Molecular Gas Film Lubrication Research Articles

0311 マイクロ・ナノスケール気体潤滑における摺動表面微細構造の形状の影響(OS302 ナノスケールの熱流動現象,オーガナイズドセッション)

Nakamori et al. found experimentally that the friction between a partly polished diamond coating and a metal surface was drastically reduced to zero as relative speed increased to a few m/s. [Diamond Relat. Mater., 14, (2005), 2122]. It seems that diamond coating took off the counter surface because sliding was noiseless in their experiment. In the previous work, we successfully reproduced lift force large enough to suspend the slider used in the experiment and found that this effect became notable only for micro-/nanoscale gas flow [IFS-Tsinghua University Joint Workshop 2009, Proceedings of 6th International Conference on Flow Dynamics, 584 (2009)]. In the present paper, we investigate the effect of configuration of micro-/nanoscale structure on sliding surface on molecular gas-film lubrication. Since micro-/nanoscale gas flows between two sliding surface cannot be treated as a continuum, we use the direct simulation Monte Carlo (DSMC) method.

S1603-1-4 凹凸を有する走行面上の3自由度浮上浮動ヘッドの分子気体潤滑解析(情報機器コンピュータメカニクス)

Recently, the space between the flying head slider and the disk has been reduced to I Onm or less. Consequently, recording media with grooves such as discrete track media (DTM) and bit-patterned media (BPM), are considered to be some of the most promising media for achieving ultrahigh track densities. Thus, it is becoming increasingly important to analyze the static and dynamic characteristics of flying head sliders over DTM/BPM media using the molecular gas-film lubrication (MGL) equation. In this paper, we first use the perturbation method in the frequency domain to obtain not only the stiffness and damping produced by the air film but also the negative stiffness caused by the attractive van der Waals (vdW) force. The perturbation method was applied to a slider with 3 degrees-of-freedom (3-DOF) over an asymmetric groove-slider configuration, which caused a rolling motion in addition to translational and pitching motions. The dependence of the dynamic characteristics such as spacing fluctuations on the groove wave number (frequency) were numerically obtamed.

P-HDI-05 MOLECULAR GAS-FILM LUBRICATION ANALYSES OF A SLIDER OVER A DISK WITH GROOVES : STATIC AND DYNAMIC FLYING CHARACTERISTICS OF A 3-DOF SLIDER(Head/Disk Interface and Tribology,Technical Program of Poster Session)

Recently, the space between the flying head slider and the disk has been reduced to 10nm or less. Consequently, recording media with grooves such as discrete track media (DTM) and bit-patterned media (BPM), are considered to be some of the most promising media for achieving ultrahigh track densities. Thus, it is becoming increasingly important to analyze the static and dynamic characteristics of flying head sliders over DTM/BPM media using the molecular gas-film lubrication (MGL) equation. In this paper, we first use the perturbation method in the frequency domain to obtain not only the stiffness and damping produced by the air film but also the negative stiffness caused by the attractive van der Waals (vdW) force. The perturbation method was applied to a slider with 3 degrees-of-freedom (3-DOF) over an asymmetric groove-slider configuration, which caused a rolling motion in addition to translational and pitching motions. The dependence of the dynamic characteristics such as spacing fluctuations on the groove depth and the frequency were numerically obtained.

Dynamic Analysis Schemes for Flying Head Sliders Over Discrete Track Media

It is becoming increasingly important to analyze the static and dynamic characteristics of flying head sliders over discrete track media (DTM) and bit patterned media (BPM) using the molecular gas-film lubrication (MGL) equation. In this study, we obtained the dynamic characteristics of the air bearing of the read/write head by considering not only the stiffness and damping produced by the air film, but also the negative stiffness caused by the attractive van der Waals force; these quantities were calculated in the frequency domain using a perturbation method. The dependence of the dynamic characteristics on the groove depth and frequency were calculated numerically. Moreover, the cubic interpolated propagation (CIP) method, a highly accurate and numerically stable scheme, was extended to the two-dimensional MGL problem in the time domain and the time evolution of the pressure produced by a single projection on the running disk, which is the simplest configuration of BPM, was calculated numerically.

2303 2次元CIPスキームによるナノメータ浮上ヘッドの分子気体潤滑解析(要旨講演,情報機器コンピュータメカニクス)

Recently the spacing between the slider and the disk has been reduced to 10nm or less, and analysis of the slider dynamics becomes increasingly important. To perform this analysis, the highly accurate and numerically stable cubic interpolated propagation (CIP) method was applied to the 2-dimensional molecular gas-film lubrication (MGL) equation. First, static pressures caused by running discrete track media (DTM) are shown quantitatively (Case I). Secondly, dynamic pressures caused by the translational motion of a running disk (Case II) and a running wavy disk (Case III) having small amplitudes under a fixed finite-width slider were analyzed by the CIP method and were found to be in good agreement with the results obtained by the linearized analysis. The dynamic pressure generated when a running wavy disk has a large amplitude under a fixed finite-width slider accounting for the van der Waals pressure were shown quantitatively. Dynamic pressures caused by moving single projeciton (Case IV) and running disk with step (Case V) under a fixed finite-width slider were also analyzed by the CIP method and were shown quantitatively.

