U.S. patent application number 15/035893 was filed with the patent office on 2016-10-06 for control method for the accerlation of a vacuum pump, in which method the input current of the control device is limited.
The applicant listed for this patent is Oerlikon Leybold Vacuum GmbH. Invention is credited to Markus Liessmann.
Application Number | 20160290349 15/035893 |
Document ID | / |
Family ID | 51982534 |
Filed Date | 2016-10-06 |
United States Patent
Application |
20160290349 |
Kind Code |
A1 |
Liessmann; Markus |
October 6, 2016 |
CONTROL METHOD FOR THE ACCERLATION OF A VACUUM PUMP, IN WHICH
METHOD THE INPUT CURRENT OF THE CONTROL DEVICE IS LIMITED
Abstract
A control method for an acceleration of a vacuum pump, in
particular a turbomolecular pump, having an electric motor and a
control device in which, in a first acceleration phase, the input
current of the control device increases up to a maximum value
Is,max and, in a second acceleration phase, the control device is
operated at the maximum value Is,max of the input current.
Inventors: |
Liessmann; Markus;
(Dormagen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Oerlikon Leybold Vacuum GmbH |
Koeln |
|
DE |
|
|
Family ID: |
51982534 |
Appl. No.: |
15/035893 |
Filed: |
November 13, 2014 |
PCT Filed: |
November 13, 2014 |
PCT NO: |
PCT/EP2014/074517 |
371 Date: |
May 11, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04D 27/0261 20130101;
F04D 25/06 20130101; F04D 27/004 20130101; F04D 19/04 20130101;
H02P 6/20 20130101; H02P 23/009 20130101; F05D 2260/85
20130101 |
International
Class: |
F04D 27/00 20060101
F04D027/00; F04D 25/06 20060101 F04D025/06 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 14, 2013 |
DE |
10 2013 223 276.4 |
Claims
1. Control method for an acceleration of a vacuum pump, in
particular a turbomolecular pump, having an electric motor and a
control device, in which in a first acceleration phase, the input
current of the control device increases up to a maximum value
I.sub.s,max and in a second acceleration phase, the control device
is operated at the maximum value I.sub.s,max of the input
current.
2. Control method of claim 1, wherein the rated speed n.sub.max of
the vacuum pump is reached at the end of the second acceleration
phase.
3. Control method of claim 2, wherein the input current of the
control device decreases to an operating value after the second
acceleration phase.
4. Control method of one of claims 1 to 3, wherein, in the first
acceleration phase, the input current of the control device
increases, in particular in a constant manner, to the maximum value
I.sub.s,max.
5. Control method of claim 4, wherein the input current of the
control device reaches the maximum value I.sub.s,max at the end of
the first acceleration phase.
6. Control method of one of claims 1 to 5, wherein the motor
current is constant during the first acceleration phase, the motor
current in particular having a constant maximum value
I.sub.s,max.
7. Control method of one of claims 1 to 6, wherein the motor
current decreases during the second acceleration phase.
8. Control method of one of claims 1 to 7, wherein the motor
current decreases to an operating value after the second
acceleration phase.
9. Control method of one of claims 1 to 8, wherein the rotational
speed of the vacuum pump increases in the first acceleration phase
and in the second acceleration phase.
10. Control method of claim 9, wherein the rotational speed of the
vacuum pump increases faster in the first acceleration phase than
in the second acceleration phase.
Description
[0001] The invention relates to a control method for the
acceleration of a vacuum pump, in particular a turbomolecular
pump.
[0002] Vacuum pumps, such as turbomolecular pumps, have a rotatably
supported rotor shaft in a pump housing. The rotor shaft carries at
least one rotor that in the case of turbomolecular pumps comprises
a plurality of rotor discs. The rotor cooperates with a stator
which in the case of a turbomolecular pump is a stator with a
plurality of stator discs, with the stator discs being arranged
between the rotor discs. The rotor shaft is driven by an electric
motor that usually is arranged directly on the rotor shaft.
Further, a control device is provided that is arranged either
inside or outside the pump housing and that controls the vacuum
pump according to different operating parameters.
[0003] A particularly critical moment is the control of the
acceleration of the vacuum pump. Here, the pump is run from
standstill or a very low rotational speed to the rated speed or the
operating speed at which the vacuum pump has the maximum output.
