HK1115843A - Method and apparatus for turning a sheet during its transport through a printing press - Google Patents

Description

Method and device for turning over a sheet during transport through a printing press

Technical Field

The invention relates to a method and a device for turning a sheet during transport through a printing press.

Background

In order to keep the production costs of multicolour sheet-fed printing presses low, the printing units are designed for printing on only one side of the sheet, so that the printing units can be produced with a high repetition rate. If a sheet is to be printed on both sides on a sheet-fed printing press with printing units arranged in series, a sheet turning device is provided between the last printing unit for printing the front side and the following printing unit for printing the rear side. Conventional turning devices consist of a transfer cylinder, a storage cylinder and a turning cylinder between the printing cylinders of the printing unit. The transfer drum has a gripper system for holding the sheet on the leading edge. The storage cylinder has a double diameter of the printing cylinder and has two gripper systems for holding the sheet on the front edge and two suction gripper systems for holding the sheet on the rear edge. The turning drum has a jaw system for holding a trailing sheet edge on the storage drum. All the cylinders guiding the sheets are driven in rotation synchronously, for example, by means of a gear mechanism.

The gripper systems of the storage cylinder and the overturning cylinder respectively consist of single grippers arranged along a straight gripper closing line. The gripper closing line is parallel to the axis of rotation of the storage cylinder or the tipping cylinder, respectively. Viewed in the axial direction of the storage cylinder and the reversing cylinder, the gripper closing lines of the reversing cylinder and the storage cylinder form a common tangent line during sheet transfer, through which a center line passing through the axis of rotation extends.

For turning, the sheet is transferred by a gripper system of the transfer drum to a gripper system of the storage drum for a leading edge of the sheet. The trailing edge of the sheet is held by the associated suction gripper system of the storage cylinder during the rotation on the storage cylinder. The sheet is passed by the leading edge gripper system of the storage cylinder beside the tangent line. When the trailing edge of the sheet reaches the tangent, a transfer to the tong gripper of the reversing cylinder takes place. The sheet is released from the surface of the storage cylinder while the drum continues to rotate, and the suction action of the suction gripper is stopped. The suction air of the suction gripper is conducted via a rotary joint to the storage cylinder, as described in DE4210009a 1. The suction air is maintained only in the range of the rotational angle of the storage drum during the transfer of the rear edge from the transfer drum to the reversing drum. The free-fly phase of the sheet begins when the leading edge gripper system of the storage drum opens at a predetermined rotational angle. The sheet is held on only one sheet edge by the gripper of the reversing cylinder until the sheet is transferred to the gripper system of the following printing cylinder.

When the sheet is released from the storage drum, the sheet has a different speed on the edge gripped by the gripper than the new trailing edge, which has flown freely. Before leaving the storage drum, the trailing edge of the future sheet is moved at the tracking speed of the storage drum. The future trailing edge velocity then decreases to zero. The direction of movement of the rear edge is then changed from zero to the speed of the path produced by the rotation of the pincer gripper of the turnover drum.

Based on the speed change, the sheet is moved out of its ideal path due to dynamic forces and other external disturbance forces. Sheets that are guided freely by the trailing edge tend to strike the corrugations and strike the components of the storage drum and the guide elements by a striking action, which leads to undesirable printing results.

In order to improve the release of the sheet from the surface of the storage drum, in the turning device according to DE 19949412 a1, the storage drum is configured with an open-edged recess. Air is carried through the recess into a low-pressure region which is produced in the space between the storage drum, the reversing drum and the sheet during the sheet detachment. The control of the suction air on the trailing edge of the sheet is not affected.

Disclosure of Invention

The object of the present invention is to provide a method and a device for turning a sheet during transport through a printing press, which can achieve better printing results by improving sheet guidance.

According to the invention, a method for turning a sheet during transport through a printing press is proposed, wherein the sheet is moved on a first transport device on a sheet edge running ahead on a desired trajectory and the sheet edge running behind is transferred to a second transport device, wherein: after the transfer, the sheet is tensioned in a predetermined range of rotation angles.

