EP2401521A1

EP2401521A1 - A method and an apparatus for controlling vibrations

Info

Publication number: EP2401521A1
Application number: EP10707937A
Authority: EP
Inventors: Tony Lehto; Jani Yli-Alho; Reijo PIETIKÄINEN
Original assignee: Metso Paper Oy
Current assignee: Valmet Technologies Oy
Priority date: 2009-02-24
Filing date: 2010-02-11
Publication date: 2012-01-04
Also published as: FI20095177A0; FI121092B; WO2010097503A1

Abstract

An apparatus for controlling vibrations of a machine, the apparatus comprising at least: a measuring unit (1) for measuring vibrations, a pulse generating unit (3) for generating counter motions, the pulse generating unit comprising at least: a hydraulic actuator (5) and a device (6) for controlling the flow of hydraulic fluid. Furthermore, the apparatus comprises a control unit (2) for controlling the pulse generating unit on the basis of measurement data from the measuring unit. The actuator (5) is a chamber with solid walls, at least one of the walls being flexible and being configured to yield by the effect of pressure. Furthermore, the invention relates to a method for controlling vibrations of a machine.

Description

A METHOD AND AN APPARATUS FOR CONTROLLING VIBRATIONS

Field of the invention

The invention relates to an apparatus for controlling vibrations and movements of machines/machine parts. Furthermore, the invention relates to a method for controlling vibrations and movements of machines/machine parts. The solution is suitable, for example, for controlling vibrations of paper and cardboard machines, finishing devices for paper and cardboard, as well as continuous fibrous web presses.

Background of the invention

Vibration of various machines and machine parts during their use is, in many cases, a phenomenon to be eliminated or at least attenuated.

Oscillation and vibration occurring in paper machines and finishing devices for paper (coating machines, calenders, reel-ups, slitter-winders) pose quite a significant problem. These devices contain several sources of vibration, the most significant ones including rolls and cylinders that comprise a large mass rotating at a high speed. The oscillation and vibration of the rolls and cylinders cause marks in the paper being manufactured.

The moving and rotating parts of the paper machine and the finishing devices of paper also cause vibration in the foundations of these devices. These vibrations disturb the running of the devices and may cause permanent changes in their supporting structures. Furthermore, the vibrations caused by different machine parts/devices placed on the same foundation generate combined effects of vibrations, which results in that the entire machine vibrates periodically or chaotically.

In mineral material processing devices as well, such as crushers, screens and conveyors, various kinds of vibrations are caused by the operation of these machines. For example the feeding of the material to be crushed to the crusher causes shocks and vibration in the entire crusher. The oscillation and vibration of mineral material processing devices are currently damped by springs and large-sized hydraulic cylinders.

Machine vibration can be controlled by active, semi-active or passive methods. In the active methods, a suitably phased excitation force is introduced in the system, wherein the structure is either made to vibrate in a controlled manner, or the vibration can be totally compensated for. Active actuators include, for example, hydraulic actuators, pneumatic actuators, and electromechanical actuators.

Within the scope of prior art, no actuator is available for application in which both a great force and a rapid movement are needed simultaneously. The force obtained from an electromechanical actuator, such as, for example, a piezo actuator and a linear motor, in rapid movements is small. The force obtained from a hydraulic actuator is great, but the speed is limited. Presently available servo hydraulic actuators have an operating frequency lower than 50 Hz. Seal friction is another significant negative factor in hydraulic actuators.

It is a problem with the hydraulic solutions for damping vibrations that the hydraulic actuators used in them have a long response time to the detected vibrations. Because the vibration damper does not react to vibrations fast enough, the vibrations have time to cause problems in apparatuses and in the manufacturing process before the situation improves. A situation may also occur in which the vibration damper is constantly "late" because of the long response time. Thus, sufficient damping is not attained at any stage, despite of the continuous adjustment of the actuator.

Brief summary of the invention

It is an aim of the solution according to the invention to eliminate drawbacks and faults of the above-presented solutions of prior art for damping vibrations.

To achieve this aim, the apparatus according to the invention is primarily characterized in what will be presented in the independent claim 1. The method according to the invention is, in turn, primarily characterized in what will be presented in the independent claim 6. The other, dependent claims will present some preferred embodiments of the invention.

The basic idea of the invention is that a counterforce for the vibration of the machine or machine parts is generated by a pulse generator unit comprising a hydraulic actuator and a device for controlling the flow of hydraulic fluid. The actuator is a chamber with solid walls, at least one of the walls being flexible. The structure of the actuator enables a rapid movement.

