. Thus, the
user can construct and perform ultrahigh vacuum evacuation in a
container by a single pump system. By a combination of the
turbomolecular pump and the dry vacuum pump, the pumps can evacuate
the container respectively to the medium vacuum range and the
ultrahigh vacuum range by appropriate respective consumed power.
Therefore, according to the present invention, there is provided a
pump system that does not essentially operate in a low evacuation
efficiency state, i.e., a state where evacuation in the ultrahigh
vacuum range is performed by a single pump comprising a positive
vacuum pump or a state where evacuation in the atmospheric pressure
range is performed by a single pump comprising a kinetic vacuum
pump.
[0098] The expression "the first vacuum pump 1 and the second
vacuum pump 2 are coupled together into an integral unit" means
that the first vacuum pump 1 and the second vacuum pump 2 are
coupled and integrated into a physically single pump unit, as shown
in FIG. 1A. In this case, a controller for controlling the whole
pumps in the vacuum evacuation apparatus may be mounted on the pump
unit or may be installed in the vicinity of the pump unit.
[0099] As shown in FIGS. 1A, 1B and 1C, the second vacuum pump 2
comprises a screw-type dry vacuum pump having a pair of screw
rotors 52a, 52b rotatably disposed in a pump casing (described
below).
[0100] FIG. 2 is a schematic cross-sectional view showing
structural details of the first vacuum pump 1 of the vacuum
evacuation apparatus shown in FIGS. 1A through 1C.
[0101] As shown in FIG. 2, the turbomolecular pump as the first
vacuum pump 1 comprises a pump casing 9, and a turbine blade
pumping assembly 10 and a thread groove pumping assembly 20 which
are disposed in the pump casing 9 and successively arranged from an
inlet port side to an outlet port side of the turbomolecular pump.
The turbine blade pumping assembly 10 comprises a plurality of
turbine blades 11 as an array of multistage rotor blades and
multistage stator blades 14 disposed immediately downstream of the
corresponding turbine blades 11. The multistage turbine blades 11
are integrally formed on a substantially cylindrical rotor 12
fixedly mounted on a rotational shaft 13 that is rotatably disposed
centrally in the pump casing 9. The multistage stator blades 14 are
held between spacers 15 stacked in the pump casing 9 and are fixed
in the pump casing 9. The turbine blades 11 as rotor blades and the
stator blades 14 are alternately disposed in the turbine blade
pumping assembly 10.
[0102] The thread groove pumping assembly 20 comprises cylindrical
thread grooves 21 disposed on an outer circumferential surface of
the cylindrical rotor 12, and a cylindrical thread groove spacer 22
disposed so as to face the outer circumferential surfaces of the
cylindrical thread grooves 21. The thread groove spacer 22 is fixed
to the pump casing 9.
[0103] The turbomolecular pump also includes a stator 25 disposed
in the rotor 12. The stator 25 has a base 26 fixed to a lower
flange 91f of the pump casing 9 and a sleeve 27 extending axially
upwardly from the base 26. The sleeve 27 of the stator 25 supports
a bearing motor assembly 30 including a motor 31 for applying
rotational drive forces to the rotational shaft 13 and bearings 32,
33, 34 for rotatably supporting the rotational shaft 13.
[0104] The bearing motor assembly 30 comprises a motor 31 for
applying rotational drive forces to the rotational shaft 13, an
upper radial magnetic bearing 32 for radially supporting the
rotational shaft 13, a lower radial magnetic bearing 33 for
radially supporting the rotational shaft 13, and a thrust magnetic
bearing 34 for canceling thrust forces generated by the pressure
difference developed between the inlet side and the outlet side by
evacuation operation of the evacuation assembles. The motor 31
comprises a high-frequency motor. Each of the upper radial magnetic
bearing 32, the lower radial magnetic bearing 33, and the thrust
magnetic bearing 34 comprises an active magnetic bearing.
[0105] The pump casing 9 has an upper flange 9uf on its upper end.
The inlet port SP is defined radially inwardly of the upper flange
9uf. A vacuum container (vacuum chamber) to be evacuated by the
vacuum evacuation apparatus is connected to the upper flange 9uf.
Further, the base 26 of the stator 25 has a flange 26f, and the
outlet port DP is defined radially inwardly of the flange 26f. The
evacuation passage component 3 (see FIG. 1) is connected to the
flange 26f, and the first vacuum pump 1 comprising a turbomolecular
pump communicates with the second vacuum pump 2 by the evacuation
passage component 3.
[0106] FIG. 3 is a schematic cross-sectional view showing
structural details of the second vacuum pump 2 of the vacuum
evacuation apparatus shown in FIGS. 1A through 1C. As shown in FIG.
3, the second vacuum pump 2 comprises a screw-type dry vacuum pump.
The second vacuum pump 2 comprises a pump casing 50, and two
parallel rotational shafts 51a, 51b disposed in the pump casing 50.
The rotational shafts 51a, 51b are rotatably supported by
respective pairs of bearings 53. The rotational shaft 51a supports
a screw rotor 52a fixed thereto which has a right-hand screw
thread, and the rotational shaft 51b supports a screw rotor 52b
fixed thereto which has a left-hand screw thread. The screw rotors
52a, 52b are juxtaposed in alignment with each other between the
bearings 53 which support the rotational shafts 51a, 51b.
[0107] As shown in FIG. 3, small clearances are defined between
outer circumferential surfaces of the screw rotors 52a, 52b and an
inner circumferential surface of the pump casing 50, allowing the
screw rotors 52a, 52b to rotate out of contact with the pump casing
50. The screw rotors 52a, 52b have mutually confronting regions
where the right- and left-hand screw threads loosely mesh with each
other to allow the screw rotors 52a, 52b to rotate out of contact
with each other. Magnet rotors 54 are fixed respectively to ends of
the rotational shafts 51a, 51b. The pump casing 50 has an inlet
port SP and an outlet port DP that are formed in a side wall
thereof which lies parallel to the sheet of FIG. 3. The inlet port
SP of the second vacuum pump 2 is connected to the outlet port DP
of the first vacuum pump 1 by the evacuation passage component 3
(see FIG. 1). The bearings 53 which are remote from the magnet
rotors 54 are fixed to the pump casing 50, and the other bearings
53 which are close to the magnet rotors 54 are fixed to a bearing
housing 55 and a bearing holder 56. The bearing housing 55 is fixed
to the pump casing 50, and the bearing holder 56 is fixed to the
bearing housing 55.
