Drum/Transfix Assembly - Tektronix Phaser 380 Service Manual

5
Theory of Operation
Drum/transfix assembly
5-14 Phaser 380 Color Printer
The drum/transfix assembly forms the key portion of the printer where imaging
takes place. The main features of the drum/transfix assembly are the pressure
spring load assembly, the drum, the transfix roller mounted on an eccentric
shaft, and the latch/cam system which interfaces with I/O board 3. The load
assembly supports the eccentric shaft by springs during image transfer. The
transfix roller/eccentric shaft assembly provide the pressure for image transfer.
The latch/cam system starts and stops the transfix operation. The transfix roller
is kept in its unloaded position except during image transfer and transfix roller
oiling.
In operation, the image to be printed on paper is first "printed" on the rapidly
rotating drum. The paper pre-heater heats up the sheet of paper prior to image
transferring. The sheet of heated paper is then passed between the drum (now
rotating much more slowly) and the transfix roller.
The transfix cam solenoid on I/O board 3 is energized to release the
spring-loaded eccentric shaft cam to engage the transfix gear. The process gear
drives the transfix gear, which, in turn, rotates the eccentric shaft to the loaded
roller position in contact with the drum. Under the pressure between the drum
and the transfix roller, the image is transferred to the sheet of paper. The process
motor further rotates the transfix gears until the latch catches and stops the
eccentric shaft cam. The transfix gears are disengaged and the transfix roller is
unloaded.
An encoder wheel and sensor on the left end of the drum monitors the drum's
speed as well as its "home" position. Also necessary for printing is the drum
heater, which is similar to a hair blow dryer. It blows heats along the inside
surface of the drum to heat the outer surface to a constant 53
imaging. A temperature sensor in contact with the drum surface monitors the
drum's temperature. The main board interprets the sensor's signal and turns on
the drum heater and fan to heat the drum, or turns on the drum fan alone to cool
the drum.
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