Sheet-transporting drum and printing machine having the sheet-transporting drum

Abstract

A sheet-transporting drum includes sheet-supporting areas each being formed of a first comb segment and a second comb segment having segment teeth. At least one of the comb segments is rotatable for adaptation to a sheet format. A mechanical leading-edge gripper is provided on the first comb segment and a pneumatic trailing-edge gripper is provided on the second comb segment. A mechanical trailing-edge gripper is additionally disposed on the second comb segment and is deactivatable in particular by format adjustments. This advantageously allows either the trailing edge of a sheet to be securely held down mechanically or a full-bleed print to be applied to the sheet when the trailing edge of the sheet is held down pneumatically. A sheet-fed printing machine is also provided.

Claims

1. A sheet-transporting drum in a sheet-processing machine, the sheet-transporting drum comprising: at least one sheet-supporting area formed of a first comb segment and a second comb segment each having respective segment teeth; at least one of said first and second comb segments being rotatable for adaptation to a sheet format; a mechanical leading-edge gripper being disposed on said first comb segment; a pneumatic trailing-edge gripper being disposed on said second comb segment; and a deactivatable mechanical trailing-edge gripper being disposed on said second comb segment, said pneumatic trailing-edge gripper being disposed between said mechanical trailing-edge gripper on said second comb segment and tips of said segment teeth on said second comb segment.

2. The sheet-transporting drum according to claim 1, which further comprises an adjustment device for pivoting said second comb segment relative to said first comb segment to align either said pneumatic trailing-edge gripper or said mechanical trailing-edge gripper on said second comb segment with a trailing edge of a respective sheet to be transported.

3. The sheet-transporting drum according to claim 2, wherein said adjustment device has an adjustment drive connected to said second comb segment and a control unit.

4. The sheet-transporting drum according to claim 1, wherein at least one of said mechanical trailing-edge gripper or said mechanical leading-edge gripper has a gripper bar with grippers fixed thereto, said gripper bar extending over a width of the sheet-transporting drum.

5. The sheet-transporting drum according to claim 4, wherein each said mechanical gripper has respective flat gripper fingers and gripper pads.

6. The sheet-transporting drum according to claim 1, wherein said pneumatic trailing-edge gripper is a suction groove.

7. The sheet-transporting drum according to claim 1, wherein the sheet-transporting drum is a jetting cylinder.

8. A sheet-fed printing machine, comprising: a sheet-transporting drum according to claim 1.

9. A digital sheet-fed printing machine, comprising: a sheet-transporting drum according to claim 1; and inkjet heads disposed above said sheet-transporting drum.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIGS. 1A and 1B are diagrammatic, side-elevational views of comb segments of a sheet-transporting drum in two different positions;

(2) FIG. 2 is a fragmentary, top-plan view of the sheet-transporting drum;

(3) FIG. 3 is a lateral-sectional view of the sheet-transporting drum; and

(4) FIG. 4 is a longitudinal-sectional view of a digital printing machine.

DETAILED DESCRIPTION OF THE INVENTION

(5) Referring now in detail to the figures of the drawings, in which mutually corresponding elements and components have the same reference numerals and in which the figures are not drawn to scale, and first, particularly, to FIG. 4 thereof, there is seen a sheet-fed printing machine 100 embodied as a digital printing machine. A respective sheet 1000 coming from a feeder 1 is transported through a printing unit 2 to a delivery 3 in a direction of transport T. The transporting of a respective sheet 1000 is mainly carried out by cylinders, namely transfer cylinders 5 and a sheet-transporting drum 10, embodied as a jetting cylinder. In the exemplary embodiment, the jetting cylinder 10 has three sheet-supporting areas 21. Inkjet heads 4 are disposed above the jetting cylinder 10. The inkjet heads 4 print on a sheet 1000 that is transported past the inkjet heads 4 by the jetting cylinder 10 at a short distance.

(6) FIGS. 1A and 1B illustrate a section of a sheet-transporting drum 10, namely a first comb segment 11 and a second comb segment 12, which may be adjusted to adapt a sheet-supporting area to a sheet format, i.e. the length, of a respective sheet 1000. The first comb segment 11 and the second comb segment 12 have respective teeth 14 engaging in a rake-like way, causing the first segment 11 and the second segment 12 to mesh with one another. The second comb segment 12 may be pivoted about a pivot axis 13 and may carry out a pivoting movement S.