[0108] FIG. 4 is a cross-sectional view taken along line IV-IV of
FIG. 3. As shown in FIG. 4, the magnet rotors 54 are identical in
structure and disposed parallel to each other. Each of the magnet
rotors 54 includes a yoke 54b made of a magnetic material and a
ring-shaped magnet 54a mounted on the outer circumferential surface
of the yoke 54b. The ring-shaped magnet 54a is magnetized into
eight poles, so that each magnet rotor 54 has eight magnetic poles
on its outer circumferential surface. Though each magnet rotor 54
is shown as a structure having eight magnetic poles in the
illustrated embodiment, the number of the magnetic poles should be
an even number of magnetic poles (2n: n=1, 2, . . . ). The magnet
rotors 54 are disposed in facing relation to each other with their
different magnetic poles being magnetically attracted to each
other, and are disposed so as to keep a clearance C defined
therebetween. The screw rotors 52a, 52b are capable of rotating
smoothly in opposite directions in synchronism with each other
because of a magnetic coupling between the magnet rotors 54. In
order to increase forces for synchronously rotating the screw
rotors 52a, 52b, a plurality of pairs of magnet rotors 54 may be
mounted on the rotational shafts 51a, 51b.
[0109] The screw-type dry vacuum pump includes two armatures 57 for
generating forces to rotate the magnet rotors 54. Each of the
armatures 57 is of a three-phase (U, V, W) configuration with an
iron core 57a and three windings 57b which are disposed in the
vicinity of a portion of the outer circumferential surface of one
of the magnet rotors 54. The two armatures 57 are mounted on inner
walls of the pump casing 50 remote from the region where the magnet
rotors 54 face each other. The magnetic forces which attract the
magnet rotors 54 to each other are canceled by attractive forces
that act between the magnet rotors 54 and the iron cores 57a.
Adjacent two of the windings 57b in the respective phases of each
of the armatures 57 are angularly spaced from each other by 60
degrees about the rotational shaft 51a or 51b.
[0110] The windings 57b in the phases, that are denoted by U.sub.1,
V.sub.1, W.sub.1, U.sub.1', V.sub.1', W.sub.1', and the iron cores
57a of the armatures 57, and the magnet rotors 54 jointly make up a
dual-shaft synchronous brushless DC motor. The windings 57b in the
phases U.sub.1', V.sub.1', W.sub.1' are coiled in the opposite
direction to the windings 57b in the phases U.sub.1, V.sub.1,
W.sub.1. Depending on the positions of the magnetic poles of the
magnet rotors 54, six currents I.sub.UV, I.sub.VW, I.sub.WU,
I.sub.VU, I.sub.WP, I.sub.UW flowing through the respective
windings 57b in the phases U.sub.1, V.sub.1, W.sub.1, U.sub.1',
V.sub.1', W.sub.1' are switched to rotate the magnet rotors 54.
[0111] The screw-type dry vacuum pump shown in FIGS. 3 and 4 is
capable of rotating the two screw rotors 52a, 52b synchronously in
the opposite directions by a simple structural motor having
permanent magnets and windings for rotating the permanent magnets.
Therefore, the screw-type dry vacuum pump does not need any timing
gears for synchronizing the two screw rotors 52a, 52b, and hence is
free of lubricating oil and realizes low vibrations and low noise.
If lubricating oil is used to lubricate the bearings and timing
gears, the lubricating oil leaks out when the pump is tilted, and
hence mounting posture of the pump is limited. However, the
oil-free pump according to the present invention can be mounted in
a posture that can freely be selected, and does not produce
significant vibrations and noise caused by contact of the timing
gears.
[0112] Since the screw-type dry vacuum pump having the above
structure is used as the second vacuum pump 2, any vibrations that
are transmitted from the second vacuum pump 2 to the first vacuum
pump 1 can be suppressed, and thus the second vacuum pump 2 can be
integrally coupled to the first vacuum pump 1. When the first
vacuum pump 1 and the second vacuum pump 2 are integrally coupled
to each other, the second vacuum pump 2 can be mounted at a freely
selectable posture. Furthermore, when the integral unit of the
first vacuum pump 1 and the second vacuum pump 2 is attached to an
object to be evacuated, e.g., a vacuum container (vacuum chamber),
the integral unit can be mounted at a freely selectable
posture.
[0113] A mounting posture for mounting the second vacuum pump 2
shown in FIGS. 3 and 4 on the first vacuum pump 1 will be described
below with reference to FIGS. 1A through 1C. As shown in FIGS. 1A
through 1C, the second vacuum pump 2 is mounted on the first vacuum
pump 1 with the two screw rotors 52a, 52b being juxtaposed parallel
to the lower surface of the first vacuum pump 1. Specifically, the
screw rotors 52a, 52b of the second vacuum pump 2 have respective
axes 52ax, 52bx which are perpendicular to the axis 1x of the
rotational shaft 13 of the first vacuum pump 1 and spaced by the
same distance from the lower surface of the first vacuum pump
1.
[0114] FIGS. 5A, 5B and 5C are views showing another examples of
mounting postures in the case where the second vacuum pump 2 is
mounted on the first vacuum pump 1, FIG. 5A is a front elevational
view, partly in cross section, FIG. 5B is a side elevational view,
partly in cross section, and FIG. 5C is a bottom view, partly in
cross section.
[0115] As shown in FIGS. 5A through 5C, the second vacuum pump 2 is
mounted on the first vacuum pump 1 with the two screw rotors 52a,
52b being juxtaposed parallel to the lower surface of the first
vacuum pump 1. Specifically, the screw rotors 52a, 52b of the
second vacuum pump 2 have respective axes 52ax, 52bx which are
perpendicular to the axis 1x of the rotational shaft 13 of the
first vacuum pump 1 and vertically spaced one above the other from
the lower surface of the first vacuum pump 1.
[0116] In the vacuum evacuation apparatus shown in FIGS. 1 and 5,
the first vacuum pump 1 comprising a turbomolecular pump and the
second vacuum pump 2 comprising a dry vacuum pump are integrally
connected together into an integral unit, and the second vacuum
pump 2 have respective rotational shafts whose axes lying
perpendicularly to the axis of the rotational shaft of the first
vacuum pump 1.