The apparatus according to the basic idea comprises at least a measuring unit for measuring vibrations, a pulse generator unit for generating counter- motions, as well as a control unit for controlling the pulse generator unit on the basis of measurement data from the measuring unit. The pulse generator unit, in turn, comprises at least a device for controlling the flow of hydraulic fluid, as well as a quick-operated hydraulic actuator comprising a chamber with solid walls, at least one of the walls being flexible.

The actuator may preferably be a pressure cell whose wall bulges by the effect of oil pressure. Thus, the cell expands and contracts as the pressure changes, and at the same time, the actuator generates a motion. A motion of some tens of micrometers is often sufficient for vibration control. The length of the motion is thus often significantly shorter than the diameter or transverse dimension of the movable wall of the actuator.

The actuator generating a frictionless motion under the control of the device for controlling the flow of hydraulic fluid may also be of a different type, for example an accordion-folded pressure chamber, a cylindrical expanding chamber, or just a conventional cylinder with seals which are particularly low- friction or elastic.

Preferably, the device used for controlling the flow of hydraulic fluid is a control valve, in which at least one coil is arranged around a control member for moving the control member in a magnetic field. The control member controls the volume flow of the pressurized medium. In other words, at least one element moving the control member is directly connected thereto. The control member is formed as a cylindrical piece that is at least partly hollow inside. The valve contains at least one outflow chamber for the pressurized medium. The medium flows to the outflow chamber from either an inflow chamber or an inflow channel through a flow guide. The control member is positioned in such a manner in relation to the flow guide that it is capable of controlling the volume flow of the medium through the flow guide. Said at least one coil arranged on the outer surface of the control member is at least partly surrounded by the pressurized medium.

The valve contains at least one shaped magnet to which electric current is supplied to generate a magnetic field. The coil arranged on the outer surface of the control member is positioned in relation to the magnet/magnets in such a way that the magnetic flux density is the highest possible in the environment of the coil of the control member. As a result, the movements of the control member are fast and precise, and correct positioning of the control member is easy and rapid.

It is not necessary to provide the valve with a separate heavy stem, wherein the entire valve is smaller in size and lighter in weight, wherein it can be installed more easily in connection with actuators. The control member itself is naturally lighter in weight as well, wherein it can be moved faster, and thus the flow of the medium can also be controlled faster. In pilot tests, response times of 0.1 ms have been measured as the reaction time of the control member. Furthermore, it has been found that increasing the flow from zero to full flow or closing the same from the full flow to zero may be reached even in approximately 1 ms. As a consequence of all this, the positioning of the actuator to the desired operating state is fast.

Especially in view of damping the vibrations, it is very advantageous that the step response of the actuator becomes faster. Furthermore, by means of the valve it is also possible to attain other than sine wave.

The different embodiments of the above-described arrangement, taken separately and in various combinations, provide various advantages. A significant advantage provided in one embodiment lies in that the force that damps the vibration is generated in the correct location.

Using various embodiments of the invention, it is possible to damp high- frequency machine vibrations, for example, in the following applications: vibrations of rotating machine parts, such as rolls and shafts, in the press section of a paper machine, in a dryer, in a coating machine, in a calender, or in reel-ups; damping vibrations of static frame structures: frames of a paper machine, a calender, a coating machine, a cutting machine; controlling vibrations of static auxiliary devices, such as transverse structures of a paper machine, maintenance bridges, measuring frameworks, doctor beams, damper beams, application nozzle beams, etc. - generating controlled vibration or turbulence in a material flow, such as controlled mixing or pulsing of the fibre suspension to prevent flocculation in the pulp circulation of a paper machine, in an approach system, in a head box or a former; elimination of vibration/bouncing of a paper reel in reel-up by introducing an excitation supporting force to the reel via a reel core, an impression roller, or king rolls.

In addition to vibration damping, the combination of an actuator and a quick- operated valve can be used to produce a fast linear motion at a high speed. This can be utilized, for example, in the following applications: closing the roll system of a calender and producing or accelerating a quick opening movement, loading levers for the stack of rolls in a multinip calender; relief of a calender roll for the time of passing a splicing; - quick positioning of the beam of an actuator: for example, the quick turning of a doctor blade or the beam of an induction heating device farther away from the roll upon the occurrence of a web break or a "pile".

