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Digital Microprocessor Subsystem
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The digital microprocessor subsystem is a part of the control board. All analog signals are converted
to digital form, and the 16-bit microprocessor on the control board handles all Motor control
functions in the digital domain. Since analog circuits are eliminated, there are no pots to adjust, no
operational amplifier circuits to tweak, and no soldering or component changes are required. The
digital microprocessor receives commands from the outside world in either analog or digital form,
depending upon the selected interface option. The command parameter can be position, velocity, or
torque. The digital microprocessor compares the commanded variable with the actual measured
value of the controlled variable, and makes small corrections continuously so that the Motor always
obeys the command. The digital microprocessor receives its feedback information from the
Motor’s built-in resolver via the resolver interface circuit subsystem. Digital filters may be applied
which alter Motor behavior to improve the repeatability, or to eliminate mechanical resonances:
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A digital integrating function may be selected which improves the repeatability of the
Motor by making it respond to very small command signals. With the integrator, the Motor
can provide zero position error even under full load torque.
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A digital notch filter may be employed to cut out certain frequencies from the Motor
response so that mechanical resonances will not cause the Motor to oscillate. If the Motor
is attached to a load which has a strong natural frequency of oscillation, the Motor can be
made insensitive to it merely by setting the notch frequency to the same frequency. A
100Hz resonance can be eliminated, for instance, simply by initializing the Driver Unit
with the RS-232C command “NP100”.
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A digital low-pass filter may be employed to modify Motor frequency response and make
the Motor smooth and quiet. Again, the low-pass filter is implemented digitally, and setting
up the filter frequency is as simple as asking for it. There are two independent low-pass
filters available.
Brushless Microprocessor Commutation
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The digital microprocessor uses the digitized position information obtained from the resolver
interface to determine when to apply current to the Motor phases, and how much. The amount of
current applied to each Motor phase is determined by a mathematical function that takes into
account the torque command level, the Motor position, and the Motor velocity. These factors are
taken into account to compensate for the Motor non-linearity and to produce a smooth output
torque.
Power Amplifier Subsystem
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The Motor windings are driven by a current regulated unipolar switching power amplifier that
delivers the current designated by the commutation logic circuits to each of the Motor phases. The
power amplifier monitors its internal voltages to protect itself from damage. If the AC line is too
high or too low, the power amplifier will disable itself and activate alarm indicators. If the amplifier’s
internal DC bus voltage is too high as a result of Motor regeneration, the monitor circuits will switch
on a power resistor to dissipate some of that excess energy. If the power amplifier temperature is
too high, it will activate an alarm signal. For any of the alarm conditions, the type of the alarm is
communicated back to the digital microprocessor, which activates the alarm condition indicators to
identify the specific nature of the alarm condition.
Resolver Interface Subsystem
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Position and velocity feedback signals are provided by the resolver interface circuit. This circuit
provides the excitation signal to the resolver, and receives the three phase resolver analog signals.
These signals are decoded by the resolver-to- digital converter (RDC) to produce digital cyclic
absolute position and velocity feedback signals. The cyclic absolute position data is used by the
commutation circuits and is used internally to maintain absolute position data.
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