Sheet feeding or delivering – Feeding – By means to convey sheet
Reexamination Certificate
1999-04-14
2001-07-03
Skaggs, H. Grant (Department: 3651)
Sheet feeding or delivering
Feeding
By means to convey sheet
C271S096000, C271S265010
Reexamination Certificate
active
06254090
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to vacuum holddown devices, more specifically to a method and apparatus for a print media holddown using a vacuum force, and particularly to automatically adapting a holddown for various print media sizes used by a hard copy apparatus employing wet dye printing.
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,” “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 at the holes in the drum surface. [The term “drum” as used hereinafter is intended to be synonymous with any curvilinear implementation incorporating the present invention; while the term “platen” can be defined as a flat 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 covered ports. Thus, a sheet of paper that is smaller than the total vacuum field is not 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” printing environments, that is, in hard copy apparatus such as in an ink-jet printer that uses a liquid dye. [The terms “liquid dye,” or “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, with a drum surface employing a field of discrete vacuum holes, the localized vacuum pressure against the underside of the paper 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 influence regions of the holes in the field. Moreover, in an ink-jet environment, air flow due to 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.
Another problem occurs in ink-jet printing when the pen-to-paper spacing varies across the surface of the paper. If this spacing variation is rapid, print defects occur due to droplet trajectory errors and flight time differences. Such spacing variation occurs if the paper is locally deformed by vacuum ports of significant size, e.g., greater than about one to two millimeters.
There is a need for a vacuum holddown that can automatically adjust to a relatively universal variety of sizes of a flexible material. The holddown system should operate while being moved at a relatively high speed (e.g., for a drum rotating at approximately 30-inches/second). Moreover, 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 an apparatus for receiving and holding a flexible material sheet thereon, the apparatus including a mechanism for producing a vacuum, and further including: a mechanism for receiving and holding the flexible material on a first surface, the first surface having a plurality of sectors wherein each of the sectors has associated therewith a mechanism for triggering ducting of a vacuum force from the mechanism for producing a vacuum to each of the sectors respectively; a plurality of mechanisms for containing a vacuum subjacent the surface, one mechanism for containing a vacuum associated with each of the plurality of sectors, respectively, wherein each mechanism for containing a vacuum is fluidically coupled to an individual one of the sectors; and a mechanism for manifolding the vacuum force from the mechanism for producing a vacuum to the plurality of mechanisms for containing a vacuum such that when the mechanism for triggering is open to atmospheric pressure the mechanism for contain a vacuum is in a first state wherein no vacuum force is passed through to the one of the sectors associated with the mechanism for triggering open to atmospheric pressure, and when the mechanism for triggering is covered by the flexible material the mechanism for containing a vacuum is in a second state wherein the vacuum force is passed through to the one of the sectors associated with the mechanism for triggering closed to atmospheric pressure.
In another basic aspect, the present invention provides a method for securing variably sized, individual sheets of print media to a platen surface using vacuum mechanism for generating a vacuum force. The method includes the steps of: providing a platen having surface with a plurality of discrete vacuum channels therein wherein the channels are arranged in sets associated with discrete sectors of the surface, each of the channels being fluidically coupled by a passageway through the platen to one of a plurality of vacuum plenum chambers subjacent the surface wherein one of the vacuum plenum chambers is associated with each of the sets, the plenum chamber having a mechanism for opening and closing the passageway and for segregating the chamber into an exterior region and an interior region, wherein the mechanism for opening and closing is biased to a passageway-open position against atmospheric pressure and is pulled to a passageway-closed position when the vacuum force is manifolded to the exterior region, wherein the platen surface has length and width dimensions for sequentially accommodating different sized print media, and wherein the surface has at least one vacuum port associated with each of the sets fluidically coupled to the mechanism for generating vacuum force; subjecting each of the plenum chambers to the vacuum force via the exterior region, the vacuum force having a predetermined value sufficient for closing the passageways
Chen Angela
Rasmussen Steve O.
Rhodes John D.
Wotton Geoff
Hewlett--Packard Company
Skaggs H. Grant
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