Ribbon Deck - Printronix P9012 Maintenance Manual

Ribbon Deck

(Figure 2–22 through Figure 2–24)
The ribbon deck assembly contains two dc servomotors that move the ribbon
continuously while there is shuttle action. One motor acts as the driver,
drawing the ribbon against opposing torque exerted by the other motor.
When a length of metal tape at either ribbon end is detected by the ribbon
guide at either side of the shuttle, the two motors exchange roles and ribbon
travel is reversed. This system maintains a relatively constant ribbon speed
and tension.
The ribbon moves only while the shuttle is in motion. When the printer is on
and no faults have occurred, the ribbons will be tensioned by the application
of NRIBEN from the MCU PCBA. When NRIBMOV is applied, the ribbon
will move. NRIBMOV is applied when DCMOD comes on starting the
shuttle.
The NRIBMOV and NRIBEN signals enable gates which control power to
the ribbon drive motors.
When an end of ribbon sensor is activated, the corresponding latch turns on
the related FET.
When the right end of the ribbon is detected, the latch is set to the opposite
state and the motors reverse roles.
When the shuttle motor is not running, that is, DCMOD not modulating and
NRIBMOV is high, both FETs are held off and the motors act in opposition,
as the voltage provides feedback to resist ribbon movement, provided
NRIBEN is not deactivated by a printer fault.
NRIBENMOV
NRIBEN
RIGHT
DETECTOR
LEFT
DETECTOR
2–32
+36V
RIBBON
DIRECTION
CONTROL
Figure 2–22. Ribbon Deck Block Diagram
RIBBON
+5V DC MOTOR
DRIVERS
Principles of Operation
M
M