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2-24 Phaser 8400/8500/8550/8560 Color Printer Service Manual
Theory of Operation
Printing
To print, the Drum rotates at a speed dependent upon print resolution. As the
Drum reaches the correct speed, the jets begin to fire to deposit the image on
the oiled portion of the Drum. As the jets fire, the Printhead moves from right
to left to complete the image on the drum.
When printing, the printer performs a “six-jet interlace”, in which each jet lays
down a particular number of pixel columns, depending on the print resolution.
Each jet lays down one pixel column for each Drum rotation, which varies from
eight to 16 rotations, depending on the print resolution. Interlacing “averages
out” the variability between jets as it interlaces each jet with other jets. In
some test prints, the Printhead moves to the right and lays down 309 parallel
bands of ink. Each band is composed of 15 pixel columns of dots from an
individual jet.
Jet substitution allows a better performing jet to be used in place of a missing
or poorly performing neighboring jet. When the printer is in the jet substitution
mode, the Printhead makes a second, right to left movement to deposit the
pixel columns of the substituted jets. See
“Jet Substitution Mode” on
page 6-12.