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Tractor Motor Control Circuit
The tractor motor controls the transport of fanfold paper and determines print
accuracy. Since the CPU must therefore constantly control the operation of this motor
along with the printing process, a stepping motor for driving the tractor is driven by
clock pulses generated by the CPU (driving frequency: 3333.333 Hz).
A 200-step hybrid type stepping motor is used as the tractor motor and is driven by
1–2 phase excitation at a driving frequency of 3333.333 Hz. With regard to the
precision of paper transport by the tractor, a high resolution of 0.0211667 mm (1/1200
in) per clock pulse is realized by an 8-pin high-precision tractor and a high-precision
gear train. In the case of a 400 dots per 25.4 mm (400 dpi) printer, 1 raster period of
the LED is generated by 3 clock pulses of the tractor motor to digitally link the write-in
to the LED head with the feeding of paper.
Electrical System and Adjustments
Timer interrupt
Stepper motor driver circuit
(constant-current chopper type)
Figure 3–26. Tractor Motor Control Block Diagram
CPU
Clock pulse
generation
Tractor motor
3–47
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