Printronix P9012, Maintenance Manual

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2–34 Principles of Operation
Paper Feed Control Circuits
(Figure 2–25 and Figure 2–26)
The paper feed motor contains two pairs of coils, driven in sequence. As the
electromagnetic detent locking the rotor is released, the rotor is advanced one
increment, and the detent is set again. One pair of coils is driven by the
push–pull signal, PFM1/PFM2, and the other pair by PFM3/PFM4.
The drive signals are controlled by the four phase paper feed signals, PF1,
PF2, NRUN1, and NRUN2 generated in paper feed logic. Each pair of
PF1/PF2/NRUN1/NRUN2 pulses increments the motor one step to advance
paper 1/288 inch.
When paper is to be advanced either to the next character line, to the top of
form, to a selected vertical tab or by being put under EVFU control, the
corresponding profile of paper movement velocity is selected by the MCU to
obtain precise paper control. Paper is accelerated at a variable rate to
optimize both speed and precision and decelerated at a variable rate that
prevents overshoot. To achieve this modulated paper movement, paper feed
logic generates PF1, PF2, NRUN1, and NRUN2 regulated by the velocity
profile software.
NRUN1/PF1 and NRUN2/PF2 each drive identical independent control
circuits. Either circuit operates when the paper feed pulse passes through
gates and drives a push–pull current amplifier circuit that provides drive
current to one pair of motor coils.
CURRENT
DRIVER
CURRENT
DRIVER
PFM1
PFM2
PFM3
PFM4
NRUN1/PF1
NRUN2/PF2
TO PAPER
FEED MOTOR
Figure 2–25. Paper Feed Control Circuits Block Diagram