Stiction problem of annular-shaped laser textured bump on a hard disk

The stiction force strongly depends on the bump parameters. Numerical simulation has been used to estimate the stiction force. Several schemes have been proposed. In these schemes, the relation between the elastic deformation of bumps and the load plays a very important part. To estimate the stiction force of annular shaped bumps, the solution of the cylindrical contact problem of Hertz theory is used. But this solution doesn't converge so that it may not give the correct solution for the annular contact problem. This paper presents an exact solution of elastic deformation of laser textured bumps for the annular type. The exact and precise solution is obtained numerically and analytically. The contact problem is reduced to a pair of integral equations of the Fredholm type. It can be solved by a simple numerical method. The solution can be used for the numerical estimation of the bump deformation during the CSS process. The results are compared with former researches.     

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.     

Effect of peak radius on design of W-type donut shaped laser textured surfaces

Friction/stiction behavior of ultra high density magnetic disk drives can be controlled by controlling the size and shape of the laser bumps using a laser texturing tool. Different laser bump parameters like rim radius, rim height, peak radius and number of bumps (under the slider) play an important role in the design of laser textured disk surfaces. In the present study, an algorithm is developed for generation of W-type laser bumps on the computer. W-type laser surfaces with a Gaussian height distribution have been generated and contact analyses of these surfaces have been carried out. Design curves have been generated to calculate critical number of asperities required to minimize wear and stiction. Effect of the coefficient of friction on the number of bumps has also been studied.     

The effects of texture height and thickness of amorphous carbon nitride coating of a hard disk slider on the friction and wear of the slider against a disk

In order to minimize the stiction force caused by contact of the extremely smooth surfaces of head sliders and disks in hard disk drives, texture is usually applied on the disk surface. For future contact/near-contact recording, the stiction-induced high friction between slider and disk will become a problem. Texture on the slider/disk interface will still be an expected method to reduce friction. Recently, it was suggested to texture the slider surface. A protective coating is usually required on the textured slider surface to reduce wear of the texture. The results showed that texture on the slider surface was effective in reducing the friction between head sliders and disks. On the other hand, the texture and coating on the slider surface increase the spacing between the read/write element and the magnetic layer of the disk. The necessary and effective texture height and coating thickness are still not clear. In the present research, island-type textures with different heights (3–18 mn) were formed on slider surfaces by ion-beam etching. Amorphous carbon nitride (a-CN_x) coatings of different thicknesses (0–50 nm) were coated on the textured slider surfaces as a protective overcoat. The friction and wear properties of these sliders were evaluated by constant-speed drag tests against hard disks coated with diamond-like carbon (DLC). The results show that 2 nm texture on a slider surface is sufficient for low (0.3–0.5) and stable friction of the slider against the disk in a drag test, and coatings thicker than 5 nm show similar wear resistances of the texture on slider surfaces.     

Detecting oscillation amplitude and defects of hard disk rotating in high speed by laser Doppler technique

Laser Doppler technique is widely used in industry for the purpose of detecting vibration and oscillation. Many researchers have found that using non-contact laser vibrometry to measure surface roughness of disk under dynamic status is more difficult than that of the static condition. In this paper, we proposed a laser Doppler technique for the purpose of measuring the oscillation amplitude and defects of hard disk rotating in high speed. Laser light source, optical Doppler system, detector and data process system were integrated in our experimental system. The whole system was calibrated using a sinusoid generator. The method for converting the measured voltage signals into the corresponding size data was described in detail. It was found that the average size of defects of the hard disk in our experiment is from 1 μm to 5 μm. The developed technique may be useful for quality control in real time in mass production processes.     

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.     

Roughness effects on head–disk interface durability and reliability

This paper deals with the tribological reliability and durability issues in modern magnetic recording hard disk drives, where the slider flies at typically less than 10 nm. Specifically, we investigate the effect of disk surface roughness on the above performance characteristics. The durability of the interface is investigated using low-pressure on-track tests. The drive-level reliability data are presented to confirm general conclusions reached from the component-level testing. Component-level slider–disk clearance measurements are also used to better understand how the roughness affects both durability and reliability. Finally, we discuss possible explanations for the experimentally observed relationships.     

