U.S. patent application number 10/737378 was filed with the patent office on 2005-02-10 for controller of vacuum pump.
Invention is credited to Kawaguchi, Masahiro, Koshizaka, Ryosuke, Kuramoto, Satoru, Sato, Daisuke, Yamamoto, Shinya.
Application Number | 20050031468 10/737378 |
Document ID | / |
Family ID | 32763933 |
Filed Date | 2005-02-10 |
United States Patent
Application |
20050031468 |
Kind Code |
A1 |
Kawaguchi, Masahiro ; et
al. |
February 10, 2005 |
Controller of vacuum pump
Abstract
A vacuum pump has a pump mechanism section that performs
evacuation to set a space to be evacuated to a predetermined degree
of vacuum and an electric motor section for driving the pump
mechanism section. A controller of the vacuum pump executes
deceleration control to decrease a rotational speed of the electric
motor section when an increase in load torque of the vacuum pump
per unit time abruptly changes upward.
Inventors: |
Kawaguchi, Masahiro;
(Kariya-shi, JP) ; Yamamoto, Shinya; (Kariya-shi,
JP) ; Sato, Daisuke; (Kariya-shi, JP) ;
Koshizaka, Ryosuke; (Kariya-shi, JP) ; Kuramoto,
Satoru; (Kariya-shi, JP) |
Correspondence
Address: |
WOODCOCK WASHBURN LLP
ONE LIBERTY PLACE, 46TH FLOOR
1650 MARKET STREET
PHILADELPHIA
PA
19103
US
|
Family ID: |
32763933 |
Appl. No.: |
10/737378 |
Filed: |
December 16, 2003 |
Current U.S.
Class: |
417/410.1 ;
417/20; 417/423.4; 417/53 |
Current CPC
Class: |
F04B 49/06 20130101 |
Class at
Publication: |
417/410.1 ;
417/423.4; 417/053; 417/020 |
International
Class: |
F04B 049/00; F04B
001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 18, 2002 |
JP |
2002-366856 |
Claims
1. In a controller of a vacuum pump having a pump mechanism section
that performs evacuation to set a space to be evacuated to a
predetermined degree of vacuum, the improvement comprising an
electric motor section for driving said pump mechanism section,
wherein, when an increase in load torque of said vacuum pump per
unit time abruptly changes upward, deceleration control to decrease
a rotational speed of said electric motor section is carried
out.
2. The controller according to claim 1, wherein said load torque of
said vacuum pump is calculated based on a value of a current
supplied to said electric motor section.
3. The controller according to claim 1, wherein said increase in
load torque of said vacuum pump per unit time is monitored
repeatedly at a predetermined time interval and that monitoring is
continued even after it is determined that said increase in load
torque of said vacuum pump per unit time has increased
abruptly.
4. The controller according to claim 1, wherein, when said increase
in load torque of said vacuum pump per unit time is greater than a
predetermined value, it is determined that said increase in load
torque of said vacuum pump per unit time has abruptly changed
upward and said deceleration control is carried out.
5. The controller according to claim 1, wherein, when a rate of
change in said increase in load torque of said vacuum pump per unit
time is greater than a predetermined value, it is determined that
said increase in load torque of said vacuum pump per unit time has
abruptly changed upward and said deceleration control is carried
out.
6. The controller according to claim 4, wherein said deceleration
control is carried out to reduce said increase in load torque of
said vacuum pump per unit time to a predetermined target value.
7. The controller according to claim 5, wherein said deceleration
control is carried out to reduce a rate of change in said increase
in load torque of said vacuum pump per unit time to a predetermined
target value.
8. The controller according to claim 1, wherein said electric motor
section is controlled in such a way that said load torque of said
vacuum pump does not exceed a predetermined upper limit.
9. The controller according to claim 1, wherein said electric motor
section includes a synchronous motor type or inductive motor type
brushless motor.
10. The controller according to claim 1, wherein a load-lock
chamber provided side-by-side with respect to a process chamber in
a semiconductor production apparatus is said space to be exhausted
by said vacuum pump.
11. The controller according to claim 1, wherein said increase in
load torque of said vacuum pump per unit time is monitored
repeatedly at a predetermined time interval, and that monitoring is
stopped after it is determined that said increase in load torque of
said vacuum pump per unit time has abruptly changed upward.
12. The controller according to claim 11, wherein a number of times
said deceleration control is repeated is restricted.
