Eng Hong Ong

A PZT micro-actuated suspension for high TPI hard disk servo systems

A piezoelectrically actuated suspension for high TPI (tracks per inch) hard disk drives is presented. Two reinforced piezoelectric microactuators, placed in parallel between the base plate and the spring beam, are used for the secondary actuation. A stroke of 1.2 /spl mu/m at the head was observed when driven by 30 V. The first torsion and the sway mode frequencies are 6.28 kHz and 10.5 kHz, respectively. In addition, the actuated suspension also has some distinguishing features such as, a C-channel and meanderline springs for shock-resistance enhancement. A possible vertical motion of the suspension is helpful for contact-start-stop (CSS) friction reduction and gramload adjustment. It also makes the suspension free from twist due to two layers of piezoelectric plates on both sides of the beam. As a result, the developed actuated suspension can be used to support high TPI hard disk drive servo systems.

A Unified Control Scheme for Track Seeking and Following of a Hard Disk Drive Servo System

This paper proposes a new nonlinear time-varying unified control scheme (UCS) for track-seeking and track-following in hard disk drives (HDDs) so as to avoid problem of mode switching. The proposed control scheme utilizes the concept of the conventional composite nonlinear feedback (CNF) scheme to achieve fast and smooth seeking. In order to be advantageous over the conventional CNF control, the UCS consists of both linear and nonlinear time-dependent components, which are independent of absolute seeking error. Simulation and implementation results show that, during track-seeking mode, the proposed scheme has a significantly better performance robustness against variations in seek length as compared to the conventional CNF control. For track-following, disturbance and noise models are involved in the problem formulation and sub-optimal H ¿ method is used to design the controller so as to achieve high head-positioning accuracy. It turns out that the unified controller removes 27.8% of the nonrepeatable disturbances and noise.

Reliability Evaluation of Piezoelectric Micro-Actuators With Application in Hard Disk Drives

Piezoelectric micro-actuators have been extensively studied and used in hard disk drive head positioning systems. In these cases, piezoelectric micro-actuators/sensors experience high frequency cyclic loading during their operations. The fatigue failure and the lifespan of such micro-actuators become a concern of researchers and engineers. However, the probability and statistics based reliability theory has not been well developed for piezoelectric micro actuators. In this paper, a probabilistic approach is presented to evaluate the reliability of piezoelectric micro-actuators. Based on the relationship between the lifetime degradation mechanism of piezoelectric actuators and the electric field strength, an interference model of electric load and strength is introduced for the reliability study of piezoelectric micro-actuators. Furthermore the reliability model is expanded into a 2-D case to take into account the effects of both driving voltage and temperature. A 2-D interference model incorporating the 2-D strength and load is proposed to obtain the relationship among the reliability, usage cycles, driving voltage and temperature. A case study of a piezoelectric micro-actuator used in a disk drive head positioning system demonstrates the application of the proposed approach.

Midfrequency Runout Compensation in Hard Disk Drives Via a Time-Varying Group Filtering Scheme

Conventional add-on feedback filters that are designed to compensate for midfrequency (mid-f ) repeatable runout (RRO) in a hard disk drive (HDD) servo system either have a long filter transient or constitute a large sensitivity hump as well as poor stability margins. This paper presents a novel linear time-varying (LTV) group filtering scheme for the compensation of a few mid- f RRO harmonics. While having a short filter transient that ensures fast disturbance attenuation, the proposed filter does not constitute to any substantial unnecessary sensitivity function gain amplification at the steady state. Simulation and implementation results show the effectiveness of this group filtering scheme.

A low-turbulence-high-bandwidth actuator for 3.5" hard disk drives

To achieve high TPI (tracks per inch) for hard disk drives, the actuator/suspension assembly must have high bandwidth and induce less air turbulence [therefore, lower TMR (track misregistration)]. In this paper; a systematic way of estimating the optimal arm length of an actuator to achieve high bandwidth is proposed. Also, alternative cross sections for the actuator arms are proposed for higher bandwidth and the reduction of air turbulence. Experimental results are presented for verification purposes.

Feasibility of Modeling Air Bearing as Linear Springs in Hard Disk Drive Dynamics Simulation

A model to predict the shock response of a 1.8-inch hard disk drive (HDD) is developed and validated by experiment. The head-actuator assembly (HAA), spindle disk and flexible base are included in the proposed model. The feasibility of modeling the air bearing as linear springs is investigated for HDD operating shock simulation. Result shows that as far as the vibration of the arm-suspension assembly is concerned, the air bearing between the disk and slider can be modeled by linear springs to speed up the simulation. However, if head/disk interface is concerned, the air bearing should not be modeled as linear springs in the studies of head-disk interface.

A novel in-slider piezoelectric micro-actuator for hard disc drives

The newly introduced 2.5/sup th/ generation (2.5G) dual-stage actuator model, three-piece slider incorporating a piezoelectric micro-actuator into a 50% nano-slider to provide ultra-fine positioning capability, is developed and evaluated in combination with the parallel control architecture for a dual-stage actuator servo system, showing high potentiality for the next generation hard disk drive (HDD) applications.

Servo Control Design for a High TPI Servo Track Writer With Microactuators

This paper proposes modifications to enhance the original generalized Kalman-Yakubovic-Popov (G-KYP) lemma-based sensitivity function shaping technique that Q-parameterizes the controller and solves for the desired finite impulse response filter Q(z) using linear matrix inequalities (LMI) optimization. By representing Q(z) with an infinite impulse response filter and including an extra LMI that is derived based on the bounded real lemma into the original LMI optimization algorithm, our modifications avoid such problems as unnecessary increase and decrease in sensitivity gain at various frequency ranges, large sensitivity peak, degradation in noise rejection, and insufficient stability robustness against plant uncertainty. In other words, the proposed scheme achieves a better compromise between disturbance and noise rejection performance and stability robustness. The proposed control design was applied to a servo track writing platform. Experimental results show that the control design based on our proposed scheme further reduces the true PES NRRO 3sigma from 6 nm to 5.7 nm and improves the closed-loop stability robustness by 5.1%.

Adaptive neural network compensation of pivot nonlinearity in hard disk drives

In this paper we propose an adaptive NN control design to compensate for the pivot nonlinearity. To capture the time-varying uncertainties and nonlinearity, the adaptive tuning scheme is employed for NN weights, receptive center and width. The simulation and experimental results shows the effectiveness of the proposed scheme.

Time-Varying Compensation for Mid-Frequency Repeatable Runout in Hard Disk Drives via a Linear Feedback Scheme

Abstract Conventional add-on feedback filters for mid-frequency (mid- f ) repeatable runout (RRO) compensation in a hard disk drive (HDD) servo system either have a long filter transient or constitute a large sensitivity hump and poor stability margins. This paper presents a novel linear time-varying (LTV) group filtering scheme for the compensation of a few mid- f RRO harmonics. While having a short filter transient that ensures a fast disturbance attenuation, the proposed group filter does not cause any substantial unnecessary sensitivity function gain amplification at the steady state. Implementation results show the effectiveness of the proposed scheme used to compensate two mid- f RRO harmonics simultaneously.