U.S. patent application number 10/524688 was filed with the patent office on 2006-09-07 for vacuum pump and method of starting the same.
Invention is credited to Hiroyuki Chino, Naoki Iijima, Takeshi Kawamura, Jiro Watanbe, Kiyoshi Yanagisawa.
Application Number | 20060198735 10/524688 |
Document ID | / |
Family ID | 31943869 |
Filed Date | 2006-09-07 |
United States Patent
Application |
20060198735 |
Kind Code |
A1 |
Iijima; Naoki ; et
al. |
September 7, 2006 |
Vacuum pump and method of starting the same
Abstract
The present invention relates-to-a-vacuum pump and a method of
starting a vacuum pump. The vacuum pump includes a pump rotor (1)
rotatably disposed in a casing (2), and a pump-rotor controller
(15) for controlling rotation of the pump rotor (1) in a forward
direction or a reverse direction in accordance with a predetermined
pattern at the time of starting the vacuum pump.
Inventors: |
Iijima; Naoki; (Tokyo,
JP) ; Watanbe; Jiro; (Tokyo, JP) ; Chino;
Hiroyuki; (Tokyo, JP) ; Yanagisawa; Kiyoshi;
(Tokyo, JP) ; Kawamura; Takeshi; (Tokyo,
JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW
SUITE 700
WASHINGTON
DC
20036
US
|
Family ID: |
31943869 |
Appl. No.: |
10/524688 |
Filed: |
August 11, 2003 |
PCT Filed: |
August 11, 2003 |
PCT NO: |
PCT/JP03/10207 |
371 Date: |
March 9, 2006 |
Current U.S.
Class: |
417/44.1 |
Current CPC
Class: |
F04C 2270/03 20130101;
F04C 2270/80 20130101; F04C 2220/12 20130101; F05D 2260/607
20130101; F04C 2270/701 20130101; F04D 27/0292 20130101; F04C
18/126 20130101; F04C 28/06 20130101; F04C 28/28 20130101; F04D
19/04 20130101; F04C 13/005 20130101; F04C 18/16 20130101; F04C
2270/17 20130101 |
Class at
Publication: |
417/044.1 |
International
Class: |
F04B 49/06 20060101
F04B049/06 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 20, 2002 |
JP |
2002-239728 |
Claims
1. A vacuum pump comprising: a pump rotor rotatably disposed in a
casing; and a pump-rotor controller for controlling rotation of
said pump rotor in a forward direction or a reverse direction in
accordance with a predetermined pattern at the time of starting
said vacuum pump.
2. A vacuum pump according to claim 1, wherein said predetermined
pattern includes a combination of at least two of rotation of said
pump rotor in said forward direction, rotation of said pump rotor
in said reverse direction, and stop of said pump rotor.
3. A vacuum pump according to claim 2, wherein said predetermined
pattern is set in said pump-rotor controller such that said pump
rotor is driven in the order of the rotation in said forward
direction, the stop, and the rotation in said forward
direction.
4. A vacuum pump according to claim 2, wherein said predetermined
pattern is set in said pump-rotor controller such that said pump
rotor is rotated in the order of said reverse direction and said
forward direction.
5. A vacuum pump according to any one of claims 1 to 4, further
comprising: a state-judging device for judging whether said pump
rotor is rotated normally or not at the time of starting said
vacuum pump; wherein when said state-judging device judges that
said pump rotor is not rotated normally at the time of starting
said vacuum pump, said pump rotor is rotated in accordance with
said predetermined pattern.
6. A method of starting a vacuum pump having a pump rotor rotatably
disposed in a casing, comprising: controlling rotation of said pump
rotor in a forward direction or a reverse direction at the time of
starting said vacuum pump in accordance with a predetermined
pattern; and rotating said pump rotor in said forward direction in
a steady state for evacuation.
7. A method of starting a vacuum pump according to claim 6, wherein
said predetermined pattern includes a combination of at least two
of rotation of said pump rotor in said forward direction, rotation
of said pump rotor in said reverse direction, and stop of said pump
rotor.
8. A method of starting a vacuum pump according to claim 7, wherein
said predetermined pattern is set such that said pump rotor is
driven in the order of the rotation in said forward direction, the
stop, and the rotation in said forward direction.
9. A method of starting a vacuum pump according to claim 7, wherein
said predetermined pattern is set such that said pump rotor is
rotated in the order of said reverse direction and said forward
direction.
