FIELD OF INVENTION The invention relates to a deflection adjustable roll used in fiber web machines, preferably in paper, board and pulp machines The invention relates also to a system for loading a deflection adjustable roll. Particularly, though not exclusively, the invention relates to controlling a loading of a shell which is implemented by on- off valves, in a deflection compensated roll in which a loading function of a load element is separated from a lubrication function.

BACKGROUND OF THE INVENTION

It is known that a shell of a deflection adjustable shell can be loaded from inside hydraulically by means of loading elements.

Nowadays there can be, for example, 65 loading elements arranged between a shaft and a shell of a roll in one roll which is loaded hydraulically by means of the loading elements. Also such rolls have been presented in which controlling of the loading elements can take place in groups or individually. In a roll with one zone same pressure is affecting under all loading elements which pressure is controlled by means of one valve which is common for all loading elements. In rolls with multiple zones the loading elements are divided in groups or zones of 2 to 8 elements and each zone has an own control valve. The amount of zones is largest when every loading element has an own valve or the loading elements are single controlled. In rolls according to modern technology the valves are located outside the roll. In current loading elements, typically, loading and lubrication functions are combined and lubrication oil is also supplied via a loading pressure line. A valve is adjusting pressure of a flowing liquid. Pressurizing the lubrication oil to a loading pressure level causes higher energy losses than pressurizing the lubrication oil to a lubrication pressure level. The lubrication and the loading pressure levels can be influenced by means of loading element dimensioning. Patent publication DE 3815462 describes embodiments of deflection adjustable rolls in which shells are supported from inside hydrostatically by means of loading elements. A first roll shown in the publication comprises a common load pressure supply line for all loading elements and a common lubrication supply line for all loading elements and both supply lines divide into each loading element. The loading and lubrication functions are differentiated and implemented by separate hydraulic lines in the loading elements of the first roll. A second roll shown in the publication comprises loading element specific supply lines for a combined loading and lubrication function wherein the load pressure is implemented by a flowing liquid, a lubrication flow is formed of a flow-through of the flowing liquid. In the publication DE 3815462 hydraulic pressures are adjusted from outside the roll without valves inside the roll.

Patent publication US 4183128 describes a deflection adjustable roll in which pressure adjusting valves are located inside the roll in connection with each loading element.

Patent publication Fl 113794 describes a roll which is deflection adjustable in zones. A shell of the roll is loaded by means of hydraulic cylinders which are pressurized in pairs and controlled by means of a digital valve pack which is arranged outside the roll. Each hydraulic cylinder pair is pressurized by an own liquid transfer channel which is connected with one on-off valve of the digital valve pack. Inside the roll there are needed many separate liquid transfer channels which lead to on-off valves which are located outside the roll. Inside the roll there are no valves arranged for the loading function.

Also patent publication Fl 118820 describes a deflection adjustable roll in which loading and lubrication functions of the hydrostatic loading elements are combined.

It is an object of the invention to provide an alternative way for loading a deflection adjustable roll. SUMMARY

According to a first aspect of the invention there is provided a deflection adjustable roll of a fiber web machine comprising a stationary shaft, a shell arranged to be rotated around the shaft, and loading elements supported in the shaft for loading the shell from inside through a hydraulic pressure medium, and the roll comprises separate loading pressure supply and lubrication supply for the loading elements. A group of digital hydraulic first loading valves is arranged inside the roll each of them being arranged loading element specific in a flow connection with a loading cylinder comprised by the loading element.

Preferably the first loading valve comprises at least two electric controllable hydraulic on-off valves of which at least one first on-off valve is intended for charging pressure to the loading cylinder and at least one second on-off valve is intended for discharging pressure from the loading cylinder.

Preferably the roll comprises a supply pressure line which is common for all loading elements and is leading from outside the roll to inside the roll and from which a flow connection is arranged to the first loading valves.

Preferably the roll comprises a group of pressure measuring means which are arranged loading element specific in pressure connection with the loading cylinders. Preferably the first loading valve comprises an electric pressure measuring means which is in pressure connection with a pressure output comprised by the first loading valve and the pressure output is leading to the loading cylinder.

Preferably an output stage electronics is coupled for the loading valve in order to control at least coils of the on-off valves comprised by the loading valve.

Preferably the output stage electronics is arranged inside the roll close to the loading valve. Preferably at least part of a data bus is arranged in the roll.

Preferably the loading element specific output stage electronics are connected with the data bus for transmitting measuring signals of the pressure measuring means to be transmitted from inside to outside the roll and/or for transmitting control signals of the on-off valves to be transmitted from outside to inside the roll.

