In this dissertation, the design of servo control algorithms is investigated to produce high-density and cost-effective hard disk drives (HDDs). In order to sustain the continuing increase of HDD data storage density, dual-stage actuator servo systems using a secondary micro-actuator have been developed to improve the precision of read/write head positioning control by increasing their servo bandwidth. In this dissertation, the modeling and control design of dual-stage track-following servos are considered. Specifically, two track-following control algorithms for dual-stage HDDs are developed. The designed controllers were implemented and evaluated on a disk drive with a PZT-actuated suspension-based dual-stage servo system. Usually, the feedback position error signal (PES) in HDDs is sampled on some specified servo sectors with an equidistant sampling interval, which implies that HDD servo systems with a regular sampling rate can be modeled as linear time-invariant (LTI) systems. However, sampling intervals for HDD servo systems are not always equidistant and sometimes, an irregular sampling rate due to missing PES sampling data is unavoidable. With the natural periodicity of HDDs, which is related to the disk rotation, those HDD servo systems with missing PES samples can be modeled as linear periodically time-varying (LPTV) systems. For the control synthesis of HDD servos with irregular sampling rates, an explicit optimal H_infinity control synthesis algorithm for general LPTV systems is first obtained by solving discrete Riccati equations. Then, the optimal H_infinity track-following control for irregular-sampling-rate servos is synthesized. Simulation and experiment studies, which have been carried out on a set of actual single-stage hard disk drives, demonstrate that the proposed control synthesis technique is able to handle irregular sampling rates and can be used to conveniently design a track-following servo that achieves the robust performance of a desired error rejection function for disturbance attenuation. Moreover, experiment results show that compared to the currently-used methodology for irregular sampling rates, the proposed control algorithm has significantly improved the servo performance. In addition, the feedback signal in HDD servos is generated from the servo patterns that must be pre-recorded using servo track writing process before the HDD can be used. Thus, the quality of the servo track writing process is also crucial to the accuracy of positioning read/write head. Recently, self-servo track writing has been developed in order to improve the quality of the written servo patterns and reduce the cost of servo track writing process. This dissertation considers two novel controller synthesis methodologies employing a feedforward control structure for performing concentric self-servo track writing in hard disk drives. Simulation results confirm that the two proposed control synthesis methodologies prevent error propagation from the previously written tracks and significantly improve servo track writing performance.

The series Advances in Industrial Control aims to report and encourage technology transfer in control engineering. The rapid development of control technology has an impact on all areas of the control discipline. New theory, new controllers, actuators, sensors, new industrial processes, computer methods, new applications, new philosophies , new challenges. Much of this development work resides in industrial reports, feasibility study papers and the reports of advanced collaborative projects. The series offers an opportunity for researchers to present an extended exposition of such new work in all aspects of industrial control for wider and rapid dissemination. Hard disk drive systems are ubiquitous in today’s computer systems and the technology is still evolving. There is a review of hard disk drive technology and construction in the early pages of this monograph that looks at the characteristics of the disks and there it can be read that: “bit density... continues to increase at an amazing rate”, “spindle speed... the move to faster and faster spindle speeds continue”, “form factors... the trend...is downward... to smaller and smaller drives”, “performance... factors are improving”, “redundant arrays of inexpensive disks... becoming increasingly common, and is now seen in consumer desktop machines”, “reliability... is improving slowly... it is very hard to improve the reliability of a product when it is changing rapidly” and finally “interfaces... continue to create new and improved standards... to match the increase in performance of the hard disks themselves”.

The hard disk drive is one of the finest examples of the precision control of mechatronics, with tolerances less than one micrometer achieved while operating at high speed. Increasing demand for higher data density as well as disturbance-prone operating environments continue to test designers' mettle. Explore the challenges presented by modern hard disk drives and learn how to overcome them with Hard Disk Drive: Mechatronics and Control. Beginning with an overview of hard disk drive history, components, operating principles, and industry trends, the authors thoroughly examine the design and manufacturing challenges. They start with the head positioning servomechanism followed by the design of the actuator servo controller, the critical aspects of spindle motor control, and finally, the servo track writer, a critical technology in hard disk drive manufacturing. By comparing various design approaches for both single- and dual-stage servomechanisms, the book shows the relative pros and cons of each approach. Numerous examples and figures clarify and illustrate the discussion. Exploring practical issues such as models for plants, noise reduction, disturbances, and common problems with spindle motors, Hard Disk Drive: Mechatronics and Control avoids heavy theory in favor of providing hands-on insight into real issues facing designers every day.

