Rewinding machine and method for the production of rolls of web material

Abstract

A rewinding machine is described with a winding cradle defined by three rollers and including a fourth winding roller defining with the first winding roller a cradle in which the web material is pushed by a winding core to the beginning of each winding cycle, to cause severing of the web material without the need for controlled mechanical parts.

Claims

1. A method for winding a web material around a winding core and producing a roll of web material comprising: providing a first winding roller and a second winding roller forming a winding nip through which winding cores and web material pass; winding a predetermined quantity of said web material around a first winding core to form a first roll; after winding said first roll, severing the web material and starting to wind a second roll around a second winding core, wherein the web material is severed by lengthening a path of said web material between said first winding roller and a further roller, arranged upstream of said first winding roller with respect to a direction of advancement of said web material, around which said web material is guided, and wherein the first winding roller and the further winding roller rotate in a common direction.

2. The method according to claim 1, wherein the path of the web material is lengthened between said first winding roller and said further roller by pushing the web material into a cradle between said first winding roller and said further roller.

3. The method according to claim 1, wherein the web material is tensioned prior to the path of said web material being lengthened in order to facilitate severing of the web material.

4. The method according to claim 1, wherein said web material is fed at a substantially constant rate during winding of the first roll and the second roll, and during severing of the web material.

5. The method according to claim 1, further comprising: providing a third winding roller downstream from said winding nip, defining a winding cradle together with the first winding roller and the second winding roller, providing said further roller as a fourth winding roller upstream from said winding nip, defining together with the first winding roller a cradle for severing the web material; feeding the web material around the fourth winding roller and the first winding roller through said winding nip and towards the winding cradle, and winding said web material around the first winding core in said winding cradle to form said first roll; pinching the web material between said second winding core and said fourth winding roller, by moving said second core against the fourth winding roller.

6. The method according to claim 5, wherein, after the web material has been pinched between said second winding core and said fourth winding roller, said second winding core is inserted in the severing cradle between the fourth winding roller and the first winding roller, thereby lengthening the path of the web material and severing of the web material at a point between the second winding core and the first roll.

7. The method according to claim 6, further comprising: keeping said second winding core between the first winding roller, the second winding roller and the fourth winding roller to wind a first part of said predetermined quantity of web material on said second winding core; gradually displacing said second winding core and the second roll forming thereon through the winding nip and into the winding cradle defined by the first winding roller, the second winding roller and the third winding roller, while said web material continues to be wound around said second winding core; completing winding of the second roll in said winding cradle.

8. The method according to claim 7, wherein during winding of the web material around said second winding core, the second roll is kept in contact with the fourth winding roller for at least a part of advancing movement of the second roll through said winding nip.

9. The method according to claim 8, wherein a roll being wound is kept constantly in contact with at least three of said first winding roller, said second winding roller, said third winding roller and said fourth winding roller throughout a winding cycle, the fourth winding roller losing contact with said roll being wound only after said roll being wound has come into contact with said third winding roller, while remaining in contact with said first winding roller and said second winding roller.

10. The method according to claim 9, wherein a part of the web material is wound while the roll being wound is kept in contact with the first winding roller, the second winding roller, the third winding roller and the fourth winding roller.

11. The method according to claim 5, wherein said first winding roller and said second winding roller are moved away from one another during passage of the second winding core through said winding nip.

12. The method according to claim 5, wherein said first winding roller, said second winding roller, said third winding roller and said fourth winding roller rotate substantially at a common peripheral speed during a substantial part of a winding cycle of each roll.

13. The method according to claim 5, wherein said first winding roller and said fourth winding roller always rotate substantially at a common peripheral speed, and said second winding roller rotates substantially at the common peripheral speed of the first winding roller and said fourth winding roller except for a step of angular deceleration and subsequent acceleration to make the second winding core and the second roll forming thereon advance through said winding nip.

14. The method according to claim 5, further comprising forcing said second winding core between said fourth winding roller and a stationary plate located at a distance from said fourth winding roller so as to cause pinching of the web material between said fourth winding roller and said second winding core when said second winding core is forced between said stationary plate and said fourth winding roller.

15. A peripheral rewinding machine for producing rolls of web material wound around winding cores comprising: a first winding roller and a second winding roller defining a winding nip; an inserter for inserting winding cores in said winding nip, so that said winding cores pass through said winding nip; a third winding roller located downstream from said winding nip, with said first winding roller, said second winding roller and said third winding roller defining a winding cradle; a feed path for said web material that extends through said winding nip; wherein upstream from said winding nip, a fourth winding roller is present distanced from said first winding roller and forming with said first winding roller an area for severing the web material; wherein the feed path of the web material extends around said fourth winding roller and around said first winding roller in said area for severing; and wherein the first winding roller and the fourth winding roller are controlled for rotation in a common direction.