5717 2次元CIPスキームによる分子気体潤滑解析 : 単一突起通過時の圧力解析(S84-2 情報機器コンピュータメカニクス(2),S84 情報機器コンピュータメカニクス)

5717 2次元CIPスキームによる分子気体潤滑解析 : 単一突起通過時の圧力解析(S84-2 情報機器コンピュータメカニクス(2),S84 情報機器コンピュータメカニクス)

Estimation of the squeeze film effect in a surface acoustic wave motor

This paper describes the air film characteristic in the interface between the slider and stator substrate of a surface acoustic wave (SAW) motor, and the difference of the squeeze film effect by the form of the slider. Because the vibration amplitude of the SAW motor is several 10 nm order, analysis of pressure was performed by using the molecular gas-film lubrication (MGL) equation. In the analysis, the MGL equation was split into advection phase and nonadvection phase, and calculation of advection and nonadvection phases was performed by using the cubic interpolated propagation (CIP) method and the finite difference method, respectively. From analysis results it was found that the time to steady pressure of air film depends on the radius of projection arranged on the contact surface of the slider. Also found was that the steady pressure in the interface does not depend on the radius and height of the projection, but it depends on the minimum spacing between the slider and the stator substrate.

Flying characteristics in the free molecular region (influence of accommodation coefficients)

To examine molecular gas film lubrication (MGL) characteristics for spacings of several nanometers, the free molecular MGL equation, which assumes that the flow in the lubrication region is the free molecular flow and involves the Poiseuille flow rate and the shear stress coefficient for the free molecular flow region with surface accommodation coefficients as parameters, is established. The usefulness of the free molecular MGL equation for the spacings of less than several nanometers is shown by comparing with the numerically calculated characteristics of flying head sliders using the conventional expression of the MGL equation with accommodation coefficients of running disk and slider, α0 and α1, as parameters. The static pressure generation is found to depend only on the accommodation coefficient of the running disk in the free molecular region.

Dynamic characteristics of flying head slider with ultra thin spacing (CIP method and linearized method)

The cubic interpolated propagation (CIP) method, which is an effective numerical scheme for differential equations that include advection and nonadvection terms, is employed for the dynamic analyses of ultra thin gas film lubrication using the molecular gas-film lubrication equation. First, pressure generation caused by the running wavy disk under the fixed slider was analyzed by the CIP method and is found to agree well with the analytical solution for the running wavy disk with a small amplitude. 2-DOF slider dynamics with the spacing of several tens of nanometers caused by a running disk with projections were investigated by the CIP method and the linearized solutions, which show that both results agree well with each other and the CIP method is promising scheme for slider dynamics even in the near-contact region.

Active-head sliders using piezoelectric thin films for flying height control

This paper describes design and fabrication of a MEMS-based active-head slider using a PZT thin film for flying height control in hard disk drives. A piezoelectric cantilever integrated in the air bearing slider is used to adjust the flying height individually. An air bearing surface (ABS) geometry that minimizes the aerodynamic lift force generated beneath the head has been designed based on the molecular gas film lubrication (MGL) theory. The sliders with PZT actuators were fabricated monolithically by silicon micromachining process. Performance of the actuator was tested by using an optical surface profiler. Furthermore, the fabricated slider was mounted on a suspension and the flying height of the slider above a spinning disk has been measured by multiple wavelength interferometry. Change in the head-disk spacing has been successfully confirmed by applying voltage to the actuator.

The flying height analysis of patterned sliders in magnetic hard disk drives

The ultra-low spacing of patterned sliders flying above a rotating disk with smooth surface in a hard disk drive is analyzed for high areal density recording. Three types of pattern (slender, square, and broad) with the same bump area are discussed. The molecular gas film lubrication (MGL) equation and the equations of motion of the patterned slider are solved numerically to obtain the steady flying attitude. The results show that the flying height of the broad patterned slider is the greater than either that of the square patterned slider or the slender patterned slider. In addition, we analyzed the effects of bump height and the bump pitch on the slider attitude, including flying heights, pitch angles, and roll angles, are discussed.

2309 複合層におけるファンデルワールスカを考慮した磁気ヘッドスライダの浮上特性解析 : 有限幅スライダの2自由度動的挙動解析(要旨講演,情報機器コンピュータメカニクス2)

Dynamic characteristics of a magnetic head slider of a hard disk drive were analysed using 2 degrees-of-freedom (2-DOF) mechanical model considering the dynamic pressures due to the van der Waals force and the air bearing force. The corrected van der Waals force equation for multilayers and the molecular gas-film lubrication (MGL) equation were used to calculate the pressures. It was found that the statically stable flying of a slider can no longer be achived at the ultrasmall spacing due to the attractive van der Waals force. It was also found that the response of the slider to the disk surface waviness is degraded even if the staic flying is stable. The animations of the slider motion were shown in order to see the influence of the van der Waals force.

