Turning Device for Turning Over Sheets in a Printing Machine

Abstract

The invention relates to a turning device (1) for transporting and turning over sheets (2) of printing material in a printing machine, preferably an electrophotographic printing machine, said device comprising at least two belts (7, 8), which, in particular, consist essentially of a plastic material, each of said belts being deflected as closed loops over respectively at least two deflecting elements (22, 23) and being crossed in order to turn over the respective sheet by approximately 180 degrees about its axis pointing in transport direction, in which process said sheet is held by clamping and frictional engagement between abutting segments (7′, 8′) of the tensioned belt, whereby at least one of the belts (7, 8), preferably each belt, is configured in a non-elastic manner, specifically reinforced, and that, in order to tension this belt, a tensioning device is provided.

Description

The invention relates to a turning device for transporting and turning over sheets of printing material in a printing machine, preferably an electrophotographic printing machine, said device comprising at least two belts, which, in particular, consist essentially of a plastic material, each of said belts being deflected as closed loops over respectively at least two deflecting elements and being crossed in order to turn over the respective sheet by approximately 180 degrees about its axis pointing in transport direction, in which process said sheet is held by clamping and frictional engagement between abutting segments of the tensioned belt.

Turning devices of the aforementioned type are known from documents DE 100 23 151 A1 and DE 100 59 913 A1, reference being made herewith to their entire content.

For the known turning devices, the belts are tensioned in that the inherent tension of elastic belts is utilized. With respect to said belts' inherent elasticity and/or their coefficient of friction, these belts may essentially behave like rubber. However, over time, these belts are subject to fatigue and become loose and age overall, which, over time, impairs the transport and turning of the sheets.

Therefore, the object of the invention is to design and carry out the transport and turning of the sheets more safely and more reliably, and in an overall more stable manner.

In accordance with the invention, this object is achieved in that at least one of the belts, preferably each belt, is configured in a non-elastic manner, specifically rein-forced, and that, in order to tension this belt, a tensioning device is provided. Therefore, in accordance with the invention, the inherent tension due to the elasticity of the belts used is not available. In particular, to allow the belt to continue to exhibit rubber-like behavior on the outside as far as its coefficient of friction is concerned, the inventive belt is instead preferably reinforced to make it non-elastic, this potentially being achieved by various measures, for example, by inserting a core. However, it is also possible in accordance with the invention to use a jacket and/or a changed composition of the plastic material that is being used.

In accordance with the invention, tensioning devices, i.e., preferably a separate tensioning device for each belt, are provided for tensioning or for better tightening the belts. If needed, such a tensioning device can be readjusted, while the lost inherent tension of a belt cannot be restored. As a result of the inventive reinforcement of the belt, said belt can become stiffer, and the transport can become more reliable and more stable.

A modification of the invention provides that the tensioning device comprises a deflecting element which deflects or bends the belt. Preferably, however not necessarily, this is an additional deflecting element provided in addition to the minimum of two deflecting elements, preferably deflecting rollers, which determine the course of the belt loops. Such an additional deflecting element can be adjusted in order to control the desired tension, without changing the actual or main course and the alignment of the belts. This deflecting element, preferably a roller, can preferably be moved in a direction approximately transverse to the belt travel outside the belt segment holding the sheet, and in so doing, deflects a belt segment more or less severely out of its linear course and, in so doing, tightens the belt direction or the belt rotation. In this sense, it is probably better to speak of a tightening device rather than of a tensioning device.

Preferably, the deflecting element is (constantly) subjected to a force of a spring in the tensioning direction, for example, a helical spring.

In a modification of the invention, a particularly accurately adjustable belt tensioning or belt tightening is possible in that the belt is deflected essentially in S-form over two deflecting elements in the region of a tensioning device, one of said deflecting elements preferably being associated with the actual tensioning device and being movable subject to a spring force. One embodiment, which could result in additional inventive features, without, however, restricting the scope of the invention thereto, is shown by the drawings.

