Abstract
In HDD single stage servo system that uses Voice Coil Motor (VCM) as the only actuator, the sensitivity hump appears unavoidably due to the Bode's Integral Theorem (BIT), resulting in amplification of disturbances at high frequency band. This paper studies the sensitivity limitation in HDD dual-stage servo system. A low relative degree micro-actuator controller and the compensation method termed "Near-Perfect Modeling" (NPM) for both poles and zeros of the micro-actuator is used to suppress the sensitivity hump to as low as possible. Experimental results show that the sensitivity hump of the dual-stage servo loop can be reduced to very close to 0 dB. As such, high frequency disturbances would not be amplified by the servo loop and the Track Mis-Registration (TMR) would be reduced.
