Method for cutting a moving web of material

Abstract

A running web 12 is cut whilst guided between a blade 32 and a rotating abutment drum 16, the blade 32 being driven to rotate on a shaft 28 about an axis 30 parallel to that of the drum, the shaft 28

Description

The invention relates to a method for cutting a running web, comprising the steps of: guiding the web over a circumferential surface of an abutment drum; rotating a blade, that extends in the axial direction of the abutment drum, about an axis of rotation parallel to the axis of the abutment drum; holding the blade in a retracted position in which a cutting edge of the blade is spaced apart from the web on the abutment drum; and impacting the blade against die web and the surface of the abutment drum at a time when the blade passes through a plane that contains the axis of the abutment drum and said axis of rotation. If an endless web, e.g. a printed substrate web which exits from a rotary printing machine, and is wound into a coil, the diameter of the coil gradually increases, and when a certain maximum diameter has been reached, it is necessary to cut the web and to redirect the subsequent part of the web to another reel. From WO 2022 / 111869 Al, a method of the type mentioned above is known in which the blade is held in a pre-tensioned state and is then suddenly released. The object of the invention is to better control the impact movement of the blade. In order to achieve this object, the invention proposes a method in which a knife shaft that carries the blade is supported in an oscillating crank which m turn is mounted on a rotary' 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 roiaiy movement of the eccentric controls not only the feed movement of the blade towards the web and the abutment drum but also tire subsequent retraction movement. This enables a smoother transition between the feed and retraction movements. In addition, it is ensured with simple means that the reversal of the movement of the blade takes place exactly in the position in which the blade has cut through the web but has not yet cut into the abutment drum and caused damage to it. It has been found that a sufficient speed of the impact movement can be achieved by choosing an appropriate rotation speed of the eccentric. The exact timing of tire impact movement can also be precisely controlled via the eccentric drive. Although claim 1 specifies that the axis of rotation of the blade is parallel to the axis the abutment dram is parallel, no high accuracy of parallelism is required. For example, an angular deviation of up to 5° may be acceptable. Useful details and further developments of the invention are indicated 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. To achieve a straight-line movement of the knife shaft and the blade, the knife shaft may be held in a linear guide. The drive of the eccentric can be controlled, for example, by a servo motor or a stepper motor. In the following, an embodiment example will be described by reference to the drawings, wherein:: Fig. 1 is a schematic side view7 of a winder with a cutting unit; Fig. 2 the winder and the cutting unit in a state in which a cutting operation is being prepared: Fig.4 the winder and the cutting unit in a state in which the cutting operation proceeds; and Fig.4 the winder and the cutting unit in a later operating state. Fig. 1 schematically shows a winder 10 which may be installed in a rotary printing machine and serves to wind up an endless web 12 of a print substrate. Ure web 12 runs over a deflection roller 14 and is then guided over a part of a smooth peripheral surface of an abutment drum 16 and finally onto a coil 18 on a first winding core 20. The abutment drum, the first winding core 20 and a second winding core 22 are rotatable in a machine frame. The peripheral surface of the abutment drum may be smooth or may be grooved, e.g. in the form of a diamond pattern. The winding cores 20, 22 are movable in radial direction of the abutment drum. Above the abutment drum 16, a cutting gate 2.4 is arranged, which is guided for a vertical movement in the machine frame. Ilie cutting frame and the abutment drum together form a cutting unit for cutting the web 12. The cutting gate is guided on guide rods 26 and forms a bearing for the ends of a knife shaft 28 which is rotated 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 in the longitudinal direction of the shaft and protrudes radially from the surface of the shaft. A blade holder inside the knife shaft 28 has an integrated heating cartridge 34 which serves to heat the blade 32 to a temperature (e.g. 150°C) required for the material to be cut. When the knife shaft 28 and the blade 32 rotate about the axis of rotation 30, the cutting edge of the blade 32 moves on a circular trajectory 36. In the state shown in Fig. 1, the lower apex of this trajectory has a significant vertical distance to the upper apex of the abutment dram 16. Above the knife shaft 28 and parallel to it runs an eccentric shaft 38 which, by means of a servo motor 40, is rotatable about a frame-fixed axis, and carries two eccentrics 42, on which two arms of an oscillating crank 44 are supported {in the drawing, only one of the arms is visible). The entire cutting frame 24 is suspended from the oscillating crank 44. In the example shown, the knife shaft 28 has, at each end, a bearing pin 46 which is supported in an arm of the oscillating crank 44 and at the same time can also serve to support the knife shaft in the cutting gate 24. In Fig. 1, the eccentrics 42 are in an angular position in winch the oscillating crank and the cutting gate assume their highest position. In the condition shown in Fig. 1, while the web 12 is wound onto the winding core 20, both the knife shaft 28 and the eccentric shaft 38 are stationary so that, the cutting unit is inactive, except that the abutment drum 16 is involved in guiding the web onto the reel 18. As the winding operation proceeds, the diameter of the coil 18 increases gradually, and as a result the winding core 20 must be moved laterally away from the axis of the bearing drum 16. When the diameter of the coil 18 exceeds a certain maximum value, it is necessary to cut the web 12 and to guide the subsequent part of the web onto the empty second winding core 22, so as to start forming a new coil on this winding core. Shortly before this point is reached, the knife shaft 28 is driven for rotation and accelerated to an angular velocity at which the peripheral speed the cutting edge of the blade 32 approximately equals the transport speed of the web 12. At an appropriate time, the eccentric shaft 38 is also set into rotation. Fig. 2 shows the cutting unit in a stage just before the blade 32 reaches the plane P which includes both, the axis 48 of the abutment drum 16 and the axis of rotation 30. At this point in time, the peripheral speed of the cutting edge of the blade 32 on the trajectory 36 has almost reached the transport speed of the web 12 so that there is at most a minor relative movement in the horizontal direction between the blade and the web 12. Due to the rotation of the eccentric 42, the oscillating crank 44 and the cutting gate 24 are lowered so far that the trajectory 36 almost touches the peripheral surface of the abutment drum 16. Ure angular acceleration of the eccentric shaft 38 is controlled by the servo motor 40 such that that the oscillating crank reaches its lowest position exactly at the moment when the cutting edge of the blade 32 passes the plane P, and that the angular velocity of the eccentric shaft 38 at this time (or during a period shortly before and shortly after this point in time) is at maximum. This causes the blade 32 to be moved at high speed onto web 12 in order to cut it. Fig. 3 shows the point in time at which the blade 32 has reached the plane P and the cutting edge pierces the web 12. Since the oscillating crank 44 has reached its lowest point, the downward movement of the cutting gate 24 reverses at this point in time into an upward movement so that the cutting edge of the blade 32 in its lowest position reaches a point where it has cut through the web 12 but still does not cut significantly into the peripheral surface of the abutment drum 16. In this way, tire blade that is heated by the heating cartridge 34 makes a dean cut without severing the abutment dram (which can optionally have an elastic coating). In this process, the downward movement of the blade 32 is smoothly converted into an upward movement. Fig. 4 shows the situation at a slightly later point in time. Tire knife shaft 28 has continued its rotation and is then stopped in a suitable position so that it is ready for another cutting process. The angular velocity of the eccentric shaft is reduced such that the eccentric 42 comes to rest again in the position shown in Fig. 1. The first winding core 20, which carries the coil 18, has been withdrawn from the abutment dram 16, while the second winding core 22 (on to which an adhesive strip may have been applied for attaching the leading edge of the web 12) has been placed against the peripheral surface of the abutment dram 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 coil is now formed on the second winding core 22. During the time m which the leading edge of the web moves from the cutting position (at the upper apex of the abutment drum) to the gap with die second winding core 22, the web has been attraacted to the peripheral surface of the drum by a suction pressure that was applied to die web via perforations in the surface the dram. The coil 18 is released from the first winding core 20, and the first winding core is again adjusted towards the abutment drum 16 so that it is ready to take up another coil. When the coil formed on the second winding core 22 has reached its maximum diameter, the cutting unit is activated so that a new coil can be started on the first winding core 20. While in the example described here the winding cores 20 and 22 rotate counterclockwise, it is also possible to operate the winder 10 in a mode in which the winding cores rotate clockwise. In this operating mode, the web 12 is fed from the opposite side via a deflection roller 54, and the rotation directions of the abutment drum 16 and the knife shaft 30 are reversed.

