Printronix L5535, Руководство по обслуживанию

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Tractor Motor Control Circuit
II–189
Data output from the digital control circuit is equivalent to 1 V per 1 bit, and at
the D/A converter, –8 to +8 V are output, corresponding to inputs of 0000 to
1111. (Note that 0000 corresponds to 0 V). This is the voltage calculated from
pulse string comparison, but different outputs are required for positive
rotation, negative rotation, and detent (holding position). Therefore, there are
3 variable resistors connected to the D/A converter, so that the voltage can be
adjusted to obtain the correct output for the positive, negative, and detent
states. Depending on whether the motor is in the positive, negative, or detent
state, the analog switch connected to these variable resistors is switched
accordingly by the PFEED (positive rotation), PBACK (negative rotation), or
PDNT (detent rotation) signals, and the proper control voltage is thus
obtained.
For the positive rotation, negative rotation, or detent conditions, the driver
circuit is controlled by a linear system composed of an operational amplifier
supplied from +24 V and –24 V power sources, which controls rotation speed
by negative feedback of current that has flowed through the motor, to the
input side.
Further, to stop the motor, the voltage is set to adjust motor torque and
maintain the position such that the Z phase of the encoder is detecting a slit. If
the Z phase of the encoder is not detected, and A phase and B phase pulses
are detected, then current is sent to the motor that will cause as many back
rotations as pulses detected.