10. A method of starting a vacuum pump according to any one of
claims 6 to 9, further comprising: judging whether said pump rotor
is rotated normally or not; wherein said pump rotor is rotated in
accordance with said predetermined pattern when said pump rotor is
judged not to be rotated normally.
11. A method of starting a vacuum pump, comprising: judging whether
said pump rotor is rotated normally or not; controlling rotation of
said pump rotor in a forward direction or a reverse direction at
the time of starting said vacuum pump in accordance with a
predetermined pattern when said pump rotor is judged not to be
rotated normally; and rotating said pump rotor in said forward
direction in a steady state for evacuation.
Description
TECHNICAL FIELD
[0001] The present invention relates to a vacuum pump and a method
of starting a vacuum pump, and more particularly to a vacuum pump
for evacuating a gas from a chamber used in a semiconductor
fabrication apparatus or the like, and a method of starting such a
vacuum pump.
BACKGROUND ART
[0002] In a semiconductor fabrication apparatus, a vacuum pump is
widely used for evacuating a gas used in a semiconductor
fabrication process from a chamber and producing a vacuum
environment in the chamber. As this type of vacuum pump, there has
been known a positive-displacement vacuum pump having Roots-type or
screw-type pump rotors.
[0003] Generally, the positive-displacement vacuum pump comprises a
pair of pump rotors disposed in a casing, and a motor for rotating
the pump rotors. A small clearance is formed between the pair of
the pump rotors themselves and also between the pump rotors and the
inner surface of the casing so that the pump rotors are rotated in
a noncontact manner. When the pair of the pump rotors are
synchronously rotated in the opposite directions by energizing the
motor, a gas drawn from an inlet port into the casing is delivered
toward an outlet port and is thus evacuated from a chamber or the
like connected to the inlet port of the vacuum pump.
[0004] Some gases used in the semiconductor fabrication process
contain components which are solidified or liquidized when the
temperature of the gases is lowered. Generally, in the above
positive-displacement vacuum pump, the heat of compression is
generated during the process of delivering the gas toward the
outlet port, and hence the vacuum pump has a high temperature
during operation. Therefore, while the vacuum pump maintains a high
temperature, even if the vacuum pump evacuates the gas containing
the above components, the components are not solidified or
liquidized, and a good evacuation is thus carried out.
[0005] However, when the operation of the vacuum pump is stopped
and the temperature of the vacuum pump is gradually lowered, the
components contained in the gas are solidified or liquidized, and
are deposited in the clearance between the pump rotors and between
the pump rotors and the casing (hereinafter, the solidified or
liquidized components are refereed to as a product). Consequently,
such product prevents the rotation of the pump rotors, and hence
the pump rotors cannot be rotated by a starting torque of the
motor, thus causing a failure of the restart of the vacuum pump.
Further, in addition to the failure of the restart of the vacuum
pump, an excessive load is applied to the motor to cause the motor
to overheat, and hence the vacuum pump cannot be operated
safely.
[0006] Furthermore, in recent years, there has been developed a
motor-drive technique for driving an induction motor, a brushless
DC motor, or the like with the use of an inverter such as a
frequency converter. If such a motor-drive technique is used in the
vacuum pump, a torque of the motor for starting the vacuum pump is
limited by capacities of parts used in the inverter. Consequently,
the motor can generate only a limited torque, and the starting
operation of the vacuum pump tends to be more difficult.
DISCLOSURE OF INVENTION
[0007] 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 pump which can be normally started even if a
product solidified or liquidized in a casing of the vacuum pump
presents an obstacle to the rotation of the pump rotor.
[0008] Another object of the present invention is to provide a
method of starting such a vacuum pump.
[0009] In order to achieve the above object, according to one
aspect of the present invention, there is provided a vacuum pump
comprising: a pump rotor rotatably disposed in a casing; and a
pump-rotor controller for controlling rotation of the pump rotor in
a forward direction or a reverse direction in accordance with a
predetermined pattern at the time of starting the vacuum pump. The
rotation of the pump rotor in the forward direction is defined as
the rotation of the pump rotor in a direction in which a gas drawn
in the casing is delivered from an inlet side of the casing toward
an outlet side of the casing. The rotation of the pump rotor in the
reverse direction is defined as the rotation of the pump rotor in a
direction opposite to the forward direction.
