A Model for the Effect of Humidity on Stiction of the Head/Disk Interface

A model has been developed for the effect of humidity on stiction of the head/disk interface. The model combines the meniscus force of the adsorbed water film at the interface with the Greenwood-Williamson surface model, and takes into account the effects of suspension load as well as surface roughness and material properties of both the head and the disk. It correctly predicts the trend for stiction vs. relative humidity as obtained from experimental data.     

The Role of Slider/Disk Roughness in 1 Tb/in.2 Magnetic Recording

To achieve 1 Tb/in.² magnetic recording areal density, the head/disk spacing, or the flying height of the slider, has become so small that both the disk surface roughness and the slider air-bearing surface roughness need to be considered. In this region, the intermolecular force and the contact force become more significant due to the roughness of the two surfaces. This article targets two points: 1) slider/disk roughness effects on intermolecular force and 2) slider/disk roughness requirement for 1 Tb/in.² areal density. A probability model is built to simulate the intermolecular force and the contact force, and these two forces are introduced into the modified compressible Reynolds equation governing the air-bearing pressure of the slider. The equation is solved by the finite volume method based on an unstructured triangle-based mesh. The simulation results show that in 1 Tb/in.² areal density magnetic recording the effects of slider/disk roughness on the intermolecular force are negligible. Smaller R _a values will have fewer effects on flying performance.     

Concepts and Limitations of Using Optical Profilometry for Air Bearing Simulations of Hard Disk Sliders

The topography of hard disk sliders is commonly measured with optical profilometers that produce a regularly spaced matrix of topography data corresponding to the pixel array of the CCD camera. This paper explores a new concept that combines optical profilometry and air bearing simulations to achieve an accurate method for predicting fly height early in the manufacturing process. Various sources of error in the topography measurement are analyzed with regards to their impact on the accuracy of air bearing simulations. The findings are illustrated by a feasibility study based on numerical simulations of a slider with a negative pressure air bearing design.     

Design of Carbon Surface Functional Groups on the Viewpoint of Lubricant Layer Structure

Chemical modification technique with X-ray photoelectron spectroscopy has been used for a quantitative analysis of surface functional groups of the carbon overcoats. As the nitrogen content in the carbon overcoat layer increases, the total abundance of functional groups on the carbon overcoat surface increases. The increase of the functional groups leads to an increase of a physisorbed lubricant layer ratio.

Increase of the physisorbed layer ratio on the carbon overcoat surface showed a higher durability on the head/disk interface, and decreased the spin-off of the lubricant on a high rotation of the disk. The increase of the physisorbed layer leads to a higher recovery of the lubricant defect by the wear, and the increase of functional groups on the carbon overcoat surface leads to a stronger interaction of the lubricant with the carbon overcoat surface is estimated.     

磁盘速度与容纳系数对硬盘气膜静态特性的影响

随着硬盘(Hard disk drives,HDDs)中浮动块与磁盘间飞行高度的降低,气体分子与磁头/磁盘间的交互作用逐渐增强,磁盘速度及容纳系数(Accommodation coefficients, ACs)对气膜承载特性的影响越来越重要。采用一种无网格法—最小二乘有限差分(Least square finite difference, LSFD)法,对简化的分子气膜润滑(Molecular gas film lubrication, MGL)方程进行求解,研究了磁盘速度、磁头和磁盘表面ACs对HDDs超低飞高气膜静态特性的影响。数值结果表明：对称性分子交互作用时,磁头和磁盘表面ACs对气膜静态特性的影响明显;非对称性分子交互作用时,磁盘表面ACs对气膜静态特性的影响较大,而磁头/浮动块表面ACs的影响较小;不同ACs条件下,随着磁盘速度或最小飞行高度的增加,压力幅值点位置的变化较均匀。     

A Combined Molecular Dynamics and Finite Element Analysis of Contact and Adhesion of a Rough Sphere and a Flat Surface