13. (canceled)
14. A method for controlling evacuation of a space to predetermined
degree of vacuum, the method comprising: using an electric motor to
drive a pump mechanism to evacuate the space; monitoring the load
torque of said vacuum pump per unit time; and when the load torque
abruptly changes upward, performing deceleration control to reduce
the rotational speed of said electric motor.
15. A controller of controlling evacuation a space to a
predetermined degree of vacuum, the controller comprising: a pump
mechanism section that performs evacuation and an electric motor
section for driving said pump mechanism section, wherein, when an
increase in load torque of said vacuum pump per unit time abruptly
changes upward, deceleration control to decrease a rotational speed
of said electric motor section is carried out.
16. The controller according to claim 15, wherein said load torque
of said vacuum pump is calculated based on a value of a current
supplied to said electric motor section.
17. The controller according to claim 15, wherein said increase in
load torque of said vacuum pump per unit time is monitored
repeatedly at a predetermined time interval and that monitoring is
continued even after it is determined that said increase in load
torque of said vacuum pump per unit time has increased
abruptly.
18. The controller according to claim 15, wherein, when said
increase in load torque of said vacuum pump per unit time is
greater than a predetermined value, it is determined that said
increase in load torque of said vacuum pump per unit time has
abruptly changed upward and said deceleration control is carried
out.
19. The controller according to claim 15, wherein, when a rate of
change in said increase in load torque of said vacuum pump per unit
time is greater than a predetermined value, it is determined that
said increase in load torque of said vacuum pump per unit time has
abruptly changed upward and said deceleration control is carried
out.
20. The controller according to claim 18, wherein said deceleration
control is carried out to reduce said increase in load torque of
said vacuum pump per unit time to a predetermined target value.
21. The controller according to claim 19, wherein said deceleration
control is carried out to reduce a rate of change in said increase
in load torque of said vacuum pump per unit time to a predetermined
target value.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a controller of a vacuum
pump having a pump mechanism section that performs evacuation to
set a space to be evacuated to a predetermined degree of vacuum,
and an electric motor section for driving the pump mechanism
section.
[0002] There is known a semiconductor production apparatus of a
type that has a load-lock chamber provided side-by-side with
respect to a process chamber that performs film deposition and
other processes to a wafer (substrate) as described in, for
example, Japanese Patent Laid-Open Publication No. 9-306972.
[0003] This apparatus performs wafer exchange between the process
chamber and the semiconductor production apparatus exterior via the
load-lock chamber. A vacuum pump that sets the load-lock chamber to
a predetermined degree of vacuum is connected via a valve to the
load-lock chamber. This valve is designed in such a way as to be
able to connect or disconnect the load-lock chamber to or from the
vacuum pump in terms of pressure when it is externally
manipulated.
[0004] Wafer exchange between the load-lock chamber and the process
chamber is carried out under a state where the load-lock chamber is
disconnected from the semiconductor production apparatus exterior
in terms of pressure, and is set to a predetermined degree of
vacuum by the vacuum pump. Wafer exchange between the load-lock
chamber and the semiconductor production apparatus, on the other
hand, is carried out under a state where the load-lock chamber is
disconnected from the process chamber in terms of pressure and is
set back to the atmospheric pressure.
[0005] Work efficiency in semiconductor production is improved by
performing film deposition and other processes in the process
chamber disconnected from the load-lock chamber in terms of
pressure while wafer exchange between the load-lock chamber and the
semiconductor production apparatus exterior is executed.
[0006] At the time of depressurizing the load-lock chamber under
atmospheric pressure to a predetermined degree of vacuum again, the
load-lock chamber is connected to the vacuum pump by setting the
valve to an open state from the closed state and then the load-lock
chamber is evacuated. At this time, in the case where the valve is
switched to the open state from the closed state while the vacuum
pump is driven, the pressure in the vacuum pump suddenly increases
to atmospheric pressure from the predetermined degree of vacuum,
abruptly increasing the pressure load (pressure load associated
with evacuation) of the vacuum pump. When an electric motor is used
as the drive source for the vacuum pump, the abrupt increase in
pressure load quickly increases the output torque of the electric
motor or the load torque of the vacuum pump.
[0007] One way to prevent the components of the vacuum pump from
being damaged by the sudden increase in load torque of the vacuum
pump is to control the electric motor using a controller in such a
way that the load torque of the vacuum pump does not exceed a
predetermined upper limit. The time charts in FIGS. 2(a) and 2(b)
show examples of the mode of the control. A broken line 91 in FIG.
2(a) indicates the drive frequency when a synchronous motor type
brushless motor is used as the electric motor. A broken line 92 in
FIG. 2(b) indicates the value of a current supplied to the electric
motor. The current value correlates with the size of the output
torque of the electric motor section or the load torque of the
vacuum pump.
