Rear Pad Research Articles

Influence of Active Cooling at the Trailing Edge on the Thermal Behavior of a Tilting-Pad Journal Bearing

In tilting-pad journal bearings (TPJB) with a non-flooded lubrication concept, higher maximum pad temperatures occur than with a flooded bearing design due to the lower convective heat transfer at the pad edges. In this paper, we present an approach to influence the thermal behavior of a five-pad TPJB by active cooling. The aim of this research is to investigate the influence of additional oil supply grooves at the trailing edge of the two loaded pads on the maximum pad temperature of a large TPJB in non-flooded design. We carry out experimental and numerical investigations for a redesigned test bearing. Within the experimental analysis, the reduction in pad temperature is quantified. A simulation model of the bearing is synthesized with respect to the additional oil supply grooves. The simulation results are compared with the experimental data to derive heat transfer coefficients for the pad surfaces. The experimental results indicate a considerable reduction of the maximum pad temperatures. An overall lower temperature level is observed for the rear pad in circumferential direction (pad 4). The authors attribute this effect by a cooling oil carry-over from the previous pad (3). Within the model limits, a good agreement of the simulation and experimental results can be found.

Evaluation of the Quality of Solder Joints within Silicon Solar Modules Using Magnetic Field Imaging

Solar cells and modules are already a mature technology in mass production. It is critical to optimize and to systematically monitor their performance. The introduction of automated soldering processes and the increasing usage of novel contacting schemes can cause harmful defects, e.g., missing and defective contacts, and, thus, affect the electrical performance of solar modules after production or in field usages. Herein, magnetic field imaging (MFI) is utilized to do a non‐destructive, quantitative analysis of the modules to investigate the quality of the soldering contacts. In detail, the cross connector, interconnector, and rear‐side pads are investigated. The typical in‐field observed defects are presented. For the first time, the quality of rear‐side pads under operation is studied in detail. It is shown that 1) directly after production, the current conduction takes place not only via the rear pads but also via the press‐on contact between the bare aluminum and the rear‐side ribbons; 2) an off‐centered ribbon on the pad leads to abnormal current distribution; and 3) single rear‐side pad breaks as a function of thermal cycles due to thermo‐mechanical stress.

Balanced contact method: Reduction of thermomechanical stress in silicon solar cells induced by interconnection

In this study, a new method to reduce the thermomechanical stress in silicon solar cells induced during the cell interconnection process is proposed. By repositioning the rear pads such that the silicon solar cells are bonded to the front copper conductors ended at the same locations as the outer edges of the outermost rear pads along the busbar direction. Finite element modelling predicts that stress reduction of >50% was achieved when solar cells are interconnected by conventional tabbing or Multi-busbars (MBB) and it was confirmed by the derived stress measured by the micro-Raman spectroscopy. Front busbars terminated with a reduced contact area can further increase the tolerance of any potential misalignment arising from process variations.

Machinery condition prediction based on wavelet and support vector machine

This paper studies the use of wavelet and support vector machine (SVM) in machinery condition prediction. SVM is based on the VC dimension theory of statistical learning and the principle of structural risk minimization, and has shown advantages in solving the problem with limited sample, nonlinear and high dimensional pattern recognition. The soft failure of mechanical equipment makes its performance drop gradually, which occupies a large proportion and has certain regularity. The performance can be evaluated and predicted through early state monitoring and data analysis. The paper models the vibration signal from the rear pad of a gas blower and analyzes the 1-step and multi-step forecasting of wavelet transformation and SVM (WT-SVM model) and SVM model.

Trapping Electron Assisted Magnetic Recording

Moving towards 10 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> areal density, finding a proper recording scheme with enough write-ability is the most challenging task of a magnetic recording system. Some recording schemes with enhanced write-ability, such as HAMR, MAMR, graded media, etc., have been proposed to achieve higher recording density. Here we propose a new alternative approach for enhanced writing-trapping electron assisted magnetic recording (TEAMR). In the TEAMR configuration, an electrical bias is applied to the main pole of the write head with the disk media and the other parts of head slider grounded. As the main pole area is very small, the electrostatic force produced by electrical potential is a few orders smaller than the air bearing force at the rear pad. Therefore, it will not affect the flying performance of the head slider. At the nanometer head media spacing, a very strong electrical field is produced in the head media interface. This strong electrical field will cause free electrons to accumulate (be trapped) at the interfacial surfaces of metallic magnetic grains. These trapped electrons are localized in the surface atoms of magnetic grains and will alter the valance-electron band filling of those surface atoms. For many magnetic materials, the extra band-filling electrons reduce the magnetic anisotropy energy and make it easier to be magnetically switched. In this work, the TEAMR effect was proved by the experiment study on Co alloy based commercial disk media. The first principle calculation on L1 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ordered FePt crystal shows that the magnetic anisotropy can be reduced to zero with around 0.38 electrons trapped into 1 unit cell of FePt. Further increase in trapped electrons will change the magnetic easy axis from out-of-plane to in-plane, which is considered as a negative magnetic anisotropy. With the magnetic anisotropy reduction at the surface atoms of each grain, micromagnetic simulation result shows that the effective switching field can be reduced to around 11% of anisotropy field for a 1.6 ? 1.6 ? 3.2 nm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> FePt grain. Thus TEAMR can be another good candidate for energy assisted recording requiring very little modification to the current perpendicular magnetic recording system.

