U.S. patent application number 11/853942 was filed with the patent office on 2008-03-13 for operation control device and method of vacuum pumps.
This patent application is currently assigned to ANEST IWATA CORPORATION. Invention is credited to Takamitsu Nakayama, Kazuaki Satoh.
Application Number | 20080063534 11/853942 |
Document ID | / |
Family ID | 38727514 |
Filed Date | 2008-03-13 |
United States Patent
Application |
20080063534 |
Kind Code |
A1 |
Nakayama; Takamitsu ; et
al. |
March 13, 2008 |
OPERATION CONTROL DEVICE AND METHOD OF VACUUM PUMPS
Abstract
An operation control devices and operation methods thereof so as
to eliminates the difficulties in such a case of introduction of
vacuum sensors and/or inverter control is disclosed. The disclosure
relates to a control of plural sets of vacuum pumps. In order to
comply with the subjects to overcome the difficulties, the
disclosure proposes to utilize current detection approach instead
of direct pressure detection approach, while showing how to
estimate a vacuum degree achieved under the operation of the pumps
as well as presenting a method on the control of the number of
pumps. It is also described how organically a current detecting
device, a vacuum degree estimating device, a working pump control
device and related methods to satisfy the subjects are linked. The
usefulness of the disclosure is also revealed.
Inventors: |
Nakayama; Takamitsu;
(Yokohama-city, JP) ; Satoh; Kazuaki;
(Yokohama-city, JP) |
Correspondence
Address: |
ROSSI, KIMMS & McDOWELL LLP.
P.O. BOX 826
ASHBURN
VA
20146-0826
US
|
Assignee: |
ANEST IWATA CORPORATION
Yokohama-shi
JP
|
Family ID: |
38727514 |
Appl. No.: |
11/853942 |
Filed: |
September 12, 2007 |
Current U.S.
Class: |
417/6 ;
417/44.11 |
Current CPC
Class: |
F04C 2240/403 20130101;
F04C 28/02 20130101; F04C 2270/56 20130101; F04C 28/06 20130101;
F04C 2270/07 20130101 |
Class at
Publication: |
417/6 ;
417/44.11 |
International
Class: |
F04B 49/06 20060101
F04B049/06; F04B 41/06 20060101 F04B041/06 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 12, 2006 |
JP |
JP2006-247398 |
Claims
1. An operation control device of plural vacuum pumps for
depressurizing gas inside at least one tank and/or chamber and so
on, comprising: a current detecting means which detects a current
flowing in a motor that drives the vacuum pumps; and a control
means which reduces the number of the vacuum pumps under operation,
while judging whether a target vacuum and/or substantially vacuum
condition is reached, based on the situation that a current value
detected by said current detection means converges within a
predetermined range.
2. The operation control device of claim 1, wherein the control
means further comprises a vacuum-degree-estimation means to judge
that a threshold criterion value is reached when a current value of
the motor under watch reaches the predetermined range, the
threshold criterion value being predetermined in advance of a
target-vacuum value and to conclude that said target-vacuum value
is reached in case when the current value stays within the
predetermined range for a predetermined span of time after the
threshold criterion value is reached; wherein when the
vacuum-degree-estimation means concludes that the threshold
criterion value or the target-vacuum value within the predetermined
range is reached, the number of the pumps under operation is
reduced.
3. The operation control device of claim 1, wherein the
target-vacuum value within the predetermined range is reset at a
lower value as an operation hours of the vacuum pumps is
accumulated.
4. The operation control device of claim 2, wherein the control
means further comprises a pump operation control means; which
designates one of the plural pumps as a pump under watch, stops at
least one pump other than the pump under watch when said
vacuum-degree-estimation means concludes, based on a current value
of the motor driving the pump under watch, that said threshold
criterion value or said target-vacuum value within the
predetermined range is reached and shifts the pump under watch
evenly one by one among the whole pumps.
5. The operation control device of claim 4, wherein in a case where
any one of the vacuum pumps is unable or difficult to be operated,
the operation of the pump unable or difficult to be operated is
skipped and the other next pump is designated as a pump under
watch.