The solution is suitable, for example, for controlling vibrations of paper and cardboard machines, finishing devices for paper and cardboard (coating machines, calenders, reel-ups, slitter-winders), as well as continuous fibrous web presses. The solution according to the invention can also be used for the vibrating motion of screens needed in mineral preparing machines (rock crushers), and even for producing the movement of crushers. The solution is also suitable for damping vibrations occurring in vehicles and working machines (for example, active suspension, compensation of wander of the engine or the cabin).

Description of the drawings

In the following, the invention will be described in more detail with reference to the appended principle drawings, in which

Fig. 1 illustrates the principle of the assembly of the apparatus;

Fig. 2 shows a quick-operated control valve;

Fig. 3 shows another quick-operated control valve;

Figs 4 to 1 1 illustrate some applications.

For the sake of clarity, the drawings only show the details necessary for understanding the invention. The structures and details that are not necessary for understanding the invention but are obvious for anyone skilled in the art have been omitted from the figures in order to emphasize the characteristics of the invention.

The symbols shown in the figures denote primarily to functions that can be implemented with one or more components or parts of one or more components. The components can be connected to each other in various ways to achieve the desired function. Detailed description of the invention

An assembly according to the basic idea of the solution is shown in Fig. 1. The apparatus according to the example comprises a measuring unit 1 , a control unit 2, and a pulse generator unit 3.

The measuring unit 1 is configured to measure vibrations of a machine or machine part 4. The measuring unit 1 comprises suitable measuring means and/or sensors. Information about vibration can be obtained, for example, by means of an eddy current sensor, a laser range-finder, a strain gauge, a piezo sensor, or another corresponding sensor. The sensor can be positioned at any place where sufficient information is obtained for controlling damping. For the control, the sensor measures suitable variables relating to the vibration, on which variables control data is generated by the control unit 2.

The control unit 2 is configured to control the pulse generator unit 3 on the basis of measurement data from the measuring unit 1 . The control unit 2 can be implemented in a variety of ways, and it can be, for example, integrated in the rest of the control system. Preferably, the control unit 2 is implemented at least partly by software.

The pulse generator unit 3, in turn, is configured to generate counter-motions against the vibration. The pulse generator unit 3 comprises at least a hydraulic actuator 5 (not shown in Fig. 1 ) as well as a device 6 for controlling the flow of hydraulic fluid (not shown in Fig. 1 ).

The actuator 5 should be such that it is capable of changing its position sufficiently quickly. In many cases, the movement of the actuator 5 does not need to be large, since the amplitude of the vibration is in many cases small. The frequency of the vibration, in turn, is high in many cases, for which reason the actuator 5 must operate quickly. Preferably, the actuator 5 is a chamber with solid walls, at least one of the walls being flexible, wherein the wall yields according to the pressure effective in the chamber. In an example, the actuator 5 is a pressure cell, whose one wall yields by the effect of pressure. Because the frequency of the vibration is in many cases high, the control device 6 must also operate sufficiently quickly. The device 6 for controlling the flow of hydraulic fluid must be capable of controlling the movement of the hydraulic fluid sufficiently quickly and with a sufficient volume flow. In an example, the device 6 for controlling the flow of hydraulic fluid is a quick- operated control valve, which will be called a "high-speed valve" hereinbelow. The high-speed valve operates very quickly, because the moving mass of the valve stem is minimized and the movement of the stem is implemented by an electromagnetic voice coil. The coil is integrated in the valve stem, and it comprises only one moving part. The solution makes it possible to use the valve continuously without overheating or other breaks. In the following, some structures of such a high-speed valve will be described in more detail with reference to Figs. 2 and 3.

Fig. 2 shows an embodiment as a 2/2 valve. The control valve suitable for the control device 6 shown in the figure comprises a valve body 7 which is designed to be hollow inside for positioning the parts of the valve inside the body 7. The body 7 can be formed of a uniform, housing-like element 7a that forms the bottom and end walls, and of a bonnet element 7b attached thereto, as shown in Fig. 2. The body 7 of the valve 6 can also be composed of separate bottom and bonnet elements, and side walls attached thereto. If desired, the valve 6 can also be produced without the bonnet.

A magnet 8 is arranged inside the body 7, which is preferably an electric magnet, but a permanent magnet can also be used. The coil 9 of the magnet is wound around the core 8a of the magnet. Electric current is supplied to the coil 9 of the magnet via conductors 10 in order to generate a magnetic field.

