WO2010043754A1

WO2010043754A1 - Apparatus and method for winding up a fibrous web

Info

Publication number: WO2010043754A1
Application number: PCT/FI2009/050284
Authority: WO
Inventors: Timo Virtanen; Pekka Vantola; Jari Tiitta; Kenneth ÅKERLUND; Markku JÄRVENSIVU; Marko Jorkama; Sami LUMIJÄRVI
Original assignee: Metso Paper, Inc.
Priority date: 2008-10-17
Filing date: 2009-04-15
Publication date: 2010-04-22
Also published as: DE112009002505T5; FI20080581A0

Abstract

Apparatus and method for winding up a fibrous Web around a wind-up core (22) into a roll, the device comprising at least one nip roll for forming a nip load onto the roll to be wound up (22), the nip load and/or some other roll supporting force is arranged to be formed at least partly by means of a hydraulic actuator or hydraulic actuators (5) so that the pressure and/or volume flow adjustment of one hydraulic actuator or several hydraulic actuators (5) is arranged by means of a digital valve group (7).

Description

Apparatus and method for winding up a fibrous web

The invention relates to an apparatus for winding up a fibrous web around a wind- up core into a roll, which apparatus has at least one nip drum for forming a nip load onto the roll to be wound up, the nip load and/or some other roll supporting force being arranged to be formed at least partly by means of a hydraulic actuator or actuators.

The invention also relates to a method for winding up a fibrous web around a wind- up core into a roll, in which method a nip load is formed to achieve a radial com- pression to the roll to be wound up, the nip load and/or some other roll supporting force being formed at least partly by means of a hydraulic actuator.

One embodiment of the invention relates to a reeler for continuous winding of a fibrous web around a reel spool into a machine roll, the reeler comprising a reel-up drum so that a nip load can be formed between the machine roll and the reel-up drum and that the machine roll can be moved in relation to the reel-up drum by means of a rolling car and rolling car locking levers, in accordance with the increase of the machine roll diameter.

A second embodiment of the invention concerns a wind-up unit for a slitter winder, in which the fibrous web is wound around a core or a similar wind-up shaft into rolls so that the set change, i.e. the termination/finishing of the completed wind-up and the beginning of a new one is carried out with a considerably lower speed compared to the normal production speed. The slitter winder's wind-up unit has certain uniformities with the reeler, but also considerable technological differences, which are due, among other things, partly to the scale and partly to the required characteristics of the wound product.

A reeler is an apparatus, which winds a material produced as a continuous fibrous web to a roll form into a machine roll. In the production process of a fibrous web winding up is usually the first partial process, in which the continuous production is interrupted to be continued in sequences. The machine roll is formed around a reel spool acting as the wind-up core, i.e. the fibrous web on one machine roll has a beginning and an end. The continuous increase in the machine roll size is an ongoing trend in the field, causing a constant need for the development of reelers. In practice, the reel spool dimensioning determines the maximum size for the machine roll. However, because a dynamic environment is concerned, and the fibrous web is a wound material susceptible to various defects, the task of the reeler in maintaining the operating efficiency of a paper or board machine is very significant. One reason for the continuous increase in the machine roll size is the desire to have fewer beginnings and ends impeding or disturbing the production or reducing the operating efficiency in the production of fibrous webs.

Hydraulic actuators are generally used for the generation of motions and forces in present reelers. Actuators get their driving force from a hydraulic aggregate in the form of a pressure medium or pressurised hydraulic oil. Typical objects are, for example, motions of different cars, levers, such as locking jaws or levers, rotating motions, such as rotating a primary wind-up device onto rails, etc. In older pope reelers, also pneumatic cylinders were used as actuators. A drawback with pneumatics is the small power level obtained from the actuators, which usually is not sufficient for the present reelers. Also the actuator size increases along with the power requirements, and hydraulic actuators have virtually replaced pneumatic ac- tuators in reeler embodiments, due to their small size and big power generation ability. From the state of the art there is known, e.g. Fl 20022030, disclosing a further developed solution.

A fibrous web coming from a fibrous web machine is wound into machine rolls that are as big as possible, with a width of as much as over 10 m and a diameter of 4 m by using a reeler. After this the fibrous web is processed in reprocessing machines (e.g. slitter winder, unwinder/intermediate reeler/reeler, calendar, and coating machine). The nip force between the roll and one or several drums is typically adjusted in the slitter winder and reelers. Nip force is typically controlled by means of power and/or pressure adjustments. In the nip force adjustment during wind-up one tries to obtain a smooth adjustment and wants to avoid quick changes, which would cause possible wind-up defects to the roll. Again, on the other hand e.g. during the change of the reel spool of the reeler and the set change of the slitter winder there is a need for very fast position controls. Also the switch from position control to power control should happen fast and without exceeding the specified power. A combined power and position control is typically done by a servo valve and hydraulic cylinder.