6. An operation control method for plural vacuum pumps for
depressurizing a gas inside at least one tank and/or chamber,
comprising the steps of: detecting a current flowing into a motor
that drives the vacuum pumps; and reducing the number of the vacuum
pumps under operation, while judging whether a target vacuum and/or
substantially vacuum condition is reached, based on the situation
that a current value detected by said current detection means
converges within a predetermined range.
7. The operation control method of claim 6, further comprising the
steps of: designating one of the plural pumps as a pump under
watch; judging that a threshold criterion value is reached when a
current value of the motor under watch reaches the predetermined
range, the threshold criterion value being predetermined in advance
of a target-vacuum value; concluding that said target-vacuum value
is reached in case when the current value stays within the
predetermined range for a predetermined span of time after the
threshold criterion value is reached; stopping at least one pump
other than the pump under watch when it is concluded that said
threshold criterion value and/or said target-vacuum value within
the predetermined range is reached, based on a current value of the
motor driving the pump under watch; and shifting said pump under
watch evenly to the other next pump one by one among the whole
pumps.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an operation-control device
and an operation-control method of vacuum pumps such as a scroll
pump, a vane pump and the like, especially to a case where plural
set of vacuum pumps are provided.
[0003] 2. Description of the Related Art
[0004] In conventional operation-control methods for vacuum pumps
such as a scroll pump, a vane pump and the like, a frequency
control by an inverter is introduced and the speed of an AC motor
which drives a vacuum pump is controlled by using a signal of a
pressure-sensor detecting a pressure of gas inside a vacuum tank to
be depressurized. As for a pump load control by means of an
inverter, a prior art, for instance, such as JP-A-H9-4591/1997
(hereafter, referred to as a patent document 1) has been known.
[0005] As shown in FIG. 5, in the patent document 1 is illustrated
a control-step constitution, wherein the speed of an AC motor 04,
which drives a vacuum blower (vacuum pump) 03 connected to a vacuum
tank 01, is controlled by a frequency converter (inverter) 05, and
the speed is increased when the operation differential pressure of
the pump decreases and demand power goes down, while the speed is
decreased when the operation differential pressure of the pump
increases and demand power goes up; so that the input power poured
into the motor driving the pump is kept constant. Further, the
pressure P inside the vacuum tank 01 is detected for the estimation
of vacuum condition.
[0006] In the conventional operation-control approaches for the
vacuum pump as shown in the patent document 1, a pressure (vacuum)
sensor is used for estimating the vacuum condition, since the
vacuum condition in the tank 01 is detected as pressure P. In case
when dust and/or water droplets in the tank or the vacuum facility
room adhere to the probe of the sensor, it is afraid that the
signals are not accurate and unexpected failure may happen. Thus,
special sensors of a dust-free type and/or a waterproof type are
required in order to prevent the invasion of dust and/or water
droplet. Consequently, there arises a problem of cost increase as
to equipment and/or facility.
[0007] Furthermore, a speed control inverter always accompanies
electronic noise which causes undesirable problems to the
surrounding electrical/electric equipment if it is nearby the
inverter.
[0008] On the other hand, in case where a constant vacuum condition
is needed, for instance, in case where a highly depressurized
vacuum condition is required in a vacuum chamber of semiconductor
production devices, plural sets of vacuum pumps are provided. And
even when one of the pumps is out of service due to failure or
maintenance and exhaust ability is lessened, the remaining pumps
hold the predetermined required vacuum condition.
[0009] However, driving plural sets of pumps results in an increase
of power consumption and maintenance costs. Furthermore, providing
plural pumps may increase failure frequency of the pumps,
maintenance frequency of the pumps along with affiliated facility
and man-hours for repairing.
SUMMARY OF THE INVENTION
[0010] In view of the above-stated background, the present
invention is aiming at: eliminating the difficulties in such a case
of introduction of vacuum sensors and/or inverter speed control;
realizing the operation of plural vacuum pumps wherein the increase
of facility costs is restrained, the maintenance frequency is
reduced and the man-hour of repair work is lessened; and providing
an operation control device and an operation control method which
are compatible with the just-stated aims.