They show in

FIG. 1 a perspective view of a turning device of this type as disclosed by prior art, and

FIG. 2 a side elevation of a turning device in accordance with the invention.

FIG. 1 shows an embodiment of a turning device 1 in accordance with prior art disclosed by DE 100 59 913 A1.

A sheet 2, in particular of a printing material, is transported to the right through the turning device 1 as shown by the illustration. The transport and turning are achieved by means of two belts 7, 8, which are arranged in such a manner that two belt segments 7′ and 8′ extend in transport direction and, in so doing, clamp the sheet 2 between them for transport. In this arrangement, the belts 7, 8 are set at an angle or crossed in such a manner that, upstream of a crossing region 10, the belt segment 7′ is on top and the belt segment 8′ is on the bottom, and that, downstream of the crossing region 10, the belt segment 8′ is on top and the belt segment 7′ is on the bottom. As a result of this crossing of the belts 7, 8, the sheet 2 held between the belt segments 7′, 8′ is flipped by 180 degrees about its axis pointing in transport direction, so that, after the turn-over, the two outer edges 16, 16′ are interchanged, and the former underside is now on top. The advantage of such a turning device, in contrast with a turning pocket, for example, is that the same lead edge of the sheet 2 continues to point in transport direction after said sheet has been turned over.

The belts 7, 8 are supported by the deflecting rollers 3, 4, 5 and 6. In this arrangement, the belt 7 is supported by an upper deflecting roller 3 and by a lower deflecting roller 4. The belt segment 7′ carrying the sheet 2 moves between the underside of the deflecting roller 3 and the upper side of the deflecting roller 4, and the returning belt segment 7′ moves from the underside of the deflecting roller 4 to the upper side of the deflecting roller 3. Correspondingly, the belt segment 8′ of the belt 8 moves from the lower deflecting roller 5 on the top toward the upper deflecting roller 6 on the bottom, and the returning belt segment 8′ of the belt 8 moves from the upper side of the deflecting roller 6 to the lower side of the deflecting roller 5. To prevent the returning belt segments 7′ and 8′ from rubbing against each other or against the advancing belt segments 7′ and 8′, measures have to be taken. For example, this can be achieved by minimally inclining the position of the deflecting rollers 3, 4, 5 and 6. To achieve the aforementioned purpose, it is also possible to use distancing rollers with collars.

Inasmuch as, referring to the described turning device 1, the turning sheet 2 must be held securely by the belt segments 7′ and 8′ and must remained aligned while being turned over, it is suggested that at least three guide rollers 11, 12 and 13 be provided downstream of the crossing region 10. These guide rollers 11, 12 and 13 are alternately arranged on the belt segments 7′ and 8′ in such a manner that the belts 7 and 8 are minimally deflected out of the linear direction, so that the force with which these belt segments 7′ and 8′ act on the sheets 2 is increased, this requiring an inherent elasticity of the belts 7 and 8 that are used.

Inasmuch as the turning sheet 2 acts on the belts 7 and 8 with transverse forces, it is suggested that at least one of the guide rollers 11, 12 and 13 be provided with at least one holding collar 14. Preferably, the guide rollers 11, 12 and 13 are arranged in such a manner that two guide rollers 11 and 13 are located in the upper region and that a lower guide roller 12 is arranged between them. The second upper guide roller 13 has a holding collar 14 in its rear region, i.e., on side 15, on which the outer edge 16 of the sheet 2 is moved upward downstream of the crossing region 10. In this manner, it is ensured that the absolute positioning and the relative positions of the belt segments 7′ and 8′ are maintained and, in so doing, also the positioning of the relatively thin sheet 2 is maintained.