[0008] When the valve is switched to the open state from the closed
state at time t1, as shown in FIGS. 2(a) and 2(b), the abrupt
increase in pressure load of the vacuum pump caused by the
switching rapidly increases the value of the current supplied to
the electric motor. That is, the load torque of the vacuum pump
rapidly increases.
[0009] When the controller determines that the current value of the
electric motor has reached a predetermined upper limit i2 at time
t2, it rapidly reduces the drive frequency of the electric motor
toward a drive frequency fmin on the low-speed side of the
rotational speed of the electric motor from a drive frequency fmax
on the high-speed side. The reduction in drive frequency lowers the
rotational speed of the electric motor, thereby suppressing an
increase in pressure load of the vacuum pump. This restricts the
output torque of the electric motor or the load torque of the
vacuum pump so that the torque does not exceed a predetermined
upper limit, i.e., the upper limit of a torque corresponding to the
upper limit i2 of the supply current.
[0010] Although the aforementioned control mode prevents the
components of the vacuum pump from being damaged by an excess
increase in load torque of the vacuum pump, a rapid rise in load
torque occurs when the closed state of the valve is switched to the
open state. At this time, an increased speed in load torque differs
significantly between the before and after time t1 at which the
rise has started, i.e., an abrupt upward change in the increased
speed of the load torque, and the state at which the increased
speed is great, continues until the current value of the electric
motor reaches the predetermined upper limit i2.
[0011] Even if the control mode prevents an excess increase in load
torque of the vacuum pump, therefore, the components of the vacuum
pump may be shocked significantly by an abrupt upward change in the
increased speed of the load torque or continuation of the state at
which the increased speed is great after the upward change. This
causes the components of the vacuum pump to be damaged.
[0012] To prevent the components of the vacuum pump from being
damaged, the components may be reinforced to be stronger. This
however, undesirably leads to enlargement and weight increase of
the vacuum pump.
[0013] Accordingly, it is an object of the present invention to
provide a controller of a vacuum pump that can improve the
durability of the vacuum pump without size enlargement or weight
increase that may originate from reinforcement of the vacuum
pump.
SUMMARY OF THE INVENTION
[0014] To achieve the objects, according to one aspect of the
invention, there is provided a controller of a vacuum pump, which
performs deceleration control to decrease the rotational speed of
an electric motor section when an increase in load torque of the
vacuum pump per unit time abruptly changes upward.
[0015] In the case where with the vacuum pump activating, the
outside air is led into the space to be evacuated so that the
pressure in the space rapidly rises, for example, as the pressure
torque of the vacuum pump (pressure load associated with
evacuation) increases, the output torque of the electric motor
section, i.e., the load torque of the vacuum pump tends to rise. In
this case, the increase in load torque of the vacuum pump per unit
time (increased speed of the load torque of the vacuum pump) may
change upward from the state where it is nearly zero to the state
where it exceeds a certain level. In other words, the increase in
load torque of the vacuum pump per unit time may rapidly change
upward.
[0016] The controller of the present invention performs
deceleration control to decrease the rotational speed of the
electric motor section when an increase in load torque of the
vacuum pump per unit time abruptly changes upward. This reduces
shocks applied to the components of the vacuum pump by the abrupt
upward change in the increase in load torque of the vacuum pump per
unit time or the continuous state where the increase in load torque
of the vacuum pump per unit time is large after the upward change
of the load torque when the load torque rises. It is therefore
unnecessary to reinforce the components of the vacuum pump in order
to improve the shock resistance, thereby preventing a
reinforcement-originated size increase or weight increase of the
vacuum pump.
[0017] According to this aspect of the invention, it is possible to
more accurately grasp how much the increase in load torque of the
vacuum pump per unit time has changed in a predetermined time, as
compared with the mode that carries out deceleration control based
on the increase in load torque of the vacuum pump per unit time. In
this specification, the "rate of change in the increase in load
torque of the vacuum pump per unit time" represents how much the
increase in load torque of the vacuum pump per unit time has
changed per unit time.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a schematic diagram of a semiconductor production
apparatus and a vacuum pump;
[0019] FIG. 2(a) is a time chart showing the drive frequency in an
electric motor section and FIG. 2(b) is a time chart showing the
current value in the electric motor section; and
[0020] FIGS. 3(a) and 3(b) show time charts in another embodiment,
FIG. 3(a) being a time chart showing the drive frequency in an
electric motor section, while FIG. 3(b) is a time chart showing the
current value in the electric motor section.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] One embodiment of the invention as embodied in a vacuum pump
for evacuating a load-lock chamber in a semiconductor production
apparatus is described below with reference to the accompanying
drawings.
