Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
A METHOD FOR CONTROLLING THE NORMAL FREQUENCY OF VIBRATION AND A VIBRATION DAMPER
Document Type and Number:
WIPO Patent Application WO/2007/088240
Kind Code:
A1
Abstract:
The present invention relates to a method for controlling the normal frequency of an intermediate roller of a calender by means of improved roller support. The method is characterised in that by means of the roller support in the control of the lowest nominal frequency of the movement mode of the roller or a roller position said lowest normal mode is shifted to a desired frequency range. The invention also relates to a vibration damper for damping the vibration of an intermediate roller of a calender and/or eliminating the barring phenomenon, for example, which damper includes a body part (4) and an upper disc spring (31) above it and a lower disc spring (32) below it. The damper is characterised in that the damper may be tuned to operate at a desired frequency and to be suitable for a desired tuning frequency by using at least one flexibility element (10, 11, 12, 13; 21, 22) in order to provide a mutual contact between at least the upper disc spring (31) and the body part (4) as desired.

Inventors:
OLKKONEN, Mika (Taaniontie 1 C 16, Järvenpää, FI-04400, FI)
KAISANLANTI, Mika (Kansakoulunkatu 30 A 13, Järvenpää, FI-04400, FI)
LEINONEN, Erkki, J. (Kasvitarhankatu 1, Järvenpää, FI-04400, FI)
Application Number:
FI2007/050021
Publication Date:
August 09, 2007
Filing Date:
January 17, 2007
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
METSO PAPER, INC. (Fabianinkatu 9 A, Helsinki, FI-00130, FI)
OLKKONEN, Mika (Taaniontie 1 C 16, Järvenpää, FI-04400, FI)
KAISANLANTI, Mika (Kansakoulunkatu 30 A 13, Järvenpää, FI-04400, FI)
LEINONEN, Erkki, J. (Kasvitarhankatu 1, Järvenpää, FI-04400, FI)
International Classes:
D21G1/00; F16F3/00; F16F9/00
Attorney, Agent or Firm:
LAHTI, Heikki (PATENTIA, Sinimäentie 8 B, Espoo, FI-02630, FI)
Download PDF:
Claims:

Claims

1. A method for controlling the normal frequency of an intermediate roller of a calender, particularly for damping vibration and/or eliminating the "barring" phenomenon, for example, in a material web machine by means of improved roller support by using a damper that includes a body part (4), above which there is an upper disc spring (31) and below which there is a lower disc spring (32), characterised in that, by means of the roller support, in the control of the lowest normal frequency of the movement mode of a roller or roller position said lowest normal mode is shifted to a desired frequency range, that the damper is engaged into operation by means of the upper disc spring (31) by pressurising a medium chamber (12), whereby the upper disc spring is drawn into contact with the body part (4) of the damper, and that the vibration damper is tuned to operate at a desired frequency and to be suitable for a desired tuning frequency by means of at least one flexibility element (10, 11, 12, 13; 21 , 22), whereby a mutual contact between at least the upper disc spring (31) and the body part (4) is provided when desired.

2. A method as claimed in claim 1 , characterised in that the movement mode of a rigid component of the roller or roller position is lowered lower than the normal frequency of the movement mode of the originally more rigidly supported component or roller position.

3. A method as claimed in claim 1 and/or 2, characterised in that the normal frequency of the lowest normal mode is controlled by tuning the vibration damper to operate at a desired frequency, whereby the damper is used including at least one flexibility element (10, 11, 12, 13; 21 , 22), by means of which at least the upper disc spring (31) and the body part (4) of the damper are brought into mutual contact when necessary.

4. A vibration damper for damping the vibration of a calender roller, preferably an intermediate roller of a calender, for example, and/or for eliminating the "barring" phenomenon, for example, in a material web machine, which damper includes a body part (4), above which there is an upper disc spring (31) and below which there is a lower disc spring (32), characterised in that the damper is engaged into operation by means of the upper disc spring by pressurising a medium chamber (12), whereby a first piston member (10) draws the upper disc spring (31) into contact with the body part (4) of the

damper, and that the vibration damper is tuneable to a desired frequency and to be suitable for a desired tuning frequency by means of at least one flexibility element (10, 11, 12, 13; 21, 22), whereby a mutual contact between at least the upper disc spring (31) and the body part (4) may be provided when desired.

