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Theory of Operation 33
THEORY OF
OPERATION
Croma24 Service Manual
Stepper Motor Controller
Figure 2-6. Stepper Motor Controller.
The media is driven by a Stepper Motor, which drives the media in
a direction perpendicular to the length of the printer. The media
in the printer can advance forward and backward, depending upon
the commands which the Stepper Motor receives from the micro-
processor.
The Stepper Motor Controller contains two identical circuits, one
for each winding of the stepper motor. The circuit is a combination
of two simpler types of circuits and can be thought of as a variation
of either one.
A digital-to-analog (D/A) converter receives digital data from the
CPU and generates a sine wave output. This signal is fed into a
comparator circuit that measures the current through the winding
of the stepper motor. If the current is too low, a pulse of 24 V is
generated. When the current goes above the output of the wave-
form generator, the pulse turns off. Every time the output of the
waveform generator is changed by the microprocessor, the motor
moves 1 “micro-step”.
Each circuit contains four main blocks (see Figure 2-6):
1. Reference waveform generator
The microprocessor uses a D/A (digital to analog) converter to
set the desired level for the current in the stepper motor
winding. The output of the D/A converter varies in time to
create a reference waveform. This reference waveform is
centered around 10 V.