U.S. patent application number 11/900446 was filed with the patent office on 2008-03-13 for method of controlling the stopping operation of vacuum pump and device therefor.
Invention is credited to Yoshiaki Fujiwara, Kentaro Ishihara, Ryosuke Koshizaka, Osamu Uchiyama, Shinya Yamamoto.
Application Number | 20080063536 11/900446 |
Document ID | / |
Family ID | 38704900 |
Filed Date | 2008-03-13 |
United States Patent
Application |
20080063536 |
Kind Code |
A1 |
Koshizaka; Ryosuke ; et
al. |
March 13, 2008 |
Method of controlling the stopping operation of vacuum pump and
device therefor
Abstract
A method for controlling the operation of a vacuum pump when
stopping the gas transferring operation thereof, the vacuum pump
having a housing in which a pump chamber is formed and a gas
transferring body which is rotatably disposed in the pump chamber
for transferring gas, the method comprises the steps of reducing
rotational speed of the gas transferring body to a first preset
speed below a second preset speed that is lower than a normal speed
of the gas transferring body during normal gas transferring
operation of the vacuum pump, maintaining the speed of the gas
transferring body below the second preset speed, and stopping the
rotation of the gas transferring body when the temperature of the
housing reaches a predetermined temperature which is lower than
that of the housing during the normal gas transferring operation of
the vacuum pump.
Inventors: |
Koshizaka; Ryosuke;
(Kariya-shi, JP) ; Yamamoto; Shinya; (Kariya-shi,
JP) ; Fujiwara; Yoshiaki; (Kariya-shi, JP) ;
Ishihara; Kentaro; (Kariya-shi, JP) ; Uchiyama;
Osamu; (Kariya-shi, JP) |
Correspondence
Address: |
MORGAN & FINNEGAN, L.L.P.
3 World Financial Center
New York
NY
10281-2101
US
|
Family ID: |
38704900 |
Appl. No.: |
11/900446 |
Filed: |
September 10, 2007 |
Current U.S.
Class: |
417/32 ;
417/462 |
Current CPC
Class: |
F04C 28/06 20130101;
F04C 29/04 20130101; F04C 28/08 20130101; F04C 2280/02 20130101;
F04C 23/005 20130101; F04C 2270/17 20130101; F04C 2220/12 20130101;
F04C 25/02 20130101; F04C 18/126 20130101; F05C 2201/0442 20130101;
F04C 18/16 20130101 |
Class at
Publication: |
417/032 ;
417/462 |
International
Class: |
F04B 49/20 20060101
F04B049/20; F04B 49/06 20060101 F04B049/06 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 12, 2006 |
JP |
P2006-247196 |
Claims
1. A method for controlling the operation of a vacuum pump when
stopping the gas transferring operation thereof, the vacuum pump
having a housing in which a pump chamber is formed and a gas
transferring body which is rotatably disposed in the pump chamber
for transferring gas, comprising the steps of: reducing rotational
speed of the gas transferring body to a first preset speed below a
second preset speed that is lower than a normal speed of the gas
transferring body during normal gas transferring operation of the
vacuum pump; maintaining the speed of the gas transferring body
below the second preset speed; and stopping the rotation of the gas
transferring body when the temperature of the housing reaches a
predetermined temperature which is lower than that of the housing
during the normal gas transferring operation of the vacuum
pump.
2. The method according to claim 1, wherein the vacuum pump further
has a cooling passage through which coolant flows for cooling the
housing and the step further includes the additional step of:
flowing the coolant in the cooling passage before the speed of the
gas transferring body is reduced to the speed below the second
preset speed.
3. The method according to claim 1, wherein the step further
includes the additional steps of: rapidly increasing the rotational
speed of the gas transferring body in the range below the second
preset speed while the gas transferring body is being rotated at
the speed below the second preset speed after the reducing the
rotational speed of the gas transferring body; and reducing the
rotational speed of the gas transferring body below the second
preset speed.
4. A device for controlling the operation of a vacuum pump when
stopping the gas transferring operation thereof, the vacuum pump
having a housing in which a pump chamber is formed, a gas
transferring body rotatably provided in the pump chamber for
transferring gas, the device comprising: means for controlling the
stopping operation of the vacuum pump; and detection means for
detecting the temperature of the housing and generating a detection
signal when the temperature of the housing reaches a predetermined
temperature which is lower than a temperature of the housing during
normal operation of the vacuum pump when gas is being transferred
by the gas transferring body; wherein the controlling means is
operable to reduce rotating speed of the gas transferring body to a
speed below a second preset speed that is lower than a normal speed
of the gas transferring body during normal gas transferring
operation of the vacuum pump in response to a pump-stop command
signal for stopping the gas transferring body and also to stop the
rotation of the gas transferring body in response to the detection
signal from the detection means.
5. The device according to claim 4, the vacuum pump further having
a cooling passage being formed therein through which coolant for
cooling the housing passes and a means for opening and closing the
cooling passage, wherein the means for controlling the stopping
operation of the vacuum pump is operable to open the means for
opening and closing the cooling passage before the rotational speed
of the gas transferring body is reduced to the speed below the
second preset speed.
