Spherical Pad Research Articles

Dynamic Studies on Lube-Surfing Recording

This paper studies the full processes of touchdown, lube-surfing, and takeoff of thermal flying-height control sliders by simulation. It is observed that for a conventional slider, the lube-surfing process is not stable, and the slider may transfer to the full flying state or be in the solid contact with the disk. While for the spherical pad design, a stable lube-surfing state is achieved. It is taken into account that the spherical pad can further reduce the short-range forces, which play crucial roles in lube-surfing recording. The requirement and budget for the lube-surfing recording are discussed.

Contact recording review

Various contact recording technologies for hard disk drives are reviewed. The advantages and disadvantages of each approach to contact recording are analyzed. Experimental detection methods and simulation models for the contact force are introduced. Some important technologies related to contact recording are addressed. The effects of lubricant and the short range forces on contact recording are discussed, and the dynamic flying characteristics of a slider with spherical pad at trailing edge are studied. It is suggested that a thermal protrusion slider with a spherical pad at the trailing edge may be a possible approach for the success of contact recording.

Numerical Simulation of a “Spherical Pad” Slider Flying Over Bit Patterned Media

Bit patterned media are being studied as a promising approach for achieving storage densities beyond 1 Tb/in2 in magnetic recording disk drives. In this investigation we study the flying characteristics of a so-called ldquospherical pad sliderrdquo where a spherical pad is implemented on the top of the trailing pad of a traditional slider. We numerically simulate the flying characteristics and slider attitude of the spherical pad slider and compare this design with a traditional slider flying over the same bit patterned media. The effect of the design parameters of the bit pattern and the spherical pad on the flying characteristics is investigated.

Effect of van der Waals Forces in a Near Contact Head-Disk Interface

The minimum flying height, elastic deformation, and attractive pressure caused by van der Waals force under static air-bearing pressure were analyzed numerically using a spherical pad slider and a flat disk model. Parametric analysis revealed that when the pad radius of curvature was 20 mm, the minimum possible flying height was about 1 nm. The smallest roughness height, for reducing the van der Waals attractive force to less than the meniscus force, is ~ 0.5 nm.

Dynamic instability of flying head slider and stabilizing design for near-contact magnetic recording

The dynamic instability of a flying head slider is described, and a design guideline is presented for a slider that can stably fly at a height of less than 5 nm. The current use of shrouded Rayleigh step-bearing slider has been a good way to increase air-bearing stiffness and damping while reducing meniscus adhesion and friction forces, but does not have enough ability to achieve a small flying height less than 5 nm. On the basis of meniscus interfacial force theory, I proposed a spherical pad slider that is inherently stable in the near-contact regime and that has high durability against intermittent contact, which is necessary for future high-density magnetic recording. This design concept is being partly realized by thermal flying height control technique.

Study of a Spherical-Pad Head Slider for Stable Low-Clearance Recording in Near-Contact Regime

A slider with an air-bearing surface that has a small spherical pad around the read/write elements on the trailing center pad was developed to reduce the meniscus and friction forces and slider clearance loss. While the slider which has a spherical pad of a radius less than 10 mm, the meniscus force is reduced to less than 10% of the air-bearing lift force, thus, flying height modulation is decreased and instability are suppressed. Evaluation using an air-bearing surface model with a spherical pad showed that slider clearance was increased by 1 nm at a 5-nm nominal flying height. Evaluation using touchdown-takeoff testing of a spherical pad slider fabricated by depositing carbon on the center pad air-bearing surface by means of the lift-off resist technique showed that the spherical pad slider had a very small friction force and acoustic emission output up to a 5-nm interference height. It thus provides instability-free sliding in the near-contact regime.

1105 ニアコンタクト浮上に対する素子部球状スライダの適用検討(要旨講演,一般セッション:情報機器コンピュータメカニクス)

A slider with an air-bearing surface that has a small spherical pad around the read/write elements on the trailing center pad was developed to reduce the meniscus and friction forces and slider clearance loss. Flying height modulation and slider instability are suppressed by the reduction of the meniscus force to less than 10% of the air-bearing lift force and the use of a spherical pad with a radius of less than 10 mm. Evaluation using an air-bearing surface model with a spherical pad showed that slider clearance was increased by 1 nm at a 5-nm nominal flying height. Evaluation using touchdown-takeoff testing of a spherical pad slider fabricated by depositing carbon on the center pad air-bearing surface by means of the lift-off resist technique showed that the spherical pad slider had a very small friction force and acoustic emission output up to a 5-nm interference height. It thus provides instability-free sliding in the near-contact regime.

Contact Model for a Pad Asperity and a Wafer Surface in the Presence of Abrasive Particles for Chemical Mechanical Polishing

ABSTRACTA contact model for a single spherical (pad) asperity and a flat (wafer) surface, with an interface filled with spherical (abrasive) particles is introduced. Finite element method is used to determine the deformation characteristics of a single spherical abrasive indenting a hyper-elastic pad material. The asperities in Greenwood and Tripp (GT) model, which is widely used for the contact of rough spheres, are replaced with the spherical particles. Relations are developed to predict pad-to-particle-to-wafer contact in two distinct regimes, where a) pad and the wafer are separated by the particle; and b) all three bodies come in contact simultaneously. The results of the model show that the abrasive particles in the (pad) asperity-wafer interface causes the contact to be distributed over an area larger than that predicted by the Hertz model, while the maximum contact pressure becomes relatively lower. The fraction of the load carried by pad-to-wafer and pad-to-abrasive-to-wafer varies along the contact interface of the pad asperity and wafer.

