Image Processing Reference
In-Depth Information
image quality, productivity, and substrate latitude. Although ink-jet printing is
another digital technology that is architecturally simple, it has its own limitations
regarding volume and speed. Kodak stream ink-jet technology is a continuous system
that reportedly enables offset caliber reliability, productivity, cost, and quality with the
full bene
ts of digital printing for high-volume commercial applications. On the other
hand, the EP process is utilized today as a key technology for high-volume full digital
color printing in which four primary colors (cyan, magenta, yellow, and black) are
developed by architecting the engine in six basic xerographic process steps: charge,
expose, develop, transfer, fuse, and clean.
The toner-based digital printing process involves a circulating photoreceptor (PR)
in the form of a belt or a drum. The PR is light sensitive; it is insulating in the absence
of light and conductive when light is present. The
first step in the EP process is
''
where a high voltage wire deposits electrons or ions on the PR in the dark
causing a uniform charge buildup. The
charging,
''
CMYK
separations, provided by the DFE, are
then utilized to selectively expose
the charged PR drum or belt according to the binary halftoned image pattern. The
resulting spatial charge distribution, called the latent image, corresponds to the desired
image to be printed. It is then
through the use of raster output scanners (ROS)
by depositing oppositely charged toner
particles exclusively in the charged regions thus forming a toned image on the PR. The
toned image is
developed
''
''
transferred
to paper by electrostatic forces and made permanent by
''
''
where heat and pressure are applied to melt the toner particles and adhere
them to the paper. Finally, the PR is mechanically and electrostatically
fusing,
''
''
cleaned
of
''
''
residual toner and then recirculated to the charging system for the next image.
1.4.1 I MAGE - ON -I MAGE AND T ANDEM P RINT E NGINES
Several print engine architectures have been developed to produce full-color prints
image-on-image (IOI), tandem, etc. [5
7]. The fundamental difference between
tandem architecture and IOI architecture is where the four-color
-
image is
constructed. In the IOI architecture, used in the iGen3 and iGen4 production presses,
the four-color image is constructed one on top of the other on the PR belt in one
complete revolution. Figure 1.4 shows the
CMYK
skeleton
view of the system, with
''
''
outlines of the feeders, marking paper handling, and
finishing systems. Once the
magenta layer is developed, yellow, cyan, and black are developed on top of
the prior toner layer. This four-color image is then transferred in a single step to the
substrate. The basic steps of the IOI xerographic process used in iGen3 and iGen4
print engines are precharge, charge
=
recharge, expose, develop, pretransfer, transfer,
=
=
detack
recharge, expose, and
develop) are performed up to four times to achieve the single pass, four color process.
The advantages of single step transfer are that it eliminates at least four oppor-
tunities for image misregistration or disturbance or transfer efficiency loss. In the
tandem architecture (Figure 1.5), used in the DC8000 printer, each primary is
stripping, and cleaning. Three of these steps (charge
rst
developed on an individual PR and then separately transferred to the paper directly
(or through an intermediate transfer drum or belt), thus making it more dif
cult to
maintain high accuracy in the registration of each primary because of the four
separate transfer steps.
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