16. The rewinding machine according to claim 15, wherein said inserter, said first winding roller and said fourth winding roller are positioned and controlled such that a winding core moved towards the fourth winding roller serves to pinch the web material between said fourth winding roller and said winding core.

17. The rewinding machine according to claim 15, further comprising an arrangement for lengthening the web material until said web material is severed between the first winding roller and the fourth winding roller on completion of winding of each roll.

18. The rewinding machine according to claim 16, wherein said first winding roller, said fourth winding roller and said inserter are positioned and controlled so as to make said winding core move inside a cradle for severing the web material defined between the first winding roller and the fourth winding roller, thereby lengthening a path of the web material and causing severing of the web material between said winding core and a roll being formed in the winding cradle.

19. The rewinding machine according to claim 16, wherein said fourth winding roller and said first winding roller are movable in a controlled manner in relation to one another to increase distance between a center of said first winding roller and a center of said fourth winding roller on completion of winding of a roll of web material, thereby lengthening a path of the web material between said first winding roller and said fourth winding roller up until the web material is severed.

20. The rewinding machine according to claim 15, wherein upstream from said winding nip, a stationary plate is present at a distance from said fourth winding roller and defining with said fourth winding roller a channel for insertion of said winding cores, the distance between the stationary plate and the fourth winding roller being such that a winding core inserted in said channel is forced against the fourth winding roller and serves to pinch the web material between said winding core and said fourth winding roller.

21. The rewinding machine according to claim 20, wherein said stationary plate defines a rolling surface for the winding cores tangent to the second winding roller.

22. The rewinding machine according to claim 15, wherein said second winding roller is controlled at a cyclically variable peripheral speed to make a winding core advance through the winding nip.

23. The rewinding machine according to claim 15, wherein said third winding roller is controlled at a variable peripheral speed to tension the web material on completion of winding of each roll.

24. The rewinding machine according to claim 15, wherein said first winding roller and said fourth winding roller are controlled to rotate at a substantially common constant peripheral speed.

25. The rewinding machine according to claim 15, wherein said fourth winding roller is supported with a movable axis and controlled so that said fourth winding roller moves closer to the winding nip when a new winding core advances towards and through said winding nip.

26. The rewinding machine according to claim 15, wherein said first winding roller and said second winding roller are positioned and controlled to move away from each other so as to modify width of said winding nip to enable passage of a winding core through said winding nip.

27. The rewinding machine according to claim 15, wherein said first winding roller, said second winding roller, said third winding roller and said fourth winding roller are positioned and controlled so that a roll forming around a winding core is always in contact with at least three of said first winding roller, said second winding roller, said third winding roller and said fourth winding roller.

28. The rewinding machine according to claim 15, wherein said first winding roller, said second winding roller, said third winding roller and said fourth winding roller are positioned and controlled so that a roll forming around one winding core is in contact with the first winding roller, the second winding roller, the third winding roller and the fourth winding roller for at least a part of a winding cycle, during which the roll being formed completes a plurality of rotations around an axis of the roll.

29. The rewinding machine according to claim 15, wherein said first winding roller, said second winding roller, said third winding roller and said fourth winding roller are positioned and controlled so as to define a straight path along which a winding core advances from a position upstream from said winding nip where winding starts to a position downstream from said winding nip where winding stops.

30. The rewinding machine according to claim 15, further comprising air delivery nozzles located between said first winding roller and said fourth winding roller.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood by following the description and the accompanying drawing, which shows a practical non-limiting embodiment of the invention. More specifically, in the drawing:

(2) FIGS. 1 to 8 show a first embodiment of the rewinding machine according to the invention, in a work sequence which illustrates the operating method;

(3) FIGS. 9 to 16 show a second embodiment of the rewinding machine according to the invention and an operating sequence of said machine;

(4) FIG. 17 shows a schematic view of a rewinding machine in a further embodiment;

(5) FIGS. 18 to 25 show an operating sequence of the rewinding machine of FIG. 17;

(6) FIG. 26 shows a further embodiment of the rewinding machine according to the invention;

(7) FIGS. 27 and 28 show a further embodiment of the rewinding machine according to the invention with a different arrangement for obtaining severing of the web material upon completion of winding of each roll or log.