[0022] As shown in FIG. 1, a process chamber 12 is provided
side-by-side with respect to a load-lock chamber 13 in a
semiconductor production apparatus 11. Deposition processes, such
as vacuum deposition or sputtering on a wafer, are carried out in
the process chamber 12. Those processes are executed after the
process chamber 12 is set to a predetermined degree of vacuum by
using an unillustrated evacuation system.
[0023] Wafer exchange between the exterior (atmospheric pressure
space) of the semiconductor production apparatus 11 and the process
chamber 12 is carried out via the load-lock chamber 13. That is, a
passage for exchanging a wafer at the time of wafer exchange is
provided between both chambers 12 and 13 and a gate valve 14 that
connects and disconnects both chambers 12 and 13 to and from each
other in terms of pressure is provided in that passage. Further,
the semiconductor production apparatus 11 is provided with a
passage for wafer exchange between the load-lock chamber 13 and the
exterior of the semiconductor production apparatus 11, and a gate
valve 15 that connects and disconnects the load-lock chamber 13 and
the exterior to and from each other in terms of pressure is
provided in that passage.
[0024] A vacuum pump 20 is connected to the semiconductor
production apparatus 11 via an exhaust passage 16. The vacuum pump
20 evacuates the load-lock chamber 13 as a space to be evacuated. A
first valve 17, which connects and disconnects the load-lock
chamber 13 and the vacuum pump 20 to and from each other in terms
of pressure when manipulated externally, is provided in the exhaust
passage 16.
[0025] The load-lock chamber 13 is communicated with the exterior
of the semiconductor production apparatus 11 via an outside-air
inlet passage 18. A second valve 19, which can connect and
disconnect the load-lock chamber 13 and the exterior to and from
each other in terms of pressure when manipulated externally, is
provided in the outside-air inlet passage 18.
[0026] The vacuum pump 20 has a pump mechanism section 21 that
evacuates the load-lock chamber 13 to set the chamber 13 to a
predetermined degree of vacuum and an electric motor section 22 for
driving the pump mechanism section 21. The electric motor section
22 is comprised of a synchronous motor type brushless motor,
specifically a brushless DC motor, and is driven by power supplied
from an inverter 30 that constitutes the controller. The rotational
speed of the electric motor section 22 is adjusted by adjusting the
drive frequency (rotational-speed instruction value) in the supply
current from the inverter 30.
[0027] In this embodiment, the electric motor section 22 is driven
by a steady voltage by the inverter 30 and the value of the supply
current to the electric motor section 22 correlates with the
magnitude of the output torque of the electric motor section 22,
i.e., the load torque of the vacuum pump 20.
[0028] The inverter 30 has an electronic control unit (ECU) 31
equipped with a microcomputer and a current detector 32. The ECU 31
and the current detector 32 constitute motor control means. The
current detector 32 detects the value of the supply current to the
electric motor section 22 and provides the ECU 31 with the detected
information. The current detector 32 constitutes detection means
that detects the value of the supply current to the electric motor
section 2. The ECU 31 adjusts the drive frequency in the supply
current to the electric motor section 22 based on the detected
information provided by the current detector 32.
[0029] The ECU 31 computes the output torque of the electric motor
section 22 or the load torque of the vacuum pump 20 based on the
detected information from the current detector 32, i.e., the value
of the supply current to the electric motor section 22. Based on
the load torque, the ECU 31 computes an increase in load torque of
the vacuum pump 20 per unit time (which hereinafter is referred to
as the increased speed of the load torque of the vacuum pump 20 for
the sake of convenience). The ECU 31 repeatedly monitors the
increased speed of the load torque of the vacuum pump 20 at a
predetermined time interval.
[0030] When the ECU 31 determines that the increased speed of the
load torque of the vacuum pump 20 is greater than a predetermined
value, the ECU 31 determines that there has been an abrupt upward
change in the increased speed of the load torque of the vacuum pump
20. Having made this decision, the ECU 31 changes the drive
frequency in the supply current to the electric motor section 22 to
the low-speed side of the rotational speed of the electric motor
section 22, i.e., reduces the drive frequency, in order to decrease
the increased speed of the load torque of the vacuum pump 20. This
control is referred to as deceleration control.
