Air Bearing Dynamics of Sub-Ambient Pressure Sliders During Dynamic Unload

1999 ◽  
Vol 121 (3) ◽  
pp. 553-559 ◽  
Author(s):  
Yong Hu ◽  
Paul M. Jones ◽  
Kangjie Li
Keyword(s):  
High Speed ◽  
Ambient Pressure ◽  
Strong Dependence ◽  
Hard Disk Drives ◽  
Air Bearing ◽  
Trailing Edge ◽  
Suction Force ◽  
Motion Sequence ◽  
Fly Height ◽  
Bearing Dynamics

The increasing effort to use sub-ambient pressure air bearing sliders for dynamic load/unload applications in magnetic hard disk drives requires desirable air bearing characteristics during the dynamic unload event. This paper establishes air bearing design criteria for achieving a smooth head unload performance, through a correlation study between the modeled unloading air bearing dynamics of two 30 percent proximity recording sub-ambient pressure sliders and motion sequence of the same sliders by a high-speed video camera. It is shown that the air bearing lifting force quickly responds to changes in fly height and pitch, while the suction force is relatively resistant to changes in fly height, but somewhat more sensitive to changes in pitch. This unique distinction results in different decreasing rates between the air bearing lifting and suction forces during the unload process, creating a strong dependence of the unloading characteristics on the location of the suction cavities. Both the modeled unloading air bearing dynamics and experimentally recorded motion sequence illustrate that a toward-trailing-edge located suction force acts to pitch the slider up, while the moment produced by a toward-leading-edge located suction force induces a negative pitch motion, resulting in an excessive flexure deformation and dimple separation. Therefore, placing the suction cavities towards the trailing edge offers a reliable unloading performance for the sub-ambient pressure air bearing sliders.

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.

scholarly journals Parametric Investigations at the Head-Disk Interface of Thermal Fly-Height Control Sliders in Contact

2012 ◽  
Vol 2012 ◽  
pp. 1-11 ◽  
Author(s):  
Sripathi V. Canchi ◽  
David B. Bogy ◽  
Run-Han Wang ◽  
Aravind N. Murthy
Keyword(s):  
Hard Disk Drives ◽  
Air Bearing ◽  
Head Disk Interface ◽  
Bearing Surface ◽  
Surface Design ◽  
Disk Interface ◽  
Height Control ◽  
Experimental Findings ◽  
And Control ◽  
Fly Height

Accurate touchdown power detection is a prerequisite for read-write head-to-disk spacing calibration and control in current hard disk drives, which use the thermal fly-height control slider technology. The slider air bearing surface and head gimbal assembly design have a significant influence on the touchdown behavior, and this paper reports experimental findings to help understand the touchdown process. The dominant modes/frequencies of excitation at touchdown can be significantly different leading to very different touchdown signatures. The pressure under the slider at touchdown and hence the thermal fly-height control efficiency as well as the propensity for lubricant pickup show correlation with touchdown behavior which may be used as metrics for designing sliders with good touchdown behavior. Experiments are devised to measure friction at the head-disk interface of a thermal fly-height control slider actuated into contact. Parametric investigations on the effect of disk roughness, disk lubricant parameters, and air bearing surface design on the friction at the head-disk interface and slider burnishing/wear are conducted and reported.

Effect of Dimple Offset on the Operational Shock Performance of Small Form Factor Disk Drives

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Puneet Bhargava ◽  
David B. Bogy
Keyword(s):  
Form Factor ◽  
Hard Disk Drives ◽  
Leading Edge ◽  
Disk Drive ◽  
Air Bearing ◽  
Disk Drives ◽  
Small Form ◽  
Small Form Factor ◽  
Bearing Dynamics ◽  
Operational Shock

This paper discusses the effect of varying the suspension load dimple location on the shock robustness of small form factor hard disk drives. We use the CML shock simulator, which simulates the structural as well as the air bearing dynamics of the disk drive simultaneously. The location of the dimple is varied and simulations are run for various load positions on the back of the slider, while adjusting the pitch static attitude (PSA) and the roll static attitude (RSA) of the slider such that the flying attitude of the slider remains the same. We simulate shocks of 0.5 ms pulse width for a commercially available slider and suspension designs for a 1 in. drive. We observe that shock resistance is optimal when the dimple is offset toward the leading edge of the slider. This behavior is explained on the basis of a linearized air bearing model. It is also observed that moving the dimple too much toward the leading edge causes the mechanism of shock failure to change resulting in lower shock tolerances.