[0011] In order to resolve the problems mentioned above, the
present invention provides an operation control device of plural
vacuum pumps for depressurizing a gas inside at least one tank
and/or vacuum facility room and so on, including: a current
detecting means which detects a current flowing in a motor that
drives the vacuum pumps; and a control means which reduces the
number of the vacuum pumps actually under operation, while judging
whether a target vacuum or substantially vacuum condition is
reached, based on a situation that a current value detected by the
current detection means converges within a predetermined range.
[0012] According to the present invention, the current flowing in
the motor is detected, and it is judged that a target vacuum or
substantially target vacuum condition is realized when the current
value converges within a predetermined range. Therefore, it is not
necessary to provide with vacuum sensors for pressure detection of
a vacuum tank as conventionally used, so that equipment costs can
be restrained and a remarkable cost effectiveness can be obtained,
especially in case where special sensors of a dust-free type and/or
a waterproof type are required, depending on the service condition
as to a vacuum tank or a vacuum facility room.
[0013] Since the gas to be exhausted is reduced when a target
vacuum or substantially target vacuum condition is realized, it is
possible to hold the vacuum condition or to reach the target vacuum
condition without operation of an unnecessary pump. Therefore, it
becomes possible to decrease the number of plural working vacuum
pumps, to reduce the amount of power consumption as a result and to
prolong maintenance intervals by stopping the operation of an
unnecessary pump. In the control for operation and start/stop of
the pumps, speed control equipment such as inverters and the like
is not provided. Therefore, undesirable effect due to inverters on
surrounding equipment is avoidable.
[0014] According to another constitution of the present invention,
the control means of the operation control device further includes
a vacuum-degree-estimation means to judge that a threshold
criterion value is reached when a current value of the motor under
watch reaches the predetermined range, the threshold criterion
value being predetermined in advance of a target-vacuum value and
to conclude that said target-vacuum value is reached in case when
the current value stays within the predetermined range for a
predetermined span of time after the threshold criterion value is
reached; in which when the vacuum-degree-estimation means concludes
that the threshold criterion value or the target-vacuum value
within the predetermined range is reached, the number of the pumps
under operation is reduced.
[0015] The another constitution of the above mentioned makes it
possible to decrease the number of plural working vacuum pumps and
to reduce the amount of power consumption as a result, because the
target vacuum can be reached without large current after the
depressurized pressure reaches the threshold criterion value. In
addition, it is made possible that the number of pumps and the
amount of power consumption are reduced after surely estimating
that the target vacuum (negative pressure) is reached when the
detected current stays for a predetermined span of time in the
predetermined range.
[0016] According to another aspect of the present invention, the
target-vacuum value within the predetermined range is reset at a
lower value as the operation hours of the vacuum pumps are
prolonged.
[0017] By the above constitution, more accurate judgment on a
vacuum-degree-completion is carried out, while the operation hours
are taken into consideration. Here, the consideration is given in
such a manner that the aforementioned predetermined current range,
whereby the threshold-criterion value is regarded as reached, is
lowered in connection with operation hours. In addition, the reason
of this lowering is that a load demand for the vacuum pumps
decreases gradually in proportion to the accumulated operation
hours because of a running-in effect as to rotating and/or sliding
wear-elements.
[0018] Another aspect of the present invention is characterized in
that the operation control device includes a pump operation control
means, which designates one of the plural pumps as a pump under
watch, stops at least one of the pumps other than the pump under
watch when the vacuum-degree-estimation means concludes, based on a
current value of the motor driving the pump under watch, that the
threshold criterion value or the target-vacuum value within the
predetermined range is reached and shifts the pump under watch
evenly one by one among the whole pumps.
[0019] According to a method of the present invention of
controlling plural vacuum pumps, the method includes the steps of
designating a pump under watch, stopping the pumps other than the
pump under watch and shifting the pump under watch one by one among
the whole pumps; thereby such operation manner can be evaded that a
specific pump is always working, the other pumps are kept under
suspension, and the operation unevenness among the plural pumps is
incurred as a result. Therefore, plural pumps are evenly employed
and maintenance work for each pump is equalized. Thus, the increase
in efficiency of maintenance work can be promoted.
