Improving Stability Margins of Rotational Vibration Feed-Forward Compensator

This work focuses on stability analysis and design for rotational vibration feed-forward (RVFF) compensator for hard disk drive (HDD) servo control system. We consider the effect of the coupling phenomenon between the voice coil motor (VCM) control current and the rotational vibration acceleration measurements. The coupling creates an undesirable feedback loop, which affects stability of the RVFF compensator as well as it limits the achievable system performance. In this work we present a method for the parasitic coupling mitigation. This method uses self-induced coupling vibration prediction to remove the coupling signal component from the rotational vibration (RV) acceleration measurements. We consider linear time invariant coupling estimator, which is more appealing for analysis in frequency domain, as well as its nonlinear adaptive version, which is more suitable for robust operation in uncertain environment.