A METHOD OF WINDING A WEB

TECHNICAL FIELD

[0001]The invention relates to a method of winding a continuously produced flexible web, e.g. a paper web or a non-woven material web, to form a parent roll. The invention also relates to a controller for an apparatus for winding a flexible web, a computer program, a carrier comprising the computer program, and an apparatus for winding a flexible web.

BACKGROUND

[0002]In the manufacture of various types of tissue products such as facial tissue, bath tissue, paper towels and the like, the dried tissue web or sheet coming from the tissue machine is wound into a parent roll which is temporarily stored for further processing. Thereafter, the parent roll may be unwound and the sheet is converted into a final product form. Such a process may also be used for other types of paper, or for non-woven materials.

[0003]In winding the tissue web into a large parent roll, it is vital that the parent roll be wound in a manner which prevents major defects in the parent roll and which permits efficient conversion of the parent roll into the final product, whether it be boxes of facial tissue sheets, rolls of bath tissue, rolls of embossed paper towels, and the like. Ideally, the parent roll has an essentially cylindrical form, with an even cylindrical major surface and two smooth, flat, and parallel end surfaces. The cylindrical major surface and the end surfaces should be free of ripples, bumps, waviness, eccentricity, wrinkles, etc., In other words, the parent roll should be “dimensionally correct”. Likewise, the form of the parent roll must be stable, so that it does not depart from its cylindrical shape during storage or routine handling. In other words, the parent roll should be “dimensionally stable”. Defects can force entire parent rolls to be scrapped if they are rendered unsuitable for high speed conversion.

[0004]To provide parent roll characteristics that are favorable to converting operations, U.S. Pat. No. 5,901,918A suggests engaging the tissue web against a reel spool with a transfer belt which traverses an unsupported span between two support rolls. The web is transferred from the transfer belt to the parent roll as the parent roll is urged against the sheet/transfer belt at a point within the unsupported span. The resulting deflection of the transfer belt is detected and, in response, the reel spool position is changed to control the deflection at a desired level. Accordingly, a predetermined light nip pressure can be applied to the parent roll as the tissue web is wound thereon and large parent rolls of high bulk tissue can be manufactured with desired properties when unwound.

[0005]Although said transfer belt solution has proved highly advantageous, there is a desire to further facilitate converting operations based on a parent roll with a flexible web of paper or non-woven material.

SUMMARY

[0006]An object of the invention is to facilitate converting operations based on a web parent roll with a flexible web of paper or non-woven material.

[0015]The web may be a paper web, or a web of non-woven material.

[0016]It is understood that the caliper of the rolled-up web in the first parent roll is the caliper, or thickness, of the first web when it has been rolled up onto the first parent roll. The caliper of the rolled-up web may also be referred to as an In Wound Caliper (IWC). Preferably, the one or more values of a caliper of the rolled-up web are determined while the first web is directed around the first reel spool to form the first parent roll. The caliper may be determined repetitively, e.g. in a control loop for the movement of the first reel spool. For example, one value of the caliper may be determined upon another value of the caliper, and so on.

[0017]Moving at least one of the first reel spool and the engagement member in relation to the other of the first reel spool and the engagement member, may be done in dependence of one or more target values of the caliper of the rolled-up web in the first parent roll, in addition to said determined values of the caliper of the rolled-up web in the first parent roll. Thereby, the method may comprise comparing said determined values of the caliper of the rolled-up web with respective target values. In some embodiments, the target value of a portion of the web may be dependent on the radial location in the first parent roll of the portion of the web. Thereby, the target value may vary with the radial location. In other embodiments, the target value may be constant throughout the first parent roll.

[0018]Preferably, the step of moving at least one of the first reel spool and the engagement member in relation to the other of the first reel spool and the engagement member, is done during said step of advancing the first web into the nip. By moving at least one of the first reel spool and the engagement member in relation to the other in dependence of said determined caliper of the rolled-up web in the first parent roll, the caliper of the rolled-up web in the first parent roll can be controlled. For example, one or more of the determined rolled-up web caliper values can be used to calculate a setpoint or a reference speed for at least one of the first reel spool and the engagement member. Thereby, the caliper of the rolled-up web in the first parent roll may be kept constant, or according to a preset rolled-up web caliper shape, through the complete winding of the first parent roll.

