Method for cutting a moving web of material

Abstract

Method for cutting a running web (12), comprising the steps of: - guiding the web (12) over a circumferential surface of a support drum (16); - rotating a blade (32) extending in the axial direction of the support drum about an axis of rotation (30) parallel to the axis (48) of the support drum (16); - retaining the blade (32) in a retracted position in which a cutting edge of the blade is spaced apart from the web (12) on the support drum;and- impact of the blade (32) against the track and against the surface of the support drum at a time when the blade passes through a plane (P) which contains the axis (48) of the support drum and the said axis of rotation (34), characterized in that a cutter shaft (28) carrying the blade (32) is mounted in a crank rocker (44) which in turn is mounted on a rotatably driven eccentric (42), and that the impact movement of the blade (32) is controlled by controlling the drive of the eccentric (42).

Description

The invention relates to a method for cutting a moving web, comprising the steps of:guiding the web over a circumferential surface of an abutment drum;rotating a blade extending in the axial direction of the abutment drum about a rotation axis parallel to the axis of the abutment drum;retaining the blade in a retracted position, wherein a cutting edge of the blade is spaced from the web on the abutment drum; andpushing the blade against the web and against the surface of the abutment drum at a time when the blade passes through a plane containing the axis of the abutment drum and said axis of rotation.When an endless web, for example a printed web of printing material which leaves a rotary printing press, is wound up into a roll, the diameter of the roll gradually increases, and when a certain maximum diameter has been reached, it is necessary to cut the web and to transfer the subsequent part of the web to another roll.WO 2022 / 111869 A1 discloses a method of the type mentioned at the beginning, in which the blade is held in a prestressed state and then abruptly released.The object of the invention is to better control the impact movement of the blade.To achieve this object, the invention proposes methods in which a knife shaft carrying the blade is mounted in a crank arm which is in turn mounted on a rotationally drivable eccentric, and in which the impact movement of the blade is controlled by controlling the drive of the eccentric.The invention has the advantage that the rotational movement of the eccentric not only controls the advancing movement of the blade in the direction of the web and the abutment drum, but also the subsequent retracting movement. This allows a smoother transition between advancing and retracting movement. In addition, it is ensured with simple means that the reversal of movement of the blade takes place exactly in the position in which the blade has severed the web but has not yet cut into the abutment drum and damage it. It has been found that by suitably selecting the rotational speed of the eccentric, a sufficient speed of the impact movement can be achieved. The precise timing of the impact movement can also be precisely controlled by driving the eccentric.Although it is specified in claim 1 that the axis of rotation of the blade is parallel to the axis of the abutment drum, high accuracy of parallelism is not required. For example, an angular deviation of up to 5° may be acceptable.Practical details and further developments of the invention are specified in the dependent claims.Depending on the material of the web to be cut, the cutting process can be optimized by heating the blade to a suitable temperature.In order to achieve a rectilinear movement of the knife shaft and the blade, the knife shaft can be held in a linear guide.The output of the eccentric can be effected, for example, via a servomotor or a stepping motor.An exemplary embodiment is described below with reference to the drawings, in which: FIG. 1 is a schematic side view of a winder with a cutting unit; FIG. 2 shows the winder and the cutting unit in a state where a cutting operation is prepared; FIG. 4 shows the winder and the cutting unit in a state in which the cutting operation takes place; and FIG. 4 shows the winder and the cutting unit in a later operating state.Figure 1 schematically shows a winder 10, which may be installed in a rotary printing press and serves to wind an endless web 12 of a printing substrate. The web 12 runs over a deflection roller 14 and is then guided over a part of a smooth circumferential surface of an abutment drum 16 and is finally wound onto a roll 18 on a first winding core 20. The abutment drum, the first winding core 20 and a second winding core 22 are rotatably mounted in a machine frame. The circumferential surface of the abutment drum may be smooth or may have a grooving, for example in the form of a diamond pattern. The winding cores 20, 22 are displaceable in the radial direction of the abutment drum.Above the abutment drum 16 there is arranged a cutting gate 24 which is guided for vertical movement in the machine frame. The cutting gate and the abutment drum together form a cutting unit for cutting the web 12, which cutting gate is guided on guide rods 26 and forms a bearing for the ends of a knife shaft 28 which is rotatable about a rotation axis 30 by means of a drive not shown. A blade 32 is rigidly mounted on the knife shaft 28 and extends longitudinally of the shaft and projects radially from the surface of the shaft. A blade support member inside the cutter shaft 28 has an integral heater cartridge 34 which serves to heat the blade 32 to a temperature (of, for example, 150°C) required for the material to be cut. As the knife shaft 28 and blade 32 rotate about the axis of rotation 30, the cutting edge of the blade 32 moves on a circular trajectory 36.Above the knife shaft 28 and parallel thereto extends an eccentric shaft 38 which is rotatable about an axis fixed to the frame by means of a servomotor 40 and carries two eccentrics 42 on which two arms of a crank arm 44 are mounted (only one of the arms is visible in the drawing). The entire cutting gate 24 is suspended from the crank arm 44. In the example shown, the knife shaft 28 has a bearing pin 46 at each end, which is mounted in an arm of the crank rocker 44 and at the same time can also serve for mounting the knife shaft in the cutting gate 24. In FIG. 1, the eccentrics 42 are in an angular position in which the crank arm and the cutting gate assume their highest position.While the web 12 is being wound onto the winding core 20, in the state shown in FIG. 1, both the knife shaft 28 and the eccentric shaft 38 are held stationary, so that the cutting unit is inactive, except that the abutment drum 16 is involved in guiding the web onto the winding 18.As the winding process progresses, the diameter of the package 18 gradually increases, and as a result, the winding core 20 must be moved laterally away from the axis of the abutment drum 16. When the diameter of the roll 18 reaches a certain maximum value, it is necessary to cut the web 12 and to direct the subsequent part of the web onto the empty second winding core 22 in order to start the formation of a new roll on this winding core.Shortly before this time is reached, the knife shaft 28 is rotated and accelerated to an angular velocity at which the peripheral velocity of the cutting edge of the blade 32 approximately matches the speed of travel of the web 12. At a suitable time, the eccentric shaft 38 is also rotated.Figure 2 shows the cutting unit in a stage just before the blade 32 reaches the plane P containing both the axis 48 of the abutment drum 16 and the axis of rotation 30. The circumferential speed of the cutting edge of the blade 32 on the trajectory 36 has at this point in time approximately reached the transport speed of the web 12, so that there is at most a slight relative movement between the blade and the web 12 in the horizontal direction. Due to the rotation of the eccentrics 42, the crank arm 44 and the cutting gate 24 have lowered to such an extent that the trajectory 36 almost touches the circumferential surface of the abutment drum 16. The angular acceleration of the eccentric shaft 38 is controlled by the servomotor 40 so that the crank arm reaches its deepest position just at the moment the cutting edge of the blade 32 passes the plane P, and that the angular velocity of the eccentric shaft 38 is maximum at this time (or during a period just before and just after this time). As a result, the blade 32 is pushed at high speed onto the web 12 to cut it.Figure 3 shows the time at which the blade 32 has reached the plane P and the cutting edge pierces the web 12. At this time, since the crank arm 44 has reached its lowest point, the downward movement of the cutter gate 24 reverses to an upward movement so that the cutting edge of the blade 32 in its lowest position reaches a point at which it has severed the web 12 but has not yet appreciably cut into the circumferential surface of the anvil drum 16. In this manner, a clean cut is made with the blade heated by the heater cartridge 34 without damaging the anvil drum (which may optionally have a resilient coating). The downward movement of the blade 32 is thereby continuously converted into an upward movement.FIG. 4 shows the situation at a somewhat later point in time. The cutter shaft 28 has continued to rotate and is then stopped at an appropriate position so as to be ready for another cutting process. The angular speed of the eccentric shaft is reduced in such a way that the eccentrics 42 come to a standstill again in the position shown in FIG. 1. The first winding core 20 carrying the package 18 has been moved away from the abutment drum 16, while the second winding core 22 (to which an adhesive strip may have been applied to adhere the leading edge of the web 12) has been placed against the circumferential surface of the abutment drum 16 at a time when the leading edge of the cut web 12 reaches the gap between the winding core 22 and the abutment drum, so that a new package is now formed on the second winding core 22. During the time the leading edge of the web has moved from the cutting position (at the top apex of the anvil drum) to the nip with the second mandrel 22, the web has been attracted to the circumferential surface of the drum by suction pressure applied to the web via perforations in the surface of the drum.The roll 18 is detached from the first winding core 20 and the first winding core is again adjusted in the direction of the abutment drum 16 so that it is ready to take up a further roll. When the roll formed on the second winding core 22 has reached its maximum diameter, the cutting unit is activated again, so that a new roll is started on the first winding core 20.While in the example described herein the winding cores 20 and 22 are rotated counterclockwise, it is also possible to operate the winder 10 in a mode in which the winding cores rotate clockwise. In this mode of operation, the web 12 is fed from the opposite side via a pulley 54, and the directions of rotation of the abutment drum 16 and the knife shaft 30 are reversed.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedWO 2022 / 111869 A1