5. A vibration damper as claimed in claim 4, characterised in that the rigidity of the damper is selectable.

6. A vibration damper as claimed in claim 4 and/or 5, characterised in that the rigidity of each flexibility element complies with the powers of 2.

7. A vibration damper as claimed in any one of the preceding claims, characterised in that the number of the flexibility elements is optional so that one or more may be engaged into operation according to the desired tuning frequency in order to control the normal frequencies of the rollers.

8. A vibration damper as claimed in any one of the preceding claims, characterised in that the tuning may be implemented at an accuracy of 1% in any frequency range.

9. A vibration damper as claimed in any one of the preceding claims, characterised in that the upper disc spring (31) is divided into sectors.

10. A vibration damper as claimed in any one of the preceding claims, characterised in that the flexibility element arranged in the damper includes a first piston member (10) arranged in the upper disc spring (31), a piston rod (11) that extends from the first piston member through the upper disc spring to a cylinder chamber (12) arranged in the body part (4) and at the other end of which there is a second piston member (13).

11. A vibration damper as claimed in any one of the preceding claims, characterised in that the upper disc spring (31) houses an installation cavity (5) for the first piston member (10) and that a loading spring (21) is arranged between the lower surface of the piston member and the bottom surface of the cavity in order to keep the first piston member protruded from the cavity.

12. A vibration damper as claimed in any one of the preceding claims, characterised in

that the second piston member (13) may be moved back and forth in the cylinder chamber (12) by means of a medium fed into the cylinder chamber (12) surrounding the piston rod (11) in order to provide a mutual contact between the upper disc spring (31) and the body part (4).

13. A vibration damper as claimed in any one of the preceding claims, characterised in that when the upper disc spring (31) is not in operation the upper disc spring rests on small coil springs (22).

14. A vibration damper as claimed in any one of the preceding claims, characterised in that the damper is tuneable to a desired frequency by using one or more flexibility elements and, in addition, the rigidity of the damper and/or each flexibility element may be selected to be suitable depending on the desired tuning frequency, the spring constant of which rigidity may be calculated by the equation

Kspring = 4 * f 2 χ π 2 * m

Description:

A method for controlling the normal frequency of vibration and a vibration damper

Generally, the present invention relates to the control of the normal frequency of vibration and damping of vibration. More particularly, the present invention relates to a method for controlling the normal frequency of an intermediate roller of a calender by means of improved roller support, and to a vibration damper.

A preferable area of use for the present invention is a material web machine, especially in order to control high-frequency vibration and skeleton vibrations of the material web machine.

In a multi-roller calender, the applicant's "OptiLoad" calenders, for example, one dimensioning criterion for intermediate rollers is the normal frequency of the roller, which is typically the lowest normal deflection mode. The frequency of the normal mode in question must be above or below the roller's rotation frequency range by a desired margin. In calenders the aim is to dimension the normal frequency of the roller to be higher than the rotation frequency of the roller, without exception. Sometimes this dimensioning criterion results in large and expensive rollers.

In order to implement a dynamic damper, i.e. a "Tuned Mass Damper" (TMD), an accurately controlled and adjustable spring constant is required. Adjustability is needed either only at commissioning or, in the case of an adaptive vibration damper, also during use. When the required damper masses increase and when attempting to damp high- frequency vibrations (for example, barring 200 to 800 Hz or a calender skeleton vibration damper 10 Hz / 7,000 kg), large spring constants are required. Providing large spring constants in a restricted space is difficult, especially if adjustability is also required.

Currently in a fibre web machine, for example, the intermediate rollers of a calender are equipped with roller bearings at their ends and bearing housings are fastened to lightening levers of the roller with bolted joints. The lightening lever eliminates the rollers' own mass and that of auxiliary devices from the nip load of a nip between two opposite rollers. The bearing housing, lightening lever and fastenings of the lever with the body and the body of the calender form a support of the roller, which together with the roller determines the normal frequencies of the roller. The support of the roller is attempted to be formed to be so rigid that the normal frequency of the roller has a sufficient margin

compared with the rotation frequency of the roller.