[0020] Another constitution of the present invention is
characterized in that, in a case where any one of the vacuum pumps
is unable or difficult to be operated, the operation of the pump
unable or difficult to be operated is skipped and the other next
pump is designated as a pump under watch.
[0021] The above constitution makes it possible to prevent
operation unevenness among the plural sets of the vacuum pumps,
since plural pumps are evenly employed and the operation hours of
each pump are equalized.
[0022] Another constitution of the present invention relates to an
operation control method for plural vacuum pumps for depressurizing
a gas inside at least one tank and/or chamber including the steps
of: detecting a current flowing in a motor that drives the vacuum
pumps; and reducing the number of the vacuum pumps actually under
operation, while judging whether a target vacuum and/or
substantially vacuum condition is reached, based on the situation
that a current value detected by the current detection means
converges within a predetermined range.
[0023] According to the above constitution, the current to each
motor which drives each corresponding vacuum pump is detected and
it is judged that the target-vacuum or the substantial
target-vacuum is realized when the current value converges within a
predetermined range, resulting in that conventionally applied
vacuum sensors for pressure detection of a vacuum tank or a vacuum
facility room can be omitted, and the above constitution also makes
it possible to restrain equipment costs and brings remarkable cost
effectiveness especially in case in which special sensors of a
dust-free type and/or a waterproof type are required, depending on
the service condition as to a vacuum tank or a vacuum facility
room.
[0024] Moreover, the above constitution makes it possible to
decrease the number of plural working vacuum pumps, to reduce the
amount of power consumption as a result and to prolong maintenance
intervals by stopping the operation of an unnecessary pump; since
the gas to be exhausted is reduced when a target vacuum or
substantially target vacuum condition is realized, it is possible
to hold the vacuum condition or to reach the target vacuum
condition without operation of an unnecessary pump. Still
furthermore, in the control for operation and start/stop of the
pumps, speed control equipment such as inverters and the like is
not necessary. Therefore, undesirable effects due to inverters on
surrounding equipment are avoidable.
[0025] In connection with the above, still another constitution of
the present invention can be given: an operation control method
including the steps of designating one of the plural pumps as a
pump under watch; judging that a threshold criterion value is
reached when a current value of the motor under watch reaches a
predetermined range, the threshold criterion value being
predetermined in advance of a target-vacuum value; concluding that
said target-vacuum value is reached in case when the current value
stays within the predetermined range for a predetermined span of
time after the threshold criterion value is reached; stopping at
least one pump other than the pump under watch when it is concluded
that the threshold criterion value and/or said target-vacuum value
within the predetermined range is reached, based on a current value
of the motor driving the pump under watch; shifting the pump under
watch evenly to the other next pump one by one among the whole
pumps.
[0026] According to the above described invention, it is made
possible to decrease the number of plural working vacuum pumps and
to reduce a power consumption as a result, because the target
vacuum can be reached without large current after the depressurized
pressure reaches the threshold criterion point value. In addition,
the number of pumps and the amount of the power consumption are
reduced after surely estimating that the target vacuum (negative
pressure) is realized when the detected current stays for a
predetermined span of time in the predetermined range.
[0027] Moreover, according to the above constitution, is evaded
disadvantage that the operation unevenness among the plural pumps
is incurred as a result of working a specific pump at all the times
and keeping the other pumps under suspension. Therefore, plural
pumps are evenly employed and maintenance work for each pump is
equalized. Thus, the increase in efficiency of maintenance work can
be promoted.
[0028] The present invention can provide an operation control
device and operation method thereof so as to eliminate the
difficulties in such a case of introduction of vacuum sensors
and/or inverter. In addition, by the operation of plural vacuum
pumps of the present invention, the increase of facility costs is
restrained, the maintenance frequency is reduced and the man-hour
of repair work is lessened.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The present invention will now be described in greater
detail with reference to the preferred embodiments of the invention
and the accompanying drawings, wherein:
[0030] FIG. 1 shows a whole constitution of the invention;
[0031] FIG. 2 is a figure sowing power (a current value)
characteristic of a vacuum pump;
[0032] FIG. 3 illustrates a time chart as to an exemplary
embodiment of the invention;
[0033] FIG. 4 illustrates a control flowchart as to an exemplary
embodiment of the invention; and
[0034] FIG. 5 illustrates a prior art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] Hereafter, the present invention will be described in detail
with reference to the embodiments shown in the figures. However,
the dimensions, materials, shape, the relative placement and so on
of a component described in these embodiments shall be only for
explanation and shall not be construed as limiting the scope of the
invention thereto, unless any specific mention is made of.