Such an acceleration of a pump is often required in particular in
dynamic processes. In known pumps, in particular turbomolecular
pumps, a maximum current is allowed at the electric motor during
acceleration. This maximum current is constant during acceleration
until the rated speed of the vacuum pump is reached. When the
vacuum pump is operated at the rated speed, the motor current
decreases to an operating value. The same may vary depending on the
quantity of gas to be conveyed and on the type of gas, but does not
reach the maximum value reached during acceleration.
[0004] At times there is a demand to provide smaller, less powerful
power supply unit for the vacuum pump. These are power supply units
which, different from conventional power supply units, are not
designed for the nominal power of the pump, but have a lower
nominal power. In an attempt to meet this demand for smaller power
supply units it is known to reduce the maximum current of the
electric motor allowable during acceleration. It may well be
possible to thereby use smaller power supply units, but the
acceleration time until the rated speed of the vacuum pump is
reached becomes longer.
[0005] It is an object of the present invention to possibly reduce
the increase in acceleration time also when power supply units are
used that have a lower nominal power than the pump or the pump
electronics, or to reduce the acceleration time when high-capacity
power supply units are used.
[0006] The object is achieved according to the invention with the
features of claim 1.
[0007] The present control method for the acceleration of a vacuum
pump, in particular a turbomolecular pump, is based on the insight
that the motor current is not the essential critical parameter with
respect to a demanded downsizing of the power supply unit or a
shortening of the acceleration time. The motor has to be designed
in particular with regard to mechanical conditions. As a result a
maximum allowable motor current is usually reached neither during
acceleration, nor during the operation of the vacuum pump. Tests
have shown that the essential pertinent parameter is the input
current of the control device.
[0008] According to the control method of the present invention the
input current of the control device is limited to a maximum value
during a first acceleration phase. Thus, in the first acceleration
phase, the input current rises to the maximum value. Thereafter, in
a second acceleration phase, the control device is operated at the
maximum value of the input current, wherein the rated speed of the
vacuum pump is reached in particular at the end of the second
acceleration phase. In such a control method, the technically
allowable maximum current of the motor is not exceeded. As such,
when a smaller power supply unit is used, the acceleration time can
be reduced compared to a limitation of the motor current.
Similarly, when a high-capacity power supply unit is used, the
acceleration can be shortened.
[0009] It is preferred that the input current drops to an operating
value in the control device after the second acceleration phase has
been run through. An overload of the control device will thus not
occur in normal operation even for varying types of gas or
quantities of gas.
[0010] Further, it is preferred that the input current of the
control device rises in the first acceleration phase. In
particular, this is an increase to the predefined maximum value,
wherein this increase is in particular constant. Preferably the
input current of the control device thus reaches its maximum value
at the end of the first acceleration phase.
[0011] It is further preferred that the motor current is constant
in the first acceleration phase. In particular, this is a maximum
value of the motor current that is not exceeded during operation.
However, this does not have to be the maximum allowable motor
current. The same may possibly even higher, as long as this is
allowable in view of mechanical conditions. Preferably the motor
current decreases during the second acceleration phase. The
decrease in motor current during the second acceleration phase
preferably corresponds to an e-function. During the operation
following the second acceleration phase, the motor current drops to
an operating value. The same may vary in particular in dependence
on the type and quantity of the gas conveyed, but is always lower
than the maximum current applied during the first acceleration
phase.
[0012] The rotational speed of the vacuum pump preferably rises
during both acceleration phases. Preferably the rotational speed
increases faster or steeper in the first phase than in the second
acceleration phase. Preferably the increase in rotational speed is
linear in the first acceleration phase. In the second acceleration
phase the increase in rotational speed preferably follows an
e-function.
[0013] Preferably there is a marginal condition during the control
method of the present invention that the system capacity is always
lower than the motor capacity.
[0014] Tests have shown that in a vacuum pump without reduction of
the motor current, i.e. in a method according to common prior art,
the input current of the control device rises to maximally 7.3 A,
while the motor current reaches a maximum value of 7.8 A. The
acceleration time to the maximum rotational speed of the vacuum
pump is 350 s in this case.
[0015] If, as is further known from prior art, the maximum
allowable motor current is reduced to 2.8 A, due to a demand for a
use of a power supply unit with a lower rated power, the maximum
input current also decreases to 2.4 A. However, the acceleration
time is extended to 1244 s.
[0016] An exemplary test has shown that, if the control method of
the present invention is used, the acceleration time can be reduced
drastically to 628 s. Here, the maximum input current of the
control device is 2.5 A and the maximum motor current is 2.8 A.