6. The device according to claim 4, wherein the means for
controlling the stopping operation of the vacuum pump is operable
to rapidly increase the rotational speed of the gas transferring
body in the range below the second preset speed while the gas
transferring body is being rotated at the speed below the second
preset speed after the reducing the rotational speed of the gas
transferring body and also to reduce the rotational speed of the
gas transferring body below the second preset speed after the rapid
increase of the rotational speed.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a method of controlling the
stopping operation of a vacuum pump which transfers gas by moving a
gas transferring body in a pump chamber and also to a device for
practicing the method.
[0002] A vacuum pump is used to discharge gas for use in
semiconductor manufacturing processes from a process chamber and to
create a vacuum environment in the process chamber. As the vacuum
pump, a positive displacement vacuum pump is known which has roots
type or screw type pump rotors as a gas transferring body.
Generally, the displacement vacuum pump has a pair of pump rotors
which is disposed in the pump chamber of a pump casing and a motor
which drives the pump rotors to rotate.
[0003] Narrow clearances are formed between the pair of the pump
rotors and between each rotor and the inner surface of the casing
such that the pair of pump rotors rotates without contact with the
casing, and the paired pump rotors are rotated synchronously in
opposite directions. Such rotation of the pump rotors, causes gas
in the pump casing to be transferred from the suction side to the
discharge side of the casing, and then to flow out of the process
chamber which is connected a suction port.
[0004] Gas used in semiconductor manufacturing processes may
sometimes contain an element which is solidified during being
transferred (hereinafter, such solidified element is referred to as
"solid products"). Because the vacuum pump generates heat of
compression during transferring of the gas, the vacuum pump in
operation, or specifically the casing and the pump rotors of the
vacuum pump, becomes relative high in temperature. While the vacuum
pump maintains a high temperature, the casing and the pump rotors
are thermally expanded. Thus, the clearance between the pump rotor
and the inner surface of the pump chamber facing the pump rotor
becomes wider and, therefore, solid products tend to get into the
clearance and accumulate therein.
[0005] When the operation of the vacuum pump is stopped, the vacuum
pump becomes gradually lower in temperature and the
thermally-expanded casing and pump rotors contract, so that the
clearance is narrowed, so that, the solid products accumulated in
the clearance are held between the pump rotors and the inner
surface of the pump chamber. When the vacuum pump is restarted, the
pump rotors may be prevented from rotating by the solid products
held between the pump rotors and the inner surface of the pump
chamber and cannot be rotated by starting torque of a motor. If the
vacuum pump cannot be restarted by the staring torque of the motor,
a tool is engaged with a rotary shaft of the vacuum pump and then a
torque is applied to the rotary shaft by manually rotating the pump
rotors with the tool, thus removing the solid products from the
clearance and making the vacuum pump ready for restarting.
[0006] Unexamined Japanese Patent Publication No. 2004-138047
discloses a method of starting a vacuum pump which enables the
solid products to be removed without manual operation and the
vacuum pump to be restarted. According to the method disclosed in
the above publication, when restarting the vacuum pump having
therein solid products, a torque is applied from the motor to the
pump rotors for rotation in normal direction. Thereafter, the
torque applied to the pump rotors becomes zero and again a torque
is applied to the pump rotors for rotation in forward direction.
Thus, torque is applied to the solid products accumulated between
the pump rotor and the inner surface of the pump chamber. As a
result, the solid products become brittle and are broken, so that
they are removed from the clearance and, therefore, the vacuum pump
can be started without manual operation.
[0007] According to the vacuum pump starting method disclosed in
the above publication, the vacuum pump is started from a state that
the solid products are held between the pump rotors and the inner
surface of the pump chamber. Thus, solid products need to be
removed from the clearance by application of a force of the pump
rotors before it becomes possible for the vacuum pump to transfer
the gas. If solid products are held tightly or a large amount of
solid products is held between the pump rotors and the inner
surface of the pump chamber, the pump rotors need to be rotated for
many times for application of force that is enough to break the
solid products, with the result that the time for prior operation
of the vacuum pump before actual gas transferring will be
lengthened. According to the starting method disclosed in the above
publication, the vacuum pump requires a relatively long time before
gas transferring becomes possible after the vacuum pump has been
started.
[0008] The present invention, which is made in view of the above
problems, is directed to a method and an apparatus of controlling
the stopping operation of the vacuum pump. The method and apparatus
of controlling the stopping operation of the vacuum pump according
to the present invention prevents the vacuum pump from stopping in
a state that solid products are held between the inner surface of
the pump chamber and the gas transferring body and permits the
vacuum pump to be restarted rapidly for transferring of gas.
SUMMARY OF THE INVENTION
[0009] In accordance with the present invention, a method for
controlling the operation of a vacuum pump when stopping the gas
transferring operation thereof, the vacuum pump having a housing in
which a pump chamber is formed and a gas transferring body which is
rotatably disposed in the pump chamber for transferring gas, the
method comprises the steps of reducing rotational speed of the gas
transferring body to a first preset speed below a second preset
speed that is lower than a normal speed of the gas transferring
body during normal gas transferring operation of the vacuum pump,
maintaining the speed of the gas transferring body below the second
preset speed, and stopping the rotation of the gas transferring
body when the temperature of the housing reaches a predetermined
temperature which is lower than that of the housing during the
normal gas transferring operation of the vacuum pump.
