The surface of a paper or board web is evened out and polished by a multi-nip calender, which has rolls attached to the body of the calender, on top of the other, in nip contact with one another. The stack of rolls consists of an top and bottom roll and at least one intermediate roll located between them. The top and bottom rolls that work as loading rolls or a bottom roll alone compress the stack of rolls to provide a sufficient nip load. When calendering, the web travels through the calender nips formed by the superimposed rolls.

Patent application FI 982686 describes a multi-nip calender, where the top and bottom rolls are attached by their bearing housings and the rolls of the set of intermediate rolls by their abutments to the vertical guide bars on the body of the calender. The top and the bottom rolls are provided with loading cylinders attached to the body of the calender, which loading cylinders can be used to propel the bearing housings of the top and bottom rolls in a vertical direction along the guide bars. The threaded spindles traditionally used by calenders have been replaced with smooth guide bars attached to the body of the calender. The bearing housings of the shafts of the calender's intermediate rolls are attached to the abutments by using articulated arms, the abutments being movably installed in the smooth guide bars, along which the abutments can be vertically moved. The abutments of the rolls of the set of intermediate rolls are attached to the smooth guide bars by using jointing members. Between the bearing housings and the abutments of the intermediate rolls are installed relief cylinders, which can be used to relieve the nip load caused by the mass of the rolls.

In the calender described above, positioning of the rolls and the adjustment of the quick-opening gaps are carried out so that the relief cylinders of the rolls of the set of intermediate rolls are driven to the bottom, so that the rolls are in their lower position. The set of rolls is driven on using the loading cylinder of both the top and the bottom rolls or the bottom roll alone. The driven-on set of rolls is lowered by using the loading cylinder of the bottom roll to the extent of the quick-opening gap of the uppermost roll nip, after which the uppermost roll of the set of intermediate

rolls is attached to the smooth guide bars. After this, the set of rolls is lowered by using the loading cylinder of the bottom roll downwards to the extent of the quick- opening gap of the second highest roll nip, after which the second highest roll of the set of intermediate rolls is attached to the smooth guide bars. This is continued until the quick-opening gap of each calender nip is set as desired. When the quick- opening gaps of the calender rolls have been set and the rolls positioned, the set of rolls is moved into the running position by closing the roll nips by using the bottom cylinder. Alternatively, the roll nips can be closed in the desired order by using the relief cylinders connected to the articulated arms of the rolls of the set of intermediate rolls.

It is essential that the roll nips of the calenders open and close accurately enough, so that the calender's runnability is good and the quality of calendering uniform. A roll nip that opens or closes obliquely may cause a break in the web, which is harmful particularly in the on-line calenders connected to the rear of the paper machine.

In the multi-nip calender described above, positioning of the rolls, setting of the quick-opening gaps, and closing of the roll nips are usually carried out by using limit switches that react to the movement of the rolls. In order to get the rolls in the desired locations, the flow adjustment of the loading cylinders is altered on the basis of the positioning data given by the limit switches. Because of the large number of limit switches, the method is complicated and sensitive to various disturbances. On the basis of the positioning data given by the limit switch, the only thing can be concluded is whether or not the roll has passed the place measured by the limit switch, which is why the roll positioning implemented by using limit switches is often inaccurate.

The purpose of this invention is to provide a novel type of method and arrangement for positioning the rolls of a multi-nip calender in order to eliminate the above problems related to the use of limit switches.

The invention is based on the fact that the movement of the bottom roll of a multi- nip calender is measured by laser-measuring devices comprising a laser transmitter that transmits beams and a detector that receives beams, one of which is attached, for example, to the body of the calender or another stationary spot, and the other one to the bearing housing of the bottom loading roll, to the piston of the loading cylinder or other similar spot that moves in the direction of the guide bars, in the

same way as the bottom roll. The position of the bottom roll and the intermediate rolls can be determined by measuring the movement between the laser transmitter and the detector. When needed, the transmitter or the detector of the laser- measuring device can also be attached in connection with the other rolls of the calender.

More specifically, the arrangement according to the invention for positioning the rolls of a calender is characterized by what is stated in the characterizing part of claim 1.

Furthermore, the method according to the invention for positioning the rolls of a calender is characterized by what is stated in the characterizing part of claim 13.