[0036] FIG. 1 shows a whole constitution of the invention, wherein
a vacuum tank 1 is depressurized by three vacuum pumps P.sub.A,
P.sub.B and P.sub.C. The vacuum pumps P.sub.A, P.sub.B and P.sub.C
are driven by motors M.sub.A, M.sub.B and M.sub.C, respectively.
There are placed electromagnetic open/close valves V.sub.A, V.sub.B
and V.sub.C between the vacuum tank 1 and each of the vacuum pumps
P.sub.A, P.sub.B and P.sub.C, respectively. Each of the vacuum
pumps P.sub.A, P.sub.B and P.sub.C is of a rotary displacement
(volumetric) type such as of a scroll type or of a vane type,
etc.
[0037] Each of the motors M.sub.A, M.sub.B and M.sub.C is supplied
with electricity from a power source 3. Since the speed control of
each of the motors M.sub.A, M.sub.B and M.sub.C is not performed,
an inverter or the like is not prepared. Incidentally, each of the
motors needs only to be an electric motor and the present invention
is applicable to both AC motor and DC motor. In addition, a
current-detecting means 5 detects the supplied current to each
motor.
[0038] A control means 7 controls the operation and start/stop of
the vacuum pumps P.sub.A, P.sub.B and P.sub.C. The control means 7
includes a vacuum-degree-estimation means 9 to judge whether the
current signal from the current-detecting means 5 reaches a
threshold criterion value S which is set beforehand a target-vacuum
value within a predetermined range and to judge whether the current
signal from the current-detecting means 5 converges to the target
vacuum (negative pressure) value with a predetermined span of time
after the current signal reaches a threshold criterion value S, and
a pump operation control means 11 to reduce the number of the pumps
under operation when the vacuum-degree-estimation means 9 concludes
that the threshold criterion value S or the target-vacuum value
within a predetermined range is reached.
[0039] In case of the pump of a rotary displacement (volumetric)
type such as of a scroll type or of a vane type, a power (current
value) characteristic curve is shown as such a curve as in FIG. 2,
wherein the curve includes a flat straight part and a
mountain-shaped part, thereby the flat straight part corresponds to
the current convergence by way of vacuum accomplishment and the
mountain-shaped part means a large variation of the current.
[0040] Just after a commencement of depressurization of the vacuum
tank 1, power (current value) is needed since the pumps have to
compress and exhaust a high-pressure gas. In due course of
depressurization process, the gas to be exhausted is disappears
substantially. Therefore, the required power (current value) is
lessened, while a negative pressure value in the vacuum tank
converges to a substantially constant value less than or equal to
10.sup.2 Pa to 10.sup.3 Pa.
[0041] By means of the aforementioned power (current)
characteristics in such that the current value converges to a
constant value P in connection with the depressurization process,
the vacuum-degree-estimation means 9 judges whether the detected
current reaches the aforementioned predetermined range from the
constant value P minus .alpha. to the constant value P plus
.alpha., where .alpha. is allowance made for the fluctuation of
measured values. The vacuum-degree-estimation means 9 also
estimates the time when the detected current enters the range,
namely, the time when the current reaches the aforementioned,
predetermined-threshold-criterion value S. Further, the
vacuum-degree-estimation means 9 concludes that the target vacuum
(negative pressure) is completed, if the current is held within the
range for a predetermined duration of time, for instance, several
minutes.