According to a second aspect of the invention there is provided a system for loading a deflection adjustable roll according to any embodiment of the invention which system comprises an electric control unit which is located outside the roll, for controlling loading element specifically digital hydraulic first loading valves which are arranged inside the roll. Preferably the system comprises a second loading valve which is located in a supply pressure line, for controlling a common pressure level for all first loading valves. Preferably the second loading valve is arranged outside the roll.

Preferably the system comprises a pressure accumulator which is coupled with the supply pressure line.

Preferably the system comprises a loading pump which is coupled with the supply pressure line. Preferably the control unit is adapted to receive loading element specific pressure data; the control unit is adapted to determine control data of the first loading valves which control data are based on the loading element specific pressure data, on a mathematic model of a hydraulic circuit of the first loading valve which is arranged in the control unit and on an optimizing program which is optimizing opening and closing of on-off valves and is arranged in the control unit; and the control unit is adapted to send determined loading element specific control data to inside the roll for adjusting the first loading valves. Preferably the system comprises a field piping which is leading from the loading pump to the supply pressure line of the loading.

Preferably a hydraulic valve or of a group of hydraulic valves implementing a common pressure level for all loading elements is located in the supply pressure line of the loading. Pressure can be ramped and large pressure changes can be implemented and, for example, closing and opening of a nip can be achieved by means of this group of valves. In a situation when the common pressure level is increased and/or decreased, the system may be configured to use the group of valves implementing the common pressure level for all loading elements. When a loading state of the roll is continuous, the system may be configured to bypass the group of valves implementing the common pressure level for all loading elements. In the system, the supply pressure lines inside the roll may be coupled directly with the supply pressure line outside the roll when the loading state of the roll is continuous.

In some embodiments the loading pumps may be stopped when the supply pressure line is equipped with the pressure accumulator or a corresponding apparatus which is able to maintain hydraulic pressure. Then, energy consumption of the loading function can be decreased.

Preferably the system comprises a control unit which is located outside the roll for controlling loading of the roll. The control unit may receive signals of a pressure measurement which is implemented loading element specific. The pressure measurement is preferably electric. The control unit may send control signals loading element specifically to at least two on-off valves which are arranged inside the roll for increasing and/or decreasing the pressure of the loading element. The control unit may control decreasing the pressure of the supply pressure line of the loading such that the loading element specific on-off valves cause a pressure drop in the loading elements which is leading to a quick opening of the roll.

A mathematic model, for example, for each loading element, of a hydraulic circuit of the loading element may be arranged, for example, by means of software technology, in the control unit which is implementing an outside control technology of the roll, which mathematic model together with an adjustment program which is optimizing the closing and the opening of the on-off valves may determine closing and opening points of each on-off valve. When the amount of the on-off valves is minor, even two valves per loading element, the optimizing is easy and a need for the optimizing may remain very little. Implementing of the outside control technology of the roll is managed with a control unit with a rapid cycle time which may be, for instance, an industrial PC, and with the output stage electronics of the on-off valves (known power electronics as such) with which a high voltage may be produced in the coil of the on-off valve at the time of change of state of the on-off valve for speeding up the change of state. The power electronics needed by the coils of the on-off valves may also be arranged inside the roll close to the coils.

Preferably the system comprises a data bus. The data bus may be a data bus according to an industrial standard. For example Profibus is applicable for the data bus. The data bus may be used for connecting the control unit outside the roll with the actuators and measuring apparatuses which are arranged inside the roll. The data bus may be used for transmitting a measurement data to be measured in the roll, such as loading element specific pressure data, to the control unit. The data bus may be used for transmitting control signals to be sent to actuators of the roll for controlling the loading of the roll. The output stage electronics or power electronics used in connection with the actuators may be coupled via the data bus with the control unit. In connection with test apparatuses it has been observed that adjusting of pressure of a closed space may be implemented with a minor amount of on-off valves, even by means of two on-off valves per one loading element. With the invention the amount of hydraulic valves to be used may be decreased substantially in comparison with known loading elements of deflection adjustable rolls in which the flow through the valve increases as a function of the loading. Keeping the amount of the valves small and a reduction of the amount compared to prior art is followed by several advantages. Because the design of the on-off valve may be implemented as simple and rugged, a single valve is a reliable component bearing a proper fault tolerance. Thus, a roll comprising several on-off valves may be made reliable and robust and one can decrease costs of maintenance and service. During use of the roll, energy may be saved with the loading function of the deflection adjustable roll to be implemented with on-off valves because the on-off valve has in principle no leakage by its design and function. If necessary, the loading pumps may be stopped, for example, when the supply pressure line of the loading is equipped with a pressure accumulator. According to some advantageous embodiments energy consumption of the lubrication function of the loading element may also be decreased in comparison with a prior art roll. The loading function to be implemented by on-off valves separately from the lubrication function provides a tool for optimizing energy use of the roll also such that it enables optimizing the lubrication flow of the loading elements in a way which is independent from the loading. The inside loading function of the roll shell to be implemented with the on-off valves may also be exploited in connection with hydrodynamic loading elements.