There are several challenges linked with the power and position control connected to the use of a present servo valve. One challenge relating to power control is that the servo valve provides almost full (approximately 80%) pressure with a valve opening of approximately 4%. This weakens the accuracy of the adjustment and causes that already a small change in the control causes a big change in pressure. This connection between the opening and pressure is called the pressure amplification curve. The stem of the servo valve is typically moved by an electromagnetic coil. The stem mass and valve structure cause that a resonance peak is shown in the frequency response of the stem typically with small openings of +/- 5% (see Figure 1). This can also be seen as vibration in the stem's step response (see Figure 2). This vibration is also conveyed to the adjustable pressure, thus causing disturbances in the power/pressure control.

If characteristics of the servo valve are examined from the point of view of fast position controls, the above mentioned stem vibration can cause problems also in the position control. On the other hand, when one wishes to avoid fast motions, there is usually a need for big currents and thus for big valves. Big valves are again not so well suited for precise pressure control so that it is challenging to carry out high- quality power and position controls with them. The relation between the opening and current is not fully linear with servo valves, either. There are also some prob- lems related to the manufacturing technique of present servo valves. The servo valve stem is a fine-mechanically manufactured component, the manufacturing tolerances of which are very small. Because of this, the servo valve is relatively susceptible to impurities in oil or some other liquid, gas, or a mixture of these. There are also differences in the valve pressure amplification curves between dif- ferent valve units, which can cause problems especially in power control, if the valve has to be replaced. It is also not possible to control the cylinder's piston and arm side independent from each other with one servo valve.

An object of the invention is to further develop the technology of the devices winding up a fibrous web so that controllability and adjustability, and operational reli- ability would be improved, and the need for service of the functions or actuators would decrease. It is also an object of the invention to achieve a device which would be robust and durable, among others, in surprising overload situations. It is further a special object of the invention to considerably speed up response times for the hydraulic control system so that the adjustments of the said devices, such as reelers and slitter winders can be made especially fast and precisely, when desired.

It is characteristic of the apparatus of the invention that the adjustment of the pressure and/or volume flow of one or several hydraulic actuators is arranged by means of a digital valve group. The method of the invention is again characterised in that the pressure and/or volume flow of one or several hydraulic actuators is adjusted by means of a digital valve group.

The invention has common characteristics with the state of the art technology in that the power, pressure, position or other adjustments are carried out in slitter winders and reelers. Some of these adjustments control the nip force between the roll and drum/drums. In the manner disclosed by the invention, these adjustments and motions can be carried out using digital hydraulics in the manner described later in connection with different embodiments, thus achieving several of the said pursued benefits.

Especially advantageous embodiments of the invention are such hydraulic systems for a slitter winder or reeler, in which big force and big position accuracy are needed simultaneously. Such embodiments typically comprise functions affecting the fibrous web of a wound fibrous web roll or starts, motions and stops of heavy machine parts. A feature common to all of these is that the processing efficiency of the fibrous web improves, the faster the function in question can be performed. Most often the function is related to a transaction outside the actual wind-up step, such as the beginning or end of the winding up, when the production speed has had to be reduced lower than normal in order to perform the function in question. More detailed examples of advantageous embodiments are disclosed later in this application.

The invention will next be explained in more detail, referring to the enclosed drawings, in which: Figure 1 illustrates a typical frequency response for a servo valve stem with small stem openings;

Figure 2 illustrates a typical frequency response for a stem with small valve openings;

Figure 3 illustrates a wind-up embodiment of the invention; Figure 4 illustrates a second embodiment of the invention; Figures 5a and 5b illustrate a partial view of a cylinder gasket embodiment; Figure 6 illustrates an embodiment in stopping a rolling machine roll; Figure 7 illustrates a universal graph of a digital valve group for controlling a cylinder; and Figure 8 illustrates a second universal graph of a digital valve group for controlling a cylinder. In connection with the illustration of this invention, the following terms are used for facilitating the explanation: machine direction (MD) is described with the term x- direction, cross direction (CD) is called y-direction, and elevation is called z- direction. The term upstream direction is used of the incoming direction of the fi- brous web, and the term downstream direction is used of the outgoing direction of the fibrous web. The wind-up core is in this reeler connection called a reel spool and in the slitter winder connection a wind-up shaft or core, but similarly, these could be called a wind-up shaft. In this connection, the term liquid is mainly used of the pressure medium, but actually this is a fluid, the characteristics of which es- pecially include flowability. This fluid can be liquid, gas or, for example, a mixture of liquid and gas or a mixture of some other, for example, solid component part.

In connection with this invention, also the following terminology is used. Digital hydraulics refers to a system, in which at least part of the components is based on digital valves. A digital valve unit refers to a valve unit, in which there is at least one digital valve group, which again contains a number of digital valves connected in parallel in relation to the fluid flow passing through the digital valve group. A digital valve again refers to a valve intended for adjusting the fluid's volume flow, the valve having 2 - N different stepped discrete adjustment modes, especially 2 different discrete adjustment modes (open/closed), and for which the control signal to be brought from the control system has advantageously been digitalised, such as binary form. The digital valve has advantageously two modes; it is either fully open or fully closed. When the digital valve is open, the entire volume flow of liquid allowed by the digital valve passes through it, and when the digital valve is closed, no liquid at all passes through it. In this application, such a digitally controllable digital valve having two modes is also called an on/off valve and an on/off digital valve. The digital valve can also have more than two modes, in which case the valve is driven in a stepped manner from one mode to another. According to an embodiment, the digital valve advantageously has three positions; it lets the liquid flow pass to a first or second direction, or then the valve does not allow any fluid to pass through it.

