U.S. patent application number 17/594433 was filed with the patent office on 2022-06-16 for method for preventing vibration in pumps.
The applicant listed for this patent is KSB SE & Co. KGaA. Invention is credited to Martin ECKL, Joachim SCHULLERER.
Application Number | 20220186749 17/594433 |
Document ID | / |
Family ID | |
Filed Date | 2022-06-16 |
United States Patent
Application |
20220186749 |
Kind Code |
A1 |
ECKL; Martin ; et
al. |
June 16, 2022 |
Method for Preventing Vibration in Pumps
Abstract
A method for preventing or reducing mechanical vibrations of a
pump, in particular a centrifugal pump, during pump operation is
provided. A pump controller detects at least one signal of a pump
operation parameter and identifies signal fluctuations in order to
detect mechanical vibrations occurring in the pump. The pump
controller controls the frequency converter to modify the pump
speed in order to reduce a detected pump vibration.
Inventors: |
ECKL; Martin; (Frankenthal,
DE) ; SCHULLERER; Joachim; (Rheinzabern, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KSB SE & Co. KGaA |
Frankenthal |
|
DE |
|
|
Appl. No.: |
17/594433 |
Filed: |
April 14, 2020 |
PCT Filed: |
April 14, 2020 |
PCT NO: |
PCT/EP2020/060432 |
371 Date: |
October 15, 2021 |
International
Class: |
F04D 29/66 20060101
F04D029/66; F04D 15/00 20060101 F04D015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 18, 2019 |
DE |
10 2019 002 826.0 |
Claims
1-12. (canceled)
13. A method for preventing or reducing mechanical vibrations of a
pump having a frequency converter and a pump controller, comprising
the steps of: detecting with the pump controller at least one
signal of a pump operating parameter; analyzing with the pump
controller the at least one signal to identify signal oscillations
characteristic of mechanical vibrations of the pump; and changing
the pump revolution rate by the pump controller controlling the
frequency converter to reduce the mechanical vibrations of the
pump.
14. The method as claimed in claim 13, wherein the step of
analyzing the at least one signal includes calculation of a
frequency spectrum of the at least one signal by Fast Fourier
Transformation.
15. The method as claimed in claim 14, wherein at least one signal
of the at least one signal corresponds to a motor current of a pump
drive.
16. The method as claimed in claim 14, wherein at least one signal
of the at least one signal corresponds to a hydraulic final
pressure of the pump, and the hydraulic final pressure is
determined by one of both of a pressure sensor and an estimate of
an operating point of the pump.
17. The method as claimed in claim 14, wherein the step of changing
the pump revolution rate includes iteratively varying pump
revolution rate to identify a pump revolution rate at which an
amplitude of the frequency spectrum is at a minimum.
18. The method as claimed in claim 17, wherein the pump revolution
rate is iteratively varied within a predefined tolerance range.
19. The method as claimed in claim 17, wherein the pump revolution
rate is iteratively varied to identify at least one anti-resonance
of the pump, and the step of changing the pump revolution rate
includes operating the pump at the at least one antiresonance of
the pump.
20. The method according to claim 17, wherein the pump revolution
rate is varied by one or both of an interval halving method and an
optimization method.
21. The method according to claim 17, wherein the pump revolution
rate is varied by one or more of an active set method, a Newton
method, and a genetic algorithm.
22. The method as claimed in claim 14, further comprising the steps
of: storing the calculated frequency spectrum, comparing
subsequently calculated frequency spectrums to identify frequency
spectrum changes corresponding to changes in pump resonance
vibrations.
23. The method as claimed in claim 22, further comprising the step
of: outputting a signal in the event of an identified change in
pump resonance vibrations indicating one of both of pump wear and
damage to the pump structure.
24. A pump arrangement, comprising: a pump; a frequency converter;
and a pump controller, wherein the pump controller is configured to
receive at least one signal of a pump operating parameter, analyze
the at least one signal to identify signal oscillations
characteristic of mechanical vibrations of the pump, and control
the frequency converter to change the pump revolution rate to
reduce the mechanical vibrations of the pump.
