Indirect-driven Self-sensing Actuation for Dual-stage Hdds with Improved Robustness

Introduction An ever increasing need for data storage and a escalating demand of small computing machines have led to the development of Hard Disk Drives (HDDs) towards extremely high recording density and reduced form factors. The requirement of diminutive Tracks-Per-Inch (TPI) in HDDs has necessitated the use of dual-stage actuator for fine positioning of Read/Write (R/W) head as well as expanding the servo bandwidth. Dual-stage actuation using LeadZirconium-Titanate (PZT) active suspensions has currently been employed in commercial enterprise or desktop HDDs. Self-Sensing Actuation (SSA) [1] [2] employs the PZT elements as an actuator and displacement sensor simultaneously. SSA scheme is promising as the actuator and sensor arrangement is nearly collated and it can help save the cost from extra sensor. A specially design electronic circuitry [3] was used to extract the variable voltage produced by the PZT elements, which contains the useful displacement information. However, the bridge circuit is very hard to be balanced due to changes in the capacitance of PZT elements caused by temperature variations [4]. In this paper, an Indirect-Driven SSA (IDSSA) methodology is proposed to achieve higher Signal-Noise-Ratio (SNR) at nanometer resolution and robustness against variations. The whole scheme is demonstrated in a commercial dual-stage HDD.