A new local adaptive grid-generating algorithm is developed and integrated with the multi-grid control volume method to simulate the steady state flying condition of air bearing sliders in HDDs (Hard Disk Drives) accurately and efficiently. Two sliders are used to demonstrate the applicability of this method. The results show that this new local adaptive grid-generating method improves substantially the stability and efficiency of the simulation scheme.

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.

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.

This paper presents numerical analysis of the dynamic characteristics of an air bearing system of a magnetic head under ultra-thin spacing. First, the static pressure distribution is numerically calculated by using up-wind scheme for a very large bearing number and a harmonic algorithm to calculate the flux factor for the abrupt change of film thickness. Then, the dynamic characteristics are analyzed in frequency domain by a perturbation method and finite difference method. The varying tendencies of the stiffness and damping coefficient in the translation, pitch and rolling directions with the frequency and the minimum film height are obtained.

Numerical analysis of the adsorbed film thickness at the air bearing surface is conducted using the non-Langmuir adsorption model. It is found that the adsorbed film at the air bearing surface becomes significant when the viscosity of adsorbed film is higher than about 1 Pa s. The adsorbed contaminant will accumulate at the rear end of the slider, and it is possible that the accumulated liquid-like contaminant may form a liquid tail which will directly contact with the disk surface, resulting in a crush of the head/disk interface.

With the introduction of netbook computers two years ago, the demand for hard disk drives (HDD) for mobile applications has greatly increased. High shock resistance is an important requirement for the reliable performance of HDDs in such applications. In this paper we conduct a numerical investigation to understand the failure mechanism of the head disk interface (HDI) during an operational shock. Simulation results suggest that the excitation frequency spectrum has a strong influence on HDI failure. We also investigate the effect of the parking or load unload (LUL) ramp on shock resistance using a new spinning disk model. The results suggest that asymmetric excitations induced by ramp-disk collision causes failure of the HDI at lower shock magnitudes. This study can be helpful in improving the design of HDD components and air bearing sliders (ABS) for better shock performance.

It is well known that preloaded ball screws with double nut produced hysteretic motion between the rotational angle of the screw shaft and linear motion of the nut, which is called “ lost motion ”, causes positioning error of ball screws. Preloaded ball screws with a double nut have the characteristic that the loaded balls wedge into a right angle direction to a ball rolling direction because the directions of screw shaft and nut raceways differ from the ball rolling direction. Loaded balls of preloaded ball screws with a double nut have two contact points geometrically. When the ball screw is operated under the condition of screw shaft turning and nut stationary, the wedging forces of balls are produced by differences between the screw shaft and nut raceways, and then loaded balls wedge into nut grooves. When the ball wedging motion is significantly increased, loaded balls make contact with another flank of the nut groove, that is, three points contact occur. In the present study, the authors deal with the positioning errors of the X-table which is composed of a preloaded precision ball screw and a couple of linear air bearings, and the ball wedging behaviors. The ball wedging behavior is quantified by the variation of the distance from ball surface to gap sensors which are inserted into several holes. These hole passing through the top of Gothic arch groove are bored in the perpendicular to the outer surface of the cylindrical nut.

A new partial contact head disk interface (HDI) with thermal protrusion is proposed for magnetic recording with densities of 1 Tbit/in 2 and above. This HDI has the advantage of maintaining light contact between the slider and the disk, so that both the bouncing vibration amplitude and the contact force are small compared with a traditional partial contact HDI. The slider’s dynamic simulations are carried out to analyze the effect of various factors within the HDI on the slider’s dynamic performance, including the friction and adhesion between the slider and the disk, the track profile morphology of the disk and the air bearing design. It is found that the bouncing vibration amplitude can be reduced to the level of the flying height modulation (FHM) of a non-contact air bearing slider without thermal protrusion.

A femto air bearing slider with thermal protrusion is studied based on three groups of surface roughness. It is observed that the air bearing force and the contact force are proportional to the value of average roughness in the minimum flying height region studied, while the intermolecular force or the electrostatic force is the smallest for the smoothest surfaces when the minimum flying height is above a certain value. As a result, the total force on the slider is the largest on the smoothest surfaces in a certain minimum flying height region. When the minimum flying height is designed in that region, the fly-ability of the slider is maximized.

