Note: Descriptions are shown in the official language in which they were submitted.
CA 02745804 2011-06-03
PCT/EP2009/066020 - 1 -
2008P23756 WO
Method and apparatus for semiactive reduction of pressure
oscillations in a hydraulic system
The present invention relates to a method and an apparatus for
semiactive reduction of pressure oscillations in a hydraulic
system of a cold or hot rolling mill or strip handling
installation for iron, steel or aluminum materials.
It is known that periodically occurring pressure oscillations
in hydraulic systems cause various problems, for example
excessive noise development, reduction in the life of
components, interference with control loops, etc. Pressure
oscillations may be caused either in the hydraulic system
itself, for example as a result of non-uniformity of the feed
rate of pumps or by the operation of valves etc., or else may
be caused externally, for example by periodic load fluctuations
on hydraulic cylinders or motors. It is also known that severe
pressure oscillations can occur in the hydraulic system,
particularly in the case of highly dynamic hydraulic systems,
for example consisting of a highly dynamic continuous-operating
hydraulic valve (for example an electrically operated
proportional valve or servo valve) and a hydraulic cylinder or
motor.
It has been found that severe pressure oscillations can also
occur in the hydraulic systems of modern rolling mills or strip
handling installations - for example if the rollers are
positioned hydraulically -, which can lead to a reduction in
the life of components, or else to considerable damage to the
rolling mill stands and/or to defects in the rolling material.
This is due in particular to the fact that, on the one hand -
because of higher rolling forces or speeds - hydraulic systems
are used which react
CA 02745804 2011-06-03
PCT/EP2009/066020 - 2 -
2008P23756 WO
ever more quickly (more dynamically), and on the other hand -
because of more stringent requirements for the reaction time
and economy - the damping in the hydraulic systems is reduced
(for example the viscous damping in the seals of cylinders).
DE 4 302 977 Al discloses an apparatus for active suppression
of pressure oscillations in a hydraulic unit, which apparatus
has a pressure sensor, a regulating device with an associated
amplifier, and a volume compensator. The document does not
disclose specific rules for the method to be carried out or any
more detailed indications of an advantageous use of the
apparatus in a hydraulic system for a rolling mill or strip
handling installation.
Because of the high frequencies of the pressure oscillations to
be suppressed and the high pressures in modern hydraulic
systems, the actuators for active oscillation compensation
systems, in particular, are subject to very stringent
requirements. As a result of this, the actuators are no longer
compact (in particular they have a large volume) and, because
of the stringent requirements for the power density, it is only
possible to use very high-quality and expensive actuators. A
further disadvantage of active oscillation compensation systems
is that energy is additionally introduced into the hydraulic
system via the actuator, fundamentally making the stability of
the overall system worse and, particularly in the case of a
regulator which is not set exactly, this can even lead to a
deterioration in the system response (that is to say, in some
circumstances, the amplitude of the pressure oscillations is
not reduced, but is even amplified).
CA 02745804 2011-06-03
PCT/EP2009/066020 - 3 -
2008P23756 WO
The object of the invention is to provide a method and an
apparatus for semiactive reduction of pressure oscillations in
a hydraulic system of a cold or hot rolling mill or a strip
handling installation, by means of which pressure oscillations
which occur can be effectively reduced by means of a simple and
low-cost apparatus.
This object is achieved by a method of the type mentioned
initially, comprising the following method steps in the stated
sequence:
a) detection of a pressure signal by means of a pressure
sensor by permanent measurement of a pressure in the hydraulic
system;
b) determination of an alternating component of the pressure
signal;
c) determination of at least one manipulated variable, which
varies over time, in real time with the aid of a regulator,
taking account of the alternating component;
d) application of the manipulated variable to at least one
actuator, with the actuator changing a natural frequency of an
oscillation damper which is connected to the hydraulic system,
and thus reducing an amplitude of the pressure oscillations in
the hydraulic system.
In this case, a pressure signal is detected by means of a
pressure sensor (for example by means of a piezoelectric,
piezoresistive or strain gauge measurement cell), by
permanently measuring a pressure in a hydraulic system, for
example a rolling mill stand in a rolling installation. A
hydraulic system means a section (typically a hydraulic circuit
or a hydraulic axis) of a hydraulic installation, which are
hydraulically connected to one another, for example the area
between a hydraulic valve and a hydraulic cylinder, including
the hydraulic lines or hoses. An alternating component is then
determined from the pressure signal, that is to say a
CA 02745804 2011-06-03
PCT/EP2009/066020 - 4 -
2008P23756 Wa
constant component of the pressure signal is removed, and is
supplied to a regulator. The alternating component can be
determined either by an electronic filter module or by a
digital filter (for example removal of the constant component
by means of a sliding window consisting of n measured values of
the pressure oscillations (filter order n); however, it is of
course also possible for the DC component to be removed only in
the regulator algorithm); alternatively, the alternating
component can also be determined by means of a piezoelectric
pressure sensor and a charge amplifier, which is either
connected downstream from the pressure sensor or is integrated
in the pressure sensor. The regulator determines at least one
manipulated variable, which varies over time, in real time
taking account of the alternating component of the pressure
signal, and this manipulated variable is applied to at least
one actuator, thus varying a natural frequency of an
oscillation damper which is connected to the hydraulic system.