[0031] The ECU 31 keeps monitoring the increased speed of the load
torque of the vacuum pump 20 even after it has decided that the
increased speed of the load torque of the vacuum pump 20 abruptly
changed upward. More specifically, the ECU 31 in this embodiment
continuously and repeatedly performs the aforementioned speed
monitoring as long as the ECU 31 is in operation. When the ECU 31
decides through the monitoring that the increased speed of the load
torque of the vacuum pump 20 has abruptly changed upward, the ECU
31 executes the deceleration control and maintains the drive
frequency, which has been reduced by the control, until the next
timing at which it determines whether the increased speed is
greater than a predetermined value.
[0032] In the case where the ECU 31 has decided that the increased
speed of the load torque of the vacuum pump 20 abruptly changed
upward, the ECU 31 repeatedly executes the deceleration control
unless a process that has a priority over the deceleration control
is performed. One process that has a priority over the deceleration
control is a process of adjusting the value of the supply current
to the electric motor section 22 in such a way as not to exceed an
upper limit i2. This process will be discussed later.
[0033] The action of the vacuum pump 20 with the above-described
structure is discussed next referring to the time charts in FIGS.
2(a) and 2(b). A solid line 51 in FIG. 2(a) indicates the drive
frequency in the supply current to the electric motor section 22. A
solid line 52 in FIG. 2(b) indicates the value of the supply
current to the electric motor section 22 of this embodiment.
[0034] Work for wafer exchange between the process chamber 12 and
the load-lock chamber 13 is carried out under a state where the
load-lock chamber 13 is set to the same predetermined degree of
vacuum as the process chamber 12 by the vacuum pump 20 and the gate
valve 14 is open. At this time, the gate valve 15 and the second
valve 19 are closed.
[0035] Work for wafer exchange between the load-lock chamber 13 and
the outer space of the semiconductor production apparatus 11 is
carried out under a state where, with the gate valves 14 and 15
closed, the second valve 19 is opened to set the load-lock chamber
13 to the same pressure as that of the exterior space (atmospheric
pressure) and the gate valve 15 is then opened. At this time, the
first valve 17 is closed.
[0036] At the time the load-lock chamber 13 is set to a
predetermined degree of vacuum by the vacuum pump 20 after a wafer
is loaded into the load-lock chamber 13 for example, the first
valve 17 is opened with the vacuum pump 20 or the electric motor
section 22 driven, thereby starting evacuation of the load-lock
chamber 13. Time t1 in FIGS. 2(a) and 2(b) indicates the timing at
which the first valve 17 is opened, and until which the ECU 31 has
driven the electric motor section 22 with the drive frequency fmax
on the high-speed side of the rotational speed of the electric
motor section 22.
[0037] Before time t1, the first valve 17 is closed so that the
pressure load of the vacuum pump 20 associated with the evacuation
is nearly zero and the supply current to the electric motor section
22 reaches a minimum value i1.
[0038] As the first valve 17 is opened at time t1, the gas in the
load-lock chamber 13 under atmospheric pressure is rapidly led into
the pump mechanism section 21, thus quickly increasing the pressure
load of the vacuum pump 20. Accordingly, the output torque of the
electric motor section 22 or the load torque of the vacuum pump 20
rises. That is, the current value increases at time t1 in FIG.
2(b). At this time, the increased speed of the current value or the
increased speed of the load torque of the vacuum pump 20 changes
upward from zero to a non-zero increased speed. That is, as the
current value is constant before time t1, the increased speed of
the current value is zero.
[0039] The ECU 31 computes the increased speed of the load torque
of the vacuum pump 20 from the detected information from the
current detector 32. When the ECU 31 determines that the increased
speed is greater than a predetermined value, the ECU 31 decides
that an abrupt upward change has occurred in the increased speed of
the load torque of the vacuum pump 20. Based on the decision, the
ECU 31 reduces the rotational speed of the electric motor section
22 to decrease the increased speed of the electric motor section 22
to a predetermined target value, for example, the increased speed
of the load torque corresponding to a straight line 61 indicated by
the one-dot chain line in FIG. 2(b). In other words, the ECU 31
executes deceleration control on the electric motor section 22.
[0040] At this time, the ECU 31 repeatedly executes the
deceleration control to gradually reduce the drive frequency in the
supply current to the electric motor section 22. The gradual
reduction gradually lowers the rotational speed of the electric
motor section 22. That is, the drive frequency is gradually reduced
from the drive frequency fmax by the ECU 31 starting at time
t1.
[0041] The reduction in drive frequency lowers the rotational speed
of the electric motor section 22. The reduction in rotational speed
suppresses the tendency of the pressure load of the vacuum pump 20
to increase. This reduces the increased speed of the load torque of
the vacuum pump 20.
