For those who have or will struggle with resonances in your control systems, Galil has produced App-note #3502 "Using Notch Filters to Mitigate Resonance."  This note discusses the different types of resonances and what can be done to deal with them.  In particular it explains two ways to use the notch filters available in Galil controllers to solve resonance issues in real-world applications.

For the full application note, see Application Note 3502.