The invention provides significant benefits.

By using the solution according to the invention, the calender roll nips can be opened and closed in an accurate, direct position, so that the runnability and the calendering quality of the calender remain good. This is especially important in on- line calenders, where an oblique opening or closing of a roll nip easily causes a break in the web. As continuous measuring data about the changes in the positions of the rolls is obtained by using a large enough detector, the solution according to the invention can also be used to measure the velocity of movement of the rolls. The data obtained from the previous positioning of the rolls can be utilized for controlling the loading cylinders of the bottom roll, so that the flow control setting of the loading cylinders can be altered in advance, when needed, so that the roll nip closes as evenly as possible without having to make any great changes in the flow setting value of the loading cylinders. The equipment according to the invention does not contain moving parts, which is why its operation is reliable, it is easy to protect, and does not require nearly as much maintenance as the roll positioning based on the use of limit switches. Furthermore, the measuring equipment according to the invention is easy to install in the calender.

In the following, the invention is described in detail with reference to the appended drawing, which present a side view of the multi-nip calender.

The shaft of the top roll 1 of the calender according to the drawing is installed, at both ends, in bearing housings 17, which are connected to guide bars 20 attached to

the body 22 of the calender. The top roll 1 can be moved vertically along guide bars 20 by using, for example, loading cylinders 13 attached to the body 22 of the calender, their pistons 14 acting on the bearing housings 17 of the top roll 1.

Correspondingly, the shaft of the bottom roll 12 is installed, at both ends, in bearing housings 23, which are further connected to the guide bars 20. The bottom roll 12 can be moved, for example, by using loading cylinders 15 attached to the body 22 of the calender, their pistons 16 acting on the bearing housings 23 of the bottom roll 12.

There are intermediate rolls 2 to 11 located between the top roll 1 and the bottom roll 12, adapted to move between the top roll 1 and the bottom roll 12 essentially in the direction of straight lines connecting the midpoints of the aligned ends of the shafts of the top roll 1 and the bottom roll 12. The number of intermediate rolls of the multi-nip calender is preferably 1 to 14. Both ends of the shafts of rolls 2 to 11 are installed in bearing housings 18, the housings being connected to abutments 19 with the aid on articulated arms. The abutments 19 are further in sliding connection with the guide bars 20 of the body 22 of the calender. Relief cylinders are installed between the bearing housings 18 and the abutments 19 of rolls 2 to 11 of the set of intermediate rolls, relieving the nip load caused by the mass of the set of rolls.

There are also smooth guide bars 21 attached to the upper part of the body 22 of the calender, replacing the threaded spindles conventionally used in calenders.

Typically, the cross-section of the guide bars 21 is round. The abutments 19 of the intermediate rolls 2 to 11 are provided with lugs 25 or the like, which are fitted around the guide bars 21. The abutments 19 are attached to the guide bar 21, for example, by connecting members, such as friction connecting members, fitted between the lugs 25 and the guide bars 21.

A detector 24 is attached to the bearing housing 23 of the bottom roll 12 of the calender, to the piston 16 of the loading cylinder 15 or to another part that similarly moves with the bottom roll 12, and a laser transmitter is attached to the body 22 of the calender or to another stationary spot, its laser beams being directed towards the detector 24. Naturally, the detector 24 and the laser transmitter can alternatively be located so that the locations of the transmitter and the detector 24 are exchanged, so that the laser transmitter is connected to the piston 16 of the loading cylinder 15 of the bottom roll 12, to the bearing housing 23 or a corresponding part, and the detector 24 to a stationary spot. The solution according to the invention uses at least

one laser transmitter and detector couple. Typically, there is a transmitter and a detector located at both ends of the bottom roll 12.

By using the laser transmitter and the detectors 24, the movement of the bottom roll can be measured very accurately. Typically, the measuring accuracy of the device is few micrometers. The measurement can be implemented, for example, so that the dispersed laser beam coming from the transmitter is directed towards a linear CCD cell, so that the laser light touches several pixels of the cell. By counting the amounts of the radiation intensity of various pixels, one can define the location, to which the laser beam is focused. In addition to defining the position of the bottom roll 12, the solution according to the invention can be used to measure the velocity of movement in the direction of the guide bars 20 of the bottom roll 12.