[0017] The following is a detailed explanation of the invention
with reference to different graphs in comparison with prior
art.
[0018] In the Figures:
[0019] FIG. 1 is a graph showing acceleration according to prior
art at maximum motor current,
[0020] FIG. 2 is a diagram showing acceleration according to prior
art at reduced motor current,
[0021] FIG. 3 is a diagram showing an acceleration according to a
preferred embodiment of the control method of the present
invention.
[0022] FIG. 1 illustrates a control method according to prior art
which allows a maximum motor current I.sub.M,max. At the beginning
of the acceleration the motor current represented by a solid line
increases to I.sub.M,max at a time t.sub.1. The motor current is
then kept constant until a time t.sub.3. At this time, the
rotational speed of the vacuum pump represented by a dotted line
has reached the rated speed. Up to a time t.sub.6 the vacuum pump
then runs in normal operation, where fluctuations in the quantity
of gas or the type of gas conveyed may possibly occur. This results
in variations of the motor current. Further, FIG. 1 shows the
course of the input current in a dashed line. The input current of
the control device increases continuously from the start of
acceleration t.sub.1 and, similar to the motor current, varies
during operation between the times t.sub.3 and t.sub.6 in
dependence on the type of gas and the quantity of gas conveyed, for
example.
[0023] For a downsizing of the power supply unit, it is known to
reduce the motor current. This is schematically illustrated in FIG.
2, with the motor current reduced to I.sub.M,red. At a time t.sub.1
the motor current thus rises to I.sub.M,red and is kept on that
value until the vacuum pump has reached its rated speed. Due to the
reduction of the motor current, the rated speed n.sub.max is
reached only at the time t.sub.5. Between the times t.sub.5 and
t.sub.6, the operation in which the motor current may vary is again
shown schematically. Corresponding to the operation at maximum
motor current, the input current of the control unit illustrated as
a dashed line rises continuously from t.sub.1 to t.sub.5, with the
motor current being reduced to I.sub.M,red, and then varies during
operation between t.sub.5 and t.sub.6.
[0024] In particular, it is also evident from the graphs in FIG. 1
and FIG. 2 that the input current of the control device does not
exceed the current of the motor. Since it has further been found
that, possibly due to mechanical requirements to be met by the
motor, a maximum allowable current in the motor is higher than the
current I.sub.M,max, the control method of the present invention as
schematically illustrated in FIG. 3 has been developed. Here, the
acceleration was divided in two phases. The first phase is the
period t.sub.1 to t.sub.2 and the second acceleration phase is
t.sub.2 to t.sub.4. According to the invention, in a first
acceleration phase, the input current of the control device, which
is shown as a dashed line, is limited to an input current
I.sub.S,max. In the first acceleration phase, i.e. up to the time
t.sub.2, the input current of the control means constantly rises up
to the predetermined maximum value I.sub.S,max. During this first
acceleration phase the rotational speed also rises continuously,
but does not yet reach the rated speed n.sub.max. The motor current
I.sub.m is constant during this first phase.
[0025] In the second phase the input current of the control device
is limited to the maximum value I.sub.S,max. This causes a further,
although slower rise in the rotational speed of the vacuum pump
until the rated speed n.sub.max is reached. The rise in the rated
speed follows an e-function. Tests have shown that, as is also
evident from the schematic graphs, the acceleration time can be
reduced to the time, when the rated speed n.sub.max is reached. The
maximum speed is reached at a time t.sub.4. This time is earlier
than the time t.sub.6 (FIG. 2) when the maximum motor current is
reduced. In normal operation between the times t.sub.4 and t.sub.6
the rated speed remains constant and the input current of the
control device can vary.
[0026] In the second acceleration phase, i.e. between the times
t.sub.2 and t.sub.4, declines in particular corresponding to an
e-function and varies during operation between the times t.sub.4
and t.sub.6, if for example the type of gas or the quantity of gas
changes.
[0027] The method of the present invention has been described above
with reference to the demand for the use of a smaller power supply
unit. As has been explained, in particular with reference to FIG.
3, the use of a smaller power supply unit makes it possible to
reduce the acceleration time with respect to the acceleration time
achieved when the motor current s reduced.
[0028] Correspondingly, when conventional power supply units are
used, the method of the present invention can also be used to
reduce the acceleration time as compared to the acceleration time
illustrated in FIG. 1.
* * * * *