Piezo-based milliactuator on a partially etched suspension

This paper describes a piezo-based “moving-suspension” secondary actuator (called milliactuator) which provides increased servo bandwidth and reduced track-misregistration in a hard disk drive. The milliactuator comprises a pair of piezo-elements driving a relatively thick loadbeam that is partially etched in selected areas to form a honeycomb like structure. Partial etching allows more freedom in optimizing mass and stiffness to enhance the milliactuator dynamics. For a 18 mm (swage to dimple) milliactuator head gimbal assembly (HGA) with load/unload tab, we were able to achieve a first torsion frequency (T1) of 6 kHz. In a prototype drive populated with milliactuators, a new dual stage servo algorithm resulted in 60% higher bandwidth (0 dB open-loop crossover) compared to without the milliactuator. Further modifications to the milliactuator along with improvements in sampling rate and computational time could allow up to 100% higher servo bandwidth. The benefits and limitations of milliactuators are also discussed. The milliactuator provides a low cost, enhanced performance solution for high track densities