DE8703083U1 - Transport device for sheet material - Google Patents

Description

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EUROPEAN PATENT ATTORNEYS

KARL-HEINZ SCHAUMBURG. Dlpl.-Ing. DR. Dlpl.-Phys.

Nixdorf Computer AG Klaus Enqlaender, Dipi.-mg.

Fürstenallee 7 27* February 1987

4790 Paderborn N 7710 DE - SBbf

Transport device for sheet material

The invention relates to a transport device for sheet material, with several elastically deformable transport rollers arranged on a common drive axis that is adjustable in a plane transverse to the transport plane, which each form a transport gap for the sheet material with several harder counter elements opposite them that are held on a pendulum yoke.

A transport device of this type is known from DE-OS 35 11 387 and is shown there in Fig. 11. The drive axis of the transport rollers is adjustable transversely to the transport plane so that the transport rollers can be used as a sensor arrangement in addition to their transport function, which determines the thickness of the sheet material to be transported in order to be able to set or control the distance of a print head lying in the transport path from a print bar. In the known transport device, two transport rollers are arranged on the drive axis with a distance

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to each other, and the drive axle is fixed at one end but pivotably mounted, while its other end can be moved against the force of a spring in a direction transverse to the transport plane. As counter elements, the transport rollers are assigned pressure rollers that are rotatably mounted on the pendulum yoke. The pendulum yoke is pivotably mounted on a pendulum axle between the pressure rollers in the pivot plane of the drive axle of the transport rollers. This possibility of moving the pressure rollers by pivoting the pendulum yoke leads to a constant uniform pressure force of both transport rollers on the recording medium that is transported between the transport rollers and the pressure rollers.

Such a transport device works satisfactorily with simple sheet material. However, if the sheet material consists of several sheets lying on top of each other, which are firmly connected to each other at their upper and/or lower edge, the individual sheets can shift relative to each other, which, as a result of the firm mutual connection of the sheets at their edge, leads to bulges, which then form folds in the transport gap between the two respective rollers and deform the sheet material as a whole so that proper further transport is no longer possible. Such phenomena are particularly evident with multiple receipts that are to be printed in cash register printers, for example, and between whose individual receipt sheets there is copy paper that has a particularly smooth surface. If the sheet material is deformed or distorted in the way described above, proper printing of such multiple receipts at precisely specified locations is no longer possible.

These transport disturbances are attributed to the fact that the transport rollers are made of an elastically deformable material

which is pressed in by the pressure of the harder pressure rollers in the area of the transport gap, so that the sheet material lies in a transport gap that is bent according to the impression, in which it has different levels of frictional contact with the transport rollers and the pressure rollers. In addition, since the bearings of the transport and pressure rollers can never be without play and additional tolerances are caused by the suspension of the pressure rollers on a pendulum yoke and by the adjustability of the drive axle of the transport rollers, further differences in the transport effect can occur on the top and bottom of a multiple sheet material.

It is the object of the invention to provide a transport device in which transport errors of the type described above no longer occur, so that even with multiple sheet material, a flawless transport process in the transport gap is always guaranteed.

This object is achieved according to the invention for a transport device of the type mentioned at the outset in that the counter elements each have a flat, smooth pressure surface that defines the transport plane and is stationary in the transport direction.

The invention ensures that when there is mutual pressure between a transport roller and a pressure surface, the transport roller is deformed flat rather than round. This results in a correspondingly flat transport gap, in the area of which the sheet material is acted upon by equally large surfaces on both sides. One surface is the transport roller surface, which is flat due to the deformation, and the other is the pressure surface of the counter element, which is already flat. Since this pressure surface is smooth, the sheet material can be pushed against it with as little friction as possible.

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so that it not only performs a pressure function, but also a guiding function. It has been shown that by providing a flat transit gap between the transport roller and the pressure surface, a

even transport of multiple sheet material

; is possible, i.e. a mutual shifting of the individual

Sheets no longer move relative to each other in the transport gap. Therefore, deformations and distortions of the type described above are reliably avoided with multiple sheet material.