In this application, an oscillation damper means an element,
which is passive per se, for oscillation damping, for example a
X/4 resonator ("side branch resonator"), a Helmholtz resonator
etc. "Semiactive reduction of pressure oscillations" is
intended to mean reduction of an amplitude of pressure
oscillations in a hydraulic system by means of a passive
oscillation damper, in which case the natural frequency of the
passive oscillation damper can be varied by means of an
actuator. A particularly major reduction in the amplitude of
the pressure oscillations can be achieved by deliberately
applying the manipulated variable to the actuator in order to
vary a natural frequency of the oscillation damper, such that
the natural frequency of the oscillation damper is made to
match a frequency of the pressure oscillation. The manipulated
variable signal can be transmitted from the
CA 02745804 2011-06-03
PCT/EP2009/066020 - 5 -
2008P23756 WO
regulator to the actuator with or without the use of cables
(for example by radio).
In one advantageous embodiment of the method according to the
invention, the alternating component of the pressure signal is
subjected to bandpass filtering. This filtering makes it
possible to filter out of the alternating component either
particularly disturbing frequency components (which for example
coincide with a natural frequency of the rolling mill stand or
of a subsystem) or frequency components with a high amplitude
or intensity (for example from a spectrum of an FFT (Fast
Fourier Transform) or PSD (Power Signal Density)), and to
supply these to the regulator-
In one advantageous embodiment, the actuator changes a volume
in the oscillation damper, which volume corresponds to the
manipulated variable, with the volume corresponding to the
manipulated variable (a manipulated variable of zero
corresponds, for example, to the actuator being in a non-
deflected (neutral) position; a maximum manipulated variable
may then, for example, correspond to a maximum deflection in
one direction), thus varying a natural frequency of the
oscillation damper.
The method according to the invention can be carried out in a
particularly advantageous manner if the actuator changes the
volume of a Helmholtz resonator or the active length of a k/4
resonator. The natural frequency of these oscillation dampers
can be adjusted in a simple manner.
Since the pressure oscillations in a hydraulic system of a
positioning cylinder of a stand for rolling iron, steel or
aluminum materials have a direct influence on the
CA 02745804 2011-06-03
PCT/EP2009/066020 - 6 -
2008P23756 WO
quality of the rolling material, and are therefore particularly
disturbing, it is advantageous to use the method according to
the invention for a hydraulic system for a positioning cylinder
for a rolling mill stand.
In order to allow the method according to the invention to be
implemented as directly as possible, thus solving the problem
on which the invention is based, it is advantageous for the
apparatus to have a pressure sensor, which is connected to the
hydraulic system, for detection of a pressure signal, an
element for determination of an alternating component of the
pressure signal, to which the pressure signal can be supplied,
at least one regulating apparatus, to which the alternating
component can be supplied and with the aid of which at least
one manipulated variable can be determined, at least one
oscillation damper which is connected to the hydraulic system,
and at least one actuator, which is connected to the
oscillation damper and has a variable volume, to which the
manipulated variable can be supplied and via which a resonator
volume of the oscillation damper can be varied. A natural
frequency of the oscillation damper can in turn be adjusted via
the resonator volume, thus making it possible to match the
natural frequency to a frequency of the pressure oscillations.
The natural frequency can be adjusted particularly easily if
the oscillation damper is in the form of a ~,/4 or Helmholtz
resonator-
A particularly low-cost apparatus can be achieved if the
actuator is in the form of an electrical lifting spindle
actuator or hydraulic actuator. Since the actuator can be
adjusted slowly - in comparison to systems with active
oscillation compensation -
CA 02745804 2011-06-03
PCT/EP2009/066020 - 7 -
2008P23756 WO
commercially available electrical or hydraulic actuators are
completely adequate.
The apparatus according to the invention can be used in a
particularly advantageous manner if the apparatus is connected
to a hydraulic valve and a hydraulic cylinder of a hydraulic
roller positioning means. This installation makes it possible
to reduce oscillations on the rollers of a rolling mill stand
particularly easily, thus making it possible to effectively
improve the quality of the rolling material. The installation
is particularly compact when the apparatus is installed in an
intermediate plate of the hydraulic valve.
Particular advantages result from the use in a composite
casting and rolling installation, particularly in thin-strip
casting installations, and very particularly preferably in two-
roller casting installations and thin-slab casting
installations of the ESP (Endless Strip Production) type.
Further advantages and features of the present invention will
become evident from the following description of exemplary
embodiments, which are not restrictive, with reference being
made to the following figures in which, as follows:
Figure 1 shows a layout of a controlled system for semiactive
reduction of pressure oscillations in a hydraulic system,
Figure 2 shows a layout of an apparatus according to the
invention for reduction of pressure oscillations in a hydraulic
system in a rolling mill, and
Figures 3 and 4 show layouts of an oscillation damper with an
integrated actuator.