The adjusting directive (control signal) is of a digital nature, such as binary. According to the adjusting directive, the volume flow from the digital valve group and the pressure caused by the flow are adjusted by opening a certain valve combination of the digital valve group so that a desired opening of the digital valve group and a desired volume flow of the fluid are achieved. Deviating from an analogue valve, each digital valve connected in parallel can only have a limited number of adjusting modes, i.e. the digital valve only has certain discrete flowing modes. In one digital valve form, it has three modes: open / closed / quick opening. However, each digital valve preferably has simply the on/off mode; when open, the valve lets a certain volume flow through it; when closed, it completely prevents the fluid from passing through.

In most embodiments of the invention described below, the digital valve group consists of digital valves with two modes (on/off). In this case, two successive digital valves with nominal volume flow amounts, the volume flow passing through the valve with bigger nominal volume flow in the open position is always two times bigger than the volume flow of the valve with smaller nominal volume flow. A bi- narised control signal can then be brought to such a digital value group, in which the control signal's magnitude has been converted into a binary number.

As an exemplary comparison of differences in the adjustment method between an analogue valve and a hydraulic valve group, the following can be presented: if an analogue valve is adjusted with a control signal (adjusting directive), the magnitude of which is 12 units, the analogue valve stem moves a quantity comparable with 12 control units, in which case the valve lets through a volume flow that has increased respectively. Again, when a digital valve group consisting of five on/off digital valves connected in parallel to the input flow are controlled by a similarly dimensioned control signal (adjusting directive) of 12 units, in which the sizes of the volume flows the digital valves 1 , 2, 3, 4, 5 let through are respectively 1 , 2, 4, 8 and 16 units, the control signal is binarised into a control signal 01100 (0 x 2⁴ + 1 x 2³ + 1 x 2² + 0 x 2¹ + 0 x 2° = 12) (corresponding to the valves 5, 4, 3, 2, 1), and the valves 3 and 4 are opened. An embodiment of the invention is based on that during wind-up the nip pressure of the roll nip and the opening and closing of the roll nip are adjusted by a hydraulic actuator, the volume flow arriving at which is at least partly adjusted by a digital valve pack. The control messages used by the digital valve group and transmitted by the adjusting system are both in digital form, which achieves the considerable benefit in relation to analogue valves that the adjusting information does not need to be converted from digital to analogue so that no information can disappear when converting the digital control message from the adjusting system into an analogue control message.

By using a digital valve group as switching means, it is possible to control the vol- ume flow arriving at the hydraulic actuator in a very exact manner; for example, by replacing a big proportional valve with a digital valve group containing 12 on/off digital valves, the achieved adjusting resolution comprises 4096 different volume flows. In addition, the operation of the on/off digital valves is considerably fast so that it is possible to control the same hydraulic actuator with the same digital valve group both when changing the location of the drum or roll required by a big change in volume flow when opening or closing the roll nip, and when changing the nip pressure required by a relatively small change in volume flow.

The adjustment of the nip pressure of the roll nip N between the drum pair 2 formed by two drums 21 , 22 is described in Figure 3. The drum pair 2 can be lo- cated, for example, in the reeler in which the fibrous web W travels between the drums, the fibrous web being wound up around the second drum 21 , 22 upon passing through the roll nip N. A hydraulic cylinder 5 is connected to the drum 21. The hydraulic liquid pressure in the pressure cylinder 51 of the hydraulic actuator 5 (hydraulic cylinder) is adjusted by the digital valve group 7. The pressure of the hydraulic liquid in the pressure cylinder generates a certain force, with which the piston 52 affects the drum 21. In this case the drum 21 directs the force F to the stationary counter toll 22, causing a certain nip pressure to the roll nip N between the drum pair 2.

Pressure of the hydraulic liquid in the pressure cylinder 51 is generated by open- ing a suitable valve or suitable valves V; V1..V8 in the digital valve group 7. The digital valve group has eight valves VL. V2 of different sizes so that the liquid flow passing through them always doubles upon transferring from a smaller digital valve to the next size. The difference between the volume flows of two digital valves with successive volume flow amounts is thus 100%, i.e. the volume flow of the valve with the bigger volume flow is always two times bigger than that of the valve with a smaller volume flow. Thus, the valve sizes are, for example, valve V1 one l/min, valve V2 two l/min, valve V3 four l/min, etc. Such different volume flows can be achieved, for example, with valves of different diameters, different opening lengths or a combination of these. For example, when a nip pressure of 10 kN is desired to be achieved to the roll nip, the adjusting system 3 opens the valve V1 in the digital valve group 7 so that hydraulic liquid is flowing to the pressure cylinder 51 with the speed of 1 l/min, and the force F directed to the counter drum 22 by the drum 21 increases. If the force F or the nip pressure is not the desired one, the valve V1 will be closed and the valve V2 opened, and the nip pressure and/or force F is again examined. Thus, by opening and closing the valves V; V1..V2 in the digital valve group 7 one searches for the valve combination which best gen- θrates the desired nip pressure. The digital valve group in Figure 3 comprises 8 valves so that there are 28 = possible different volume flows, i.e. the resolution of the digital valve group is 256. When the principally used nip pressures are known, virtually all nip pressures coming to question can be generated by a suitable step- ping of the volume flow amounts of individual valves in the digital valve group and by a suitable number of valves. The adjusting system again obtains the pressure/force information it needs from the power sensor 4, which is connected to the shaft 21 a of the drum 21.