Effect of Ultra-Thin Liquid Lubricant Films on Dynamics of Nano-Spacing Flying Head Sliders in Hard Disk Drives

2004 ◽  
Vol 126 (3) ◽  
pp. 565-572 ◽  
Author(s):  
Norio Tagawa ◽  
Noritaka Yoshioka ◽  
Atsunobu Mori
Keyword(s):  
Film Thickness ◽  
Hard Disk Drives ◽  
Lubricant Film ◽  
Flying Height ◽  
Air Bearing ◽  
Disk Drives ◽  
Lubricant Film Thickness ◽  
Liquid Lubricant ◽  
Lubricant Films ◽  
Bearing Dynamics

This paper describes the effect of ultra-thin liquid lubricant films on air bearing dynamics and flyability of nano-spacing flying head sliders in hard disk drives. The dynamics of a slider was monitored using Acoustic Emission (AE) and Laser Doppler Vibrometer (LDV). The disks with lubricant on one half of disk surface thicker than the other half as well as with uniform thickness lubricant were used to investigate the interactions between the slider and lubricant film experimentally. As a result, it was found that the flying height at which the slider-lubricant contact occurs depends on the lubricant film thickness and it increases as the lubricant film thickness increases. Its flying height is also dependent on the mobile lubricant film thickness under the condition that the total lubricant film thicknesses are the same and the lubricant bonded ratios are different. It increases as the mobile lubricant film thickness increases. The slider-lubricant contact flying height based on the theory for capillary waves is in good agreement with the experimental results. Regard to air bearing dynamics due to the slider-lubricant interactions, it also depends on the mobile lubricant thickness as well as the total lubricant film thickness. However, we should carry out more experimental and theoretical studies in order to confirm and verify these experimental results. In addition, the effect of nonuniform lubricant film thickness on head/disk interface dynamics has been studied. It was found that the lubricant film thickness nonuniformity caused by the slider-lubricant interactions could be observed.

Dynamic Stability and Spacing Modulation of Sub-25 nm Fly Height Sliders

1997 ◽  
Vol 119 (4) ◽  
pp. 646-652 ◽  
Author(s):  
Yong Hu ◽  
David B. Bogy
Keyword(s):  
Dynamic Stability ◽  
Hard Disk Drives ◽  
Dynamics Simulation ◽  
Inertia Force ◽  
Roll Motion ◽  
Air Bearing ◽  
Skew Angle ◽  
Disk Interface ◽  
Bearing Stiffness ◽  
Fly Height

Designing a reliable sub-25 nm spacing head/disk interface for today’s magnetic hard disk drives demands a greater dynamic stability and a smaller spacing modulation. An air bearing dynamic simulator with multiple features is developed to investigate the dynamic characteristics of three shaped-rail negative pressure sub-25 nm fly height sliders. Various simulations including air bearing stiffness, impulse response, surface roughness induced spacing modulation, bump response, and track seeking dynamics are performed. The results indicate that the roughness induced spacing modulation decreases with the increase of the air bearing stiffness and the decrease of the slider size. The suspension dynamics is integrated into the air bearing dynamics simulation for the track accessing motion by modal analysis. It is concluded that the fly height modulation during a track accessing event is attributed to many factors such as the effective skew angle, the seeking velocity, and the roll motion caused by the inertia of the moving head. The extent of the roll motion effect depends on the air bearing roll stiffness and the level of the inertia force of the moving head. Larger roll stiffness and smaller inertia force produce a smoother track accessing performance.

Experimental Study of the Resonances of the Slider Modulations by Laser Doppler Vibrometer

2014 ◽  
Author(s):  
Peng Peng ◽  
Narayanan Ramakrishnan ◽  
Vijay Kumar ◽  
Brian Karr
Keyword(s):  
Hard Disk Drives ◽  
Laser Doppler Vibrometer ◽  
Vertical Direction ◽  
Voice Coil Motor ◽  
Areal Density ◽  
Air Bearing ◽  
Magnetic Spacing ◽  
Resonance Frequencies ◽  
Bearing Design ◽  
Fly Height

The magnetic spacing of Hard Disk Drives (HDD) needs to be reduced for increasing areal density. It is therefore very challenging to maintain constant fly height at a sub-2nm clearance. Any resonance of the slider or suspension can cause modulations on fly height and thus impacting the writing efficiency. Various research was carried out for the flying stability of the slider [1–4], especially in the off-track direction caused by voice coil motor (VCM) as well as PZT actuation. However, the resonances of the slider modulations in vertical direction have not been well researched. In the study, a method of using heater oscillation to examine the slider resonances has been proposed. The experiments have been performed on two suspension designs and two air bearing designs to demonstrate the effectiveness of this approach. The experimental results showed a shift of resonance frequencies due to a design change of the suspension. The air bearing design also played a role in the heater time constant and thus affecting the magnitude of resonances. Further, larger resonances were observed in a lower clearance setting than passive fly.