[0117] When the dry vacuum pump and the turbomolecular pump are in
operation, they produce vibrations in substantially the same
directions, i.e., their vibrational energies are intensive in
substantially the same directions. Specifically, the dry vacuum
pump and the turbomolecular pump produce vibrations due to
unbalanced rotating bodies in the radial directions of their
rotational shafts. If the rotational shaft of the turbomolecular
pump and the rotational shafts of the dry vacuum pump in the
unitized vacuum evacuation apparatus according to the present
invention are disposed parallel to each other, then it is possible,
though very small probability, for the turbomolecular pump and the
dry vacuum pump to simultaneously produce rotary vibrations in the
radial directions perpendicular to the axes of the rotational
shafts, causing resonant vibrations. If such radial vibrations are
generated, they tend to be added to each other and the added
vibrations are transmitted as excessive vibrations to the vacuum
container side. According to the present invention, the axes of the
rotational shafts of the dry vacuum pump and the axis of the
rotational shaft of the turbomolecular pump extend perpendicularly
to each other, thereby minimizing radial vibrations generated by
the rotational shaft of the first vacuum pump that is attached to
the vacuum container.
[0118] As described above, the turbomolecular pump that is
generally used as the first vacuum pump can be mounted at a freely
selectable posture, and hence can be installed in any desired
orientation on the vacuum container. Therefore, the turbomolecular
pump as the first vacuum pump makes a great contribution to the
degree of freedom of design around the vacuum container. When the
two pumps are combined together into a pump unit for use as the
vacuum evacuation apparatus according to the present invention, the
axis 1x of the first vacuum pump 1 to be directly attached to the
vacuum container is held in alignment with the center of gravity of
the unitized vacuum evacuation apparatus. If the vacuum evacuation
apparatus is installed in a horizontal orientation, then no
torsional moment occurs around the axis 1x of the first vacuum pump
1, allowing the vacuum container with the vacuum evacuation
apparatus installed thereon to be deformed in a simplified manner
or allowing the installation process to be simplified. The
vibrations produced by the vacuum evacuation apparatus do not
include torsional vibrations, and hence can easily be suppressed.
It is important to suppress vibrations because the vacuum
evacuation apparatus is installed in the vicinity of the vacuum
container or is connected directly to the vacuum container.
[0119] The bearings that support the rotational shaft of the first
vacuum pump 1 and the bearings that support the rotational shafts
of the second vacuum pump 2 may comprise rolling bearings made of a
self-lubricating material or including grease in roller races,
self-lubricating journal bearings, or non-contact bearings such as
gas bearings or magnetic bearings. These bearings allow the
rotational shafts to rotate in stable conditions regardless of
mounting directions of the vacuum evacuation apparatus. Since the
vacuum evacuation apparatus according to the present invention has
an appearance as a single pump unit, the user does not usually
think that it contains the dry vacuum pump and the turbomolecular
pump combined together. General dry vacuum pumps use low-viscosity
lubricating oil such as mineral oil to lubricate the bearings, and
hence have certain limitations on the mounting directions thereof.
On the other hand, turbomolecular pumps have their rotational
shafts rotatably supported by ball bearings that are lubricated
mainly by grease, or non-contact bearings, so that the
turbomolecular pumps are free of limitations with respect to
directions in which they are mounted. The dry vacuum pump according
to the present invention uses the bearings which can support the
rotational shafts without using low-viscosity lubricating oil such
as mineral oil, and thus does not pose limitations on the mounting
directions of the pump unit.
[0120] A controller for controlling the whole pump unit will be
described below. The first vacuum pump 1 and the second vacuum pump
2 have respective actuators, i.e., motors. However, in the case
where motor power supplies for the motors have uniformized
specifications and are housed in one housing, common components can
be used to construct a single controller, thus downsizing the
controller and reducing the cost of the controller, compared to the
respective controllers. The controller should preferably installed
on the first vacuum pump. Specifically, the dry vacuum pump is
heated up to a higher temperature than the turbomolecular pump
because of the heat generated when the dry vacuum pump compresses a
gas up to the atmospheric pressure. The turbomolecular pump has a
vibration level much lower than the positive displacement dry
vacuum pump. Accordingly, the controller having a number of
electronic precision components should be installed on the
turbomolecular pump, rather than the dry vacuum pump, as the
turbomolecular pump is less liable to exert unwanted thermal and
vibrational effects on the controller. The controller thus
installed is effective to increase the overall reliability of the
pump unit.
[0121] FIGS. 6A and 6B are front elevational views showing a vacuum
evacuation apparatus with a controller 4 installed on the first
vacuum pump 1.
[0122] In an example of FIG. 6A, the controller 4 is attached to an
outer circumferential surface of the first vacuum pump 1.
[0123] In an example of FIG. 6B, the controller 4 is attached to a
lower surface of the first vacuum pump 1. The controller 4 may be
attached to the first vacuum pump 1 through a mount portion
incorporating a vibro-isolating mechanism therein. The
vibro-isolating mechanism may comprise a vibro-isolating rubber
(natural rubber, nitrile rubber, silicone rubber, fluoro rubber,
etc.) or a spring.
[0124] In FIGS. 6A and 6B, the controller 4 is installed on the
first vacuum pump 1. However, the controller 4 may be installed in
any selected position spaced from the first vacuum pump 1.
[0125] FIGS. 7A and 7B are cross-sectional views showing
embodiments in which a bottom component of the first vacuum pump 1
and a pump casing of the second vacuum pump 2 are integrally joined
to each other.
[0126] In an example of FIG. 7A, a bottom component 40 of the first
vacuum pump 1 and a pump casing 50 of the second vacuum pump 2 are
integrally joined to each other to form an integral unit 60.
[0127] In an example of FIG. 7B, a bottom component 40 of the first
vacuum pump 1 and a pump casing 50 of the second vacuum pump 2 are
integrally joined to each other to form an integral unit 60 which
has an evacuation passage 3a defined therein which provides fluid
communication between the first vacuum pump 1 and the second vacuum
pump 2.
[0128] As shown in FIGS. 7A and 7B, the bottom component 40 and the
pump casing 50 are integrated into a common part, so that the
number of parts used is reduced and hence the cost thereof is
reduced, and the overall unit takes up a reduced volume. As shown
in FIG. 7B, the integral unit 60 may incorporate the evacuation
passage 3a for the two pumps. If the evacuation path of the two
pumps can be shortened, the conductance of the pump unit is
increased, and the volume of the second vacuum pump 2 can be
reduced. Then, the cost of the entire pump unit can be further
reduced and the volume taken up by the entire pump unit can be
reduced. Furthermore, since the bottom component 40 and the pump
casing 50 are integrated, thermal conductivity of the two pumps can
be improved. The second vacuum pump 2 which compresses a gas up to
the atmospheric pressure consumes more electric power and generates
more heat than the first vacuum pump 1 at the ultrahigh vacuum
side. If the second vacuum pump 2 is cooled by cooling water, the
increased thermal conductivity between the two pumps allows only a
cooling mechanism incorporated in the first vacuum pump 1 to cool
the two pumps efficiently (to radiate heat from the two pumps
efficiently).
