3-64 Service ManualThe media size set for the media tray assembly is transmitted to the switch (media size) by moving theseguides. The media size is detected by the on/off information of these switches.Pick arm assemblySince 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. Thedriving force, from the pick arm drive motor on the pick arm assembly, is transmitted to the two pick rolls to feedmedia.When the pick rolls pick up media, the remaining media decreases, and the media out actuator will lower andinteract 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. Thisforce generation is inherent in the fundamental design of the pick arm. If light media is used, it picks verygently. If a heavy media is used, it picks very aggressively. No customer adjustments are necessary, thereforeno special trays are needed for card stock or labels. The gearing in the arm is designed so the input torquefrom the motor produces a movement about the pivot of the arm. This movement produces a downward forceat the pick rolls. The friction between the pick roll and the paper produces a frictional locking condition. If thepaper is physically held and not allowed to feed, then the motor stalls. Slippage between the roll and the paperis 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 paperbends and moves up the wear strip.Sensor (media low)Sensor (media low)Media out actuatorMedia out actuatorPick roll assembliesPick roll assembliesSensor (media empty)Sensor (media empty)
