Photocopying – Projection printing and copying cameras – Detailed holder for photosensitive paper
Reexamination Certificate
1999-04-14
2001-01-09
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Detailed holder for photosensitive paper
C355S076000, C355S047000
Reexamination Certificate
active
06172741
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to vacuum holddown apparatus and method of operation and, more specifically to a cut-sheet print media vacuum holddown particularly useful for a wet dye hard copy apparatus, such as an ink-jet printer.
2. Description of Related Art
It is known to use a vacuum induced force to adhere a sheet of flexible material to a surface, for example, for holding a sheet of print media temporarily to a platen. [Hereinafter, “vacuum induced force” is also referred to as “vacuum induced flow,” or just “vacuum flow,” or more simply as just “vacuum” or “suction”.] Such vacuum holddown systems are a relatively common, economical technology to implement commercially and can improve throughput specifications. For example, it is known to provide a rotating drum with holes through the surface wherein a vacuum through the drum cylinder provides a suction force through the drum surface. [The term “drum” as used herein is intended to be synonymous with any curvilinear implementation incorporating the present invention, whether a full cylinder as shown in the exemplary embodiment, a semi-cylinder embodiment, hemispherical embodiment, or the like, as would be recognized by a person skilled in the art. While the term “platen” can be defined as a flat, or planar, holding surface, in hard copy technology it is also used for curvilinear surfaces, such as a common typewriter rubber roller; thus, for the purposes of the present application, “platen” is used generically for any shape paper holddown surface used in a hard copy apparatus.] In a hard copy apparatus, such as a copier or a computer printer, a platen is used either to transport cut-sheet print media to an internal printing station or to hold the sheet media at the printing station while images are formed, or both. [In order to simplify discussion, the term “paper” is used hereinafter to refer to all types of print media; no limitation on the scope of the invention is intended nor should any be implied.] One universal problem is the management of different sized paper. Open holes around the edges of a sheet smaller than the dimensions of the vacuum field in the platen surface results in vacuum losses for holding the paper. In other words, too many exposed vacuum ports results in a change of the flow forces in each vacuum port and a loss of holding pressure at paper sheet covered ports. Thus, a sheet of paper that is smaller than the total vacuum field may not be firmly adhered to the surface. Known apparatus generally rely on a user manually switching operational functions to adjust the vacuum field to match the size of the paper in current use.
Another problem has become evident as attempts have been made to employ vacuum for holding paper in “wet dye” printing environments, for example, in hard copy apparatus such as in an ink-jet printer that uses a liquid ink. [The term “wet dye” or just “dye” is used herein as generic for all such hard copy apparatus, whether employing ink (which may itself be dye-based or pigment-based), a wet toner, or other liquid colorant.] The art of ink-jet technology is relatively well developed. Commercial products such as computer printers, graphics plotters, copiers, and facsimile machines employ ink-jet technology for producing hard copy. The basics of this technology are disclosed, for example, in various articles in the Hewlett-Packard Journal, Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No. 1 (February 1994) editions. Ink-jet devices are also described by W. J. Lloyd and H. T. Taub in Output Hardcopy [sic] Devices, chapter 13 (Ed. R. C. Durbeck and S. Sherr, Academic Press, San Diego, 1988).]
For example, in an ink-jet printer with a drum surface platen employing a field of discrete vacuum areas, the localized vacuum pressure against regions of the underside of the paper adjacent the vacuum areas draws the wet dye through the capillaries of the paper material before the dye has time to set. This results in alternating dark and light concentrations of dye in the final image correlating to the individual vacuum force influence regions of the holes in the field. Non-uniform saturation leads to deformation of the paper as the ink dries, commonly known as “paper cockle.” Moreover, in an ink-jet environment, vacuum forces through ports around the periphery of the paper could affect ink drop firing trajectories, resulting in misprints or random artifacts in the final image.
There is a need for a vacuum paper holddown that is suited for use in a wet dye printing environment.
SUMMARY OF THE INVENTION
In its basic aspects, the present invention provides a platen surface structure for a vacuum holddown of a hard copy mechanism for printing with wet dye on print media, the hard copy mechanism having a vacuum generating mechanism for producing a predetermined vacuum force. The structure includes: the vacuum holddown having a platen; the platen having a first surface for receiving print media thereon, the first surface having predetermined width dimension in a predetermined first axis of symmetry, and the first surface having a plurality of vacuum channels distributively arranged in parallel wherein each of the channels is substantially parallel to the first axis of symmetry, adjacent channels having substantially identical predetermined channel shape and channel dimensions; each of the channels has at least one vacuum port associated therewith, fluidically coupling each of the channels, respectively, to the vacuum generating mechanism, each of the channels are separated from adjacent channels thereto by platen surface structure ribs, wherein each of the ribs is substantially parallel to the first axis of symmetry, such that the ribs form a print media receiving surface; and the ribs having predetermined rib shape and rib dimensions and the channels have the predetermined channel shape and channel dimensions such that the vacuum force is distributed through the channels and imparted to regions of print media received on the ribs and spanning the channels to hold the print media to the platen first surface, wherein the first surface provides leading and trailing edge holddown on the platen.
In another basic aspect, the present invention provides a vacuum platen device for an ink-jet apparatus having a mechanism for producing a vacuum, Fv. The device includes: a platen having an outer platen surface and an inner platen surface wherein print media sheets are sequentially delivered to the outer platen surface from a predetermined media delivery direction, the platen having a first axis perpendicular to the predetermined media delivery direction and a second axis parallel to the predetermined media delivery direction; the outer platen surface having an outer platen surface structure having a repeated pattern of vacuum channels in the outer platen surface wherein each of the channels has a channel major axis substantially parallel to the first axis and a channel minor axis substantially parallel to the second axis; the outer platen surface structure having platen surface structure ribs, each of the ribs separating a pair of the vacuum channels, the ribs having a rib major axis substantially parallel to the first axis and a rib minor axis substantially parallel to the second axis; and each of the vacuum channels having a least one vacuum port from the outer platen surface to the inner platen surface, fluidically coupling each of the vacuum channels to the mechanism for producing a vacuum, respectively, and wherein the ribs have a predetermined rib shape and rib dimensions and the channels have a predetermined channel shape and channel dimensions such that the vacuum force is distributed through the channels and imparted to regions of the print media received on the ribs and spanning the channels to hold the print media to the outer platen surface, and wherein the platen fur
Chen Angela
Rasmussen Steve O.
Rhodes John D
Wotton Geoff
Adams Russell
Hewlett--Packard Company
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