A Simplified Dynamic Model for the Analysis of the Slider Off-Track Motion Due to Head-Disk Interactions

A five-degree-of-freedom model was developed for the analysis of the off-track motion of the magnetic head slider in a hard disk drive. The air bearing was integrated into the dynamic system by combining its stiffness and damping matrices with those of the suspension. Simulation was conducted for the slider in intermittent contact with circumferentially located bumps on a rotating magnetic disk. For a single bump, the excitation to the transverse displacement of the slider is close to that of an impulse. However, for multiple bumps in a sequence, the excitation gives an effect similar to that of a step force function. The maximum transverse displacement increases almost linearly with both the coefficient of friction and the skew angle. The average contact force is determined by the maximum contact force, the contact time ratio, and the shape factor of the contact force, which change with the bump spacing and the rotational speed of the disk. The steady-state transverse displacement is related to the average contact force. As the bump spacing decreases, the average contact force increases, resulting in a greater transverse displacement. Based on the system dynamic characteristics alone, changing the rotational speed of the disk has only a small impact on the average contact force and, thus, on the transverse displacement. At zero skew angle with the bump path close to a rear pad edge, significant transverse motion occurs because of the excited roll mode and the coupling between the roll angle and the transverse displacement. The off-track motion of the slider is dominated by the rotational mode of the actuator arm and the sway mode of the suspension, as verified by comparing the results of the transverse displacement from the 5DOF model to that from a 2DOF model of the transverse motions of the actuator arm and suspension. The effects of the roll angle on the transverse displacement through coupling were found to be responsible for the difference in the transverse displacements obtained from the two models.

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

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.

Wear Characteristics of Padded Air Bearing Sliders During a Contact Take-Off Process

The pressing and challenging demand for resolving the stiction/glide-height conflict, driven by today’s ever decreasing head/disk spacing, forces us to constantly search for new technologies. One of them is padding the slider’s air bearing surface. Although the padded air bearing sliders can significantly reduce the stiction, the wear of these landing pads becomes a central issue. This paper attempts to analytically predict the wear characteristics of the landing pads during a contact take-off process. A wear factor derived from the adhesive wear law is employed to measure the wear extent of the landing pads. The contact force profile and wear factor of each pad are calculated through the partial contact air bearing simulation of a slider’s take-off process. It is found that the rear pad wears an order magnitude more than the leading pads. The wear volume of the rear pad increases exponentially with pad height, interface roughness and altitude. Raising the leading pads alone slightly reduces the wear of the rear pad. Placing the rear pad away from the slider’s trailing edge, however, substantially alleviates the wear of the rear pad. Finally, a lightly textured pad/disk interface decreases the pads’ wear to a minimum value for a given padded air bearing design. [S0742-4787(00)01903-2]

A402 パッド型ジャーナル軸受内の潤滑流体の流れに関する研究

In this report, in order to evaluate influence of pad shape on the behaviour of Taylor vortices in submerged multi-pad journal bearings, fluid film flow in bearing clearance and fluid flow between pads were visualized experimentally. Critical Taylor number decreased with an increase of pad spacing irrespective of pad shape. Two-dimensional flow field between pads were measured by Particle Image Velocimetry. In the case of streamlined pads, fluid flow entered rear pad fluently.

Tribology of Tri-Pad Sliders©

The tribology of tri-pad sliders is investigated for hydrogenated and nitrogenated carbon overcoated disks. Friction and stiction during contact-start-stop testing are measured for both types of disks and the acoustic emission signal is studied to investigate the modes of slider vibrations during steady-state flying. Finite element simulations of the steady-state slider vibrations are performed and the results are compared with experimental observations. The optical fluorescence spectra are studied for the aluminum oxide and aluminum oxide-titanium-carbide (Al2O3TiC) portions of the slider. In addition, wear of the rear pad of a tri-pad slider is determined for fixed-track testing using nanoindentations. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in San Francisco, California, October 13–17, 1996

Speed Dependence, Takeoff and Stiction of a New Class of Gas Bearing Sliders

While searching for a less-speed-sensitive programmable air bearing slider, the author noted that the primary reason for the sluggish takeoff and large dependence of fly height on speed is the very common 10 mrad taper. This taper is found on many sliders in the railed, taper/flat class. A single, plane wedge bearing operating at a large bearing number and a pitch angle considerably below that which gives maximum lift does not suffer from such speed sensitivity. The “inlet throttled” condition of the bearing inlet fixes the mass flux into the bearing gap. Because a single pad of this type has poor pitch stability, the author placed two of these pads in a tandem configuration, and abandoned rails. The result defines a new air bearing class, called Tango, which has front and rear pads, each having inlet throttled leading edges. Some members of this class offer takeoff velocities equalling and even improving more-complex designs using subambient pressure. In addition, numerical and hardware experiments have verified the considerably reduced sensitivity of fly height to speed, a reduced sensitivity to crown distortion, and improved stiction. Disk designers benefit by not having to accept a longer takeoff run when the fly height decreases.

Comparison of numerical and experimental flying characteristics of tri-pad sliders

The flying characteristics of a tri-pad slider are calculated numerically and compared with measurements using a commercially available, interferometry based flying height tester. The effect of crown, camber and edge blends on both rails and rear pad is investigated. The simulations indicate that the flying characteristics depend strongly on the edge blend of the rear pad. A sensitivity analysis using a Monte Carlo technique in conjunction with a finite element based air bearing solver is performed to determine the variation in flying height due to manufacturing tolerances.