GB2168041A

GB2168041A - Turning over sheets in printing equipment

Info

Publication number: GB2168041A
Application number: GB08529618A
Authority: GB
Inventors: Arno Wirz
Original assignee: Heidelberger Druckmaschinen AG
Current assignee: Heidelberger Druckmaschinen AG
Priority date: 1984-12-08
Filing date: 1985-12-02
Publication date: 1986-06-11
Also published as: JPH0344982B2; GB2168041B; DE3444849C2; DE3444849A1; JPS61140444A; GB8529618D0

Abstract

Sheets are rotated about an axis running in the direction of sheet travel while being transported between offset printing units. The transport device, Figure 2, may comprise conveyor chains 13 carrying gripper bridges 16 on support rails 17, the bridges being rotatable about axis 18. This enables double-sided single-colour printing using similar printing plates in both printing units. <IMAGE>

Description

SPECIFICATION Turning over sheets in printing equipment This invention relates to a method and apparatus for turning over sheets in printing equipment, e.g.

sheets which are being transported by a sheet transport device from one small offset printing unit to another.

Despite being kept simple in design, modern small offset presses have achieved a high degree of automation, e.g. in respect of the preselection of the printing run, or the automatic introduction of printing plates. These presses are therefore especially suitable for cheaply running off all sorts of very small jobs. The simple operation and maintenance of these small offset presses also means that they can be used by semi-skilled personnel.

In increasing measure, the business of small offset printing works is changing in the direction of even very small orders having to be printed in two colours, for example to increase the advertising effectiveness or layout clarity of the printed matter.

Paper and shipping costs can also often be saved by printing the sheets on both sides. Dissertations or theses can be quoted as an example of this.

However, printing the sheets twice with one and the same single-colour small offset presses takes a great deal of time, and is therefore expensive.

If one were to produce two-colour offset presses which could be converted from two-colour singleside printing to "work and back" printing, using the known turning devices as employed in normal offset presses, the expense required for this would be out of all proportion to the simplicity of the small offset presses. Furthermore, one could hardly expect the above-mentioned semi-skilled personnel to carry out the conversion of such turning equipment, which would require a great deal of technical knowledge and care.

Accordingly, it is an object of the present invention to provide a method of transporting and turning sheets in small offset presses which is appropriate to the simplicity of design of this type of press, on the one hand, and to its high degree of automation, on the other hand, and which permits simple operation of small offset presses working on this principle.

According to the present invention, there is pro vided a method of turning over sheets which are being transported by a sheet transport device from one printing unit to another, wherein a sheet, after leaving one printing unit and before reaching a subsequent printing unit, is turned (provided that the sheet transport device is at the relevant setting) about an axis of rotation running in the direction of sheet travel. This method is quite suitable for smaller sheet formats, and permits the sheet transport device to be of simple, inexpensive design and moreover very simple to operate. Similar printing plates can be used in both printing units, since the sheets are merely turned about their longitudinal axes.

The invention also includes an apparatus for carrying out this method, wherein a sheet transport device, disposed between two printing units, is provided with a plurality of gripper bridges spaced at equal intervals; each of these gripper bridges is equipped with at least two grippers which hold the head of a sheet; each gripper bridge is so mounted in the sheet transport device that it can be turned about an axis of rotation running in the direction of sheet travel; and control means are provided which (provided that they are at the relevant setting) turn each gripper bridge through 1800 about the aforementioned axis of rotation during travel between the two printing units. On the assumption that the small offset presses or other printing units concerned were using only sheets of one format, e.g.

only DIN A4 format sheets, all the operator would have to do would be to set the control device to the relevant setting for turning the sheets. Simple operations of this nature can be expected of semiskilled workers.

The invention further includes an apparatus for carrying out the method defined above, wherein a turner wheel is disposed between two printing units; the turner wheel has a plurality of radial transport arms; gripper bridges are provided on the outer ends of these arms, these gripper bridges being rotatable and being equipped with grippers; the axes of rotation of the gripper bridges run in the direction of sheet travel; and control means are provided which (provided that they are at the relevant setting) turn the gripper bridge which is holding a sheet taken from the delivery section of the first printing unit through 1800, before this sheet is passed on to the subsequent printing unit. A device of this nature can be used both in a convertible two-colour small offset press and also to link two separate small offset presses.