Theoretical Prediction of Ramp Loading/Unloading Process in Hard Disk Drives

1999 ◽  
Vol 121 (3) ◽  
pp. 568-574 ◽  
Author(s):  
J. P. Peng
Keyword(s):  
Reynolds Equation ◽  
Dynamic Performance ◽  
Hard Disk Drives ◽  
Air Bearing ◽  
Disk Drives ◽  
Suction Force ◽  
Coupled Equations ◽  
Loading And Unloading ◽  
Volume Method ◽  
Unloading Time

Air bearing slider dynamic performance during the ramp loading and unloading processes was investigated theoretically in this paper. The air bearing was modeled by the modifiedcompressible Reynolds equation, and it was solved by the finite volume method. Slider dynamic equations were derived in this paper to include the ramp loading/unloading mechanism. These two sets of coupled equations were solved iteratively. Both Tripad and negative pressure air bearing (NPAB) were included in the analysis. Effects of loading/unloading velocity, disk rotational speed, as well as suspension flexure stiffness, were investigated. Slider-disk impact will occur during the Tripad loading process, especially at high loading velocity. On the other hand, this impact can be avoided for an NPAB at loading velocity up to 200 mm/s. However, an NPAB requires a longer unloading time due to its suction force. This unloading process is further delayed if a soft flexure is combined with an NPAB.

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.

Characteristics of Air Bearing Suction Force in Magnetic Recording Disks

1996 ◽  
Vol 118 (3) ◽  
pp. 549-554 ◽  
Author(s):  
Jih-Ping Peng ◽  
Cal E. Hardie
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Pressure Effect ◽  
Ambient Pressure ◽  
Air Bearing ◽  
Element Analysis ◽  
Suction Force ◽  
Operation Conditions ◽  
Wide Range ◽  
Bearing Number

Some fundamental characteristics of the subambient pressure air bearing suction force were investigated analytically and numerically. The performance of air bearing suction force is strongly determined by the cavity bearing number, in which the cavity region recess depth is used as the characteristic film thickness. Although the optimal recess depth for maximum, suction force varies for different operation conditions, the optimal cavity bearing number can be found in a wide range of applications. The analytical model was confirmed by a finite element analysis. Examples of different disc velocities, slider dimensions, and ambient pressure effect were presented.

Design and Analysis of Slider’s Landing Pads for Fast Take-Off Performance in Magnetic Hard Disk Drives

1999 ◽  
Vol 121 (4) ◽  
pp. 955-960 ◽  
Author(s):  
Yong Hu
Keyword(s):  
Contact Force ◽  
New Technology ◽  
Hard Disk Drives ◽  
Hard Disk ◽  
Disk Drive ◽  
Air Bearing ◽  
Trailing Edge ◽  
And Performance ◽  
Magnetic Hard Disk ◽  
Pad Wear

Exponential growth in both capacity and performance has been exhausting a lot of existing technologies in magnetic hard disk drive industry, one of them being laser zone texturing. Maintaining such a rapid growth requires innovative technologies. Adding landing pads to a slider’s air hearing surface (ABS) appears to be able to further stretch the glide/stiction envelope into the ultra-low glide and stiction regime. To materialize this new technology, the pad wear needs to be minimized, underlining the importance of the fast take-off air bearing characteristics. This paper analyzes the slider’s landing pad designs for fast take-off performance through the partial contact air bearing simulation of a take-off process. Two landing pad designs (3-pad and full texture) are created on a suhambient pressure ABS. The contact force and its center profiles as well as the evolution of the contact pressure contour are used to characterize the movement of the contact location during the take-off process. The effects of the absolute and relative pad heights as well as the rear pad location on both the transition of the contact location and the rate of contact force decrease are calculated. While raising leading pads delays the transition of the contact location from the leading pads to rear pad, distancing the rear pad from the trailing edge greatly facilitates the movement of the contact location from the rear pad to the trailing edge. A fully textured ABS with a reasonably low and uniform pad height as well as rear pads being well distanced from the trailing edge offers a fast take-off performance.

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