Incremental printing of symbolic information – Ink jet – Medium and processing means
Reexamination Certificate
2002-02-06
2004-12-28
Nguyen, Lamson (Department: 2853)
Incremental printing of symbolic information
Ink jet
Medium and processing means
C347S101000, C347S102000, C347S020000, C347S021000, C347S129000, C347S134000, C347S112000, C271S196000, C271S194000, C271S264000, C271S197000, C271S276000, C271S275000, C400S635000, C400S634000, C400S048000, C346S134000
Reexamination Certificate
active
06834949
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention of the instant application relates to a device for simultaneously holding by suction and transporting a sheet.
In the field of transport devices, articles which are to be transported are frequently retained by suction or negative pressure on an underlying surface which moves the articles. In this regard, the articles are retained on the underlying surface by a difference in pressure above the article and beneath the underlying surface. In the case of such transport devices, the problem arises that the negative pressure has to act upon the underside of the articles through openings formed in the underlying surface. Further in this regard, marginal regions of flat articles, in particular, should be held firmly on the underlying surface, so that suction holes have to be provided also in and beyond the marginal regions. In particular, in the case of endless belts, individual suction holes are often not firmly assigned to the base surface of the respective article. Furthermore, articles with differing base surfaces are transported, at least serially, on the aforementioned underlying surfaces, so that open suction holes are usually located outside the base surfaces of the articles, and considerable quantities of air flow into suction chambers through the suction holes. Such open suction holes result in considerable pressure losses and in large pressure differences in the marginal regions of the articles, these pressure differences being manifested in correspondingly pronounced airflows.
In order to provide a remedy therefor, the German Published Non-prosecuted Patent Application (DE-OS) 4406 739 has proposed constructing the underlying surface for the articles from a plurality of layers formed with recesses provided with labyrinths for the discharging air, which increase the flow resistance thereto. A more uniform suction force for holding the articles, which is supposed to be effective, in particular, in the marginal regions of the articles, is thereby achieved, the intent thereof being for the reduced flow speed to result in reduced energy requirements. The underlying surface or the transporting belt thus has the same flow resistance over the entire length thereof.
The German Published Non-prosecuted Patent Application (DE-OS) 197 28056 discloses adapting the suction force of the underlying surface to the respective local requirements. In this regard, in the case of sections of the transport belt whereon, in fact, no article is present, a respectively effective negative pressure can be set accordingly. This effect is achieved in a comparatively costly manner in that a multiplicity of suction chambers are arranged beneath the belt and are, respectively, provided with a dedicated negative-pressure source and can be adjusted in terms of suction capacity in accordance with the respective requirements.
The aforedescribed airflow is particularly pronounced and disruptive when flat articles travel into a flat operating station. This is true, for example, for the passage of paper sheets into a printing unit, in particular, an ink-jet printer. Such sheets have a surface area with which they cover a relatively larger region, respectively, of the underlying surface. The respective sheet closes the suction holes directed towards the bottom surface thereof, with the result that a considerable differential pressure, by which the sheet is pressed against the underlying surface, is produced in this region. The suction holes which are not covered, in particular, immediately outside the border or margin of the respective sheet, can be adapted well to the airflow, with the result that a comparatively low differential pressure prevails thereat. These pressure differences, which are noticeable in the marginal region of the flat article, in particular, produce considerable airflows and vortices, which may frequently have disadvantageous consequences for the functioning of the operating stations. This is the case, for example, with printing units wherein the airflow adversely affects the ink which is to be applied to the sheet, i.e., the printing operation. In particular, if the printing head is arranged at only a slight distance above the sheet, the slight distance results in considerable flow speeds, in particular, at the sheet margins, which adversely effect the application of the ink to the sheet specifically in the marginal regions of the sheet, for example, in that the ink is applied over the sheet with different levels of dampness or, for example, in the case of an ink-jet printing unit, ink droplets are whirled about in a vortex and thus adversely affect the printed image at least in the marginal regions of the sheet.
SUMMARY OF THE INVENTION
Starting from the device for simultaneously holding by suction and transporting a sheet as described in general in the introduction hereto, it is an object of the invention of the instant application to provide a straightforward improvement in the construction thereof so that, upon the occurrence of a negligible reduction in the holding force of the underlying surface, the airflows occurring in a respective printing unit are largely reduced.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a device for holding a sheetlike article on a movable underlying surface for transporting the sheetlike article at least in one direction selected from the group thereof consisting of a direction into and a direction out of an operating station having a printing unit, comprising a member having a surface underlying the sheetlike article, the sheetlike article being retainable by pneumatic pressure on the surface, a screening device disposed locally fixedly with respect to an operating station, the screening device serving for reducing an airflow in a region of the printing unit at least with respect to adjacent regions, the reduction in the airflow resulting from the sheetlike article being held on the underlying surface.
In accordance with another feature of the invention, the printing unit is an ink-jet unit.
In accordance with a further feature of the invention, the underlying surface is on a movable belt formed with through-passage holes.
In accordance with an added feature of the invention, the screening device has a sheet-like mesh formed with holes and disposed beneath the underlying surface, the holes of the mesh being of such number and size that, as a result of flow resistance thereof, there is an adequate reduction in the airflow in the region of the printing unit.
In accordance with an additional feature of the invention, a virtually limited first suction chamber is disposed beneath the region of the printing unit, the screening device having a throttle opening via which the first suction chamber is connected to a negative-pressure source.
In accordance with yet another feature of the invention, the holding and transporting device includes further suction chambers connected to the negative-pressure source, the further suction chambers being located adjacent to the first suction chamber and having a greater negative pressure than that of the first suction chamber.
In accordance with yet a further feature of the invention, the mesh is disposed beneath a cover plate formed with pass-through openings, the cover plate covering the suction chambers and serving for guiding the belt.
In accordance with yet an added feature of the invention, the mesh is connected to the cover plate.
In accordance with yet an additional feature of the invention, the connection of the mesh to the cover plate is selected from the group thereof consisting of integral and releasable connections.
In accordance with still another feature of the invention, the underlying surface is on a continuous transport belt formed with holes around the length thereof and guidable in given sections by the cover plate.
In accordance with a concomitant feature of the invention, the pneumatic pressure is at least one pressure selected from the group thereof consisting of positive and negative pr
Greenberg Laurence A.
Heidelberger Druckmaschinen AG
Liang Leonard
Mayback Gregory L.
Nguyen Lamson
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