Non-warping heated platen

Details Non-warping heated platen Non-warping heated platen

2000-12-01

2002-10-08

Gordon, Raquel Yvette (Department: 2853)

Incremental printing of symbolic information

Ink jet

Medium and processing means

Reexamination Certificate

active

06460990

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to hard copy apparatus, more specifically to an ink-jet printer employing a heated, planar platen, and particularly to non-warping heated platen assemblies.
2. Description of the Related Art
A variety of hard copy printing technologies—for example impact, thermal, laser, ink-jet—are commercially available. In order to describe the present invention, exemplary embodiments in the form of ink-jet printers are depicted. No limitation on the scope of the invention is intended by the use of such exemplary embodiments nor should any be implied therefrom. 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).
FIGS. 1A and 1B
depict an ink-jet hard copy apparatus in which the present invention is useful; in this exemplary embodiment, an engine for computer printer
101
employing a media vacuum transport is illustrated. In general, the carriage scanning axis is designated the x-axis, the print media transport axis is designated the y-axis, and the pen firing direction onto the media is designated the z-axis. Operation is administrated by an electronic controller (not shown; usually a microprocessor or application specific integrated circuit (“ASIC”) printed circuit board). It is well known to program and execute imaging, printing, print media handling, control functions and logic with firmware or software instructions using such a controller.
Paper sheets
22
from an input supply (not shown) are sequentially captured and fed by a vacuum belt mechanism to an internal printing station, or “print(ing) zone,”
28
. A thin, endless-loop belt
26
is mounted tightly between belt drive rollers
62
,
64
. Drive roller
62
is coupled to a stepper device (not shown ) for accurately positioning the sheet in the y-axis with respect to the pen
20
. A vacuum box
40
, coupled by an appropriate conduit
48
to a vacuum source
50
(
FIG. 1B
only) has a platen
42
having a plurality of vacuum ports
44
(
FIG. 1B
only) therethrough. The belt
26
is generally porous, allowing a vacuum flow to pull through the belt via the ports
44
. The paper sheet
22
is captured in an upstream (with respect to the pen
20
and associated print zone
28
) support zone
55
by the vacuum force exerted thereon as the sheet is received from the input supply and its associated pick mechanisms (not shown). In another upstream, pre-print zone
51
, the sheet can be engaged by a controlled pinch roller
53
device. In the print zone
28
, one or more ink-jet pens
20
, mounted on an encoder controlled scanning carriage (not shown), scan the adjacently positioned paper sheet
22
and graphical images or alphanumeric text are created. Each pen
20
has one or more printhead mechanisms (not seen in these views) for “jetting” minute droplets of ink to form dots on the adjacently positioned sheet
22
of print media. Each minute droplet is directed at an artificially imposed row and column grid on the print media known as a picture element (“pixel”) using digital dot matrix manipulation to form alphanumeric characters or graphical images. Once a printed page is completed, the print medium is ejected from the belt
26
.
For ink-jet printing, it is desirable to maintain a relatively minute, close tolerance, printhead-to-media spacing (z-axis) in order to maximize the accuracy of ink drop placement for optimized print quality. One factor for design optimization is platen flatness. In the state of the art, it is desirable to have a printhead-to-media spacing of less than about one millimeter (“mm”). If the platen
42
(or belt
26
riding across the surface thereof) is too close to the printheads at any region of the printing zone
28
or immediately adjacent thereto where pen-to-paper might interfere, smudging of wet ink or damaging pen-media crashes can occur.
To improve ink-jet apparatus performance (ink-media interaction, dry time, print quality, throughput, and the like as would be known to practitioners of the art), it is often advantageous to heat the platen
42
.
FIG. 2
is an exemplary embodiment of a vacuum belt subsystem
200
, including a specific embodiment of a heated platen
42
in accordance with the present invention. A transport portion, or region,
66
of the belt
26
slides over a support surface
52
of the vacuum platen
42
, having ports
44
arranged for communicating vacuum pressure to the surface
52
. Paper sheets
22
are sequentially directed onto the transport portion
66
by known manner paper supply pick and feed mechanisms (not shown). Conductive heating of the belt
26
is accomplished by the use of one or more heaters
70
that are about 1-millimeter below the platen support surface
52
, in this embodiment, fabricated of a ceramic material for conducting the applied heat. The heaters
70
are comprised of an array of printed, linear, resistive heating elements
72
. The individual heating elements
72
extend between the rows of vacuum ports
44
that are defined on the support surface
52
of the platen
42
. At the edges of the support surface
52
, the individual elements
72
are joined (as at reference numeral
74
) and the termini of the heaters are enlarged into two contact pads
76
for connecting to a known manner source of electrical potential. The heaters
70
are arranged so that one heater resides on the central portion of the platen
42
immediately in the print zone
28
. There are also two heaters
70
in the platen
42
entry region
130
, referred to as “entry region heaters,” viz. a pre-printing operations region. Similarly, two “exit region heaters” are provided at the exit region
132
of the platen, viz. A post-printing operations region. Further details of this specific embodiment are described in CONDUCTIVE HEATING OF PRINT MEDIA is described by common inventor Wotton et al., in U.S. patent application Ser. No. 09/412,842, filed Oct. 5, 1999 (assigned to the common assignee herein); however, details other than those incorporated herein are not required in order to understand the present invention.
Under normal operating conditions, the platen
42
may experience temperatures in the approximate exemplary range of zero to 150° Centigrade (it will be recognized to those skilled in the art that the actual range will be dependent upon the specific implementation). Such temperature excursions, temperature transients, and cross-platen gradients can cause a platen
42
to warp.
Previous solutions include employing long warm-up time, the use of high cost materials, or providing high power controls (e.g., using 220 volt circuits), and the like to resolve the problems. However, long cool-down times may still need to be employed to ensure flatness is kept within predetermined tolerances.
Therefore, there is a need for methods and apparatus that comprise non-warping heated platen.
SUMMARY OF THE INVENTION
In its basic aspects, the present invention provides a heated platen apparatus, having a media transport surface, including: a planar heater, forming said surface and having a predetermined thickness “t”; a planar base, having a predetermined thickness “T,” substantially greater than “t,” and having a low coefficient of thermal expansion; and an attachment conjoining said heater and said base, wherein the attachment provides a high thermal resistance and said surface remains planar regardless of temperature changes of said heater.
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