高密磁记录系统的动力学分析

讨论多聚酯流体润滑的IBM3370磁头/磁盘系统,以期提高磁记录密度。润滑模型中考虑超薄流体润滑的剪薄效应,并用有限差分法对润滑方程进行求解,应用摄动理论建立IBM3370磁头/磁盘系统的动力学模型,分别对气体润滑和液体润滑的2自由度磁头的动力响应进行仿真。仿真结果表明,液膜润滑的磁头飞浮高度在20nm时,磁头仍能保持较好的稳定性。     

磁头/磁盘系统静态特性实验研究

通过实验来研究磁盘转速对磁头飞行姿态和磁头读写性能的关系.研究表明:磁头滑块飞行高度和俯仰角伴随着磁盘转速的增大而增大;磁盘转速增大,磁头飞行高度增加,降低了磁头读出信号的能力,与此同时,信噪比也大幅下降.实验研究结果为磁头/磁盘结构设计提供了依据.     

磁盘高速运行过程中磁头运行状态的监测方法

随着磁头磁盘间有效距离的不断降低,磁头可能以飞行、冲浪和滑行三种状态工作,为了使磁头能够稳定工作,必须实时监测和识别磁头所处的状态。提出一种利用摩擦电流来实时监测磁头工作状态的方法。利用空气轴承电动机、热飞高控制磁头、功率加载控制单元、静电计、加载/卸载单元、静电屏蔽箱等组建了摩擦电流的测试系统。通过每隔0.1 V逐步给飞高控制磁头加载电压的方式,改变磁头磁盘间的距离,测量了不同磁头磁盘间距时的摩擦电流,得出了区分三种工作状态的摩擦电流区间。当摩擦电流值在10~(-4)μA以下时,磁头工作在稳定的飞行状态;当摩擦电流值在6~50μA时,磁头工作在冲浪状态;当摩擦电流值在140μA以上时,磁头工作在滑行状态。     

磁头磁盘系统动特性参数及系统稳定性分析

对硬盘系统的动特性进行了数值仿真，其中磁头结构为IBM3370，润滑模型中引入了二阶泊松流因子，保证建模精度。利用摄动法建立了气体润滑的静态方程，并给出了数值解。讨论了最小膜厚度、磁盘转速和磁头倾角对空气膜刚度系数、阻尼系数以及对系统稳定性的影响。结果表明，通过最小膜厚度、磁盘转速和磁头倾角的优化可以改善硬盘的设计。其中磁头倾角的优化可以同时满足硬盘高刚度和高稳定性的要求。     

硬盘磁头飞行姿态的实验研究

用动态飞行高度测试仪DFHT测试了在不同转速下磁头的飞高、俯仰角和侧翻角,磁头飞行高度和俯仰角,随着磁盘转速的增大而增大,而侧翻角则先增加后减小。由结果可以看出,随着转速的增加,俯仰角变化比较大,说明磁盘转速对磁头的左右翻转运动的影响比较大,而侧翻角变化相对比较微弱,用动态电性能测试机测试相同情况下不同转速下输出磁信号的幅值,可以看出随着飞高的增加,输出信号的幅值也随着减小。     

计算机磁头/磁盘超薄气膜润滑稳定性

以任意拉森数的超薄气体润滑方程为基础,给出磁头刚体小扰动对空气轴承滑块 (ABS)气膜压强摄动方程。采用算子分裂法求解气膜压强和非结构三角网格的有限元法解压强摄动方程,得到气膜的刚度系数和阻尼系数矩阵。模态分析得到磁头气固耦合系统的固有频率,衰减率和振型。以Ω型磁头为例,分析了在不同气膜厚度和磁盘转速下的磁头稳定性。研究结果表明,磁头稳定性对气膜厚度很敏感,在小气膜厚度运行时,系统固有频率高,稳定性好;磁头升沉和纵倾运动的动力耦合,使磁头系统固有频率和衰减率降低,对稳定性不利;高转速的磁盘对磁头稳定性不利,但影响不大。     

超薄气体润滑磁盘／磁头系统动力学分析

应用修正后的雷诺方程描述超薄气体轴承的润滑特性,应用伽辽金近似建立气体轴承有限元法分析模型。使结构动力学模型与气体动力润滑模型有机地集成起来,建立了气体轴承-磁头结构的系统动力学模型。在考虑表面粗糙度对磁头飞浮稳定性影响时,引进方向模式参数以描述磁盘的表面形貌,仿真结果表明,粗糙表面能有效降低磁头瞬态响应时间,通过参数合理设计可阻止磁头的共振响应,粗糙度的方向特征对动力学的响应有一定的影响,但随着膜厚与粗糙峰高比率的增大,方向特征的影响将逐步降低。     

硬盘磁头电信号动态测试实验研究

根据硬盘磁记录工作原理可知,磁头输出电信号的强弱直接反应了磁头飞行高低的变化,因此本文通过测试硬盘在低频率振动下磁头电信号的变化情况来分析磁头的飞行状况.结果表明当激振频率小于25Hz时,其电压输出值的波动很小,输出结果具有一定的规律性.当频率大于50Hz时,电压输出波动幅度就比较大.磁头在磁盘表面的振动幅度也比较历害...     

