Laser Imaging; Overview - Tektronix PHASER 560 Service Manual

5
Theory of Operation

Laser imaging

Overview

5-4 Phaser 560 Color Printer
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The laser printer prints an image on paper using a technique called laser
electrophotography . The printer uses the electrographic process known as
Discharged Area Development or "write black." In this process, a digitally
modulated laser, scans laterally across a negatively charged, rotating
photoconductive belt. Where the belt is exposed by the laser beam is where the
image is written and toner is transferred.
In the color print process, the photoconductive belt rotates past the laser scanner
and the toner cartridges four times, once for each primary color and black.
During each sucessive pass, the laser exposes the portions of belt that
correspond to the primary color's component of the image. Toner is attracted to
the laser-exposed portions of the belt. As the photoconductive belt rotates it
passes the accumulator belt. As the name implies, the accumulator belt
accumulates or picks up each primary layer of toner from the photoconductive
belt and holds it, layer upon layer, until it contains the entire image. At this
point, a sheet of paper is advanced past the accumulator belt and the toner is
transferred to the sheet of paper. The paper advances to the fuser where heat
and pressure permanently bond the toner to the paper. From the fuser, the
paper is driven to the output tray.
A photoconductive belt cleaning blade scrapes residual toner off of the belt
before the next primary color's toner is applied to the belt. This prevents each
toner from contaminating the next color's layer. The cleaning blade is in
constant contact with the belt. An accumulator belt cleaner scapes residual toner
off of the accumulator belt. This prevent an image from one print contaminating
or "ghosting" on the next print. The blade only comes in contact with the belt
once the accumulated toner layers are transferred to the sheet of paper.
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