Drive Configuration
Controller Tuning
5.4.5 Filters
Filters can be used to enhance the properties of the controller loop for example by compensating me-
chanical resonances. Although filters can improve the controller loop, filters should be applied cautious
for the following reasons:
Controller loops with filters are often more sensitive to changes to the axes.
Filters increase the complexity of the controller-loop. Therefore a robust setting is more difficult to
find.
Consider that only resonances which violate the stability criterion (see section 5.4.4) need to be
compensated.
The design of a filter should be done with the
Bode
tool based on a
Bode
measurement. Different filter
types can be selected. But in most cases
Notch2
is applied and will be described below.
Only for position measurement with poor resolution (e.g incremental encoders)
Lowpass1
or
Lowpass2
are used to smooth the signal. In this case the frequency
fd
is set 3 to 10 times the bandwidth of the
controller and for
Lowpass2
the damping
Dd
is set to 0.7. Consider that the application of lowpass fil-
ters will reduce the phase-margin and therefore affect the stability of the controller. It is recommended
to verify the stability of the controller with the
Bode
tool after a filter is modified.
Notch2
The following equation shows the transfer function of the
Notch2 filter
:
F
i
(
s
)=
ω
d
2
ω
n
2
s
2
+
2
D
n
ω
n
s
+ω
n
2
s
2
+
2
D
d
ω
d
s
+ω
d
2
with the following relation to the configuration parameters:
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Figure 57: Tuned position controller with a gain crossover frequency f
gc
of 500Hz and a phase margin of 48.2°. The
black arrows indicate the effect of parameter changes in Bode and Nyquist plot (qualitatively).