磁头热变形对飞行高度影响的数值分析

计算机硬盘向小型化和高密度存储量方向发展,硬盘磁头的飞行高度越来越低,同时磁头的厚度也越来越小,更容易发生热变形,从而影响飞行高度。目前产品设计中采用多种措施降低热变形以图保证飞行高度稳定性,影响了其他性能。用数值仿真的方法分析磁头热变形与其稳态飞行高度之间的关系,再利用高阶滑移模型修正超薄气膜雷诺方程,采用加权余量法和有限元方法求解气膜压力方程组,得出气膜压力分布,建立磁头在盘片上飞行的简化物理模型,分析磁头热变形与稳态飞行高度之间的关系。计算结果表明,一定的热变形反而有利于稳定磁头飞行高度。     

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。     

Effect of hard-disk drive spindle motor vibration on dynamic microwaviness and flying-height modulation

In order to achieve higher recording densities up to 1 Terabit per square inch using conventional magnetic recording technologies, the recording slider will need to be physically spaced very close to the rotating disk, possibly via the use of an air-bearing surface. However, as the recording slider is flying at such ultra-low spacing of few nanometers over a high-speed rotating disk, it is experiencing disturbances from various different sources and of a wide frequency range. These disturbances may cause the recording slider to vibrate significantly, a condition known as flying-height modulation (FHM), which may result in data loss and possibly head–disk interface failure. A significant source of slider excitation is due to low frequency surface topographical features of the rotating disk, termed dynamic microwaviness. Dynamic microwaviness is a dynamic property of the disk and differs from regular topographical microwaviness, which is a static property. Most research works on dynamic microwaviness and FHM have been focused at the component level, using somewhat idealized conditions, such as high performance air-spindle motors that exhibit very low vibration amplitudes. In this paper, actual hard-disk drive spindle motors are used to investigate the effect of spindle motor vibration on dynamic microwaviness and FHM. It is found that there is a clear connection between spindle motor vibration and dynamic microwaviness that affects FHM.     

Numerical Simulation of the Head/Disk Interface for Patterned Media

The use of patterned media is a new approach proposed to extend the recording densities of hard disk drives beyond 1 Tb/in.². Bit-patterned media (BPM) overcome the thermal stability problems of conventional media by using single-domain islands for each bit of recorded information, thereby eliminating the magnetic transition noise (Albrecht et al., Magnetic Recording on Patterned Media, 2003). Considering steady state conditions, we have transferred the pattern from the disk surface onto the slider surface and have investigated the pressure generation due to the bit pattern. To reduce the numerical complexity, we have generated the bit pattern only in the areas of the slider near the trailing edge, where the spacing is small. Cylindrical protrusions were modeled using very small mesh size on the order of nanometers to obtain the flying characteristics for the entire slider air bearing surface (ABS) using the “CMRR” finite element Reynolds equation simulator (Duwensee et al., Microsyst Technol, 2006; Wahl et al., STLE Tribol Trans, 39(1), 1996). The effect of pattern height, pattern diameter, slider skew angle, and slider pitch angle on flying height of a typical slider is investigated. Numerical results show that the flying height decreases for a patterned slider and the change in flying height is a function of the pattern height and ratio of the pattern diameter to the pattern pitch. In comparison to discrete track media, the flying height loss is larger for a patterned slider disk interface for the same recessed area of pattern.     

Particle Contamination on a Thermal Flying-Height Control Slider

Particle contamination on a slider in a hard disk drive (HDD) affects the HDD’s reliability. With the introduction of the thermal flying-height control (TFC) slider, the temperature in the head–disk interface (HDI) becomes non-uniform, which induces a temperature-gradient dependent force on particles moving in the HDI. The present article investigates the effect of this force, the so called thermophoretic force, on a particle’s motion in the HDI as well as its effect on particle contamination on the TFC slider. By numerical simulation of the particle’s trajectory together with an analytical analysis, we show that the thermophoretic force is always negligible compared to the Saffman lift force, which points to a direction parallel to the thermophoretic force. We conclude that the current particle contamination simulator without any thermophoretic forces included would not be significantly altered by the inclusion of these forces.     