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.     

Two nanometer IBD overcoats development for magnetic and tribology improvement

To reduce the overcoat thickness to achieve higher recording density, 2 nm carbon overcoat produced by ion-beam-deposition (IBD) was designed to replace conventional IBD/sputtered-CN dual layer overcoat. Different combinations of overcoat films were deposited with various thicknesses by DC sputter or IBD. Optimized Z-Tol lubricant and additive were coated on the overcoat films. We found that a new designed IBD overcoat with optimized lubricant can effectively decrease the total head-disk spacing interface which results in 1.5 dB OW, 0.4 dB SNR, 0.7 dB SpN and 0.013 dBm Nm, better and higher than the previous design. It also shows promising tribological performance due to the more diamond like structure and higher lubricant bonding ratio.     

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。     

Numerical study on energy transmission for rotating hard disk systems by structural intensity technique

The main purpose of this paper is to apply structural intensity technique to indicate the magnitude and direction of vibration energy flow for a rotating system, so as to modify and control the energy flow path to reduce the vibrational problems. Numerical simulations are carried out for a rotating flexible disk-spindle system supported by ball bearing and flexible shaft by the finite element method, and the vibrational energy transmission caused by an eccentric mass is analyzed by using structural intensity technique. The structural intensities in hybrid 1D, 2D and 3D elements, which are used to model different components of HDD, are obtained. Three different damping effects on the diversion and dissipation of energy flow are investigated. The calculated results show that different types of damping or dampers have different effect on energy flow path in HDD. Through numerical simulation, a more reasonable design scheme may be explored by scientifically arranging damping components for HDD to further suppress its vibration and noise problems.     

Development of a novel cubic boron nitride cutting tool with a textured flank face for high-speed machining of Inconel 718

Nickel-based superalloys such as Inconel 718 offer several advantages, including high-temperature strength and high corrosion resistance; this has led to a rapid increase in the demand for such materials, particularly in the aircraft industry. In contrast, these alloys are known to be among the most difficult-to-cut materials because of their mechanical and chemical properties, and tools used for this purpose have extremely short lifetimes. Recently, cubic boron nitride (CBN), which is the second hardest of all known materials, has received significant attention as a material for cutting tools and has already established itself in many fields of application. However, the performance of CBN tools is still insufficient for practical use, especially in the high-speed machining of Inconel 718. To overcome this problem, we first conducted orthogonal cutting experiments on Inconel 718 and performed cross-sectional observations of the CBN cutting tool in order to identify its wear mechanisms in continuous cutting operations under high-speed machining conditions (300 m/min). As a result, it was found that fatal tool failure occurs through crater and flank wear because of diffusion led by high cutting temperatures and subsequent chip adhesion to the tool flank face, accompanied by cutting edge chipping. Based on these results, a CBN cutting tool with a textured flank face was newly developed to improve the cutting tool life. Experimental: results showed that micro grooves generated on the flank face significantly suppressed the cutting edge chipping and remarkably extended the lifetime of the CBN tool during high-speed machining of Inconel 718.     

Tribology of X-1P vapor lubricated hard disks

The tribological characteristics of vapor lubricated X-1P films on carbon coated disks were investigated as a function of lubricant thicknesses (0.2–2 nm) and compared with traditionally dip-coated X-1P and PFPE films. Glide and flyablity tests were performed and the lubricant redistribution in the ‘wear track’ was investigated using a surface reflectance analyzer (SRA). A critical lubricant thickness was found to exist for X-1P below which lubricant accumulation was observed, while lubricant loss was found to be present if the thickness of the lubricant film was greater than the critical thickness.     

硬盘驱动架NC加工过程几何仿真研究

针对硬盘驱动架加工特性和企业的特点,提出加工过程仿真精益解决方案,解决硬盘驱动架加工过程刀具无法定义和特殊工艺无法实现的问题,实现硬盘驱动架NC加工过程的几何仿真.     