The adjusting arrangement 1 according to Figure 4 is used for positioning the wind-up core 21 of the reeler 9 in relation to the reel-up drum 22 and for adjusting the nip pressure of the roll nip N in the drum pair 2 formed by the reel-up drum and the wind-up core.

If conventional adjusting arrangement realised with a big adjusting valve were used for transferring the wind-up core 21 of the reeler in relation to the reel-up drum 22 and for maintaining the nip pressure, the adjustment would easily start to sway; the volume flow change of the hydraulic liquid in the hydraulic means 5 required to maintain the nip pressure between the drums 21 , 22 is relatively small, when again the change in the volume flow of the hydraulic liquid needed for transferring the location of the wind-up core in the said hydraulic actuator is relatively big. When the adjustment transfers from the positioning of the location between the drums 21 , 22 to the adjustment of the nip pressure existing in the roll nip between the said drums or vice versa, a big adjusting valve has difficulties already due to its mass to transfer from one adjusting mode to another so that the adjustment easily starts to sway. The sway of the adjustment again causes uneven wind-up of the fibrous web onto the reeling core.

In the invention, the on/off digital valves V in the digital group are small, and their action is fast. In the adjusting arrangement 1 shown in Figure 4, the same digital valve group 7 is used both for adjusting the position of the wind-up core 21 in relation to the stationary wind-up cylinder 22 and also the nip pressure of the roll nip N between the wind-up core 21 and the reel-up drum 22. The adjusting arrangement 1 has an adjusting system 3, which receives information indicating the position of the wind-up core 21 from the position sensor 4; 4a and measuring information 4 indicating the force directed to the reel-up drum 22 by the wind-up core 21 either continuously or sequentially. The position sensor 4; 4a observes the thickness s of the fibrous web layer W on the wind-up core 21 so that it is generally located in the immediate vicinity of the outer surface of the fibrous web W wound onto the wind- up core. Observing the thickness of the fibrous web layer can be performed either by a mechanical position sensor, as in the figure, or on the basis of some characteristics of the fibrous web. In the mechanical observation method the position sensor 4; 4a is moved in the direction of the solid-head arrow as the thickness of the fibrous web layer s increases, the said position sensor transmitting information on the position of the outer surface of the fibrous web to the adjusting arrangement. In Figure 4 the position sensor 4; 4a is arranged on the side of the reel-up drum, on top of the fibrous web, and it is moved in the direction of the solid-head arrow as the thickness of the fibrous web layer increases. However, the position sensor can just as well be located, for example, in wind-up cars or some other structure of the reeler or slitter winder. In some cases the sensor can also measure some physical characteristic of the fibrous web, such as light transmission ability, on the basis of which the thickness s of the fibrous web layer on the wind-up core is calculated in the adjusting system 3. The arrangement also includes the power sen- sor 4; 4b measuring the force F the wind-up core 21 applies to the reel-up drum 22. The power sensor is active only when the roll nip N is closed. Instead of the power sensor it is also possible to use a pressure sensor, which measures directly the nip pressure existing in the roll nip N between the reel-up drum and the wind-up core. The analogue position and force measuring messages 41; 41a, 41b of the power sensor 4; 4b and position sensor 4; 4a are transmitted to the adjusting system 3, in which they are processed according to the adjusting function G(s) of the adjusting system for adjusting the pressure existing in the roll nip and the position of the wind-up core 21 and the reel-up drum 22 by means of control messages 31 to be transmitted to the digital valve unit 7. The control messages 31 from the adjusting system 3 are already in digital format so that they need not be converted into analogue format, contrary to the control messages to be transmitted to analogue valves. When the roll nip N is closed, the pressure existing in the roll nip is adjusted on the basis of the measuring results 41 ; 41 b transmitted by the power sen- sor 4; 4b, by opening and closing suitable individual digital valves in the digital valve group through the control messages 31. When the thickness s of the fibrous web W on the wind-up core has increased so much that the wind-up core 21 has to be moved in relation to the reel-up drum 22, suitable on/off valves V; VL. V5 in the digital valve group 7 are opened so that the volume flow of the liquid arriving at the hydraulic cylinder 5 is sufficient to generate a certain hydraulic liquid pressure to the pressure cylinder, which again generates the motion of the lever arm 5; 52 (piston) connected to the desired wind-up core 21. By altering the magnitude of the volume flow it is possible to control the transfer speed of the wind-up core in the direction of the solid-head arrow. Even if the adjusting mode was altered fast from the adjustment of the pressure existing in the roll nip N in relation to the location between the reeling core 21 and the reeling cylinder and back, no significant sway occurs in the adjustment, because changes in volume flow are controlled by fast-acting on/off valves. In the arrangement 1 shown in Figure 4, the digital valve group 7 has five on/off digital valves V; V1..V5 so that the resolution of the adjusting resolution for the digital valve group in question is 2⁵ = 32 modes, which is sufficient for most reelers. By increasing the number of digital valves in the digital valve group, even high resolution abilities can be achieved fast; for example, with 16 on/off valves it is possible to achieve the adjusting resolution 2¹⁶ = 65536 different modes.