A MEMS-Based Active-Head Slider for Flying Height Control in Magnetic Recording

This paper describes design and fabrication of a MEMS-based active-head slider using a PZT thin film for flying height control in hard disk drives. A piezoelectric cantilever integrated in an air bearing slider is used to adjust the flying height individually. A novel air bearing surface (ABS) geometry that minimizes the aerodynamic lift force generated beneath the head has been designed on the basis of the molecular gas film lubrication (MGL) theory. The slider with PZT actuator was fabricated monolithically by silicon micromachining. Performance of the actuator was tested by using an optical surface profiler. Furthermore, the fabricated slider was mounted on a suspension and flying height of the slider above a spinning disk has been measured by means of interferometry. Change in the head-disk spacing has been successfully confirmed by applying voltage to the PZT actuator.

CVDダイヤモンド膜を有する摺動面の分子気体潤滑に関するDSMC解析(OS19b マイクロスケール流れに対するシミュレーション技術とその応用)

CVDダイヤモンド膜を有する摺動面の分子気体潤滑に関するDSMC解析(OS19b マイクロスケール流れに対するシミュレーション技術とその応用)

A database for interpolation of poiseuille flow rate for arbitrary Knudsen number lubrication problems

A complete database for Poiseuille flow rate is advanced by solving the linearized Boltzmann equation numerically. The effects of surface accommodation coefficients, α1 and α 2, and inverse Knudsen number, D, on the Poiseuille flow rate are considered. The present database extends existing published results from 0.7≤α1α2≤1.0 to 0.1≤α1 α2≤1.0. It can be easily implemented in the modified molecular gas film lubrication (MMGL) equation, which governs ultra‐thin gas film lubrication problems. In addition, the database for low accommodation coefficients is valuable in the analysis and application of MEMS devices and their further development. The characteristics of squeeze film damping are utilized as examples to illustrate the implementation of the present database to the linearized MMGL equation with effects of gas rarefaction and non‐symmetric molecular interaction taken into account. The reaction forces, which include spring forces and damping forces, and the cutoff squeeze number of a squeeze film for a micro‐accelerometer are derived analytically and discussed.

3213 アクティブヘッドスライダの動特性解析と設計

This paper describes dynamic analysis of an active head slider with a dual-slider structure. Tracking ability of the slider and the head to microwaviness has been investigated using a three-degree-of-freedom slider model and the MGL (molecular gas film lubrication) theory. In order to improve the tracking ability, the air-bearing pad below the head should be made short and air-bearing center of the pad should be close to the rear end. It is found that the dual-slider structure is superior to the conventional slider to achieve high tracking ability.

HDI-03 DYNAMIC CHARACTERISTICS OF FLYING HEAD SLIDER WITH ULTRA-THIN SPACING : CIP METHOD AND LINEARIZED METHOD

The aubic interpolated propagation (CIP) method ^[1], which is an effective numerical scheme for differential equations that include advection and nonadvection terms, is employed for the dynamic analyses of ultra-thin gas film lubrication using the molecular gas-film lubrication (MGL) equation ^[2]. 2-DOF slider dynamics with the spacing of several tens of nanometers caused by a running wavy disk and projections are investigated herein.

3206 長波方程式による液体潤滑剤の変形・流動解析 : ディスクの周期性を考慮した液膜変形解析

The long wave equation and molecular gas-film lubrication (MGL) equation is used to analyze the lubricant evolution under a flying head slider. We examine the effects of waviness of disk on the lubricant modulation. The obtained results show that air bearing shear stress strongly affect the shape of lubricant deformation just under slider and the thinning/thickening rate of lubricant thickness depends on disk topography especially wave amplitude.

718 分子気体潤滑方程式に基づくナノメータ浮上特性解析 : 境界面の適応係数が任意の場合の圧力・せん断力解析

718 分子気体潤滑方程式に基づくナノメータ浮上特性解析 : 境界面の適応係数が任意の場合の圧力・せん断力解析

Adjoint Design Sensitivity Analysis of Molecular Gas Film Lubrication Sliders

This paper proposes an analytical design sensitivity analysis (DSA) to topological parameters of MGL (molecular gas film lubrication) sliders by introducing an adjoint variable method. For the analysis of slider air bearings, we used the spatial discretization of the generalized lubrication equation based on a control volume formulation. The residual functions for inverse analysis of the slider are considered as the equality constraint functions. The slider rail heights of all grid cells are chosen as design variables since they are the topological parameters determining air bearing surface (ABS). Then, a complicated adjoint variable equation is formulated to directly handle the highly nonlinear asymmetric coefficient matrix and vector in the discrete system equations of slider air bearings. An alternating direction implicit (ADI) scheme is utilized to efficiently solve large-scale problem in special band storage. The simulation results of DSA are directly compared with those of finite-difference approximation (FDA) to show the effectiveness and accuracy of the proposed approach. The overall sensitivity distribution over the ABS is reported, and clearly shows to which section of the ABS the special attention should be given during the manufacturing process. It is demonstrated that the proposed method can reduce more than 99 percent of the CPU time in comparison with FDA, even though both methods give the same results.