Abstract
Hard disk drives (HDDs) used for data servers are exposed to various vibrations. These vibrations are mainly caused by the cooling fan that controls the temperature inside the server. The vibration affects the positioning accuracy of magnetic heads that read/write digital data. This is an obstacle to obtaining high data transfer rates. To compensate for vibration, the control system for the magnetic heads must have higher frequency control bandwidth as the spectra of these vibrations have peaks up to 10 kHz. In current HDDs, the control system is a triple-stage system consisting of a voice coil motor (VCM), a milliactuator, and a microactuator. In this article, we propose a design strategy for a triple-stage control system to compensate for vibration. The design strategy addresses unstable controllers in the control system. The gain of the feedback controllers of the VCM and milliactuators is increased to expand the control bandwidth. Although these feedback loops become an unstable system due to the increase in the controller gain, the controller for the microactuator is designed to stabilize the overall feedback loop. As a result, the control system achieves high control bandwidth. The performance of the proposed control system is calculated based on the compensation of the vibration caused by the data server. The proposed design can improve positioning accuracy by approximately 48%–58% compared with the conventional controller design.
Highlights
C YBER-PHYSICAL systems (CPSs) are widely utilized in various industrial applications [1]–[3]
We proposed a design strategy for the control system of a triple-stage actuator system in an hard disk drives (HDDs)
The control system must increase the control bandwidth to be higher than 10 kHz to compensate for the acoustic vibration
Summary
C YBER-PHYSICAL systems (CPSs) are widely utilized in various industrial applications [1]–[3]. In a triple-stage actuator system, control bandwidth can be increased by employing milli and microactuators because the primary resonance frequency of these actuators is higher than that of the VCM. We propose a control design method based on the parallel controller design, which can increase the control bandwidth to reach 10 kHz for compensation of acoustic vibration. By using the proposed design method, the control bandwidth of the overall feedback loop is increased higher than 10 kHz. To verify the effectiveness of the proposed design, a performance calculation is performed based on experimental data. To verify the effectiveness of the proposed design, a performance calculation is performed based on experimental data These data include the measured frequency response of each actuator and the measured acoustic vibration caused by the cooling fan. The stability performance of the overall feedback loop satisfies the traditional criteria, and the three-sigma value of the microactuator output is less than the stroke limitation [28], [32]
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