Understanding Instabilities of TFC Femto-Slider and Pico-Slider via Surface Force Theory

2018 ◽  
Author(s):  
Kyosuke Ono
Keyword(s):  
Dynamic Instability ◽  
Surface Force ◽  
Disk Surface ◽  
Adhesive Contact ◽  
Contact Theory ◽  
Height Control ◽  
Meniscus Force ◽  
Static Instability ◽  
Vdw Force ◽  
Fly Height

We formulated the surface pressure of a disk surface that consists of three layers of diamond-like-carbon (DLC) as well as bonded and mobile lubricants based on the asperity adhesive contact theory. We demonstrated that this surface force could well evaluate the touchdown behaviors of a thermal fly-height control (TFC) slider. This theory shows that the touchdown behaviors of a current TFC femto-slider are mainly governed by the asperity meniscus force rather than the van der Waals force (vdW). However, it is shown that the static instability of a pico-slider was generated from the vdW force. Moreover, it is estimated that the dynamic instability of the pico-slider was mainly caused by the meniscus force rather than the vdW force. This surface force theory can allow us to understand consistently various phenomena of slider dynamics.

Correlation of Disk Topography Waves With Nanometer Scale Lubricant Moguls

2017 ◽  
Author(s):  
Andrey Ovcharenko ◽  
Tom Karis ◽  
Jih-Ping Peng
Keyword(s):  
Shear Stress ◽  
Surface Topography ◽  
Areal Density ◽  
Disk Surface ◽  
Peak Height ◽  
Lubricant Thickness ◽  
Height Control ◽  
Magnetic Performance ◽  
Carbon Overcoats ◽  
Fly Height

Magnetic recording disk carbon overcoats are lubricated with nanometer thick films of perfluoropolyether lubricant. It is well-known that lubricant thickness redistribution takes place due to air shear stress oscillation at air bearing resonant frequencies and also due to shear stress oscillation induced by disk topography waves on test tracks. We extended this work to demonstrate correlation between surface topography and lubricant redistribution on whole disk surfaces. Lubricant moguls are shown to form over regions of the disk surface which have topography waves that are half the slider length, and the lubricant thickness peak is out of phase down track from the topography peak height. There is a critical relative humidity above 20% beyond which moguls are readily formed by the slider flying at 10 nm without thermal fly height control. The significance of the lubricant redistribution for drive magnetic performance has long been the subject of debate. These results demonstrate that lubricant thickness redistribution on the order of atomic diameters can degrade magnetic performance, and that the surface topography waves alone can degrade areal density by as much as 2%.

An Insight Into the Nonlinear Touchdown Dynamics of TFC Active Slider

2013 ◽  
Author(s):  
Gang (Sheng) Chen ◽  
Jianfeng Xu ◽  
J.-Y. Chang
Keyword(s):  
Nonlinear Dynamics ◽  
Hard Disk Drives ◽  
Disk Surface ◽  
Flying Height ◽  
Disk Drives ◽  
Height Control ◽  
Intermittent Contact ◽  
Fly Height ◽  
Insight Into ◽  
Small Spacing

Storage of 10 Tb/in 2 in hard disk drives within the next decade requires a significant change to reduce the physical spacing as little as 0.25 nm at the read-write transducer location. A lot of tribology issues exist to such a low flying height, the touch down and take off instability and hysteresis, the flying height avalanche, the influences of surface topography and morphology, the lubricant modulation and pick-up, robust air bearing surface and suspension design, just to name a few. Understandings of the complex tribo-dynamics issues in the near contact and contact states are very important to further reduce the flying height. At such a small spacing intermittent contact between the slider and disk surface becomes inevitable and the current MEMS-based thermal fly-height control (TFC) technology needs further improvement to satisfy the future needs. How to control the slider to reduce touchdown instability and eventually eliminate bouncing has been a pressing and challenging research topic. Most of existing work on touchdown dynamics applied conventional nonlinear dynamics theory and spectrum as well as harmonics analysis, which could suffer from the assumptions of small nonlinearity and stationary. This study presents a concurrence plot and Lyapunov exponent analysis which could offer an insight to the problem in the context of contemporary nonlinear dynamics theory.

