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Asia-Pacific Magnetic Recording Conference, 2004. APMRC 2004

Date 16-19 Aug. 2004

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  • Asia-Pacific Magnetic Recording Conference 2004. Digest of APMRC 2004 (IEEE Cat. No. 04EX942)

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  • Asia-Pacific Magnetic Recording Conference

    Page(s): i - xii
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  • [Breaker page]

    Page(s): 1
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  • Aerodynamic vibration analysis coupled by fluid analysis of internal HDDs

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    The influence of aerodynamic excitation and the structural vibration analysis of arms and disks based on the excitation force that can be calculated by airflow analysis are evaluated. Then, a very easy-to-use system to calculate airflows and to follow up with evaluating vibration characteristics of internal structural bodies in HDD is developed. Airflow calculation is based on direct numerical simulation; therefore, actual fluidic phenomenon is reproduced. View full abstract»

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  • VCM design to improve dynamic performance of actuator in a disk drive

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    PES design margin of current hard disk drive becomes getting smaller as track density of high-capacity disk drives increases. In the present work, a new actuator design concept is introduced for reducing one of the actuator vibration modes so called a butterfly mode that normally limits expansion of servo bandwidth. The new actuator has single coil with four sections having respective particular directions. By adjusting the length and direction of the sections of the VCM coil, the forces perpendicular to track seeking direction can be balanced with each other, and then the butterfly mode is not excited by the resultant force of VCM. Contribution of the proposed actuator design for the PES management is verified by numerical simulations. As a result, the servo bandwidth is to be increased so that PES can be decreased due to improved dynamics of the proposed method. View full abstract»

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  • Design and development of milliactuator embedded suspension for dual stage system in hard disk drives

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    To realize higher track density of HDD, the servo bandwidth should be higher, however, is limited by the mechanical resonances of the arm, coil of the VCM and ball bearing pivot. One approach to overcoming the problem is using dual stage servo system. For this system, we have suggested new milliactuator based on the shear mode of piezoelectric elements to drive the head suspension assembly. The initial model introduced is the APMRC 2002, and now we improve that model. The milliactuator is added flexure structure for femto slider and applied optimal design process. The objective function is to maximize frequencies of 2nd torsional mode and sway mode with stable compliance of the disk flutter. The improved suspension with milliactuator is analyzed about shock characteristics for mobile application. View full abstract»

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  • Flow-induced vibration of head gimbal assembly under various conditions

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    The flow-induced vibration of a head gimbal assembly (HGA), known as "windage", is a very large obstacle for achieving the higher track densities in hard disk drives (HDDs). We show the natures of windage to develop lower-windage HGAs in this paper. For the slider radius location, when slider is on outer diameter, windage is much larger than other positions. At the high temperature, resonant frequencies decrease and their amplitude increase. For some modes, there is optimized Z-height. These knowledge are useful when we evaluate HGAs and to optimize HGAs with experimental design. View full abstract»

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  • Development on in-phase actuator mechanism in hard disk drives papers

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    This research shows the new design concept of an actuator in hard disk drives. The actuator which has several higher-order mechanical resonance determine the stability and mechanical noise suppression ability of the servo control system. We presented the new design concept that higher resonance are made in-phase to the first major resonance. In this concept, all the resonance with high gain are in-phase but the out-phase resonance's gain are reduced. It is shown that the prototype actuator based on this concept can be compensated only by the compensator which is designed for the first major resonance. View full abstract»

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  • Experimental and numerical studies about the effect of airflow on slider vibration with and without a disk damper

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    As the recording density and data transfer rate of a hard disk drive increase, TPI and rotational speed have been increased so that a single actuator alone may not be enough to control TMR budget. High-speed rotation of a disk induces airflow inside HDD cavity and the influence of airflow on HSA has become critical as TPI increases. A disk damper, which is designed to suppress the disk flutter, changes the airflow significantly so that the E-block and slider are open to the flow with relatively large pressure fluctuation. The effect of disk damper shape on the airflow field is studied numerically and experimentally from the aerodynamic point of view. Unsteady airflow in HDD cavity is simulated numerically by using a large eddy simulation method and frequency spectrum of the pressure fluctuation near the slider is obtained. Numerical results are compared with experimental results for three different-shape disk dampers and two types of E-blocks. The relationship is analyzed between the vibration of the slider and the pressure fluctuation of the airflow near the slider. A newly proposed shape of disk damper shows good characteristics on suppressing the vibration of the slider due to the airflow. View full abstract»

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  • Effect of tribocharging on lubricant redistribution

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    In hard disk drives, lubricant is used to increase the durability of the head/disk interface by reducing wear and the potential for catastrophic failure if and when the slider contacts the disk during the operational mode of the drive. It is desirable to maintain the original distribution of the mobile layer over the life of the drive in order to realize the expected reliability of the head/disk interface. However, this task is quite elusive as the distribution of the lube changes due to usage coupled with environmental and other effects. In this paper, we show that lubricant can also massively redistribute itself due to tribocharging. We also show that this behavior is quite dependent on the relative humidity of the system. View full abstract»

