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Particle intrusion into the head–disk interface (HDI) is becoming a concern in hard disk drives. Numerical studies of particle movement in HDI are of great importance for reducing particle-induced damage. In this investigation, we study the particle rebound mechanism in HDI. Not only the particle–slider collision but also particle–particle collision models are developed, which are divided into three types, including the collisions of particle and surface (P–S), particle and edge (P–E), and particle and particle (P–P). The subsequent response of particles after the collision, which includes rebound and adhesion, is calculated considering the collisional energy loss. The proposed adhesion/rebound model can more accurately present the particle trajectories in HDI and accumulation on the air bearing surface (ABS). We find that particles are likely to accumulate on the leading rail surfaces of the slider due to the air flow drag and Saffman lift. Considering the adhesion and rebound, particles with a larger diameter are more likely to fly away from the slider after the collision. The existence of particle rebound, to a certain degree, reduces contamination on ABS. [ABSTRACT FROM AUTHOR]

Heat-assisted magnetic recording (HAMR) technology is a great way to achieve higher storage density. In HAMR, dynamic performance of the head–disk interface (HDI) is critically important for the read/write stability. Lubricant bridge formation and lubricant transfer can significantly deteriorate HDI performance. In this paper, a 3-D full-atom model of a slider-lubricant-disk substrate system is established to study the dynamic performance of HDI in HAMR. The overlayers of the slider and disk substrate are made of diamondlike carbon, and the main lubricating ingredient is perfluoropolyether (PFPE). The formation and breaking of the lubricant bridge are investigated with the slider moving up and down. It is found that during the moving down process, PFPE molecules escape from the lubricant layer, and a lubricant bridge between the slider and disk is formed. During the moving up process, the lubricant bridge becomes thin and eventually breaks. The stable value of PFPE weight percentage on the slider during the moving up process is always larger than that during the moving down process. This is because of easier transfer of lubricant molecules to the slider in the low flying height region. The formation height is smaller than the breaking height, but these values are closer when the operational temperature is higher. [ABSTRACT FROM AUTHOR]

The lateral flow in hard disk drives is greatly disturbed because of the arm swinging rapidly during track seeking, which can greatly affect off-track residual vibrations during track following of the head-gimbal assembly (HGA), as well as the slider. Until now, no simulation studies have been performed to investigate off-track residual vibrations of the HGA that consider lateral flow effects. In this paper, the effect of track-seeking on off-track residual vibrations of the HGA is investigated for air and helium environments using the so-called “fluid dynamic mesh” and the “fluid-structure interaction” methods for the first time. Three different angular acceleration profiles (a square wave, a triangular wave, and a sinusoidal wave) are investigated as a function of seek time (10 and 5 ms). Results show that the smoothening of sharp transitions in the seek profile improves the performance of off-track residual vibrations 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 must be considered for a square-wave angular acceleration profile. Simulation results show that helium improves the track-following accuracy compared to air because of the lower windage forces acting on the HGA. We observe that the sinusoidal-wave angular acceleration performs best for 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. [ABSTRACT FROM PUBLISHER]

Currently, heat-assisted magnetic recording (HAMR) technology has been proposed as a method for enabling higher storage density. In this paper, the molecular dynamic simulation method was used to investigate the consumption and recovery of the lubricant perfluoropolyether (PFPE) layer under rapid heating and cooling through HAMR. A full-atom model for the 3-D slider-lubricants-disk substrate system was built for this paper. The lubricant adheres to the diamond-like carbon substrate, and the space between the slider and the lubricant is filled with helium atoms. It is found that HAMR laser heating results in the gradual consumption of the PFPE lubricant, and that the target operational temperature T0 significantly affects the consumption of the PFPE lubricant on the disk substrate. The extent of lubricant consumption increases sharply when T0 is above 600 K. The lubricant’s weight percentage on the disk substrate rises up again when cooling occurs. But it cannot be completely recovered. On the other hand, the bearing pressure reduces the degree of consumption of the PFPE lubricant by laser heating. However, the effect of bearing pressure on the amount of remaining PFPE lubricant becomes weak when T0 is above 800 K. [ABSTRACT FROM AUTHOR]

The lubricant bridge connecting the slider and the disk will significantly deteriorate the read–write stability of the hard disk drive. This paper builds a model of disk-lubricant-slider system. The coarse-grained bead-spring model is used to represent perfluoropolyethers molecules. And the molecular dynamic method is used to study the formation time and the molecule number of the lubricant bridge under different disk rotation speeds and slider flying heights. Furthermore, the influence of lubricant bridge on the pressure acting on the slider pad is also studied. [ABSTRACT FROM AUTHOR]

Previous works investigated particle trajectories in hard disk drives (HDDs) with the actuator arm and the head gimbals assembly at a fixed position. Actually, internal fluid field characteristics of HDDs can be greatly changed by the arm swing during track-seeking operations, which can affect particle trajectories and trapping status. In this paper, using the dynamic mesh method in a 2.5 in HDD for the first time considers the arm swing in the computational fluid dynamics (CFD) simulation. Al2O3 particle trajectories in this HDD are studied by the CFD solver FLUENT with user-defined functions. The trapping criterion for Al2O3 particles is used as a boundary condition for colliding surfaces. Simulation results reveal that the particle undergoes a larger number of collisions with the disk surface for the average seek time of 12 ms than for the average seek time of 6 ms. In addition, the faster the arm swings, the larger the number of particles that gather near the arm, and the shorter time it will take for particles to be trapped. Moreover, particle-surface collisions can successively take place many times in the helium flow. Furthermore, the particles are trapped slower in the helium-filled drive than in the air-filled drive. [ABSTRACT FROM AUTHOR]