25. The pump arrangement as claimed in claim 24, wherein the pump
is a centrifugal pump.
26. The pump arrangement as claimed in claim 25, wherein the
centrifugal pump is a waste water pump, solids pump or supply pump.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
[0001] The invention relates to a method for preventing or reducing
mechanical vibrations during the operation of a pump, in particular
a centrifugal pump.
[0002] Mechanical vibrations in centrifugal pumps lead to increased
wear and tear and unwanted noise during operation. The causes of
vibrations can be manifold. Causes can be externally excited
vibrations, for example due to the rotation of the pump impeller,
or free vibrations due to the natural frequencies of the built-in
pump.
[0003] Free vibrations occur especially in solid pumps. Solid pumps
are centrifugal pumps for the transport of pumped media with
strongly abrasive solid parts, for example, suspensions of slag,
coal or ore in mining. Occasionally, the pumped medium may also
contain stones or other rigid elements which, when hitting the pump
structure, may produce shocks during pump operation which cause the
free vibrations of the pump to be excited. This effect also occurs
increasingly in pumps for the waste water sector.
[0004] A particularly unfavorable case occurs if the rotational
frequency of the impeller, i.e. the set pump revolution rate,
equals the natural frequency of the built-in pump or corresponds to
an integer multiple of the natural frequency. In this case,
resonance vibrations occur, i.e. the two causes of vibration
mutually amplify each other. It is similarly problematic when the
set rotational frequency of the impeller coincides with the
pipeline resonance of the conveying system.
[0005] Such a resonance case is exemplified in FIG. 1. This figure
shows the frequency response of a ready-to-use built-in centrifugal
pump. The natural frequencies at which the system oscillates freely
have the frequency values f.sub.1, f.sub.2, f.sub.3. The frequency
response, i.e. the position of the natural frequencies f.sub.1,
f.sub.2, f.sub.3, depends on the specific pump structure, the
selected installation position, the materials used and the
installed bearings. If the rotational frequency of the pump wheel
which is set by means of the frequency converter is identical to or
is instead an integer multiple of one of the natural frequencies
f.sub.1, f.sub.2, shown, the system is excited by the externally
excited rotation of the impeller and an amplified resonance
vibration of the pump occurs. If the rotational frequency of the
impeller is instead in the range of one of the anti-resonances
drawn here af.sub.1, af.sub.2, this effect is minimal and there is
no vibration or only a very small vibration.
[0006] The idea of the present application builds on the above
knowledge and proposes a method, which by targeted measures during
the operation of the pump reduces the risk of the occurrence of
possible vibrations, especially resonances, to a minimum.
[0007] This object is achieved by a method according to the
features of claim 1. Advantageous embodiments are the subject of
the dependent claims.
[0008] For the implementation of the method, the use of a frequency
converter for changing the revolution rate of the pump is decisive.
However, it does not matter whether such a frequency converter is
integrated into the pump, attached to the pump housing or installed
separately from the pump. The same applies to the pump controller
for the implementation of the method, which may be an integral part
of the pump, but also may be installed as a separate unit to the
pump, optionally in conjunction with a separate frequency
converter.
[0009] The solution according to the invention of the present
application consists in varying the revolution rate by a pump
controller for a pump with a frequency converter during the
operation of the pump in such a way that mechanical vibrations of
the pump are reduced as optimally as possible. Another core aspect
of the invention also consists of the pump independently
identifying its existing natural frequencies during operation by
means of suitable signal evaluation in order to be able to
optimally adapt the set pump revolution rate based on this
knowledge.
[0010] The pump therefore does not need information about its
frequency response which has already been generated in advance and
stored in the pump but can instead determine this independently
during operation. For this purpose, the pump records a signal
during pump operation which characterizes a pump operating
parameter, which is influenced by occurring mechanical vibrations.