A control member 1 1 is at least partly in contact with the magnet 8, said control member being designed as a cylindrical piece that is at least partly hollow inside. A coil 12 is arranged around the control member 1 1. Electric current is supplied to and discharged from the coil 12 via conductors 13a, 13b. The volume flow of the medium supplied by the valve 6 to the actuator 5 is controlled by adjusting the quantity and direction of the control current supplied to the coil 12. The coil can be formed, for example, of litz wire or aluminium foil. Advantageously, litz wire is used, which is a very strong coil material. When litz wire is used, it is possible to utilize higher control frequencies and still the losses are smaller. As the coil material, it is also possible to use other conductor materials in the form of a wire comprising one or several threads.

As an extension to the core 8a of the magnet there is an outflow chamber 14 separated from an inflow chamber 20 by means of a cylindrical wall 14a. The control member 1 1 is arranged around the core 9a of the magnet and the wall 19 of the outflow chamber in such a manner that it extends over the entire length of the wall 19 and partly around the core 8a of the magnet. In this section the inner surface of the stem is in contact with the outer surface of the core 8a of the magnet.

Thus, the control member 1 1 restricts the outflow chamber 14 of the valve and its walls inside itself. Correspondingly, the inflow channel 20 of the valve remains outside the control member. The coil wound on the outer surface of the control member 1 1 is thus located inside the inflow chamber 20, surrounded by the medium contained therein.

At the valve bonnet end of the wall 19 of the outflow chamber, a flow guide 17 is arranged to guide the flow of medium from the inflow chamber 20 to the outflow chamber 14 when the control member 1 1 has been moved to a position in which it does not prevent the flow. In the embodiment of Fig. 2, the flow guide 17 consists of holes 17a made in the wall of the outflow chamber.

In the operating mode of the valve 6 shown in Fig. 2, the other end of the control member 1 1 is in contact with a damping plate 16 attached to the valve bonnet 7b. Thus, the control member covers the holes 17a of the flow guide 17 and prevents the medium from flowing from the inflow chamber 20 to the outflow chamber 14 and further via the outflow chamber 18 to the actuator connected to the valve.

The valve body 7a, the bonnet 7b, the magnet 8, and the valve stem 11 define the inflow chamber 20 of the valve, to which an inflow channel 21 is connected for supplying pressurized medium to the inflow chamber 20. As seen in the figure, the magnet 8 is designed in such a manner that a magnetic gap 22 is formed therein. The magnetic gap 22 has a narrow shape. This design produces an efficient magnet with a steady magnetic flux in the magnetic circuit. The length of the control member 1 1 and the location of the coil 12 in relation to the length of the control member are arranged in such a manner that the coil 12 is positioned substantially in the magnetic gap 22, wherein the movements of the control member 11 are rapid and precise.

Two springs 23 are attached symmetrically around the control member 1 1 in such a way that the first end of the spring is attached to the control member 11. The second end of the spring 23 is attached to the wall of the inflow chamber 20. The springs 23 press the control member 1 1 against the damping plate 16 when the control member is not being controlled. It is also possible to use the spring 23 as a supporting structure for the conductors 13a and 13b of the coil 12, wherein the durability of the conductors improves.

The control valve 6 according to Fig. 2 functions in the following manner: By means of the electric current supplied to the coil 9 of the magnet via the conductor 10, a magnetic field is generated by the magnet 8. Pressurized medium is constantly supplied to the inflow chamber 20 of the valve 6 via an inlet port 21. When the valve 6 is not being controlled, i.e. current is not supplied to the coil 12 arranged around the control member 11 , the spring 23 presses the control member 1 1 against the damping plate 16. Thus, the control member 1 1 covers the holes 17a arranged in the flow guide 17 and closes the flow path of the medium from the inflow chamber 20 to the outflow chamber 14.

When control current is supplied to the coil 12 arranged around the control member 1 1 , said control current moving the control member 1 1 away from the damping plate 16, a flow path is opened for the medium via the holes 17a of the flow guide 17 to the outflow chamber 14 and through the same via the outflow channel 18 to the actuator connected to the valve 6. When the flow of the medium is reduced, the control member 1 1 is moved towards the damping plate 16 by means of the control current supplied to the coil 12. The springs 23 boost this movement. Fig. 3, in turn, shows another embodiment of the high-speed valve 6. The control valve 6 shown in the figure comprises a valve body 7. The valve body 7 is provided with a lead-through for a flow channel 21 , for supplying pressurized medium to the valve 6. The flow channel 21 extends continuously through the entire valve 6, and it is divided into a inflow channel 21 a and an outflow channel, i.e. a tank channel 21 b, by means of a blocking plug 26.

