Yaskawa LEGEND-MC - Manual (Page 46)

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LEGEND-MC User’s Manual
Resonance shows up as a pair of complex poles with a real part. A notch filter attempts to cancel the
unwanted poles by placing zeroes on top of them and placing new poles in a more desirable location. The
following diagram shows the pole-zero configuration of a general system with resonance and a notch
filter:
A notch filter can be extremely helpful when used properly, however it is not right for every system.
Incorrect placement of the Notch can cause system instability, and a notch filter puts extra overhead on the
CPU of the controller. A general rule of thumb is to only use a notch when resonance has been found that
cannot be eliminated with the controller’s standard PID filter of the controller. Also, the notch filter is
only effective with a single resonant frequency.