By means of the current technique only a finite rigidity can be accomplished for the support of the roller, i.e. the rigidity of the support cannot be increased limitlessly to a desired value. Due to technical and economic reasons, the lightening levers and bearing housings, etc. are serialised. For large rollers the rigidity of the support may drop too low compared with the rotation frequency. When the size of the roller increases, so does the price of the roller. If there are several intermediate rollers - in a conventional 12-roller

OptiLoad calender, for example, there are 10 intermediate rollers - and if the roller size has to be increased due to the normal frequency, the cost factor is considerable.

It is well known previously that generally the means to implement an adjustable spring constant is to use a cantilever whose flexible length is changed as a spring. It is most common to implement a damper by fastening a mass component directly to the cantilever, whereby the flexible length of the cantilever is the distance from a fastening point. The spring constant is changed by changing the flexible length, whereby the dynamic damper comprises the cantilever and the mass component. Thus, the mass component is the vibrating mass of the damper and the length of the cantilever is the flexible length of the damper. In practice, it is easy to achieve a desired rigidity of the cantilever, but what becomes a problem is that it is difficult to find a sufficiently rigid fastening point. If the fastening point is not sufficiently rigid and if the fastening point is flexible, the cantilever will not be sufficiently rigid. Thus, the problem is that, while it is easy to implement a large adjustable spring constant by means of a cantilever, the rigidity of the fastening point is not sufficient.

The German patent specification 10133888 discloses a method for using calenders. According to the specification, in a roller stack including an upper roller and a bottom roller and three intermediate rollers and including at least one soft-surface roller, the middle roller is arranged to the side from the vertical nip line. In the specification, the vibration of at least two rollers in the nip line and the roller to the side from the nip line are measured and analysed and the result obtained is used to control an actuator by means of which the location of the roller to the side from the nip line can be positioned.

One object of the present invention is to eliminate or at least substantially reduce the weaknesses of vibration damping associated with conventional material web machines.

Another object of the present invention is to provide a new and inventive method for controlling the normal frequency of an intermediate roller of a calender. According to one aspect of the present invention, the second object of the invention is to provide a method for controlling the normal mode of the movement mode of a roller or roller position. A third object of the present invention to provide a new and inventive vibration damper for damping the vibration of a roller of a calender of a material web machine and for reducing the barring phenomenon, for example. According to another aspect of the present invention the fifth object of the invention is to provide a vibration damper whose rigidity would be tuneable.

In order to achieve the objects of the invention, the method for controlling the normal frequency of an intermediate roller of a calender by means of improved roller support according to the invention is generally characterised in that by means of the roller support in the control of the lowest normal frequency of the movement mode of the roller or roller position said lowest normal mode is shifted to a desired frequency area. Preferably, so that the support of the roller or roller position is "loosened", whereby the actual lowest deflection mode of the roller is raised to a higher frequency.

Thereby the movement mode of a rigid component of the roller or roller position may be lowered slightly lower than what would be the normal frequency of the movement mode of the originally more rigidly supported component or roller position. One advantage is, for example, that the rollers may now be made lighter and thus cheaper.

In order to achieve the objects of the invention, the vibration damper for damping the vibration of a calender roller, preferably an intermediate roller of the calender, for example, and/or for eliminating the barring phenomenon, for example, is generally characterised in that the vibration damper may be tuned to operate at a desired frequency by using at least one flexibility element whose rigidity or the rigidity of which damper can be selected to be suitable for a desired tuning frequency. According to the invention, it is preferable that the rigidity of each flexibility element complies with the powers of 2. The number of the flexibility elements is preferably optional so that one or more can be engaged into operation according to the desired tuning frequency.

According to the invention it is thus possible to control the normal frequencies of the rollers. In addition, an extensive design frequency may be applied, i.e. +/- 25%. Another advantage is that, thanks to the invention, tuning may be implemented at an accuracy of

1% in any frequency range.