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  • Sensitivity analysis and design optimization for head interconnect

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    The higher data rate has raised greater concern on the design of head interconnect which bridges communications between read/write (R/W) electronics and recording heads. This paper focuses on design issues relating to impedance matching and crosstalk that are important with regard to quality of signal transmission for high data rate recording. The influence of trace configuration on the impedance and crosstalk are analyzed. In this paper a new approach based on design of experiment (DoE) method is applied to such design problems. With the design consideration of uncontrollable sources, crosstalk is optimized with the robust design techniques. View full abstract»

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  • Effects of functional end-group on nano-tribology characteristics of ultra-thin liquid lubricant films in hard disk drives

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    This paper describes the effects of functional end-group on nano-tribology characteristics of ultra-thin liquid lubricant films in hard disk drives. In the experiments, the spreading characteristics of ultra-thin liquid lubricant films have been investigated by using the disks with two kinds of lubricants which have different end-groups. The effect of molecularly thin lubricant films on nano-spacing flying head slider hysteresis behavior for touch-down and take-off process also has been studied. In addition, the behavior of two kinds of lubricants films for contact sliders has been investigated. Based on these experiments, it may be concluded that the functional end-group does affect the tribological performance of lubricants in head-disk interface. View full abstract»

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  • Improvement of L/UL performance using load/unload mechanism control considering disk vibration characteristics

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    Load/unload dynamic characteristics are affected by various parameters; load/unload speed, disk rotating speed, disk vibration and so on. The effect of load/unload process on various parameters was investigated by the experiment. As a result of experiment, the load performance was found to be better for lower load speed and disk rpm. On the other hand, it was confirmed to be better for lower unload speed and higher disk rpm in unload process. Also, the effect of disk vibration was studied for load/unload process. The amplitude of disk vibration can affect in a relative ramp-disk gap and the disk vertical velocity affects in a relative slider-disk speed during load/unload process. As the results of 1000 unload cycles, the non-contact region was changed as the function of disk rotating speed. The non-contact region was smaller in a lower disk rpm. This paper proposes a new control system in order to improve the load/unload performance. View full abstract»

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  • Microtribodynamics of pseudo-contacting head-disk interfaces intended for 1 Tbit/in2

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    A nonlinear dynamic model that includes realistic roughness, adhesion and friction, as well as the dynamics of a flying and contacting HDI was developed to characterize a pseudo-contacting HDI, intended for 1 Tbit/in2. A pseudo-contacting recording system is designed to fly at few nanometers using an air-bearing and at the same time some features of the air-bearing surface are designed to contact with the rotating disk during operation. The model was favorably compared with flyability measurements, and then applied to a pseudo-contacting interface to investigate adhesion, friction, and contact forces as well as bouncing vibration. Contrasting earlier studies adopting a simple Coulomb friction, the friction model used in this work calculates the friction force at the interface, accounting for roughness and adhesion. It was found that unlike a fully flying HDI, adhesion plays a positive role in attaining pseudo-contact recording by reducing bouncing vibrations. View full abstract»

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  • Measurement of thickness of molecularly thin lubricant film by using ellipsometric microscopy

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    Controlling the kinetic behaviors of molecularly thin lubricant is a key technology for designing head-disk interfaces (HDIs) of hard disk drives (HDDs). Direct visualization of molecularly thin lubricant films is useful in investigating kinetic properties such as replenishment or retention of thin lubricant films. To meet this demand, we demonstrated that the ellipsometric microscope can provide real-time visualization with a sub-nm thickness resolution. In this paper, we present a method of measuring the thickness of the lubricant film. In this method, the phase difference between the lights reflected from the film-covered and uncovered regions of the disk is obtained from the polarizer angles; then the thickness is calculated from the phase difference. We verified the feasibility of the method theoretically and experimentally. Measurement error of less than 0.2 nm was experimentally achieved for molecularly thin lubricants. This method provides real-time and quantitative imaging of molecularly thin lubricants and can provide useful information for designing HDIs for high-density HDDs. View full abstract»

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  • Disk burnishing for head wear reduction

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    Disk burnishing has been incorporated as a final process of disk surface finishing for reducing asperity height. We considered that disk burnishing must also reduce head wear. Conventionally, there have been two burnishing techniques, "Head Burnishing" (HB) and "Tape Burnishing" (TB). We proposed a burnishing technique, "Contact Burnishing" (CB) that used hard spherical sliders. In this paper, we show the effects of CB and TB on reducing head wear and close with the future direction for disk burnishing study. We compared pin wear on disk surfaces with and without CB and TB. Pin wear was reduced by both techniques. However, the wear rate decrease by them was not enough to realize zero wear. We consider TB and CB should be studied further to increase the asperity height reduction efficiency while maintaining disk surface quality. View full abstract»