The recorded signal is subsequently investigated by the pump for
the presence of any vibrations, in particular resonance vibrations.
Such a vibration is subsequently reduced by a suitable revolution
rate change.
[0011] In the recorded signal, in particular signal fluctuations
can be identified which are caused by mechanical vibrations of the
pump. The amplitude of the identified oscillation frequency(ies) of
the signal is reduced by a matching change of revolution rate.
According to the advantageous embodiment of the method, therefore,
the frequency spectrum of the recorded signal is considered. It is
advantageous if the signal is first transformed into its frequency
spectrum by means of transformation, in particular by means of a
Fast Fourier Transformation, so as to identify the corresponding
frequency values and associated amplitudes of occurring signal
vibrations.
[0012] The motor current or currents of the pump drive proves to be
a suitable operating signal for the identification of any
vibrations. The current values are available to the frequency
converter used anyway, so that no further sensors are required.
Since mechanical vibrations of the pump system are also reflected
by magnetic induction in the motor windings of the pump drive and
accordingly in the current of the motor, the motor therefore acts
as an effective sensor that can be available at any time. By
appropriate current analysis, mechanical vibrations of the pump
system can be identified with sufficient accuracy. This possibility
exists independently of the motor type of the electric pump drive
used.
[0013] As an alternative or additional operating parameter for the
determination of the frequency-response of the pump, the pump
pressure is suitable, for example, in particular the final pressure
of the pump. Here, too, mechanical vibrations are reflected in the
signal profile. The final pressure of the pump can be determined,
for example, by means of existing pressure sensors and can be
transformed into its frequency spectrum by signal transformations,
in particular a Fast Fourier Transformation.
[0014] For the signal acquisition, however, a suitable sensor does
not necessarily have to be kept available. Alternatively, for
example. the current pump pressure can be determined mathematically
by means of operating point estimation. A possible method for this
is disclosed in DE102018200651, the content of which is fully
included at this point.
[0015] According to a possible embodiment, the method can be
carried out iteratively with varying pump revolution rate, for
example, to identify that pump revolution rate at which the
amplitude of an identified vibration is as minimal as possible. The
pump thus analyzes the frequency spectrum of the repeatedly
recorded signal again after the change of revolution rate and
checks whether the variation of the revolution rate has led to a
decrease in the corresponding amplitude.
[0016] The iterative implementation of the steps of the method can
provide an arbitrary or random or else controlled change of
revolution rate. If the amplitude increases, for example, then the
change of revolution rate carried out between two iterations is
reversed, otherwise it is retained. It is also conceivable to drive
continuously through a certain full range of revolution rates and
subsequently set the revolution rate with the lowest amplitude for
pump operation.
[0017] An alternative is the use of suitable methods and algorithms
for identifying a local or global amplitude minimum with the
associated revolution rate. An interval halving method and/or an
optimization method are conceivable, such as an active-set method
and/or a Newton method, to determine as quickly as possible the
appropriate revolution rate which leads to an amplitude minimum. A
genetic algorithm is also conceivable which, although comparatively
slow, enables the identification of a global minimum frequency
response.
[0018] The setting of the revolution rate or the variation thereof
during the iterations of the method also depends on which operating
conditions are predetermined, for example by the pump operator. It
is conceivable, for example, that the pump operator specifies a
constant pump revolution rate or specifies only a small tolerance
range for revolution rate changes. During the iterations of the
method, a revolution rate variation is then carried out only within
the previously defined tolerance range. In such a case, an
iterative implementation of the method is usually sufficient, in
which all or at least some of the permitted revolution rates are
operated at to determine the corresponding amplitude minimum for
this range.
[0019] If, on the other hand, no specification has been made by the
operator for a permissible revolution rate range, i.e. it can
instead be the full, technically possible revolution rate range of
the pump, it is expedient if the method uses one of the
aforementioned methods for identifying the appropriate revolution
rate.