Two versions of embodiments of the invention are described below with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a side view which shows a two-colour small offset press, which can be changed over from single-sided two-colour printing to sheet work and conversely; Figure 2 is a section through the sheet transport device of the press of Figure 1; Figure 3 is a side view which shows two small offset presses linked by a turner wheel sheet transport device according to the invention; and Figure 4 is a section through the turner wheel sheet transport device in Figure 3.

The printing units 10 and 11 of the two-colour small offset press in Figure 1 are connected by a sheet transport device 12. This sheet transport device 12 consists essentially of conveyor chains 13 running round sprocket wheels 14 and 15 carrying, for example, seven gripper bridges 16 spaced at equal intervals. Each gripper bridge 16 is, as can be seen from Figure 2, mounted on a support rail 17 attached to the conveyor chain 13, and is free to rotate. The axis of rotation of the bearing 18 of the gripper bridges 16 runs in the direction of sheet travel. Each gripper bridge 16 is equipped with at least two grippers 19, which are best designed to be symmetrical in shape, i.e. have the form of pincers or tongs. Toothed belts can be used in place of conveyor chains.

The sheet transport device 12 is screened off by side walls 20. The sprocket wheels 14 of the conveyor chain 13 are located in the first printing unit 10 and work together with the latter's impression cylinder 21. The other sprocket wheels 15 are situated above a feeder table 22, over which a suction conveyor belt 23 runs and which is fitted with feed rollers 24 at the top. A dryer 25 is arranged above the sheet transport device 12 in the first printing unit 10.

A means of control, not shown in detail, in the lower chain strand 8 of the conveyor chain 13 can in the corresponding setting rotate the gripper bridges 16 through 180O about their bearings 18. The means of control may be a guide rail, for example, in which a guide roller joined to the gripper bridge in question rolls along. When the control means of the sheet transport device 12 is in the corresponding setting, the gripper bridges 16 are not rotated in the lower chain strand 8. If pincer grippers are used, the gripper bridges 16 cannot be rotated in the upper chain strand 9 of the conveyor chain 13. With standard grippers in the delivery section, the gripper bridge 16 rotates back into its original position in the upper chain strand 9.

The mode of operation of the convertible twocolour small offset press as described is as follows: The suckers 26 lift up the first sheet 7 from the top of the front pile 27 and pass it to the feed rollers 24.

These feed the sheet 7 to the impression cylinder 21 of the printing unit 10. In the nip of this printing unit 10 the sheet 7 receives its first printing, indicated by the triangle 28. The sheet transport device 12 takes the single-sided printed sheet 7 from the impression cylinder 21 and along the path of the chain strand 8.

As soon as the sheet 7 has completely left the sprocket wheels 14 (position 1), the rotation of the gripper bridge 16 carrying the sheet 7 begins. The sheet is rotated about its longitudinal axis in the course of this. Between position 1 and position 2 of the turning process - these positions are shown both in Figure 1 and Figure 2-the top, printed side of the sheet 7 being transported is exposed to the dryer. In position 3 of the turning process the sheet 7 and therefore also the gripper bridge 16 carrying it are vertical. The next positions 4,5 and 6 of the turning process are merely intended to show the rest of the rotation of the sheet and also to make it clear that in position 6, the sheet 7 is fully turned by the time it arrives on the feeder table 22 and is released by the grippers 19 of the gripper bridge 16 on to the suction belt 23.This guides the head of the sheet between the feed rollers 24, which in turn pass the sheet 7 on to the impression cylinder 21 of the second printing unit 11. Here, the unprinted back of the turned sheet 7 receives a further printing, as shown by the triangle 29. The chain delivery device 30 takes the double-sided printed sheet 7 from the impression cylinder 21 of the second printing unit and takes it to the delivery pile.