DETAILED DISCLOSURE OF EMBODIMENTS OF THE INVENTION

(8) FIGS. 1 to 8 show a first embodiment of a continuous peripheral rewinding machine according to the invention and an operating sequence, which shows in particular the exchange phase, i.e. unloading of a log or roll, winding of which has been completed, and the insertion of a new winding core to begin the formation of a subsequent log or roll.

(9) FIGS. 1 to 8 show the main elements of the rewinding machine according to the invention, limited to what is required for understanding the concepts underlying the invention and operation of the machine. Construction details, auxiliary units and further components known per se and/or which can be designed according to the known art, are not illustrated in the drawing or described in further detail; a person skilled in the art can design these further components on the basis of his experience and knowledge in the field of paper converting machines.

(10) In short, in the embodiment illustrated in FIGS. 1 to 8 the machine, indicated overall by 2, comprises a first winding roller 1 with a rotation axis 1A, arranged alongside a second winding roller 3 having a rotation axis 3A. The axes 1A and 3A are parallel to each other. Between the two winding rollers 1 and 3 a winding nip 5 is defined, through which a web material N is fed to be wound around a winding core A1 around which a first roll or log L1 forms. As will become clear from the description below, the winding cores also cross the winding nip 5, since they are inserted in the machine upstream of the nip 5 and finish receiving the web material N wound around them when they are in the winding cradle defined not only by the rollers 1 and 3, but also by a third winding roller 7, downstream of the winding nip 5. 7A indicates the rotation axis of the third winding roller 7, parallel to the axes 1A and 3A of the first winding roller 1 and the third winding roller 3 respectively.

(11) In the present description and the accompanying claims, the definition upstream and downstream refers to the advancing direction of the web material and axis of the winding core, unless otherwise specified.

(12) The third winding roller 7 is provided with a movement towards and away from the winding nip 5. For said purpose, in some embodiments, the third winding roller 7 is supported by a pair of arms 9 hinged around an axis 9A to pivot according to the double arrow f9.

(13) Upstream of the winding nip 5, the first winding roller 1 and the second winding roller 3, a core feed device 11 is arranged, which can be designed in any suitable manner.

(14) The winding cores can come from a core winder, combined with the web material N processing line in which the rewinding machine 2 is inserted.

(15) The winding core feeder 11 is configured in this embodiment so as to define a core feeding path PA, which terminates near the first winding roller 1 and the second winding roller 3 upstream of the winding nip 5. In this area means for temporarily retaining the winding cores can be provided. In some embodiments these retaining means can comprise a bar or roller 13 opposite a lamina or a series of elastic laminas 15. The winding core feed path PA extends between the roller or bar 13 and the lamina(s) 15.

(16) The winding core feeder 11 is combined with an inserter 17 to insert the winding cores towards the roll formation area. In some embodiments the inserter 17 is a pusher. In the embodiment example illustrated, the inserter 17 comprises one or more pivoting arms hinged around a pivoting axis 17A and defining a push element 17B which cooperates with the cores to insert them in the winding area, i.e. in the winding head of the rewinding machine 2 as will be described in further detail below with reference to the operating sequence illustrated in FIGS. 1 to 8.

(17) In some embodiments, between the terminal area of the feeder 11 and the second winding roller 3 a stationary plate 19 is positioned provided with a shaped surface 19A, 19B, the function of which will be described in further detail below. Upstream of the winding nip 5 defined between the first winding roller 1 and the second winding roller 3 a fourth winding roller 21 is positioned, with a rotation axis 21A substantially parallel to the axes 1A, 3A and 7A of the first winding roller 1, the second winding roller 3 and the third winding roller 7 respectively. In some embodiments the fourth winding roller 21 is supported by a pair of pivoting arms 23 hinged around the pivoting axis 23A. In some embodiments, the pivoting arms 23 supporting the fourth winding roller 21 have an arched shape as illustrated in the drawing.

(18) Between the first winding roller 1 and the fourth roller 21 an area for severing the web material is defined, i.e. an area in which the web material is severed to generate a free trailing edge of the roll L1 during the completion phase and a free leading edge to start winding of the next roll L2. In practice said severing area can be defined by (or comprise) a nip or cradle 25 for severing the web material. As will be clarified below, the web material is severed by insertion of the new winding core in this severing nip or cradle 25.

(19) As shown in FIG. 1, during winding of a first roll L1 around a first winding core A1 the web material N is fed, according to the arrow fN, around the fourth winding roller 21, around the first winding roller 1 and winds on the roll L1 being formed which is retained, in this phase of the winding cycle, in the winding cradle defined by the three winding rollers 1, 3 and 7. The reference number 27 indicates a guide roller for the web material N positioned upstream of the winding head defined by the winding rollers 1, 3, 7 and 21.

