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The following topics are dealt with: HDD mechanics; recording systems; tribology and interface dynamics; spindle motor and actuators; lubricant; air bearings; vibrations; servo and control
To achieve an ultra-low flying height in magnetic head sliders for next generation hard disk drives, we are investigating individual in-situ technique to adjust flying height using a built-in thermal actuator to compensate for flying-height deviations and variations. To resolve this lack of agreement, we optically evaluated the slider's flying height at multiple positions using flying-height tester...
In this paper, a novel reset nonlinear PI-lead filters control scheme in parallel structure is proposed. The uniformly bounded-input and bounded-state (UBIBS) stability is proved and the proposed scheme also can achieve asymptotic tracking of the constant reference signals and rejections to constant output disturbances. The scheme is applied in the hard disk drives in the tracking-seeking and track-following...
Two nonlinear head-disk interface (HDI) models are proposed to investigate the dynamic behavior of air bearing sliders for hard disk drives (HDDs). It is noted that the air bearing sliders have obvious nonlinear behavior for ultra-low flying heights
This paper describes the comparison of the micro-grid method and a 3D FEM for predicting the medium field in perpendicular recording systems. The microgrid method uses Fourier series expansion to simulate the three dimensional (3D) field emanated from the perpendicular medium under the air bearing surface (ABS) of the read sensor. The proposed method can account for the effect of the recorded transitions...
This paper presents a new method to efficiently predict op-shock performance of hard disk drives (HDD). Structural components of HDD are modeled using state space formulation based on modes superposition principle. The air bearing is modeled as a non-linear spring dependent on slider's flying height and pitch angle; to obtain the air bearing stiffness the compressible Reynolds equation is evaluated...
Coarse-grained molecular dynamics simulations have been applied to study the effect of polymer functionality on surface morphology of lubricant films. An effective molecular-mesh scanning method was newly introduced to detect the location of film surface. For comparisons, two kinds of double-functional perfluoropolyether (PFPE) Zdol 2000 and Zdol 4000 whose molecular weight was double that of Zdol...
The flying stability of a thermal actuated slider is simulated. Its static flying height is not sensitive to short range interactions. Although its flying height vibration induced by a shock is relative larger, it can stand for a larger shock to achieve stable flying height comparing to a normal slider with same flying height The thermal actuated slider is especially suitable for ultra low flying...
This paper describes a novel method used to realize in-situ mechanical impedance measurement of air bearing in hard disk drive (HDD). It is originated from simultaneously sensing and actuating (SSA) method. In this method, an active cantilever is merged into a slider of HDD. It works with a patch of PZT, coating onto its top surface. This PZT cantilever is capable of sensing the mechanical impedance...
A dynamic model was developed to simulate the interaction between the suspension lift-tab and the ramp of a one-inch load/unload drive by considering the contact and separation states. The indentation depth, bouncing distance, contact force and fractional contact time, which are closely related to the wear and material transfer at the interface, were studied with consideration of the ramp angle, the...
In this study, we have tried LES model for inner-disk flowfield to investigate the flow disturbance and the flow structure driven by the co-rotating disks without any obstruction. The boundary pattern between inner region and outer region obtained lobe-shape structure clearly and its number has been validated on experimental data by our previous study. Two kinds of disturbances in the outer region...
Pushing recording density towards Tb/in2 and beyond requires reducing flying height, the mechanical spacing between head-slider and disk-media, to 2.5~3 nm or even lower. One critical challenge at such ultra-low flying height is how to come up with super-stable head-disk interface design so as to achieve stable flying height even with the strong appearance of the short-range interaction forces, such...
Characterization of slider motion induced by contact is becoming a critical aspect of developing advanced head-disc interfaces. While vertical and sway (side-to-side) motions induced by contact have been studied, very little is known about down-track motions. Moreover, we also simultaneously measure the pitch and roll of the slider during this contact event. We have employed three separate and independent...
The hard disk drive has proved as pivotal as the printing press in terms of its impact on human society. This paper examines both the history of and the prospects for the technology supporting these remarkable devices. Certainly for the next few years, conventional magnetic recording will continue its advance and provide ever higher capacities. There are several new technology features such as perpendicular...
To achieve an ultra low flying height, a multi-functional PFPE lubricant was synthesized. The molecule was achieved by combining several PFPE unit molecules. The novel lubricant contains extra polar functional-groups in the middle of the molecule. These functional-groups enhance the lubricant and substrate interaction, which results in reduction of the lubricant monolayer thickness. Through this molecular...
This paper presents an approach to compensating for the dominant frequency component of non-repeatable runout (NRRO). Frequency of the dominant component is estimated by the least mean square (LMS) algorithm within a short time window. Based on the frequency estimate, the basis function algorithm is applied to adaptively identify the magnitude and phase of the dominant component. The performance of...
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