Theory Of Operation; Processes And Configuration; Electrophotography Process; Development Unit - Lexmark C920 Service Manual

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Theory of operation

Processes and configuration

In this printer, the toner of four colors (magenta, cyan, yellow, and black) melts and deposits dots on paper,
which record color image information. This printing process is called the electrophotography process.

Electrophotography process

In the electrophotography (EP) process, 6 steps take place to image toner on the page:
1.
Charge
2.
Expose
3.
Develop
4.
Transfers
5.
Fuse
6.
Clean / Erase
Charge–The heart of the EP process centers around the photoconductor (or photodeveloper). The
photodeveloper unit is layered with an organic substance that makes it sensitive to light. At the beginning of EP
process, the entire surface of the photodeveloper is negatively charged by a charge roller which is located within
the photoconductor unit itself. This charge is directed to the photosensitive medium at a low voltage, thus
reducing the generation of ozone to a very low level.
Expose–Once the photodeveloper is charged, the initial image is recorded by irradiating light from the LED
printhead. This forms an electrostatic or "latent" image (an invisible image) on the surface of the light-sensitive
photodeveloper. The area on the photodeveloper where the electrostatic image is written has been partially
discharged (less negative) so that there is a charge difference between the electrostatic image and the rest of
the surface area of the photodeveloper.
Note: Since light from the LED array varies depending on the individual LED printheads, the light emitting
value (light quantity value) is stored in the EPROMs on the print head controller board (one for each color
station). Given that the LED printhead and EPROM on the printhead controller board of this printer are
paired, the EPROM on the printhead controller board should always be replaced whenever the LED
printhead is replaced.

Development unit

Toner is agitated by the cartridge hopper and then fed to the supply roll. The supply roll then transfers the toner
in between the development roll and doctor blade. The doctor blade, which is made of conductive rubber, is fitted
to the development roll and used to smooth the toner evenly across the surface of the development roll.
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Service Manual