Advantageously, the sheet is moved on a circular path on a first transfer drum, the leading sheet edge is held in a mechanical gripper, the trailing sheet edge is held in a suction gripper, the trailing sheet edge of the sheet is transferred to a gripper system of an adjacent, synchronously rotating second transfer drum, wherein suction air on the suction gripper is switched off during the transfer, the sheet is held by the mechanical gripper in a predetermined first range of rotation angles after the transfer and is released from the mechanical gripper after leaving the range of rotation angles, and the sheet is braked in a predetermined second range of rotation angles after the release from the mechanical gripper.

The sheet is advantageously braked by the suction air of the suction gripper being connected to the sheet in a suction manner.

Advantageously, the braking force is adjusted as a function of the sheet thickness.

According to the invention, a device for turning sheets during transport through a printing press is proposed, comprising a first transfer drum having a gripper system for holding the sheets on a leading and a trailing sheet edge, wherein the gripper system on the trailing sheet edge always consists of a row of spaced-apart suction grippers, which are connected to a controllable suction air source, comprising a second transfer drum having a gripper system for receiving the sheets on the trailing sheet edge from the first transfer drum, and comprising at least one drive for synchronously pivoting the transfer drums, wherein a braking assembly for the sheets wound off the first transfer drum is provided.

Advantageously, the suction gripper is designed as a brake.

Advantageously, the suction gripper can be loaded to suck air in dependence on the angle of rotation.

Advantageously, the brake assembly is fixedly arranged relative to the frame.

Advantageously, the braking assembly generates an electric or magnetic field that acts in tension on the sheet.

Drawings

The invention is described below by way of example, with reference to the accompanying drawings, in which:

figure 1 shows two printing units and a turning device of a sheet-fed printing press,

figure 2 is a perspective view of the drum of the turning device,

figure 3 is a schematic view of the control of suction air on a suction gripper,

FIG. 4 is a graph of the control of suction air on a cartridge, an

FIG. 5 is a schematic view of tensioning a sheet using a magnetic field.

Detailed Description

Fig. 1 shows two printing units 1, 2 of a sheet-fed printing press, each having an inking unit 3, 4, a dampening unit 5, 6, a plate cylinder 7, 8, a transfer cylinder 9, 10 and a printing cylinder 11, 12. Between the printing units 1, 2, there is a reversing device with a transfer cylinder 13, a storage cylinder 14 and a reversing cylinder 15. All rollers and drums are coupled with one gear train and revolve in the direction of the arrow. The printing cylinders 11, 12, the transfer cylinder 13, the storage cylinder 14 and the reversing cylinder 15 have gripper systems 16-21 for holding the sheet 22 on the edge of the sheet running ahead. The storage cylinder 14 additionally has a suction gripper system 23, 24 for holding the sheet 22 on the trailing sheet edge. Pneumatic sheet guides 25 to 27 are arranged along the transport path of the sheet 22 between the storage drum 14 and the reversing drum 15, from which sheet guides the blow air 28 and the suction air 29 are discharged. The suction gripper systems 23, 24 are fed via a pneumatic rotary joint 30 on a journal 31 of the storage cylinder 14. A suction line 32 leads from the rotary union 30 to a suction connection of a suction fan 33. The suction port is in turn connected to a bypass air valve 34, which may be controlled by a motor. The rotational position of the storage drum 14 is detected by the rotational angle transmitter 36 on the transfer drum 13. The rotational angle transmitter 36, the motor 35, and the fan 33 are connected to a control device 37.