[0010] In a preferred aspect of the present invention, the
predetermined pattern includes a combination of at least two of
rotation of the pump rotor in the forward direction, rotation of
the pump rotor in the reverse direction, and stop of the pump
rotor.
[0011] In a preferred aspect of the present invention, the
predetermined pattern is set in the pump-rotor controller such that
the pump rotor is driven in the order of the rotation in the
forward direction, the stop, and the rotation in the forward
direction.
[0012] In a preferred aspect of the present invention, the
predetermined pattern is set in the pump-rotor controller such that
the pump rotor is rotated in the order of the reverse direction and
the forward direction.
[0013] According to the present invention, if the product
solidified or liquidized in the casing prevents the rotation of the
pump rotor, the pump rotor is rotated in accordance with a
predetermined pattern to thereby remove the product, thus enabling
the vacuum pump to be started normally.
[0014] In a preferred aspect of the present invention, the vacuum
pump further comprises a state-judging device for judging whether
the pump rotor is rotated normally or not at the time of starting
the vacuum pump; wherein when the state-judging device judges that
the pump rotor is not rotated normally at the time of starting the
vacuum pump, the pump rotor is rotated in accordance with the
predetermined pattern.
[0015] According to the present invention, when the pump rotor can
be rotated normally, a normal-starting operation is carried out,
thus enabling the vacuum pump to be started quickly.
[0016] According to another aspect of the present invention, there
is provided a method of starting a vacuum pump having a pump rotor
rotatably disposed in a casing, comprising: controlling rotation of
the pump rotor in a forward direction or a reverse direction at the
time of starting the vacuum pump in accordance with a predetermined
pattern; and rotating the pump rotor in the forward direction in a
steady state for evacuation.
[0017] In a preferred aspect of the present invention, the
predetermined pattern includes a combination of at least two of
rotation of the pump rotor in the forward direction, rotation of
the pump rotor in the reverse direction, and stop of the pump
rotor.
[0018] In a preferred aspect of the present invention, the
predetermined pattern is set such that the pump rotor is driven in
the order of the rotation in the forward direction, the stop, and
the rotation in the forward direction.
[0019] In a preferred aspect of the present invention, the
predetermined pattern is set such that the pump rotor is rotated in
the order of the reverse direction and the forward direction.
[0020] In a preferred aspect of the present invention, a method of
starting a vacuum pump further comprises judging whether the pump
rotor is rotated normally or not; wherein the pump rotor is rotated
in accordance with the predetermined pattern when the pump rotor is
judged not to be rotated normally.
[0021] According to another aspect of the present invention, there
is provided a method of starting a vacuum pump, comprising: judging
whether the pump rotor is rotated normally or not; controlling
rotation of the pump rotor in a forward direction or a reverse
direction at the time of starting the vacuum pump in accordance
with a predetermined pattern when the pump rotor is judged not to
be rotated normally; and rotating the pump rotor in the forward
direction in a steady state for evacuation.
BRIEF DESCRIPTION OF DRAWINGS
[0022] FIG. 1 is a cross-sectional view showing a vacuum pump
according to a first embodiment of the present invention;
[0023] FIG. 2 is a schematic view showing a control system
including a pump-rotor controller according to the first embodiment
of the present invention;
[0024] FIG. 3 is a schematic view showing a control system
including a pump-rotor controller according to a second embodiment
of the present invention;
[0025] FIG. 4 is a schematic view showing a control system
including a pump-rotor controller according to a third embodiment
of the present invention;
[0026] FIG. 5 is a schematic view showing a control system
including a pump-rotor controller according to a fourth embodiment
of the present invention; and
[0027] FIG. 6 is a schematic view showing a control system
including a pump-rotor controller according to a fifth embodiment
of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0028] A vacuum pump and a method of starting a vacuum pump
according to embodiments of the present invention will be described
below with reference to the drawings.
[0029] Although a vacuum pump according to the present embodiments
is used for evacuating a gas from a chamber used in a semiconductor
fabrication apparatus, the present invention is not limited to such
an application. FIG. 1 is a cross-sectional view showing a vacuum
pump according to a first embodiment of the present invention.
[0030] As shown in FIG. 1, the vacuum pump according to the first
embodiment comprises a pair of pump rotors 1, 1 each having a screw
groove, a casing 2 for housing the pump rotors 1, 1, and a motor 3
for rotating the pump rotors 1, 1. The casing 2 has an inlet port 7
for drawing a gas therein and an outlet port 8 for discharging the
gas therefrom. The pump rotors 1, 1 are fixed respectively to two
shafts 4, 4 which are rotatably supported by bearings 5, 5.