FIG. 1 is a perspective view of the turning device. This shows how the turning of a sheet 2 in the direction of the arrows 17 takes place. During this process, at the beginning of the turning device 1, the rear edge 16′ moves up, i.e., toward the zenith, and the front outer edge 16 is down in the crossing region 10. Then, the upper outer edge 16′ moves forward and down, and the lower outer edge 16 moves backward and up, so that, at the end of the turning device 1, the formerly rear outer edge 16′ is in front and the formerly front outer edge 16 is in back, in which case the descriptions “back” and “front” are with respect to the viewer of FIG. 1.

The turning operation is supported by guiding devices 19, 20 and 21. One guiding device 19 is used for guiding the edge 16′ of the sheet 2, said guiding device 19 starting on side 15, at which the outer edge 16′ of the sheet 2 is moved upward, and then extending forward in such a manner that the outer edge 16′ is guided up to the end position of the sheet 2, when said sheet leaves the turning device 1. Only the course of the guiding device 19 has been drawn; for simplification, the mount of said device has been omitted. It is essential that the guiding device 19 on side 15 extend far enough toward the back and be mounted in such a manner that the mount does not impair the turning of the sheet 2.

Another guiding device 20 is used to guide the outer edge 16 which is moved upward downstream of the crossing region 10, until the sheet 2 has reached the end position. In so doing, the edge 16, or the area of the sheet 2 adjoining the edge 16, slides upward on the guiding device 20, until said sheet has reached the horizontal plane.

The third guiding device 21 is used to support the edge 16′ toward the end of the turning operation, so that said edge is prevented from hanging down. To achieve this, the guiding device 21 extends far enough toward the outside that it reaches up to the edge 16′. It is shown cut off in FIG. 1 in order to not completely hide the lower deflecting roller 4.

The embodiment of FIG. 1 also shows that each of the deflecting rollers 3, 4 and 6 is provided with two holding collars 14 in order to ensure a safe guiding of the belts 7, 8 which are configured as V-belts.

In a side elevation, FIG. 2 shows in a much more schematic and basic manner an embodiment of an inventive turning device based on a turning device 1 as in FIG. 1. The turning device as in FIG. 2 is not true to scale and shown truncated in its longitudinal extension.

The turning device as in FIG. 2 comprises the deflecting rollers 3, 4, 5 and 6, on which rotate the belts 7, 8 having belt segments 7′, 7″, 8′ and 8′. In addition, in accordance with the invention, the belt segments 7″, 8′ are guided over guide rollers 22, 23 and are essentially deflected approximately in an S-form. In so doing, the guide rollers 22, which can be moved in the directions of double arrows 24, are subject to the spring bias of springs 25 in the outward pointing directions 26 of the double arrows 24. As a result of this, the belts 7, 8, which are manufactured in accordance with the invention so as to display essentially no inherent elasticity, are tightened in such a manner that the guiding belt segments 7′, 8′ abut against each other in a taut manner, and securely clamp and transport, as well as turn over, a sheet located between them.

Claims

1. Turning device for transporting and turning over sheets of printing material in a printing machine, preferably an electrophotographic printing machine, said device comprising at least two belts, which, in particular, consist essentially of a plastic material, each of said belts being deflected as closed loops over respectively at least two deflecting elements and being crossed in order to turn over the respective sheet by approximately 180 degrees about its axis pointing in transport direction, in which process said sheet is held by clamping and frictional engagement between abutting segments of the tensioned belt, characterized in that

at least one of the belts is configured in a non-elastic manner, specifically reinforced, and that, in order to tension this belt, a tensioning device is provided.

2. Turning device as in claim 1, characterized in that the tensioning device comprises a deflecting element which deflects or bends the belt.

3. Turning device as in claim 2, characterized in that the deflecting element is a roller.

4. Turning device as in claim 2 or 3, characterized in that the deflecting element is subject to a spring bias in tensioning direction.

5. Turning device as in claim 2, 3 or 4, characterized in that the belt is deflected essentially in S-form over two deflecting elements in the region of a tensioning device.