550-sheet tray Sensor A Sensor B
Tray full unblocked unblocked
Tray low blocked blocked
Tray empty blocked unblocked
Note: Media size sensing through sensor blocking sequence
Pick arm assembly
# Sensor A
1 Media out actuator
2 Sensor (media empty)
3 Pick roll assemblies
4 Sensor (media low)
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.
4062
Appendix C: Theory of operation
547
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