[0042] On the other hand, the above constant value P is scheduled
to be reset at a lower value as the operation hours of the vacuum
pump P.sub.A, P.sub.B or P.sub.C is accumulated. That is, the
setting value P at the time of commissioning of the pumps is
reduced to a value kP (P multiplied by a coefficient k) in such a
manner that kP=0.9P, kP=0.8P and so on, where k is a parameter
dependent of the operation hours of the vacuum pump P.sub.A,
P.sub.B or P.sub.C and k has a decreasing tendency in relation to
increased operation hours.
[0043] More specifically, since a load demand for the vacuum pumps
decreases gradually in proportion to the accumulated operation
hours because of a running-in effect as to rotating and/or sliding
wear-elements, a consideration for operation hours can give more
accurate judgment on a vacuum-degree-completion. In addition, the
consideration is given in such a manner that the aforementioned
predetermined current range, whereby the threshold-criterion value
S is regarded as reached, is lowered in connection with operation
hours.
[0044] Judgment on whether the depressurized pressure reaches the
threshold criterion value S, which is set beforehand the
target-vacuum value, or the target-vacuum value is made by
detecting the current to each of the motors M.sub.A, M.sub.B and
M.sub.C which drives each of the vacuum pumps P.sub.A, P.sub.B and
P.sub.C respectively. Therefore, the present invention can do
without conventionally applied vacuum sensors for pressure
detection of a vacuum tank and the present invention makes it
possible to restrain equipment costs and brings a remarkable cost
effectiveness especially in case in which special sensors of a
dust-free type and/or a waterproof type are required, depending on
the service condition as to a vacuum tank or a vacuum facility
room.
[0045] When the depressurized pressure reaches the threshold
criterion value S, which is set beforehand the target-vacuum value,
the target-vacuum can be realized without operation of an
unnecessary pump because the gas to be exhausted is reduced. When
the target vacuum has been realized, the vacuum state can be held
without operation of an unnecessary pump. Accordingly, it becomes
possible to decrease the number of plural working vacuum pumps, to
reduce the amount of power consumption as a result and to prolong
maintenance intervals by stopping the operation of an unnecessary
pump. In the control for operation and start/stop of the pumps,
speed control equipment such as inverters and the like is not
provided. Therefore, undesirable effects on surrounding equipment
due to inverters are avoidable.
[0046] In succession, with reference to the time chart of FIG. 3
and the flowchart of FIG. 4, the explanation will be given about
how the pump operation control means 11 reduces the number of the
pumps under operation when the vacuum-degree-estimation means 9
concludes that the depressurized pressure reaches the threshold
criterion value S.
[0047] As shown in FIG. 4, all the vacuum pumps P.sub.A, P.sub.B
and P.sub.C are under operation at the beginning (S1) and the
vacuum pump P.sub.A is chosen as a pump to be watched, and the
current I.sub.A thereof is monitored (S2). Whether the current
I.sub.A is within a range of
P-.alpha..ltoreq.|.sub.A.ltoreq.P+.alpha. is judged (S3) and, in
case in which the judgment is YES (affirmative), whether the
duration thereof is not less than a predetermined time span t.sub.0
is further judged (S4). If the judgment is YES (affirmative) in
succession, then the target-vacuum is regarded as realized and the
vacuum pumps P.sub.B and P.sub.C are stopped, while only the
operation of the pump P.sub.A is continued (S5).
[0048] It can be allowed to stop the vacuum pumps P B and P.sub.C,
without the judgment on whether the duration of the condition S4 is
not less than a predetermined time span to, when it is judged
whether the current I.sub.A is within a range of
P-.alpha..ltoreq.|.sub.A.ltoreq.P+.alpha. (S3) and the judgment is
YES (affirmative), namely, when the depressurized pressure reaches
the threshold criterion value S.
[0049] And while the monitoring of the current I.sub.A is
continued, whether I A exceeds P+.alpha. because of the
deterioration of the vacuum state is judged (S6). If the I A
becomes greater than P+.alpha., then all the vacuum pumps P.sub.A,
P.sub.B and P.sub.C are operated again (S7). In succession, the
pump to be monitored is shifted to the vacuum pumps P.sub.B(S8) and
the vacuum state is watched in such a manner that the current
I.sub.B for the pump P.sub.B is watched by the same approach as the
above-mentioned vacuum pump P.sub.A is watched. In case in which
the vacuum pump P.sub.B is designated as the pump to be monitored,
the pumps to be stopped are shifted to the pumps P.sub.A and
P.sub.C and the only pump to be operated is shifted to the pump
P.sub.B(S9).