The use of a counter element that is stationary in the transport direction instead of a pressure roller offers the particular advantage that such a counter element can take on additional tasks that must be fulfilled in the automatic control of a transport device. For example, it is possible to install light barriers in a counter element that is stationary in the transport direction, so that the arrival of a top or bottom edge of a sheet in the transport gap can be recognized almost immediately and, when using the transport device in a printer, better use of space is possible when printing the sheet material.

Advantageously, the pressure surface at its rear end in the transport direction transitions into an inclined surface that widens the transport gap in a funnel shape. This design facilitates the reliable introduction of the sheet material into the transport gap, as it gives it an entry shape similar to a pressure roller.

The pressure surface is preferably the front surface of a pressure body, the width of which transversely to the transport direction corresponds at least to the width of the transport roller opposite it. If there are several transport rollers,

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So several pressure bodies are provided on the pendulum yoke, each of which is opposite a transport roller. The width of each pressure body can also be dimensioned so that one pressure body is provided for several transport rollers. This is particularly advantageous when the transport rollers are located next to each other at a relatively small distance.

The pressure surface is preferably polished in order to keep its friction coefficient as low as possible. Depending on the material of the pressure surface, this is important for the proper functioning of the transport device in the sense described above.

The pendulum yoke and the pressure bodies can be made in one piece. In this case in particular, they are advantageously made of plastic and, for example, manufactured as a single injection-molded body. It is important that the plastic material used is harder than that of the transport rollers.

An embodiment of the invention is described below with reference to the figures. They show:

Fig. 1 A schematic representation of a transport device seen in the transport direction and

Fig. 2 is a side view of the arrangement according to Fig. to illustrate a transport gap in which a sheet material is located.

Fig. 1 shows a transport device which contains a drive axle 10 with two transport rollers 11 and 12« The drive axle 10 is with its one end 13 in its

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Longitudinally fixed but pivotable in a bearing arrangement 14 and can be moved with its other end 15 against the force of a spring 16 in the direction of arrow 17 in order to adjust the transport rollers 11 and 12.

to carry out a thickness evaluation of a sheet material 18 that is to be transported and is shown in Fig. 1 by a dashed line parallel to the drive axis 10. I

Above this arrangement of the transport rollers 11 and 12 and the sheet material 18, a pendulum yoke 19 is provided, which is suspended on a pendulum axis 20 in the pivot plane of the drive axis. The pendulum yoke 19 carries two pressure bodies 21 and 22, each of which is opposite a transport roller 11 and 12 and, in the embodiment shown, has a width that is equal to that of the transport rollers.

11 and 12. The pendulum yoke 19 can be pivoted in the direction of arrow 23 and is mounted on the pendulum axis 20 with a bearing block. The pendulum axis 20 is arranged in a stationary manner in a housing (not shown). The pivot bearing is also arranged in a stationary manner and the spring 16 is connected to a stationary point. The housing can be a printer housing in which the transport device is arranged in order to feed the sheet material 18 to a printing station in a direction perpendicular to the drawing plane.

The two pressure bodies 21 and 22 have a flat front surface 25 and 26, respectively, which corresponds to the respective transport roller 11 and 12.

12. This front surface 25 or 26 merges at its rear end in the transport direction into an inclined surface 27 or 28, which facilitates the introduction of the sheet material 18 into the respective transport gap 29 or 30 formed between a transport roller 11 or 12 and a front surface 25 or 26.

If the drive shaft 10 for the transport rollers 11 and 12 is moved in the direction of arrow 17, the pendulum yoke 19 follows this movement by pivoting accordingly in the direction of arrow 23. In this way, a constant uniform pressure is ensured between the transport rollers 11 and 12 and the respective pressure body 21 and 22, so that a uniform and tilt-free transport of the sheet material 18 is achieved.

