|Publication number||USRE39441 E1|
|Application number||US 10/771,262|
|Publication date||Dec 26, 2006|
|Filing date||Feb 3, 2004|
|Priority date||Nov 29, 2000|
|Also published as||US6571702, US20020062750|
|Publication number||10771262, 771262, US RE39441 E1, US RE39441E1, US-E1-RE39441, USRE39441 E1, USRE39441E1|
|Inventors||Geoff Wotton, Robert M. Yraceburu, Steven B. Elgee|
|Original Assignee||Hewlett-Packard Development Company, L.P.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (14), Non-Patent Citations (1), Referenced by (5), Classifications (12), Legal Events (6)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This invention relates to computer printers, and particularly to media transport mechanisms and vacuum hold-down devices.
Some approaches for thermal inkjet printing use a vacuum platen as part of the media transport. Essentially, a sheet of media to be printed is carried on an air-transmissive belt over a flat plate that contains a multitude of apertures. A vacuum device below the plate draws air into the apertures, creating a pressure differential that flattens the media sheet against the plate, with the web sliding over the plate to feed the sheet past a printing device. The printing device may be a thermal ink jet pen that reciprocates over the sheet in a scan direction perpendicular to the feed direction, and which lays down successive swaths of ink droplets to generate a printed image.
The platen may be heated to facilitate rapid drying of aqueous ink, and the vacuum effect holds the sheet in a flat stable position as the ink dries. This avoids curling or “cockle” effects that can distort the media surface in areas where large quantities of ink are imprinted, due to the dimensional effect of moisture on paper and other media. When the media is held flat during the drying process, a flat result is generated.
While effective for many applications, vacuum platen have certain limitations. First, smaller media that does not cover most of the platen area leave substantial platen areas open. This permits air to be drawn into the area below the platen, bypassing the sheet, and thereby requiring substantial airflow capacity to maintain adequate relative pressure on the sheet. For a minimally sized sheet, nearly the entire area of the platen may be open to airflow. This requires a large vacuum blower, with attendant problems of size, power consumption, and noise. Further, for the platen to be maintained at an elevated temperature needed for ink drying, increased heating power is needed to offset the cooling effect of ambient air flowing through the platen. Also, open areas surrounding a small media sheet may still have depressed temperatures compared to covered regions, and subsequent large media may encounter non-uniform platen temperatures that may impair printing results. In addition, temperature gradients may occur near media edges, leading to non-uniform drying.
An additional concern even for platens optimized for a particular media width is that unless a continuous end-to-end stream of media is passed over the platen, there will be large open areas of the platen ahead of the leading edge of the first sheet, and following the training edge of the last sheet. This generates similar disadvantages to those discussed above regarding media width.
The present invention overcomes the limitations of the prior art by providing a printer having a media transport with a rigid, air-transmissive platen. A movable air-transmissive flexible web overlays the platen. A suction device communicates with the platen to draw air through the web and through the platen such that a sheet of media carried on the web is biased toward the platen. A valve sheet overlays or underlies the platen, and includes a plurality of shut-off elements, each movable in response to temperature changes between a closed position in which the element contacts a portion of the platen to prevent air flow through that portion of the platen, and an open position, in which the element is spaced apart from the platen to admit air to the platen portion. The shut off elements may include resistive heaters and bimetallic strips, so that application of electricity generates heat to flex the strip to an open position.
The belt is an air-transmissive mesh screen, or may be any perforated or porous sheet having a low air flow resistance, small thickness, and flexibility. The outlet end roller 30 is motorized to drive the belt in a feed direction 36, which defines the feed axis perpendicular to the scan axis 16. The movement of the belt is controlled by control circuitry (not shown) that also controls the pen scanning, ink droplet expulsion, and all other operations of the printer to provide coordinated action. A pair of paper guides 40 upstream of the inlet end of the media transport adjust in concert to the width of a media sheet 42, centering the sheet within a media supply tray (not shown) on a midline of the platen parallel to the feed axis, and preventing skewing of the sheet. The guides may include sensors that feed back the guide positions to the controller so that the controller may establish other printer functions based on the inferred media width.
An airflow limiting sheet 52 overlays the upper surface of the plate, and defines a multitude of apertures 54, each registered with and centered on a respective plate hole 45. The apertures have a limited diameter less than that of the plate holes 45, so that the pressure drop during air flow is greatest across the apertures. The apertures are sized in conjunction with the capacity of the blower to generate a required flow rate at a pressure differential of at least a 10 inch water column between the plenum and ambient to ensure the media sheet is secured adequately against the platen.
In the preferred embodiments, the sheet thickness is preferably about 0.25 mm, and the aperture diameter about 0.6 mm, although these may vary widely in different applications. An active valve sheet 56 overlays the airflow limiting sheet 52, and includes movable flaps 60 that are registered each with a respective aperture. The flaps are movable between a closed position as illustrated by flaps 60, in which the flaps remain coplanar with the valve sheet 56 and fully overlay and obscure the respective apertures 54 to prevent downward airflow, and an open position 60′ in which the free ends of the flaps rise upward from the plane as the flaps flex in response to energizing of an air flow control mechanism discussed below. In an alternative embodiment, the valve sheet may be below the plate 44. However, with the sheet above the plate, the air pressure differential advantageously assists in scaling off closed valve elements.