[0042] The ECU 31 adjusts the drive frequency in such a way that
the value of the supply current to the electric motor section 22
does not exceed the upper limit i2. This adjustment is carried out
by priority over the deceleration control. That is, when deciding
that the current value has reached the upper limit i2, the ECU 31
rapidly reduces the drive frequency of the electric motor section
22 from a drive frequency f1 at that time (time t3 in this
embodiment) toward the drive frequency fmin on the lower-speed
side.
[0043] The reduction in the rotational speed of the electric motor
section 22 based on the rapid decrease in drive frequency
suppresses the tendency of the output torque of the electric motor
section 22 to increase, i.e., the load torque of the vacuum pump
20, so that the torque does not exceed the upper limit
corresponding to the upper limit i2. Then, the ECU 31 adjusts the
drive frequency to keep as high as possible the rotational speed of
the electric motor section 22 to accomplish highly efficient
evacuation of the load-lock chamber 13 within the range where the
current value does not exceed the upper limit i2.
[0044] The upper limit i2 of the current value has been set to
prevent the components of the vacuum pump 20 from being damaged by
the output torque of the electric motor or the load torque of the
vacuum pump 20 from becoming excessively large.
[0045] When the pressure load of the vacuum pump 20 decreases due
to the depressurization of the load-lock chamber 13 by the vacuum
pump 20, the ECU 31 increases the drive frequency toward the drive
frequency fmax to make the rotational speed of the electric motor
section 22 as high as possible (between time t4 and time t5) within
the range where the current value does not exceed the upper limit
i2. At this time, the pressure load of the vacuum pump 20 is
decreased although the drive frequency is increased so that the
load torque (i.e., the current value) of the vacuum pump 20 shows a
tendency to decrease in the embodiment.
[0046] This embodiment can provide the following advantages.
[0047] (1) The ECU 31 performs deceleration control to decrease the
rotational speed of the electric motor section 22 when an increase
in load torque of the vacuum pump 20 abruptly changes upward. This
can reduce the increased speed at the time the load torque of the
vacuum pump 20 rises. It is therefore possible to reduce shocks
applied to the components of the vacuum pump 20 when the increased
speed of the load torque of the vacuum pump 20 abruptly changes
upward or in the state where the increased speed is high and
continues after the upward change. This eliminates the need to
reinforce the components of the vacuum pump 20 in order to improve
the shock resistance, thereby preventing enlargement and weight
increase of the vacuum pump 20 that would otherwise be originated
from the reinforcement.
[0048] (2) The ECU 31 computes the load torque of the vacuum pump
20 based on the value of the supply current to the electric motor
section 22. This makes it unnecessary to particularly provide a
torque sensor or another device to detect the load torque of the
vacuum pump 20. This leads to cost reduction and simplification of
the structure.
[0049] (3) The ECU 31 repeatedly monitors the increased speed of
the load torque of the vacuum pump 20 at a predetermined time
interval and keeps doing the monitoring even after it determines
that the increased speed of the load torque of the vacuum pump 20
has abruptly changed upward. Accordingly, the rotational speed of
the electric motor section 22 is controlled adequately according to
a change in the increased speed of the load torque of the vacuum
pump 20 even after the deceleration control has started.
[0050] (4) When the increase in load torque of the vacuum pump 20
is greater than a predetermined value, the ECU 31 decides that the
increased speed of the vacuum pump 20 has abruptly changed upward
and executes the deceleration control. This eliminates a process
for computing a difference in the increased speed of the load
torque of the vacuum pump 20 as compared with the mode that
compares, for example, the increased speed of the load torque of
the vacuum pump 20 at a predetermined time and the increased speed
at a predetermined time different from the former predetermined
time. That is, the arithmetic operation in the ECU 31 is made
simpler to reduce the load thereon.
[0051] In the time chart in FIG. 2(b), as the pressure load
associated with evacuation of the vacuum pump 20 is nearly constant
(nearly zero), the value of the increased speed of the load torque
of the vacuum pump 20 before time t1 at which the rise of the load
torque of the vacuum pump 20 has started becomes a constant value
(zero). In such a case, it is possible to accurately determine
whether the increased speed of the load torque has abruptly changed
upward or not by merely determining whether the increased speed of
the load torque is greater than a predetermined value or not. In
this case, therefore, it is possible to accurately determine
whether the increased speed of the load torque has abruptly changed
upward or not without calculating the difference in increased
speed.
