Xerox Nuvera 100, Service Manual

Page: 65 / 304

General Information 1-65
Printing
When printing, the printer performs a “four-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; this varies from 30 to 44 rotations (30 @ 409 dpi and
44 @ 600 dpi). Each jet travels horizontally the distance of 125 to
181 pixels (125 @ 409 dpi and 183 @ 600 dpi) to lay down its 30 to
44 pixel columns within that pixel field. The 125 to 181 pixel-wide
field of each jet overlaps the pixel field of six other jets; this is where
interlacing occurs.
During the horizontal movement of the printhead, extra 1 or 2-step
movements are made to properly align the pixel columns and prevent
a column from overlapping another column. The actual number of
steps depends on the print resolution.
Physically, each jet is horizontally located 22/300 of an inch from its
neighbor.
Interlacing “averages out” the variability between jets by interlacing
each jet with three other jets. As shown in the Figure 1-28, of the
pixel columns printed by any single jet, only two of its pixel columns
are actually ever adjacent. Usually they are separated by three other
pixel columns produced by other jets, hence the name four-jet
interlace. Because of the physical spacing between jets and the pixel
field that each jet travels, the pixel columns of any one jet actually
interlaces with the pixel columns of six other jets, although no more
than four at any one time.
During some diagnostic printing, such as the Cleaning Test Print, the
printhead slews to the right and lays down 112 parallel bands of ink.
Each band is about 1.86 mm (0.073 inch) wide and is composed of 30
pixel columns of dots from an individual jet. As the printhead slews to
the right, the drum rotates 30 times; the number of pixel columns
each set of jets deposits on the drum. (A set of jets is one of the 112
vertical arrangements of low density, medium density, clear and high
density jets.) With no interlacing, the test print reveals the
deficiencies of a single jet compared to the rest. Only in the Test Print
2: Weak/Missing Jets (I-mode) and the Print Jets Test Page test print,
does the printhead simply slew sideways with no jet interlacing.