Hydrogen bonding in lubricants for hard disk drives

Hydrogen bonding interaction within a small ensemble of water molecules, that within a group of water molecules and end-groups of Z-dol and Z-tetraol, and the effect of electrolyte ionic pair such as LiCl upon these interactions were examined by the molecular dynamics method based on the potential given by a semi-empirical SCF quantum mechanics. It was revealed that the strength of the hydrogen bond increased rapidly as the size of droplet increased, relating to the population density of hydroxyl units, and that such interaction was amplified significantly by the presence of electrolyte ionic pair. An extraordinary interaction was thus predicted between Z-tetraol and aqueous solution of alkali halide. An experimental study thence conducted revealed that Z-tetraol and aqueous NaCl solution (2 M) formed an extremely stable water-in-oil type emulsion. The emulsion consists of spheroids of several nanometers across wherein several thousands of water molecules are encased by several tens of Z-tetraol end-groups. The interfacial layer of each spheroid is formed and stabilized by the hydrogen bonding interaction between the hydroxyl units of the tetraol-ends and water molecules enhanced by the electrolyte ionic pairs. When disks coated with Z-tetraol were tested for flyability at high humidity, the head-disk interaction detected acoustically increased with time. Spontaneous formation of globules resulting from interaction of tetraol end-groups and water molecules assisted by ubiquitously present alkali halide contaminant would account for the observed increase of the head-disk interaction. Possible structures of perfluoropolyether lubricants ideal for magnetic disk application are discussed.     

Contact-induced off-track vibrations of air bearing-slider-suspension system in hard disk drives

Contact-induced vibration of air bearing-slider-suspension system is a crucial issue for slider flying stability and head positioning precision of 1 Tbit/in² hard disk drives. In this paper, the contact-induced off-track vibrations of air bearing-slider-suspension system are investigated by simulation. A dynamic simulator is developed to calculate the interactions between the air bearing dynamics and vibrations of slider-suspension assembly. The simulation model consists of a finite element model of suspension assembly, an air bearing model based on the generalized lubrication equation, and a slider–disk contact model based on the probability distributions of surface roughness. A sequential method is used to couple all these models and analyses. The time history of the slider and suspension motions, together with the time-varying forces including air bearing force, air shear forces, contact force and friction force can be obtained. The effects of different contact conditions, such as the contact intensity, friction coefficient, and disk surface waviness on off-track vibrations are investigated numerically in details. The results reveal some mechanisms on how these factors contribute to the off-track vibrations of suspension assembly.     

Adaptive multilevel method for the air bearing problem in hard disk drives

An adaptive grid-generating algorithm is constructed and integrated with the multigrid method to form a numerical scheme that suits slider air-bearing simulation of hard disk drives. The relative truncation error, a by-product of the multigrid method, is used in grid adaptation criteria. Finer meshes are constructed over nodes of the current finest grid where the relative truncation error exceeds a predetermined tolerance. The union of these finer meshes forms a new level of grid, which may not cover the entire domain of the coarse grid underneath. The final grid system thus constructed is composed of levels of uniform grids with decreasing mesh sizes. This composite grid structure incorporates with numerical resolution as needed and efficiency of computation. A shaped rail, negative pressure slider is used to demonstrate the effectiveness of this numerical scheme. Compared with the traditional multigrid method, the proposed adaptive multilevel method can significantly reduce the computation work for achieving the same level of accuracy.     

The decomposition mechanisms of a perfluoropolyether at the head/disk interface of hard disk drives

The decomposition mechanisms of a perfluoropolyether (ZDOL) at the head/disk interface under sliding friction conditions were studied using an ultra‐high vacuum tribometer equipped with a mass spectrometer. Chemical bonding theory was applied to analyze the decomposition process. For a carbon coated slider/CN_x disk interface, the primary decomposed fragments are CFO and CF₂O, caused by the friction decomposition and electron bombardment in the mass spectrometer. For an uncoated Al₂O₃–TiC slider/CN_x contact, CF₃ and C₂F₃ fragments appear in addition to CFO and CF₂O, resulting from the catalytic reactions and friction decomposition, indicating that the decomposition mechanism associated with friction leads to the breaking of the main chain of ZDOL and forms CF₂=O, which reacts with Al₂O₃ to produce AlF₃, and the rapid catalytic decomposition of ZDOL on the AlF₃ surface follows. Moreover, the effects of frictional heat, tribocharge, mechanical scission and Lewis acid catalytic action, generated in friction process, on the decomposition of ZDOL are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Behavior of ultrathin liquid lubricant films for contact sliders in hard disk drives

In this paper, we describe the behavior of ultrathin liquid lubricant films for contact sliders in hard disk drives. In the experiments, the ultrathin liquid lubricant film behavior is investigated using Zdol and cyclotriphosphazene-terminated PFPE lubricant which have different end groups as a function of lubricant film thickness. The disks are examined with a scanning microellipsometer before and after contact slider experiments. It is found that the lubricant film thickness profiles almost do not change, when the lubricant film thickness is less than one monolayer. It can also be observed that lubricant film thickness instability due to dewetting occurs as a result of slider-disk contacts for the tested lubricants and the films undergo spontaneous redistributions, resulting in significantly nonuniform film thickness profiles, when the lubricant film thickness is thicker than one monolayer. In addition, it is found that the observed behavior of ultrathin liquid lubricant films for cyclotriphosphazine-terminated PFPE lubricant contrasts markedly with that for Zdol. The difference between cyclotriphosphazene-terminated PFPE lubricant and Zdol is only the functional end group. Therefore, it may be concluded that their unstable lubricant behavior depends on the chemical structure of functional end groups.     