Small perturbation and modal-analysis methods were employed to systematically study a damped slider’s dynamic characteristics. We found that a design with grooves distributed on a trailing pad effectively improved the slider’s damping at higher frequencies, and the damping ratio was dependent on the number of grooves, their depth, location, width, length, distribution, orientation, and types. A higher damping ratio could be obtained by optimizing these parameters. The femto slider with distributed damping grooves on a trailing pad had a higher damping ratio in the third mode, and hence, its responses to disk parallel and wavy motion were greatly reduced. This new design for the damped slider was an effective solution reducing the slider’s modulation.

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.

Air bearing vibrations at nanometer clearance levels are a major impediment to reducing head media spacing. Modern air bearings typically exhibit debilitating self-excited vibrations at fly heights of about 1–2 nm. At this point, peak head media spacing and contact pressures will increase, leading to performance and reliability issues. There has been considerable work performed to understand and improve air bearing stability at and around the point of contact, resulting in numerous experimental methods and design concepts in the literature. An area where additional research is worthwhile is the statistical behavior of contact vibrations. This paper explores the time dependence of fly height by using a simplified 2D air bearing with a mechanics based contact simulation. A comparison with measurements of fly height vibration demonstrates the utility of the simplified model and underscores the importance of proper time scale considerations.

In this paper a study is presented towards the effect of elastic deformation of the bearing surface of axial externally pressurized centrally pivoted modular air bearings. To this purpose shallow pocket, tapered and grooved air bearings are selected, which look the most promising to apply in small dimensions and with very small film thickness. The elastic deformation is calculated numerically by simultaneously solving the 2D-Reynolds equation for compressible fluids and the 3D-elasticity equation. The effect of the elastic distortion on the bearing performance is visualized in graphs presenting the load capacity and flow as a function of the film thickness. The results obtained from numerical calculation are verified experimentally.

Grooved thrust air bearings are widely used to support high-speed, low-loaded shafts in many rotating systems because of their low friction, noiseless operation, and simple structure. Several types of groove geometries, such as straight line, spiral, and herringbone, are commonly used in actual applications. Among them the spiral groove is mainly used. However, as far as the authors know, there is no theoretical evidence that the spiral groove is an optimized groove geometry in all possible groove geometries. This paper describes the optimum design for the groove geometry of thrust air bearings according to various objective functions, such as air film thickness, bearing torque, dynamic stiffness of air film, and combinations of same. In an optimum design, groove geometries are expressed by the third degrees of spline function, and sequential quadratic programming is used as the optimization method. We found that groove geometry optimizing air film thickness or friction torque takes the form of a spiral groove. The geometry optimizing the dynamic stiffness is the modified spiral groove. Some numerical results are compared with the measured data, and good agreements can be seen between them.

The start-up friction coefficient is a parameter which is very useful for engineers who design hydrodynamic bearings. It is most often issued from an approximation. Several studies can be found in the literature on this topic but most of them are concerned with air bearings or are only numerical. Some studies are more general and deal with the transient thermal behaviour in journal bearings as well as in thrust bearings. Other studies deal with the friction coefficient during running, at a fixed rotational speed. The aim of this study is to provide experimental measurements of the bush torque during start-up of plain journal bearings, varying the specific pressure. Thus, the friction coefficient at start-up (deduced from measurements) is obtained for four different bearings varying feeding conditions, radial clearance and length.

The slider of a Load/unload (LUL) drive can be loaded to a high flying stable state under certain conditions, which positions the read/write transducers much higher from the disk surface than the normal flying height (FH) and resulting in the issues in read or write. To avoid the issues caused by the high flying loading, it is necessary to find ways to recognize the existence of the high FH and eliminate it in the design stages. In this paper, we introduce a method that can identify the existences of the multiple FHs in loading process conveniently. The basic idea is to plot surfaces of air bearing forces in a domain of flying attitude, and then check if multiple FHs exist to generate the same air bearing forces that match the suspension forces. The analysis results indicate that the method is easy and efficient in identifying multiple FHs in loading process.

The behavior of the liquid-like adsorbed film on two types of air bearing surface with three dimension geometry was investigated by using the pumping effect with the Langmuir adsorption. The results shows that the contaminant tends to accumulate on the recession area of the air bearing surface. The viscosity of the adsorbed film will change the adsorbed film thickness distribution greatly.