The perspective view according to fig. 2 shows the printing cylinders 11, 12, the transfer cylinder 13, the storage cylinder 14 and the reversing cylinder 15 in more detail. The effective diameter of the storage cylinder 14 is twice as large as the diameter of the printing cylinders 11, 12. The storage cylinder 14 comprises concentrically arranged, tire-shaped holders 38.1-38.4 with an outer sheet support surface. Two sets of holders 38.1, 38.2; 38.3, 38.4 are used to support the sheet 22 and engage one another in a comb-like manner. In the sheet support surface, suction grooves 39.1 to 39.4 extend in the circumferential direction of the storage cylinder 14 and are connected to a fan 33 via a rotary joint 30. The gripper systems 19, 20 comprise a plurality of individual grippers 40 each on a gripper shaft 41. The opening and closing of the individual grippers 40 is effected by means of a cam gear and a gear transmission. The suction gripper systems 23, 24 each comprise a plurality of suction heads 42, which act on the rear sheet edge of a sheet 22. The grippers of the gripper system 21 are designed as tong grippers each having two cooperating gripper fingers 43, 44. The gripper fingers 43, 44 are cam-controlled to perform an oscillating movement about a gripper axis 45 during the rotation of the reversing cylinder 15.

The transfer of a sheet 22 from the storage cylinder 14 to the reversing cylinder 15 is now described with reference to the schematic illustration in fig. 3 and the diagram in fig. 4. Figure 3 shows in outline the gripper system 18 of the transfer drum 13, the gripper systems 19, 20, 23, 24 of the storage drum 14 and the revolving circles 46-48 of the gripper system 21 of the turning drum 15. The straight lines connecting the midpoints of these circles 46, 47, and 48 are transfer centers 49, 50.

When the angle of rotation α is 70 °, the suction groove 39.1 of the holder 38.1 is loaded with a negative pressure p 1. The pressure profile in the suction groove 39.1 is given by curve 50. When the angle of rotation α is 75 °, the leading sheet edge reaches the transfer center 49, at which the sheet 22 is transferred from the gripper system 18 of the transfer drum 13 to the gripper system 19 of the storage drum 14. When the angle of rotation α is 130 °, the trailing suction groove 39.2 of the holder 38.2 is loaded with a negative pressure p 1. The pressure profile in the suction groove 39.2 is indicated by curve 51. When the angle of rotation α is 160 °, the connection of the suction groove 39.1 to the fan 33 is interrupted. When the angle of rotation α is 195 °, the trailing sheet edge of the sheet 22 reaches the transfer center 49, wherein the suction head 42 of the suction gripper system 23 is loaded with a negative pressure p 2. The pressure profile over the suction head 42 of the suction gripper system 23 is given by the curve 52. In the further run, the leading sheet edge of the first sheet 22 passes by the transfer center 50. When the angle of rotation α is 350 °, the vacuum p2 on the suction head 42 of the suction gripper system 23 is switched off and the suction head 42 is ventilated. When the angle of rotation α is 360 °, the trailing edge of the first sheet 22 reaches the transfer center 50 and is received by the gripper fingers 43, 44 of the gripper system 21, the previously advancing sheet edge being released from the gripper system 19. The first sheet 22 starts to peel off from the holders 38.1 and 38.2 from the rotation angle α of 22 °. Until the angle of rotation α becomes 35 °, the first sheet 22 is guided only by the gripper system 21 of the reversing cylinder 15. The suction head 42 of the suction gripper system 23 is again subjected to the underpressure p3 from the angle of rotation α of 35 °. By switching on the suction air again, the first sheet 22 is held again by the suction head 42 of the suction gripper system 23 from the rotation angle α of 90 °. The free end of the first sheet 22 at the end of the following run is tensioned. In this case, the suction head 42 of the suction gripper system 23 performs a relative movement with respect to the sheet 22. After the end of the trailing sheet has been transferred to the gripper system 21, the braking phase for the end of the trailing run continues until the angle of rotation α is 130 °. Depending on the sheet length, the suction head 42 of the suction gripper system 23 leaves the sheet trailing edge in an angular range between α 190 ° and α 130 °.

The described sheet transport is repeated periodically. When a sheet 22 is received by the gripper system 19 at an angle of rotation α of 75 °, a preceding sheet 22 is transported in the same manner by the gripper system 20 and the suction gripper system 24 on the opposite holders 38.3, 38.4. The curves 53, 54 reflect the course of the negative pressure p1 in the suction grooves 39.3, 39.4 of the holders 38.3, 38.4. The curve 55 describes the profile of the suction air of the suction head 42 of the suction gripper system 24. The braking phase for the sheet 22 travelling ahead of the first sheet 22 takes place in an angle range between α 215 ° and α 310 °.