[0031] One of the shafts 4, 4 has a motor rotor 3a fixed thereto,
and a motor stator 3b is disposed so as to enclose the motor rotor
3a. The motor rotor 3a and the motor stator 3b constitute the motor
3. In this embodiment, the motor 3 comprises an induction motor.
Timing gears 6, 6 are fixed to end portions of the shafts 4, 4,
respectively, and the pair of the pump rotors 1, 1 are
synchronously rotated in the opposite directions by the timing
gears 6, 6. A small clearance is formed between the pair of the
pump rotors 1, 1 themselves and also between the pump rotors 1, 1
and the inner surface of the casing 2 so that the pump rotors 1, 1
are rotated in a noncontact manner.
[0032] With the above structure, when the pair of the pump rotors
1, 1 are rotated by energizing the motor 3, a gas is drawn from the
inlet port 7 and delivered from an inlet side to an outlet side of
the casing 2 along the screw grooves of the engaging pump rotors 1,
1, and is then discharged from the outlet port 8. In this manner,
the gas is continuously delivered from the inlet side to the outlet
side, thereby evacuating the gas from a chamber (not shown in the
drawings) connected to the inlet port 7. The chamber is
incorporated in a semiconductor fabrication apparatus.
[0033] As shown in FIG. 1, the vacuum pump of this embodiment
comprises a control system 10 for controlling the operation of the
vacuum pump. The control system 10 incorporates a pump-rotor
controller 15 therein for controlling rotation of the pump rotors
1, 1 and stop of the pump rotors 1, 1.
[0034] FIG. 2 is a schematic view showing the control system
including the pump-rotor controller according to the first
embodiment of the present invention.
[0035] As shown in FIG. 2, the control system comprises a
three-phase power source 11, an earth leakage breaker (ELB) 12, an
electromagnetic contactor 13, and a thermal protector 14. The
three-phase power source 11 is connected to the electromagnetic
contactor 13 through the earth leakage breaker (ELB) 12, and the
electromagnetic contactor 13 is connected to the motor 3 through
the thermal protector 14. The pump-rotor controller 15 for
controlling the rotation of the pump rotors 1, 1 (only one pump
rotor is schematically shown in FIG. 2) and the stop of the pump
rotors 1, 1 is connected to the electromagnetic contactor 13. A
circuit breaker (CB) may be used instead of the earth leakage
breaker (ELB) 12.
[0036] A start-switch (not shown) of the vacuum pump is connected
to the pump-rotor controller 15, and when the start-switch is
operated, a start-command signal is sent from the pump-rotor
controller 15 to the electromagnetic contactor 13. The
electromagnetic contactor 13 is activated in response to the
start-command signal, and a three-phase voltage is applied to the
motor 3 from the three-phase power source 11. Therefore, a
rotational torque for rotating the pump rotors 1, 1 in forward
directions is imparted to the pump rotors 1, 1 from the motor 3,
thus starting the vacuum pump. The thermal protector 14 is provided
for breaking current supplied from the three-phase power source 11
to stop the operation of the vacuum pump when the motor 3 is
overloaded, thus preventing the overload and the overheat of the
motor 3 from occurring.
[0037] The pump-rotor controller 15 includes a timer 16, and when
the vacuum pump is started, the pump rotors 1, 1 are rotated or
stopped in accordance with a predetermined pattern set in the timer
16 in advance. In this embodiment, the pattern of the timer 16 is
set such that the pump rotors 1, 1 are driven in the order of (1)
forward-direction rotation (rotation of the pump rotors 1, 1 in the
forward directions), (2) stop, and (3) forward-direction rotation.
When the pump rotors 1, 1 are rotated in the forward directions,
one of the pump rotors 1, 1 is rotated in one direction (e.g.
clockwise direction) and another pump rotor 1 is rotated in the
opposite direction (e.g. counterclockwise direction). In this case,
the gas is drawn from the inlet port 7 into the casing 2, and
delivered toward the outlet port 8 and discharged from the outlet
port 8. The rotation of the pump rotors 1, 1 in the forward
directions is defined as the rotation of the pump rotors 1, 1 in
directions in which the gas drawn in the casing 2 is delivered from
the inlet port 7 toward the outlet port 8.