[0010] In accordance with the present invention, a device is used
for controlling the operation of a vacuum pump when stopping the
gas transferring operation thereof. The vacuum pump has a housing
in which a pump chamber is formed and a gas transferring body
rotatably provided in the pump chamber for transferring gas. The
device includes means for controlling the stopping operation of the
vacuum pump and detection means for detecting the temperature of
the housing and generating a detection signal when the temperature
of the housing reaches a predetermined temperature. The
predetermined temperature is lower than a temperature of the
housing during normal operation of the vacuum pump when gas is
transferred by the gas transferring body. The controlling means is
operable to reduce rotating speed of the gas transferring body to a
speed below a second preset speed that is lower than a normal speed
of the gas transferring body during normal gas transferring
operation of the vacuum pump in response to a pump-stop command
signal for stopping the gas transferring body. The controlling
means is also operable to stop the rotation of the gas transferring
body in response to the detection signal from the detection
means.
[0011] Other aspects and advantages of the invention will become
apparent from the following description, taken in conjunction with
the accompanying drawings, illustrating by way of example the
principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The features of the present invention that are believed to
be novel are set forth with particularity in the appended claims.
The invention together with objects and advantages thereof, may
best be understood by reference to the following description of the
presently preferred embodiments together with the accompanying
drawings in which:
[0013] FIG. 1 is a plan cross-sectional view of a roots pump of a
first embodiment according to the present invention;
[0014] FIG. 2(a) is a cross-sectional view taken along the line A-A
in FIG. 1;
[0015] FIG. 2(b) is a cross-sectional view taken along the line B-B
in FIG. 1;
[0016] FIG. 2(c) is a cross-sectional view taken along the line C-C
in FIG. 1;
[0017] FIG. 3 is a graph showing change of rotation speeds of rotor
and change of temperature of a rotor housing according to the first
embodiment of method of controlling the stopping operation of the
vacuum pump; and
[0018] FIG. 4 is a graph showing change of rotation speeds of rotor
and change of temperature of a rotor housing according to a second
embodiment of method of controlling the stopping operation of the
vacuum pump.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] The following will describe the first preferred embodiment
of a method and apparatus of controlling the stopping operation of
a roots pump as a vacuum
[0020] pump which transfers gas in a semiconductor manufacturing
equipment with reference to FIGS. 1 through 3. The front and the
rear of the roots pump in the following description are indicated
by the double-headed arrow Y in FIG. 1.
[0021] Referring to FIG. 1, the roots pump 10 of the first
preferred embodiment includes a multistage roots pump 11A having a
plurality of sets of rotors as a gas transferring body and a single
stage roots pump 11B having only one set of rotor and these roots
pumps 11A and 11B are assembled integrally. Since the multistage
roots pump 11A and the single stage roots pump 11B are different
from each other only in the number of sets of rotors, the same
reference numerals will be used to denote the same or similar
elements or components and the description thereof will be omitted
in the following description. FIGS. 2(a) through 2(c) show
cross-sectional views of the multistage roots pump 11A and FIGS.
2(b) and 2(c) are provided without diagrammatic representations of
a cooling passage.
[0022] As shown in FIG. 1, the multistage roots pump 11A and the
single stage roots pump 11B include a front housing 13, a rotor
housing 12, a rear housing 14 and a gear housing 33, respectively.
The front housing 13 is fixed to the front end of the rotor housing
12 and a sealing body 36 is fixed to the front end of the front
housing 13. The rear housing 14 is fixed to the rear end of the
rotor housing 12 and the gear housing 33 is fixed to the rear end
of the rear housing 14. The front housing 13, the rotor housing 12,
the rear housing 14 and the gear housing 33 are made of ductile
iron.
[0023] As shown in FIG. 2(b), the rotor housing 12 of the
multistage roots pump 11A includes a cylinder block 15 and a
plurality of partition walls 16. The partition walls 16 are also
made of ductile iron. The cylinder block 15 includes a pair of
blocks 17, 18 and each partition wall 16 includes a pair of wall
elements 161, 162. As shown in FIG. 1, a space serving as a pump
chamber 39 is formed between the front housing 13 and its adjacent
partition wall 16 in the rotor housing 12 of the multistage roots
pump 11A. Similarly, spaces serving as pump chambers 40 through 42
are formed between any two adjacent partition walls 16, and a space
serving as pump chamber 43 is formed between the rear housing 14
and its adjacent partition wall 16, respectively.
[0024] Meanwhile, the rotor housing 12 of the single stage roots
pump 11B has no partition wall 16 and it is made of a cylinder
block 15 which includes a pair of blocks 17 (only one block 17
being shown. In FIG. 1). A space as a pump chamber 50 is formed by
the front housing 13, the rear housing 14 and the cylinder block 15
in the rotor housing 12 of the single stage roots pump 11B.
[0025] Rotary shafts 19, 20 are rotatably supported in parallel
relation to each other through radial bearings 21, 22, respectively
in the front housing 13 and the rear housing 14 of the multistage
roots pump 11A and the single stage roots pump 11B. The rotary
shafts 19, 20 are positioned in the axial direction by being fixed
to the rear housing 14 through the double row radial bearings 21,
22 positioned at the rear end of the multistage roots pump 11A and
the single stage roots pump 11B.
