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This paper presents a systematic, semi-automated method for identifying parameters and parametric uncertainty for a set of dualstage hard disk drives. A modal analysis technique is selected to extract parameters from a batch of frequency response data. In order to avoid redundancy in modal parameters, two methods are presented to reduce model order. One method combines experimental data to directly extract fewer parameters. The second method uses an optimized model truncation methodology. Finally, convex optimization and singular value decomposition are employed to obtain a minimally conservative, lower-order approximation of uncertain parameters. The result is a reduced-order state space model with parametric uncertainty to be used in robust [H.sub.2] control synthesis for a trackfollowing hard disk drive servo. Index Terms--Dual-stage actuation, model reduction, parametric uncertainty, robust control, system identification.

This paper presents the system modeling, design, and analysis of multirate robust track-following controllers for a dual-stage servo system with a microelectromechanical systems (MEMS) microactuator (MA) and an instrumented suspension. A generalized model is constructed which includes a nominal plant, disturbances, uncertainties, and multirate sensing and control. Two major categories of controller design methodologies are considered. The first includes synthesis methodologies that are based on single-input single-output (SISO) design techniques, and includes the sensitivity decoupling (SD) and the PQ methods. In this case, a high sampling-rate inner loop damping control is first implemented using the auxiliary sensor signals. Subsequently, a low-rate outer loop controller is designed for the damped plant using either the SD or PQ design methods. The second category of design methodologies includes those based on multirate, multi-input multi-output (MIMO) design techniques, including mixed [H.sub.2]/[H.sub.[varies]], mixed [H.sub.2]/[micro], and robust [H.sub.2] synthesis. In this case, a set of controllers, which is periodically time-varying due to multirateness, is designed by explicitly considering plant uncertainty and hence robust stability. Comparisons are made between all the design techniques in terms of nominal [H.sub.2] performance, robust stability, and robust performance between these controllers, when the feedback controller is closed around the full order, perturbed plant. The advantages and disadvantages of each of these methods are discussed, as well as guidelines for their practical implementation. Index Terms--Hard disk drives, multisensing, robust control.

In a hard disk drive with a dual-stage actuator the standard rotary actuation of the voice coil motor (VCM) is combined with an additional micro- or milli-actuation to accomplish high-bandwidth and highly accurate track following. For extremely high density recording, the servo control algorithm designed for a specific dual-stage actuator needs to maintain high performance track following in lieu of external disturbances and uncertainties in the dynamic response induced by product manufacturing tolerances. Essential in the robust design of a servo control algorithm is to bound these uncertainties and design a robust track following servos accordingly. In this paper, we present an experiment based methodology to characterize and bound the uncertainties in the dynamic response of a dual-stage actuator in the form of an uncertainty model. Subsequently, the uncertainty model is used for the analysis and synthesis of a robust dual-stage servo controller that is able to optimize position error variance in the presence of uncertainty information. Index Terms--Dual-stage actuator, robust control, servo control, uncertainty.

This paper proposes a robust track-following controller design method for a dual-stage servo system in magnetic hard disk drives (HDDs). The method formulates the problem of minimizing track misregistration (TMR) in the presence of plant uncertainty and variation as a multiobjective optimization problem. Tracking error minimization is naturally formulated as an [H.sub.2] norm minimization problem, while the robust stability issue is addressed by some [H.sub.[infinity]] norm bounds. This mixed [H.sub.2]/[H.sub.[infinity]] control problem can then be formulated as a set of linear matrix inequalities (LMIs) and be efficiently solved through convex optimization algorithms. To enhance the system's tracking performance and stability robustness, the method explicitly takes attenuation of airflow-excited suspension vibration into consideration by an inner loop fast rate damping and compensation controller that utilizes the output of a strain gauge sensor on the suspension surface. Analysis and simulation show that a system designed by this method can achieve good tracking performance while still keeping stability robustness to plant variation and high-frequency spillover. Index Terms--Hard disk drives, [H.sub.2] control, [H.sub.[infinity]] control, servo control.

Structural resonance modes of the head stack and suspension assembly are one of the major limiting factors for achieving higher head-positioning servo performance in hard disk drives. This paper discusses the vibration suppression control of a PZT actuated suspension dual-stage servo system. A PZT strip on a PZT actuated suspension is utilized as a vibration sensor to control both the voice coil motor (VCM) actuator butterfly mode and the suspension sway mode. The vibration suppression controller is designed using the [H.sub.[infinity]] control design method. Experimental results show that an attenuation of 15 dB can be achieved for both the suspension sway mode and the VCM butterfly mode, and the rms of the head off-track motion due to airflow excited vibration can be reduced by approximately 30% with the proposed vibration suppression control scheme. Index Terms--Dual-stage servo, hard disk drive, vibration damping control, windage.

