Dell 5535dn Service Manual page 259

Detection of media size
The media size set for the media tray assembly is transmitted to the switch (media size) by moving these
guides. The media size is detected by the on/off information of these switches.
Pick arm assembly
Sensor (media empty)
Media out actuator
Sensor (media low)
Pick roll assemblies
Since all media trays are functionally equivalent in terms of the switch (media size), sensor (media empty),
sensor (media low), only the components of one tray are described here.
The pick arm assembly is a mechanical unit supplying media from the media tray assembly to the printer. The
driving force, from the pick arm drive motor on the pick arm assembly, is transmitted to the two pick rolls to
feed media.
When the pick rolls pick up media, the remaining media decreases, and the media out actuator will lower and
interact with the sensor (media low) and sensor (media empty) to determine the amount of media remaining.
The pick arm assembly (autocompensator) is a paper pick device that generates its own normal force. This
force generation is inherent in the fundamental design of the pick arm. If light media is used, it picks very
gently. If a heavy media is used, it picks very aggressively. No customer adjustments are necessary, therefore
no special trays are needed for card stock or labels. The gearing in the arm is designed so the input torque
from the motor produces a movement about the pivot of the arm. This movement produces a downward force
at the pick rolls. The friction between the pick roll and the paper produces a frictional locking condition. If the
paper is physically held and not allowed to feed, then the motor stalls. Slippage between the roll and the paper
is theoretically impossible. When the motor is energized, the pick rolls are driven down into the stack,
increasing the normal force and drive force until the bending strength of the paper is overcome and the paper
bends and moves up the wear strip.
Switch (media size)
This switch (media size) sets the size of media supplied from each media tray assembly. A signal indicating the
media size is transmitted as a voltage to the printer system card assembly.
Sensor (media empty)
If media runs out in a media tray assembly, the actuator lowers and the actuator flag, unlocks the sensing area
of the sensor (media empty). The sensor light is transmitted. When the sensing area is blocked (media is
present), the signal is off.
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Diagnostic aids