A numerical method is presented to study the air-flow pattern and particle trajectory in the head–disk interface (HDI) in this paper. It first solves the generalized steady-state Reynolds equation with slip boundary conditions to get the slider attitude. Then, it solves the reduced Navier–Stokes equation to get the air flow velocity distribution in the HDI. The motion equations of particles are solved to obtain the particle trajectory in the HDI by using the fourth-order Runge–Kutta method. Air flow characteristics and particle behaviors are investigated to illustrate the relationship between the air flow and particle trajectory. The effect of the particle release height is also studied. The simulation results show that particle trajectories basically overlap air flow streamlines in the horizontal plane. The particle moves a longer horizontal distance at a lower particle release height. The difference between the horizontal velocity of the particle and the air flow indicates that the Saffman force points to the disk in the transition region close to the leading edges of leading pads. Moreover, the peak values of the air flow vertical velocity in the previously mention location increase with the reduction of the particle release height. And the air flow vertical velocity along the particle trajectory is almost two times larger than that of the particle at the leading edges of leading pads. The results also show that the drag force of the air flow mainly drives particles up toward the air bearing surface at the leading edges of leading pads, but not the Saffman force. [ABSTRACT FROM PUBLISHER]

The presence of particles, which can intrude into the air bearing, is one of the most common factors in the failure of hard disk drives (HDDs). Previous studies have investigated particles trajectories with the assumption of ideal trapping or reflecting boundary conditions in air-filled drives. However, only the colliding particle with insufficient energy to escape the potential well will be trapped by the surface. In this paper, considering the particle-surface energy during the collision, the trapping criterion of the incident normal critical velocity ( V\text {ni}^{\mathrm {\ast }}) for Al2O3 particles is developed as the boundary conditions for different colliding surfaces inside a 2.5 in drive. Then, trapping status for Al2O3 particles and particles trajectories inside the drive are simulated by using the commercial computational fluid dynamics solver FLUENT with user-defined functions. The results reveal that the particles will travel longer distances until trapped by HDD components when considering the trapping criterion. In addition, smaller particles will more likely degrade the head–disk interface reliability, since they easily stick on the disk surface. [ABSTRACT FROM PUBLISHER]

The reliability and stability of hard disk drives (HDDs) are especially important as the areal recording density is rapidly increasing and target to 10 Tb/in2 in the future. The vibrations of the head gimbals assembly (HGA) are inevitable by internal fluid flow and external shock impulses. In this paper, a 3-D finite-element model of an HDD is developed. The internal flow-induced HGA vibrations are investigated by a fluid–structure interaction approach. The external shock-induced vibrations of HGA are also analyzed. The investigated filling gases in the HDD include air and helium. [ABSTRACT FROM AUTHOR]

Nowadays, hard disk drive filling with helium has emerged to achieve highly stable magnetic recording. The bearing force in helium is different from that in air. This paper uses the 3-D direct simulation Monte Carlo method to investigate the bearing force over bit-patterned media in the filling gases of air and helium under different conditions, including groove depth, ambient temperature, slider surface temperature, rotation speed of the disk, and different velocity losses during the collision process between the gas molecules and the slider. [ABSTRACT FROM AUTHOR]

This paper presents a numerical method to simulate the particle trajectory in the head–disk interface (HDI). The simulator solves the reduced Navier–Stokes equation with the second-slip boundary conditions to get the air velocity distribution, then solves the motion equations of particles and obtains the trajectories of the particles in the HDI using the binary Lagrange interpolation and the fourth-order Runge–Kutta method. The calculated trajectories of particles follow well with the air streamlines in the recessed regions. The particle density, diameter, and initial entering velocity have different effects on particle movement. Furthermore, particle velocity behaviors in the recessed regions are investigated for the first time. The particle is accelerated or decelerated by the action of the drag force and becomes close to the velocity of local air flow. Such effects are more obvious for small particles than large particles. The particle velocity becomes very small when it is close to the leading edge of the trailing pad. The numerical results also show that the particle goes up when it crosses the transition regions, and the particle moves upward more sharply with higher initial entrance height due to the larger vertical velocity of the local air flow. [ABSTRACT FROM AUTHOR]

In this paper, a heater-slit design was investigated to reduce the crosstalk effects of thermal track positioning control (TPC) heating on the thermal flying height control, using a coupling thermal-structural simulation and air-bearing simulation. The results show that the slit design helps to achieve a large head displacement along crosstrack direction and flying height reduction at head elements, due to the reduction of the mechanical constraints on the thermally induced expansion of the slider body. The undesirable flying height reduction at side edge of trailing pad of the slider can be improved by further optimization of slit design. Thus, the heater-slit design overcomes the limitation on the air-bearing surface design for TPC slider. [ABSTRACT FROM AUTHOR]

In the pursuit of high areal recording density towards 10 Tb/in^2, it is necessary to improve the positioning accuracy of the magnetic head in the hard disk drive head-positioning control system. Ultrasonic motors are novel electric motors well used in positioning control. Contact stresses can exist in the friction material and rotor. Obtaining the details of the stress distribution due to the inelastic deformation is important. A contact model of traveling wave ultrasonic motor (TWUSM) is proposed. A 2-D finite element model between stator and friction material is then developed. The evolution of deformation in friction material and rotor due to the mechanical surface loading is presented. [ABSTRACT FROM PUBLISHER]