Two magnets are arranged inside the body, a first magnet 8a and a second magnet 8b. The coils 9a, 9b of the magnets have been wound around the magnets 8a, 8b. The first magnet 8a partly surrounds the inflow channel 21 a and the second magnet 8b partly surrounds the tank channel 21 b. Electric current is supplied to the first magnet 8a via a first conductor 10a, and electric current is supplied to the second magnet 8b via a second conductor 10b.

A control member 28 surrounding the flow channel 21 is at least partly in contact with both magnets 8a, 8b. The inner surface of the first end 28a of the control member 28 is in contact with the surface of the first magnet 8a, and the inner surface of the second end 28b of the control member is in contact with the surface of the second magnet 8b. A first coil 12a is arranged around the first end 28a of the control member 28, and a second coil 12b is arranged around the second end 28b of the control member 1 1. To conduct the electric current required by the first coil 12a, conductors 13a' and 13a" are connected thereto. To the second coil 12b, electric current is conducted via conductors 13b' and 13b". The volume flow of the medium supplied by the valve 6 to the actuator is controlled by controlling the quantity and direction of the control current supplied by the control member 28 to the first coil 12a and/or the second coil 12b.

An outflow chamber 14 surrounding the flow channel is provided apart from the flow channel 21. From the inflow channel 21 a, a lead-through 25 is arranged to guide the medium to the outflow chamber 14. From the outflow channel 21 b, a lead-through 29 is arranged to guide the medium from the outflow chamber 14 to the tank channel 21 b. The lead-throughs 25 and 29 act as flow guides for the valve 6.

The cylindrical control member 28 is arranged movable in the outflow chamber 14. The length of the control member 28 is selected in such a manner that it extends over the length of the outflow chamber 14. The first coil 12a and the second coil 12b wound on the surface of the control member 28 are at least partly inside the outflow chamber 14, surrounded by the medium contained therein.

On the surface of the control member 28 at the flow channel 21 side, a flow channel 27 is arranged to guide the medium from the inflow channel 21 a to the outflow chamber 14. The flow channel can be a groove formed on the surface of the control member 28, or a hole penetrating the control member. The flow of the medium is also guided from the outflow chamber 14 to the outflow channel 21 b via a lead-through 29 arranged in the outflow channel and via the flow channel 27.

The flow of the medium is guided by moving the control member 28 in accordance with the arrow marked in the figure. In the situation shown in

Fig. 3, the control member 28 is in such a position that there is no flow of the medium via the flow guide 25 and the flow channel 27 to the outflow chamber

14. When the control member 28 is moved in the direction of the first magnet

8a, the medium is capable of flowing via the lead-through 25 and the flow channel 27 from the inflow channel 21 a to the outflow chamber 14. The outflow chamber 14 is connected to the outflow channel 18a guiding the medium to the actuator. When the control member 28 is moved in the direction of the second magnet 8b, the medium is allowed to flow via the flow channel 27 and the lead-through 29 into the tank channel 21 b. The valve 6 is also provided with at least one spring 23 enhancing the movement of the control member.

The position of the control member 28 can be adjusted either by supplying control current to both coils 12a and 12b simultaneously, or by supplying control current only to the first coil 12a or to the second coil 12b. We shall now show, by way of example, some embodiments in which a counterforce against the vibration of a machine or machine parts is generated by a pulse generator unit. In an embodiment to be presented as the first example, the vibration or motion of a machine or machine part 1 is controlled by a hydraulic actuator 5 controlled by a high-speed valve 6.

In the embodiment shown in Fig. 4, the high-speed valve 6 is used for controlling the actuator 5. The oil volume of the actuator 5 can be connected to a second control circuit (not drawn) for adjusting oil pressure in a slow loop and the slow motion of the actuator. The high-speed valve 6, in turn, is used for controlling a quick motion in response to vibration of the machine 4.

