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Behavior models used in CIP Motion
Chapter 2
Rockwell Automation Publication MOTION-RM003I-EN-P - February 2018
77
The following filters can be applied to provide additional compensation and
control to the torque value.
Lead-Lag Filter
A lead-lag filter is provided in the torque reference path. This filter can be used in
the lead configuration to boost velocity or acceleration loop bandwidth, or in the
lag configuration to compensate the high frequency gain boost associated with
compliant load mechanics.
In this equation, Kn represents the Lead-Lag Filter Gain, or high frequency gain of
the filter (the low frequency gain is always 1), and wn represents the Lead-Lag
Filter Bandwidth associated with the pole of the filter:
•
If Kn > 1, the filter provides lead compensation.
•
If Kn < 1, the filter provides lag compensation.
•
If Kn = 0 the lead-lag filter becomes a pure low pass filter.
•
If Kn = 1, the filter is disabled.
When used as a lag filter (Kn < 1), this filter can be effective in compensating for
the gain boosting effect of natural mechanical resonance frequencies that are
within the acceleration/velocity loop bandwidth.
Low Pass Filter
The Low Pass Filter is effective in resonance control when the natural resonance
frequency is much higher (>5x) than the control loop bandwidth. This filter
works by reducing the amount of high-frequency energy in the device output that
excite the natural resonance. The Low Pass Filter design can be single pole or
multiple poles. Care should be taken, however, to limit the amount of phase lag
introduced by this filter to the control loop to avoid potential instability.
Notch Filter
The notch filters are effective in resonance control when the natural resonance
frequency is higher than the control loop bandwidth. Like the Low Pass filter, the
notch filter works by significantly reducing the amount of energy in the device
output that can excite the natural resonance. It can be used even when the natural
resonance frequency is relatively close to the control loop bandwidth. That is
because the phase lag introduced by the notch filter is localized around the notch
frequency. For the notch filter to be effective, the Notch Filter Frequency has to be
set very close to the natural resonance frequency of the load.
Torque filters
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