[0129] If the second vacuum pump 2 is not cooled by cooling water,
then in order to lower the thermal conductivity between the
fastening surfaces of the first vacuum pump 1 and the second vacuum
pump 2, it is effective to combine a thermal insulation with the
fastening portion or to reduce the cross-sectional area of a
contacting region of the fastening portion, or both to combine a
thermal insulation with the fastening portion and to reduce the
cross-sectional area of a contacting region of the fastening
portion. If the second vacuum pump 2 is not cooled by cooling
water, then it is forcedly air-cooled. As described above, the
second vacuum pump 2 which compresses a gas up to the atmospheric
pressure consumes more electric power and generates more heat than
the first vacuum pump 1. If the second vacuum pump 2 is forcedly
air-cooled, its exhaust heat performance is much lower than the
cooling water. If the thermal conductivity between the two pumps is
high, the heat may be transferred from the second vacuum pump 2 to
the first vacuum pump 1, possibly impairing the normal operation of
the first vacuum pump 1. Consequently, the thermal conductivity
between the two pumps is lowered to minimize the heat transfer from
the second vacuum pump 2 to the first vacuum pump 1. An air-cooling
fan that is designed to match the cross-sectional area of the
second vacuum pump 2 is used to locally air-cool the second vacuum
pump 2 to discharge the heat therefrom. If the heat from the second
vacuum pump 2 is transferred to the first vacuum pump 1 and both
the first vacuum pump 1 and the second vacuum pump 2 need to be
air-cooled, then it is necessary to install the fan and to design
and install a duct or cover for guiding an air flow in order to
apply the air flow efficiently to the two pumps. If only the second
vacuum pump 2 is locally air-cooled, the installation of the fan
and the designing and installation of the duct or cover are
simplified. The thermal insulation material may be ceramics
(alumina, yttria, zirconia, etc.), stainless steel alloy, or
plastics (PEEK, PTFE, etc.).
[0130] FIG. 8 is a schematic front elevation view showing an
embodiment in which a vibro-isolating mechanism 61 is provided
between fastening surfaces of the first vacuum pump 1 and the
second vacuum pump 2. According to the present invention, since the
screw rotors 52a, 52b of the second vacuum pump 2 are capable of
rotating in opposite directions in synchronism with each other
because of a magnetic coupling between the magnet rotors 54, the
second vacuum pump 2 does not need any timing gears for
synchronizing the two screw rotors 52a, 52b, so that any vibrations
of the second vacuum pump 2 are greatly reduced. Even so, the
second vacuum pump 2 which compresses a gas up to the atmospheric
pressure vibrates to an extent greater than the first vacuum pump 1
comprising a turbomolecular pump. Therefore, as shown in FIG. 8,
the vibro-isolating mechanism 61 for isolating vibrations from the
second vacuum pump 1 is provided at the fastening portion of the
first vacuum pump 1 and the second vacuum pump 2, and thus any
vibrations that are transmitted from the second vacuum pump 2 to
the first vacuum pump 1 can be reduced. The vibro-isolating
mechanism 61 may comprise a vibro-isolating rubber (natural rubber,
nitrile rubber, silicone rubber, fluoro rubber, etc.) or a
spring.
[0131] In the vacuum evacuation apparatus shown in FIG. 8, the
evacuation passage component 3 interconnecting the outlet port of
the first vacuum pump 1 and the inlet port of the second vacuum
pump 2 is made of a vibro-isolating material. If the evacuation
passage component 3 is made of a highly rigid material or has a
highly rigid structure, then it may transmit vibrations from the
second vacuum pump 2 to the first vacuum pump 1. Since the
evacuation passage component 3 is made of a vibro-isolating
material, it can minimize vibrations transmitted from the second
vacuum pump 2 to the first vacuum pump 1. The vibro-isolating
material may be a rubber material such as natural rubber, nitrile
rubber, silicone rubber or fluoro rubber, and may be in the shape
of a tube or a block. When a vacuum is created in the evacuation
passage component 3 which is made of a vibro-isolating material
such as rubber, it tends to be deformed under the differential
pressure between the pressure in the evacuation passage component 3
and the atmospheric pressure. Though the evacuation passage
component 3 is deformed to different degrees depending on the
material and shape thereof, a helical spring of metal may be placed
in the evacuation passage component 3 to prevent the evacuation
passage component 3 from being deformed. The helical spring thus
placed in the evacuation passage component 3 does not prevent the
evacuation passage component 3 from being bent or curved. The
length of the helical spring may be determined as desired relative
to the length of the evacuation passage component 3.
[0132] FIG. 9 is a schematic side elevational view showing an
embodiment in which the first vacuum pump 1 and the second vacuum
pump 2 are fastened to each other by a fastening component combined
with a vibro-isolating mechanism. As shown in FIG. 9, a fastening
component 62 is disposed between the first vacuum pump 1 and the
second vacuum pump 2. A plurality of vibro-isolating bushings 63
are mounted on the fastening component 62. The fastening component
62 is fixed to the first vacuum pump 1 by fastening bolts 64 that
are threaded through the respective vibro-isolating bushings 63
into the first vacuum pump 1.
[0133] The fastening component 62 has an evacuation passage 62a
defined therein which is held in fluid communication with the inlet
port SP of the second vacuum pump 2 and an evacuation passage 62b
defined therein which is held in fluid communication with the
outlet port DP of the second vacuum pump 2. The evacuation passage
62a of the fastening component 62 is connected to the outlet port
DP (see FIG. 2) of the first vacuum pump 1 by an evacuation passage
component 3. The evacuation passage 62b of the fastening component
62 serves to vent the outlet port DP of the second vacuum pump 2 to
the atmosphere. The evacuation passage component 3 is made of a
vibro-isolating material such as rubber or the like.
[0134] FIGS. 10A, 10B and 10C are views showing the structure of a
fastening assembly comprising the fastening component 62 and the
vibro-isolating bushings 63. FIG. 10A is a cross-sectional view of
the fastening assembly, FIG. 10B is a bottom view of the fastening
assembly, and FIG. 10C is an exploded perspective view of one of
the vibro-isolating bushings 63.