A combined molecular dynamics and finite element model and simulation of contact and adhesion between a rough sphere and a flat surface has been developed. This model uses the results of molecular dynamics (MD) simulations, obtained using an embedded atom potential, of a nanoscale Ru-Ru asperity contact. A continuum finite element model of an elastic–plastic microscale Ru-Ru contact bump is then created. In this model, the surface roughness is represented by a system of nanoscale asperities, each of which is represented by a nonlinear hysteretic force vs. distance relationship. The nonlinear hysteretic character of these relations is determined from curve-fits of the MD results. Load vs. interference and contact area vs. interference are determined using this two-scale model for loading and unloading. Comparisons with a single-scale continuum model show that the effect of the nanoscale asperities is to reduce both the adhesion and the real area of contact. The choice of Ru as the material for this work is due to its relevance in microswitches.     

Reversed Micelle Structures in PFPE Lubricant Thin Films on Magnetic Disk Surface Observed by Non-Contact AFM

PFPE lubricants (Fomblin Z-dol) for hard disk surface lubrication have two hydroxyl groups, one at each end of the molecules, and form stable insoluble monolayers at the water surface. In this study, molecular weight-fractionated PFPE lubricant monolayers were transferred from the water surface to solid substrates such as a hydrophilized silicon wafer, gold-sputtered mica, and a hard disk after adjusting the two-dimensional density of the lubricant molecules. The molecular structures of the PFPE lubricant molecules at the solid surfaces were observed by the cryogenic non-contact AFM under ultra-high vacuum. At the hydrophilic silicon wafer surface we could observe a single lubricant molecule in a random coil sphere shape. However, at the non-polar gold surface we confirmed the formation of reversed micelle structures. At the hard disk surface we detected various sizes of reversed micelles of PFPE lubricant in a flat oval shape.     

预浓缩技术离子色谱法测定硬盘部件表面痕量阴离子

本文建立了一种采用预浓缩技术-离子色谱法测定硬盘部件表面痕量阴离子的方法。通过纯水对硬盘部件表面进行清洗,溶于水的表面痕量阴离子采用预浓缩技术浓缩富集,离子色谱进行测定。该方法选择的色谱条件是采用IonPac AS12A离子交换柱,碳酸盐等度淋洗,抑制型电导检测。用该方法对实际硬盘部件表面的痕量阴离子进行测定,测定结果加标回收率在96%～104%,具有灵敏度高,选择性好,操作简单等特点。     

A Simulation Scheme with Coupled Dynamic Models for the Slider and the Suspension Lift-Tab during the Unloading Process of a Hard Disk Drive

A numerical scheme was developed to simulate the interaction between the suspension lift-tab and the ramp of a load/unload-type hard disk drive with consideration of the contact and separation states. The suspension stiffnesses and effective masses were determined based on experiments and finite element analysis. The slider motion was simulated with a degenerated two-degree-of-freedom model, and the results were used as input to a single-degree-of-freedom model for the lift-tab motion. The ramp profile was converted, based on the lateral velocity of the suspension, to a vertical displacement versus time. Computational efficiency was achieved by using a head–disk constraint, instead of a full air-bearing solution, based on dual-scale considerations. The simulation results show that the maximum indentation depth at the tab–ramp engagement increases with an increase in the effective masses, lateral velocity, or ramp angle or with a decrease in the contact stiffness. The bouncing height and bouncing distance of the lift-tab increase with an increase in the contact stiffness, effective masses, lateral velocity, or with a decrease in the suspension stiffnesses. The air-bearing separation time decreases as the suspension stiffnesses, lateral velocity, or ramp angle increases. The coefficient of friction of the tab–ramp interface was found to have a slight influence on the lift-tab behavior on the inclined portion of the ramp.     

