CTM2-copyprocesses.pdf
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Overview
Charge
Exposure
Development
Transfer and Separation
Cleaning
Quenching
Fusing
Photocopying Processes
Overview
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1.
Scanning
An exposure lamp illuminates the original. Light reflected off the original is used to create the
image on a drum*. In analog machines, the light is reflected through a series of mirrors,
eventually striking the drum directly. For multi-copy runs, the original must be scanned for each
copy.
In digital machines, the reflected light is passed to a
CCD
or
CIS
, where it is converted into an
analog data signal. This data is further converted to a digital signal, processed, and stored in
memory. To print, the data is retrieved and sent to a laser diode. For multi-copy runs, the original
is scanned only once and stored to a hard disk.
* In this overview section we refer to the
photoconductor
as a
drum
just for simplicity. However, be aware that the
photoconductor is often an OPC belt rather than a drum.
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Photocopying Processes
Overview
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2.
Charging
A charge is applied to the
photoconductor drum. There are a
variety of methods for this. Some
machines apply a positive charge,
others apply a negative. Most use a
non-contact corona wire—though
some use a contact, charge roller.
The drum holds the charge because
the photoconductive surface of the
drum has a high electrical
resistance–unless exposed to light.
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8
7
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3.
Exposure
In an analog machine, the light
reflected off the original is redirected
to the drum. In a digital machine, the processed data from the scanned original is retrieved from
memory or from a hard disk and transferred to the drum by one or more laser beams. In both
cases, the areas exposed to light lose some or all of their charge. This writes an electrostatic
image on the drum.
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Photocopying Processes
Overview
4.
Development
Toner is attracted to the latent image on the drum. The exact process varies depending on
whether the drum holds a positive or negative charge. Most analog machines are Write to
White—the toner is attracted to unexposed areas on the drum. Most digital machines are Write to
Black—the toner is attracted to exposed areas.
5.
Transfer
The image is transferred to paper. Some machines transfer the image directly from the drum.
Others use an intermediary transfer belt. Transfer belts are particularly common in color
machines. The four colors are layered onto the belt, and then the final image is transferred to the
paper in one step.
6.
Separation
The paper can be separated from the drum (or image transfer belt) electrostatically or
mechanically. Charge coronas, discharge plates, pick-off pawls and sharply curved paper paths
are all used. Often a machine will combine two or more methods.
7.
Cleaning
The remaining toner is cleaned off the drum. Most machines use a cleaning blade to wipe off the
excess toner. Some add a cleaning brush or cleaning roller to improve efficiency.
8.
Quenching
Light from a lamp neutralizes the remaining charge on the drum’s surface.
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Photocopying Processes
9.
Fusing
Heat and pressure are used to melt the toner and
attach it to the page. The hot roller [A] is usually
heated by one or more
halogen lamps
. The
pressure roller [B] may or may not be heated.
[A]
[B]
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Charge
Overview
Charge refers to the application of a uniform electrostatic charge to a photoconductor in darkness. At
present, two kinds of electrostatic charge methods are widely used in Ricoh products. The most
common is the corona electrostatic charge method (non-contact type), which takes advantage of the
corona discharge produced when a high voltage is applied to a fine wire. The other is the
electrostatic charge roller method (contact type), which provides an electrostatic charge by applying a
high voltage to a roller and contacting the roller to the photoconductor.
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Photocopying Processes
Charge
Corona Charge
Corotron Method—Positive charge (Se)
A power pack applies several thousand volts of
electricity to a charge wire and a corona discharge is
generated from the charge wire. The corona discharge
ionizes air particles and the positive ions concentrate
around the charge casing and photoconductive surface
(Selenium). The photoconductor (insulator in darkness)
stops the positive ions. The positive ions induce a
negative electrostatic charge in the aluminum base,
retaining the electrostatic charge.
050101.pcx
Scorotron Method—Negative charge (OPC)
When several thousand volts of electricity are
applied to a charge wire [A], a corona discharge is
generated from the charge wire. The corona
discharge ionizes air particles and the negative
ions concentrate around the charge casing [B] and
grid [C]. The negative ions adhere to the photo-
conductor [D] (insulator in the darkness), causing
positive electrostatic charge in the aluminum base
[E], retaining the electrostatic charge.
[A]
[B]
[C
[D]
[E]
050102.pcx
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