[0020] According to a further advantageous embodiment of the
invention, however, the method can not only serve to reduce
occurring vibrations, but the determination according to the
invention of the frequency response is also suitable for pump
monitoring, for example, to detect wear or any damage to the pump
mechanism at an early stage. As has already been explained in
detail above, a core aspect of the invention is to determine the
frequency response of the pump. This depends essentially on the
pump design, its installation position, the materials used and the
installed bearing components. A change in one of these factors, for
example due to wear or material damage, leads to a change of the
frequency response of the pump. The pump therefore preferably
stores the determined frequency response and monitors this by
running repeating measurements for frequency shifts of the
identified relevant frequencies. If such a frequency deviation is
detected, this is an indication of wear and tear or of pump damage.
The pump can then produce a corresponding warning message or carry
out an appropriate measure.
[0021] Further investigation of the frequency change can also
distinguish between wear and damage. Usually wear leads to a
creeping change in the frequency response, while pump damage, for
example bearing damage or impeller breakage, results in a sudden
change in frequency response. The pump therefore takes into account
in its evaluation the time-related component of the detected change
to differentiate between wear and damage. The degree of change can
also be included.
[0022] In addition to the method according to the invention, the
present invention also relates to a pump, preferably a centrifugal
pump, particularly preferably a waste water pump or a solids pump
or a supply pump, with an internal or external frequency converter
and an internal or external pump controller for carrying out the
method according to the invention. Accordingly, such a pump is
characterized by the same advantages and properties as have already
been explained in detail above based on the method according to the
invention. A repeated description is omitted for this reason.
[0023] In addition, the use according to the invention of a pump,
in particular a centrifugal pump, as a waste water pump, a solids
pump or a supply pump is proposed by the application. The
minimization according to the invention of occurring mechanical
vibrations is especially important for waste water pumps or solids
pumps, so that the application of the method according to the
invention in such pump types brings far-reaching advantages.
[0024] Further advantages and properties of the invention are to be
explained in more detail below on the basis of an exemplary
embodiment shown in the figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1: shows a possible frequency response of an installed
and operational centrifugal pump,
[0026] FIG. 2: shows a time diagram of a periodic signal and
[0027] FIG. 3: shows the calculated frequency spectrum of the time
signal from FIG. 2.
DETAILED DESCRIPTION
[0028] The invention according to the present application describes
a method for the targeted prevention of undesirable vibration
amplifications in the resonant case during the operation of a pump,
in particular a solids pump, a waste water pump or another supply
pump, by means of a frequency converter. The foundation for the
targeted prevention of these resonant vibrations is that such
resonance cases must initially be detected by the pump controller,
but preferably without having to retrofit the pump with a special
sensor system such as accelerometers. However, there is nothing to
prevent fitting the pump with additional sensors, for example
accelerometers, which may increase the accuracy of the method if
necessary.
[0029] Since the mechanical vibrations are a consequence of the
interaction between the structure and the force of the motor, these
mechanical vibrations can also be seen as a superposition in the
drive currents of the pump current of the pump drive. Since the
intensity of the individual superimposed vibrations is of interest
here, the evaluation of the motor currents is carried out by
analyzing the frequency spectrum of the recorded motor signal,
which the pump controller obtains by executing the Fast Fourier
Transformation (FFT).
[0030] This procedure can be briefly illustrated based on the
representations of the FIGS. 2, 3. FIG. 2 shows a time diagram of a
recorded signal, which was generated here for the sake of
simplicity by a superposition of three sinusoidal signals with
different frequencies. By applying the FFT, the time signal can now
be decomposed into its harmonic components, and it results in the
frequency amplitude spectrum represented in FIG. 3, from which, as
expected, the individual frequencies of the sinusoidal signals can
be read out.