[0135] As shown in FIGS. 10A and 10B, the fastening component 62
has a plurality of through holes 62h, and flanges 62f (see FIG.
10A) projecting radially inwardly from the inner circumferential
wall surfaces of the through holes 62h. As shown in FIG. 10C, each
of the vibro-isolating bushings 63 includes an upper member 63a
comprising a large-diameter ring-shaped portion and a
small-diameter ring-shaped portion, and a lower member 63b
comprising a ring-shaped portion. As shown in FIG. 10A, the upper
member 63a is mounted on the fastening component 62 in such a
manner that the small-diameter ring-shaped portion is fitted in a
circular hole defined by the inner circumferential surface of the
flange 62f of the fastening component 62 and the large-diameter
ring-shaped portion having a lower surface is held against the
upper surface of the flange 62f. The lower member 63b is fitted
over the outer circumferential surface of the small-diameter
ring-shaped portion of the upper member 63a and held against the
lower surface of the flange 62f. The fitting surfaces of the upper
member 63a and the lower member 63b are integrally united together
by an adhesive bonding or the like, causing the upper member 63a
and the lower member 63b to grip the flange 62f of the fastening
component 62. In this manner, all the vibro-isolating bushings 63
are mounted in place on the fastening component 62. Then, the
fastening bolts 64 are inserted through the respective
vibro-isolating bushings 63, and threaded into the first vacuum
pump 1 with washers 65 interposed between the heads of the
fastening bolts 64 and the vibro-isolating bushings 63. Therefore,
the fastening component 62 is securely fastened to the first vacuum
pump 1 with the vibro-isolating bushings 63 disposed therebetween.
The fastening component 62 and the second vacuum pump 2 are
fastened to each other by bolts or the like.
[0136] As shown in FIGS. 10A through 10C, since the first vacuum
pump 1 and the second vacuum pump 2 are fastened to each other
using a vibro-isolating mechanism comprising a plurality of
vibro-isolating bushings 63, the level of vibrations that are
transmitted from the second vacuum pump 2 to the first vacuum pump
1 can be lowered.
[0137] FIGS. 11A and 11B are front elevation views showing
embodiments in which a pump unit (vacuum evacuation apparatus)
having the first vacuum pump 1 and the second vacuum pump 2 that
are integrated is mounted on a vacuum container (vacuum chamber) 5.
In FIGS. 11A and 11B, the pump unit (vacuum evacuation apparatus)
shown in FIG. 1 is mounted on the vacuum container (vacuum chamber)
5.
[0138] In the embodiment shown in FIG. 11A, the pump unit which
includes the first vacuum pump 1 and the second vacuum pump 2 that
are integrally connected to each other is mounted on a lower
surface of the vacuum container 5 with the axis of the first vacuum
pump 1 extending vertically. The axes of the screw rotors 52a, 52b
of the second vacuum pump 2 are perpendicular to the axis of the
first vacuum pump 1.
[0139] In the embodiment shown in FIG. 11B, the pump unit which
includes the first vacuum pump 1 and the second vacuum pump 2 that
are integrally connected to each other is mounted on a side surface
of the vacuum container 5 with the axis of the first vacuum pump 1
extending horizontally. The axes of the screw rotors 52a, 52b of
the second vacuum pump 2 are perpendicular to the axis of the first
vacuum pump 1.
[0140] The pump unit which includes the first vacuum pump 1 and the
second vacuum pump 2 that are integrally connected to each other
may be mounted on an upper surface of the vacuum container 5.
Further, the pump unit which includes the first vacuum pump 1 and
the second vacuum pump 2 that are integrally connected to each
other as shown in FIGS. 5A through 5C may be mounted on the vacuum
container 5 in the same mounting postures as those shown in FIGS.
11A and 11B.
[0141] Another mounting posture in which the second vacuum pump 2
is mounted on the first vacuum pump 1 will be described below.
[0142] FIGS. 12A and 12B are views showing a mounting posture in
which the second vacuum pump 2 is mounted on a side surface of the
first vacuum pump 1, FIG. 12A is a side elevational view, partly in
cross section and FIG. 12B is a bottom view.
[0143] As shown in FIGS. 12A and 12B, the second vacuum pump 2 is
mounted on a side surface of the first vacuum pump 1. Specifically,
the first vacuum pump 1 has a cylindrical pump casing with a flat
cut surface on an outer circumferential surface thereof, and the
second vacuum pump 2 is fixed to the flat cut surface. In the
embodiment shown in FIGS. 12A and 12B, the axis 1x of the first
vacuum pump 1 and the axes 52ax, 52bx of the respective screw
rotors 52a, 52b of the second vacuum pump 2 are parallel to each
other. In the embodiments shown in FIGS. 1 and 5, the rotational
shaft of the first vacuum pump 1 and the rotational shafts of the
second vacuum pump 2 are perpendicular to each other to prevent
radial resonant vibrations from being produced. According to the
present invention, since the screw rotors 52a, 52b of the second
vacuum pump 2 are capable of rotating in opposite directions in
synchronism with each other because of a magnetic coupling between
the magnet rotors 54, the second vacuum pump 2 does not need any
timing gears for synchronizing the two screw rotors 52a, 52b, so
that any vibrations of the second vacuum pump 2 can be greatly
reduced. Consequently, no significant radial resonant vibrations
are not produced even though the rotational shaft of the first
vacuum pump 1 and the rotational shafts of the second vacuum pump 2
are perpendicular to each other.
[0144] FIGS. 13A, 13B and 13C are views showing an embodiment in
which the second vacuum pump 2 is mounted on a side surface of the
first vacuum pump 1, and the first vacuum pump 1 and the second
vacuum pump 2 are fastened to each other by a fastening component
combined with a vibro-isolating mechanism. FIG. 13A is a side
elevational view, partly in cross section, of the first vacuum pump
1 and the second vacuum pump 2, FIG. 13B is a bottom view, partly
in cross section, of the first vacuum pump 1 and the second vacuum
pump 2, and FIG. 13C is a cross-sectional view showing structural
details of a fastening assembly that fastens the first vacuum pump
1 and the second vacuum pump 2 shown in FIGS. 13A and 13B.
[0145] As shown in FIGS. 13A and 13B, the second vacuum pump 2 is
mounted on a side surface of the first vacuum pump 1, and a
fastening component 62 is disposed between the first vacuum pump 1
and the second vacuum pump 2. A plurality of vibro-isolating
bushings 63 are mounted on the fastening component 62. The
fastening component 62 is fixed to the first vacuum pump 1 by
fastening bolts 64 that are threaded through the respective
vibro-isolating bushings 63 into the first vacuum pump 1. As shown
in FIG. 13C, the fastening component 62, the vibro-isolating
bushings 63, and the fastening bolts 64 are identical in structure
to those shown in FIGS. 10A through 10C, and are installed in
position in the same manner as shown in FIGS. 10A through 10C.