[0038] Therefore, when the vacuum pump is started, first, the
rotational torque for rotating the pump rotors 1, 1 in the forward
directions is imparted to the pump rotors 1, 1 from the motor 3.
Thereafter, the rotational torque imparted to the pump rotors 1, 1
is reduced to zero once. Subsequently, the rotational torque for
rotating the pump rotors 1, 1 in the forward directions is imparted
to the pump rotors 1, 1 from the motor 3 again.
[0039] In this manner, when the vacuum pump is started, the pump
rotors 1, 1 are rotated and then stopped, and are rotated again.
Therefore, forces of the pump rotors 1, 1 can be applied to a
product deposited in the clearance between the pump rotors 1, 1 and
the casing 2. As a result, the product which has been solidified is
embrittled and removed, thus enabling the vacuum pump to be started
normally. In the case where a pattern for allowing the pump rotors
1, 1 to repeat its rotation and stop several times is set in the
timer 16, the reliability of removal of the product can be further
enhanced. After the vacuum pump is started normally, the pump
rotors 1, 1 are rotated in the forward directions in a steady state
for evacuation.
[0040] Next, a vacuum pump and a method of starting a vacuum pump
according to a second embodiment of the present invention will be
described with reference to FIG. 3. The basic structure of a vacuum
pump of this embodiment is the same as that of the first
embodiment, and will not be described in detail below.
[0041] FIG. 3 is a schematic view showing a control system
including a pump-rotor controller according to the second
embodiment of the present invention.
[0042] As shown in FIG. 3, a control system of this embodiment
comprises a three-phase power source 11, an earth leakage breaker
(ELB) 12, and a frequency converter 21. The three-phase power
source 11 is connected to the frequency converter 21 through the
earth leakage breaker (ELB) 12, and the frequency converter 21 is
connected to the motor 3. The frequency converter 21 comprises a
rectifier 22, a power transistor 23 for generating a waveform to
rotate the motor 3, and a frequency-conversion controller 24 for
controlling the frequency converter 21. A pump-rotor controller 15
for controlling rotation of the pump rotors 1, 1 and stop of the
pump rotors 1, 1 is connected to the frequency converter 21.
[0043] The pump-rotor controller 15 includes a timer 16, as with
the first embodiment. Specifically, when a start-switch (not shown)
is operated, a start-command signal is sent from the pump-rotor
controller 15 to the frequency converter 21, and a three-phase
voltage is applied to the motor 3 from the three-phase power source
11. Thus, the pump rotors 1, 1 are rotated in accordance with a
predetermined pattern set in the timer 16 in advance. In this
embodiment, as with the first embodiment, the pattern is set in the
timer 16 such that the pump rotors 1, 1 are driven by the motor 3
in the order of (1) forward-direction rotation, (2) stop, and (3)
forward-direction rotation. A pattern for allowing the pump rotors
1, 1 to repeat its rotation and stop several times may be set in
the timer 16.
[0044] Although an induction motor is used as the motor 3 in this
embodiment, the induction motor can be replaced with a brushless DC
motor by replacing the frequency-conversion controller 24 with a
brushless-DC-motor controller. In this case also, as in the case of
the induction motor, the pump rotor can be rotated in accordance
with a predetermined pattern.
[0045] Next, a vacuum pump and a method of starting a vacuum pump
according to a third embodiment of the present invention will be
described with reference to FIG. 4. The basic structure of a vacuum
pump and parts of a control system denoted by identical reference
numerals are the same as those of the first embodiment, and will
not be described in detail below.
[0046] FIG. 4 is a schematic view showing a control system
including a pump-rotor controller according to the third embodiment
of the present invention.
[0047] As shown in FIG. 4, a control system comprises a three-phase
power source 11, an earth leakage breaker (ELB) 12, a first
electromagnetic contactor 13A, a second electromagnetic contactor
13B, and a thermal protector 14. An induction motor is used as the
motor 3. The first electromagnetic contactor 13A and the second
electromagnetic contactor 13B are connected to a pump-rotor
controller 15, respectively, and are activated by receiving an
operation-command signal from the pump-rotor controller 15. The
three-phase power source 11 is connected to the first
electromagnetic contactor 13A and the second electromagnetic
contactor 13B through the earth leakage breaker (ELB) 12, and the
first electromagnetic contactor 13A and the second electromagnetic
contactor 13B are connected to the motor 3 through the thermal
protector 14. The first electromagnetic contactor 13A applies a
three-phase voltage of the three-phase power source 11 to the motor
3 with the phase sequence being kept as it is. On the other hand,
the second electromagnetic contactor 13B applies the three-phase
voltage of the three-phase power source 11 with the phase sequence
being inverted from the phase sequence of the three-phase voltage
of the three-phase power source 11.