Numerical Method of Analyzing Contact Mechanics between a Sphere and a Flat Considering Lennard-Jones Surface Forces of Contacting Asperities and Noncontacting Rough Surfaces

2012 ◽  
Vol 134 (1) ◽  
Author(s):  
Kyosuke Ono
Keyword(s):  
Numerical Method ◽  
Contact Mechanics ◽  
Rough Surfaces ◽  
Present Theory ◽  
Adhesive Contact ◽  
Adhesive Force ◽  
Surface Forces ◽  
Contact Theory ◽  
Magnetic Disk ◽  
Lennard Jones

A new numerical method of analyzing adhesive contact mechanics between a sphere and a flat with sub-nanometer roughness is presented. In contrast to conventional theories, the elastic deformations of mean height surfaces and contacting asperities, and Lennard-Jones (LJ) surface forces of both the contacting asperities and noncontacting rough surfaces including valley areas are taken into account. Calculated contact characteristics of a 2-mm-radius glass slider contacting a magnetic disk with a relatively rough surface and a 30-mm-radius head slider contacting a currently available magnetic disk with lower roughness are shown in comparison with conventional adhesive contact theories. The present theory was found to give a larger adhesive force than the conventional theories and to converge to a smooth sphere-flat contact theory as the roughness height approaches zero.

A Study of the Hydroelastic Instabilities of Supercavitating Hydrofoils

1960 ◽  
Vol 4 (04) ◽  
pp. 28-38
Author(s):  
Paul Kaplan ◽  
C. J. Henry
Keyword(s):  
Dynamic Instability ◽  
Experimental Studies ◽  
Surface Flow ◽  
Small Range ◽  
Equal Importance ◽  
Static Instability ◽  
Elastically Restrained ◽  
Density Ratios ◽  
Oscillating Foil ◽  
Stream Direction

Presented herein are the results of a theoretical study of the static and dynamic hydroelastic instabilities of rigid supercavitating hydrofoils on elastic supports. A two-dimensional theory is used to define the unsteady hydrodynamic force and moment acting on the oscillating foil, which is assumed to be elastically restrained in translation normal to the free-stream direction and in rotation about a prescribed axis which is normal to the plane of flow. All other motions are neglected. The effects of variation in the elastic and inertial properties, as well as the effect of varying the position of the upper surface flow-separation point on the possibility of either form of instability, are determined. Also, the effect of cavitation number over a small range near zero is hypothesized. The theory predicts that dynamic instability (bending-torsion flutter) is possible at the density ratios typical of supercavitating operation. This is in contrast to the results for fully-wetted flow, where the occurrence of flutter is unlikely at the structural-to-fluid density ratios typical of hydrodynamic operation. The flutter possible in supercavitated operation is also more severe than that indicated for fully-wetted flow. Furthermore, it is shown that for the supercavitating hydrofoil, static instability (torsional divergence) and dynamic instability are of equal importance which again differs from the results in fully-wetted flow where static instability was shown to be the more important practical problem. Recommendations are made for experimental studies to verify these theoretical results.

Numerical Simulation of Touchdown/Takeoff Hysterisis of Spherical Pad Slider by Considering the Liquid Bridge Between the Slider and Lubricant-Disk

2008 ◽  
Author(s):  
Hui Li ◽  
Jianhua Li ◽  
Junguo Xu ◽  
Yuki Shimizu ◽  
Kyosuke Ono ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Liquid Bridge ◽  
3D Model ◽  
Three Dimensional ◽  
Disk Surface ◽  
Force Model ◽  
Disk Interface ◽  
Meniscus Force ◽  
Geometry Model ◽  
Balance State

This work carries on a numerical simulation of the touchdown/takeoff (TD/TO) hysterisis of the spherical pad slider. It numerically studies the meniscus bridge’s formation and meniscus force interaction between the spherical pad and lubricant over the disk surface. It proposes a geometry model for the lubricant bridge, and correspondingly, a force model for the meniscus force acting on the spherical pad slider due to the lubricant bridge. By solving the liquid balance state at the meniscus boundary, it obtains the geometry of the liquid bridge. A parametric study is done to study the effects of the geometry of spherical pad, Hamaker constant of lubricant-disk, and surface energy of lubricant on the formation of the liquid bridge. The overflow phenomenon is analyzed to find out the acceptable dimension of the spherical pad design. Moreover, a three-dimensional (3D) model of spherical pad slider/disk interface is built to study the steady-state flying of the spherical pad slider. The different parameters are analyzed to study their effects on the TD/TO hysteresis.

Performance Optimization of Thermal Nano-Actuator for Fly Height Control in Disk Drives

2009 ◽  
Author(s):  
Haisan Tan ◽  
Bo Liu ◽  
Mingsheng Zhang ◽  
Shengkai Yu
Keyword(s):  
Performance Optimization ◽  
Power Input ◽  
Vertical Position ◽  
Disk Drives ◽  
Height Control ◽  
Line Spacing ◽  
Simulation Results ◽  
Heater Design ◽  
Fly Height ◽  
Actuator Design

Slider with thermal fly height control (TFC) uses a thermal heater to produce localized thermal protrusion and adjust the vertical position of the read/write head. This paper reports authors’ efforts in exploring large protrusion stroke with minimal heater power input whilst preserving heater robustness in the TFC slider, with an optimized thermal nano-actuator design. Effects of both heater line width and line spacing on TFC slider performances are investigated. A novel ‘Stream-River’ heater design approach is proposed. Simulation results conclude that the “Stream-River” approach is of both high power-protrusion efficiency and high heater robustness.