[0019]The caliper of the rolled-up web is important for later converting operations based on the first parent roll. The direct control of the caliper of the rolled-up web made possible by the invention facilitates later converting operations based on the first parent roll. For example, compared to the web thickness before roll-up the rolled-up web caliper provides better control of the winding process. To determine the rolled-up web caliper from the web thickness before roll-up, knowledge of how the web behaves when rolled up is required. In particular, tissue is soft and changes thickness to a relatively large degree when it is rolled up. In addition, determining the web thickness before roll-up may require sensors which are sensitive and exposed to the dusty environment around the tissue machine.

[0020]Moving at least one of the first reel spool and the engagement member in relation to the other of the first reel spool and the engagement member, may comprise moving at least one of the first reel spool and the engagement member away from the other of the first reel spool and the engagement member.

[0021]In some embodiments, moving at least one of the first reel spool and the engagement member in relation to the other of the first reel spool and the engagement member, comprises moving only the first reel spool. In other embodiments, only the engagement member is moved. In further embodiments, the engagement member as well as the first reel spool are moved.

[0022]In some embodiments, the method comprises determining a position for the first reel spool in dependence of a determined value of the caliper of the rolled-up web. Thereupon, the first reel spool is moved so as to reach the determined position. In some embodiments, the method comprises determining a speed of the first reel spool in dependence of a determined value of the caliper of the rolled-up web. Thereupon, the first reel spool is moved so as to reach the determined speed.

[0023]In alternative (b) according to the invention, the second parent roll may not be the first parent roll. The second parent roll may be formed after the forming of the first parent roll. The second roll may be formed in the machine in which the first parent roll was formed. Thus, the engagement member used when forming the first parent roll may be the engagement member used when forming the second parent roll. However, in some embodiments, the engagement member used when forming the second parent roll is not the engagement member used when forming the first parent roll. The second parent roll may be formed by winding the second web onto the second parent roll.

[0024]In alternative (b), at least one of the second reel spool and the engagement member is moved in relation to the other of the second reel spool and the engagement member, in dependence of the determined values of the caliper of the rolled-up web in the first parent roll.

[0025]For example, while forming the first parent roll, and determining the values of the caliper of the rolled-up first web, the at least one of the first parent roll and the engagement member is moved in relation to the other of the first parent roll and the engagement member, in dependence of said determined values of the caliper of the rolled-up first web. As the first parent roll is formed, values of the roll diameter, and also values of the position of the first reel spool and/or the position of the engagement member, are recorded. Further the recorded values of the roll diameter are correlated to the recorded values of the position of the first parent roll and/or the position of the engagement member. The correlated values are stored.

[0026]While forming the second parent roll the diameter of the second parent roll is determined, e.g. based on the position of the second parent roll, and using the correlated values, the at least one of the second parent roll and the engagement member is moved in relation to the other of the second parent roll and the engagement member, in dependence of said determined diameter. The values of the first parent roll diameter and the position of the first parent roll and/or the position of the engagement member while forming the first parent roll are dependent on the determined values of the caliper of the rolled-up first web. Thus, in alternative (b), instead of determining one or more values of the caliper of the rolled-up web in the second parent roll, the caliper of the rolled-up web in the second parent roll is controlled in dependence on the determined values of the caliper of the rolled-up web in the first parent roll.

[0027]In some embodiments, the method comprises alternative (a) and also alternative (b) in claim 1. In other embodiments, the method comprises alternative (a) in claim 1, wherein the method may or may not comprise alternative (b). In other embodiments, the method comprises alternative (b) in claim 1, wherein the method may or may not comprise alternative (a).

[0028]Preferably, the method comprises determining a value of a diameter parameter indicative of the diameter of the first parent roll or a change of the diameter of the first parent roll, and determining a value of a web length parameter indicative of a length of web wound onto the first parent roll, wherein at least one of said rolled-up web caliper values is determined based on the diameter parameter value and the web length parameter value. For example, a plurality of values of the diameter parameter, and a plurality of values of the web length parameter, may be determined as the first parent roll is formed. Thereby, said rolled-up web caliper values may be determined based on respective of the diameter parameter values and respective of the web length parameter values.