Corrosive effect of acrylic acid on magnetic head and media of an operating hard disk drive

Magnetic heads and media in a magnetic hard disk drive are often attacked by corrosive gases, such as hydrochloric acid, sulphur dioxide and acrylic acid, ect. In this paper, we investigate the corrosion progress of heads and media subject to contact-start-stop (CSS) operation under diluted acrylic acid vapor attack. It is found that under elevated temperature and humidity, acrylic acid vapor not only accelerates the magnetic hard disk media corrosion rate at carbon overcoat pinhole locations, but also induces new corrosion products such as cobalt acrylate and nickel acrylate. Different corrosion pattern at tribological contact area and non-contact area in an operating hard disk drive are observed and the related corrosion mechanism is discussed. This paper presents a view of corrosion products and corrosion progress at the different locations of magnetic heads and media under the diluted acrylic acid vapor attack in an operating hard disk drive.     

A robust, discrete, near time-optimal controller for hard disk drives

This paper presents a robust, discrete, near time-optimal control algorithm for hard disk drives. Building on the continuous-time control law of Newman [Trans. Automatic Control 35 (7) (1990) 841] and Newman and Souccar [J. Dynamic Syst. Measure. Control 113 (1991) 363], the chattering phenomenon for continuous-time systems is first examined, and it is shown how additional chattering can occur in the discrete-time case. A criterion for the selection of control parameters to prevent chattering in the discrete-time case while assuring controller stability is then suggested. The controller developed is applied to a commercial hard disk drive. Compared to the more commonly used PTOS, the proposed controller significantly reduces chattering while maintaining comparable seek time to reach the destination track.     

计算机硬盘磁头滑块的设计与加工研究

研究计算机硬盘磁头滑块承载面结构的设计理论与加工方法。分析了现有磁头滑块的结构特点及其设计理论和设计方法;利用光刻及干法刻蚀的工艺及设备,进行了所设计磁头滑块的微加工;并利用三维表面形貌测量仪对所加工的磁头进行了加工质量分析,给出实验测量值与设计值的比较结果。     

Molecular tribology of disk drives

A good molecular level understanding of the tribological properties of the materials at the slider-disk interface is essential to the future development of disk drive technology. This paper provides a short overview of the molecular tribology of disk drives related to the selection of lubricant materials for the slider-disk interface. Besides providing criteria for lubricant selection, this paper briefly discusses our current understanding of stiction and friction forces, lubricant degradation, lubricant mobility, spin-off, and lubricant transfer to sliders. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of environmental conditions on the stiction behavior of laser textured hard disk media

The effect of relative humidity and temperature on the stiction behavior of laser textured and mechanically textured hard disk media is investigated using contact–start–stop testing. The coefficient of stiction for mechanically textured media was found to increase dramatically at high humidity while it remained nearly unchanged for laser textured media. A physical model is used to explain the differences in the stiction behavior between laser textured and mechanically textured media as a function of relative humidity. The model suggests that the differences between laser textured and mechanically textured media are due to the different bearing characteristics of the two types of media. The effect of increasing temperature was found to reduce stiction at high humidity for mechanically textured media. The effect of temperature on stiction appears to be related to changes in lubricant properties with temperature.     

磁悬浮硬盘驱动器及其静电防护设计

磁悬浮硬盘可以提高硬盘的转速，减少寻道时间，提高存取速度。但完全悬浮在空中的硬盘会因与空气的高速摩擦而产生静电，危害硬盘信息存储的安全性。这里针对研究开发磁悬浮硬盘技术中的静电干扰问题，提出了安全可靠的解决办法。     

粉末高温合金盘的切削加工

介绍了粉末高温合金盘的应用和发展趋势,并通过和其他几种材料盘类零件的切削加工情况进行比较,指出了其制造和切削过程中存在的问题,同时探讨了提高粉末高温合金盘切削加工效率的几点措施,包括典型粉末高温合金盘的加工工艺路线以及粉末高温合金盘切削加工对刀具和设备的需求.     