The positioning of the rolls 1 to 12 of the calender and the adjustment of the quick- opening gaps are carried out so that the relief cylinders between the bearing housings 18 and the abutments 19 of the rolls 2 to 11 of the set of intermediate rolls are first driven to the bottom, so that the intermediate rolls 2 to 11 descend to their lowest position with the aid of the articulated arms. After this, the set of rolls is driven on using the loading cylinders 13,15 of both the top roll 1 and the bottom roll 12 or the bottom roll 12 alone. The loading cylinders 13,15 are controlled by changing their flow value settings. The driven-on set of rolls is lowered, by using the loading cylinders 15 of the bottom roll 12, to the extent of the quick-opening gap of the roll nip between the top roll 1 and the uppermost intermediate roll 2, after which the uppermost intermediate roll 2 is fastened to the guide bars 21 by using fastening members. Then the set of rolls is lowered, by using the loading cylinders 15 of the bottom roll 12, to the extent of the quick-opening gap of the second highest roll nip, and then the second highest intermediate roll 3 is fastened to the guide bars 21 by using fastening members. This is continued until the quick- opening gap of each calender nip is set as desired. The movement of the bottom roll 12 is measured by using the laser measuring devices described above, whereupon the quick-opening gaps of the roll nips can be accurately set to the desired size.

After the set of rolls of the calender has been positioned and the quick-opening gaps of the roll nips set, the set of rolls is moved to its running position by closing the roll nips, starting from the lowest roll nip, by lifting the bottom roll 12 by using the pistons 16 of the bottom cylinders 15. Alternatively, the roll nips can also be closed in the desired order by using the relief cylinders of the rolls 2 to 11 of the set of intermediate rolls.

In the control of the loading cylinders 13,15, the data obtained from previous positioning can be used, so that the flow control setting of the loading cylinders 13, 15 can be altered in advance, when needed, so that the roll nip closes as quickly and smoothly as possible without having to make any great changes in the flow control settings of the loading cylinders 13,15.

In addition to those described above, the invention may also have alternative embodiments.

The mounting of the intermediate rolls 2 to 11 of the calender can also be implemented, for example, by the manner described in patent application FI 982686, in which the bearing housing 18 of each intermediate roll 2-11 is pivotally attached to the abutment 19 by an articulation, the abutment being attached by a sliding contact to the guide bars 20 fastened to the body of the calender. A swinging arm is rigidly attached to each bearing housing 18 at the first end, the second end of the arm extending to the opposite side of the articulation in relation to the bearing housing 18. Furthermore, a relief cylinder is installed between each abutment 19 and the other end of the swinging arm to turn the swinging arm around the articulation to change the position of the bearing housing 18 and the roll pillowed to it in relation to the abutment 19. Consequently, the calender uses no smooth guide bars 21 that replace the threaded spindles. Any adjustments caused by the changes in the diameters of the rolls and other long movements are carried out by the loading cylinders 13,14, and the abutments 19 of the intermediate rolls 2-11 are locked to the guide bar 20 fastened to the body of the calender. As the bearing housings 18 of the rolls are allowed to move in relation to the abutments 19 because of the articulation, the relief cylinders, installed between the abutments 19 and the ends of the swinging arms, generally carry out the relief and quick opening of the roll nips.

The calender can have a fixed top roll 1, which is rigidly attached at its bearing housings 17 to the guide bars 20,21 or directly to the body 22 of the calender.

When the fixed top roll 1 is used, the calender does not need the upper loading cylinders 13 either, whereupon the set of rolls is closed and positioned by using the loading cylinders 15 of the bottom roll 12 and the relief cylinders of the intermediate rolls 2-11. It is not necessary to locate the guide bars 20,21 and the rolls attached to them in a vertical direction, but they can also be inclined.

The rolls of the calender can also be attached to the body 22 of the calender by other means than the guide bars 20,21, for example, by articulation. If necessary, the detectors or transmitters of the laser-measuring device can be attached, in addition to or instead of the bottom roll 12, to a part that similarly moves with one or more of the other rolls 1-11 of the calender, so that the position of these rolls can also be defined directly by means of the measuring device.