Different embodiments of the present invention will be illustrated or have been illustrated only in connection with one or some aspects of the invention. A person skilled in the art appreciates that any embodiment of an aspect of the invention may be applied in the same aspect of the invention and in other aspects alone or as a combination with other embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a first deflection adjustable roll, a loading function of which is arranged by means of on-off valves inside the roll;

Fig. 2 shows a loading element in which a lubrication function is separated from the loading function; Fig. 3 shows a first valve coupling for the loading function of a single loading element and which is suitable for controlling small changes in state;

Fig. 4 shows the valve coupling of Fig. 3 which is connected with a power electronics with some electric couplings;

Fig. 5 shows a second valve coupling which is located outside the roll in the supply pressure line and which is suitable for making a pressure level change which affects all loading elements such as ramping a pressure state;

Fig. 6 shows a first way for coupling the power electronics of the first valve couplings, for example, in serial form with a bus;

Fig. 7 shows a second way for coupling the power electronics of the first valve couplings, for example, in star form with a bus;

Fig. 8 shows a second embodiment of the roll according to the type of Fig. 1. DETAILED DESCRIPTION

In the following description, like reference characters denote like elements. It should be appreciated that the illustrated drawings are not entirely in scale, and that the drawings mainly serve the purpose of illustrating embodiments of the invention.

Fig. 1 shows a deflection adjustable roll, a shell 1 of which is loaded against a shell 8 of another roll for handling (for example, pressing) a fiber web in a nip formed in between the shells 1 ; 8 of the rolls. The shell 1 is loaded from inside by means of loading elements 6, shown to be six pieces in the roll, by way of example. During loading, a movable loading member 7 of the loading element 6 is arranged against an inner surface of the shell 1 and the loading elements 6 are supported at their second ends in a stationaty shaft 2 of the roll. The shaft 2 is supported at its ends by means of shaft supports 4 such as bearing houses in a structure outside the roll, for instance, in a frame of a paper machine or a floor 5. Preferably the shaft 2 is fixed non-rotatable during use but a rotating position of the shaft may be adjusted supported by the shaft supports 4, i.a., in order to direct the roll. End sealings 3 are arranged between the shell 1 and the shaft 2 for sealing a lubrication medium volume which is formed inside the roll. The loading elements 6 are loaded by means of on-off hydraulic valves Pi ... P _N . A lubrication function is separated from a loading function in the loading elements 6. For loading the loading elements 6 a hydraulic loading system is necessary which comprises, for instance, a loading pump with a hydraulic unit, a field piping (not shown in the figures) and loading element specific loading lines. The loading valves which adjust the loading are located inside the roll in Fig. 1 , wherein loading element specific loading lines which are led via an end of the roll are not needed. A supply pressure line Ps of the loading is led inside the roll from which a desired pressure is modified for the loading elements 6. Because a pressure of a closed space (a loading cylinder 20 of the loading element 6) is adjusted and no flow from this space is present, the adjustment may be implemented even with two on-off valves. The pressure of each loading element is measured in the arrangement, preferably by an electric pressure measurement PTi...PT _N . An advantage with the electric pressure measurement is a possibility to react fast to changing states of pressure, and a small need for space and service required by signal conductors to be lead from the loading cylinders 20 of the loading elements 6 to a control technology outside the roll.

A mathematic model of a hydraulic circuit of the loading element may be arranged, for example, by means of software technology, in the control unit (not shown in the figures) which is implementing an outside control technology of the roll, which mathematic model together with an adjustment program which is optimizing the closing and the opening of the on-off valves may determine closing and opening points of each on-off valve. When the amount of the on-off valves is minor, even two valves per loading element, the optimizing is easy and a need for it is very little. Implementing of the outside control technology of the roll is managed with a control unit with a rapid cycle time which may be, for instance, an industrial PC, and with the output stage electronics of the on-off valves (known power electronics as such) with which a high voltage may be produced in the coil of the on-off valve at the time of change of state of the on-off valve for speeding up the change of state. Hydraulic liquid necessary for the loading is supplied in Fig. 1 to the roll from outside the roll through a supply pressure line P _s which is formed in the shaft 2 and is common for all loading elements 6. The supply pressure line Ps is divided inside the roll, preferably inside the shaft 2, to on-off valve couplings P^ ... P _N which are arranged for each loading element 6. A hydraulic pressure flow is lead from each on-off valve coupling via a hydraulic channel, preferably inside the shaft, to the loading cylinder 20 comprised by each loading element 6.

