Effect of the Intermolecular Forces on the Flying Attitude of Sub-5 NM Flying Height Air Bearing Sliders in Hard Disk Drives

2002 ◽  
Vol 124 (3) ◽  
pp. 562-567 ◽  
Author(s):  
Lin Wu ◽  
D. B. Bogy
Keyword(s):  
Hard Disk Drives ◽  
Three Dimensional ◽  
Disk Surface ◽  
Intermolecular Forces ◽  
Flying Height ◽  
Positive Pressure ◽  
Vertical Force ◽  
Air Bearing ◽  
Triangular Cell ◽  
Flying Attitude

When the spacing between the slider and the disk is smaller than 10 nm, the effect of the intermolecular forces between the two solid surfaces can no longer be ignored. This effect on the flying attitude of practical slider designs is investigated here numerically. The three-dimensional slider surface is discretized into non-overlapping unstructured triangles. The intermolecular forces between each triangular cell of the slider and the disk surface are formulated, and their contributions to the total vertical force, as well as the pitch and roll moments, are included in a previously developed steady state air bearing design code based on a multi-grid finite volume method with unstructured triangular grids [3–5]. It is found that the van der Waals force has significant influence on the flying height and has non-negligible effect on the pitch angle for both positive pressure sliders and negative pressure sliders, when the flying height is below 5 nm. When the flying height is below 0.5 nm, the repulsive portion of the intermolecular force becomes important and also has to be included.

Effect of Intermolecular Forces on the Static and Dynamic Performance of Air Bearing Sliders: Part II—Dependence of the Stability on Hamaker Constant, Suspension Preload and Pitch Angle

2005 ◽  
Vol 128 (1) ◽  
pp. 203-208 ◽  
Author(s):  
Vineet Gupta ◽  
David B. Bogy
Keyword(s):  
Pitch Angle ◽  
Dynamic Performance ◽  
Hard Disk Drives ◽  
Intermolecular Forces ◽  
Flying Height ◽  
Total Force ◽  
Air Bearing ◽  
Force Increase ◽  
The Stability ◽  
Fly Height

Intermolecular and surface forces contribute significantly to the total forces acting on air bearing sliders for flying heights below 5 nm. Their contributions to the total force increase sharply with the reduction in flying height, and hence their existence can no longer be ignored in air bearing simulation for hard disk drives. Various experimentally observed dynamic instabilities can be explained by the inclusion of these forces in the model for low flying sliders. In this paper parametric studies are presented using a 3-DOF model to better understand the effect of the Hamaker constants, suspension pre load and pitch angle on the dynamic stability/instability of the sliders. A stiffness matrix is used to characterize the stability in the vertical, pitch, and roll directions. The fly height diagrams are used to examine the multiple equilibriums that exist for low flying heights. It has been found that the system instability increases as the magnitude of the van der Waals force increases. It has also been found that higher suspension pre load and higher pitch angles tend to stabilize the system.

Simulating the Air Bearing Flying Height in a Humid Environment

2007 ◽  
Author(s):  
Shuyu Zhang ◽  
Brian Strom ◽  
Sungchang Lee ◽  
George Tyndall
Keyword(s):  
Hard Disk Drives ◽  
Hard Disk ◽  
Disk Drive ◽  
Flying Height ◽  
Test Cases ◽  
Air Bearing ◽  
Humid Environment ◽  
Bearing Design ◽  
Flying Attitude ◽  
Saturation Vapor

For a hard disk drive operating in a humid environment, the water vapor in the slider’s air bearing is typically compressed beyond its saturation vapor pressure, causing the vapor to condense. Consequently, the air bearing pressure decreases and the slider’s flying attitude adjusts to balance the forces from the suspension. A method for calculating this air bearing response to humid air is presented. Using one particular air bearing design as an example, several test cases are analyzed to illustrate the air bearing response for various temperatures and humidity levels. The calculated flying heights agree with those measured in commercial hard disk drives.