[0146] FIG. 14 is a schematic front elevation view showing an
embodiment in which a check valve 6 is provided in an evacuation
passage component 3 which interconnects an outlet port of the first
vacuum pump 1 and an inlet port of the second vacuum pump 2. As
shown in FIG. 14, the pump unit which includes the first vacuum
pump 1 and the second vacuum pump 2 that are integrally connected
to each other is mounted on the vacuum container 5. The check valve
6 is disposed in the evacuation passage component 3 which
interconnects the outlet port of the first vacuum pump 1 and the
inlet port of the second vacuum pump 2.
[0147] According to the present invention, the first vacuum pump 1
comprising a turbomolecular pump and the second vacuum pump 2
comprising a dry vacuum pump are integrally connected together into
an integral pump unit including the evacuation passage component 3
therein. Therefore, the pressure conditions for the evacuation
passage component 3 are known. When one of the first and second
vacuum pumps 1, 2 fails to operate, e.g., when the dry vacuum pump
becomes faulty in operation, the back pressure of the
turbomolecular pump increases suddenly. By providing the check
valve 6 which automatically closes under the differential pressure
in the evacuation passage component, the pressure at the exhaust
side of the turbomolecular pump can be prevented from abruptly
rising.
[0148] FIG. 15 is a schematic front elevation view showing an
embodiment in which a bypass pipe 7 interconnecting the inlet port
of the first vacuum pump 1 and the inlet of the second vacuum pump
2 is provided for bypassing the first vacuum pump 1. As shown in
FIG. 15, the bypass pipe 7 interconnects the inlet port of the
first vacuum pump 1 and the inlet of the second vacuum pump 2 is
provided. The bypass pipe 7 serves to directly discharge a gas from
the inlet port of the first vacuum pump 1 into the inlet of the
second vacuum pump 2, thereby bypassing the first vacuum pump 1.
Consequently, even when the vacuum in the vacuum container 5
breaks, a sudden load buildup can be prevented from being exerted
on the first vacuum pump 1, and hence the rotating body of the
first vacuum pump can be protected against damage.
[0149] Further, a bypass valve 8 which is opened to connect the
inlet port of the first vacuum pump 1 directly to the inlet of the
second vacuum pump 2 is provided in the bypass pipe 7 in the event
of an abrupt increase of the pressure in the vacuum container 5.
The bypass valve 8 can be automatically opened and closed under
pressure conditions in the bypass pipe 7. Such pressure conditions
can be established with ease because the bypass pipe 7 is
constructed under optimum conditions between the first vacuum pump
1 and the second vacuum pump 2 which are integrally connected
together into a pump unit according to the present invention.
[0150] In the above embodiments, the second vacuum pump 2 is
illustrated and described as a screw-type dry pump. However, the
second vacuum pump 2 may comprise a roots dry pump, a diaphragm
pump, or a scroll pump. However, if the second vacuum pump 2
comprises a diaphragm pump, then because the diaphragm pump is a
pump having an evacuation principle for evacuating a gas by moving
a diaphragm up and down to cause volumetric changes, the vertically
moving direction (vibrating direction) of the diaphragm and the
axial direction of the first vacuum pump should preferably be
parallel to each other for the purpose of reducing overall
vibrations of the vacuum evacuation apparatus.
[0151] Next, a controlling process of the controller which controls
the first vacuum pump 1 and the second vacuum pump 2 will be
described below.
[0152] (1) Usually, the evacuation rate of a pump is controlled by
adjusting the opening area of the suction side with a control valve
or the like. According to the present invention, however, the
pressure in the vacuum container to be evacuated is controlled by
controlling at least one of the rotational speed of the first
vacuum pump 1 and the rotational speed of the second vacuum pump 2,
rather than by adjusting the opening (opening area) of a valve
disposed between the vacuum container and the pump. In this manner,
the evacuation rate of each of the vacuum pumps 1, 2 is adjusted to
adjust the overall evacuation rate of the pump system as the vacuum
evacuation apparatus. In other words, the pressure in the vacuum
container can be controlled by the single pump system without the
need for a control valve other than the vacuum pumps.
[0153] (2) FIG. 16 is a set of graphs showing comparison results in
which the rotational speeds of first and second vacuum pumps were
changed to adjust the pressure in a vacuum container in a pump
rotational speed control process which was performed on a vacuum
evacuation apparatus according to the present invention and a
vacuum evacuation apparatus according to the related art, in the
case of the first vacuum pump comprising a turbomolecular pump and
the second vacuum pump comprising a dry pump.
[0154] With the vacuum evacuation apparatus according to the
present invention, the piping interconnecting the first vacuum pump
(turbomolecular pump) and the second vacuum pump (dry pump) is very
short. After pressure adjustment in the vacuum container is
started, the rotational speed of the first vacuum pump is lowered,
and when the pressure in the vacuum container reaches a certain
level (start point of deceleration of the second pump), the second
vacuum pump starts to reduce the rotational speed thereof. Since
the piping interconnecting the first vacuum pump and the second
vacuum pump is short, the pressure in the vacuum container quickly
changes in response to the reduction in the rotational speed of the
second vacuum pump. As a result, the pressure in the vacuum
container can reach a target pressure, i.e., the adjustment of the
pressure in the vacuum container can be completed, in the shortest
period of time. With the vacuum evacuation apparatus according to
the related art, however, since the piping interconnecting the
first vacuum pump and the second vacuum pumps is longer, the
pressure in the vacuum container changes with a delay in response
to the reduction in the rotational speed of the second vacuum pump,
with the result that it consumes a certain period of time for the
pressure in the vacuum container to reach a target pressure.
[0155] When the first vacuum pump 1 and the second vacuum pump 2
are integrally connected together into an integral pump system, the
second vacuum pump 2 should desirably be mounted on the first
vacuum pump 1. Consequently, it is desirable for the second vacuum
pump 2 to have outer dimensions smaller than those of the first
vacuum pump 1.
[0156] Next, specific numerical values of the outer dimensions of
the first vacuum pump 1 and the second vacuum pump 2 will be
described below. The dimensions described below do not include
those of electric components such as drivers, a controller,
air-cooling fans, etc., but include only pump evacuation sections
and actuators (motors).
