Paper Feed Control Circuits Block Diagram - Printronix p300 Maintenance Manual

2–6. Paper Feed State
o. Paper Feed Control Circuits (Figure 2–36)
The paper feed motor contains two pairs of coils, driven in sequence. As the electromagnetic detent lock-
ing 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 two phase paper feed signals, PF1 and PF2, generated in paper feed
logic. Each pair of PF1/PF2 pulses increments the motor one step to advance paper one dot row.
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 from
the velocity PROM 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 and PF2 at a frequency regulated by addressed velocity
PROM content.
PF1 and 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.
PF1
NPFD
PF2
Figure 2–36. Paper Feed Control Circuits Block Diagram
P300/P600 Principles of Operation
–continued
CURRENT
DRIVER
CURRENT
DRIVER
PFM1
PFM2
TO PAPER
FEED MOTOR
PFM3
PFM4
2–55