The Effect of Track-Seeking Motion on Off-Track Vibrations of the Head Gimbal Assembly in HDDs

The effect of track-seeking on off-track residual vibrations of the head-gimbal assembly (HGA) is investigated for air and helium environments using the so-called “fluid dynamic mesh” method and the “fluid-structure interaction” method. Three different angular acceleration profiles (square wave, triangular wave and sinusoidal wave) are investigated as a function of seek time (10 ms and 5 ms). Results show that smoothening of sharp transitions of the seek profile improves the performance of off-track residual vibrations during track-following and shortens the track-following time of the head positioning servo system. In addition, the effect of lateral flow (windage) on off-track residual vibrations during track-following must be considered for a square wave angular acceleration profile. Simulation results show that helium improves the track-following accuracy compared to air due to the lower windage forces acting on the HGA. We observe that the sinusoidal wave angular acceleration performs best among the three angular acceleration profiles investigated. Furthermore, seek time is found to have only a small effect on off-track residual vibrations during track-following.

Effect of Molecular Weight on Lubricant Depletion in a Heat Assisted Magnetic Recording System

A model for studying lubricant depletion in HAMR slider/disk system was developed based on molecular dynamics simulation. We found that the lubricant molecular weight has small effect on lubricant depletion.

Advanced Numerical Modeling of Nonlinear Elastic Cable With Recovery Characteristics

Cable driven parallel robots (CDPRs) have many advantages such as low inertia and large workspace. These advantages lead to the industrial applications. CDPRs mainly use Dyneema polymer cable for more high sensitivity because it has advantage of the lower weight than steel wire. However, the polymer cable is continuously deformed when actuating the CDPR because of the elasto-plastic cable characteristics such as recovery. In this paper, numerical cable recovery was proposed using the modified burger model. Finally, the models were simulated and compared with the experimental profiles. As the result, the simulations are good agreement with the experimental profiles.

Head Disk Spacing Effect on Heat Transfer in Heat Assisted Magnetic Recording

Heat transfer at nanometer scale attracts a lot of interest from both academia and industries. The hard disk drive (HDD) industry cares about the heat transfer between the head and disk, as several heating and thermal sensing elements are integrated into the HDD system. Understanding the heat transfer mechanism and its dependency on spacing becomes very critical for heat assisted magnetic recording (HAMR). In this paper, we propose a new method to study the head disk spacing effects on heat transfer by introducing a small perturbation to the spacing while maintaining the heating source unchanged. The dependency of heat transfer on the nanoscale spacing provides insights to the understanding of heat transfer mechanisms inside the nanoscale gap.

Sensitivity Analysis on Solder Joint Fatigue Life of Solid State Drives by Finite Element Method and Monte Carlo Simulation

We proposed a method to estimate a distribution of fatigue life of solid state drives (SSDs) due to thermal cycling excitation by using finite element method and Monte Carlo simulation. In the developed finite element model, we utilized the Anand model to represent the viscoplastic behavior of the solder balls, and we also utilized the Prony series to represent the viscoelastic behavior of the polymer material in underfill. We determined a fatigue life of the SSD by using the Morrow’s energy-based fatigue model. Finally, we determined a distribution of fatigue life considering the manufacturing tolerance of the design variables and the variation of material properties in the Monte Carlo simulation. Finite element analysis shows that the outermost solder ball at the corner of dynamic random access memory was the most vulnerable component under the thermal cycling excitation. We also show that temperature profile and diameter of solder ball affect dominantly the fatigue life of the SSD.

Advanced Numerical Modeling of Nonlinear Elastic Cable With Permanent Stretch Using Cable Driven Parallel Robot

Since cable driven parallel robots (CDPRs) have many advantages, they have been used in many industrial fields. Fully constrained CDPRs mainly use Dyneema polyethylene because it has advantage of the lower weight than steel wire. However, the polyethylene cable has complex elastic characteristics (e.g. permanent stretch and hysteresis). In this paper, the advanced numerical modeling of nonlinear elastic cable with permanent stretch using cable driven parallel robot was derived and simulated for various cable condition. Based on the advanced numerical nonlinear cable model, the simulation was carried out under the various cable lengths and tensions. Compared to the experimental results, the simulation results are good agreement with the experimental data.

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

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.

Design and Implement the Readout Circuit of an In-Cell High-Resolution Capacitive Touch Panel

This paper proposes a high resolution capacitive touch panel readout circuit to sense the Variation by self-capacitance method. This AM display of in-cell structure includes an active architecture for improved resolution, that controlling the TFT (Thin-film transistor) to make the accuracy better. In addition, the panel has 60 sensing point per 0.88 inches and the proposed readout circuit used switched capacitor charge amplifier (SCCA) to sensing the charge change and enhances the SNR (Signal-to-noise) by eliminating the baseline. The experimental results show that the proposed readout circuit SNR achieves 38dB and the frame rate is 200Hz.

Airborne and Structure-Borne Transmission of High Frequency Fan Vibration in a Storage Box

In this paper, contributions of airborne and structure-borne vibrations to head positioning error of a HDD at high frequencies up to 10 kHz were investigated. The L8 array test was conducted with four two-level factors about vibration isolation between fans and HDDs: A) Removing bracket, B) Attaching foam on backplane, C) Filling foam in the next column, and D) Filling foam in the upper and lower slots. The test results showed there were less interaction between airborne and structure-borne vibration. Then, we set a model of fan vibration transmission and the model parameters were determined so that errors between the estimated and measured values were minimized. As the results, it was confirmed that about 80% of the power of PES was caused by the airborne vibration at the normal case.

Molecular Dynamics Study of Lubricant Evaporation and Fragmentation in Heat-Assisted Magnetic Recording With Pulsed Laser Heating

Molecular dynamics simulations are performed to investigate the effect of high frequency laser heating on the thermal stability of lubricant on a disk surface. Lubricant morphology, lubricant evaporation, and lubricant fragmentation are studied as a function of laser pulse duration, power density, and frequency. The results show that lubricant depletion increases with laser pulse duration.