A three dimensional finite element model of a rigid sphere lightly sliding over an elastic-perfectly plastic multilayered medium under thermo-mechanical surface loading is developed in order to investigate the mechanical and thermal responses during the light sliding contact of a spherical corner or thermal protrusion of a slider with a rotating disk. In this simulation, the effects of the magnetic recording layer thickness t and sliding contact parameters such as normal load F and friction coefficient μ on maximum temperature T max of head-disk interface (HDI) and maximum scratch depth h on the multilayered disk media are analyzed for both glass and aluminum disks. The results show that the magnetic recording layer thickness t has a negligible effect on the maximum temperature T max of the HDI and scratch depth h on the disk for both types of substrates, but the sliding contact parameters strongly affect the temperature variation and mechanical deformation of the HDI. In addition, the effect of the disk material is also very pronounced.

Thermal flying height (TFC) control technology has been used in the past few years to achieve a lower flying height for higher storage areal density. In this paper, a slider with dual thermal protrusion, one produced by the laser used to heat the disk in HAMR and the other one used for TFC, is programmed with feedback control to reduce the flying height modulation (FHM) due to disk waviness and to attenuate the external disturbances. A numerical simulation is conducted to investigate the feasibility of the system. The results show that FHM of the dual protrusion slider is reduced significantly when the protrusion heights and locations are optimized. External disturbance induced FHM can be suppressed as well. This scheme can benefit HAMR because it will provide a more consistent flying height and more freedom to compensate external disturbances.

Transient thermo-mechanical contact between a rigid sphere sliding over an elastic-plastic sphere with a larger radius is studied using finite element analysis. Plastic deformation and temperature rise in the contact zone between the two spheres are investigated.

The lubricant applied to the disk in a hard drive is a critical component for head-disk interface reliability. In Heat Assisted Magnetic Recording (HAMR), the heat supplied to the disk by the laser will add new thermal considerations to lubricant performance. Investigations into how the lubricant behaves at the small time and length scales seen in HAMR systems need to be conducted numerically. Published works on HAMR lubricant modeling have considered only the van der Waals contribution to disjoining pressure, commonly called the dispersive component, and do not consider the film thickness dependence of viscosity. However, lubricants with reactive end groups such as Fomblin Zdol are widely used, and such simple disjoining pressure and viscosity models do not capture certain lubricant behavior. We have developed a simulation tool that incorporates film thickness dependencies of viscosity and polar and dispersive disjoining pressure into a continuum lubrication model. We investigate the effect of initial thickness on lubricant flow and evaporation under HAMR write conditions considering both components of disjoining pressure and thin-film viscosity. Simulation results indicate the effect of including polar disjoining pressure depends on the initial lubricant thickness. The inclusion of viscosity thickness dependence does not affect simulation results under scanning laser conditions but will be important in reflow simulations.

Thermo-mechanical contact and micro-wear of head disk interface (HDI) are investigated using the improved HDI contact model and theories of frictional heat generation and heat transfer. In analytical simulations, dynamic contact parameters such as material properties, sliding velocity, and surface interference are based on actual HDI design and operation. The resulting contact pressure and temperature distribution show that the micro-wear on the carbon film of a head slider would be significantly attributed to the degradation of carbon material caused by frictional heat generation during sliding contact.

A new numerical analysis method for elastic adhesive contact mechanics between a sphere and a flat with a sub-nanometer roughness is presented. In contrast to conventional theories, the elastic deformations of both contacting asperities and mean height surface and Lennard-Jones (LJ) surface forces of both contacting asperities and all rough surfaces including valley areas are taken into account New adhesive force of contacting asperity is used from asperity contact analysis. Calculated results for head-disk asperity contact with current low roughness are shown in comparison with conventional theories. The relationship among present theory, mean height surface theory and perfectly smooth surface theory is discussed.

In this study, the lubricant depletion caused by laser heating was investigated for lubricant films with thicknesses greater than and less than one monolayer. The conventional lubricants Zdol2000 and Ztetrao12000 were used. It was found that the critical temperature at which lubricants start to deplete by laser heating strongly depends on the lubricant film thickness. To analyze the lubricant depletion mechanism, we carried out temperature programmed desorption (TPD) spectroscopy on the tested lubricant films. It was found that the lubricant depletion characteristics induced by laser heating could be explained using the experimental TPD spectroscopy results for the tested lubricant films. It was also found that the depletion mechanism involved the desorption or decomposition of the lubricant molecules that interacted with the diamond-like carbon thin films when the lubricant film thickness was less than one monolayer.