Investigation of Lubricant Transfer between Slider and Disk Using Molecular Dynamics Simulation

A model for lubricant transfer from a rotating magnetic recording disk to a magnetic recording slider is developed using molecular dynamics simulation. The combined effect of disk velocity and local air-bearing pressure changes on lubricant transfer is investigated. The simulation results indicate that local pressure changes in the absence of disk circumferential velocity can cause lubricant redistribution on the disk, while local pressure changes on a moving disk can result in lubricant transfer from the disk to the slider. The amount of lubricant transferred from the disk to the slider and the lubricant buildup on the disk are a function of the local pressure change and disk velocity. The amount of lubricant transferred from the disk to the slider and the height of lubricant buildup on the disk surface decrease with an increase in the number of functional groups of the disk, a decrease in the local pressure change, and a decrease in the disk circumferential velocity.     

Effect of Air and Helium on the Head–Disk Interface During Load–Unload

The tribological characteristics of the head–disk interface are investigated during load–unload for air and helium-filled drives as a function of the pitch static angle and the roll static angle between slider and disk. A custom-made experimental tester inside a sealed environmental chamber was used to determine the regions of “safe” pitch static angle and “safe” roll static angle in air and helium environment during the load–unload process. The presence of head–disk contacts during load–unload were evaluated by measuring the acoustic emission signal and the decrease in rotational speed of the spindle. Scanning electron microscopy and optical surface analysis were used to investigate wear of the slider and the redistribution of lubricant on the disk surface after 10,000 load–unload cycles. The results indicate that the tribological performance of the head–disk interface is improved in helium environment compared to air environment.     

Thermomechanical finite element analysis of slider-disk impact in magnetic storage thin film disks

Oblique impact of a slider with a rotating disk in a hard disk drive was analyzed using the finite element method. A three dimensional, thermomechanical, impact model was developed to study the mechanical and thermal response during the impact of a spherical slider corner with a rotating disk. The model was validated by comparing the finite element results with analytical solutions for a homogeneous glass substrate disk. Impact penetration, stress and incurred flash temperature were obtained for various normal impact velocities. The effects of material layers on the disk were also investigated by introducing layers with different material properties and thicknesses. It was found that for a rounded slider corner and a critical normal impact velocity of 0.03 m/s studied in this work, the layers have insignificant effects on the mechanical response and small but predictable effects on the flash temperature.     

Ultra-low-flying-height design from the viewpoint of contact vibration

The design of a head-disk interface for ultra-low flying height has been studied from the viewpoint of contact vibration. It is known that a super-smooth disk is necessary for a slider to fly at an ultra-low flying height; however, such a disk increases the friction force, which potentially increases the vibration of the slider. To solve this problem, the head-disk interface must be optimized to reduce this increased vibration. It has been shown that a large pitch angle and center-pad-mounted read/write elements have advantages in terms of slider/disk contact. It has also been found that a micro-texture on the air bearing surface can prevent contact vibration. Moreover, a frequency-shift-damping slider was found to damp the vibration effectively. To further investigate these findings, numerical simulation and modeling of slider dynamics during contact have been performed. Their results revealed two zones of contact vibration: a stable zone and an unstable zone.     

Analysis of Surface Textured Air Bearing Sliders with Rarefaction Effects

A numerical model is developed to study the effect of texture on air bearing sliders for large Knudsen numbers. The effect of texture location, texture size, and density on the pressure generation is studied. First, a textured plane slider parallel to the disk surface is investigated, and the texture parameters are determined that result in optimum pressure generation. Then, a plane inclined slider is studied using optimum texture parameters found in the parallel slider case. Thereafter, the effect of texture on the steady state flying characteristics of an actual magnetic recording slider is investigated. Finally, the flying height modulation, pitch, and roll motion of a textured slider (pico and femto form factors) are determined numerically by exciting the slider using a step on the disk. Comparison of the results for textured and untextured sliders is made. It is found that textured sliders show better dynamic performance compared to the untextured sliders in terms of stiffness and damping.     

Tribological performance of nano-thin fluoropolymer coated sliders

With the increase in recording density, any accumulation on slider surface can cause serious problems, such as high fly–stiction and extensive slider–disk interaction. Therefore, how to mitigate the accumulation on slider surface and thus, improve the stability and reliability of head–disk interface is becoming an important issue. In this work, a nanothin fluoropolymer overcoat with very good oleophobic and hydrophobic properties was applied on slider surface with a dipping process. Tribological performance, such as fly–stiction, normal stiction, and takeoff and landing processes, of the coated sliders was studied. Test results show that although normal stiction is not lowered, normal stiction modulation is reduced obviously by the overcoat. Fly–stiction and its modulation of coated sliders are much smaller than those of uncoated sliders. Coated sliders show much better takeoff and landing performance during contact start stop tests. After tests, the surfaces of tested sliders and disks were examined with an optical microscope, surface reflectance analyzer, and TOF–SIMS to interpret the tribological performance of the coated sliders. It can be concluded that the fluoropolymer overcoat reduces the amount of accumulation on slider surface and thus, improves the tribological performance of the coated sliders.