(20) Preferably the feed speed of the web material N is substantially constant. By substantially constant a speed is understood that varies slowly in relation to the winding speed and as a result of factors that are independent of the operations performed by the components of the winding head described above, which are controlled so that the winding cycle, unloading of the roll formed, insertion of the new core and starting of the winding of a new roll can be performed at constant feed speed of the web material towards the winding roller unit and in particular towards the fourth winding roller 21.

(21) During the winding phase of the roll L1, outside the so-called exchange phase, which constitutes a transitory phase during operation of the machine, the peripheral speed of the winding rollers 1, 3, 7 and 21 is substantially the same and the various winding rollers all rotate in the same direction, as indicated by the arrows in the drawing. By substantially the same in this case a speed is meant, which can vary within the limit of the need to control the compactness of the winding and the tension of the web material N between the winding roller 21 and the winding roller 7, for example to compensate for the variation in tension which could be caused by displacement of the center of the roll being formed along the path between the winding rollers. In some embodiments this difference between peripheral speed of the rollers can be typically between 0.1 and 1% and preferably between 0.15 and 0.5%, for example between 0.2 and 0.3%, it being understood that said values are indicative and non-limiting.

(22) In FIG. 1 the roll L1 in the winding cradle 1, 3, 7 has been practically completed with winding of the desired quantity of web material around the first winding core A1. A second winding core A2 has been provided in the terminal area of the core feeder 11. The reference letter C indicates a line or series of glue points applied on the outer surface of the second winding core A2. In some embodiments the glue C is positioned so that it does not come into contact with the push element 17B of the inserter 17 when the second winding core A2 is inserted towards the winding cradle. Preferably the glue C is applied along a continuous or discontinuous line, substantially parallel to the axis of the winding core.

(23) FIG. 2 shows the beginning of the subsequent exchange phase. The second core A2 is engaged by the inserter 17 and made to gradually advance towards an insertion channel 31 defined between the fourth winding roller 21 and the stationary plate 19 and more precisely the surface 19A of the latter. This surface 19A preferably has a concave shape, substantially parallel to the surface of the winding roller 21. As shown in particular in FIG. 2, in this phase the new winding core A2 is pressed against the fourth winding roller 21, pinching the web material N between the second winding core A2 and the cylindrical surface of the fourth winding roller 21. The distance between the surface 19A of the stationary plate 19 and the cylindrical surface of the fourth winding roller 21 is preferably less than the diameter of the winding core, at least in the initial section of the channel 31, so that the winding core is forcedly inserted in the channel 31. This is made possible by the nature of the material used to manufacture the winding core, typically cardboard, which allows a substantially elastic diametral deformation. The pressure with which the winding core A2 is pushed against the web material N and the cylindrical surface of the winding roller 21 arranged opposite thereto generates a friction force between the core and the surfaces with which it comes into contact (surface 19A and web material N supported by the winding roller 21), which causes an angular acceleration of the second winding core A2 due to the difference in speed between the surface 19A (fixed) and the web material N which advances at the feed speed. As a result of this, the second winding core A2 begins to roll on the surface 19A of the stationary plate 19 at a speed such that the axis of the winding core advances at a speed equal to half the feed speed of the web material. During this movement the core remains in contact with the fixed surface 19A of the stationary plate 19 and with the web material N pressed against the cylindrical surface of the fourth winding roller 21. The portion of surface 19B upstream of the portion of surface 19A serves as a lead for entry of the winding core into the channel 31.

(24) FIG. 3 shows the immediately following step, in which the second winding core A2, rolling on the second part of the surface 19A of the stationary plate 19, has come into contact with the cylindrical surface of the second winding roller 3. The reciprocal distance between the fourth winding roller 21 and the second winding roller 3 is variable and in this phase is slightly less than the diameter of the winding core A2, thus it remains pressed against the two winding rollers 21 and 3 so as to correctly maintain control of the core. The configuration and position of the stationary plate 19 and the winding rollers 3 and 21 can be chosen and adjusted so that the axis of the fourth winding roller 21 does not have to move when switching from the condition shown in FIG. 1 to the condition of FIG. 3.

(25) The surface portion 19A of the stationary plate 19 is preferably concave and has a form and a position such that the space available for transit of the winding core is sufficiently limited to maintain a slight interference between core and parts 21, 19 of the machine.

(26) As a result of the advancing movement by rolling of the core on the stationary plate 19 to the position of FIG. 3, the winding core A2 begins to roll towards the inside of the cradle 25 defined between the fourth winding roller 21 and the first winding roller 1. As a result of the interference between the winding core A2 and the roller 21 on one side, and the surface 19A of the stationary plate 19 on the other, the advancing movement by rolling of the core A2 remains controlled.