Also suppression of vibrations generated in the roll nip can be connected to the adjusting arrangement according to Figure 4. Amplitude and frequency are meas- ured from the vibrations by using an acceleration transducer or power sensor, for example, on the shaft of either drum (21 or 22). The vibration messages are transmitted to the adjusting system 3, which controls the valves in the digital valve group 7 to open and close in accordance with its adjusting function G(s) so that the wind-up core 21 can be made to vibrate artificially in the phase opposite to the observed vibration.

Deficiencies of the servo valve were previously described in connection with power, pressure and combined power/pressure and position adjustment in slitter winders and reelers. When using digital valve groups of the invention virtually all above mentioned problems can be avoided. The digital valve group can thus consist of several on/off valves with different diameters or valves that otherwise let through different volume flows. These valves are controlled to open and close by a different control unit so that it is possible to achieve the desired pressure/flow on the side of the cylinder piston and arm. The valve response times are fast, typically 1 - 5ms. Compared to the servo valve, at least the following advantages are achieved with the digital valve:

1. For power and/or pressure control, it is possible to achieve with the valve a pressure amplification curve of linear or desired form on a wide area,

2. An opening / flow relation of fully linear or desired form can be achieved by a suitably selected digital valve group for location control, 3. It is possible to generate fast and undisturbed controls (no exceeding as with servo valves),

4. No fine-mechanical stem, i.e. the valve characteristics stay the same upon changing the valve,

5. The digital valve is not sensitive to impurities,

6. Failure of one on/off valve or even several on/off valves does not make the whole digital valve group inoperative.

If again current slitter winders and reelers are examined it can be noted that their running speeds and capacities have continuously increased. At the moment, the running speeds and accelerations are already so high that in some cases, for example, the power/pressure circuits operating with servo valves and used in the adjustment of the nip load and the nip force control realised with them are no longer optimal. A second way to increase the capacity of machines is to speed up the operation of position controllers active in change situations. Here the limits of the present technology have been met and the speeding up of motions is difficult without digital valve groups. Also failure situations reduce the capacity of machines. The reliability, fault tolerance and robustness of digital valves, for example, against impurities in hydraulic oil are a significant factor in the increase of total capacity.

Some especially advantageous embodiments and methods for the invention will be explained next in connection with wind-up units in reelers and slitter winders: a) Cylinder characteristics, e.g. gasket friction are adjusted by altering the pressures on the piston and/or arm side. In Figure 5a there is shown an example of the gasket 54 between the cylinder 51 and the piston 52, possibly used in power control circuits, when no pressure difference p influences over the gasket. The gasket 54 is here a two-part gasket so that there is provided a Teflon-based gasket ring 541 against the cylinder pipe 51 , and below it there is provided an elastic, somewhat compressible O-ring 542. Due to the pressure difference p in Figure 5, the O- ring 542 seals the gasket groove 521 of the piston 52 and, at the same time, it presses the gasket ring 541 tightly against the wall of the cylinder 51. The bigger the pressure difference is over the piston, the tighter the O-ring is flattened against the edge of the gasket groove, pressing simultaneously the gasket ring 541 upwards against the wall of the cylinder 51. Hydraulic pressure affects the elastic, somewhat compressible O-ring so that the bigger the absolute pressure, the more the O-ring is compressed. In this case, the impact of the pressure difference is reduced, and the gasket ring is not pressed so strongly upwards in the radial direction towards the cylinder surface to be sealed. Thus, by altering the pressure levels in the cylinder chamber, different cylinder frictions can be achieved over the piston with the same pressure difference. With a conventional O-ring made of rubber there occurs virtually no compression so that a bigger pressure difference only means a bigger sealing force, and the actual pressure level does not affect the sealing force. b) The gasket friction is altered by pulse-type pressure control, transferring from the area of static friction into the area of dynamic friction. Static friction between the cylinder and piston is clearly bigger than dynamic friction. In steady control, for example upon starting, the friction force of the cylinder gasket decreases fast. In unfavourable conditions, the gasket moves between the static friction mode and the dynamic friction mode, generating a so-called slip-stick phenomenon. This phenomenon can be eliminated by pulse-type control, because the gasket stays all the time on the dynamic friction area. This can also be done in connection with the gasket embodiment previously explained in item a). It is at the same time possible to affect the cylinder dynamics so that high pressure corresponds to a more rigid cylinder. Higher pressure makes oil virtually more solid because, among other things, air in the oil is compressed more tightly. c) The sleeve locks holding the roll of a slitter winder is controlled by means of a digital valve group. The sleeve locks for a king/pulley roll cutter hold the customer rolls in place in the transverse direction of the slitter winder during wind-up i.e. set- ting. There are two sleeve locks, one on the service side of the slitter winder and one on the operating side of the slitter winder. The sleeve locks typically move in the z-direction and y-direction. Hydraulic actuators are used for moving both directions.