[0029]For example, where the tissue web is engaged against the reel spool with a transfer belt, such as in said U.S. Pat. No. 5,901,918A, the diameter of the first parent roll can be determined by measuring the position of the first reel spool, and the deflection of the transfer belt caused by the first parent roll. Thereby, any angle between the direction of movement of the reel spool and the direction of deflection of the transfer belt is preferably taken into account. The length of web wound onto the first parent roll may be determined based on an integral of the rotational speed of a support roll for the transfer belt and the diameter of the support roll. For example, the length of web wound onto the first parent roll may be determined by integrating the rotational speed of the support roll and multiplying the integral with the support roll radius.

[0030]Similarly, in machines where the tissue web is engaged against the reel spool by a reel drum, the diameter of the first parent roll can be determined by the position and diameter of the reel drum, and by measuring the position of the first reel spool. The length of web wound onto the first parent roll may be determined based on an integral of the rotational speed of the reel drum and the diameter of the reel drum. For example, the length of web wound onto the first parent roll may be determined by integrating the rotational speed of the reel drum and multiplying the integral with the reel drum radius. The rotational speed may be determined by pulses counted from a tachometer on the reel drum.

[0031]Alternatives are possible. In some embodiments, the diameter of the first parent roll may be determined by the position of the first reel spool and a sensor, e.g. a laser sensor, that measures the position of the first parent roll periphery. Further, the length of web wound onto the first parent roll may be determined based on an integral of the rotational speed of the first parent roll and the determined diameter of the parent roll. For example, the length of web wound onto the first parent roll may be determined by integrating the rotational speed of the first parent roll and multiplying the integral with the first parent roll radius.

[0032]In other embodiments, the length of web wound onto the first parent roll may be determined based on the rotational speed and diameter of a reel drum or a belt support roll, and the diameter of the first parent roll may be determined based on the rotational speed of the first parent roll and the determined length of web wound onto the first parent roll. For example, the number of rotations of the first parent roll may be determined by integrating the first parent roll rotational speed, and the first parent roll diameter may be determined by dividing the length of web wound onto the first parent roll by π and the number of first parent roll rotations.

[0033]For calculating the caliper of the rolled-up web (IWC) in the first parent roll, two diameter values D1, D2, determined at different points in time during the winding process, may be determined. The diameter values may be indicative of a change of the diameter. Further, the length of web ΔL wound onto the first parent roll in the time period between said points in time, may be determined. The caliper of the rolled-up web (IWC) may then be determined as follows:

$\mathrm{IWC}=\frac{\pi \left(D{2}^2-D{1}^2\right)}{2\Delta L}$

[0034]Preferably, the method further comprises determining a deflection of or a load on the engagement member, wherein at least one of the first reel spool and the engagement member is moved in relation to the other in dependence of the determined deflection of or load on the engagement member as well as in dependence of at least one of said determined rolled-up web caliper values.

[0035]For example, as suggested, in some embodiments the engagement member comprises an endless flexible belt supported for rotation around a plurality of support rolls. Thereby, a predetermined path of travel including a free span between a pair of neighboring support rolls may be determined. Thereby, the amount of deflection of said flexible member from said predetermined path of travel may be determined. For determining the deflection, a sensing device may be mounted adjacent to said flexible member. Thereby, the first reel spool may be moved in relation to the flexible member in dependence of said measured deflection as well as in dependence of said determined rolled-up web caliper value.

[0036]In some embodiments, the movement of at least one of the first reel spool and the engagement member in relation to the other, is done to keep the rolled-up web caliper constant during the parent roll build-up. Thereby, the movement of at least one of the first reel spool and the engagement member in relation to the other, may be such that the deflection of or the load on the engagement member is kept within minimum and maximum boundary values.

[0037]The object is also reached with a controller according to claim 4, a computer program according to claim 5, a carrier according to claim 6, and an apparatus according to any one of the claims 7-9.