[0031] Due to the FFT of the motor currents, the pump can therefore
detect mechanical vibrations which are reflected in the recorded
motor current. In the following step, the pump or the pump
controller then seeks to set the pump revolution rate so that the
resulting rotational frequency of the impeller does not fall on a
natural frequency of the pump or a multiple of such a natural
frequency. For this purpose, the revolution rate is initially
varied and in a further step a spectrum analysis of the currently
recorded motor current is again performed at a changed revolution
rate. If the amplitude of the occurring current oscillation has
become smaller, this is an indication that the mechanical vibration
could be successfully reduced by the revolution rate variation. The
method is now carried out iteratively to achieve as small an
amplitude value of the occurring fluctuations in the current signal
as possible. Finding the ideal revolution rate can in principle be
carried out according to two scenarios:
Scenario 1: The Required Rotational Frequency is Subject to Fixed
Requirements.
[0032] According to scenario 1, the rotational frequency may only
have a certain value. This may have energy-related reasons or the
intended purpose requires a certain (fixed) revolution rate. In
this case, the pump operator defines a tolerance value in the pump
controller by which the circulating frequency may deviate maximally
from the setpoint, for example .+-.3 Hz. The pump controller then
varies the revolution rate within the allowable tolerance range and
iteratively finds out the revolution rate at which the vibration
amplitude is minimal. Often even very small variations are
sufficient to depart from the natural frequency of the system and
thus to minimize the occurring mechanical vibrations.
Scenario 2: There are No Special Requirements for the Rotational
Frequency.
[0033] If there are no process-side requirements for the rotational
frequency, the pump controller can change the pump revolution rate
at will. This allows a targeted search for an anti-resonance and
setting the final operating revolution rate of the pump to this
anti-resonance. The easiest way (and thus the one with the lowest
memory and process requirements) to determine the appropriate
revolution rate (antiresonance) from the available revolution rate
range is based on bisection. Mathematical optimization methods are
faster and more effective, such as the "active-set method" or the
"Newton method". A global optimum can also be reliably determined
by means of a genetic algorithm.
[0034] Alternatively or in addition to the motor currents, the
signal of the final pressure of the pump can also be examined, in
that similarly to the motor current here too the frequency spectrum
is analyzed and evaluated for corresponding resonance frequencies
by means of Fast Fourier Transformation. The final pressure can be
calculated, for example, with a pressure sensor of the pump or else
by means of operating point estimation.
[0035] To increase the signal quality, both signals (final pressure
and motor current) can also be merged by means of sensor data
fusion. If this is not possible, current and pressure signals can
also be evaluated individually. For the sensor fusion, for example
the individual signal values can be evaluated as shown above and
then merged by means of weighting. It is also conceivable to define
ranges of interest in which the individual results of the
separately evaluated signals can be weighted differently. For
example, the result of the evaluation of the motor currents for
frequency ranges between 10 and 200 Hz is used, while the result of
the final pressure evaluation for higher frequencies is taken into
account.
[0036] A particular advantage of the method presented here is that
the pump itself can find its natural frequencies and therefore no
mathematical process model, which would be complex to develop, is
required. The main application of the method presented here is the
prevention or reduction of vibrations to reduce wear and noise
during pump operation. In addition, the process can also provide a
contribution to wear and damage monitoring and can warn the user in
case of damage.
Wear Monitoring
[0037] With the presented method, the frequency response of the
built-in pump is permanently monitored. However, as mentioned
above, this depends on the construction of the pump, the
installation position, the materials and the bearings. Therefore a
change in the frequency response is in any case an indication that
one or more of these variables have changed, for example due to
wear and tear. This information can then be used for wear
monitoring, for example in combination with the solution from DE 10
2018 200 651, to which express reference is made at this point. A
combination of these two approaches makes it possible to evaluate
the wear condition more precisely.
Warning of Damage
[0038] In contrast to wear, which leads to a very slow change in
frequency response, pump damage would change the frequency response
abruptly and significantly. Damage can be, among many other things,
a bearing or impeller break. Due to the rapid change of the
frequency response, the pump controller can reliably separate wear
and tear and damage and in the event of damage can issue a warning
to the operator.
* * * * *