Printing - Xerox Phaser 8400 Service Manual

Printing

To print, the drum starts rotating 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 by interlacing 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 jet substitution mode is used, the printhead
makes a second, right to left movement to deposit the pixel columns of the jets being
substituted. Refer to "Jet Substitution Mode" on page 6-9.
Service Manual 2-25