With regard to the other special characteristics and advantages of the invention, reference is made to the appended set of claims and the following special part of the description of the invention, in which one preferred embodiment of the invention is explained by way of example and by means of an example and by reference to the appended drawings, where

Figure 1 shows a deflection mode of a roller when an intermediate roller rests on a lightening cylinder,

Figure 2 shows a deflection mode of a roller when an intermediate roller is against a stopper,

Figure 3 shows frequency responses when the roller rests on the lightening cylinder and when the roller is against the stopper, Figure 4 shows a top plan view of a vibration damper,

Figure 5 shows a cross-sectional view of the vibration damper shown in Figure 4 along the line A-A in Figure 4, and

Figure 6 shows an enlarged view of the area marked by a dot-dash line in Figure 5, and

Figure 7 shows one preferable example of arranging suspension between an upper disc spring and a body part.

Reference is made to Figure 1. The figure shows a phenomenon based on measurement results, showing the deflection mode of a roller when an intermediate roller rests on a lightening cylinder. In the example illustrated by the figure the normal frequency of the mode is 15.7 Hz.

Reference is made to Figure 2. The figure shows a phenomenon based on measurement results, showing a deflection mode of a roller when an intermediate roller is against a stopper, which is a fixed support in the example of the figure. In the example illustrated by the figure the normal frequency of the mode is 11.9 Hz.

Reference is made to Figure 3. The figure illustrates frequency responses of Figures 1 and 2. The thicker line shows the case where the roller rests on the lightening cylinder

(Figure 1) and the thinner line shows the case where the roller is against the stopper (Figure 2). It can be seen that the difference between the normal modes or the change in

the normal modes is clearly noticeable.

According to this invention roller support may be modified so that the lowest normal mode, which is typically also the most harmful normal mode, is controllable and may be shifted to a desired frequency range. Thus, according to the invention the roller support is "loosened" so that the actual lowest deflection mode of the roller rises to a higher frequency. Thereby the movement mode of a rigid component of the roller / a roller position drops slightly lower than what would be the normal frequency of the originally more rigidly supported roller.

This lowered movement mode of the rigid component may be damped by using Gerb viscous elements, for example, or some other corresponding elements. The movement mode in question may be damped as in this movement mode the roller does not deflect but the roller position of the roller moves rigidly around its support joint. The actual frequency of the deflection mode of the roller may now be lower. Due to this, the roller may be smaller especially with regard to its diameter and thus the roller may be lighter and cheaper.

A mode where the roller is deflected is difficult to damp as thereby the largest deviation in relation to a straight geometrical rotation axle is in the middle of the roller, where the largest movement also takes place and where additional dampers or the like cannot be built.

A vibration damper or damper according to the invention is suitable for damping the vibration of a calender roller, preferably an intermediate roller of a calender and/or for eliminating the barring phenomenon, for example.

Reference is made to Figure 4, which shows a top plan view of the damper and Figure 5, which shows a cross-sectional view of the damper along the line A-A in Figure 4.

The damper according to the invention includes a body part 4, which mainly forms the mass of the damper. The body part is connected to a vibrating structure either directly or by means of a cantilever supporting the mass. In the case of a material web machine, the body structure is typically a roller. The vibration of the roller may be harmful vibration, which may result in a "barring phenomenon".

The body part 4 of the damper is cylindrical in the example shown in Figures 4 and 5 and an upper plate-like disc spring 31 is arranged above the body part and a lower plate-like disc spring 32 is arranged below the body part.

The lower disc spring may be in one piece. From the point of view of operation, it is preferable according to the invention that the upper disc spring 31 in the damper is divided into sectors. The sector division of the upper disc spring is illustrated by a dotted line in Figure 4. It should be noted that optionally the lower disc spring 32 may also be divided into sectors.

Reference is made to Figure 6, which shows an enlarged view of the area marked with a dot-dash line in the figure. This illustrates a flexibility element arranged in the damper according to the invention by means of a cross-sectional view. The flexibility element arranged in the damper includes a first piston member 10 arranged in the upper disc spring 31 , a piston rod 11 that extends from the first piston through the upper disc spring to a cylinder chamber 12 arranged in the body part 4 of the damper and at the other end of which there is a second piston member 13.