Analysis and measurement of torque hysteresis of pivot bearing in hard disk drive applications

During hard disk drive (HDD) operation in the track-following, short seek and seek settling modes, the motion of the actuator, which is supported by a pivot bearing cartridge, has very small amplitudes. The effect of hysteresis friction from the pivot bearing becomes significant, impacting servo performance. Often such effects are not well understood and thus, it is not being taken into consideration during servo design. A study of the hysteresis friction behaviour of pivot bearings is presented. An integrated test apparatus for pivot bearing analysis was designed and built where a Laser Doppler Vibrometer (LDV) was used to accurately measure the displacement and velocity of the actuator for feedback control. Using this test apparatus, the hysteresis friction behaviour in both frequency and time domain was analysed. The effects of pre-load, oscillating magnitude and oscillating frequency were investigated. The results obtained can now be used for servo design and pivot bearing evaluation.     

Performance of cutting tools with dimple textured surfaces: A comparative study of different texture patterns

Recently, surface texturing has received much attention as a method of enhancing the tribological properties of a cutting tool surface. However, effective texture patterns and dimensions on a tool surface are still difficult to obtain and suitable textures can be obtained only by trial and error. In order to overcome this problem, we newly develop cutting tools with dimple-shaped textures having different dimensions and arrays, generated on the tool rake face. In addition, we evaluate their crater wear resistance and cutting forces in steel material cutting. Furthermore, under various cutting conditions, the performances of the cutting tools with dimple-shaped textures are compared with those of tools with groove-shaped textures in order to establish a guideline for designing appropriate surface textures on cutting tool surfaces. A series of cutting experiments demonstrate that the dimple textures significantly improve the crater wear resistance and the tribological behavior on the tool rake face, and they exhibit a superior performance compared with those with groove textures, especially in a severely lubricated environment.     

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.     

Interface technology of ultra-low flying height and highly stable head–disk interface for perpendicular magnetic recording

This paper reports authors’ efforts in slider and interface technologies with extremely small and very high stability head–disk spacing. The dual shallow step strategy is proposed in the femto form-factor slider design. It is found that the dual shallow step design is very effective in reducing flying height modulation (FHM) caused by disk waviness and enhancing the cooling effects on the read/write elements. A simple geometric model is built to explain the schematic of the improvement in FHM.     

Head and media design considerations for reducing thermal asperity

Recent use of magnetoresistive (MR)/giant-magnetoresistive (GMR) heads in disk drives requires tighter control on particle contamination that may generate thermal asperities at the head/disk interface. In this study, the effects of slider air bearing surface (ABS) design and media on TA reduction capability are investigated. The motion of particles at the head/media interface is simulated numerically. Drive level TA tests are performed using a particle injection chamber. It is observed that a new ABS design, that has an aerodynamic U-shaped rail and a central airflow passage, is beneficial in reducing the particle contamination on the slider. Scratch-resistance of the media surface is correlated to TA reduction capability of the media; more scratch-resistant media produced less TA. On the other hand, the adhesion properties of the media have minor effects on TA reduction, as the particles that usually generate TA in a drive are too small to spin off the media.     

Effects of flying height deviations on glide height tests for manufacturing hard disks

In this study, theoretical analysis and experiments were carried out to investigate the effects of avalanche-point deviation and the deviation between the calibration and test-flying heights during the glide head calibration in the glide height tests for manufacturing hard disks. To obtain accurate glide height test results and improve the reproducibility of the test, flying height control should be carried out by limiting the acceptable deviation range of the flying heights of the glide heads. When the avalanche-point deviation is zero, the test results using different calibrated rails (or heads) are the same when they are used to detect the same defect. To avoid wrong test results due to avalanche-point deviation, the test-flying height should be the same as the calibration flying height because the difference of the output voltages of any two rails (or heads) is zero in this case. If these two deviations cannot be eliminated completely, the calibration and test-flying heights should be carefully selected because the error still can be minimised depending on the selection of the flying heights.