[0052] (5) The ECU 31 carries out the deceleration control to
reduce the increased speed in load torque of the vacuum pump 20 to
a predetermined target value. This controls the increased speed of
the load torque of the vacuum pump 20 in such a way as to come
closer to or seek the predetermined target value. The control can
reduce the increased speed at the rising of the load torque of the
vacuum pump 20 greater than the increased speed in the prior
art.
[0053] (6) The ECU 31 controls the electric motor section 22 in
such a way that the load torque of the vacuum pump 20 does not
exceed a predetermined upper limit or the upper limit of the load
torque corresponding to the upper limit i2. Accordingly, the ECU 31
restricts the maximum value of the load torque that acts on the
vacuum pump 20, making it possible to prevent deformation, damage
or the like of the components of the vacuum pump 20 that originates
from an excess load torque.
[0054] (7) The deceleration control is performed by the ECU 31 by
changing the drive frequency in the supply current to the electric
motor section 22 toward the low-speed side of the rotational speed
of the electric motor section 22. The change in drive frequency
toward the low-speed side reduces the rotational speed of the
electric motor section 22, thereby decreasing the pressure load of
the vacuum pump 20. The reduction in pressure load lowers the
increased speed of the load torque of the vacuum pump 20.
[0055] (8) The electric motor section 22 is constructed by a
synchronous motor type brushless DC motor. This makes it easier to
enhance the durability of the electric motor section 22 as compared
with a motor with a brush. Further, the rotational speed of the
electric motor section 22 is adjusted by adjusting the drive
frequency in supply current regardless of the load torque that acts
on the vacuum pump 20.
[0056] (9) The load-lock chamber 13 is the relay point at the time
a work item is exchanged between the atmospheric pressure space
surrounding the semiconductor production apparatus 11 and the
process chamber 12. Therefore, the pressure in the load-lock
chamber 13 is frequently increased to atmospheric pressure from a
predetermined degree of vacuum. That is, a rapid increase in load
torque originating from a sudden increase in pressure load of the
vacuum pump 20 that evacuates the load-lock chamber 13 frequently
occurs in the vacuum pump 20. It is therefore particularly
effective to improve the durability of the vacuum pump 20 by using
the inverter 30 that has the motor control means of the embodiment
in such a mode.
[0057] The invention can also be applied in the following mode
without departing from the scope of the present invention.
[0058] In the illustrated embodiment, the ECU 31 is constructed in
such a way that when the ECU 31 decides that an increased speed in
load torque of the vacuum pump 20 is greater than a predetermined
value, the ECU 31 determines that the increased speed of the vacuum
pump 20 has abruptly changed upward and executes the deceleration
control to reduce the rotational speed of the electric motor
section 22. Instead of the control, the ECU 31 may compute the rate
of change in the increased speed of the load torque of the vacuum
pump 20 or the amount of change in increased speed per unit time
and may execute the deceleration control when deciding that the
computation result is greater than a predetermined value. This
modification allows the controller to accurately grasp how much the
increased speed of the load torque of the vacuum pump 20 has
changed in a predetermined time even when the increased speed of
the load torque of the vacuum pump 20 before time t1 is not
constant.
[0059] In this case, the ECU 31 computes, for example, the
difference between the increased speed of the load torque at the
current point of time and the increased speed of the load torque at
a predetermined time prior to the current time. When the ECU 31
determines that the computation result of subtracting the increased
speed of the load torque at a predetermined time prior to the
current time from the increased speed of the load torque at the
current time, i.e., the difference in the amounts of the increased
speed is greater than a predetermined value, the ECU 31 decides
that an abrupt upward change has occurred in the increased speed of
the load torque of the vacuum pump 20. Having made the decision,
the ECU 31 carries out the deceleration control to reduce the
increased speed of the load torque of the vacuum pump 20.
[0060] The increased speed of the load torque of the vacuum pump 20
need not show a tendency of linear increase over the entire period
from the time (time t1) at which the ECU 31 has started reducing
the drive frequency to the point at which the current value of the
electric motor section 22 reaches the upper limit i2. For example,
if the increased speed of the load torque starting at time t1 is
made smaller than that in the prior art, the increased speed of the
load torque may be made greater than that in the prior art until
the current value reaches the upper limit i2 thereafter. This makes
the time for the current value to reach the upper limit i2 shorter
than in the prior art while reducing the increased speed
immediately after a rise in the load torque of the vacuum pump 20
has started.