If single-sided two-colour printing is desired, the means of the control (not shown) of the sheet transport device 12 is simply adjusted so that the gripper bridges 16 do not rotate while running along the the lower chain strand 8. In this case the sheet 7, which has already been printed once, is fed to the second printing unit 11 without being turned, so that it receives a second printing on the same printed side.

The sheet transport device 12 can be driven buy a spur gear 32, for example, mounted on the shaft of the sprocketwheels 14 and engaging with a drive gear (not shown), which can be mounted on the shaft of the impression cylinder 21.

Unlike the first version of the invention, the second version consists of two separate single-colour small offset presses which can be linked by a turner wheel sheet transport system 35 in the event of there being a series of very small jobs requiring single-sided two-colour printing or two-sided single-colour printing. In this instance, it then becomes economic if two otherwise independent small offset presses working in single-colour operation are linked by this turner wheel sheet transport system 35. It is advantageous here if a sheet guide 38 is pushed in underneath the chain delivery device 30 of the first small offset press 36 and if the second small offset press 37 can be made slightly mobile, for example by means of transport rollers 39.

The turner wheel sheet transport system 35 consists basically of the trolley 40, in the side walls of which the shaft 42 ofthe turner wheel 43 is mounted free to rotate. The four-part bearing star 44 is situated in the middle of this shaft 42. A rotating gripper bridge 45 is fitted to each free arm of this bearing star 44. The axis of rotation of the bearing 46 runs in the direction of rotation, i.e. at right angles to the arm extending out from the star bearing 44. Each gripper bridge 45 is equipped with two pincer grippers 47. The turner wheel 43 is driven by a spur gear 48 mounted on the shaft 42. The other drive gears working together with this spur drive gear are not shown.

By means of control equipment, which is not shown, the gripper bridges 45 can be turned through 180O about the axis of their bearings during a certain arc of the turner wheel 43 while the latter is rotating.

Afurther sheet transport system consisting of circulating conveyor chains 51 with pincer gripper bridges fitted to them is mounted on the trolley 40 immediately adjacent to the turner wheel 43. The conveyor chains 51 run over thee different sprocket wheel pairs 53. This sheet transport system 50 also includes an air-blown feeder table 54 with a suction roller 55 at its top end, over which the conveyor chains 51 lead the sheets 7 transported by the pincer grippers 52. A transparent cover 56 extends over the top of the turner wheel sheet transport system 35 from the first small offset press 36 to the delivery area of the second small offset press 37. It shou Id also be mentioned that the width of the complete trolley 40 and and parts mounted on it is designed so that it can be pushed in between the side frames of the adjacent small offset presses 36 and 37. Before this is done, however, the sucker 26 in the sheet mechanism of the small offset press 37 must either be removed or swivelled up out of the way.

The mode of operation of the equipment as described is as follows: After the small offset presses 36 and 37 are linked together by the turner wheel sheet transport system 35, this unit, composed of three parts put together, can be used either as a two-colour small offset press or as a work and back press. Let us assume that the printing press unit described is set for work and back printing. The suckers 26 take the first sheet 7 from the top of the front pile and passes it to the feed rollers 24, which feed the sheet 7 to the impression cylinder 21 of the first small offset press 36. After the first printing has been done the chain delivery device 30 takes the single-sided printed sheet from the impression cylinder 21 and sends it to the turner wheel 43. The unprinted side of the sheet slides along the sheet guide 38.

The gripper bridges of the chain delivery device 30 release the sheet to a gripper bridge 45 of the turner wheel 43. As soon as the sheet 7 has completely left the chain delivery device 30, that is, shortly after position 1, the gripper bridge starts to rotate about its bearing. This turns the sheet 7 about its longitudinal axis, taking it through the positions 2,3,4, 5 and 6 as shown. In position 6 the sheet has been completely turned over, and is taken by a pincer gripper bridge 52 of the sheet transport system 50 and led to the suction roller 55 over the feeder table 54. Since the printed side of the sheet slides over the feeder table 54 here, it is advantageous if an air cushion is generated over the top of the feeder table 54 by blowing air underneath the sheet 7 being transported, which prevents the side already printed from being smeared.The suction roller 55 pushes the sheet between the feed rollers 24, which in turn ensure that the sheet 7 arrives properly in the grippers of the impression cylinder 21 of the second small offset press 37. The sheet 7 receives its second printing here, but on the back, as indicated by the triangle 29, since it has been turned over by the turner wheel 43. The double-sided printed sheet is then taken by the chain delivery device and sent to the delivery pile.

