ElmoMC SimplIQ Digital Servo Drives-Bell Getting Started - Manual (Page 89)

The SimplIQ for Steppers Getting Started & Tuning and Commissioning Guide
MAN-BELGS (Ver. 1.1)
89
3 4 5 6 7 8 9 10 15 20 30
-70
-60
-50
-40
-30
-20
d
B
3 4 5 6 7 8 9 10 20 30
-180
-160
-140
-120
-100
-80
-60
-40
d
e
g
ω
Figure 82: Bode plot of a motor with flexible load (resonance model)
At low frequencies, well below the oscillations, the transfer function rolls down
with a fixed slope and fixed phase angle. This behavior is due to the double
integration that relates the system position to its torque input. At the higher
frequency axis, Figure 82 presents two well-known phenomena. The first, at the
frequency of 10, is called anti-resonance. At this frequency torque is passed from
the motor to the load and the load oscillates wildly, but hardly any motion is
seen on the motor shaft. This is the frequency in which the load would freely
oscillate if the inertia of the motor were infinite. The second, at frequency 11, is
the resonance. In the resonant frequency the motor and the load oscillate about
each other, in opposing directions.
The anti-resonance and the resonance are well seen also in the Nichols chart
below. At the anti resonance frequency, about
10
= ω , the plot has a minimum
on the dB scale and the phase increases. At the resonant frequency of 11
= ω , the
plot attains a maximum on the dB scale, and the phase drops again.
-360 -315 -270 -225 -180 -135 -90 -45 0
-80
-70
-60
-50
-40
-30
-20
-10
0
d
B
deg
ω=1
ω=2
ω=4
ω=6
ω=8
ω=10
ω=10.5
ω=11
ω=16
ω=30
ω=60
L(j ω)
Figure 83: Nichols plot of a motor with flexible load (resonance model)