[0048] The pump-rotor controller 15 is constructed so as to rotate
the pump rotors 1, 1 in forward directions or reverse directions in
accordance with a predetermined pattern set in the pump-rotor
controller 15 in advance through the first electromagnetic
contactor 13A and the second electromagnetic contactor 13B.
Specifically, an operation-command signal is sent from the
pump-rotor controller 15 to the first electromagnetic contactor 13A
and the second electromagnetic contactor 13B alternately in
accordance with the predetermined pattern. The pattern is set in
the pump-rotor controller 15 such that the pump rotors 1, 1 are
rotated in the order of the reverse directions and the forward
directions. When the pump rotors 1, 1 are rotated in the forward
directions, one of the pump rotors 1, 1 is rotated in one direction
(e.g. clockwise direction) and another pump rotor 1 is rotated in
the opposite direction (e.g. counterclockwise direction). In this
case, the gas is drawn from the inlet port 7 into the casing 2 and
discharged from the outlet port 8. On the other hand, when the pump
rotors 1, 1 are rotated in the reverse directions, the pump rotors
1, 1 are rotated in directions opposite to the directions of the
pump rotors 1, 1 which are rotated in the forward directions. The
rotation of the pump rotors 1, 1 in the reverse directions is
defined as the rotation of the pump rotors 1, 1 in directions
opposite to the forward directions.
[0049] The operation of the vacuum pump having the above structure
of this embodiment will be described in detail below. When a
start-switch (not shown) of the vacuum pump is operated, first, the
operation-command signal is sent from the pump-rotor controller 15
to the second electromagnetic contactor 13B. By activating the
second electromagnetic contactor 13B, the three-phase voltage
having an inverted phase sequence is applied to the motor 3 through
the second electromagnetic contactor 13B, and hence the rotational
torque for rotating the pump rotors 1, 1 in the reverse directions
is imparted to the pump rotors 1, 1 from the motor 3. Thereafter,
the pump-rotor controller 15 stops sending the operation-command
signal to the second electromagnetic contactor 13B. At the same
time, the operation-command signal is sent from the pump-rotor
controller 15 to the first electromagnetic contactor 13A. By
activating the first electromagnetic contactor 13A, the three-phase
voltage of the three-phase power source 11 is applied to the motor
3 through the first electromagnetic contactor 13A with the phase
sequence being kept as it is. Therefore, the rotational torque for
rotating the pump rotors 1, 1 in the forward directions is imparted
to the pump rotors 1, 1 from the motor 3.
[0050] In this manner, by rotating the pump rotors 1, 1 in the
reverse directions or the forward directions at the time of
starting the vacuum pump, the forces of the pump rotors 1, 1 can be
applied to the product deposited in the gap between the pump rotors
1, 1 and the casing 2. As a result, the product is removed, thus
enabling the vacuum pump to be started.
[0051] Next, a vacuum pump and a method of starting a vacuum pump
according to a fourth embodiment of the present invention will be
described with reference to FIG. 5. The basic structure of a vacuum
pump and parts of a control system denoted by identical reference
numerals are the same as those of the second embodiment, and will
not be described in detail below.
[0052] FIG. 5 is a schematic view showing a control system
including a pump-rotor controller according to the fourth
embodiment of the present invention.
[0053] As shown in FIG. 5, a pump-rotor controller 15 is
constructed so as to send a start-command signal 101 for starting
the vacuum pump and a control signal 102 for rotating the pump
rotors 1, 1 in the forward directions or the reverse directions in
accordance with a predetermined pattern to the frequency-conversion
controller 24 of the frequency converter 21. A pattern is set in
the pump-rotor controller 15 such that the pump rotors 1, 1 are
rotated in the order of the reverse directions and the forward
directions at the time of starting the vacuum pump, as with the
third embodiment.
