Article: Performance Comparison Between Triple-Stage Actuator Systems in HDDs

IFAC-PapersOnLine has published an article written by Takenori Atsumi, Chiba Institute of Technology, Narashino, Chiba, 275-0016 Japan, and Shota Yabui, Nagoya University, Nagoya, Aichi, 464-8603 Japan.

Abstract: “In this paper, we present a comparison study between three triple-stage actuator systems of the magnetic-head positioning system in hard disk drives (HDDs). As of year 2019, we have four kinds of actuators for the magnetic-head positioning system: voice coil motor (‘VCM’), ‘Milli’ actuator with two piezoelectric (PZT) elements, ‘Micro’ actuator with two PZT elements, and a “Thermal” actuator that consists of heaters embedded in the magnetic head and move read/write elements a few nanometers in a horizontal direction with thermal expansion. This means that we are able to build three kinds of triple-stage actuator systems: ‘VCM + Milli + Micro’, ‘VCM + Milli + Thermal’, and ‘VCM + Micro + Thermal’. In order to find the best triple-stage actuator system for upcoming 1000 kTPI (track pitch: 25 nanometer) HDD era, we examine case studies and estimate the position error signals and movements of actuators of the track-following control systems under the external vibration in a file server. In this case study, it is shown that achievable disturbance-rejection performances of these triple-stage-actuator systems depend on not only the frequency responses the actuators but also the stroke limitations of the actuators. As a result, we found that the triple-stage actuator system that consist of the VCM, the Milli actuator, and the Micro actuator has the best performance for 1000 kTPI HDD.“