(27) Advancing of the second winding core A2 towards and into the severing cradle defined between the winding rollers 1 and 21 causes a deformation of the path of the web material N. In FIGS. 1 and 2, in fact, the path of the web material N is straight and tangent to the winding rollers 1 and 21. As a result of advancing of the second winding core A2, however, the web material is pushed inside the severing cradle 25, with a consequent increase in the length of the path of the web material between the pinching point of the web material by the core A2 against the fourth winding roller 21 and the point of tangency of the web material N on the first winding roller 1. This lengthening of the path causes an elastic lengthening of the web material, since the speed of the winding rollers 1 and 21 remains substantially constant and equal to the feed and advancing speed of the web material N.

(28) Continuing the rolling of the winding core A2 and therefore lengthening of the path of the web material N, the latter will reach the condition of maximum lengthening and will tear, forming a trailing edge LC of the first roll L1 completed around the first winding core A1 and a leading edge LT of the beginning of winding of a second roll L2 around the second winding core A2. As a result of the rolling and advancing of the second winding core A2, the glue line C applied on the outer surface of the second winding core A2 is in this phase in the area in which the web material N is pinched between the second winding core A2 and the fourth winding roller 21. In this way the initial portion terminating in the leading edge LT of the web material N just severed due to the lengthening described above is anchored to the second winding core A2.

(29) In the subsequent FIG. 4 the second winding core A2 has continued its advancing movement, losing contact with the stationary plate 19 and coming into contact with the first winding roller 1. In this phase, therefore, the second winding core A2 is in a winding cradle defined by the three rollers 1, 3, 21. Since in this phase the three rollers rotate substantially at the same angular velocity, the core A2 remains in this position rotating around its own axis so that one or more loops of web material form around it. The stay time of the second winding core A2 in the position of FIG. 4 can be controlled by simply adjusting the peripheral speed of the winding rollers 1, 3 and 21. The second winding core A2 will remain substantially in this position, without advancing further, for as long as the peripheral speed of the winding rollers 1, 3 and 21 remains the same. The next advancement is obtained for example by decelerating the second winding roller 3 as described below. It is therefore possible to set as required the quantity of web material N which winds around the winding core A2 by retaining the latter and the second roll L2 that forms around it in the winding cradle 1, 3, 21 for the desired time.

(30) FIG. 5 shows the next phase in the winding cycle. The second winding core A2 on which the second log or roll L2 is forming must be transferred from the area upstream of the nip 5 to the area downstream of said nip, i.e. from the winding cradle defined by the first winding roller 1, by the second winding roller 3 and by the fourth winding roller 21, towards and into the winding cradle defined by the first winding roller 1, by the second winding roller 3 and by the third winding roller 7.

(31) For said purpose, as can be seen in FIG. 5, the first winding roller and the second winding roller 3 move away from each other, in a controlled manner according to the advancing speed of the winding core A2 and the feed speed of the web material N. This is because the higher the feed speed of the web material, the higher the speed at which the diameter of the second roll L2 forming around the second winding core A2 increases. Furthermore, the lower the advancing speed of the core A2, the greater the increase in diameter of the second roll L2. As mentioned, the advancing movement of the core A2 and the roll L2 during winding around it is obtained by modifying the peripheral speed of the winding rollers. More specifically, in the example illustrated, the second winding roller 3 is slowed down so that the second winding core A2 begins to roll through the winding nip 5 with the advancing speed of the axis of the core A2 equal to half the difference between the peripheral speeds of the first winding roller 1 and the second winding roller 3.

(32) In view of the fact that the winding core has received a certain quantity of web material N and therefore the roll or log L2 has already partly formed around it, the distance between the winding rollers 1, 3 is increased to allow the passage of the new roll L2 being formed.

(33) In some preferred embodiments of the invention, as illustrated, the reciprocal spacing, i.e. moving away from each other of axes 1A and 3A of the first winding roller 1 and the second winding roller 3, is performed by moving the two winding rollers 1 and 3 symmetrically and synchronously. For said purpose the winding rollers 1 and 3 are each supported by a pair of arms indicated respectively by 1B and 3B in the drawing. The arms 1B and 3B are hinged around pivoting axes 1C and 3C. Suitable actuators, not shown, for example in the form of electronically controlled electric motors, drive the movement of the rollers away from each other and then back again. Similar actuators can be used to control also the movements of the axes 7A and 21A of the other winding rollers 7 and 21.

