Analysis of Microwaviness-Excited Vibrations of a Flying Head Slider in Asperity Contact Regime

2016 ◽  
Author(s):  
Kyosuke Ono
Keyword(s):  
Hard Disk Drives ◽  
Adhesive Contact ◽  
Flying Height ◽  
Design Parameters ◽  
Lubricant Layer ◽  
Asperity Contact ◽  
Head Slider ◽  
Spacing Variation ◽  
Parameter Values ◽  
Fly Height

The flying height of a head slider in hard disk drives has been decreased close to 1 nm but still must be reduced to ∼0.5 nm in order to increase recording density. At such a narrow spacing, variation in head/disk spacing caused by microwaviness (MW) becomes a significant concern [1]. Some comprehensive numerical simulations of slider dynamics in the near-contact and contact regimes have been conducted [2–5]. However, the real physics behind slider dynamics does not seem to be fully elucidated because the head-disk interfacial force changes with differences in interfacial design conditions such as the air-bearing surface, surface roughness, and lubricant layer. In this study, we evaluated head-disk interfacial forces by asperity adhesive contact theories with measured asperity parameter values. The MW-excited vibrations of a thermal fly-height control (TFC) slider in proximity and asperity contact regimes were simulated by changing the design parameters. It was found that the simulated results allow us to understand typical experimental results reported in previous literature.

Analysis of Microwaviness-Excited Vibrations of a Flying Head Slider in Proximity and Asperity Contact Regimes

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Kyosuke Ono
Keyword(s):  
Hard Disk Drives ◽  
Force Model ◽  
Total Force ◽  
Asperity Contact ◽  
Contact State ◽  
Head Slider ◽  
Adhesion Contact ◽  
Head Surface ◽  
Wide Range ◽  
Spacing Variation

The vibration characteristics of a thermal fly-height control (TFC) head slider in the proximity and asperity contact regimes attract much attention, because the head–disk spacing (HDS) must be less than 1 nm in order to increase the recording density in hard disk drives. This paper presents a numerical analysis of the microwaviness (MW)-excited vibrations in the flying head slider during the touchdown (TD) process. We first formulate the total force applied to the TFC head slider as a function of the HDS, based on rough-surface adhesion contact models and an air-bearing force model. Then, the MW-excited vibrations of a single-degree-of-freedom (DOF) slider model at TD are simulated by the Runge–Kutta method. It is found that, when the MW amplitude is less than the spacing range of static instability in the total force, the slider jumps to a contact state from a near-contact or mobile-lubricant-contact state. It then jumps to a flying state even when the head surface is protruded further by increasing the TFC power. When the MW amplitude is relatively large, a drastically large spacing variation that contains a wide range of frequency components below 100 kHz appears in the static unstable region. These calculated results can clarify the mechanisms behind a few peculiar experimental phenomena reported in the past.

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.

Numerical Analysis of Microwaviness-Excited Vibrations of a Flying Head Slider at Touchdown

2017 ◽  
Author(s):  
Kyosuke Ono
Keyword(s):  
Adhesion Force ◽  
Hard Disk Drives ◽  
Force Model ◽  
Air Bearing ◽  
Single Degree Of Freedom ◽  
Disk Interface ◽  
Head Slider ◽  
Bearing Stiffness ◽  
Bearing Force ◽  
Parameter Values

As an extension of the study presented in ISPS 2016, vibration characteristics of a commercially used head slider in hard disk drives at touchdown are analyzed by using a single degree-of-freedom (DOF) slider model, improved asperity adhesion force model, and air-bearing force model. Using parameter values at the head/disk interface, the total interfacial force was evaluated for various air bearing stiffness ratios r. Microwaviness (MW)-excited slider vibration was simulated near the boundary of instability onset (r = 2.4), and slight instability conditions at r = 2. It was found that the simulated results at r = 2.4 and 2 agree well with the touchdown vibrations of actual slider at ID and MD, respectively. The possibility of surfing recording is discussed.

Experimental and Numerical Investigation of Dynamic Instability in the Head Disk Interface at Proximity

2005 ◽  
Vol 127 (3) ◽  
pp. 530-536 ◽  
Author(s):  
Rohit Ambekar ◽  
Vineet Gupta ◽  
David B. Bogy
Keyword(s):  
Dynamic Instability ◽  
Hard Disk Drives ◽  
Areal Density ◽  
Simulation Software ◽  
Flying Height ◽  
Stable Fly ◽  
Lubricant Thickness ◽  
Disk Interface ◽  
The Difference ◽  
Fly Height

As the flying height decreases to achieve greater areal density in hard disk drives, different proximity forces act on the air bearing slider, which results in fly height modulation and instability. Identifying and characterizing these forces has become important for achieving a stable fly height at proximity. One way to study these forces is by examining the fly height hysteresis, which is a result of many constituent phenomena. The difference in the touchdown and takeoff rpm (hysteresis) was monitored for different slider designs, varying the humidity and lubricant thickness of the disks, and the sliders were monitored for lubricant pickup while the disks were examined for lubricant depletion and modulation. Correlation was established between the observed hysteresis and different possible constituent phenomena. One such phenomenon was identified as the Intermolecular Force from the correlation between the lubricant thickness and the touchdown velocity. Simulations using 3D dynamic simulation software explain the experimental trends.