In one example of the invention the upper disc spring 31 houses an installation cavity 5 for the first piston member 10 according to Figure 6. In order to keep the first piston member protruded from the cavity a loading spring 21 is arranged between the lower surface of the piston member 10 and the bottom surface of the cavity so that it is partly above the upper surface of the disc spring 31.

The second piston member 13 may be moved back and forth in the cylinder chamber 12 by means of a medium fed into the cylinder chamber 12 surrounding the piston rod 11 so that by means of the movement of the second piston member the body part 4 and the upper disc spring 31 can be brought into mutual contact in order to engage the disc spring into use in the damper. The contact is engaged into operation by means of the upper disc spring, for example, by pressurising the medium chamber 12. Thereby the first piston member 10 draws the upper disc spring 31 into contact with the body part 4 of the damper. The rigidity of the contact is decisive; hydraulic force is only needed to keep the contact closed.

Reference is made to Figures 7 and 8, which show an alternative example of engaging the disc spring into operation. In the situation of the example, the upper disc spring 31 is not in operation, or it "floats", without interfering with the operation of the damper, on small coils springs 22, which are arranged in the form of a circle around the piston rod 11 between the upper disc spring 31 and the body part 4 of the damper. When the upper disc spring 31 is engaged into operation the medium chamber 12 is pressurised and the first piston member 10 draws the disc spring 31 into contact with the body part 4 of the damper. The rigidity of the contact is decisive; hydraulic force is only needed to keep the contact closed.

This example may be generalised. Frequency adjustment of +/- 25% may be implemented by means of six separately engaged springs at an accuracy of 0.7% independently of frequency and mass. Alternatively, a smaller number of springs to be engaged may be used and/or the frequency rage may be expanded at the cost of accuracy.

Reference is made to Figure 7. According to the invention, small coil springs 22 are arranged between the first piston member 10 and the upper disc spring 31. These coil springs may replace the loading spring 21 explained in connection with Figure 6, fitted below the first piston member 10 around the piston rod 11. Alternatively, the coil springs 22 may operate in parallel with or in addition to the loading spring 21. According to the invention, by means of the loading spring and the several coil springs the spring constant K of the flexibility element 10, 11, 21 (22,) 12, 13 of the damper can be controlled better and more accurately.

According to the invention, the damper according to the invention may be tuned to a desired frequency by using one or more flexibility elements. In addition, the rigidity of the damper and/or each flexibility element may be selected to be suitable depending on the desired tuning frequency.

According to the invention, it is preferable that the rigidities of the flexibility elements preferably comply with the powers of 2. The number of the flexibility elements is preferably optional so that one or more may be engaged into operation according to the desired tuning frequency. According to the invention, this allows controlling the normal frequencies of the rollers. In addition, an extensive design frequency may be applied, i.e.

+/- 25%. Another advantage is that, thanks to the invention, the tuning may be implemented at an accuracy of 1 % in any frequency range.

Example - the barring phenomenon of a calender

A principle that is analogous to the example of reducing the barring phenomenon to be explained below may be applied to damping the skeleton vibration of a calender, for example.

Barring occurs in a calender in the frequency range of 350 Hz. The problem has been found to also randomly occur at the frequency of 372 Hz. A dynamic damper installed in a bearing housing of a roller has been supposed to be able to eliminate the vibration problem. A sufficient vibrating mass is assessed at 25 kg. A damper is designed for the frequency 360 Hz +/- 25%. Thereby the lower limit frequency of the operation of the damper is 0.75 x 360 Hz = 270 Hz and the upper limit frequency is 1.25 x 360 Hz = 450 Hz. The required spring constant for the lower limit frequency and the upper limit frequency is calculated by the equation kspring = 4 * f 2 x if * m, whereby k 270H z = (7.195 x 10 7 ) N/m k 450H z = (1.999 x 10 8 ) N/m

Let the structure of the damper generally resemble Figures 4 and 5. In the damper according to the invention the darkened sectors of the lower disc spring 31 and the upper disc spring 32 (cf. Figure 5) are dimensioned so that the sum of their rigidities corresponds to the spring constant requirement at the lower limit frequency (71.95 kN/mm). These disc springs keep the device "in shape" and are always used or need not be disengaged ever. The part of the circle remaining white in Figure 5 is divided into smaller sectors.