(34) While the core A2 with the second roll L2 being formed around it advances through the winding nip 5 due to the difference in peripheral speed of the first winding roller 1 and the second winding roller 3, the fourth winding roller 21 is shifted forward by pivoting the pair of arms 23 around the pivoting axis 23A to accompany the core A2 and the roll L2 in the movement through the winding nip 5. In this way during all this phase of the winding cycle, the new roll L2 being formed around the second winding core A2 remains constantly in contact with the three rollers 1, 3, 21.

(35) The gradual advancing movement of the second winding core A2 and the second roll L2 through the winding nip 5 (FIG. 6) brings the second roll L2 into contact with the cylindrical surface of the third winding roller 7, which in the meantime has moved closer to the winding nip 5 after the first roll L1 has been unloaded from the winding cradle defined by the winding rollers 1, 3 and 7, as can be seen in the sequence of FIGS. 3 and 4. This unloading movement is obtained in a per se known manner by adjusting the peripheral speeds of the winding roller 3 and/or of the winding roller 7, so that the peripheral speed of the winding roller 7 is temporarily higher than the peripheral speed of the winding roller 3.

(36) Since the latter is in any case decelerated to allow advancing of the second winding roller A2 through the winding nip 5, the third winding roller 7 could be maintained at a constant peripheral speed. However, in order to speed up unloading of the roll L1 formed during the preceding cycle, it may be advantageous to accelerate also the winding roller 7, obtaining a greater difference between peripheral speed of the winding roller 7 and peripheral speed of the winding roller 3. Acceleration of the third winding roller 7 also provides the further advantage of tensioning the web material N before the tearing or severing phase (FIG. 3) if said acceleration begins slightly before the phase of insertion of the second winding core A2 in the severing cradle 25.

(37) Returning to FIG. 6, it is observed that at this moment the second winding core A2 with the roll L2 being formed around it is instantaneously in touch with all four winding rollers 1, 3, 7 and 21.

(38) The winding cycle continues, still maintaining the difference in peripheral speed between the winding roller 1 and the winding roller 3, until the new core A2 is completely positioned in the winding cradle defined by the rollers 1, 3, 7 as shown in FIG. 7. This further transit phase of the second winding core A2 from the midline of the winding nip 5 inside the winding cradle 1, 3, 7 is accomplished after moving away the second roll L2 being formed by the fourth winding roller 21, which can re-set to its initial position corresponding to that of FIG. 1, as can be seen in FIG. 7, where a third winding core A3 is also illustrated which has been positioned in the feeder 11 to start the next switchover cycle.

(39) FIG. 8 shows the final winding phase of the second roll L2 around the second core A2, a phase in which the machine is in the same position as the one illustrated in FIG. 1.

(40) The configuration of the parts of the rewinding machine illustrated in FIGS. 1-8 is such that the path followed by the center of the winding cores A1, A2 from the moment they come into contact with the two rollers 1, 3 to the moment when the roll begins to be unloaded between the rollers 3 and 7, losing contact with the roller 1, is substantially straight. This allows more regular winding and facilitates the use of tail-stocks which can be inserted in the opposite ends of the winding cores in order to improve control of the rotation and advancing movement of the core and roll during the winding cycle, combining the technique of peripheral winding with an axial or central winding, as described for example in the U.S. Pat. No. 7,775,476 and in the publication US-A-2007/0176039.

(41) FIGS. 9 to 16 show a modified embodiment of the rewinding machine according to the invention. The same reference numbers indicate parts which are identical or equivalent to those described with reference to FIGS. 1 to 8 and will not be described again. In this embodiment the axis 21A of the fourth winding roller 21 is kept in a substantially fixed position, so that the new winding core A2 performs a part of its movement (FIGS. 13 and 14) keeping in contact with only the first and second winding roller 1 and 3, instead of with three winding rollers. This constitutes substantially the only difference between the embodiment of FIGS. 9 to 16 and the embodiment of FIGS. 1 to 8, while the method with which the web material is severed in the two cases remains substantially the same.

(42) The embodiment of FIGS. 9 to 16 has greater construction and control simplicity, since it is not necessary to perform a cyclic pivoting movement of the fourth winding roller 21 around the pivoting axis 23A of the arms 23, which results in a simpler and cheaper configuration. The initial part of the winding is performed in contact with only two winding rollers, i.e. rollers 1 and 3, as in the traditional machines.

(43) FIG. 17 shows a further embodiment of a rewinding machine according to the invention, the operation of which is illustrated in the sequence of the successive FIGS. 18 to 25. In FIGS. 17 to 25 identical numbers indicate parts that are identical or corresponding to those of FIGS. 1 to 16.