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  • Vibration interaction characteristics of disks-spindle

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    The purpose of this paper is to develop both numerical and experimental way that can be effectively used for vibration interaction prediction of the disk-spindle systems in HDD. First, the work focuses on the effective modeling method for the analysis of the vibration interaction of whole disks-spindle system. Second, the analytical results had been verified through the proposed experimental method using externally induced excitations for disk-spindle system in product assembly. The two set results agree very well. As shown, the numerical modeling and experiment methods can provide much information on design before to make hardware and verify it in lab. View full abstract»

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  • A new phase-delay free method to detect back EMF zero crossing points for sensorless control of spindle motors

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    This paper introduces a new phase-delay free rotor position detecting method for the sensorless control of brushless DC spindle motors. It applies a digital filtering procedure to identify the true and false zero-crossing points of the phase back EMFs, the latter of which are caused by the terminal voltage spikes of the commutating freewheeling currents. The suggested method is inherently top speed-limitation free and independent of the motor parameters. It can be applied in all kinds of spindle motors from 1" micro drives to 3.5" high-speed enterprise server drives. The developed prototype of SpinBox based on the invented method has experimentally confirmed its correctness and effectiveness in wide-speed range. View full abstract»

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  • Evaluation of fluid dynamic bearing spindle by vibration base

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    We propose a new evaluation method for damping characteristics and frequency characteristics of these bearing spindles using a high-frequency vibration base. In this study, we measured damping characteristics and frequency characteristics of these bearing spindles using the high-frequency vibration base. Damping coefficient and other parameters were estimated by step response and its simulation results. View full abstract»

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  • A numerical study on rotating-shaft spindles with nonlinear fluid dynamic bearings

    Page(s): 34 - 35
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (317 KB) |  | HTML iconHTML  

    The purpose of this paper is to present a numerical model predicting shock response of a rotating-shaft spindle motor with nonlinear FDB. The paper consists of the following three parts: 1) the first part is an effective way to represent nonlinear FDB load characteristics; 2) the second part of the paper is to integrate the nonlinear FDB model with an existing spindle vibration model to predict nonlinear spindle response; 3) the third part of this paper is to demonstrate the numerical model through use of two numerical examples View full abstract»

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  • A bipolar-starting and unipolar-running method to drive an HDD spindle motor at high speed with large starting torque

    Page(s): 36 - 37
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    This paper presents a method to drive an HDD spindle motor at high speed with large starting torque by utilizing a bipolar-starting and unipolar-running algorithm. It proposes a novel inverter circuit to switch from bipolar to unipolar drive, or vice versa. It also develops a DSP-based BLDC motor controller not only to drive the BLDC motor with bipolar or unipolar method, but also to switch from one method to the other at any speed. And the effectiveness of the proposed method is also verified by using the developed controller experimentally View full abstract»

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  • Modeling of hard disk drives for vibration analysis using a flexible multi-body dynamics formulation

    Page(s): 38 - 39
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    This paper presents a flexible multi-body dynamics formulation to analyze vibration of hard disk drives. The formulation is applied in analyzing vibration of VCM-actuators assembly and disks-spindle system. There are flexible components as well as rigid bodies in the system. Governing equations of motion of the VCM-actuators assembly and disks-spindle system are derived by using a Lagrangian formulation. Elastic deformations of flexible bodies are described by modal coordinates from a finite element formulation. After obtaining the formulations, modal analysis and shock response are analyzed. The numerical analyses are significantly faster compared to a full finite element approach, and is potentially useful when the system requires repeated analysis of the model of the entire system when certain design variables are changed View full abstract»

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  • Design of hydrodynamic bearing for mobile HDDs

    Page(s): 40 - 41
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    This paper reports on the basic design of a Hydrodynamic bearing with an oil circulation mechanism that has the express function of eliminating bubbles that remain inside the bearing cavity that would otherwise adversely affect the disruption-free nature of the oil film in the bearing.[1]-[2]. View full abstract»

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  • Optimization of initial value compensation for settle control in hard disk drives

    Page(s): 42 - 43
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (239 KB) |  | HTML iconHTML  

    A method is proposed for optimal settle control using 1-degree-of-freedom (1-DOF) control and initial value compensation (IVC) in hard disk drives. A feedforward control signal is injected into the control system during settle control to compensate the initial conditions when switching from seek to settle control. A transfer matrix from initial conditions to feedforward control input is calculated by least square optimization to minimize a cost function defined by position error, control effort and jerk. Simulation and experimental results are presented View full abstract»

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  • New RRO data collection method for HDD

    Page(s): 44 - 45
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    In this paper, a new method to collect RRO disturbance data is proposed. The estimated RRO disturbance obtained from the proposed method will not be affected by the variation of the actuator model. Test results show that the servo tracking performance can be significantly improved by using the estimated disturbance to compensate the actual RRO disturbances View full abstract»

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