This paper presents a microfabricated actuator designed for high precision servo-positioning in a magnetic hard disk drive. The device is actuated using electrostatic force generated with parallel-plate capacitive electrodes. The displacement of these electrodes is measured using a dedicated capacitive sensing interface, allowing closed-loop control to be used to extend the servo bandwidth. Using the sensing electronics and a simple phase-lead compensator, a prototype device was used to actuate a 1.6 mg ceramic slider over a 1.2 kHz bandwidth. Using optical position measurements, the same actuator was used to achieve a 2.5 kHz bandwidth. Index Terms - Actuator, disk drive, micro-electromechanical systems, position control.

This paper discusses the design and experimental verification of a new direct adaptive control scheme for disk file track-following servo systems. The adaptive controller acts as an add-on compensator to an existing fixed compensator, which stabilizes the feedback system. The control objective is to minimize the frequency weighted variance of the tracking position error signal in the presence of external random vibrations. The proposed adaptive control scheme was implemented on a TMS320C30 DSP board, and was tested on two different disk drives. The drives were subjected to stochastic input disturbances or random vibrations. Simulation and experimental results are in close agreement and show that the proposed adaptive scheme significantly improves the error rejection capabilities of the control system, without significantly increasing its bandwidth nor decreasing its open loop stability margins.

This paper describes the design, fabrication, position sensing, and control of an electrostatically-driven microactuator. The polysilicon microactuator, together with an on-chip electronic buffer, were fabricated by the Modular Integration of CMOS and microStructure (MICS) technology. The microactuator has a linear dimension of 310[[micro]meter x 340[[micro]meter] x 1.7[[micro]meter] and a 'long throw' range of motion of [+ or -]4[[micro]meter]. The driving comb fingers of the microactuator can generate up to 0.3[micro]N of electrostatic force, which is able to pull the suspended microactuator across the substrate at an acceleration of over 270 G's. The lateral position of the microactuator, relative to the substrate, is capacitively sensed by a Kalman filtering scheme, which achieves a position estimation error covariance below 0.01 [[micro]meter] RMS. A state-variable feedback loop operates at a closed loop bandwidth of over 11 kHz. Experimental results are given.

A new decoupled track-seeking controller for a dual-stage servo system of a magnetic disk drive has been developed. The controller is applied to the dual-stage system with a push-pull piezoelectric (PZT) micro-actuator and enables high-speed one-track seeking and short-span track seeking. A one-track seeking controller was designed in three steps: 1) a voice coil motor (VCM) feedforward controller was designed to prevent overshoot in response of VCM actuator; 2) a feedforward loop from the VCM reference signal to the PZT actuator was designed in order to de-couple the dual-stage actuator system; 3) a feedforward controller for the PZT actuator was designed such that an output PES (position error signal) only follows a PES reference signal. In the design of the short-span seeking controller, the PZT actuator's stroke limit was considered. Simulations and experiments show that the proposed dual-stage track-seeking controller performs better than the conventional single VCM servo. Index Terms--Decoupled seeking control, dual-stage actuator, magnetic disk drive, motion control.

This paper presents an adaptive repetitive controller for active tracking (rejecting) of unknown periodic trajectories (disturbances). The proposed control law is based on a modified filtered- x least mean squares (MFX-LMS) algorithm with a novel variable step size that improves the convergence rate and fades the steady state excess error in a stochastic environment. A novel secondary path modeling scheme is also proposed to adaptively compensate for the dynamic mismatches between the internal model of the MFX-LMS and the real dynamic system in an online fashion. We further discuss the application of this adaptive controller in servo mechanisms for hard disk drives (HDDs) that use bit patterned media recording in which full spectrum tracking of a periodic trajectory is crucial. Finally, comprehensive numerical simulations and experimental implementations are presented for an HDD servo system that is subjected to periodic disturbances known as repeatable run-out. [ABSTRACT FROM AUTHOR]