DESCRIPTION OF THE DRAWINGS

[0038]Below embodiments of the invention will be described with reference to the drawings, in which

[0039]FIG. 1 is a schematic side view of a machine for making soft high bulk tissue sheets,

[0040]FIG. 2 is a schematic side view of a winding section of the machine illustrated in FIG. 1,

[0041]FIG. 3 is an enlarged view of a part of the winding section in FIG. 2,

[0042]FIG. 4 is a schematic block diagram of a controller of the machine in FIG. 1,

[0043]FIG. 5 is a flow diagram depicting steps in a method according to an embodiment of the invention,

[0044]FIG. 6 is a view of a part of a winding section of a machine in an alternative embodiment of the invention,

[0045]FIG. 7 and FIG. 8 are flow diagrams depicting steps in a method according to an alternative embodiment of the invention, and

[0046]FIG. 9 is a view of a part of a winding section of a machine used in the method depicted in FIG. 7 and FIG. 8.

DETAILED DESCRIPTION OF EMBODIMENTS

[0047]FIG. 1 shows schematically a machine for making tissue sheets. Even though reference is here made to a tissue machine, it should be noted that the invention is equally applicable to machines for making other types of paper, or for making non-woven materials.

[0048]Parts of the machine in FIG. 1 are described in U.S. Pat. No. 5,901,918A incorporated herein by reference. Shown is a headbox 1 which deposits an aqueous suspension of papermaking fibers onto an inner forming fabric 3 as it traverses a forming roll 4. An outer forming fabric 5 serves to contain the web 6 while it passes over the forming roll and sheds some of the water. The web 6 is transferred to a throughdrying fabric 11 with the assistance of a vacuum transfer roll 12.

[0049]The throughdrying fabric 11 carries the web over the throughdryer 13, which blows hot air through the web to dry it while preserving bulk. The web is then transferred to a yankee 14.

[0050]After the yankee the web is transferred to a transfer belt 18. The transfer belt 18 passes over two support rolls 21 and 22 before returning to pick up the dried tissue sheet again. The sheet is transferred to the parent roll 25 at a point between the two support rolls 21, 22. The parent roll 25 is wound on a reel spool 26, which is driven by a center drive motor 27 acting on the shaft of the reel spool.

[0051]Control of the web properties of the web unwound from the parent roll can be aided by imparting a predetermined amount of web tension to the incoming web during winding, such as by programming the level of speed difference between the transfer belt 18 and the outer surface of the building parent roll 25. In most instances, a positive draw (the percentage by which the speed of the surface of the parent roll exceeds the speed of the transfer belt) is required at the parent roll in order to impart the web tension needed to provide a stable parent roll.

[0052]On the other hand, too much positive draw will unacceptably reduce the machine direction stretch in the web. Therefore, the amount of positive draw will depend upon the web properties coming into the parent roll and the desired properties of the web to be unwound from the parent roll. Generally, the speed of the surface of the parent roll will be about 10 percent or less faster than the speed of the transfer belt, more specifically from about 0.5 to about 8 percent faster, and still more specifically from about 1 to about 6 percent faster. Of course, if the web approaching the parent roll already has sufficient tension provided by other means earlier in the tissue making process, a negative or zero draw may be desirable.

[0053]The transfer and winding of the sheet is illustrated in more detail in FIG. 2. In the free span between the two support rolls 21, 22 the sheet 15 contacts and transfers to the parent roll 25. Reference numbers 26, 26′ and 26″ illustrate three positions of the reel spool during continuous operation. As shown, a new reel spool 26″ is ready to advance to position 26′ as the parent roll 25 is building. When the parent roll has reached its final predetermined diameter, the new reel spool is lowered by an arm 27 into a position 26′ against the incoming sheet at some point along the free span between the support rolls. Said position 26′ is generally relatively close to the first support roll 21, thereby avoiding a hard nip between the support roll and the reel spool.

[0054]The reel spool 26 is supported by a pair of carriages 37, one of which is illustrated in FIG. 3. As the parent roll 25 builds, the reel spool moves toward the other support roll 22 while at the same time moving away from the transfer belt 18. The reel spool 26 can be moved by an actuating arrangement 39, in this example comprising one or more hydraulic cylinders 39. The reel spool 26 can be moved in either direction as illustrated by the double-ended arrow. As a result, the parent roll nip substantially traverses the free span as the parent roll builds to its predetermined size. As the sheet is transferred to a new reel spool, the sheet is broken and the parent roll 25 is moved out to continue the winding process with the new reel spool.