Over the past decade there has been a significant increase the demand of hard disk drives (HDD) for the mobile platforms. In such applications, a mobile HDD is often subjected to harsh working environment. For example, components like DVD drive and built-in speakers present in a laptop can excite its HDD and hence can degrade its read/write (R/W) performance. In this study, we develope a complete model for a mobile HDD to analyze and characterize its vibration performance due to external disturbances. The current model includes a spinning disk, a fluid dynamic bearing (FDB) based spindle motor, a base plate, an actuator assembly (E-block and suspension) and a detailed model for the air bearing slider. Prediction of slider dynamics during an excitation essentially requires the solution of coupled fluid-structure problem in which head gimbal assembly (HGA) is coupled with the disk-support system through the air bearing. Off-track displacement of the slider is used to quantify the vibration performance of the HDD for excitation of different frequencies and orientations. It is observed that during an excitation, the sway modes of the actuator assembly provide the most significant contribution to the off-track vibration. This knowledge about the vibration characteristics of mobile drive can be used to design better a vibration isolation system for mounting a HDD in a laptop.

Combined smart bearing (CSB) integrates two oil free bearing technologies to take advantage of the strengths of each bearing with minimizing each other weaknesses. It is for enhancing dynamic stability and load carrying capacity [1]. Moreover, CSB have a shorter length than size of hybrid bearing suggested by Heshmat in same performance [2]. So, it has the advantage of the design in high speed turbo machinery. This paper presents vibration control of a high speed rotor supported by CSB. An experiment set-up of a rotor bearing system is built. And rotor dynamic analysis of the rigid rotor on critical speeds is performed. For the experimental approach, unbalance responses of the rigid rotor supported by each bearings: air foil bearing (AFB) and CSB are compared to verify the effectiveness of the CSB. First, the PD control parameters of the magnetic bearing were to find out in stable range experimentally. Then according to the angle of unbalance experiments, compared the performance of AFB and CSB. The result, the shaft vibration in a critical speed is significantly suppressed by the CSB rather than AFB.

The stability, reliability, efficient performance of high speed turbo machinery is very important, and accordingly has increased the demand for advanced bearings. In order to meet the advanced bearing needs, Heshmat proposed a hybrid foil-magnetic bearing [1]. The hybrid bearing combining the two bearings takes advantage of the strengths of each while compensating for each other’s weaknesses. This paper presents dynamic characteristics of the combined smart bearing (CSB) of different structure from Heshmat’s bearing. The CSB and test rig were designed, fabricated and carried out the test. Numerical predictions of Air foil bearing (AFB) and CSB were compared the dynamic force performance, and analysis of bearings are performed by finite element method (FEM). Experiments were conducted to determine the structural static and dynamic characteristics of AFB. The dynamic characteristics of AFB and CSB compared depending on the rotating speed change. The experimental results were obtained the dynamic characteristics of the CSB 50% higher than value of the stiffness effect. In addition to, the CSB 100% higher than value of the damping effect.

The pumping effect proposed by the authors is used to analyze the contamination of the air bearing in hard disk drive. Three different types of air bearing surface are considered in the focus on the accumulation of the contamination at the rear pad where the minimum spacing is located. It is found that the contamination tends to accumulate at both the front and the rear ends of the air bearing surface pad where the shear stress of air film is interrupted due to due to the dramatic change in the spacing. The accumulation at the tailing edge of the air bearing is the most detrimental. The thickness of adsorbed film at the tailing edge increases suddenly when the terrace length at the tailing edge exceeds a critical value, which is in between 15 μm and 35 μm in this article.

Perfluoropolyether (PFPE) lubricants were chemically modified to maximize their thermal stability for application in heat assisted magnetic recording (HAMR). Benzophenone (BP) was introduced to react with the hydroxyl end group in PFPE to act as a free radical stabilizer. Modification of the PFPE by benzophenone was confirmed by evaluation of the chemical shift and the area change of the hydroxyl peak in the 1 H NMR spectra. The thermal stability of modified PFPE lubricants was studied using thermo-gravimetry. The improvement in the thermal stability was found to be a function of the amount of substituted hydroxyl groups in PFPE.