On the Effect of Isotropic Hardening on the Coefficient of Restitution for Single or Repeated Impacts Using a Semi-Analytical Method

A semi-analytical method is proposed for the simulation of moderately high-speed impacts of a relatively hard particle on an elastic–plastic substrate. Potential applications of the current modeling approach include shot-peening and ultrasonic peening as well as impacts on functional surfaces such as mechanical seals or bearings. The coefficients of restitution for single impacts on an elastic–perfectly plastic semi-infinite body or one with isotropic hardening have been computed for various impact velocities. The current approach is three dimensional and numerically efficient in terms of CPU time and memory space required. Numerical results are in good agreement with those obtained by other authors for elastic–perfectly plastic behavior. Coefficients of restitution resulting from repeated impacts at a constant initial velocity are also studied. Finally, equations fitting these numerical results are proposed.     

A Critique of Rolling Contact Fatigue Criteria for Bearing Rings with Hoop Stresses

Tensile residual and interference fit stresses not treated in classical bearing formulations are known to reduce bearing rolling contact fatigue (RCF) life. Recent modifications of such theory to account for these stresses have simply included them in the computation of a single yield stress type criterion—either maximum shear or equivalent stress. An alternative modification is proposed and demonstrated for fatigue crack initiation that recognizes the primary influence of the maximum range of shear stress but includes the effect of normal stress on the critical planes, as in other successful bulk fatigue criteria for multiaxial nonproportional stress cycle fatigue.     

Degradation of Disk Lubricant: Ramification in Disk Drives and Direct Detection by TOF-SIMS

The degradation of Z-dol catalyzed by Lewis acid centers on the slider surface leads to chain scission forming one type of fragment terminated with a fluorocarbonyl end-group and the other with a trifluoromethoxy end-group. The former, in contact with humid air, converts to a fluorinated carboxylic acid Z-COOH. Z-COOH is an excellent scavenger for alkali or alkaline earth metal ions. Z-COO^-M⁺ thus formed is a strong surfactant, and, in a humid environment, forms microdroplets embodying water in the core. Metal ions thus scavenged on a disk surface can be readily detected by TOF-SIMS, and the microdroplets by optical microscopy in the dark-field mode. The presence of fragments having a trifluoromethoxy end-group on the disk surface can also be established by TOM-SIMS. A careful intensity analysis of peaks due to anions having a trifluoromethoxy end-group permits a semi-quantitative assessment of the extent of degradation. The study has also shown that degradation is caused by such production processes as tape-polishing and by such disk drive operations as the head flying over a single track or over a band in a seek-mode.     

硬盘测试多机器人协同系统研究

针对当前硬盘测试工艺中自动化程度低、生产效率低、检测设备不易维护等问题,采用多智能体协同技术对硬盘测试工艺进行了自动化改造,分析了硬盘测试过程中多机器人协同原理,介绍了基于Profibus-DP的硬盘测试多机器人控制系统及控制软件,设计并实现了一种用于硬盘测试的Profibus-DP多机器人协同控制系统。研究结果表明,采用Profibus-DP多机器人协同技术极大地提高了硬盘测试的生产效率。     

硬盘物理隔离的安全方法

提出了一种利用硬盘变址与硬盘读写保护区相结合的技术，解决内外网隔离、私密信息及软件兼容性问题的新硬盘安全方法。利用该方法可以形成硬盘新安全标准，使计算机安全站在一个更加坚实的基础上。     

Effect of Slide-to-Roll Ratio on Interior Stresses Around a Dent in EHL Contacts

The present, study extends the transient EHL point contact model and subsurface stress field calculation model to examine the influence of a surface dent on interior stresses in an EHL point contact under various slide-to-roll conditions. Results revealed that under the pure rolling condition the effect of a surface dent on the stresses is quite negligible. The presence of a shallow surface dent is unlikely to reduce the contact fatigue, life so long as pure rolling motion and good lubrication conditions are maintained. Unfortunately, the same cannot be said of the contact if it is operating in the boundary lubrication regime.