(7) A mechanical gripper 15, embodied as a mechanical leading-edge gripper for holding down the leading edge of a sheet 1000, is disposed on the first comb segment 11. The second comb segment 12 is provided with a pneumatic gripper 19 and with a mechanical gripper 15. As shown in FIG. 1A, the second comb segment 12 is pivoted relative to the first comb segment 11 in such a way that the mechanical gripper 15 thereof holds down the trailing edge of a sheet 1000. The pneumatic gripper 19 of the second comb segment 12 does not act directly on the trailing edge of the sheet 1000 but only on the trailing part of the sheet 1000. The mechanical trailing-edge gripper and/or the mechanical leading-edge gripper has a gripper bar 32 with grippers fixed thereto, the gripper bar 32 extends over the width of the sheet-transporting drum 10.

(8) If the trailing edge of the sheet 1000 is not to be held down by the mechanical trailing-edge gripper 15 but instead by the pneumatic gripper 19, the second comb segment 12 is pivoted farther in the clockwise direction S relative to the first comb segment 11, deactivating the mechanical trailing-edge gripper 15 and positioning the pneumatic gripper 19 in the region of the trailing edge of the sheet. The pivoting movement S is caused by an adjustment device 22, which has an electric motor M and a control unit 23 and is also used to adjust the sheet-supporting areas 21 formed by the teeth 14 of the comb segments 11, 12, in order to accommodate the sheet format.

(9) FIG. 2 is a top view of the sheet-transporting drum 10 showing that the sheet-transporting drum 10 includes at least a first comb segment 11 and a second comb segment 12, which is supported to rotate/pivot relative to the first comb segment 11 about a pivot axis 13, which corresponds to the middle or central axis of the sheet-transporting drum 10, in order to adjust the sheet-transporting drum 10 to accommodate different format lengths of sheets 1000 to be transported. Each one of the comb segments 11, 12 has teeth 14 that engage in interspaces between the teeth 14 of the respective other comb segment 12, 11.

(10) When the second comb segment 12 is adjusted towards the first comb segment 11 to accommodate a smaller sheet format, the teeth 14 move deeper into the interspaces, causing the interspaces to narrow. In order to accommodate a larger sheet format, the second comb segment 12 is moved away from the first comb segment 11, causing the interspaces to widen.

(11) The gripper system 15 of the sheet-transporting drum 10 has gripper pads 16 and gripper fingers 17 associated therewith on the front edge of the first comb segment 11 to clamp/cover the sheet of printing material. The second comb segment 12 has nozzle-shaped suction elements 18 disposed thereon for attracting the trailing edge of the sheet of printing material 1000 by suction. The suction elements 18 are disposed in a row and are connected to a (non-illustrated) suction air source. Alternatively, a suction groove may be provided instead of the suction nozzles 18. The gripper system 15 of the sheet-transporting drum 10 has gripper pads 16 and gripper fingers 17 associated therewith on the rear edge of the second comb segment 12 to clamp the sheet of printing material. Thus, a mechanical leading-edge gripper 15, a mechanical trailing-edge gripper 15 and a pneumatic trailing-edge gripper 19 are provided. In order to adjust the required distance between the gripper system 15 and the suction elements 18 as a function of the format length, the suction elements 18, together with the second comb segment 12, are pivoted relative to the gripper system 15 of the first comb segment 11 about the pivot axis 13 until they are in a position in which the suction elements 18 are close to the trailing edge of the sheet of printing material 1000 held in the gripper system and underneath the sheet. As described above, a format adjustment may likewise occur in such a way that the trailing edges of the sheets 1000 are held by the mechanical trailing-edge gripper 15.

(12) The first comb segment 11 and the second comb segment 12 may have suction grooves 20 that ensure that a sheet 1000 rests securely thereon.

(13) FIG. 3 is a lateral sectional view of the sheet-transporting drum 10 of FIG. 2.