Overlaying the valve sheet is an upper heater layer 61 with a heater element network (not shown) in the form of resistive traces on the surface of the plate, which generate an output of 10-20 mW per square mm. Alternative heating methods may be employed. The heater covers the entire plate, and has apertures over the valve apertures to avoid limiting air flow, and to avoid interfering with flexure of the valve elements. The heater layer preferably includes a lower portion of a thermally insulating material to minimize heat transfer from the heater to the valve sheet.
The belt 24 overlays the heater layer, and moves across the heater sheet surface in the feed direction 36. The feed direction coincides with the direction in which the valve flaps extend, so that the belt slides smoothly over elevated arms without snagging and damaging arms, and to minimize friction. The belt rests on the heater sheet without a gap, and with minimal force, except as generated by vacuum forces on the media sheet. As shown, the media sheet has a leading edge 62 that is shown positioned over a region in which the flaps are elevated to the open position 60′. By maintaining flaps in the open position underneath all portions of the sheet the entire sheet is flattened against the platen. Some marginal open valves beyond the sheet edges on all sides are tolerated, with the blower having adequate capacity to maintain the needed partial vacuum in the plenum even when these areas are open. With a blower rated at 40 cubic feet per minute, an open area of 70 square inches is tolerated while maintaining the needed pressure differential. This is significantly less than the typical area of the entire platen, necessitating the closing of many or most of the valves where the platen is not covered by the media sheet, to allow the use of a practical and economical use of a limited capacity blower, with attendant advantages in size, power consumption, and quietness.
As shown in
As shown schematically in
A controller circuit 92 has a ground line 94 connected to each column, connecting to the conductor 72 of each resistor in each block of that column. Each row is connected by one of several row-addressing power lines 96. For symmetrical operation with reduced connections, rows 82 and 82′ connect to a common line, as do rows 84 and 84′. The several blocks of the wider central row 80 connect to a single power line. The central block has a width established for the narrowest media that can be used on the platen. Any number and size of outer rows may be employed to improve resolution, and to accommodate a wider range of media widths.
The circuit may address each sector individually in a multiplexed operation in which each column (or row) is sequentially activated by switching the ground line to ground, and simultaneously setting the power lines to the activate the appropriate blocks for that column. By rapidly sequencing through the columns, a power pulse adequate to maintain heat for keeping valves open is delivered. However, in the preferred embodiment, a simpler system may be used, since the only open regions will be a rectangular central region that may or may not extend off either end. Thus, the circuit need only disable the rows that extend beyond the media width, and the columns in advance of the media leading edge, and behind the media trailing edge. This permits constant unpulsed lower currents adequate to maintain valve opening heat without electromagnetic noise from switching much high currents.
The system operates by the user setting the paper guide to a suitable width, which communicates with the control circuitry. Peripheral rows entirely beyond this width are disabled by preventing current flow from heating the resistors and opening the valves. This is done by preventing voltages from being applied on the associated power lines.
Initially, all sectors are closed. Other sensors detect the position of the leading edge, and infer the position of the leading edge as feeding proceeds during printing by monitoring the motion and position of a belt roller or other element linked to the feed mechanism progress. In advance of the leading edge encountering each new sector, the control circuit opens the valves in the enabled rows of each column by grounding the associated ground line.
For printing multiple sheets in a single job, the sheets may be fed with the leading edge of each subsequent sheet following near the trailing edge of prior sheet, so that columns need not be disabled between sheets. As the final sheet in a job is printed, the ground line of each column is disabled to allow the flaps to close, after the trailing edge of the sheet fully departs the column.
While the above is discussed in terms of preferred and alternative embodiments, the invention is not intended to be so limited.
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|US8066283 *||Apr 1, 2011||Nov 29, 2011||Seiko Epson Corporation||Recording device|
|US8356815||Oct 12, 2011||Jan 22, 2013||Seiko Epson Corporation||Recording device|
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|US9688494||Apr 22, 2011||Jun 27, 2017||Douglas Machine Inc.||Apparatus and methods for producing shrink-wrap packaging|
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|U.S. Classification||101/232, 355/76, 271/183|
|International Classification||B41F13/24, B41J11/06, B41J11/00|
|Cooperative Classification||B41J11/06, B41J11/0085, B41J11/002|
|European Classification||B41J11/06, B41J11/00S, B41J11/00C1|
|Dec 20, 2006||REMI||Maintenance fee reminder mailed|
|Jan 9, 2007||FPAY||Fee payment|
Year of fee payment: 4
|Jan 9, 2007||SULP||Surcharge for late payment|
|Nov 30, 2010||FPAY||Fee payment|
Year of fee payment: 8
|Jan 9, 2015||REMI||Maintenance fee reminder mailed|
|Jun 3, 2015||LAPS||Lapse for failure to pay maintenance fees|