[0026] A plurality of rotors 23 through 27 is formed integrally
with the rotary shaft 19 of the multistage roots pump 11A.
Similarly, a plurality of rotors 28 through 32, which is of the
same number as the above rotors 23 through 27, is formed integrally
with the rotary shaft 20 of the multistage roots pump 11A. The
rotors 23 through 32 are of substantially the same shape or profile
and size as viewed in the direction of axes 191, 201 of the rotary
shafts 19, 20. The thicknesses of the rotors 23 through 27 become
smaller in this order. Similarly, the rotors 28 through 32 are
formed with thickness which become smaller in this order.
[0027] Two rotors 23 and 28 are accommodated in the pump chamber 39
so as to mesh with each other. Similarly, pairs of the intermeshing
rotors 24 and 29, 25 and 30, 26 and 31, 27 and 32 are accommodated
in the pump chambers 40, 41, 42, 43, respectively, so as to mesh
with each other. Meanwhile, in the single stage roots pump 11B,
rotors 51, 52 are formed integrally with the rotary shaft 19, 20,
respectively. The rotors 51, 52 are accommodated in the pump
chamber 50 so as to mesh with each other. The rotary shafts 19, 20
are made of ductile iron.
[0028] Small clearances are formed between the rotors 23, 28 and
the front housing 13 and also between the rotors 23 through 32 and
their adjacent partition walls 16, respectively. Similarly, small
clearances are formed between the rotors 27, 32 and their adjacent
opposite rear housing 14. That is, the clearances are formed
between rotors 23 through 32 and the inner surfaces of the pump
chamber in which the rotors 23 through 32 are accommodated.
Therefore, the rotors 23 through 32 are rotatably arranged without
contact with the inner surfaces of the pump chambers 39 through
43.
[0029] In normal operation, the rotary shafts 19, 20 are thermally
expanded from the rear ends of the rotary shafts 19, 20 in
connection with the radial bearings 21, 22 toward the front ends of
the rotary shafts 19, 20. The rotor housing 12 and the rear housing
14 are also thermally expanded. Because the rotary shafts 19, 20
are higher in temperature than the rotor housing 12 and the rear
housing 14, the rotary shafts 19, 20 are more thermally expanded
than the rotor housing 12. Thus, rotors 23 through 32 are moved
toward the front end of the multistage roots pump 11A in normal
operation as compared to when the roots pump operation is stopped.
The moving distances of the rotors 23, 28 located at the front of
the rotors 23 through 32 are the largest of all the rotors 23
through 32. Therefore, the clearances in the pump chambers 39
through 43 are formed so as to be narrower in this order. That is,
the clearance in the pump chamber 39 is the largest of all the
clearances in the pump chambers 39 through 43.
[0030] The gear housing 33 is fixedly mounted to the rear housing
14 of the multistage roots pump 11A and the single stage roots pump
11B. The rotary shafts 19, 20 extend through the rear housing 14
into the gear housing 33. Gears 34, 35 are mounted for engagement
with each other on the ends of the rotary shafts 19, 20 which
extend into the gear housing 33. An electric motor MA is mounted to
the gear housing 33 of the multistage roots pump 11A and an
electric motor MB is mounted to the gear housing 33 of the single
stage roots pump 11B, respectively.
[0031] Driving forces of the electric motors MA, MB are transmitted
through a shaft couplings 44 to the rotary shafts 19 in the
multistage roots pump 11A and the single stage roots pump 11B.
Therefore, the rotary shafts 19 are rotated by the electric motors
MA, MB in the direction of arrows R1 in the FIGS. 2(a) through
2(c). Then, the rotating force of the rotary shafts 19 is
transmitted through the gears 34, 35 to the rotary shafts 20. The
rotary shafts 20 are rotated in opposite direction from the rotary
shafts 19, as indicated by arrows R2 in FIG. 2(a) through 2(c), and
synchronously because of the intermeshing gears 34, 35 mounted on
the rotary shaft 19, 20.
[0032] The rotors 23 through 27, 51 are rotatable in the direction
of the arrows R1 by the driving force of the electric motors MA, MB
and the rotors 28 through 32, 52 are rotatable in the direction of
the arrows R2. Thus, the paired rotors 23, 28 are rotatable in
opposite directions and synchronously with each other. Similarly,
the pairs of the rotors 24, 29, the rotors 25, 30, the rotors 26,
31 and the rotors 27, 32 are rotatable in opposite directions and
synchronously with each other. In addition, the rotors 23 through
32 rotate at the same rotation speed as the electric motor MA and
the rotors 51, 52 rotate at the same rotation speed as the electric
motor MB.
[0033] As shown in FIG. 2(b), a passage 163 is formed in each
partition wall 16 of the multistage roots pump 11A which has an
inlet 164 and an outlet 165. Thus, the any two adjacent pump
chambers 39, 40, 41, 42, 43 are connected with each other through
the passage 163 in the partition wall 16 between the above two
adjacent pump chambers.