[0157] (1) In the case where the second vacuum pump according to
the present invention comprises a dual-shaft positive displacement
pump (screw rotors) and a magnetic coupling motor, the ultimate
performance that can be achieved by the second vacuum pump is 400
Pa or lower.
TABLE-US-00001 TABLE 1 General General evacuation General outer
General axial volume rates dimensions mm dimensions mm ratios First
vacuum 100 L/s Diameter: 100 110-150 1 pump 6000 L/min Second
vacuum 15 L/min Width: 90 110 0.4 pump
[0158] The ratio of the general evacuation rate of the second
vacuum pump and the general evacuation rate, which is assumed to be
1, of the first vacuum pump: 1/400
[0159] The ratio of the general axial dimension of the second
vacuum pump and the general axial dimension, which is assumed to be
1, of the first vacuum pump: 1-0.7
[0160] The ratio of the general volume of the second vacuum pump
and the general volume, which is assumed to be 1, of the first
vacuum pump: 0.4
TABLE-US-00002 TABLE 2 General General evacuation General outer
General axial volume rates dimensions mm dimensions mm ratios First
vacuum 300 L/s Diameter: 150 200-240 1 pump 18000 L/min Second
vacuum 45 L/min Width: 130 160 0.4 pump
[0161] The ratio of the general evacuation rate of the second
vacuum pump and the general evacuation rate, which is assumed to be
1, of the first vacuum pump: 1/400
[0162] The ratio of the general axial dimension of the second
vacuum pump and the general axial dimension, which is assumed to be
1, of the first vacuum pump: 0.8-0.6
[0163] The ratio of the general volume of the second vacuum pump
and the general volume, which is assumed to be 1, of the first
vacuum pump: 0.4
[0164] (2) In the case where the second vacuum pump that can be
used in the above combination is a diaphragm pump, the ultimate
performance that can be achieved by the second vacuum pump is 400
Pa or lower.
TABLE-US-00003 TABLE 3 General General evacuation General outer
General axial volume rates dimensions mm dimensions mm ratios First
vacuum 100 L/s Diameter: 100 110-150 1 pump 6000 L/min Second
vacuum 5 L/min Width: 80 200 1 pump
[0165] The ratio of the general evacuation rate of the second
vacuum pump and the general evacuation rate, which is assumed to be
1, of the first vacuum pump: 1/1200
[0166] The ratio of the general axial dimension of the second
vacuum pump and the general axial dimension, which is assumed to be
1, of the first vacuum pump: 1.8-1.3
[0167] The ratio of the general volume of the second vacuum pump
and the general volume, which is assumed to be 1, of the first
vacuum pump: 0.4
TABLE-US-00004 TABLE 4 General General evacuating General outer
General axial volume rates dimensions mm dimensions mm ratios First
vacuum 300 L/s Diameter: 150 200-240 1 pump 18000 L/min Second
vacuum 20 L/min Width: 160 330 2.6 pump
[0168] The ratio of the general evacuation rate of the second
vacuum pump and the general evacuation rate, which is assumed to be
1, of the first vacuum pump: 1/900
[0169] The ratio of the general axial dimension of the second
vacuum pump and the general axial dimension, which is assumed to be
1, of the first vacuum pump: 1.7-1.4
[0170] The ratio of the general volume of the second vacuum pump
and the general volume which is assumed to be 1, of the first
vacuum pump: 2.6
[0171] As can be seen from the above comparison results, in the
case where the first vacuum pump comprises a turbomolecular pump
and the second vacuum pump comprises a dual-shaft positive
displacement pump (screw rotors) with magnetic coupling motor, the
volume of the second vacuum pump can be smaller than the volume of
the first vacuum pump, and thus there is no limitation on the
mounting posture when the second vacuum pump is mounted on the
first vacuum pump.
[0172] As a turbomolecular pump and a dual-shaft positive
displacement pump are used respectively as the first vacuum pump
and the second vacuum pump, it is possible to integrally connect a
plurality of second vacuum pumps to the first vacuum pump which has
an evacuation capacity that is several times greater than each of
the second vacuum pumps.
[0173] FIG. 17 is a schematic view showing a vacuum evacuation
apparatus according to an embodiment of the present invention,
which includes a single first vacuum pump 1 and a plurality of
second vacuum pumps 2 integrally connected to the first vacuum pump
1. As shown in FIG. 17, the two second vacuum pumps 2 are
integrally connected to the single first vacuum pump 1. The outlet
port of the first vacuum pump 1 is connected to the inlet ports of
the second vacuum pumps 2 by respective individual evacuation
passage components 3. Since the plural second vacuum pumps 2 are
integrally connected to the single first vacuum pump 1, it is
possible to construct a roughing pump system having an evacuation
capacity which matches the evacuation capacity of the first vacuum
pump 1.
[0174] FIG. 18 is a schematic view showing a vacuum evacuation
apparatus according to an embodiment of the present invention,
which includes a single first vacuum pump 1 and a plurality of
second vacuum pumps 2 integrally connected to the first vacuum pump
1 by evacuation passages. As shown in FIG. 18, the two second
vacuum pumps 2 are integrally connected to the single first vacuum
pump 1, providing an integral pump unit that is mounted on a lower
surface of the vacuum container 5. The outlet port of the first
vacuum pump 1 is connected to the inlet ports of the second vacuum
pumps 2 by an evacuation passage component 3. Since the plural
second vacuum pumps 2 are integrally connected to the single first
vacuum pump 1, it is possible to construct a roughening pump system
having an evacuation capacity which matches the evacuation capacity
of the first vacuum pump 1.
[0175] Inasmuch as the two second vacuum pumps 2 are connected in a
parallel layout to the single first vacuum pump 1, the second
vacuum pumps 2 have their overall evacuation capacity doubled. When
the pressure control in the vacuum container is performed, the two
parallel second vacuum pumps 2 can control the pressure in the
vacuum container 5 more finely and quickly than a single second
vacuum pump 2.
[0176] If a single second vacuum pump 2 is used, a failure of the
second vacuum pump 2 leads to a shutdown of the first vacuum pump
1, resulting in a quick pressure buildup in the vacuum container 5.
However, in the case where the vacuum evacuation apparatus includes
the two second vacuum pumps 2, even if one of the second vacuum
pumps 2 fails to operate, the other second vacuum pump 2 operates
to keep the pressure in the outlet port of the first vacuum pump 1
below an allowable pressure level. Therefore, a situation where the
first vacuum pump 1 shuts down to cause a quick pressure buildup in
the vacuum container 5 can be avoided.