On a test bench for studying lubrication in a spherical bearing: simulations and experimental validation

In this paper a test bench dedicated to the analysis of a lubricated spherical pair is presented. The experimental set-up has been used to validate a numerical code that has been developed by the authors in order to simulate a complex lubricated spherical pair that affects the reliability of a novel continuous variable transmission (CVT). The test bench is modular and can be adapted to other lubricated pairs, either cylindrical or spherical. The stand is equipped with an I/O control card and allows the on-line acquisition of some important parameters. As for the numerical code, the finite-difference method has been used to solve the indirect problem in the lubricated spherical pad, under the condition of hydrodynamic regime, with externally pressurized inlets. Two simulators are needed since the physical properties of the test bench and the real system are different. The one that simulates the behavior of the spherical pair in the test stand has been used to ascertain the numeric approach prediction capability. Indeed, the experimental tests gave results which are in very good correspondence with the numerical predictions. Hence, the second simulator, which has been tailored on the particular spherical pair the CVT is equipped with, gained reliability in predicting the behavior of the real system under different load and speed conditions. These predictions have been useful in achieving new insights into the novel CVT, which, under this new light, has been criticized by making the point that its range of application in automotive is, at the actual state of the art, rather limited, in spite of a high intrinsic complexity. Copyright © 2006 John Wiley & Sons, Ltd.

Influence Of Solder Joint Shape On The Thermo-Mechanical Reliability Of CSP's

Not only the stand-off height but also the shape of a solder joint has a strong influence on the joint reliability under temperature cycling. The shape determines the size of the local stress and strain concentrations. It is therefore very important to know well the joint shape after reflow. In a previous paper closed analytical expressions were derived for liquid bump shapes, as a function of pad size and bump height [1]. The bump deformation as a function of the chip weight could be derived from the force constant. In the present paper closed analytical expressions are derived for the force constant for liquid bumps having unequal spherical pad sizes. It turns out that the force constant for compression can be optimized as a function of the ratio of those pad sizes. The shape of the bump and especially the contact angle is of interest for modeling activities where geometrical effects do play a role. Furthermore from the variation in bumps heights on a chip an estimate can be made of the tilt of the chip after assembly. The solder profile estimation by the analytical expressions is validated by experimental results. Also a comparison with the solder profile estimation by the simulation software Surface Evolver is done. Both comparisons showed that the analytical estimation of the standoff height is very good as long as the gravitation energy contributed by the chip weight is less than 10% of the total energy. Finally, an example is shown where the analytical model and Surface Evolver are the geometrical input for a finite element model. The example considers a CSP assembled at both sides of the printed circuit board.

Influence of Pad Pivot Friction on Tilting-Pad Journal Bearing Measurements—Part I: Steady Operating Position©

This paper presents measured results for the eccentricity ratios for two tilting-pad journal bearing. Comparison between a bearing with spherical seated ball and socket pad pivots and one with line contact rocker-back pad pivots is made. The bearings have a length to diameter ratio of 0.75, offset ratios of 0.50, preloads of about 0.320, a journal diameter of 70 mm and a radial machined pad clearance of 113.0 μm. Measurements were made for a range of speed-load conditions encompassing a Sommerfeld number range of 0.1 to 2.0. Comparison of the eccentricity magnitude for the two bearing agreed within uncertainty levels. For the bearing with rocker-back pad pivots, the journal attitude angle with respect to the applied load direction is nearly zero. Attitude angles range from 13° to 33° for the bearing with spherical seated ball and socket pad pivots. The deviation from zero attitude angle for this bearing increased with increasing speed. A hypothesis for larger pad pivot friction in the ball and socket pivot is presented to explain the variation in attitude angle between the two bearings. Presented at the 53rd Annual Meeting in Detroit, Michigan May 17–21, 1998

Influence of Pad Pivot Friction on Tilting-Pad Journal Bearing Measurements—Part II: Dynamic Coefficients©

This paper presents measured results for the dynamic stiffness and damping force coefficients for two tilting-pad journal bearings. Comparison between a bearing with spherical seated ball and socket pad pivots and one with line contact rocker-back pad pivots is made. The bearings tested were preloaded five pad designs with load directed on the pivots. The bearings have length to diameter ratios of 0.75, offset ratios of 0.50, preloads of about 0.320, a journal diameter of 70 mm, and radial machined pad clearances of 113.0 μm. Measurements were made for a range of speedload conditions encompassing a Sommerfeld number range of 0.1 to 2.0. Comparison of the principal stiffness and damping coefficients for the two bearings show the same trends. Nearly zero cross-coupled stiffness coefficients were measured for the bearing with rocker-back pad pivots. For the bearing with spherical seated pad pivots, non-dimensional cross-coupled stiffness coefficients for Kxy ranged from -1.2 to -0.9 and for Kyx ranged from -3.8 to 0.8. A hypothesis for increased pad pivot friction in the ball and socket is presented to explain the variation in cross-coupled stiffness coefficients between the two bearings. Presented at the 53rd Annual Meeting in Detroit, Michigan May 17–21, 1998

Influence of Turbulence on Performance Characteristics of the Tilting Pad Thrust Bearing

The influence of fluid film turbulence on the performance of centrally-pivoted tilting pad thrust bearings was analyzed. Major features of the analysis are: (1) today’s two predominant “engineering” turbulent flow theories are delineated and their quantitative predictions compared; (2) a spherical pad profile was assumed, and (3) an equal area technique was used in the finite difference equations. The results confirmed earlier predictions of increases in power loss and load capacity when compared to a laminar solution. Also, no significant differences were found between the results predicted by the two predominant turbulent flow theories. Power loss, load capacity, and hydrodynamic oil flow are given for 13, 15, and 17 in. sizes. Comparisons of laminar and turbulent numerical results are presented.