[0034] In the multistage roots pump 11A, an inlet 181 is formed
through the block 18 for fluid communication with the pump chamber
39, as shown in FIG. 2(a). As shown in FIG. 2(c), an outlet 171 is
formed through the block 17 for communication with the pump chamber
43. In the single stage roots pump 11B, an inlet and an outlet, are
formed in the block 17 and the block 18, respectively, for
communication with the pump chamber 50.
[0035] As shown in FIG. 1, the multistage roots pump 11A is
connected through a supply passage 45 to the single stage roots
pump 11B. Specifically, the outlet of the single stage roots pump
11B is connected through the supply passage 45 to the inlet 181 of
the multistage roots pump 11A. In the single stage roots pump 11B
of the roots pump 10, rotations of the rotors 51, 52 by the
electric motor MB introduces gas through inlet into the pump
chamber 50, and the rotation of the rotors 51, 52 transfers the gas
from the outlet to the supply passage 45.
[0036] In the multistage roots pump 11A, when the rotors 23 through
32 are rotated by the electric motor MA, the gas flowed from the
single stage roots pump 11B through the supply passage 45 is
introduced into the pump chamber 39 through the inlet 181, and then
the gas is transferred by the rotations of the rotors 23, 28
through the inlet 164, the passage 163 and the outlet 165 of the
partition wall 16 into the pump chamber 40. Similarly, the gas is
further transferred in the roots pump 10 from one pump chamber to
another while being compressed gradually. The gas is compressed to
the maximum pressure in the pump chamber 43 and discharged out of
the roots pump 10 through the outlet 171.
[0037] Referring to FIG. 2(a), a cooling device 54 is disposed on
the top surface of the rotor housing 12 or the block 18 and another
cooling device 55 is disposed on the bottom surface of the block
17. The cooling device 54 is connected to a supply pipe 541 and a
discharge pipe 542. Similarly, the cooling device 55 is connected
to a supply pipe 551 and a discharge pipe 552. Coolant from a
coolant supply source T is transferred through the supply pipes
541, 551 to the cooling devices 54, 55 and then returned into the
coolant supply source T through the discharge pipes 542, 552. Thus,
the coolant passing through the cooling devices 54, 55 cools the
cylinder block 15 in the rotor housing 12. The cooling devices 54,
55, the supply pipes 541, 551 and the discharge pipes 542, 552
cooperate to form a cooling passage through which the coolant for
cooling the rotor housing 12 passes. A valve V, which is a part of
the cooling passage, is provided between the supply pipes 541, 551
and the coolant supply source T as a means for controllably opening
or closing the supply pipes 541, 551. The valve V is provided by an
electromagnetically-operated three-way valve which is operable to
control the supply of coolant by opening or closing the supply
pipes 541, 551.
[0038] As shown in FIG. 1, the electric motors MA, MB are
electrically connected to an inverter 65 which is in turn
electrically connected to a control device 75 which provides
command or control signals to the inverter 65. The control device
75 includes a central processing unit (CPU) 75a and a memory 75b.
The central processing unit 75a executes various processing
according to control programs stored in the memory 75b. That is,
the control device 75 controls the inverter 65 by the central
processing unit 75a according to the control programs stored in the
memory 75b. In the first preferred embodiment, the control device
75 or the central processing unit 75a, which forms a means for
controlling the stopping operation of the vacuum pump of the
present invention, controls the stopping operation of the roots
pump 10 according to the stopping operation control programs stored
in the memory 75b.
[0039] The memory 75b stores therein data of a predetermined normal
rotor speed for the rotors 23 through 32, 51, 52. This normal rotor
speed data represents a predetermined rotor speed of the rotors 23
through 32, 51, 52 during the normal operation of the roots pump 10
for gas transferring in a semiconductor manufacturing device. The
memory 75b further stores therein data of a predetermined first
preset rotor speed for the rotors 23 through 32, 51, 52 which
represents a rotor speed to which the rotor speed is reduced from
the aforementioned normal rotor speed in performing the pump
stopping operation control.
[0040] The above first preset rotor speed is set below a
predetermined second preset rotor speed for rotors 23 through 32
and the rotors 51, 52 which is also stored in the memory 75b. The
second preset rotor speed represents such a rotor speed that makes
possible preventing rapid reduction of the clearances between the
inner surfaces of the pump chambers 39 through 43 and the rotors 23
through 32, 51, 52 facing such inner surfaces without increasing
the temperature of the rotor housing 12 during the rotation of the
rotors 23 through 32, 51, 52.
[0041] The memory 75b still further stores therein data of a
predetermined increased rotor speed for the rotors 23 through 32,
51, 52. The increased rotor speed data represent a rotor speed
increased from the aforementioned first preset rotor speed in
performing the pump stopping operation control. The increased rotor
speed is set below the above predetermined second rotor speed. In
the present first preferred embodiment, the rotors 23 through 32
are rotated at substantially the same speed as the electric motor
MA, and the rotors 51, 52 rotated at substantially the same speed
as the electric motor MB. That is, the rotation speeds of the
rotors 23 through 32 and rotors 51, 52 are the same as that of the
electric motors MA, MB. The inverter 65 uses an alternating-current
power supply 77 as a power source based on the command control of
the control device 75 and is operable to control the electric
motors MA, MB in accordance with the above rotor speed data and
changes the rotation speeds of the rotors 23 through 32 and rotors
51, 52 accordingly.