When sliding was introduced, the surface indentation generated significantly high pressure spikes with a strong directional preference. These high-pressure spikes cause severe stress concentrations either below the trailing edge of the dent, if it moves faster than the opposing surface, or below the leading edge of the dent, if it moves slower than the opposing surface. The maximum von Mises stress moved close to the surface and significantly increased in value as compared to the smooth surface solution. For the case of simple sliding, the maximum von Mises stress is even greater than the value calculated for the boundary lubrication case.

In regard to maximum tensile principle stresses, the presence of a dent increased the stresses only marginally over the smooth surface solutions. It is unlikely that surface indentation would significantly reduce the contact fatigue life due to Mode 1-type crack initiation.     

表面粗糙度对硬盘超低飞高气膜静态特性的影响

硬盘(Hard disk drives,HDDs)是当前信息存储的主要器件,它的尺寸越来越小、容量越来越大,磁头的飞行高度越来越低.基于考虑气体稀薄效应修正Reynolds方程的线性流比(Linearized flow rate,LFR)模型,采用一种无网格法-最小二乘有限差分(Least squarefinite difference,LSFD)法,求解引入压力流因子和剪切流因子的量纲一雷诺方程,并且研究表面粗糙度对硬盘超低飞高(1～2 nm)气膜静态特性的影响.数值结果表明,表面粗糙度对超低飞高气膜压力分布和承载力的影响较大,而对压力中心的影响较小;飞行高度越低和/或表面粗糙度值越大,对压力分布及承载力的影响越明显;在粗糙度值相同的条件下,仅磁头粗糙且取横向粗糙度时,系统压力分布最高,气膜承载力最大;各种情况下,表面粗糙度对压力中心的变化影响不大,说明磁头飞行比较平稳,系统稳定性较好;另外,基于LFR模型研究表面粗糙度对硬盘气膜静态特性的影响,不仅数值结果精度高,并且具有很高的计算效率.     

Performance Characteristics of Worn Journal Bearings in Both Laminar and Turbulent Regimes. Part II: Dynamic Characteristics

The effects of geometric change due to wear on the dynamic characteristics of journal bearings are determined theoretically in both laminar and turbulent regimes. The dynamic characteristics such as spring and damping coefficients and whirl onset speed of a rigid rotor supported by two identical symmetrically aligned bearings are analyzed by a semianalytical finite element method, and the numerical results for various wear depth parameters are indicated in graphical form.

The geometric change due to wear has significant effects on the principal spring coefficients and on the cross-coupled damping coefficients. The whirl onset speed for a worn journal bearing whose wear depth parameter is larger than 0.3 becomes higher than the speed for a nonworn bearing.     

A Method of Calculation for Contact Pressure between Femoral Head and Cup of Artificial Hip Joint

Abstract

A method of calculation for contact pressure between a hard femoral head and soft plastic cup of a hip joint was studied. Providing that the contact pressure is proportional to the radial deformation of the cup, an equation of equilibrium in terms of a nondimensional parameter was derived. Once the magnitude of the parameter is determined by solving the equation, the contact pressure distribution is easily obtained. An effect of the radial clearance between a femoral head and cup on contact pressure was evaluated using the equation. Furthermore, the effect of Young's modulus and thickness of a plastic cup on contact pressure were also evaluated. According to the results, contact pressure increased with an increment of clearance and Young's modulus. The contact pressure increased with a decrement of thickness of the plastic cup. The analytical solution was compared with the finite element method (FEM) analysis and the agreement was confirmed. An equation of frictional torque was also derived     

硬脆材料超光滑表面磨削技术的现状及发展趋势

概述了具有光滑表面的硬脆材料的应用前景，介绍了国内外在硬脆材料超光滑表面精密磨削技术上的发展现状，提出了获得硬脆材料超光滑磨削表面的主要技术措施，并从国情实际情况出发，提出了我国在超精密磨削技术方面今后应开展的研究工作。