Improved Analysis of Unstable Bouncing Vibration and Stabilizing Design of Flying Head Slider in Near-Contact Region

2006 ◽  
Vol 129 (1) ◽  
pp. 65-74 ◽  
Author(s):  
Kyosuke Ono ◽  
Masami Yamane
Keyword(s):  
Parametric Study ◽  
Contact Region ◽  
Disk Surface ◽  
Design Guidelines ◽  
Flying Height ◽  
Asperity Contact ◽  
Adhesion Forces ◽  
Characteristic Model ◽  
Head Slider ◽  
Contact Characteristic

This paper describes an improved analytical study of the bouncing vibration of a flying head slider in the near-contact region and gives quantitative designs guideline for realizing a stable flying head slider, based on the results of a parametric study. First, we numerically calculated the general characteristics of the contact and adhesion forces between a smooth contact pad and disk surface by considering asperity contact, the lubricant meniscus, and elastic bulk deformation. As a result, it was shown that the contact characteristics can be represented by a simple model with five independent parameters when the asperity density is large and the asperity height is small as in cases of current slider and disk surfaces. Then, we numerically computed the slider dynamics in a two degree of freedom slider model with nonlinear air-bearing springs by using the simplified contact characteristic model. As a result, we have obtained a self-excited bouncing vibration whose frequency, amplitude and touchdown/takeoff hysteresis characteristics agree much better with the experimental results compared with our previous analysis. From a parametric study for takeoff height, we could obtain design guidelines for realizing a stable head slider in a low flying height of 5nm or less.

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.

Diffusion Equation for Spreading and Replenishment in Submonolayer Lubricant Film

2014 ◽  
Author(s):  
Kyosuke Ono
Keyword(s):  
Diffusion Equation ◽  
Continuum Mechanics ◽  
Hard Disk Drives ◽  
Flying Height ◽  
Lubricant Layer ◽  
Height Control ◽  
Polar Groups ◽  
Diffusion Characteristics ◽  
Head Surface ◽  
Bonding Ratio

It is important to evaluate the lubrication and replenishment effects of the submonolayer mobile lubricant in hard disk drives because increased recording density can only be achieved through near-contact or surfing recording without head wear. It is known that the minimum friction coefficient can be obtained at a specific bonding ratio [1]. In recent times, the lubricant thickness has been reduced to one monolayer and the thickness of the mobile lubricant layer, to less than 0.3 nm to reduce lubricant pickup on the head surface. Matthes et al. [2] shown that a certain fraction of the layer of currently used mobile lubricants with multiple polar groups is important for reducing head wear. Canchi and Bogy [3] experimentally studied the depletion caused by thermal flying height control (TFC) head contact and reflow speed for various lubricants. Although the diffusion characteristics of perfluoropolyalkylether (PFPE) lubricants layers with a thickness of a few nanometers can be evaluated by a diffusion equation based on continuum mechanics [4], the validity of the conventional equation in the submonolayer lubricant region is not clear. Mate [5] showed that the spreading of a pancake-shaped Z-dol lubricant layer with subnanometer thickness can be quantitatively evaluated by a diffusion equation based on continuum mechanics. Ono [6] showed that the replenishment process of a depleted groove generated by slider touchdown operation can be fairly evaluated by the conventional diffusion equation if the effective ratio of the Hamaker constant to the lubricant viscosity is properly chosen. However, the identified effective viscosity is too high to be estimated from other experimental data [5, 7]. Moreover, the validity of the diffusion equation based on continuum mechanics remains unclear in the submonolayer region.

Temperature Study of Embedded Contact Sensor for HDDS by Using Scanning Thermal Microscopy

2014 ◽  
Author(s):  
Masaru Furukawa ◽  
Junguo Xu ◽  
Jianhua Li ◽  
Kiyoshi Hashimoto ◽  
Makoto Satou
Keyword(s):  
Hard Disk Drives ◽  
Disk Drives ◽  
Scanning Thermal Microscopy ◽  
Height Control ◽  
Head Slider ◽  
Self Bias ◽  
Key Factor ◽  
Contact Sensor ◽  
Sensor Temperature ◽  
Fly Height

An embedded contact sensor (ECS), which is a thermal sensor built into a head slider, has been used for contact detection between the head slider and the disk in hard disk drives. Our previous research showed that ECS could successfully detect pits on the disk and spacing modulation between the head and disk. In this work, the sensor temperature effect caused by self heating and by the thermal fly height control (TFC) heater was studied in a non-flying condition for better understanding ECS. The results showed that the temperature dependency of the TFC heater was 10 times that of ECS self-bias heating. TFC heating is dominant and the key factor in ECS sensitivity to pit detection and spacing monitoring.

Experimental and Numerical Investigation of Dynamic Instability in the Head Disk Interface at Proximity

2004 ◽  
Author(s):  
Rohit Ambekar ◽  
Vineet Gupta ◽  
David B. Bogy
Keyword(s):  
Dynamic Instability ◽  
Hard Disk Drives ◽  
Areal Density ◽  
Simulation Software ◽  
Flying Height ◽  
Stable Fly ◽  
Lubricant Thickness ◽  
Disk Interface ◽  
The Difference ◽  
Fly Height

As the flying height decreases to achieve greater areal density in hard disk drives, different proximity forces act on the air bearing slider, which results in fly height modulation and instability. Identifying and characterizing these forces has become important for achieving a stable fly height at proximity. One way to study these forces is by examining the fly height hysteresis, which is a result of many constituent phenomena. The difference in the touchdown and takeoff rpm (hysteresis) was monitored for different slider designs, varying the humidity and lubricant thickness of the disks, and the sliders were monitored for lubricant pickup while the disks were examined for lubricant depletion and modulation. Correlation was established between the observed hysteresis and different possible constituent phenomena. One such phenomenon was identified as the Intermolecular Force from the correlation between the lubricant thickness and the touchdown velocity. Simulations using 3D dynamic simulation software explain the experimental trends.

Sign in / Sign up

Export Citation Format

Share Document