When the loading pressure of the loading element 6 is adjusted with a minor amount of on-off valves, increase and decrease of the pressure in a desired time with a certain ramp is advantageous to implement by means of a pressure level ramping which is common for all loading elements. This may be implemented, for example, with a pressure valve 50 (Fig. 5) according to digital valve technology, by means of which the common pressure level for all loading elements can be increased, decreased and maintained on a level from where there is a short way to move to loading element specific pressures with the on-off adjustment. The common pressure valve 50 which is in the continuous load state common for all loading elements may be bypassed and the on-off valves Pi ... P _N inside the roll are coupled directly with the supply pressure line Ps. Then the loading pumps may, if necessary, be stopped when the supply pressure line Ps of the loading is equipped with a pressure accumulator, for instance, because the on-off valves Pi .. . P are in principle non-leaking. So the energy consumption of the loading function can be reduced. Figs. 3 and 4 show preferable on-off valve couplings Pi ... PN. Small load changes of the loading elements 6 can be controlled and adjusted with such loading valves Pi ... PN. The pressure level of the supply pressure line Ps is controlled by means of a supply pressure valve group 50, arranged outside the roll, which is coupled to the supply pressure line Ps. Common pressure level changes for all loading elements 6 can be made by means of a supply pressure valve group 50. Fig. 5 shows a preferable supply pressure valve group 50.

Lubrication medium flows inside the shell 2 through the loading elements 6. The lubrication flow is brought to the loading elements 6, for instance, via a group of lubrication pressure lines Q _s which may be divided to lubrication valves Qi . .. Q _N which adjust the lubrication medium flow of each loading element. Thus, a lubrication supply for each loading element is separate from the loading pressure supply. An implementation of the separated lubrication flow is not dealt with more specifically here. The lubrication medium is outputted from inside the shell 2 to outside the roll, for example, below the shaft 2 via an output channel 9 from an output pool 19. The output channel 9 is arranged inside the shaft 2 of the roll and the output flow can be conveyed through the same or another end of the shaft 2 as the input flow.

A loading element 6 in which the lubrication function is separated from the loading function and which is suitable to be used in the roll of Fig. 1 is shown in Fig. 2. The loading element 6 comprises a piston 7 which is loadable in direction of an inner surface of the roll shell 1 and an arm 10 separate from the piston which is arranged in an lubrication medium cylinder 12 which is formed inside a skirt 11 of the piston. The arm 10 is attached fixed to the shaft 2 of the roll, more specifically, to a recess 13 formed in the shaft 2, for example. The arm 11 is sealed relative the shaft 2 and a lubrication medium flow to be conveyed in between the loading element 6 and the shell 1 is lead through the shaft 2 into a lubrication medium channel 14.1 which is arranged inside the arm 10 and ends to the lubrication medium cylinder 12. A second lubrication medium channel 14.2 leads from the lubrication medium cylinder 12 to a lubrication medium recess 16 formed in a face surface 15 of the piston. A volume of the lubrication medium cylinder 12 can change along the movement of the piston 7 wherein a total length of the lubrication medium channel 14.1 , 14.2 is changing. The lubrication medium flows from the lubrication medium recess 16 to the face surface 15 which is forming a part of a slide shoe of the loading element 6. The recess 13, the arm 10 and the skirt 11 of the piston 7 define in between themselves the loading cylinder 20 of the loading element 6. A first seal 17 is mounted between an inner surface of the skirt 11 of the piston 7 and the arm 10. A second seal 18 is mounted between an outer surface of the skirt 11 of the piston 7 and a surface of the recess 13. The loading cylinder 20 is formed pressure tight by the first seal 17 and the second seal 18 which allow the movement of the piston 7. The first seal 17 prevents mixing of the lubrication medium flow and the hydraulic liquid for the loading.

The lubrication function of the loading element 6 can be implemented by arranging to the arm 11 of Fig. 1 the first lubrication medium flow channel 14.1 into which the lubrication medium flow can pass via the lubrication medium supply channel Qs. From the flow channel 14.1 the lubrication medium results into a cylinder volume 12 defined by the arm 10 and the piston 7 and further from there, via the second lubrication medium flow channel 14.2 which is formed in the piston 7, to the lubrication medium recess 16 formed in the face surface 15 of the piston 7. In a loading situation, when the lubrication medium pressure is suitable, a suitable lubrication medium film is between the face surface 15 and the inner surface of the shell 2.