Fig. 5 shows an arrangement in which the braking assembly for the sheet 22 is arranged stationary relative to the machine frame. The braking assembly consists of a generator 58 for an alternating magnetic field and a pneumatic guide 59 for the sheet 2. As sheet 22 passes by generator 58, an electric current is induced in the ferromagnetic material of sheet 22 or of the printed ink on sheet 22. The magnetic field generated by the eddy currents reacts with the magnetic field of the generator 58, so that the sheet 22 is braked. The braking effect can be adjusted to the sheet thickness and/or locally on the sheet 22 by changing the field strength of the magnetic field of the generator 58. The occurrence of waving in the sheet 22 and the described beating effect on the trailing sheet edge can thus be avoided or reduced. The guide 59 prevents the sheet 22 from contacting the generator 58.

Reference numerals

1, 2 printing mechanism 29 sucks air

3, 4 inking mechanism 30 rotary joint

5, 6 wetting mechanism 31 journal

7, 8 plate cylinder 32 suction duct

9, 10 transfer drum 33 suction fan

11, 12 print cylinder 34 bypass air valve

13 transfer cylinder 35 motor

14 storage cylinder 36 corner transmitter

15 turn over drum 37 controlling means

16-21 gripper system 38 holder

22-sheet 39 suction groove

23, 24 suction gripper system 41 gripper shaft

25-27 sheet guide 40 single gripper

28 blowing air 42 suction head

43, 44 gripper finger

45 gripper shaft

46-48 circle of revolution

49, 50 transfer centers

Curve 51-57

58 generator

59 guide device

Claims (9)

1. Method for turning a sheet during transport through a printing press, wherein the sheet is moved on a first transport device on a preceding sheet edge on a desired trajectory and wherein a following sheet edge is transferred to a second transport device, characterized in that: after the transfer, the sheet (22) is tensioned in a predetermined range of rotation angles.

2. A method according to claim 1, characterized in that: the sheet (22) is moved on a circular path (47) on a first transfer cylinder (14), the leading sheet edge is held in a mechanical gripper (19, 20), the trailing sheet edge is held in a suction gripper (23, 24), the trailing sheet edge of the sheet (22) is transferred to a gripper system (21) of an adjacent, synchronously rotating second transfer cylinder (15), wherein the suction air on the suction grippers (23, 24) is cut off during the transfer, the sheet (22) is held by the mechanical grippers (19, 20) in a predetermined first range of rotation angles after the transfer and the sheet (22) is released from the mechanical grippers (19, 20) after leaving the range of rotation angles, after release from the mechanical gripper (19, 20), the sheet (22) is braked in a predetermined second angle range of rotation.

3. A method according to claim 2, characterized in that: the sheet (22) is braked by connecting the suction air of the suction grippers (23, 24) to the sheet (22) in a suction manner.

4. A method according to claim 2, characterized in that: the braking force is adjusted according to the sheet thickness.

5. A device for turning over the sheet during the transport through the printing press,

having a first transfer drum with a gripper system for holding the sheets on the advancing and trailing sheet edges, wherein the gripper system on the trailing sheet edge always consists of a row of spaced-apart suction grippers which are connected to a controllable suction air source,

a second transfer drum having a gripper system for receiving the sheet from the first transfer drum on the trailing edge of the sheet,

and has at least one drive for synchronously rotating the transfer drums,

characterized in that a braking assembly (23, 24, 30-37, 58) is provided for the sheet (22) unwound from the first transfer drum (14).

6. The apparatus of claim 5, wherein: the suction grippers (23, 24) are designed as braking devices.

7. The apparatus of claim 6, wherein: the suction grippers (23, 24) can be loaded in relation to the angle of rotation in order to suck air.

8. The apparatus of claim 5, wherein: a brake assembly (58) is fixedly disposed relative to the frame.

9. The apparatus of claim 5, wherein: the braking assembly (58) generates an electric or magnetic field that acts to tension the sheet.