Printhead; Figure 5-5 The Printhead - Tektronix Phaser 340 Service Manual

5
Theory of Operation

Printhead

The printhead is the heart of the printer. The printhead spans nearly the length
of the drum. Using its 352 ink-jet nozzles (88 jets for each primary color), with
just a horizontal motion of slightly less than 5 mm (0.2 inches), the printhead can
print the entire image on the rotating drum. The printhead produces two sized
drops of ink: a large drop for 300 dpi printing and a smaller drop for 600 dpi
printing.
Drum
Reservoir
Jet stack
Head drive board
9100-16

Figure 5-5 The printhead

The printhead's jet stack is fabricated from a stack of chemically etched steel
plates which are brazed together to form the ink-jet array. Channels formed by
the stacked plates route ink past the 352 individual, piezoelectric crystal-driven
diaphragms, which force the ink in droplets out the 352 corresponding nozzles.
Looking at the printhead face, the nozzles are arranged in four rows with the
yellows nozzles forming the top row, the magenta nozzles forming the next row
24 pixels below, and the cyan row forming the third row 24 pixels below the
magenta row. The black nozzles are located 12 pixels below and 2 to the left of
the cyan nozzles. Each nozzle is separated horizontally by 28 pixels. (Pixel
spacing is at 300 pixels per inch.) During the printing process, the printhead
travels 28 pixels horizontally to provide complete coverage.
The ink-jet array is bonded to a cast aluminum ink reservoir. The reservoir
supplies the molten ink to the ink-jet array. Heaters in the reservoir and the
o
ink-jet array maintain the ink at a temperature of about 140 C for printing. The
level of the ink in the reservoir is kept at a constant level. The level is detected
by a sensor probe which senses the conductance of the ink at the probe tip.
Service Manual 5-7