It should be noted that in various alternative and/or functionally equivalent technical implementations there may naturally be two superimposed disc springs above, for example, of which one is always engaged and the other is divided into parts.

The total spring constant of the flexibility element according to Figure 6 must naturally be such that the upper limit frequency of 450 Hz is achieved when all the springs of the

flexibility element are engaged.

I<45OHZ - k 27 oHz = (1.279 x 10 8 ) N/m

When in the damper according to the invention the disc spring 31 above the flexibility element is divided into sectors, i.e. when the white area in the figure is divided into six springs to be engaged separately, which may be separate coil springs, for example, so that their mutual rigidity ratios comply with the powers of two of 2° to 2 5 , the following relative rigidities are obtained:

2° = 1

2 1 = 2

2 2 = 4

2 3 = 8

2 4 = 16

2 5 = 32

The sum of relative rigidities is: 1 + 2 + 4 + 8 + 16 + 32 = 63

The rigidities of the individual springs may be calculated from this. The smallest spring (relative rigidity of 1 ):

^smallest = 1/63 X kt o tal_whites = (2.03 X 10 ) largest = 32/63 X k t otal_whites = (6.497 X 10 7 )

These springs to be engaged separately allow implementing any spring constant in the range k to tai_whites - k 2 70Hz = (1.279 x 10 8 ) N/m at the accuracy of the rigidity of the smallest spring (the maximum error is half the smallest spring constant if the springs comply with the series accurately). The normal frequency of the damper is calculated when only the smallest spring is engaged:

fdamper = 1/2π X Vk spri ng/m

fsmallest_engaged- 1/211 X V(k270Hz + k sma n θS t)/25 - (273.783)

The frequency step is at its largest when moving from the lowest (0 springs engaged)

frequency to the next (see the frequency equation) and, in addition, the decisive matter from the point of view of frequency behaviour is not the difference in hertz between the tuning frequency and the frequency to be damped but their relative difference, i.e. by how many percentage points the frequencies differ from each other. Therefore, the operation of the damper (tuning accuracy) is at its worst at the lowest frequency. Thus, the inaccuracy of the tuning in the whole operation range is better than:

δtuning = (fsmallest_engaged " 270) = (3.783) (δtuning /2) / 270 = 0.701 %

The springs to be engaged to achieve the spring constant required at any given time are obtained from the binary representation of the figure.

The desired tuning frequency is obtained by measuring the frequency of the harmful vibration. The common spring constant of the spring, which are to be engaged and which corresponds to this frequency, is calculated and divided from the spring constant of the smallest spring. Thereby a figure in the range 0 to 63 is obtained. The binary representation of the figure obtained shows the combination to be engaged. If the figure obtained, i.e. rounded, is 13, for example, the binary representation is 001101 (0 x 2 5 + 0 x 2 4 + 1 x 2 3 + 1 x 2 2 + 0 x 2 1 + 1 x 2° = 13), i.e. the smallest, third smallest and fourth smallest spring must be engaged.

The achieved 0,7% maximum error in tuning accuracy is already excellent. It would be possible to reduce the number of the springs to be engaged by one or expand the operation frequency range. Figure 7 shows a "magnification coefficient" K as a function of the frequency ratio r at two different attenuation values (1% and 1.25%); K indicates how large a multiple the displacement of the attenuation mass is as compared with the impulse and thus how effective the damper is. The frequency ratio here corresponds to the ratio between the tuning frequency and the frequency of the vibration to be damped, which varies in the range r = 0.993 to 1.007 according to the example above. In a real damper the attenuation should be increased to protect the damper device against oversized vibration amplitudes. At the same time the tuning accuracy requirement of the damper is reduced. In theory, small attenuation and sufficient tuning accuracy reduce the size of the mass required, i.e. small attenuation is a desirable characteristic. In this case the mechanics must endure or allow large amplitudes.

The invention has been described above only by way of example. This does not limit the invention but many modifications and alternative solutions and functionally equivalent implementations are possible within the scope of the inventive idea, which is defined by the appended set of claims.