Discrete time adaptive controller for suppression of resonance in hard disk drive servo system

Mechanical resonant modes of the actuator severely impede the efforts in achieving high precision in head positioning servo system of hard disk drives (HDD). Hence it is important that these modes be properly compensated. The conventional approach is to use a notch filter in cascade with the nominal controller, which works well if the resonant frequencies are known and do not vary during operation. However, in reality, frequency and damping ratio of the resonant modes vary in mass-produced systems. They also get changed over time due to wear and tear. As a result, auto-tuning or adaptation of the notch filters is required to maintain the performance at the same level. In this paper, a discrete time adaptive controller is presented in a simple and yet efficient way to suppress the effects of resonant modes. Effectiveness of the proposed compensator is demonstrated through simulation and experiments by implementing the compensator for a Voice Coil Motor (VCM) actuator used in HDD.