[0042] A temperature sensor S is provided for detecting the
temperature of the rotor housing 12 of the multistage roots pump
11A. The temperature sensor S is located at a position on the outer
periphery of the pump chamber 43 which is closest to the outlet 171
and has highest temperature among the pump chambers 39 through 43.
The temperature sensor S is a detection means which generates to
the control device 75 a detection signal when the rotor housing 12
reaches a predetermined temperature during operation of the
multistage roots pump 11A. As shown in FIG. 2(a), the valve V is
electrically connected to the control device 75 which controls the
operation of the valve V.
[0043] FIG. 3 is a graph showing changes over time of the rotation
speeds of the rotors 23 through 32 and rotors 51, 52 and the
temperature of the rotor housing 12 of the multistage roots pump
11A in controlling the stopping operation of the roots pump 10. The
horizontal axis in the graph of FIG. 3 shows the elapse of time
during the operation of the roots pump 10 and a part of the
horizontal axis shows the elapse of time in controlling the
operation of the roots pump 10. The vertical axis shows the
rotation speed of the rotors 23 through 32, 51, 52 and the
temperature of the rotor housing 12.
[0044] Bold line G1 in the graph shows the temperature change of
the rotor housing 12 in the multistage roots pump 11A and dash-dot
line G2 shows the change of rotation speed of the rotors 23 through
32 in the multistage roots pump 11A. Chain double-dot line G3 in
the graph shows the change of the rotation speed of the rotors 51,
52 in the single stage roots pump 11B.
[0045] The following will describe the method for controlling the
stopping operation of the roots pump 10 with reference to the graph
in FIG. 3. In the roots pump 10, the single stage roots pump 11B is
provided to assist the multistage roots pump 11A in transferring
gas and, therefore, it is free from engagement of solid products.
In the multistage roots pump 11A, on the other hand, the pressure
and the thermal expansion of the casing and pump rotors are
increased in accordance with gas transfer from the pump chamber 39
to the pump chamber 43. Therefore, solid products tend to be held
in the clearance when the roots pump operation is stopped and the
casing and pump rotors of the multistage roots pump 11A contracted.
The method of controlling the stopping operation to prevent solid
products from being held in the clearance will now be described
with reference to the multistage roots pump 11A. The rotary shafts
19, 20, rotors 23 through 32, rotor housing 12 and rear housing 14
in the multistage roots pump 11A are thermally expanded by heat
generation during normal operation. Because the rotary shafts 19,
20 are higher in temperature and more expanded, the clearances
between the rear side surfaces of the rotors 23 through 32 and
their adjacent opposite partition walls 16 and between the rear
side surface of the rotor 32 and the rear housing 14 are larger
than those when the roots pump is in a stopped state. The valve V
is fully closed in normal operation of the roots pump 10.
[0046] In normal operation of the roots pump 10, the control device
75 causes the rotors 23 through 32 to be rotated at the normal
rotor speed in accordance with the normal rotor speed data, as
indicated by dash-dot line G2. In FIG. 3 and the rotors 51, 52 to
be rotated at the normal rotor speed in accordance with the normal
rotor speed data, as indicated by chain double-dot line G3 in FIG.
3. When stopping the gas transferring operation of the roots pump
10, a pump switch (not shown) is turned off and a pump-stop command
signal for stopping the roots pump 10 is transmitted to the control
device 75, accordingly. In response to this pump-stop command
signal, the control device 75 causes the valve V to fully open. As
a result, coolant is supplied from the coolant supply source T and
flows In the cooling passage, which is formed by the cooling
devices 54, 55, the supply pipes 541, 551 and the discharge pipes
542, 552, for cooling the rotor housing 12.
[0047] The control device 75 causes the rotation speed of the
rotors 23 through 32, 51, 52 to be lowered from the normal rotor
speed to a level below the second preset rotor speed in accordance
with the second preset rotor speed data and the first preset rotor
speed data. At the time, the control device 75 causes the rotors 23
through 32 in the multistage roots pump 11A to be rotated at the
first preset rotor speed and the rotors 51, 52 in the single stage
roots pump 11B to be stopped temporarily. Then, the rotors 23
through 32 are rotated at a lower speed than in normal operation
and the temperature of the rotor housing 12 is gradually lowered as
indicated by bold line G1 in FIG. 3. The rotor housing 12, the
front housing 13 and the rear housing 14 in the multistage roots
pump 11A which had been thermally expanded is gradually contracted
in accordance with the decreasing rotor speed.
[0048] Thus, the clearances between the rotors 23 through 32 and
the inner surfaces of the pump chamber 39 through 43 facing the
rotors 23 through 32 are relatively narrow as compared to those
during normal operation, but they are relatively large as compared
to those when the roots pump operation is stopped. Thus, if any
solid product enters into the clearance, it is removed by the
rotors 23 through 32 then rotating at a relatively low speed.