In the embodiment shown in Fig. 5, the high-speed valve 6 is used for controlling a separate quick and substantially frictionless actuator 5 (such as, for example, a "pressure cell") at the same time when a conventional valve 30 is used for controlling a conventional cylinder 31. The actuators 5, 31 may be coupled either in series (in the figure) or in parallel (not shown) with each other. The oil pressure controlled by the high-speed valve 6 bulges the membrane of the pressure cell 5, wherein the cell expands and generates a motion. A motion of some tens of micrometers is often sufficient (particularly for vibration control).

The actuator 5 generating a frictionless motion under the control of the highspeed valve 6 may also be of a different type, for example an accordion- folded pressure chamber, a cylindrical expanding chamber, or maybe a conventional cylinder with seals which are particularly low-friction or elastic (not sliding in small motion).

The embodiment of Fig. 6, in turn, is suitable in a fibre web manufacturing line for controlling vibration, for example, in roll systems 32 with a zone roll 33. Such roll systems 32 include, among others, the press nip and the roll systems of a machine calendar, a soft calendar, a shoe calendar, a metal belt calendar, as well as a multinip calender of a paper or cardboard machine. For example, with the increasing speed of paper machines, a deflection compensated roll system also tends to vibrate, causing a respective deterioration in the paper quality. The aim of the deflection compensation of a paper machine roll is to distribute the nip force in a controlled and uniform manner, to produce paper with a uniform quality over the entire width of the web. A deflection compensated roll 33 consists of a non-rotatable shaft and a rotatable roll shell 34. Pressure elements 35 (hydraulic glide shoes), which are controlled irrespective of each other, are mounted on the shaft. Figure 7 shows the cross-section of the deflection compensated roll 33 transverse to the machine direction. Elements 35 support the shell 34 hydrostatically, and they are used for adjusting the deflection of the roll 33. The shell 34 is adjusted to the shape of the shell of the backing roll, and in this way, a uniform paper thickness is achieved.

The deflection controlled roll 33 is pressed with a heavy load against the backing roll (calender roll). The result is the deflection of the backing roll and the formation of the roll shell.

The apparatus according to the example comprises at least a measuring unit 1 , a pulse generating unit 3 (consisting of an actuator 5 and a high-speed valve 6), a control unit 2, as well as at least one actuator effective on the roll, for example a loading shoe 35 which is simultaneously used as the above- described actuator 5.

The pulse generating unit 3 consists, in the example, of the high-speed valve 6 and the loading shoe 35. The loading shoe 35 should comprise sufficiently large flow channels. The high-speed valve 6 is preferably placed directly in connection with the loading shoe 35, wherein the flow channels are integrated in the shoe structure. The channels can thus be made large and short. In this way, pressure losses of the structure can be made as small as possible, and furthermore, an advantageous structure is achieved in view of quick vibration control.

Another option is to place the valve system at the end of the roll 33. In this case, each loading shoe 35 requires separate hydraulic pipes. Long channels increase the pressure losses, impairing the dynamics of the control to some extent.

The measuring unit 1 comprises, among other things, a feedback signal transducer. Feedback measurement data is obtained, for example, by means of an eddy current sensor, a laser range-finder, a strain gauge, a piezo sensor, or another corresponding sensor providing information about vibration. The sensor can be positioned at any place where sufficient information is obtained for controlling damping. For the control, the sensor measures the amplitude, frequency and phase angle of the vibration in relation to the multi-zone roll 33, to calculate the counterforce needed for damping the vibration. The oscillation frequency band obtained with the apparatus is about 0 to 100 Hz (the flow channels constitute a limiting factor).

In the example, the control of the vibration of the roll system 32 is based on the very quick pressure control in the oil pockets of the loading shoes 35 of the multi-zone roll 33. The pressure of the oil pocket of the loading shoe 35 is adjusted by means of a particular high-speed valve 6 at a high speed, which generates an excitation impulse inside the roll shell 34. By performing the pressure control at a sufficient speed, for example with a suitably phased pulsation, it is possible to damp the vibration of the roll 33 and/or the roll system 32. The control can be implemented as feedback control in relation to measured vibration. The vibration measurement can be taken, for example, from the bearing housings or other supporting structures of the roll, or by contactless measurement directly from the surface of the roll.

Pressure variation by the high-speed valve 6 is designed to be moderate with respect to the average pressure level in the pockets. The average pressure in the pockets can be adjusted by means of a conventional control valve, wherein the systems are separate and robust, and the vibration damping has little effect on the profile adjustment.