The demand for online storage has been increasing significantly during the last few years. Hard disk drives are the primary storage devices used in data centers for storing these online contents. The servo assembly of the dual-stage Hard Disk Drive (HDD) is composed of the Voice Coil Motor (VCM) and the Mili-Actuator (MA), where the VCM is responsible for coarse positioning at low frequency regions and the MA is responsible for fine positioning at high frequency regions. Controlling these two actuators is very critical in precision positioning of the read/write head, which is mounted at the edge of the servo assembly. In this dissertation, the precision positioning of the head during the self-servo writing process as well as feed-forward and feedback controls in the track following mode are considered. This dissertation discusses three control design methodologies for hard disk drives servo systems, in order to improve their performance as well as their reliability. The first is a state estimator for non-uniform sampled systems with irregularities in the measurement sampling time, which estimates the states at a uniform sampling time. The second is an online uncertainty identification algorithm, which parameterizes and identifies the uncertain part of transfer functions in a dual-stage HDD. The third is a frequency based data-driven control design methodology, which considers mixed H_2/H_infinity control objectives and is able to synthesize track following servo systems for dual stage actuators utilizing only the frequency response measurement data, without the need of identifying the models of the actuators. The state estimator design for non-uniform sampled systems with irregularity in the measurement sampling time is considered, where it is proposed to design an observer to estimate the states at a uniform sampling time. This observer is designed using a time-varying Kalman filter as well as a gain-scheduling observer. The Kalman filter has the optimal performance, while the gain-scheduling observer requires relatively lower computational power. Simulations are conducted involving the self-servo writing process in hard disk drives, where performance as well as computational complexity of these two observers are compared under different noise scenarios. Uncertainties in system dynamics can change the closed loop transfer functions and affect the performance or even stability of the control algorithm. These uncertainties are parameterized as stable terms using coprime factorizations, and are identified in an online fashion. The uncertainty identification, in comparison to the complete transfer function identification, requires less computational power as well as a smaller order for the identified transfer function. The proposed online uncertainty identification algorithm is utilized to factorize and identify the uncertain part of transfer functions in a dual-stage Hard Disk Drive (HDD). The dual-stage actuators' gains and resonance modes are affected by temperature variations, which in turn affect all closed loop transfer functions. Therefore, these transfer functions must be periodically updated in order to guarantee the convergence and stability criteria for the adaptive Repeatable Run-Out (RRO) following algorithm proposed in [61, 62]. Experimental results conducted on a hard disk drive equipped with dual-stage actuation, confirm the effectiveness of the proposed identification algorithm. A frequency based data-driven control design considering mixed H_2/H_infinity control objectives is developed for multiple input-single output systems. The main advantage of the data-driven control over the model-based control is its ability to use the frequency response measurements of the controlled plant directly without the need to identify a model for the plant. In the proposed methodology, multiple sets of measurements can be considered in the design process to accommodate variations in the system dynamics. The controller is obtained by translating the mixed H_2/H_infinity control objectives into a convex optimization problem. The H_infinity norm is used to shape closed loop transfer functions and guarantee closed loop stability, while the H_2 norm is used to constrain and/or minimize the variance of signals in the time domain. The proposed data-driven design methodology is used to design a track following controller for a dual-stage HDD. The sensitivity decoupling structure[34] is considered as the controller structure. The compensators inside this controller structure are designed and compared by decoupling the system into two single input-single-output systems as well as solving for a single input-double output controller.

The hard disk drive is one of the finest examples of the precision control of mechatronics, with tolerances less than one micrometer achieved while operating at high speed. Increasing demand for higher data density as well as disturbance-prone operating environments continue to test designers' mettle. Explore the challenges presented by modern hard disk drives and learn how to overcome them with Hard Disk Drive: Mechatronics and Control. Beginning with an overview of hard disk drive history, components, operating principles, and industry trends, the authors thoroughly examine the design and manufacturing challenges. They start with the head positioning servomechanism followed by the design of the actuator servo controller, the critical aspects of spindle motor control, and finally, the servo track writer, a critical technology in hard disk drive manufacturing. By comparing various design approaches for both single- and dual-stage servomechanisms, the book shows the relative pros and cons of each approach. Numerous examples and figures clarify and illustrate the discussion. Exploring practical issues such as models for plants, noise reduction, disturbances, and common problems with spindle motors, Hard Disk Drive: Mechatronics and Control avoids heavy theory in favor of providing hands-on insight into real issues facing designers every day.

An innovative and timely guide to the modeling, design and implementation of large-range compliant micropositioning systems based on flexure hinges Features innovative compact mechanism designs for large-range translational and rotational positioning Provides original and concise treatment of various flexure hinges with well-presented design and control methods Focuses on design implementation and applications through detailed examples

The fifth volume of the Series Advances in Systems, Signals and Devices, is dedicated to fields related to Systems, Automation and Control. The scope of this issue encompasses all aspects of the research, development and applications of the science and technology in these fields. Topics of this issue concern: system design, system identification, biological and economical models & control, modern control theory, nonlinear observers, control and application of chaos, adaptive/non-adaptive backstepping control techniques, advances in linear control theory, systems optimization, multivariable control, large scale and infinite dimension systems, nonlinear control, distributed control, predictive control, geometric control, adaptive control, optimal and stochastic control, robust control, neural control, fuzzy control, intelligent control systems, diagnostics, fault tolerant control, robotics and mechatronics, navigation, robotics and human-machine interaction, hierarchical and man-machine systems, etc. Authors are encouraged to submit novel contributions which include results of research or experimental work discussing new developments in the field of systems, automation and control. The series can be also addressed for editing special issues for novel developments in specific fields. The aim of this volume is to promote an international scientific progress in the fields of systems, automation and control. It provides at the same time an opportunity to be informed about interesting results that have been reported during the international SSD conferences.