Identification of the Multiple Flying Heights in a Loading Process

2008 ◽  
Author(s):  
Shuyu Zhang ◽  
Mike Suk ◽  
George Tyndall
Keyword(s):  
Stable State ◽  
Disk Surface ◽  
Flying Height ◽  
Air Bearing ◽  
Loading Process ◽  
Flying Attitude

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 Effect of the Accommodation Coefficient on Slider Air Bearing Simulation

1999 ◽  
Vol 122 (2) ◽  
pp. 427-435 ◽  
Author(s):  
Weidong Huang ◽  
David B. Bogy
Keyword(s):  
Flow Rate ◽  
Hard Disk Drives ◽  
Direct Simulation Monte Carlo ◽  
Accommodation Coefficient ◽  
Flying Height ◽  
Positive Pressure ◽  
Air Bearing ◽  
Unit Value ◽  
Slider Air Bearing ◽  
Molecular Gas Film Lubrication

In solving the slider air bearing problem, both the Molecular Gas-film Lubrication (MGL) model and the Direct Simulation Monte Carlo (DSMC) model require the accommodation coefficient as input. The accommodation coefficient represents the fraction of the air molecules that interact with solid boundaries in a diffusive manner. In general, the value 1 is used for the accommodation coefficient, which represents a fully diffusive reflection. However, in magnetic hard disk drives, the disk and slider surfaces are becoming ever smoother with different kinds of lubrication on the disk, while the temperature is becoming higher due to the faster spindle speed. Under these conditions the unit value of the accommodation coefficient may no longer be suitable. In order to understand the effect of the accommodation coefficient on the slider’s flying parameters, we used Kang’s new database for the Poiseuille flow rate Qp and Couette flow rate Qc to solve the modified Reynolds equation for two groups of sliders, e.g., negative and positive pressure sliders (“negative” refers to sliders with subambient pressure zones). The results show that, in general, the smaller the accommodation coefficient, the lower the flying height and pitch angle. Positive pressure sliders are more sensitive to the accommodation coefficient than are negative pressure sliders. The typical discrepancy in flying height is around 10%. Also, it is shown that for positive pressure sliders the lower the flying height, the larger the discrepancy percentage. [S0742-4787(00)00402-1]

Effect of Intermolecular Forces on the Static and Dynamic Performance of Air Bearing Sliders: Part II — Dependence of the Stability on Hamaker Constant, Suspension Preload and Pitch Angle

2004 ◽  
Author(s):  
Vineet Gupta ◽  
David B. Bogy
Keyword(s):  
Pitch Angle ◽  
Dynamic Performance ◽  
Hard Disk Drives ◽  
Intermolecular Forces ◽  
Flying Height ◽  
Air Bearing ◽  
Parametric Studies ◽  
The Stability ◽  
Hamaker Constants ◽  
Fly Height

Intermolecular and surface forces contribute significantly to the total forces acting on air bearing sliders for flying heights below 5nm. Their contributions to the total forces increase sharply with the reduction in flying height, and hence their existence can no longer be ignored in air bearing simulation for hard disk drives. Various experimentally observed dynamic instabilities can be explained by the inclusion of these forces in the model for low flying sliders. In this paper parametric studies are presented using a 3-DOF model to better understand the effect of the Hamaker constants, suspension pre load and pitch angle on the dynamic stability/instability of the sliders. A stiffness matrix is used to characterize the stability in the vertical, pitch and roll directions. The fly height diagrams are used to examine the multiple equilibriums that exist for low flying heights. It has been found that the system instability increases as the magnitude of the van der Waals force increases. It has also been found that higher suspension pre load and higher pitch angles tend to stabilize the system.

Air Bearing Models and Solutions for Sub-5 nm Spacings

2001 ◽  
Author(s):  
D. B. Bogy ◽  
Lin Wu
Keyword(s):  
Boundary Condition ◽  
Slip Velocity ◽  
Intermolecular Forces ◽  
Flying Height ◽  
Asperity Contact ◽  
Air Bearing ◽  
Lubrication Equation ◽  
New Equation ◽  
Physical Phenomena ◽  
Flying Attitude

Abstract When the flying height is below 5 nm, some physical phenomena that can be ignored for higher flying sliders need to be included in the modeling equations. Another challenging issue is the unavoidable asperity contact problem. It is known that zero spacing at asperities may cause some of the existing modified Reynolds equations to predict unphysical unbounded contact pressure singularities. In this paper we first review the source of these pressure singularities, showing which models have this problem and which do not. We also review here a new derivation of a compressible lubrication equation by using a different slip velocity boundary condition, in which additional slippage at the gas-solid interface due to pressure gradient is introduced. The new equation is free of any contact singularity [1]. Next we review our recent work on the non-negligible effect of the intermolecular forces on the slider’s flying attitude when the spacing is below 5 nm [2]. The additional force is attractive until the spacing is below about 0.1 nm for example and then it is repulsive. Finally we show the effect of these new force contributions on the flying attitude of a low flying slider.