By the same principle, it is possible to equip several parallel zones with individual vibration damping circuits, to obtain asymmetrical damping. The apparatus according to the example shown in Figs. 6 and 7 can be easily implemented in existing systems, because the actuators 5 (loading shoes 35) are already available in the multi-zone roll 32. Similarly, the installation is easy, if the valve system is placed at the end of the roll 33. A significant advantage lies in that the force that dampens the vibration is generated in the correct location. Thanks to this, the necessary ranges of force variation (amplitude of oscillation) are small, wherein a negative effect on the paper is not likely to occur. Furthermore, the apparatus is relatively simple, and the wearing parts of the valve 6 are replaceable.

The following example relates to roll oscillation, or the so-called barring phenomenon. The vibration and oscillation occurring in multi-roll calenders used in the finishing process of paper cause a so-called barring phenomenon. Barring may result from various reasons. It may be caused by irregularities in the paper being calendered, by the mechanical vibration produced by the calender itself, its actuators or the machines surrounding the same, or by the effect of the asymmetry of the roundness of the outer surface of the rolls. Because all rolls of the calender are in contact with each other, the vibration is transferred from one roll to another, and in the end the rolls will repeat a vibration pattern consisting of several waves. The rolls cause MD-oriented (machine direction) variations in the thickness of the paper being calendered, wherein the target quality of the paper is generally not reached. Furthermore, the rolls cause additional vibration in the calender, as well as noise.

In paper and cardboard machines, variation (oscillation) in the running speed or a change in the geometry of the roll system has been used for controlling roll oscillation (barring). A change in the geometry can be implemented, for example, by moving the location of rolls in a middle position (overlapping device). By the solution according to the example, it is possible to adjust the profile of the web quickly in the longitudinal and transverse directions, as well as to damp oscillation, if necessary.

In this embodiment, the apparatus comprises at least a measuring unit 1 , a pulse generating unit 3, a control unit 2, as well as at least one actuator 5 effective on a roll, for example a separate actuator or loading shoes for a Sym roll. Such an assembly is shown in Fig. 8. In the example, the pulse generating unit 3 comprises a quick actuator 5 and a high-speed valve 6.

In the example, the measuring unit 1 comprises roll coating sensors 1 a placed in the roll coating, for measuring roll oscillation. In a polymer roll, the measuring sensors are placed along the direction of the periphery, and possibly in several groups along the direction of the periphery in the transverse direction.

A separate actuator cylinder 5 may be an actuator connected directly or indirectly to the support of the roll, or, in the case of a Sym roll, a glide- lubricated loading shoe inside the roll shell.

The embodiment according to the example operates as follows. Sensors 1 a placed in the roll coating are used to measure high-frequency pressure variations effective in the direction of the periphery, particularly in a nip. Furthermore, the sensors can be used to measure high-frequency pressure variations effective in the cross direction of the roll, particularly in a nip.

The measured data is synchronized with the rotational movement of the roll, after which a control signal is generated in the control unit 2 to control the pulse generating unit 3 to have an advantageous effect on the vibration. For example, a suitably synchronized pulsation eliminates the roll vibration.

The device can be used to adjust a small-amplitude error in the profile, which could not be corrected with conventional valve solutions. An arrangement according to the example can be connected to existing systems. The solution can be utilized for vibration damping.

Figures 9 to 1 1 show an embodiment of the invention which is particularly suitable for generating a very short and very quick motion or supporting force in active vibration damping. This actuator according to the invention consists of an actuator 36 and a cylinder package 38, with both a main cylinder 37 and a working cylinder 39 integrated in it. By means of electric current, an electromechanical actuator 36a, i.e. a voice coil motor, generates a motion in the motor shaft 36b that moves the piston of the main cylinder 37. The piston displaces pressurized medium (oil) which, in turn, moves the working cylinder 39. For one working cylinder 39, the actuator may comprise one or more parallel main cylinders as well as a voice coil motor 36a for driving them. By means of several parallel main cylinders/voice coil motors 36a, the speed of motion of the working cylinder 39 can be multiplied in relation to the number of motors, because the displaced oil volume increases.

To obtain a greater force, the area A37 of the main cylinder can be reduced in relation to the area A39 of the working cylinder. The hydraulic transmission ratio of the device is A39/A37, and it typically receives a value between 2 and 200.

In addition to the voice coil motor, the working cylinder can be driven in parallel by a conventional (servo) valve 40. Thus, for example, the large and slow movements can be implemented with the (servo) valve, and the quick motions, in turn, with the voice coil motor.