[0003]

Claims

A method of cutting a running web (12) comprising the steps of: passing the web (12) over a circumferential surface of an abutment drum (16); rotating a blade (32) extending in an axial direction of the abutment drum about an axis of rotation (30) parallel to the axis (48) of the abutment drum (16); retaining the blade (32) in a retracted position in which a cutting edge of the blade is spaced from the web (12) on the abutment drum; and - abutting the blade (32) against the web and against the surface of the abutment drum at a time when the blade passes through a plane (P) containing the axis (48) of the abutment drum and said axis of rotation (34), characterized in that a knife shaft (28) carrying the blade (32) is supported in a crank arm (44), which in turn is supported on a rotationally drivable eccentric (42), and in that the pushing movement of the blade (32) is controlled by controlling the drive of the eccentric (42).The method of claim 1, wherein the circumferential speed of the blade (32) is controlled to coincide with the transport speed of the web (12) at the time when the blade encounters the web (12).Method according to claim 1 or 2, wherein the knife shaft (28) is mounted in a cutting gate (24), which is linearly guided during the impact movement.Method according to one of the preceding claims, in which the eccentric shaft (38) is driven via a servomotor (40) or a stepping motor.A method according to any preceding claim, wherein the blade (32) is maintained at an elevated temperature.A cutting unit comprising a blade (32) for cutting a running web (12), and a rotating anvil drum (16) having a smooth peripheral surface and being adapted to support the web (12), the blade (32) being adapted to be driven for rotation about an axis of rotation (30) extending parallel to the axis (48) of the anvil drum (16), characterised in that a knife shaft (28) carrying the blade (32) is journalled in a crank arm (44) which in turn is journalled on a rotatably drivable eccentric (42).Cutting unit according to claim 6, in which the knife shaft (28) is mounted in a cutting gate (24), which hangs from the crank arm (44) and is guided linearly by guide rods (26).Cutting unit according to claim 6 or 7, comprising a heating system (34) arranged to heat the blade (32).Winder for winding a web (12) onto a roll (18), characterized bya cutting unit according to one of Claims 6 to 8.

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