This paper considers two novel controller synthesis methodologies using a feedforward control structure for performing concentric self-servo track writing in hard disk drives. In the first methodology, it is assumed that a conventional causal track-following controller has been designed and a non-causal feedforward controller, which utilizes the stored error signal from writing the previous track, is designed using standard H\infty control synthesis techniques, in order to prevent the track errors from propagating and to achieve good disturbance attenuation. In the second methodology, both the track-following feedback controller and the feedforward controller are simultaneously designed via a mixed H2/H\infty control scheme, which involves the solution of a set of linear matrix inequalities and achieves good disturbance attenuation while preventing the propagation of track errors from the previous tracks. Simulation results confirm that the two proposed control synthesis methodologies prevent error propagation from the previously written tracks and significantly improve concentric self-servo track writing performance. [ABSTRACT FROM AUTHOR]

This paper presents a systematic, semi-automated method for identifying parameters and parametric uncertainty for a set of dual-stage hard disk drives. A modal analysis technique is selected to extract parameters from a batch of frequency response data. In order to avoid redundancy in modal parameters, two methods are presented to reduce model order. One method combines experimental data to directly extract fewer parameters. The second method uses an optimized model truncation methodology. Finally, convex optimization and singular value decomposition are employed to obtain a minimally conservative, lower-order approximation of uncertain parameters. The result is a reduced-order state space model with parametric uncertainty to be used in robust H2 control synthesis for a track-following hard disk drive servo. [ABSTRACT FROM AUTHOR]

This paper presents the system modeling, design, and analysis of multirate robust track-following controllers for a dual-stage servo system with a microelectromechanical systems (MEMS) microactuator (MA) and an instrumented suspension. A generalized model is constructed which includes a nominal plant, disturbances, uncertainties, and multirate sensing and control. Two major categories of controller design methodologies are considered. The first includes synthesis methodologies that are based on single-input single-output (SISO) design techniques, and includes the sensitivity decoupling (SD) and the PQ methods. In this case, a high sampling-rate inner loop damping control is first implemented using the auxiliary sensor signals. Subsequently, a low-rate outer loop controller is designed for the damped plant using either the SD or PQ design methods. The second category of design methodologies includes those based on multirate, multi-input multi-output (MIMO) design techniques, including mixed H2/H∞, mixed H2 /∞, and robust H2 synthesis. In this case, a set of controllers, which is periodically time-varying due to multirateness, is designed by explicitly considering plant uncertainty and hence robust stability. Comparisons are made between all the design techniques in terms of nominal H2 performance, robust stability, and robust performance between these controllers, when the feedback controller is closed around the full order, perturbed plant. The advantages and disadvantages of each of these methods are discussed, as well as guidelines for their practical implementation. [ABSTRACT FROM AUTHOR]

In a hard disk drive with a dual-stage actuator the standard rotary actuation of the voice coil motor (VCM) is combined with an additional micro- or milli-actuation to accomplish high-bandwidth and highly accurate track following. For extremely high density recording, the servo control algorithm designed for a specific dual-stage actuator needs to maintain high performance track following in lieu of external disturbances and uncertainties in the dynamic response induced by product manufacturing tolerances. Essential in the robust design of a servo control algorithm is to bound these uncertainties and design a robust track following servos accordingly. In this paper, we present an experiment based methodology to characterize and bound the uncertainties in the dynamic response of a dual-stage actuator in the form of an uncertainty model. Subsequently, the uncertainty model is used for the analysis and synthesis of a robust dual-stage servo controller that is able to optimize position error variance in the presence of uncertainty information. [ABSTRACT FROM AUTHOR]

This paper proposes a robust track-following controller design method for a dual-stage servo system in magnetic hard disk drives (HDDs). The method formulates the problem of minimizing track misregistration (TMR) in the presence of plant uncertainty and variation as a multiobjective optimization problem. Tracking error minimization is naturally formulated as an H2 norm minimization problem, while the robust stability issue is addressed by some H∞ norm bounds. This mixed H2 /H∞ control problem can then be formulated as a set of linear matrix inequalities (LMIs) and be efficiently solved through convex optimization algorithms. Th enhance the system's tracking performance and stability robustness, the method explicitly takes attenuation of airflow-excited suspension vibration into consideration by an inner loop fast rate damping and compensation controller that utilizes the output of a strain gauge sensor on the suspension surface. Analysis and simulation show that a system designed by this method can achieve good tracking performance while still keeping stability robustness to plant variation and high-frequency spillover. [ABSTRACT FROM AUTHOR]