[0061] The ECU 31 may execute the deceleration control to reduce
the rate of change in increased speed of the load torque of the
vacuum pump 20 (the amount of a change in increased speed per unit
time) toward a predetermined target value. In this case, the
predetermined target value is, for example, the rate of change in
increased speed of the load torque corresponding to a curve 62
indicated by the one-dot chain line in FIG. 3(b). FIG. 3(a) is a
time chart showing the drive frequency in the electric motor
section 22 and FIG. 3(b) is a time chart showing the current value
in the electric motor section 22. A broken line 91 in FIG. 3(a),
like that in FIG. 2(a), indicates the drive frequency of the
electric motor in the prior art, and a broken line 92 in FIG. 3(b),
like that in FIG. 2(b), indicates the value of the current supplied
to the electric motor in the prior art.
[0062] According to the modification, the rate of change in
increased speed of the load torque of the vacuum pump 20 is
controlled in such a way as to come closer or coincide with the
predetermined target value. This control makes the increased speed,
at least at the time the load torque of the vacuum pump 20 has
started rising, smaller than the increased speed in the prior art.
Of shocks applied to the components of the vacuum pump 20,
therefore, the shock that is originated from the rate of change in
increased speed of the load torque of the vacuum pump 20 can be
made smaller.
[0063] Monitoring the increased speed of the load torque of the
vacuum pump 20 by the ECU 31 may be stopped either immediately
after the ECU 31 decides that the increased speed has abruptly
changed upward or after a predetermined time elapses from the time
at which the decision was made. This can reduce the burden on the
ECU 31 associated with the monitoring as compared with the case
where the ECU 31 continuously and repeatedly executes the
monitoring as long as the ECU 31 is in operation.
[0064] In this case, the number of times the deceleration control
is repeatedly executed by the ECU 31 may be restricted. This can
permit, for example, the rotational speed of the electric motor
section 22 to be more quickly returned to a high rotational speed
that ensures the high evacuation efficiency of the vacuum pump 20,
while making the shock applied to the components of the vacuum pump
20 smaller at the time the load torque of the vacuum pump 20
rises.
[0065] If a lower limit is set for the drive frequency of the
electric motor section 22 and the electric motor section 22 is
driven in such a way that the drive frequency does not go below the
lower limit, for example, the number of repetitive executions of
the deceleration control should not necessarily be restricted.
[0066] At the time of reducing the drive frequency of the electric
motor section 22, the drive frequency may be reduced rapidly, not
gradually, toward the drive frequency fmin from the drive frequency
fmax. Even in this case, it is possible to reduce the increased
speed at the time the load torque of the vacuum pump 20 rises.
[0067] The upper limit i2 of the supply current to the electric
motor section 22 may not be provided. That is, the maximum value of
the load torque of the vacuum pump 20 may not be limited.
[0068] The load torque of the vacuum pump 20 may be grasped from
other means than the value of the supply current to the electric
motor section 22 by, for example, providing a torque sensor to
detect the load torque of the vacuum pump 20.
[0069] The electric motor section 22 may be constituted by a
synchronous motor type brushless motor other than a brushless DC
motor. Examples of this motor are a reluctance synchronous motor, a
stepping motor, an inductor type synchronous motor, a permanent
magnet synchronous motor and a hysteresis synchronous motor. The
electric motor section 22 may be constituted by an inductive motor
type brushless motor or a brushless motor different from those
mentioned above. The electric motor section 22 may also be
constituted by a motor with a brush, such as a DC motor or a
universal motor.
[0070] The electric motor section 22 may be of a type in which
rotational speed can be adjusted by adjusting the voltage value of
the supply current to the electric motor section 22. In this case,
the voltage value is equivalent to a rotational speed instruction
value.
[0071] Although the vacuum pump 20 is provided for the load-lock
chamber 13 in the above-described embodiment, the vacuum pump 20
may be for the process chamber 12. The vacuum pump 20 may be used
for other apparatuses than the semiconductor production apparatus
11 as well.
[0072] Although the electric motor section 22 is the control target
in the embodiment in the case where the first valve 17 is opened
from the state where the load-lock chamber 13 is at atmospheric
pressure, the present invention is not limited to this particular
case. For instance, deceleration control of the electric motor
section 22 may be executed to reduce the increased speed of the
load torque of the vacuum pump 20 when the electric motor section
22 is activated. In the present invention, the increased speed of
the load torque of the vacuum pump 20 is not limited only to the
point at which the speed increases from the state of zero, but may
include the case where deceleration control of the electric motor
section 22 is executed to reduce the increased speed of the load
torque even at the time the increased speed becomes greater from a
speed higher than zero.
* * * * *