HP (Hewlett-Packard) 1200C Printer User Manual


 
72 February 1994 Hewlett-Packard Journal
Media Path for a Small, Low-Cost,
Color Thermal Inkjet Printer
The DeskJet 1200C media path is heated for media independence,
requiring development of a new grit drive roller and pinch wheel
combination. A new stepper motor was developed to attain the target
speed and accuracy. Media flatteners and precise gearing with an
antibacklash device contribute to accuracy.
by Damon W. Broder, David C. Burney, Shelley I. Moore, and Stephen B. Witte
The media path is the part of a printer that moves media
past the print cartridges, stopping and accurately locating
the media for printing. The media path also constrains the
media in a plane a fixed distance from the print cartridges. A
media path should advance media accurately and quickly, be
quiet, be inexpensive, hold the media flat, and keep the media
the correct distance from the print cartridges.
Fig. 1 shows an overview of the media path of the HP Desk-
Jet 1200C printer. Media stacked in the input tray (1) is indi-
vidually picked by a media pick roller (not shown) and
driven around the curved preheat zone (2) where it is pre-
conditioned (moisture is driven off and the temperature is
raised). When the page reaches the pinch/drive rollers (3),
the main drive system (4) takes over from the pick roller
drive (not shown). Once in the print zone (5) the media is
heated further and ink is sprayed onto the page. The heating,
soaking, and drying causes the media to move out of its
plane, but the media control shims (6) help hold it flat for
better print quality. The page is then incrementally advanced
and printed upon until the entire page has been printed.
Finally, the page is fed out into the output tray (7) and the
process is ready to repeat.
Design Approach
For the office printer market, the DeskJet 1200C is designed
to support a wide variety of plain papers, to be HP LaserJet
printer compatible, to print text very quickly, to print high-
quality graphics, and to be cost competitive. These character-
istics forced the design team to face the following challenges:
Constrain plain papers flat even though plain paper tends to
cockle and curl in various directions when ink is sprayed on
and heated.
Print to 50-dot row margins for LaserJet compatibility, even
though such small margins allow very little control over
media flatness.
Fig. 1. Overview of the media
path of the HP DeskJet 1200C
printer. Media stacked in the input
tray (1) is individually picked by
a media pick roller (not shown)
and driven around the curved
preheat zone (2) where it is pre-
conditioned (moisture is driven
off and the temperature is
raised). When the page reaches
the pinch/drive rollers (3), the
main drive system (4) takes over
from the pick roller drive (not
shown). Once in the print zone
(5) the media is heated further
and ink is sprayed onto the page.
The heating, soaking, and drying
causes the media to move out of
its plane, but the media control
shims (6) help hold it flat for bet-
ter print quality. The page is then
incrementally advanced and
printed upon until the entire page
has been printed. Finally, the
page is fed out into the output
tray (7) and the process is ready
to repeat.
Main Drive System4
Pinch/Drive
Rollers
3
Input Tray
1
Output Tray
7
Print Zone
5
Preheat Zone
2
Paper Control Shims
6
Media Direction