[0055]The machine comprises a non-contacting sensing device 35. The sensing device 35 is focused on the inside of the transfer belt, preferably at a point M midway between the two support rolls 21, 22 as shown in FIG. 3.

[0056]The deflection D is herein understood as a maximum distance of the transfer belt 18 between the support rolls 21, 22 from the undeflected path of travel 36 of the transfer belt 18 in the free span.

[0057]The sensing device 35 may be a laser sensing device 35. The sensing device 35 is preferably mounted within an air purge tube 38 which maintains an air flow around the laser to prevent dust from settling on the lens of the laser.

[0058]Although a laser sensor is discussed above, alternatively, some other suitable non-contacting and contacting sensing device may be used. Such a device may involve ultrasonic sensing, a microwave or radar wave reflectance method, camera stereoscopic imaging for depth sensing, or a contacting probe such as a roller, a wheel, a metal strip, or another device whose position or deflection is measured directly.

[0059]The sensing device 35 can be positioned to always measure the deflection of the transfer belt 18 at the midpoint of the free span, regardless of the parent roll position. Thereby, the actual deflection at the parent roll nip point C may be calculated according to the position of the building parent roll 25, which traverses from one end of the open span to the other on the carriages 37 while it builds, e.g. as described in U.S. Pat. No. 5,901,918A incorporated herein by reference. Alternatively, the sensing device 35 can traverse the free span with the parent roll nip such that the laser always measures the deflection directly.

[0060]In some embodiments, two sensing devices each adjacent a respective edge of the transfer belt 18 so as to be spaced from each other in the cross machine direction. As such, undesirable tapering of the parent roll 25 can be minimized or a positive taper can even be introduced intentionally to improve the winding parameters of the particular parent roll being wound.

[0061]Reference is made also to FIG. 4. The machine comprises a programmable controller 400. The controller 400 may be a computer, a processing device, an automation control unit etc. The controller 400 may comprise a processing module 401, which may be embodied in the form of one or more hardware modules and/or one or more software modules. The term “module” may thus refer to a circuit, a software block or the like. The controller 400 may further comprise a memory 402. The memory may comprise, such as contain or store, instructions, e.g. in the form of a computer program 403, which may comprise computer readable code units. The controller 400, e.g. the processing module 401 thereof, comprises a processing circuit 404 which may be a hardware module. The instructions may be executable by the processing circuit 404, whereby the controller 400 is operative to perform a method of an embodiment described herein. FIG. 4 further illustrates a carrier 405, or program carrier, which provides, such as comprises, mediates, supplies and the like, the computer program 403 as described above. The carrier 405 may be one of an electronic signal, an optical signal, a radio signal and a computer readable medium. Moreover, the controller 400, e.g. the processing module 401 thereof, may comprise an Input/Output module 406, which may be exemplified by a receiving module and/or a sending module when applicable. The receiving module may receive commands and/or information from various devices, and the sending module may send commands and/or information to various devices.

[0062]As illustrated in FIG. 3, the sensing device 35 is connected to the controller. Thereby, the controller is arranged to receive signals from the sensing device 35, representative of the position of the transfer belt at the sensing device 35. The machine further comprises one or more position detectors 41, arranged to detect the positions of the carriages 37 for the reel spool 26. Thereby, the controller 400 is arranged to receive signals from the position detectors 41, representative of the positions of the carriages 37. Thereby, the controller is arranged to determine the position of the reel spool 26. The position detectors 41 can be provided in a variety of forms, e.g. as transducers mounted on the rods of the hydraulic cylinders 39.

[0063]The controller 400 is further arranged to control the actuating arrangement 39 for the reel spool 26, so as to control the position of the reel spool 26.

[0064]The machine further comprises a rotational speed sensor 42 for measuring the rotational speed of one of the support rolls 21. Thereby, the controller 400 is arranged to receive signals from the rotational speed sensor 42, representative of the rotational speed of the support roll 21.

