ADLINK Technology PCI-8254, User Manual

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90 Motion Control Theory
4.2.4.2 Notch Filter
Notch filter is aimed at eliminating specific resonance frequency.
The later occurs when frequency of servo response is close to the
Natural frequency of the mechanic system. Take example.
Resonance is usually found in servo motor mechanism with two or
more coupling motors. When running with one servo motor, there
shall be no vibration. When both axes servo excite operation at the
same time then vibration (resonance) come up.
See Figure below for an ideal notch filter. Where Fc represents the
Cutoff frequency, Fl the Low pass cutoff frequency, and Fh the
High pass cutoff frequency. The passable frequency band is the
Pass band and the attenuated frequency band the Stop band.
Let's explain this effect with one example. Assume a notch filter
with cutoff frequency at 100Hz, low pass cutoff frequency at 95Hz,
high pass cutoff frequency at 105Hz, sampling time at 100
microseconds, and derived coefficients A1 at 32767, A2 at -16398,
B0 at 16415, B1 at -32767, B2 at 16415 and DIV at 16433. See
Figure 7 for simulation results from sine curves at different
frequency. This figure indicates that when input signal is a 50Hz
and 200Hz sine curve it passes the filter with amplitude and phase
remains intact. But for input of 100Hz sine curve the amplitude is
attenuated and the phase delayed significantly.
Figure 4-12: An ideal notch filter (a) 50 Hz
Pass band Pass band
Stop band