Claims

1. A method for cutting a running web (12), comprising the steps:guiding the web (12) over a circumferential surface of an abutment drum (16);rotating a blade (32), that extends in the axial direction of tire abutment drum, about an axis of rotation (30) parallel to the axis (48) of the abutm ent drum (16);holding the blade (32) in a retracted position in which a cutting edge of the blade is spaced apart from the web (12) on the abutment drum: andimpacting the blade (32) against the web and tire surface of the abutment drum at a time when the blade passes through a plane (Pi that contains the axis (48) of the abutment drum and said axis of rotation (30),characterized in that a knife shaft (28) carrying the blade (32) is supported in an oscillating crank (44) which in turn is mounted on a rotary eccentric (42), and in which the impact movement of the blade (32) is controlled by controlling the drive of the eccentric (42).

2. The method according to claim 1, wherein the peripheral speed of the blade (32) is controlled such that, at the time when the blade hits the web (12), it corresponds to the transport speed of the web (12).

3. The method according to claim 1 or 2, wherein the knife shaft (28) is supported cutting gate (24) which is guided for linear motion during the impact movement.

4. The method according to any of die preceding claims, wherein the eccentric shaft (38) is driven by a servo motor (40) or a stepper motor.

5. The method according to one of the preceding claims, wherein the blade (32) is kept at an elevated temperature.

6. A cutting unit comprising a blade (32) for cutting a running web (12). and a rotating abutment drum (16) having a smooth peripheral surface and is provided for supporting the web (12), the blade (32) being is arranged to be driven to rotate about an axis of rotation (30) which is parallel to the axis (48) of the abutment drum (16), characterized in that a knife shaft (28) carrying the blade (32) is supported in an oscillating crank (44) which in turn is rotatably mounted on a rotary eccentric (42).

7. The cutting unit according to claim 6, wherein the knife shaft (28) is supported in a cutting gate (24) that is suspended from an oscillating crank (44) and is linearly guided by guide rods (26(.

8. The cutting unit according to claim 6 or 7, with a heating system (34) which is arranged to heat the blade (32).

9. A Winder for winding a web (12) onto a coil (18), characterized by a cutting unit according to one of claims 6 to 8.

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