[0065]With reference to FIG. 5, an embodiment of a method of winding a web 15 of paper material to form a parent roll will be described. The method aims at providing a caliper of the rolled-up web (IWC) according to a predetermined IWC curve. The IWC curve gives desired values of the IWC as functions of radial positions in the parent roll of the rolled-up web. The desired IWC may be constant, or it may vary with the radius of the parent roll.

[0066]The method comprises engaging the transfer belt 18 against the reel spool 26, and rotating the reel spool 26 and the transfer belt S1 to create a nip. The method further comprises advancing the web 15 of paper material into the nip and directing S2 the web around the reel spool 26 to form a parent roll of increasing diameter.

[0067]As the parent roll is formed, the amount of deflection of the transfer belt 18 is measured S3a, e.g. by means of the sensing device 35. Further, the position of the reel spool is determined S3b by means of the position detectors 41. Based on the amount of deflection of the transfer belt 18, and the position of the reel spool, the diameter of the parent roll is determined S4a, e.g. as exemplified above in the section Summary. Further, a length of web wound onto the parent roll is determined S4b. The length of web wound onto the parent roll may be determined based on an integral of the rotational speed of the support roll 21, and the diameter of the support roll.

[0068]Based on the determined diameter and length of web, a value of a caliper of the rolled-up web (IWC) is determined S5. This may be done as exemplified above in the section Summary.

[0069]The method comprises comparing S6 the determined caliper of the rolled-up web to a target caliper of the rolled-up web according to the IWC curve. Thereby, it may be determined whether the determined caliper of the rolled-up web is equal to the target caliper. The method further comprises adjusting S7, if needed, the reel spool position in relation to the transfer belt 18 so as for the determined caliper of the rolled-up web to reach the target caliper. For example, if the determined caliper of the rolled-up web is equal to the target caliper, the reel spool may be moved in relation to the transfer belt 18 according to the IWC curve. If the determined caliper of the rolled-up web is not equal to the target caliper, the reel spool position in relation to the transfer belt 18 may be adjusted to reach the target caliper. Moving S7 the reel spool is done by the hydraulic cylinders 39.

[0070]The method comprises determining S8 whether the parent roll is finished. This may involve determining whether the parent roll has obtained a predetermined final diameter. If the parent roll is not finished, the steps of measuring S3a the belt deflection, determining the reel spool position S3b, determining S4a, S4b the diameter and the web length, determining S5 a value of the rolled-up web caliper, and moving S7a, S7b the reel spool, are repeated. Thus, while the parent roll diameter is increasing, the steps of determining S4a, S4b the diameter and the web length, determining S5 a value of the rolled-up web caliper, and moving S7a, S7b the reel spool, are repeated a plurality of times.

[0071]The control loop may be programmed to move the reel spool 26 to maintain the rolled-up web caliper at a constant level during the parent roll build-up. Thereby, the movement of the reel spool may also be done to keep the belt deflection within minimum and maximum boundary values.

[0072]When the parent roll is completed S8, the reel spool 26 is removed S9 from the carriages 37.

[0073]It should be noted that in some embodiments, instead of using position detectors 41 to detect the positions of the carriages 37 for the reel spool 26, the controller 400 use the sensing device 35 arranged to detect the deflection of the transfer belt 18. Using the values of the caliper of the rolled-up web, the controller can correlate desired transfer belt deflection values with values of the target caliper of the rolled-up web according to the IWC curve. Thereby the reel spool is moved S7a, S7b in dependence of the determined values of the caliper of the rolled-up web.

[0074]In further embodiments, instead of position detectors 41 to detect the positions of the carriages 37 for the reel spool 26, the machine comprises one or more pressure sensors (not shown) arranged to detect the pressure in one or more of the hydraulic cylinders 39. Thereby, the controller 400 is arranged to receive signals from the pressure sensors. The controller is, as in the method described with reference to FIG. 1-FIG. 5, arranged to move the reel spool 26 by control of the hydraulic cylinders 39. Preferably, the controller 400 determines the pressure in the hydraulic cylinders when they are not actuated. Using the values of the caliper of the rolled-up web, the controller can correlate desired pressure values with values of the target caliper of the rolled-up web according to the IWC curve. Thereby the reel spool is moved S7a, S7b in dependence of the determined values of the caliper of the rolled-up web. An alternative embodiment of the invention will be described with reference to FIG. 6. In this embodiment, the web is transported to a nip between the parent roll 25 and an engagement member in the form of a reel drum 18. The reel drum may form a part of a pope reel. At the reel drum, the sheet is transferred to the parent roll 25. The reel drum is biased against the parent roll by means of a biasing arrangement 43, which may comprise one or more hydraulic actuators. A load sensor 35 is arranged to measure the load of the reel drum against the parent roll.

