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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 force. 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 force command level, the Motor position, and the Motor velocity. These factors are
taken into account to compensate for the Motor non-linearlities and to produce a smooth output
force.
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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