Fig. 2 shows the transport device seen from its right side. The drive shaft end 13 and the transport roller 12 are shown, which rotates in the direction of arrow 31 and transports the sheet material 18 in the direction of arrow 32. The transport roller 20 is opposed by the pressure body 22, which is arranged on the pendulum yoke 19. Its front surface 26 is the pressure surface opposite the transport roller 12, which has the lowest possible frictional resistance against the top of the sheet material 18 and is polished for this purpose. The pressure surface 26 merges at its rear end in the transport direction 32 into the inclined surface 28, which forms a funnel-shaped extension with the transport roller 12 at the entry point of the transport gap 30. Since the transport roller 12 is made of an elastically deformable material that is softer than the material of the pressure body 22, the transport roller is flattened in the area of mutual action with the pressure body 22 so that it forms a flat transport gap 30 with the pressure surface 26. A flat surface thus rests on both sides of the sheet material 18, whereby the transport roller 12 with its flattening has a large frictional resistance and the pressure surface 26 of the pressure body has a small frictional resistance to the sheet material 18. This is transported in a transport plane that is not curved. Since the pressure body 22 is arranged stationary in the transport direction, the sheet material 18 slides on the

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Pressure surface 26. The top sheet of a multiple sheet material is practically not slowed down by friction on the pressure surface 26, so that it cannot shift relative to other sheets underneath.

Such a displacement would be possible, however, if a pressure roller were to be placed opposite the transport roller 12 as a counter element, which would not flatten the pressure roller with its harder material, but would create an indentation in it. Then a mutual rolling of the two rollers acting on each other would lead to a displacement of the individual sheets of a multiple sheet material relative to each other. However, such an effect, which is aimed for in sheet separation, should be avoided in the case of multiple sheet material, where a displacement of the individual sheets relative to each other is undesirable.

Fig. 2 shows light barrier elements 33, which can be light guides, for example, indicated in dashed lines in the pressure body. These can be inserted or cast into the pressure body 22 and end with their light-receiving surface in the pressure surface 26. Here, the advantage of a pressure body 22 that is stationary in the transport direction 32 is used, which is that, due to this stationary arrangement, it can also be a carrier for evaluation elements that determine the movement of the sheet material 18. Such evaluation elements must be provided outside the area of these pressure rollers in transport devices in which pressure rollers are opposite the transport rollers. The arrangement shown in Fig. 2 means that the respective upper edge or lower edge of the sheet already leads to a signal when entering the transport gap 30 or when leaving it, whereby control processes triggered thereby within a device not shown in detail here correspond more precisely to the respective position of the

blade material 18. This makes it possible
possible, e.g. in a sheet material 18 printing
printing device to better utilize the space available for printing on the sheet j material 18, so that less loss of
the upper and lower edges of the leaf.

A further advantage of the light barrier arrangement is that &Idigr;

to see that the drive for the transport rollers only then j

must be switched on when the sheet material 18 and I

located directly in front of the transport gap 30 and immediately |

can be switched when the sheet material 18 the Trans- i

port gap 30* This minimizes the time during which the ' transport rollers 11 and 12 rub directly against the pressure surfaces 25 and 26.

Claims (9)

Expectations 1. Transport device for sheet material, with several elastically deformable transport rollers arranged on a common drive axis adjustable in a plane transverse to the transport plane, which each form a transport gap for the sheet material with several harder counter elements opposite them and held on a pendulum yoke, characterized in that the counter elements (21, 22) each have a flat, flat pressure surface (25, 26) defining the transport plane and stationary in the transport direction. 2. Transport device according to claim 1, characterized in that the pressure surface (25, 26) at its rear end in the transport direction merges into an inclined surface (27, 28) which widens the transport gap (29, 30) in a funnel shape. 3. Transport device according to claim 1 or 2, characterized in that the pressure surface (25, 26) is the front surface of a pressure body (21, 22) whose width transverse to the transport direction corresponds at least to the width of the transport roller (11, 12) opposite it. 4. Transport device according to one of the preceding claims, characterized in that the pressure surface (25, 26) is polished. 5. Transport device according to claim 3 or 4, characterized in that the pendulum yoke (19) and the pressure bodies (21, 22) are formed in one piece. 6. Transport device according to claim 5, characterized in that the pendulum yoke (19) with the pressure bodies (21, 22) is formed from a plastic. 7. Transport device according to one of the preceding claims, characterized in that the counter elements (21, 22) are provided with light barriers (33). 8. Transport device according to claim 7, characterized in that at least one light barrier element (33) is built into the respective counter element (22). 9. Transport device according to claim 8, characterized in that two light barrier elements (33) are provided, which are arranged directly at the beginning and at the end of the transport gap (30).