[0049] While the rotors 23 through 32 are being rotated at the
first preset rotor speed, the control device 75 control the
operation of the rotors 23 through 32 in such a way that the rotor
speed of the rotors 23 through 32 are rapidly increased and reduced
alternately for a plurality of times at a predetermined interval in
accordance with the increased rotor speed data. In other words,
while the rotors 23 through 32 are being rotated at the first
preset rotor speed, the speed of the rotors 23 through 32 is
intermittently increased in the range below the second preset speed
and such repeated and rapid increase in speed of the rotors 23
though 32 helps to remove solid products. In accordance with the
increased rotor speed data, the control device 75 causes the rotors
51, 52 of the single stage roots pump 11B to rapidly increase their
speed at a predetermined interval immediately before rapidly
increasing the rotor speed of the rotors 23 through 32 of the
multistage roots pump 11A. By so doing, the required driving torque
of the electric motor MA for the multistage roots pump 11A may be
reduced.
[0050] As indicated by dash-dot line G2 in FIG. 3, the rotor
housing 12, the front housing 13 and the rear housing 14 are
gradually cooled while the rotors 23 through 32 are rotating at the
first preset rotor speed and increasing their speed to the
increased rotor speed. When the temperature of the rotor housing 12
is decreased to a predetermined temperature which is lower than a
temperature of the rotor housing 12 during normal operation of the
rotors 51, 52, the temperature sensor S generates a detection
signal to the control device 75. When the rotor housing 12 reaches
the predetermined temperature, solid products in the clearances
have been almost removed and contraction of the rotor housing 12,
the front housing 13, the rear housing 14 and rotors 23 through 32,
51, 52 has been stopped, so that the clearances will not become
narrower anymore. Responding to the detection signal from the
temperature sensor S, the control device 75 stops the electric
motors MA, MA and the rotation of the rotors 23 through 32, 51, 52,
with the result that the operation of the roots pump 10 is
stopped.
[0051] The first embodiment has the following advantageous
effects.
[0052] (1) When the operation of the roots pump 10 (or the
multistage roots pump 11A) is stopped with simultaneous stop of gas
transferring, the control device 75 causes the rotation speed of
the rotors 23 through 32 to be decreased below the second preset
rotor speed which is lower than the normal rotor speed during
normal operation of the roots pump 10. The control device 75
maintains the rotors 23 through 32 at a relatively low speed which
is lower than the second preset rotor speed. The rotor housing 12,
the front housing 13, the rear housing 14 and the rotors 23 through
32 in the multistage roots pump 11A which had been thermally
expanded during normal operation are cooled while maintaining a
slightly thermally expanded state. Thus, the clearances between the
rotors 23 through 32 and their facing inner surfaces of the pump
chambers 39 through 43 are made larger than those when the roots
pump is in a stopped state, so that the rotating rotors 23 through
32 can remove any solid products accumulated in the clearances.
Solidified or liquefied products are prevented from getting into
the clearances between the adjacent opposite rotors 23 through 32
which will not become narrower when the roots pump is stopped and
being fixed into the clearances between the adjacent opposite
rotors 23 through 32. Therefore, the method of controlling the
stopping operation of the roots pump 10 can successfully prevent
solid products from being held in the clearances.
[0053] As a result, the roots pump 10 can be restarted with no
solid product present in the clearance and there is no need to
manually apply a large torque to the rotary shafts 19, 20 for
breaking solid products by rotating the rotors 23 through 32 for
many times in the background art. Thus, restarting of the roots
pump 10 requires no preliminary work of removing solid products
from the clearances, so that gas transferring operation can be
initiated immediately after a restart of the roots pump. In
addition, since there is no need to manually apply a large torque
to the rotary shafts 19, 20 as in the background art, the rotary
shafts 19, 20 need not be made rigid enough to resist the large
torque, so that the rotary shafts 19, 20 or the roots pump 10 can
be downsized.
[0054] (2) In response to a pump-stop command signal, the control
device 75 is operated to fully open the valve V, thereby allowing
the coolant to circulate for cooling the rotor housing 12. Thus,
the rotor housing 12 is cooled more efficiently by the coolant as
compared to before the valve V is fully opened. Although the rotor
housing 12 contracts by cooling, the rotors 23 through 32 keep
rotating at a speed under the second preset rotor speed, so that
the clearances between rotors 23 through 32 and their facing pump
chambers 39 through 43 are larger than those when the roots pump is
stopped and, therefore, solid products are prevented from being
held in the clearances. Cooling the rotor housing 12 by circulating
coolant, the time before the rotor housing temperature is reduced
to a predetermined level can be shortened and also the time that is
required before the roots pump 10 is stopped while solid products
being removed from the clearances can be reduced.
[0055] (3) When the temperature of the rotor housing 12 reaches a
predetermined temperature and the temperature sensor S generates a
detection signal, accordingly, the control device 75 stops the
rotations of the rotors 23 through 32. According to this method of
controlling the stopping operation, the rotors 23 through 32 are
stopped when the temperature of the rotor housing 12 becomes
relatively low and the clearances between the rotors 23 through 32
and their facing inner surfaces of the pump chambers 39 through 43
are almost completely contracted. With the clearances thus
contracted, the clearances are further narrowed and solid product
will not be held in the clearances. Thus, the rotation of the
rotors 23 through 32 cannot remove solid products, so that the
driving force of the electric motor MA rotating the rotors 23
through 32 is only wasted. Controlling the stopping operation of
the rotors 23 through 32 in accordance with the temperature of the
rotor housing 12, power consumption of the motors can be
restrained.
