124 Theory of operation EN
Multiple-feed prevention mechanism
The printer uses the separation roller in tray 2 to prevent multiple-feeding. Normally, the separation
roller rotates in the same direction as the feed roller. The separation roller is equipped with a torque
limiter, but because the force of the feed roller exceeds that of the torque limiter, the separation roller
is actually driven by the feed roller.
If multiple sheets of media are picked up, however, the low friction force between the sheets weakens
the rotational force from the feed roller to the separation roller. Consequently, the torque limiter takes
control of the separation roller, and rotates the separation roller in the reverse direction, which
removes the extra sheets.
Figure 34. Multiple-feed prevention mechanism
Printing from the optional 500-sheet tray
Note The HP LaserJet 4100 series printers support up to two optional 500-sheet feeders.
The operation sequences of the paper feeder are controlled by the paper-feeder driver. A 4-bit
microprocessor is used in the paper-feeder driver, which controls the paper feeder sequences and
the communication with the engine controller board. The engine controller board sends the pickup
command to the paper-feeder driver with the necessary timing.
The paper-feeder driver drives the solenoid in response to the pickup command. The paper-feeder
driver also returns the status of the paper feeder to the engine controller board.
A charge of +24 VDC is supplied to the paper feeder from the printer, and +3.3 V for the integrated
circuits is generated from +24 VDC inside the paper-feeder driver.
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