Instruction manual

6–17
Principles of Operation
peripherals are automatically reset. The timer interval is set through software
and has a range of 25.6 sec to 419 ms; default setting is 6.55 ms.
Analog Drive Circuitry
The analog drive functions convert 48 and 8.5 volts into the power used to
drive the motors and hammers in the printer. Sensors are used to monitor the
operation and status of critical components within the printer.
Five motors are used on the printer: paper feed, two ribbon drive, shuttle, and
platen open. The shuttle motor is a brushless DC motor, driven by current
control. The MPU encoder is used as feedback for motor commutations,
hammer fire timing, and motor stall detection. The paper feed motor is a DC
stepping motor driven by current control. The paper feed motor may be
driven in full, half, or microsteps, depending on print requirements. The
ribbon system uses two DC stepping motors that alternate drive and drag
roles when the ribbon reaches turn–around. The drive ribbon motor is
microstepped in voltage mode, while the drag motor is loaded and monitored
to maintain correct linear speed and tension. The platen open motor is driven
in current mode and can be full or half stepped. The overall current level may
be reduced for standby modes.
The paper feed, ribbon drive, and shuttle motors are driven in control loops
containing power MOSFETs, voltage and current sensors, the MECA ASIC,
and the EC processor. The platen open motor is driven by a stepping motor
controller IC and the EC processor.
Control of hammer drive is split between the controller board and the
hammer bank. Common circuits are located on the controller board, while
hammer specific circuitry is contained on the hammer bank. The controller
board sets the timing and upper drive profile for driving a hammer fire event.
The controller also contains diagnostic circuitry for the hammer system. The
hammer bank contains HBA ASICs that interpret fire commands and data
from the MECA and VX ASICs. The HBAs control lower drive MOSFETs
on the hammer bank. These determine which hammers will participate in a
fire event generated by the controller’s upper drive.