Drum Preparation - Tektronix Phaser 340 Service Manual

5
Theory of Operation
5-20 Phaser 340 Color Printer

Drum preparation

To prepare the drum, a release agent is applied to the surface of the drum. First
the drum is rotated to a speed of 51 cm per second (20 inches per second). Next,
the wick and blade of the maintenance tray are raised into contact with the
drum. To accomplish this, the process motor rotates clockwise, driving the
process drive belt and the one-way clutch compound gear. Rotating clockwise,
the compound gear's clutch drives a gear train that drives the maintenance
tray's 3-position clutch which, in turn, engages the maintenance tray camshaft.
The maintenance tray camshaft solenoid (on I/O board 1) energizes to release
the 3-position clutch, allowing it and the camshaft to rotate about one-half
revolution to the next stop. The cams on the ends of the camshaft push against
followers on each side of the maintenance tray, forcing the wick and blade
against the drum. The de-energized solenoid then holds the clutch and camshaft
in this position.
As the drum nears the end of its rotation, the solenoid energizes for a moment,
allowing the camshaft to rotate further; this lowers the wick but leaves the blade
in contact with the drum to smooth out the last of the oil on the drum.
The solenoid energizes for a third time to allow the camshaft to rotate to its
home position, and lower the blade. The point at which the blade ends contact
with the drum it leaves a bead of oil, called an oil bar. The oil bar defines the
edge of a 40 mm (1.5 inch) swath of the drum which is not oiled; this swath is
called the deadband. No ink will be deposited on the deadband during the print
cycle. Instead, the paper stripper fingers, which lift the paper off of the drum
during printing, are lowered into contact with the drum in the deadband. This
keeps them from accumulating any oil on their fingertips which would stain the
edge of the print as it is stripped off of the drum.