Sleeve locks are moved in the z-direction as position back coupled. In use there are slow and quick motions with position adjustment, exact positioning, and a power back coupled loading/lightening mode. Respective functions also exist with motions in the y-direction. In the above mentioned functions, replacing the presently used servo valves by digital valve groups improves the adjustability of the system and makes possible faster and more exact quick motions. In addition, the sealability of the digital valves improves the safety level of the system as such, and the situation gets even better when combined to pressure battery securing. Sleeve locks for king/pulley roll cutters can further be arranged so that with them it is possible to actively prevent eccentricity of the roll core or sleeve by moving the sleeve to a correct position by means of the sleeve lock by applying external force to the sleeve in one or several directions. The possible need for centring can be observed and the centring performed by means of power, acceleration, speed, position, pressure or other measurements and adjustments, using digital hydraulics. The centring need can be observed and it can also be done by machine vision.

Faster position controlled quick motions make faster the set change sequence of the slitter and thus increase the production capacity of the machines. Among other things, fast and rigid control can be achieved to the closing motion. By using pressure battery securing, i.e. by adding a pressure battery to the system, it is possible to continue the control e.g. when the hydraulic pumps stop, and thus improve the safety of the slitter. Respectively, the operation of locking levers arranged to hold the reel spool of the reeler can be arranged by means of a digital valve group. d) Power/pressure and position controls for the position of a centring reeler. In a centring reeler, each roll to be wound is supported individually against the wind-up drum. The supporting of each roll takes place in a wind-up station formed by a pair of wind-up carriers. The roll is supported from both ends by a sleeve socket (see previous section c), sleeve lock). All technical requirements and characteristics described in section c) can also be linked to this object. Further, it is possible to move wind-up carriers in the lateral direction either individually or as a carrier pair. The positioning and quick motions of this motion performed by digital hydraulics are also more precise and faster than in the traditional servo technique. Faster position controlled quick motions make faster the slitter's set change sequence, and the faster positioning of locations shortens the trim change time of the slitter, thus increasing the production capacity of the machine.

e) Considerably faster ejection of rolls than before. Finished customer rolls are pushed from the wind-up drums to the roll ejector assembly, such as a tipping device, by a roll pusher. Ejecting the rolls from the slitter winder requires great force and motion speed. In order to achieve as fast a set change as possible, the motion is position controlled in relation to other movable devices. The big volume flow and force needed for the motion cause restrictions to accelerations, decelerations, and maximum speed. By means of digital hydraulics, the roll pusher can be run to touch the roll while the roll is still rotating, because the adjustment based on pres- sure measurement or power measurement can be arranged to be very reliable. This running can, when desired, be done even when the sleeve locks are still closed. The ejection is preferably arranged to recognise the load so that, for example, when the roll begins to escape, the system would accelerate behind through pressure measurement, until the back of the tipping device is reached. After this the motion is decelerated without exceeding the maximum load.

During ejection, in which the roll pusher is run fast onto the roll surface, it can be done as has been explained above, i.e. take a gentle contact to the roll surface with low pressure after the quick motion, and then again increase the pressure/force relatively fast.