(44) The rewinding machine 2 of FIGS. 17 to 25 differs from the rewinding machine of FIGS. 1 to 8 mainly due to the different structure of the winding core feeder and inserter 17 and due to the different form of the stationary plate 19. The operating method of the machine can be substantially equal to the one described with reference to FIGS. 1 to 8 or to the one described with reference to FIGS. 9 to 16. The sequence of FIGS. 18 to 25 shows an operating method corresponding to that of FIGS. 1 to 8, i.e. in which the fourth winding roller 21 is movable cyclically during the formation of each roll or log of web material, thus maintaining the roll or log L1, L2 always in contact with at least three winding rollers.

(45) FIG. 17 shows some components of the rewinding machine not shown in FIGS. 1 to 16 and in particular: the conveying system of the winding cores towards the winding head, the core gluing unit and a perforator for perforating the web material N according to substantially equidistant transverse perforation lines, which divide the material into sheets detachable at the moment of use by tearing along the perforation line.

(46) In the example illustrated, the winding cores are conveyed downwards by gravity along a descending channel 41 by a conveyor belt 42 on which winding cores A arrive for example from a core winder, not shown. A rotating distributor 43 individually collects the cores A coming from the descending channel 41 and transfers them to a conveyor 45 which transfers the individual winding cores A, A1, A2 through a gluing unit 47. The cores A, A1, A2 can be conveyed towards the gluing unit in any other suitable manner.

(47) In this embodiment the gluing unit 47 comprises a movable element 49 for lifting the glue from a container below 51. The glue is applied while the winding core A is advanced by the conveyor 45 along a path defined between the upper branch of the conveyor 45 and a counter surface 52, the final part 52A of which is moved by an actuator 50 to allow collection of the individual cores by the inserter 17. To obtain greater accuracy and precision in glue application, the conveyor 45 is controlled in order to temporarily stop the winding core A in a position above the movable element 49, which is raised to apply a line of glue on the cylindrical surface of the temporarily stopped winding core. The line can be a continuous or a discontinuous line, for example consisting of an alignment of glue spots arranged roughly parallel to the axis of the winding core. Once the movable element has lost contact with the surface of the winding core, the latter again begins to advance towards the winding cradle.

(48) The structure of this type of gluing unit is known per se and will not be described in further detail. The glue C can be applied also with other types of gluing unit known to persons skilled in the art. It should be noted, moreover, that in the example illustrated, the gluing unit is mounted on a slide 47A, the position of which can be adjusted according to the double arrow f47 along guides 47B. This adjustment is useful for ensuring that the line of glue applied to the winding cores is in the most appropriate angular position when the winding core comes into contact with the web material N.

(49) The winding cores provided with glue C are collected individually by the inserter 17, which in this embodiment comprises a gripper 18 supported by an element 20 rotating or pivoting around the axis 17A. An actuator 22 opens and closes the gripper to collect the individual cores from the gluing unit and insert them into the channel 31 defined between the stationary plate 19 and the fourth winding roller 21. To allow collection of the individual cores A by the gripper 18 of the inserter 17, the actuator 50 raises the terminal movable part 52A of the counter surface 52.

(50) In the embodiment of FIGS. 17 to 25 the stationary plate 19 has a concave surface 19A that is longer than the one illustrated in the embodiments of FIGS. 1 to 16. Also in this case the surface 19A preferably has a substantially cylindrical form, roughly coaxial to the fourth winding roller 21 when the latter is in the position of FIG. 18. In this way a channel 31 is defined with substantially constant cross section and preferably slightly smaller than the diameter of the winding cores A. The initial position of the winding roller 21 and/or the stationary plate 19 can be modified according to the diameter of the winding cores used.

(51) FIG. 17 furthermore illustrates the perforation unit 53 for producing the transverse perforated lines in the web material N. The perforation unit 53 can comprise a beam 54 with a fixed counter blade 55 cooperating with a roller 56 provided with a plurality of perforation blades 57. The perforation unit is known per se and will therefore not be described in further detail.