Figure 9 shows a voice coil motor unit 36 according to the invention, comprising 10 successive voice coil windings 36a around the same stem 36b in such a way that each winding generates 1 kN. The number of windings has an effect on both the force and the speed to be obtained. The windings 36a of the voice coil are cooled with a separate circulation (not shown). This is necessary, because a current of several hundred amperes is conducted momentarily to the windings 36a.

Figure 10 shows a hydraulic amplifier with an arrangement, in which the piston of the working cylinder 39 is placed in the same position with the voice coil stem 36b.

Figure 1 1 , in turn, shows a situation, in which two voice coil motors 36 drive double-acting main cylinders 37. Oil is supplied to both sides of the working cylinder 39, to provide a double-acting and symmetrical motion. With the above-mentioned system according to the invention, the reciprocating pulsating motion of the stem 36b of the voice coil motor takes place with a zero load in about 0.5 ms and with a counter load of 100 kN in about 1.2 ms. The force of the stem 36b of the voice coil motor is about 1 O kN, and 5 parallel motors generate a force of 20O kN in the working cylinder, the transmission ratio being 1 :4.

One arrangement according to the invention can also be formed by coupling the stem motion generated by the voice coil motor directly to the required target, without a hydraulic cylinder. Thus, the force to be obtained is smaller, but it can be increased by coupling several voice coil motors in parallel.

As can be seen from the preceding examples, the arrangement according to the invention is suitable, for example, for controlling vibrations of paper and cardboard machines, finishing devices (coating machines, calenders, reel- ups, slitter-winders), as well as continuous fibrous web presses. The solution is also suitable for damping vibrations occurring in vehicles and working machines (for example, active suspension, compensation of wander of the engine or the cabin). The solution according to the invention can also be used, for example, for the oscillating motion of screens needed in mineral preparing machines, as well as for generating the movement of crushers.

By combining, in various ways, the modes and structures disclosed in connection with the different embodiments of the invention presented above, it is possible to produce various embodiments of the invention in accordance with the spirit of the invention. Therefore, the above-presented examples must not be interpreted as restrictive to the invention, but the embodiments of the invention may be freely varied within the scope of the inventive features presented in the claims hereinbelow.

Claims

Claims:

1. An apparatus for controlling vibrations of a machine, the apparatus comprising at least: - a measuring unit (1 ) for measuring vibrations, a pulse generating unit (3) for generating counter motions, the pulse generating unit comprising at least: a hydraulic actuator (5), a device (6) for controlling the flow of hydraulic fluid; - a control unit (2) for controlling the pulse generating unit on the basis of measurement data from the measuring unit, characterized in that the actuator (5) is a chamber with solid walls, at least one of the walls being flexible and being configured to yield by the effect of pressure.

2. The apparatus according to claim 1 , characterized in that the actuator (5) is connected to a hydraulic cylinder (31 ) configured to change the position of a machine part.

3. The apparatus according to claim 1 or 2, characterized in that the device (6) for controlling the flow of hydraulic fluid is a quick-operated control valve.

4. The apparatus according to claim 3, characterized in that the control valve (6) comprises a stem, and for moving the stem, an electromagnetic voice coil is integrated in the stem.

5. The apparatus according to any of the preceding claims, characterized in that the actuator (5) is integrated in a loading shoe (35) of a multi-zone roll (33).

6. A method for controlling vibrations of a machine, the method comprising at least: controlling vibrations of the machine; generating counter motions for the vibration by means of a pulse generating unit (3), which pulse generating unit comprises at least: a hydraulic actuator (5), a device (6) for controlling the flow of hydraulic fluid; controlling the pulse generating unit on the basis of measurement data; characterized in that the counter motions are generated by means of an actuator (5) comprising a chamber with solid walls, at least one of the walls being flexible and yielding by the effect of pressure.

7. The method according to claim 6, characterized in that the flow of hydraulic fluid is controlled by means of a control device (6) which is a quick- operated control valve.

8. The method according to claim 7, characterized in that the control valve (6) comprises a stem, and the movement of the stem is implemented with an electromagnetic voice coil integrated in the stem.

9. The method according to any of the preceding claims 6 to 8, characterized in that the actuator (5) is integrated in a loading shoe (35) of a multi-zone roll (33).

10. The method according to any of the preceding claims 6 to 8, characterized in that the actuator (5) is connected to a hydraulic cylinder (31 ) for changing the position of a machine part.