Ranking of Thermal Asperity (TA) Interaction During Seeking Under Various Fly-Height Conditions

2020 ◽  
Author(s):  
Abhishek Srivastava ◽  
Bernd Lamberts ◽  
Ning Li ◽  
Bernhard Knigge
Keyword(s):  
Theoretical Analysis ◽  
State Interaction ◽  
Idle State ◽  
Height Control ◽  
Interaction Mechanisms ◽  
Industry Standard ◽  
Maximum Benefit ◽  
Protection Mechanisms ◽  
Fly Height ◽  
Experimental Corroboration

Abstract HDD heads have various interaction mechanisms with thermal asperities (TAs), and protection mechanisms need to be put in place to ensure the head-disk interaction (HDI) resulting from them is eliminated or minimized to the highest extent possible. It is straightforward to not allow the head sit-on-track on cylinders that have such TAs on them, and the same principle can be extended to so-called high TAs (HTAs), whose height is more than the fly height of the head, so heads do not inadvertently interact with the TA even when motion is triggered on another head, since the entire head stack moves together. Similar TA interactions also occur when the head seeks across the tracks. Typical short seeks have thermal fly-height control (TFC) turned on while it is turned on during long seeks, which is greater than a few hundred tracks. Heads can also interact with TAs during retract and arrival of the head during such long seeks. Finally, background media scan (BGMS), which is an industry standard, when the drive enters an idle state. Interaction with HTAs can also occur when the drive enters such a state. Typical seek avoidance attempts to eliminate TA interaction during seeking, however it is not straightforward to determine which of the seek mechanism: TFC On during short seeks, retract/arrival during long seeks, HTA interaction during long seeks with TFC off, or idle TA interaction causes the greatest HDI. Through theoretical analysis and experimental corroboration, this paper intends to rank the various modes of TA interaction, so by developing features for eliminating or minimizing them in that order could help bring the maximum benefit for achieving minimum lifetime reduction of the head due to such interaction.

A Method to Reduce Head-Disk Interface (HDI) Degradation Risk During Thermal Asperity (TA) Mapping in a Hard Disk Drive

2020 ◽  
Author(s):  
Abhishek Srivastava ◽  
Rahul Rai ◽  
Karthik Venkatesh ◽  
Bernhard Knigge
Keyword(s):  
Hard Disk Drive ◽  
Bias Voltage ◽  
Disk Drive ◽  
Test Time ◽  
Head Disk Interface ◽  
Disk Interface ◽  
Height Control ◽  
Contact Sensor ◽  
Fly Height ◽  
Sample Set

Abstract One of the issues in thermal asperity (TA) detection using an embedded contact sensor (ECS) is the degradation caused to the read/write elements of the head while interacting with the TA. We propose a method to reduce such head-disk interaction (HDI) during TA detection and classification by flying higher at low thermal fly-height control (TFC) power, which minimizes the interaction of the TA with the head. The key idea is to scan the head at higher fly height, but with higher ECS bias voltage. Initial experiments have shown that the TA count follows a negative cubic relationship with the backoff at various bias levels, and that it follows a square relationship with bias at various backoff levels. Using a sample set, the calibration curves i.e. the golden relationship between these parameters can be established. Using these, one can start the TA detection at the highest backoff and high ECS bias, and start to estimate the nominal TA count. By mapping out these TAs and ensuring the head does not fly over them again to prevent HDI, the fly height can then be lowered, and the rest of the TA cluster can be scanned. Following this method iteratively, the entire TA cluster can be mapped out with minimal interaction with the head. Although this method entails an increase in the test time to detect and map all TAs, compared to detecting them with TFC being on, this can help improve the reliability of the drive by protecting the sensitive read/write elements especially for energy assisted recording from HDI.

Slider-Disk Contact Characterization Using a Thermal Fly-Height Control Slider

2009 ◽  
Vol 45 (11) ◽  
pp. 5026-5029 ◽  
Author(s):  
Lionel Ng ◽  
Mingsheng Zhang ◽  
Bo Liu ◽  
Yansheng Ma
Keyword(s):  
Height Control ◽  
Disk Contact ◽  
Fly Height

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.

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