[0050] In the next stage, the pump to be watched is shifted to the
vacuum pump P.sub.C (S10), and the vacuum state is monitored
watched in the same approach as the case where a vacuum pump
P.sub.A is used as a pump to be watched. In case where the vacuum
pump P.sub.C is designated as the pump to be watched, the pumps to
be stopped are shifted to the pumps P.sub.A and P.sub.B and the
only pump to be operated is shifted to the pump P.sub.C (S11).
[0051] Therefore, as shown in FIG. 4, a pump operation control
means 11 is constituted so that the control means 11 shifts a
control step by a control step in such a manner that a control step
A in the case where the vacuum pump P.sub.A is used as a pump to be
watched, a control step B in the case where the vacuum pump P.sub.B
is used as a pump to be watched, and a control step C in the case
where the vacuum pump P.sub.C is used as a pump to be watched.
[0052] A time chart of FIG. 3 shows the situation of the shifting,
namely, a shift-circulation. After the pump P.sub.A is started-up
as a first pump to be operated, the pumps P.sub.B and P.sub.C are
started with predetermined time-delays. And all the pumps are
placed under operation. The time delays are provided in order to
evade a large load, that is, an over-current due to the
simultaneous starting of plural pumps.
[0053] A mark L in FIG. 3 means a point of time when the threshold
criterion value S or the target-vacuum value is reached and the
pumps other than the pump under watch are stopped. A mark M means a
point of time when a detected current value goes out of the
aforementioned predetermined range and, therefore, the pumps under
suspension are now be restarted. The control action at the marks L
or M is repeated also in case when the pump under watch is the pump
P.sub.B or P.sub.C.
[0054] Moreover, in a case where any one of the vacuum pumps
P.sub.A, P.sub.B and P.sub.C is unable or difficult to be operated,
the operation of the pump unable or difficult to be operated is
skipped and the other next pump is designated as a pump to be
watched. For instance, when the pump P.sub.B is out of order or
under maintenance, the pump to be monitored is shifted from the
pump P.sub.A to the pump P.sub.C.
[0055] Furthermore, the electromagnetic open/close valves V.sub.A,
V.sub.B and V.sub.C are provided so as to hinder high pressure gas
from flowing-back inside the vacuum tank by the vacuum pumps
P.sub.A, P.sub.B and P.sub.C. The valve V.sub.A, V.sub.B or V.sub.C
is opened respectively after the vacuum pumps P.sub.A, P.sub.B or
P.sub.C starts running.
[0056] In addition, it is not always necessary to stop
simultaneously all the active pumps other than the pump under
watch. It can be allowed to stop the pumps one by one so as to
evade rapid change in pump-loads. Also, depending on the
vacuum-degree requirement, it can be allowed to stop some pumps out
of all the pumps other than the pump under watch.
[0057] In the above description on the embodiments, explanation has
been given based on an example of three pumps. It goes without
saying that the explanation stands in case of plural pumps such as
a case of two pumps, four pumps and/or more pumps.
[0058] As mentioned above, by a method of controlling plural vacuum
pumps, including the steps of designating a pump under watch,
stopping the pumps other than the pump under watch and shifting the
pump under watch one by one among the whole pumps, can be evaded a
disadvantage that the operation unevenness among the plural pumps
is incurred as a result of working a specific pump all the time and
keeping the other pumps under suspension. Therefore, plural pumps
are evenly employed and maintenance work for each pump is
equalized. Thus, the increase in efficiency of maintenance work can
be promoted.
[0059] The present invention eliminates the difficulties in such a
case of introduction of vacuum sensors and/or inverter control. In
addition, the present invention realizes the operation of plural
vacuum pumps wherein the increase of facility costs is restrained,
the maintenance frequency is reduced and the man-hour of repair
work is lessened. As a conclusion, the present invention can be
applicable to operation control devices and operation methods for
plural vacuum pumps.
* * * * *