[0054] The control system of this embodiment shown in FIG. 5 is
operated to start the vacuum pump as follows: When a start-switch
(not shown) is operated, the start-command signal 101 is sent from
the pump-rotor controller 15 to the frequency-conversion controller
24. At the same time, the control signal 102 for rotating the motor
3 in the reverse direction is sent from the pump-rotor controller
15 to the frequency-conversion controller 24. Therefore, the
rotational torque for rotating the pump rotors 1, 1 in the reverse
directions is imparted to the pump rotors 1, 1 from the motor 3.
Thereafter, the control signal 102 for rotating the motor 3 in the
forward direction is sent from the pump-rotor controller 15 to the
frequency-conversion controller 24, and hence the rotational torque
for rotating the pump rotors 1, 1 in the forward directions is
imparted to the pump rotors 1, 1 from the motor 3.
[0055] Although an induction motor is used as the motor 3 in this
embodiment, the induction motor can be replaced with a brushless DC
motor by replacing the frequency-conversion controller 24 with a
brushless-DC-motor controller. In this case also, as in the case of
the induction motor, the pump rotors 1, 1 can be rotated in the
forward directions or the reverse directions in accordance with a
predetermined pattern.
[0056] Next, a vacuum pump and a method of starting a vacuum pump
according to a fifth embodiment of the present invention will be
described with reference to FIG. 6. The basic structures of a
vacuum pump and a control system of this embodiment are the same as
those of the fourth embodiment, and will not be described in detail
below.
[0057] FIG. 6 is a schematic view showing a control system
including a pump-rotor controller according to the fifth embodiment
of the present invention.
[0058] The vacuum pump of this embodiment comprises a current
monitor 27 for monitoring current supplied to the motor 3. The
current monitor 27 serves as a state-judging device for judging
whether the pump rotors 1, 1 are rotated normally or not at the
time of starting the vacuum pump. When the current monitor 27
detects that current supplied to the motor 3 is in an abnormal
state, the current monitor 27 judges that the pump rotors 1, 1 are
not rotated normally. Specifically, if the product or the like
deposited in the casing 2 prevents the pump rotors 1, 1 from being
rotated, current supplied to the motor 3 is detected to be in the
abnormal state, and hence the current monitor 27 can judge that the
pump rotors 1, 1 are not rotated normally.
[0059] Further, when the current monitor 27 judges that the
rotation of the pump rotors 1, 1 is abnormal, the current monitor
27 sends an operation signal to the pump-rotor controller 15. The
pump-rotor controller 15 is activated by receiving the operation
signal to thereby rotate the motor 3 in accordance with a
predetermined pattern which is set in the pump-rotor controller 15
in advance.
[0060] Specifically, in this embodiment, the pump-rotor controller
15 does not work until the operation signal is sent from the
current monitor 27 to the pump-rotor controller 15. Therefore, when
the pump rotor can be rotated normally, the normal-starting
operation is carried out, thus enabling the vacuum pump to be
started quickly.
[0061] As a state-judging device, a rotation monitor for monitoring
the rotation of the pump rotors 1, 1 or a product monitor for
monitoring the amount of the product deposited in the casing 2 may
be provided instead of the current monitor 27. In the case where
the product monitor is provided, an optical sensor or a
thermocouple may be used for monitoring the amount of the product
deposited in the casing 2. In this case, when the amount of the
product is increased to a predetermined value, the product monitor
may send the operation signal to the pump-rotor controller 15.
[0062] Although the vacuum pump according to the embodiments of the
present invention has two pump rotors engaging with each other, the
present invention can be applied to a vacuum pump having a single
pump rotor or more than two pump rotors. In these cases also, the
rotation of the pump rotor (or pump rotors) in a forward direction
(or forward directions) is defined as the rotation of the pump
rotor (or pump rotors) in a direction (or directions) in which a
gas is delivered from an inlet side toward an outlet side. The
rotation of the pump rotor (or pump rotors) in a reverse direction
(or reverse directions) is defined as the rotation of the pump
rotor (or pump rotors) in a direction (or directions) opposite to
the forward direction (or forward directions).
[0063] As described above, according to the present invention, even
if the product solidified or liquidized in the casing prevents the
pump rotor from being rotated, the product is removed by the pump
rotor which is rotated in accordance with the predetermined
pattern. Therefore, the vacuum pump can be started normally.
INDUSTRIAL APPLICABILITY
[0064] The present invention is applicable to a vacuum pump and a
method of starting a vacuum pump, and more particularly to a vacuum
pump for evacuating a gas from a chamber used in a semiconductor
fabrication apparatus or the like, and a method of starting such a
vacuum pump.
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