[0075]The machine further comprises a rotational speed sensor 42 for measuring the rotational speed of the reel drum 18. Thereby, the controller 400 is arranged to receive signals from the rotational speed sensor 42, representative of the rotational speed of the reel drum 18.

[0076]As the parent roll is formed the diameter of the parent roll, and a length of web wound onto the parent roll, are determined. The diameter of the parent roll can be determined by determining the position of the reel spool by means of the position detectors 41, and the position and diameter of the reel drum 18. The length of web wound onto the parent roll may be determined based on an integral of the rotational speed of the reel drum 18, and the diameter of the reel drum 18.

[0077]Based on the determined diameter and length of web, a value of a caliper of the rolled-up web (IWC) is determined. This may be done as exemplified above in the section Summary. Further, the load of the reel drum against the parent roll is measured with the load sensor 35.

[0078]In response to the determined rolled-up web caliper value, and to the measured load of the reel drum against the parent roll, the reel spool 26 is moved in relation to the reel drum 18.

[0079]The control loop may be programmed to move the reel spool 26 to maintain the rolled-up web caliper at a constant level during the parent roll build-up. Thereby, the movement of the reel spool may also be done to keep the load of the reel drum against the parent roll within minimum and maximum boundary values.

[0080]Reference is made to FIG. 7-FIG. 9. In an alternative embodiment of the invention, the steps described above with reference to FIG. 5 are performed with what is herein referred to as a first reel spool 26, to form what is herein referred to as a first parent roll. Thus, while forming the first parent roll, and determining values of the caliper of a first web rolled-up onto the first parent roll, the first parent roll is moved, in dependence of said determined values of the caliper of the rolled-up first web, so as to follow the predetermined IWC curve.

[0081]In addition, the method comprises correlating and storing S51 the determined values of the first parent roll diameter and the first reel spool position. When the first parent roll is finished it is removed S9.

[0082]As illustrated in FIG. 8 and FIG. 9, the method comprises, upon removing the first parent roll, engaging the transfer belt 18 against a second reel spool 262, and rotating the second reel spool 262 and the transfer belt S10 to create a nip. The method further comprises advancing a second web of paper material into the nip and directing S22 the second web around the second reel spool 262 to form a second parent roll 252 of increasing diameter.

[0083]As the second parent roll 252 is formed, the amount of deflection of the transfer belt 18 is measured S3a2, e.g. by means of the sensing device 35. Further, the position of the second reel spool 262 is determined S3b2 by means of the position detectors 41. Based on the amount of deflection of the transfer belt 18, and the position of the second reel spool, the diameter of the second parent roll 252 is determined S4a2.

[0084]Using the values of the first parent roll diameter and the first reel spool position that were stored and correlated S51 when the first parent roll was formed, a target position for the second reel spool 262 is determined S52 as the first reel spool position that is correlated with the determined diameter of the second parent roll 252.

[0085]The method comprises determining S62 whether the determined second reel spool position is equal to the target second reel spool position. If the determined second reel spool position is not equal to the target second reel spool position, the second reel spool is moved S7b2 so as to reach the target second reel spool position.

[0086]The method comprises determining S82 whether the second parent roll is finished. If the second parent roll is not finished, the steps of measuring S3a2 the belt deflection, determining the second reel spool position S3b2, determining S4a2 the second parent roll diameter, determining S52 the target second reel spool position, and moving S7b2 if needed the second reel spool, are repeated.

[0087]Thus, since the stored values of the first reel spool position are dependent on the determined values of the caliper of the first web rolled-up onto the first parent roll, and the second reel spool 262 is moved in dependence on the stored values of the first reel spool position, the second reel spool 262 is moved in dependence on the determined values of the caliper of the first web rolled-up onto the first parent roll.