If single-sided two-colour printing is desired instead of double-sided printing, the control of the turner wheel sheet transport systems is simply altered by moving a lever. The sheet 7 is then not rotated about its longitudinal axis when being transported by the turner wheel 43. This means that the sheets 7 are sent to the delivery pile printed in two colours on one side.

It is clear that the three-part small offset press arrangement described above can also be constructed as a single unit by incorporating the turner wheel 43 as a fully integrated component linking the two printing units of a convertible two-colour small offset press. The sheet feed in the second printing unit can then be designed in such a way that the transport system 50 can be omitted.

More generally, it will be understood that the invention has been described above purely by way of example, and that various modifications of detail can be made within the ambit of the invention.

List of parts 1. Position of the sheet 2. Position of the sheet 3. Position of the sheet 4. Position of the sheet 5. Position of the sheet 6. Position of the sheet 7. Sheet 8. Chain strand 9. Chain strand 10. Printing unit 11. Printing unit 12. Sheet transport device 13. Conveyor chain 14. Sprockets 15. Sprockets 16. Gripper bridge 17. Support rail 18. Bearing 19. Gripper 20. Side walls 21. Impression cylinder 22. Feeder table 23. Suction conveyor belt 24. Feed rollers 25. Dryer 26. Sucker 27. Front pile 28. Triangle 29. Triangle 30. Chain delivery device 31. Delivery pile 32. Spur Gear 33.

34.

35. Turner wheel sheet transport system.

36. Small offset press 37. Small offset press 38. Sheet guide 39. Transport rollers 40. Trolley 41. Side walls 42. Shaft 43. Turner wheel 44. Bearing star 45. Gripper bridge 46. Bearing 47. Pincer gripper 48. Spur gear 49.

50. Sheet transport system 51. Conveyor chain 52. Pincer gripper bridge 53. Sprocket wheel pair 54. Feeder table 55. Suction roller 56. Cover 57.

Claims

1. A method of turning over sheets which are being transported by a sheet transport device from one printing unit to another, wherein a sheet, after leaving one printing unit and before reaching a subsequent printing unit, is turned (provided that the sheet transport device is at the relevant setting) about an axis of rotation running in the direction of sheet travel.

2. An apparatus for carrying outthe method claimed in claim 1,wherein: a sheet transport device, disposed between two printing units, is provided with a plurality of gripper bridges spaced at equal intervals; each of these gripper bridges is equipped with at least two grippers which hold the head of a sheet; each gripper bridge is so mounted in the sheet transport device that it can be turned about an axis of rotation running in the direction of sheet travel; and control means are provided which (provided that they are at the relevant setting) turn each gripper bridge through 180 about the aforementioned axis of rotation during travel between the two printing units.

3. An apparatus for carrying out the method claimed in claim 1,wherein a turner wheel is disposed between two printing units; the turner wheel has a plurality of radial transport arms; gripper bridges are provided on the outer ends of these arms, these gripper bridges being rotatable and being equipped with grippers; the axes of rotation of the gripper bridges run in the direction of sheettravel; and control means are provided which (provided that they are at the relevant setting) turn the gripper bridge which is holding a sheet taken from the delivery section of the first printing unit through 180 , before this sheet is passed on to the subse quent printing unit.

4. An apparatus in accordance with claim 2 or 3 wherein the sheet transport device or its control means can be changed over from normal sheet transport to sheet turning and conversely.

5. An apparatus in accordance with claim 2,3 or 4, wherein the grippers are symmetrical in shape.

6. An apparatus in accordance with claim 5, wherein the grippers are in the form of pincer grippers.

7. An apparatus in accordance with claim 2, substantially as described with reference to Figures 1 and 2 of the accompanying drawings.

8. An apparatus in accordance with claim 3, substantially as described with reference to Figures 3 and 4 of the accompanying drawings.