[0177] FIG. 19 is a schematic view showing a vacuum evacuation
apparatus according to an embodiment of the present invention,
which includes a plurality of first vacuum pumps 1 and a single
second vacuum pump 2 which are integrally connected by evacuation
passages. As shown in FIG. 19, two parallel first vacuum pumps 1
and a single second vacuum pump 2 are integrally connected together
into an integral pump unit that is mounted on a lower surface of
the vacuum container 5. The outlet ports of the two first vacuum
pumps 1 and the inlet port of the second vacuum pump 2 are
interconnected by an evacuation passage component 3. In this
manner, the plural first vacuum pumps 1 and a single second vacuum
pump 2 are integrally connected together into an integral pump
unit, and hence each of the first vacuum pumps 1 is reduced in
size.
[0178] With the two parallel first vacuum pumps 1 and the single
second vacuum pump 2 being integrally connected together, it is not
necessary for each of the first vacuum pumps to have a large-size
pump rotor which rotates at a high speed for an increased
evacuation capacity. Therefore, a safe vacuum evacuation system can
be constructed.
[0179] FIG. 20 is a block diagram of a control circuit for
controlling a vacuum evacuation apparatus including two first
vacuum pumps 1 and a single second vacuum pump 2 which are
integrally connected into an integral pump unit. As shown in FIG.
20, the control circuit includes a motor for one of the two first
vacuum pumps 1, i.e., TMP (turbomolecular pump) 1, a motor for the
other first vacuum pump 1, i.e., TMP2, an inverter (INV) for the
TMP1, an inverter (INV) for the TMP2, a motor for the second vacuum
pump 1, i.e., a DRY (dry) pump, and an inverter (INV) for the DRY
pump. The control circuit also includes a single controller (CPU)
for integrally controlling the three inverters, i.e., the INV for
the TMP1, the INV for the TMP2, and the INV for the DRY pump. The
CPU is capable of optimally controlling the pressure in the vacuum
container by controlling the rotational speeds of the motors of the
first and second vacuum pumps 1, 2 at desired rotational speed
control rates with the inverters without the need for pressure
detectors in the evacuation pipes connected to the first and second
vacuum pumps 1, 2. The control circuit shown in FIG. 20 also
includes a power factor controller (PFC) and a DC/DC converter
(DC/DC).
[0180] FIG. 21 is a graph showing how the rotational speeds of a
single first vacuum pump and two second vacuum pumps were changed
to adjust the pressure in a vacuum container in a pump rotational
speed control process which was performed on a vacuum evacuation
apparatus according to the present invention, in the case of the
first vacuum pump comprising a turbomolecular pump and the two
second vacuum pumps comprising a dry pump.
[0181] With the single first vacuum pump (turbomolecular pump) and
the two second vacuum pumps (dry pumps) being integrally connected
together by evacuation passages, after pressure adjustment in the
vacuum container is started, the rotational speed of the first
vacuum pump is lowered, and when the pressure in the vacuum
container rises, one of the second vacuum pumps starts to reduce
the rotational speed thereof. At this time, the first vacuum pump
continues speed reduction. After the first vacuum pump has stopped
reducing its rotational speed, the other second vacuum pump starts
to reduce the rotational speed thereof. Then, the second vacuum
pump which has started reducing its rotational speed earlier stops
reducing its rotational speed. The other second vacuum pump
continuously reduces its rotational speed, and when the pressure in
the vacuum container reaches a desired pressure level, the other
second vacuum pump stops reducing its rotational speed. At this
time, the pressure adjustment in the vacuum container is
completed.
[0182] Since the three vacuum pumps are interconnected, the
pressure in the vacuum container changes quickly in response to the
reduction in the rotational speeds of the second vacuum pumps, and
thus the pressure in the vacuum container can reach a target
pressure (pressure adjustment completing point), in the shortest
period of time. In addition, since the two second vacuum pumps
start and stop reducing their rotational speeds at different times,
the pressure in the vacuum container can be adjusted finely.
[0183] FIGS. 22 through 25 are schematic cross-sectional views
showing various different turbomolecular pumps for use in the
vacuum evacuation apparatus according to the present invention.
[0184] As shown in FIG. 22, the first vacuum pump 1 comprises a
turbomolecular pump having a pump casing 109, and rotor blades 111
and stator blades 114 that are alternately mounted on a rotational
shaft 113 and arranged successively from a central inlet port
defined in the pump casing 109 toward left and right opposite ends
of the rotational shaft 113. The multistage rotor blades 111 are
integrally formed on the rotational shaft 113, and the multistage
stator blades 114 are fixed to the pump casing 109.
[0185] A second vacuum pump 2 that is integrally connected to the
first vacuum pump 1 is structurally identical to the screw-type dry
vacuum pump shown in FIG. 3.
[0186] The second vacuum pump 2 has a pair of parallel screw rotors
which are parallel to a lower surface of the first vacuum pump 1.
The screw rotors have respective axes parallel to the axis of the
rotational shaft 113 of the first vacuum pump 1.
[0187] FIG. 23 shows a different posture when the second vacuum
pump 2 is mounted on the first vacuum pump 1.
[0188] As shown in FIG. 23, the axes of the screw rotors of the
second vacuum pump 2 are perpendicular to the axis of the
rotational shaft 113 of the first vacuum pump 1, and extend
parallel to each other and are spaced by a common distance from the
lower surface of the first vacuum pump 1.
[0189] FIG. 24 shows a vacuum evacuation apparatus in which the
fastening component 62 and the vibro-isolating bushings 63 shown in
FIGS. 9 and 10 are disposed between the first vacuum pump 1 and the
second vacuum pump 2 shown in FIG. 22.
[0190] FIG. 25 shows a vacuum evacuation apparatus in which the
fastening component 62 and the vibro-isolating bushings 63 shown in
FIGS. 9 and 10 are disposed between the first vacuum pump 1 and the
second vacuum pump 2 shown in FIG. 23. As shown in FIGS. 24 and 25,
since the first vacuum pump 1 and the second vacuum pump 2 are
fastened to each other using a vibro-isolating mechanism including
the vibro-isolating bushings 63, the level of vibrations that are
transmitted from the second vacuum pump 2 to the first vacuum pump
1 can be lowered.
[0191] Although preferred embodiments have been described in detail
above, it should be understood that the present invention is not
limited to the illustrated embodiments, but many changes and
modifications can be made therein without departing from the
appended claims.
* * * * *