PERFORMANCE
17
given step rate. When the step rate matches, or is a sub-harmonic of the mechanical
resonant frequency of the motor, the vibrations become severe.
Microstepping divides full step positioning into 'microsteps'; decreasing the magnitude of
the reaction torque generated. This results in a decrease in resonant vibration.
Another benefit of microstepping is an increase in the number of resolvable angular
positions. However, there are a number of factors that limit the achievable open-loop
accuracy of these positions. See the topics under Accuracy, beginning on page
X
23
X
for
further details.
ANTI-RESONANCE
Most step motors are prone to parametric instability or resonance when rotating at a rate
of 4 to 15 revolutions (800 to 3000 full steps) per second. The CN0165 incorporates a
mid-band anti-resonance compensation circuit to close the loop on this instability and
damp it out electronically.
Called mid-band instability or resonance, this phenomenon appears as a torsional
oscillation of 50 to 150 Hz while the motor is running in this speed range. The torsional
oscillation has a tendency to increase in amplitude with time until it reaches a peak equal
to the step angle of the motor. When this happens, the motor loses synchronization and
stalls.
Generally, the amplitude buildup takes from tens of cycles to hundreds of cycles to reach
this level. Several seconds may elapse from the start of the oscillation until the motor
actually stalls. Usually this is long enough to allow the motor to accelerate through this
region. Continuous operation in this speed band is impossible.
SUPERIOR M062-FD04
RAPIDSYN 34D-9208A
SIGMA 20-2350-28175
0
50Hz
100Hz
150Hz
5KHZ
10KHz
1.8 DEGREE STEP RATE
R
ESO
N
A
N
T
F
R
EQUEN
C
Y
Figure 8 - Resonance
Summary of Contents for CN0165
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