(52) The sequence of FIGS. 18 to 25 shows, similarly to the sequence of FIGS. 1 to 8, the operation of the rewinding machine in the embodiment of FIG. 17. Since the various elements and components of the machine are equivalent and operate similarly to those of the embodiment of FIGS. 1 to 8, the winding cycle will not be described again and will be self-explanatory from the preceding description and FIGS. 18 to 25. It should be noted that the different form of the surface 19A of the stationary plate 19 provides (FIGS. 19, 20) the same function described with reference to FIGS. 2 and 3. The second core A2 inserted by the inserter 17 into the channel 31 formed by the surface 19A and by the fourth winding roller 21 is pressed against the winding roller 21 so that the web material N is pinched between the core A2 and the fourth winding roller 21. The core is accelerated due to the friction force generated at the point of contact with the web material N and with the surface 19A of the stationary plate 19 and begins to roll at an advancing speed equal to half the feed speed of the web material N, moving into the severing cradle 25 (FIG. 20). In this phase the glue C causes the web material N to adhere to the new core A2 and lengthening of the path of the web material which is pushed by the core A2 into the severing cradle 25 causes rupture of the web material N, preferably along a perforation line generated by the perforator 53, between the pinching area P1 (between winding roller 21 and core A2) and the contact area P2 between web material N and first winding roller 1.

(53) To facilitate severing of the web material, the cylindrical outer surface of the first winding roller 1 can be provided with a coating (continuous or discontinuous, for example in annular bands) of material with a high friction coefficient, so-called grip to increase the friction coefficient between web material N and winding roller 1. A similar coating can be provided on the other winding rollers 3, 7 and 21 to favor the grip on the web material N and therefore more effectively transmit the force to keep the roll L1, L2 being wound in rotation. Also the surface 19A, 19B of the stationary plate can have a continuous or partial coating of material with high friction coefficient. In other embodiments one or more of the mechanical parts (rollers and stationary plate) which come into contact with the web material can have contact surfaces with the web material machined to obtain a high friction coefficient, for example using a processing that increases their roughness. A similar coating or treatment can be provided in the embodiments of FIGS. 1 to 16.

(54) The leading edge LT for the new roll L2 and the trailing edge LC for the roll or log L1 are thus generated similarly to what has already been described.

(55) The machine of FIG. 17 can be designed also with a winding roller 21 which is kept fixed during the winding cycle, which will be carried out in said case similarly to what has been illustrated in FIGS. 9 to 16.

(56) FIG. 26 shows a modified embodiment of the rewinding machine according to the invention. In this embodiment a blowing system 100 is arranged between the rollers 1 and 21. In some embodiments the blowing system 100 comprises a plurality of nozzles preferably aligned in a direction substantially parallel to the axes of the rollers 1 and 21. The blowing nozzles generate a series of air jets onto the surface of the web material N facing the rollers 1 and 21. The jet of air can facilitate severing of the web material. A similar blowing system could be provided in the embodiment illustrated in FIGS. 1 to 16.

(57) The nozzles of the blowing system 100 can be controlled to generate a jet of air synchronized with the movement of the winding core towards the inside of the severing cradle 25.

(58) In the embodiments of FIGS. 1 to 26 the severing or rupture of the web material N upon completion of the winding is obtained by lengthening of the path of the web material N between the rollers 1 and 21 caused by the movement of the winding core towards the severing cradle 25. FIGS. 27 and 28 show, limited to the severing phase of the web material, a different method of lengthening the path of the material in the section between the rollers 21 and 1. In this embodiment the distance between the centers of the rollers 1 and 21 is variable. Preferably the roller 1 has a fixed rotation axis 1A, while the roller 21 has a movable rotation axis 21A to move away from the axis 1A of the roller 1. When the winding core A2 comes into contact with the web material N, pinching it between the core and the surface of the roller 21, the distance between the centers of the two rollers 1 and 21 can be promptly and temporarily increased, causing a lengthening of the section of web material between the two rollers and therefore the severing thereof. Subsequently the two rollers can be moved near each other again and the roller 21 can if necessary perform a movement to accompany the new winding core A2 towards the nip 5 as previously described.

(59) In all the embodiments the glue C is applied to the winding cores A1, A2 so that it is in the most favorable angular position for adhesion of the free leading edge of the web material to the winding core. In practice, the angular position of the line of glue C is controlled to be as near as possible to the perforated line which breaks due to lengthening of the path of the web material between the rollers 1 and 21.

(60) The winding cores A1, A2 can consist of tubes of cardboard, paper, plastic or other material which is subsequently cut when the respective roll or log is divided into small rolls. In other embodiments the winding cores are formed of spindles which can be extracted from the completed rolls or logs and then recycled to wind subsequent rolls or log.

(61) It is understood that the drawing only shows an example provided solely by way of practical demonstration of the invention, which can vary in its forms and arrangements without departing from the scope of the concept underlying the invention. Any reference numbers in the attached claims are provided to facilitate reading of the claims with reference to the description and the drawing, and do not limit the protective scope of the claims.