Simulating the Air Bearing Pressure and Flying Height in a Humid Environment

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
Shuyu Zhang ◽  
Brian Strom ◽  
Sung-Chang Lee ◽  
George Tyndall
Keyword(s):  
Hard Disk Drives ◽  
Hard Disk ◽  
Disk Drive ◽  
Flying Height ◽  
Test Cases ◽  
Air Bearing ◽  
Disk Drives ◽  
Humid Environment ◽  
Flying Attitude ◽  
Saturation Vapor

For a hard disk drive operating in a humid environment, the water vapor in the slider’s air bearing is typically compressed beyond its saturation vapor pressure, causing the vapor to condense. Consequently, the air bearing pressure decreases and the slider’s flying attitude adjusts to balance the forces from the suspension. A method for calculating this air bearing response to humid air is presented. Using two air bearing designs, several test cases are analyzed to illustrate the air bearing response for various temperatures and humidity levels. The calculated flying heights agree with those measured in commercial hard disk drives.

Numerical Investigation of Bouncing Vibrations of a Partial Contact Slider

2007 ◽  
Author(s):  
Du Chen ◽  
David D. Bogy
Keyword(s):  
Hard Disk Drives ◽  
Disk Surface ◽  
Air Bearing ◽  
Nonlinear Dynamic Model ◽  
Frequency Spectra ◽  
Disk Interface ◽  
Partial Contact ◽  
Adhesion Contact ◽  
Contact Situation ◽  
Contact Slider

A nonlinear dynamic model is developed to analyze the bouncing vibration of a partial contact air bearing slider, which is designed for the areal recording density in hard disk drives of 1 Tbit/in2 or even higher. In this model the air bearing with contact is modeled using the generalized Reynolds equation modified with the Fukui-Kaneko slip correction and a new second order slip correction for the contact situation [1]. The adhesion, contact and friction between the slider and the disk are also considered in the model. It is found that the disk surface roughness, which moves into the head disk interface (HDI) as the disk rotates, excites the bouncing vibrations of the partial contact slider. The frequency spectra of the slider’s bouncing vibration have high frequency components that correspond to the slider-disk contact.

Performance of Sliders Flying Over Discrete-Track Media

2007 ◽  
Vol 129 (4) ◽  
pp. 712-719 ◽  
Author(s):  
Jianhua Li ◽  
Junguo Xu ◽  
Yuki Shimizu
Keyword(s):  
Estimation Method ◽  
Simulation Method ◽  
Measured Data ◽  
Flying Height ◽  
Height Loss ◽  
Air Bearing ◽  
Slider Air Bearing ◽  
Discrete Track ◽  
Flying Attitude ◽  
Manufacturing Variation

A simulation method in which grooves are virtually distributed on the slider air bearing instead of on the grooved medium surface has been developed and used to investigate the performance of sliders flying over the surface of a discrete-track medium. The simulated flying height loss due to a discrete-track medium coincides well with the measured data, whereas the average-estimation method overestimates flying height loss. Among the characteristics of a slider flying over the surface of a discrete-track medium that were studied are the flying attitude, the effect of groove parameters on flying profile, and the flying height losses due to manufacturing variation and altitude. The results indicate that when a slider is flying over the surface of a discrete-track medium, it will have a higher 3σ of flying height, be more sensitive to altitude, and will have a greater flying height loss.

Effects of Molecularly Thin Liquid Lubricant Film Materials on Slider Hysteresis Instability in Hard Disk Drives

2007 ◽  
Author(s):  
Norio Tagawa ◽  
Daisuke Tanaka ◽  
Atsunobu Mori
Keyword(s):  
Hard Disk Drives ◽  
Disk Surface ◽  
Intermolecular Forces ◽  
Experimental Results ◽  
Disk Drives ◽  
Friction Forces ◽  
Liquid Lubricant ◽  
Pressure Test ◽  
Lower Mobility ◽  
The Difference

In this study, the difference in the touchdown and takeoff pressures was monitored by using three types of lubricant materials, namely, Zdol2000, Ztetraol2000 and A20H2000 by using the pump down pressure test. The results indicated that the touchdown pressures depended on the lubricant materials; it was greatest for Ztetraol2000 and smallest for A20H2000. The takeoff pressure was greater for a lubricant with lower mobility. Considering these experimental results, it was suggested that the variation in the touchdown pressure is due to a variation in the intermolecular forces, taking into account the lubricant pickup by a slider. Further, it was suggested that the variation in the takeoff pressure is caused by a variation in the friction forces between the slider and disk surface.

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