[0056] (4) The control device 75 controls the operation of the
rotors 23 through 32 in such a way that their rotor speed is
rapidly increased while they are being at the first preset rotor
speed that is lower than the second preset rotor speed.
Accordingly, the force then applied to solid products from the
rotors 23 through 32 is increased rapidly, so that solid products
in the clearances can be removed efficiently as compared to the
case where the rotors 23 through 32 are rotated at a constant
rotation speed.
[0057] (5) The control device 75 controls the operation of the
rotors 23 through 32 such that they are rotated at the first preset
rotor speed which is lower than the second preset rotor speed and
the rotor speed is rapidly increased under the second preset rotor
speed. Thus, in controlling the stopping operation, the rotation
speed of the rotors 23 through 32 is maintained below the second
preset rotor speed. This prevents the temperatures of the rotor
housing 12 and rotors 23 through 32 from becoming higher than
necessary and the length of time in which the temperature of the
rotor housing 12 reaches the predetermined temperature is
restrained to necessity minimum.
[0058] A second preferred embodiment of the present invention will
be described with reference to FIG. 4, in which the present
invention is applied to a method for controlling the stopping
operation of a roots pump as a vacuum pump which transfer gas in a
semiconductor manufacturing device and also to a device for
practicing the method. The second embodiment differs from the first
embodiment in that the method of controlling the stopping operation
uses only the multistage roots pump 11A. Those descriptions which
have been already made with reference to the first embodiment will
be omitted.
[0059] In the second preferred embodiment, controlling of the
stopping operation of the multistage roots pump is performed in
accordance with the graph shown in the FIG. 4. The graph in FIG. 4
shows changes over time of the rotation speeds of the rotors 23
through 32 and the temperature of the rotor housing 12 in
controlling the stopping operation of the multistage roots pump
11A. The horizontal axis represents the elapsed time in operation
of the roots pump, a part of which represents the elapsed time in
controlling the stopping operation. The vertical axis of the graph
represents the rotation speed of the rotors 23 through 32 and the
temperature of the rotor housing 12.
[0060] Bold line G1 in the graph of FIG. 4 shows a change of the
temperature of the multistage roots pump 11A and dash-dot line G2
shows a change of the rotation speed of the rotors 23 through 32 in
the multistage roots pump 11A.
[0061] According to the second preferred embodiment, the control
device 75 lowers the rotation speed of the rotors 23 through 32
from a normal rotor speed to first preset rotor speed that is below
a second preset rotor speed and then keeps the rotors 23 through 32
rotating at the constant first preset rotor speed without rapidly
increasing the rotor speed at a predetermined interval as in the
first preferred embodiment. Therefore, the second preferred
embodiment has the effects similar to the effects (1) through (3)
of the first preferred embodiment.
[0062] The present invention may be practiced in other various
modifications as exemplified below.
[0063] In the above preferred embodiments, the control device 75
may control in such a way that the rotation speed of the rotors 23
through 32 of the multistage roots pump 11A is rapidly decreased at
a predetermined interval while the rotors 23 through 32 are being
rotated at the first preset rotor speed, with the valve V then
fully closed to stop supplying of coolant to the pipes 541, 551. By
thus controlling, contraction of the rotor housing 12 and rotors 23
through 32 is delayed and solid products are removed by changing
the rotor speed.
[0064] In the above preferred embodiments, controlling may be
performed in such a way that rotation speed of the rotors 23
through 32 of the multistage roots pump 11A are either increased or
decreased rapidly only once while the rotors 23 through 32 are
being rotated at the first preset rotor speed.
[0065] In the above preferred embodiments, while the rotors 23
through 32 of the multistage roots pump 11A are being rotated at
the first preset rotor speed, the control device 75 may be operable
to control in such a way that the rotation speed of the rotors 23
through 32 is increased when the current supplied to the inverter
65 is increased so that first preset rotor speed is maintained. Any
increase in the current supplied to the inverter 65 means that any
part of the rotors 23 through 32 is prevented from rotating by the
presence of solid products. Therefore, increasing the rotor speed
when the current to the inverter is increased, solid products that
prevent rotating of the rotors 23 through 32 can be broken and
removed.
[0066] In the above preferred embodiments, the control device 75
may not control the operation of the valve V.
[0067] The controlling method of the present invention may be
applied to a vacuum pump which includes the single stage roots pump
11B.
[0068] The controlling method of the present invention may be
applied also to a vacuum pump having a screw rotor as a gas
transferring body. The clearance between the screw rotors engaged
with each other is larger by being thermally expanded during normal
operation and narrower when the roots pump is stopped. The solid
products are prevented from getting into and being held in the
clearances between screw rotor and opposite housing as well as
between screw rotors.
[0069] In the above preferred embodiments, it may be so arranged
that decreasing of the rotor speed from the normal speed to the
second preset rotor speed may take place gradually.
[0070] In the above preferred embodiments, the rotation speed of
the electric motor MA, MB may be different from that of the rotors
23 through 32, 51, 52 by the shaft coupling 44.
[0071] The cooling passage may be formed within the thickness of
the rotor housing 12.
[0072] Therefore, the present examples and embodiments are to be
considered as illustrative and not restrictive, and the invention
is not to be limited to the details given herein but may be
modified within the scope of the appended claims.
* * * * *