In this study, we measured temperature dependence of viscoelastic properties of PFPE lubricant that was confined in nanometer-sized gap widths. In the viscoelastic measurement, we used the fiber wobbling method, which is the highly sensitive shear force measuring method that we have originally developed. Our experimental results showed that the temperature dependence of the lubricant’s viscosity was declined at the gap width of less than 5 nm. Since the elasticity also appeared at the gap width of 5 nm, the reduced temperature dependence is considered to be caused by the repression of molecular mobility due to the solidification of the confined lubricant.

An efficient scheme was developed to analyze the dynamics of a magnetic head slider during the unloading process. The nonlinearity of the air bearing forces and moments was described by analytical expressions obtained from a surface fitting procedure. Combined with a dual-scale suspension model, the force and moment functions determined can be used to obtain the instantaneous flying attitude of the slider and the unloading time with a very short computation time, thus providing a way of exploring a large number of parameter values of the suspension stiffness matrix.

Pushing recording density toward 1TB/in 2 and beyond requires a stable head disk magnetic recording system with 3–4nm head disk spacing. Air bearing design strategy with respect to thermally actuated writer / reader elements is investigated in this work. The goal is to significantly increase stability of the head-disk spacing for ultra-low flying height recording systems. Investigations presented in this paper indicate that placement of the air bearing pressure concentration location is an effective approach for achieving flying height stability. Proper placement can reduce the disturbance due to short range interaction forces. It was also found that lower viscosity lubricant systems exhibit less interaction disturbance during contact hysteresis characterization while controlling ambient air pressure.

Patterned media is being considered as a means for achieving a storage density beyond 1Tb/in 2 on hard disks by reducing cross talk and overcoming thermal stability problems. In this investigation, the flying characteristics of a femto-type slider over bit patterned media (BPM) is investigated. The discrete bits of the disk are modeled as cylindrical protrusions on the disk surface. The steady-state flying characteristics over BPM at ultra-low head disk spacing is simulated.

In Heat Assisted Magnetic Recording (HAMR), various thermal loads (laser, electrical current) subject the Head-Disc Interface (HDI) to intensive thermal strain / stress fields. The thermal strains, in terms of slider protrusion and media protrusion, significantly reduce the head-disc clearance and may lead to head-disc contact. Air bearings, by design, can passively adjust the fly height through so-called “self-compensation” to the protrusions. In this paper, an electro-thermo-mechanical model coupled with air bearing model has been developed to analyze the head flying characteristics under these thermal loads. The thermal protrusions induced by laser and current Joule heating, as well as their interactions, have been studied and verified with experimental results.

To understand the cause of read/write error due to lube accumulation, a model to simulate the slider’s response to “soft contact”, which can occur between a lubricant droplet on the disk and a slider, was developed. The contact impact model is based on the water-hammer pressure model with an additional damping force, where the wave-shock pressure is assumed to function as the soft contact pressure, and the damping force defines the damping characteristics of the impact which are due to the lubricant’s high viscosity. This modeling and simulation are helpful to us in understanding the read/write signal loss due to a lube droplet at head disk interface.

In this study, the effect of temperature on the spreading characteristics of ultra-thin liquid lubricant films in hard disk drives (HDD) was investigated by using three types of lubricants, namely, Zdol2000, Ztetraol2000, and A20H2000. The apparent diffusion coefficient of individual lubricants was evaluated and compared by varying the temperature of disk substrates. As a result, it was found that the mobility of each lubricant increases with the temperature. However, the rate of mobility increase is different for each lubricant, depending on the lubricant material. Furthermore, there exists no quantitative correlation between the mobility increase for ultra-thin liquid lubricant films and the viscosity decrease in bulk lubricant materials due to a rise in the temperature. It was also found that among the test lubricants, A20H2000 has the highest robustness for temperature change. In addition, it could be observed that the evaporation of the mobile fraction of lubricants occurred remarkably over a temperature range of 50– 80 °C.

A numerical method for analyzing the elastic contact mechanics due to intermolecular forces between a spherical slider and a disk is presented and typical results for a 1-μm radius sphere (which simulates a roughness asperity), 2-mm radius sphere (test slider), and 10–30-mm radius spheres (magnetic head sliders) are given. A numerical method for evaluating intermolecular forces at contacting asperities is also presented.