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Principles of Operation
Paper Motion The DPU determines when paper must be moved and how far
to move it. It communicates this to the RTPU through the shared memory.
The RTPU processor performs some paper handling operations (such as
holdback on slews), but most RTPU paper handling is done by a dedicated
microcontroller called the paper feed controller (PFC).
The PFC moves paper by looking up motion profiles and driving a sequence
of motor positions to the mechanism driver board. If the motion is a dot row
or interline advance, it is synchronized to hammer firing by a signal from the
FTIC that tell the PFC when to move.
Ribbon and Shuttle Motion The ribbon and shuttle motors are controlled
by a microcontroller on the mechanism driver board. The RTPU interface to
the ribbon/shuttle processor (RSP) is a 2400 baud asynchronous serial line. A
message protocol is used to communicate ribbon and shuttle information.
Fault Monitoring
The RTPU also monitors the hammer driver, mechanism driver, and the
electro–mechanical sensors for fault conditions. Fault conditions are reported
to the DPU.
Hammer Bank and Hammer Driver Faults
The FTIC works with the hammer driver ASIC to monitor coil shorts, opens,
average upper driven phase current, and temperature conditions. The RTPU
reads the FTIC registers to determine out–of–range conditions, and these are
passed on to the DPU.
Paper Faults
Two kinds of paper faults can occur: paper out and paper jammed. Both of
these conditions are monitored through optical sensors. The paper feed
controller watches the paper out and paper motion sensors and reports errors
to the RTPU. The RTPU passes this information on to the DPU.
Ribbon and Shuttle Faults
The mechanism driver ribbon and shuttle controller monitors fault conditions
in the drive circuits and notifies the RTPU if it finds errors. The RTPU can
also use the FTIC to measure time between magnetic pick–up (MPU) pulses,
enabling it to monitor shuttle speed and thus detect some shuttle faults.
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