Integrated plant/control design and implementation for high track density HDD servo systems

• Main Author: Gao, Tingting
• Other Authors: Cai Wenjian
• Format: Theses and Dissertations
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Electrical and electronic engineering
• Online Access: http://hdl.handle.net/10356/51254
• Institution: Nanyang Technological University

Hard disk drives (HDDs) are a kind of data storage systems that are present in computer systems. With increasing demands for higher storage capacity, the positioning accuracy becomes the most important requirement and challenging problem in HDDs. This thesis presents our research works for HDD systems. The main idea lies with exploiting the plant and controller design for the positioning accuracy improvement. The first part of the thesis focuses on the integrated plant/controller design method. By involving plant modification and controller design to achieve an optimal H2 performance requirement, a linear matrix inequality (LMI) based approach is developed for the plant damping ratio modification using the plant output, the optimal H2 controller is then designed for the modified plant. The results are demonstrated through simulation results, which turn out a better H2 performance level and stability margins than the original plant. Furthermore, the integrated plant/controller design for in-phase property is proposed, involving plant model modification followed by controller design. Such a design method can achieve better stability margins and disturbance rejection capability, and the expected performance is demonstrated through experimental results. The second part of the thesis focuses on investigation of dual-stage actuation systems to improve the positioning accuracy performance. With a newly developed micro thermal actuator (MTA) which is a slider-driven microactuator assembled with suspension, an H_{\infty} loop shaping based controller is developed and experimentally implemented on the MTA based dual-stage actuation systems. Note that one challenging problem for MTA controller design is the plant input constraint, which is more critical than moving suspension type actuator as its movement range is at a nano meter level and much smaller than micro meter level of moving suspension type. A peak-to-peak gain minimization method based controller is proposed to lower the amplitude of the input signal and experimentally compared with the traditional H_{\infty} loop shaping method. Furthermore, an anti-windup compensator is added to the MTA loop of the dual-stage systems, which is beneficial to the long-track seeking performance. Besides, the performance of PZT milliactuator based dual-stage actuation systems is experimentally studied. It shows that the PZT milliactuator driven by a current amplifier has less hysteresis and less primary resonance residues than that driven by a voltage amplifier. Furthermore, the control performances in track-seeking and track-following of the dual-stage actuation systems are thoroughly compared between these two driving methods. Parallel to the control problem, we also consider the impulsive disturbance attenuation problem, which is coupled into the measurement position error signal (PES) in HDDs. Then, an effective nonlinear filtering scheme is developed and modified.