Tribological properties of a perfluoropolyether lubricant with 3-phenylpropyl functional group for hard disk media

A new perfluoropolyether lubricant (LUB-A) with a 3-phenylpropyl functional group at both ends of the main chain was designed and synthesized by the authors for use in hard disk media, and its tribological performance was evaluated. Time-of-flight secondary ion mass spectrometry showed that LUB-A film on the disk lost none of its functional groups even after a 672 h exposure at 23 °C and 55% RH, although AM3001 lost 94% of its (3,4-dioxomethylenephenyl)methyl functional groups after the same period of exposure. It was found that cyclotriphosphazene (X-1P) was more than four times more soluble in 2 nm thick LUB-A film than in AM3001 film. The degradation ratio of read-back signals in the seek test was less than 5% over a wide range of X-1P content in LUB-A film and no micro-phase separation was induced, in contrast to AM3001 film that could not keep the degradation ratio at less than 5% without inducing micro-phase separation. LUB-A also showed better migration properties at 80 °C and 3% RH than AM3001. LUB-A was proved to be more chemically stable and to show better tribological performance than the currently popular AM3001 when it was used as a thin film mixed with X-1P.     

Investigation of micro-phase separation of the additive,cyclotriphosphazene, in lubricant films of hard disk media

The micro-phase separation of the additive, cyclotriphosphazene (X-1P), in perfluoropolyether (PFPE) lubricant films on hard disk media was studied. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) indicated that the small spots appearing on the disk surface consisted predominantly of X-1P. Observation using an atomic force microscope (AFM) revealed the micro-phase separation process to be the sudden, continuous appearance of new spots some time after coating the film. Some spots grew over previous ones, while some spots dissolved. Finally, they stopped growing and the number of spots became saturated. The solubility of X-1P in the lubricant film increased in the order of ZDIAC, ZDOL2000, ZDOL4000 and Z03, and that in bulk lubricant increased in the order of Z03, ZDOL4000, ZDOL2000 and ZDIAC. The order of solubility of X-1P in the film did not correspond to that in the bulk.     

超硬材料刀具在机械制造中的应用

介绍了我国超硬材料刀具的应用现状 ,论述了超硬材料刀具的应用在经济上的可行性 ,分析了超硬材料刀具在机械制造中应用的制约因素 ,提出了我国发展超硬材料刀具的对策     

Dynamic characteristics of permanent magnetic thrust bearing used in vessels

Journal of Mechanical Science and Technology - The axial stiffness of a permanent magnetic thrust bearing (PMTB) decreases from 109 N/m to 107 N/m compared with the sliding bearing and the...     

Pumping effect of sliders in hard disk systems

The accumulation of contaminants on the slider surface is of paramount importance in hard disk drives because only an ultra small amount of contaminants on the slider surface will cause catastrophic failures for hard disk drives with a spacing between the slider and the hard disk as small as 10 nm, which will be reduced further in the near future to about 5–6 nm in order to attain a recording density of 100 Gbit/in². In this paper the pumping effect of the slider is proposed as one mechanism of the contaminant accumulation on the slider. Analysis of the pumping effect is conducted by considering the adsorption process and the shear flow process on the slider surface in terms of the continuum. It is found that the pumping effect can be divided into two different classifications depending on the value of the parameter λ which is the ratio of the maximum shear flow of the adsorbed film to the maximum adsorption amount: the shear flow rate-controlling pumping effect for λ < 0.1 and the adsorption rate-controlling pumping effect for λ > 0.4. For the shear flow rate-controlling effect, the accumulation rate of the contaminant is directly proportional to the disk surface velocity, while inversely proportional to the flying height of the slider. An erratum to this article can be found at .     

磁力联轴器在卷筒驱动中的应用

多数移动机械的供电、供水都采用卷筒形式 ,在起重机械、港口设备及电厂输煤系统等领域中 ,电缆卷筒和水管卷简装置的使用相当广泛。卷筒驱动的形式多种多样 ,这里要介绍的是一种以磁力传递扭矩的驱动形式。磁力联轴器结构简单紧凑 ,能有效防止卷筒及电缆等其他设备的损坏事故。1　结构与特点磁力联轴器工作原理简单 ,如图 1所示 ,它靠驱动轴侧与从动轴侧之间的永磁吸引力传递扭矩 ,磁力片之间的间隙可以调整 ,间隙大 ,传递的扭矩小 ,间隙小则传递的扭矩大。图 1　磁力联轴器原理1.驱动轴　 2 .从动轴　 3.磁片　 4 .空气间隙卷筒连接在减速…     

Optimal disk clamp design to minimize stress variation of disks in a hard disk drive

To avoid disk waviness and warpage in a hard disk drive, it is desirable for the stress distribution on disks fastened to a spindle motor by a clamp to be uniform in the circumferential direction while sufficient clamping force is maintained. The objective of this work is to find a clamp configuration that minimizes the circumferential stress variation on the disks while maximizing the clamping force. Topology and shape optimization methods were employed to find the optimal clamp configuration. To facilitate the optimization problem, a model for the surface contact between the clamp and the top disk was simplified to a static model where the disk clamp and spring were connected. By incorporating the surface recess, the optimized clamp has equal stiffness in the circumferential direction, except for the four tooling hole areas. Numerical simulation confirmed that the optimized clamp reduced the stress variation by about 78% without sacrificing the clamping force; in fact, it increased the clamping force.