Ribbon Motor Drive; Paper Feed Motor Drive; Carriage Drive And Ribbon Drive Circuits - Centronics 351 Technical Manual

FWD
TACH
GRAPHICS
FREQ.
TD
VOLTAGE
CONVERTER
REV
CHI
CH2
01227
SHAFT
ENCODER
RIBBON
CASSETTE
Figure 2-4 Carriage Drive and Ribbon Drive Circuits
An H·Pattern driver operates the permanent
2.12.2 RIBBON MOTOR
DRIVE-Ribbon drive is
magnet DC motor. A closed loop, pulse-width accomplished with a 12V DC motor, controlled by
modulated speed control miiintains the print head a single-stage (transistor) drive amplifier as shown
velocity at one of two set speeds. A pulse-width in Figure 2·3. This motor will be on whenever the
modulation circuit is used to minimize transistor print head is commanded to move. A diode con-
head sink requirements by operating the tran- nected across the motor is used to protect the
sistors in a saturated mode rather than in a linear transistor driver.
mode.
To limit the acceleration motion of the carriage,
a current limiting circuit is used to shut down the ·
motor drive if the motor is activated and no
tachometer (TACH) pulses are received within 40
milliseconds. Gating circuitry prevents adjacent
legs of the H pattern from conducting
simultaneously.
3510-9800 2-6
2.12.3 PAPER FEED MOTOR
DRIVE-Figure 2-4
shows a simplified schematic of the driver cir·
cuitry for the paper feed stepper motor. A pick and
hold circuit is employed to get performance (high
pick current) and low standby current (low hold
current) with the bipolar, stepping motor used for
paper motion. A chopper maintains the current
level in the stepper motor. The pick signal sets a