The above described characteristic is possible to implement in all those situations in which something is run to touch the roll or sleeve or upon bringing individual sleeves or rolls onto a drum, for example, with a reeler, in a slitter winder ejector, pressure roll, butt seamers and other seaming devices. f) Intelligent control of the receiving station of the reel spool by digital valves. The receiving station is e.g. an unwinding station or an intermediate station for transfer rails. The motion of the wind-up drum 21 or machine roll rolling from the receiving station of the wind-up drum 21 is either stopped or decelerated. On the service and operation side, the station has a deceleration function integrated into the hydraulic actuator. A principle view of the connection is shown in Figure 6. The pressure stroke caused by the reel is discharged to the tank through fast digital valve groups 7 on the basis of feedback information of pressure transmitters 61 installed in cylinders 51. This concerns thus a fast pressure restriction function realised by digital hydraulics. Also the synchronisation of motions on the service or operation side can be done by using the same blocks. g) Realisation of the hydraulic active and/or semi-active damping of drums by a digital valve group. h) Control and self-diagnostics of a digital valve so that the digital valve itself observes failure, compensates the failure by other digital valves in the digital valve group, and reports the failure. i) Digital hydraulics is used in the slitter winder in connection with the tipping de- vice moving the rolls so that the roll motion can be well controlled. The tipping device of the slitter winder lowers the finished customer rolls from the wind-up drums of the slitter winder to the roll yard. Lowering of heavy rolls requires great force control, and that requires a big volume flow. In order to achieve as fast a set change as possible, the motion has to be as quick as possible. The motion of the tipping device is synchronised with the roil pusher. In addition, the swinging of the rolls in the tipping device has to be controlled during the motion of the tipping device. The big volume flow and force needed for the motion cause limitations to accelerations, decelerations, and maximum speed. There are also significant safety risks linked to the motion of the tipping device. All these can be controlled by a digital hydraulic system. j) When cutting the web, an actuator, e.g. drum, brush, or other beam has to be brought to the machine roll fast and loose layers possibly generating to the surface layer of the machine roll are to be pressed so that discharge can be done faster af- ter cutting. k) Impression roller is controlled, the roller being an impression roller of a king roll type reeler, centring reeler, or reeler. The advantage of digital hydraulics in impression roller embodiments is the control of big volume flows and through this the possibility to run the impression roller with quick motions faster than before, but still being able to produce a better synchronous motion between the operating and service side than with conventional hydraulics, and a more precise and faster positioning. The power control used for lightening the impression roller during wind-up can be done faster, more precisely, and with smaller pressure losses. In the sense of safety, digital hydraulics can improve the safety level of the impression roller. In addition, in slitter winder or reeler models, in which the impression roller units are attached to a linearly moving impression roller beam, the use of digital hydraulics also in moving the beam makes possible precise adjustability with different roll diameters.

Further, in a situation of web break or a possible threatening roll escape situation, the impression roller can be controlled to load the rolls with a much bigger force than the normal current value so that the rolls would not fly out of the slitter winder. By means of a suitably arranged digital valve group, such an impression roller load of a safety level type is relatively simple to arrange without weakening the usability in a normal running mode of the slitter winder.

f) Digital hydraulics is used to move the wind-up drums or cylinders during wind-up. Also in this embodiment, very good precision accuracy of a heavy machine part and, when the situation so calls, fast moving motion is required. One embodiment is here the control of belt tightness circulating around the belt roll of the belt king roll slitter. A second possible embodiment is to change the geometry of the king roll slitter to turn down the possible vibration observed near the specific vibration frequency or to otherwise improve the wind-up geometry.

m) Digital hydraulics is used for moving or loading the roll of a fibrous web. n) Digital hydraulics is used for controlling the web cutting device. The task of the cutting device is to cut the web during set change. Cutting of the web and movements of the cutting device have to be synchronised exactly in relation to the other transactions in the set change sequence. Digital hydraulics achieves faster and more precise movements than before.

