Robust H∞ compensation for external vibration on hard disk drives in mobile applications

Compensation for external vibration impact on the positioning accuracy of hard disk drives is considered with the presence of actuator uncertainty in this paper. The low-frequency mode change due to actuator pivot nonlinearity of the voice-coil- motor (VCM) actuator is described as frequency and damping uncertainty. A robust feedforward controller is then designed in continuous time domain by using H infin method to attenuate the impact with the aid of a sensor to detect external vibrations. The linear matrix inequality (LMI) approach is adopted to solve the robust H infin feedforward control design problem. The application results in a 1.8-inch disk drive with an accelerometer to measure acceleration signal show that 27% to 91% reduction of the position error signal is achieved with the robust feedforward controller when the frequency changes in 70 plusmn 50 Hz and damping in 0.4 plusmn 0.3. The effectiveness of the robust feedforward control is also demonstrated to be better than nominal feedforward control.