Printer Theory Of Operation; Electrophotographic Process (Ep Process); Ep Basics - Lexmark X500n Service Manual

Lexmark confidential until announce edited 1/4/2007

Printer theory of operation

Electrophotographic Process (EP process)

The method that all laser and LED printers use to print is called the electrophotographic process. Laser
printers use differences in charge to manipulate and move toner from the toner cartridge to the printed
page.
Even though the basic EP Process is the same for every laser and LED printer, the specifics for each printer
are different. We will discuss the Lexmark X500n MFP and its particular method of printing.

EP Basics

The Lexmark X500n is a single laser MFP that uses four toner cartridges (Cyan, Yellow, Magenta and
Black) to create text and images on media. The MFP has one photodeveloper (called a photodeveloper
cartridge or OPC) and a transfer Unit. Each color toner is painted to the photodeveloper and to the transfer
unit one color or "image" at a time. The photodeveloper and transfer unit must rotate four times to print one
page composed of the four images for a color print job. During the printing process, the printer follows the
six basic EP process steps to create its output to the page.
These six steps are:
1. Charge the photodeveloper (OPC)
2. Expose the photodeveloper (OPC)
3. Develop toner on the photodeveloper (OPC)
4. 1st and 2nd transfer of toner to the transfer Unit and then to the media
5. Fuse toner to the media
6. Clean/Erase the photodeveloper and transfer Unit
in summary, the printer RIP board receives the command to print. The RIP board then sends a signal to the
engine controller board to start the print process. The engine controller board is the command center for the
EP process. The engine card coordinates the various clutches, motors and signals.
The high voltage power supply sends a charge to various components in the EP process. The laser fires on
the photodeveloper and creates an invisible image on the surface. One toner cartridge is pushed against
the photodeveloper for each rotation of the OPC, and toner is developed on the surface of the OPC. The
image is then transferred to the transfer unit and the photodeveloper is cleaned and electrically erased. This
process continues until all four colors have been transferred to the transfer unit.
Media is picked up from the tray and carried to the registration rollers where it stops and it is timed to enter
the EP process at just the right moment. Next, it is carried to the transfer roller where the image is
transferred from the Transfer Unit to the media.
The media is carried to the fuser rollers, where heat and pressure are applied to the page to permanently
bond the toner to the page. The fuser rollers push the media into the output bin. The transfer unit is cleaned,
and the process begins again for the next page.
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