Fig. 3 shows a loading element specific loading element PI ...PN, in other words, an on-off valve coupling comprising two on-off valves. Pressure is increased by means of the first on-off valve 30 and pressure is decreased by means of the second on-off valve 31 in the loading cylinder 20 of the loading element 6. The on- off valves 30, 31 are controlled such that when the first on-off valve 30 is in open position the second on-off valve 31 is in closed position (increase of pressure) and vice versa (discharge of pressure). The supply pressure line Ps is joining in a pressure input 32 to the loading valve PI ...PN. A pressure output 33 of the loading valve Pi ...P _N is arranged in flow and pressure connection with the loading cylinder 20. The pressure input 32 is connected with an input side of the first on-off valve 30 and the pressure output 33 is connected with an output side of the first on-off valve 30. The second on-off valve 31 is connected by its input side with the pressure output 33 and by its output side with the pool 19 between the shell 1 and the shaft 2.

The loading valve PI ...PN comprises a controlled check valve 34 which is connected with the pressure output 33. A quick opening of the loading element 6 is made by means of the controlled check valve 34 by releasing the supply pressure from the supply pressure line P _s . A discharge side of the check valve 34 is connected to the pool 19. The loading valve PI ...PN comprises a pressure measuring sensor PT which is connected with the pressure output 33.

Fig. 4 shows a loading valve P _I ...PN, the coil of the first on-off valve 30 and the coil of the second on-off valve 31 of the loading valve being coupled to a power electronics 40 by electric couplings 35 and 36, respectively. The electric coupling 35, 36 can be implemented, for example, by means of a pair cable. Additionally, a signal data of the pressure measuring sensor PT can be transmitted by means of an electric coupling 37, via an output stage electronics 40, further 41 to outside the roll. A data communication between the output stage electronics and the outside of the roll can be implemented, for example, by means of an industrial bus 41. Fig. 5 shows a second loading valve 50 which is located outside the roll in a supply pressure line Ps and which is suitable for making a pressure change affecting all loading elements 6 such as ramping the pressure state. An input side of the loading valve 50 is coupled to a hydraulic line leading from, for example, a hydraulic pump. With the input side, a traditional hydraulic valve 51 of the loading valve 50 is in connection by means of which the pressure of the hydraulic liquid leading to the first on-off valve 52. A ramping of the supply pressure line Ps which is leading to the roll, to a desired constant level of the loading, can be implemented by opening the first on-off valve 52 which is coupled after the traditional hydraulic valve 51. A flow connection is established from an output side of the first on-off valve 52 to the supply pressure line Ps which is leading to the roll and to a second on-off valve 53 and to a third on-off valve 54. The second 53 and the third on-off valves 54 are closed during increasing of the pressure level. When the pressure level is decreased the first on-off valve 52 is closed and the second on-off valve 53 is opened. A line load can be adjusted to be 100 kN, for instance, when the supply pressure is about 10 bar. When the pressure adjusting function of the second loading valve 50 is bypassed the first on-off valve 52 and the second on-off valve 53 are closed and the third on-off valve 54 is opened, whereby the hydraulic line leading from a hydraulic pump or a pressure accumulator, for instance, is in direct connection with the supply pressure line Ps which is leading to the roll.

Fig. 6 shows a coupling of the power electronics 40.1 ... 40. N of the first loading valves PI ...PN in serial form to a bus 41 and Fig. 7 shows a coupling of the power electronics of the first loading valves PI ...PN in star form to a bus 41. The bus 41 can be a combination of star and serial formed buses which may comprise starlike coupling parts 42 and/or nodes 43 of single star arms 41. Fig. 8 shows a second embodiment of the roll according to the type of Fig. 1 comprising loading element specific output stage electronics 40.1 ... 40. N for each loading valve PI ...PN inside the roll. The output stage electronics 40.1 ... 40. N are coupled via a bus 41 with a control unit (not shown) which is outside the roll. The foregoing description provides non-limiting examples of some embodiments of the invention. It is clear to a person skilled in the art that the invention is not restricted to details presented, but that the invention can be implemented in other equivalent means. Some of the features of the above-disclosed embodiments may be used to advantage without the use of other features.

As such, the foregoing description shall be considered as merely illustrative of the principles of the invention, and not in limitation thereof. Hence, the scope of the invention is only restricted by the appended patent claims.