Figure 1 shows the basic design of a controlled system for
reduction of pressure oscillations in a hydraulic system
CA 02745804 2011-06-03
PCT/EP2009/066020 - 8 -
2008P23756 WO
of a rolling mill. A pressure signal for a pressure in the
hydraulic system is detected via a pressure sensor 1, the
pressure signal 2 is supplied to a high-pass filter 3 (for
details relating to the electronic circuit, see for example
page 35 in P. Horowitz, W. Hill. The Art of Electronics,
Cambridge University Press, Second Edition, 1989), which
determines the alternating component 2' of the pressure signal
2, and supplies this to a regulator 4. This regulator 4 uses a
control law to calculate a manipulated variable 6, which varies
over time, in real time, taking account of the alternating
component 2'. The manipulated variable signal is then supplied
to an amplifier 8, which operates an actuator 9, in the form of
an electrical lifting spindle actuator. The actuator 9 varies
the resonator volume of an oscillation damper 13 which is in
the form of a Helmholtz resonator, with the change in the
resonator volume corresponding to the manipulated variable 6.
The change in the resonator volume varies a natural frequency
of the oscillation damper 13, thus matching the natural
frequency of the oscillation damper to a frequency of the
pressure oscillation. This measure reduces the amplitude of the
pressure oscillation in the hydraulic system in a very simple
but effective manner.
Figure 2 schematically illustrates an apparatus for suppression
of pressure oscillations in a hydraulic system of a rolling
mill stand for iron, steel or aluminum materials. A pressure
signal 2 is detected by means of a pressure sensor 1, by
permanent measurement of a pressure in a hydraulic system 10,
with the hydraulic system comprising a hydraulic valve 11, a
hydraulic cylinder 12 and a hydraulic line. The hydraulic
system is used to position a roller 14 for rolling a rolling
material 15. In this case, the pressure sensor 1 may be located
either in the section between
CA 02745804 2011-06-03
PCT/EP2009/066020 - 9 -
2008P23756 WO
an oscillation damper 13 and the hydraulic cylinder 12 (as
shown), or in the section between the hydraulic valve 11 and
the oscillation damper 13. It is, of course, also possible to
arrange a plurality of pressure sensors between the oscillation
damper 13 and the hydraulic cylinder 12, or between the
hydraulic valve 11 and the oscillation damper 13. The pressure
signal 2 is transmitted to a digital regulator 4, which
determines a frequency band of the alternating component of the
pressure signal, and calculates a manipulated variable 6, which
varies over time, with the assistance of a control algorithm.
The manipulated variable is supplied, after amplification in an
amplifier which is not illustrated, to an actuator 9 which is
in the form of an electrical lifting spindle actuator and which
varies a resonator volume, corresponding to the manipulated
variable 6, in the oscillation damper 13, which is in the form
of a Helmholtz resonator, as a result of which a natural
frequency of the oscillation damper 13 is matched to a
frequency of the pressure oscillations, thus reducing the
amplitude of a pressure oscillation.
Figure 3 shows an oscillation damper 13, which is in the form
of a Helmholtz resonator and has an integrated actuator 9. A
manipulated variable 6 can be supplied to the actuator 9, by
which means it is possible to vary the resonator volume V,
V = LS, where L is the length and S is the cross-sectional area
of the resonator volume of the Helmholtz resonator. A natural
frequency of the oscillation damper 13 can be varied by varying
the resonator volume V, with the natural frequency f of the
Helmholtz resonator being defined by the condition:
C S'
f 2,r LL
In this case, c is the speed of sound in the hydraulic liquid,
S' is the cross-sectional area and L' is the
CA 02745804 2011-06-03
PCT/EP2009/066020 - 10 -
2008P23756 WO
length in the resonator neck, L is the length and S is the
cross-sectional area of the resonator volume V (cf. Chapter
8.3.3 Resonators in the textbook, H. Kuttruff, Acoustics - An
Introduction, Taylor and Francis, 2007).
Figure 4 shows an oscillation damper 13, which is in the form
of a X/4 resonator and has an integrated actuator 9. A
manipulated variable 6 can be supplied to the actuator 9, thus
allowing the active length L of the 2/4 resonator to be varied.
A natural frequency of the oscillation damper 13 can be varied
by varying the active length L, with the natural frequency f of
the 2/4 resonator being given by the condition:
1C
4L
In this case, c is the speed of sound in the hydraulic liquid,
and L is the active length.
The method according to the invention or the apparatus may, of
course, be used in any desired hydraulic systems for mobile
hydraulics or industrial hydraulics.
CA 02745804 2011-06-03
PCT/EP2009/066020 - 11 -
2008P23756 WO
List of reference symbols
1 Pressure sensor
2 Pressure signal
2' Alternating component of the pressure signal
3 Bandpass filter
4 Regulator
6 Manipulated variable
8 Amplifier
9 Actuator
Hydraulic system
11 Hydraulic valve
12 Hydraulic cylinder
13 Oscillation damper
14 Roller
Rolling material
