Relationship between flying-height and tracking-position control with thermal actuators for magnetic heads in HDDs

To increase a servo bandwidth of a head-positioning control system in hard disk drives, a triple-stage actuator system was developed with thermal actuators. This positioning control system consists of a voice coil motor (VCM), piezoelectric (PZT) actuators, and a thermal-positioning actuator. The thermal-positioning actuator is good for control in high frequency range because it has little negative impact caused by mechanical resonances. However, the thermal-positioning actuator causes flying-height fluctuations that may lead to worsening of the magnetic recording performances. To overcome this issue, this paper presents a control system that employs the feedforward control scheme on a thermal flying-height control system. Simulation results showed that the proposed method was able to compensate for the flying-height fluctuations during the track-following control by about 87 %.