Vacuum control for vacuum holddown

A method for securing variably sized, individual sheets of print media to a platen surface using vacuum means for generating a vacuum force, comprising the steps of:

• providing a platen having surface with a plurality of discrete vacuum channels therein wherein said channels are arranged in sets associated with discrete sectors of said surface, each of said channels being fluidically coupled by a passageway through said platen to one of a plurality of vacuum plenum chambers subjacent said surface wherein one of said vacuum plenum chambers is associated with each of said sets, said plenum chamber having a means for opening and closing said passageway and for segregating said chamber into an exterior region and an interior region, wherein said means for opening and closing is biased to a passageway-open position against atmospheric pressure and is pulled to a passageway-closed position when said vacuum force is manifolded to said exterior region, wherein said platen surface has length and width dimensions for sequentially accommodating different sized print media, and wherein said surface has at least one vacuum port associated with each of said sets fluidically coupled to said means for generating vacuum force;
• subjecting each of said plenum chambers to said vacuum force via said exterior region, said vacuum force having a predetermined value sufficient for closing said passageways by moving said means for opening and closing to said passageway-closed position such that a substantially atmospheric pressure condition exists within passageways and channels associated therewith;
• and
• transporting a sheet of print medium onto said platen surface wherein by interaction of said sheet of print medium with said vacuum ports where said print medium is in contact with said platen surface, vacuum ports covered by said sheet of print media have said means for opening and closing automatically moved to said passageway-open position due to change in pressure differential between said exterior region and said interior region of said plenum chamber thereby securing said sheet to said surface.

A cut-sheet print medium holddown device for a hard copy apparatus having a means for exerting a vacuum force, the device comprising:

• a platen having a platen outer surface having an area sufficient for sequentially accommodating different size print media sheets thereon and a plurality vacuum channels distributed thereon as discrete sets of vacuum channels, a platen inner surface, and a plurality of vacuum trigger ports fluidically coupling said platen outer surface and said platen inner surface with at least one vacuum trigger port associated with each of said discrete sets of vacuum channels;
• a plurality of vacuum plenum chambers subjacent said platen, each of said chambers having at least one fluidic coupling to one of said discrete sets of vacuum channels;
• a manifold for distributing the vacuum force from said means for exerting a vacuum force to said plenum chamber and for fluidically coupling said vacuum trigger ports from said platen inner surface to said vacuum plenum chambers such that each of said chambers is separately coupled to one of said discrete sets of vacuum channels and the trigger port associated therewith;
• a plurality of vacuum plenum valves wherein one of said plurality of vacuum plenum valves is mounted within each of said vacuum plenum chambers such that print media sheet coverage of individual vacuum trigger ports causes a pressure differential change across only the vacuum plenum valves associated with the sheet-covered vacuum trigger ports fluidically coupled thereto, automatically moving said vacuum plenum valves associated with sheet-covered vacuum trigger ports from a closed position to an open position such that the vacuum force is exerted only through vacuum channels associated with sheet-covered vacuum ports.

An ink-jet hard copy apparatus, having a vacuum means for generating a vacuum force, wherein the apparatus is adapted for using cut-sheet print media of different sizes, comprising:

• a platen having an inner surface fluidically coupled to said vacuum means and an outer surface for receiving various sized print media thereon;
• a manifold for coupling discrete sectors of said outer surface to said vacuum means;
• a plurality of vacuum operated valves, mounted in said manifold such that each of said discrete sectors is individually coupled to said vacuum force through a respective valve associated with the individual one of said discrete sectors, each of said vacuum operated valves having a first position in which a respective one of the discrete sectors is cut-off from said vacuum force and a second position in which the respective one of the discrete sectors is coupled to said vacuum force;
• and
• a plurality of vacuum-actuated trigger ports through said platen, fluidically coupled to said vacuum means and to respective ones of said vacuum operated valves associated with a respective one of the discrete sectors, one each of said trigger ports associated with one of said discrete sectors such that covering a trigger port with a region of said print media changes a pressure differential between atmospheric pressure and said vacuum force across said valve such that said valve is moved from said first position to said second position.

A vacuum holddown comprising:

• a drum having a surface for receiving and capturing cut-sheet print media of various sizes thereon wherein the surface is divided into individual sectors;
• a vacuum manifold coupled to the drum;
• at least one valve mechanism coupled to the manifold for valving a suction force to said individual sectors;
• and
• associated with each of said sectors, at least two related vacuum trigger port mechanisms for activating said valve mechanism including, a first vacuum trigger port mechanism located with respect to the associated sector for being covered by a leading edge of said cut-sheet print media and a second vacuum trigger port mechanism located with respect to the associated sector for being covered by a trailing edge of said cut-sheet print media wherein each of said vacuum trigger port mechanisms includes a means for closing a related vacuum trigger port mechanism whenever one of said two related vacuum trigger port mechanisms is covered by said cut-sheet print media.