Controlling the cutting device turning around the king roll by digital hydraulics im- proves the mutual synchronisation of the blade holders and the synchronisation of the blade movement in relation to the rotating drum. A possible counter moment for an electronic drive of the version attaching to the blade can also be eliminated by ways of digital hydraulics. o) Digital hydraulics is used as unwinding drive for a rewinding machine. When a new roll is brought to be unwound, its mass and diameter are very big, and that also its moment of inertia. Electronic drives would have to be dimensioned according to this biggest moment of inertia. When the material web is removed from unwinding, the diameter and mass of the machine roll decrease all the time. At the end of the unwinding the moment of inertia is small and an electronic drive dimen- sioned for a big machine roll does not work optimally any more. This situation is still highlighted again in the reeler, in which also the width of the roll to be brought for unwinding can vary. In this case, the width of the maximum roll at the beginning of winding can be, for example, 4m, and the diameter 1.8m. The mass of such a roll is typically approximately 10000kg. If again a narrow roll with a width of ap- proximately 0.5m is brought for unwinding, its mass is very small at the end of winding. The required total tension is also considerably smaller for a narrower material web than for a wide material web. In practice, it has not been necessary to previously rewind as big rolls as are mentioned in the example. For example, along with new gravure printing presses the need for these kinds of big customer rolls has nevertheless increased. The problem can be solved by means of a hydraulic motor and a digital valve unit. A hydraulic motor as such is known technology, and it has also been used in paper industry as power source for different devices. According to the principle explained above, the digital valve unit makes now possible that both small and big moments can be precisely generated with a hy- draulic motor. Also the adjustment of the rotating speed can be made precise. p) Alteration of the dynamics of an unwound web and stabilisation by a movable stabiliser. The material web can move freely between the machine roll and the first track control roll. Tension, moisture and thickness variations etc. in the material web cause that the material web may start to flutter or live, for example, with its specific frequency or a certain specific form, in an undesired way. This swaying may lead, for example, to a break in the web, reduction in speed, or cause visible tension variation to the material web in the final product. The problem can be reduced or it can be eliminated by attaching a driver device to the web, such as a drum, beam, etc., or by influencing the web in a non-contacting manner, for exam- pie, by means of a pressurised air beam. The web can also be influenced by, for example, a wing-like beam so that air coming with the track forms a non- contacting pressure impact onto the web. The web can be affected perpendicularly or in some other angle by pressing or moving the driver in the direction of the track by altering the span length of the free moving track. A digital valve group is very well suited for moving such a driver device to be brought near the web, because quick motions and precise adjustments can be achieved relatively simply in the manner disclosed above. q) Positioning of cutting blades and edge cutters by digital hydraulics. Nowadays the positioning of slitter cutting blades has been carried out either manually or electronically by using e.g. servo motors or similar drives for the positioning. The automatic positioning of blades by e.g. electric servo motors often comprises components that are complex, expensive and sensitive for failure. By using digital hydraulics, the positioning can be made very precise and fast. A digital hydraulic arrangement in this embodiment with its actuators has excellent fault tolerance. Hy- draulic actuators can be controlled, for example, by actuator-specific digital valve units in the following manner. The actuators move the blade transferring devices. A positioning adjustment task is given to the digital valve units, on the basis of which the digital valve units adjust precisely the desired actuator-specific volume flow and thus determine the speed and positioning accuracy of the actuators. The adjustment accuracy and speed depend on the number ("bits") of individual on/off valves in the selected digital valve group and on the valve-specific penetration of these individual on/off valves in each embodiment. Compared with servo technology, digital hydraulics is simple, fault tolerant and reliable, and it has small pressure loss. Nevertheless, very precise adjustment with excellent repeatability and fast response times are achieved with these. Figure 7 still illustrates a general graph of the digital valve group 7 that is applicable in most of the previous objects, the group comprising eight individual digital valves DV. This arrangement is especially advantageously suited for basic level solutions, in which quite extreme resolution is not necessarily needed. Figure 8 illustrates further a general graph, for example, for a slightly more demanding purpose, comprising the digital valve group 7 with twenty individual digital valves DV. With a connection according to this graph most of the embodiments present in a fibrous web reeler can be achieved, such as power control in the nip, positioning control, etc. Figure 8 shows for one individual part the digital valve DV, the nozzle OF for determining valve-specific flow, and the pressure transmitter PT for the digital valve group. In this exemplary digital valve group 7 there is still provided the safety valve SV (this is not necessarily needed in a normal digital valve group) and the differential valve DIF, by means of which the system can be set into differential connection (this is not necessarily needed in a normal digital valve group).

With the arrangement according to the graph in Figure 8 it is possible, for example, to control the nip force of a centring reeler, and vertical movements and positioning of the socket, and other systems critical to the wind-up of a fibrous web. Nip force adjustment or other power adjustment, positioning, and quick motions occur controlled by the digital valve group. Possible safety valves are open and the differential valve DIF is closed, if they are included in the system.

Quick motion up i.e. fast motion away from the actual load direction can also be implemented by using a differential connection so that the digital valves DV on the side of the arm of the digital valve group are included in the control. In this case, the piston-side digital valves DV are closed, the safety valves SV are open, and the differential valve DIF is open. This way it is possible to achieve an extremely sure and fast quick motion by using the characteristics of the digital valve group 7 in a versatile manner.

Claims

1. Apparatus for winding up a fibrous web around a wind-up core into a roll, the apparatus comprising at least one nip roll for forming nip load onto the roll to be wound up, the nip load and/or some other supporting force for the roll being ar- ranged to be formed at least partly by means of a hydraulic actuator or actuators, characterised in that the pressure adjustment and/or volume flow of one hydraulic actuator or several hydraulic actuators is arranged by means of a digital valve group.

2. Apparatus according to claim 1 , characterised in that the digital valve group consists of several on/off valves with different diameters.

3. Apparatus according to claim 1 , characterised in that the digital valve group consists of several on/off valves with identical diameters.

4. Apparatus according to claim 1 , characterised in that the digital valve group consists of several on/off valves with different volume flows.

5. Apparatus according to claim 1 , characterised in that the control signal for the digital valve group is digital, such as binary.

6. Apparatus according to claim 1 , characterised in that the control signal of each digital valve in the digital valve group is binary so that the signal means 0 or 1.

7. Apparatus according to claim 1 , characterised in that the operation of sleeve locks arranged to hold the roll of the slitter winder is arranged by means of a digital valve group.

8. Apparatus according to claim 1 , characterised in that the operation of locking levers arranged to hold the reel spool of a reeler is arranged by means of a digital valve group.

9. Apparatus according to claim 1 , characterised in that the digital valve is arranged to self observe its failure, to compensate the failure with other digital valves in the digital valve system, and to report the failure to the control system.

10. Method for winding up a fibrous web around a wind-up core into a roll, in which method nip load is formed to achieve a radial compression to the roll to be wound up, the nip load and/or some other roll supporting force is formed at least partly by means of a hydraulic actuator, characterised in that pressure and/or volume flow of one hydraulic actuator or several hydraulic actuators is controlled by a digital valve group.

11. Method according to claim 10, characterised in that the control signal for each digital valve in the digital valve group is binary so that the signal means 0 or 1.