Shijing Wu

Simulation of HGA Vibration Characteristics Inside the Helium-Filled Hard Disk Drive

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.

Simulation of cross-talk between thermal track positioning control and thermal flying height controla)

In this study, a coupling analysis of thermal-structural simulation and air-bearing simulation has been performed to investigate the cross-talk effects between thermal track positioning control (TPC) and thermal flying height control (TFC) on the static flying attitude of a TPC-TFC slider. Simulation results show that the TPC heating induced head protrusion towards disk is comparable to the head actuation stroke along the cross-track direction. By optimizing the distance of TPC heater to air bearing surface, and the distance of TPC heater to the slider center line, it can obtain a large TPC actuation stroke and a small head protrusion towards disk. Moreover, it is found that the TPC heating will cause large protrusion of the side edge of trailing pad and change the flying characteristics significantly. A trade-off performance between cross-talk effects and TPC actuation stroke along cross-track direction is needed.

Simulations of Particle Trajectories in Hard Disk Drives Considering the Trapping Criterion

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 (Vni*) 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.

Simulation of Air Flow and Particle Trajectories in the Head–Disk Interface

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.

Modeling of formation and breaking of lubricant bridge in the head–disk interface by molecular dynamic simulation

Abstract The technology of heat-assisted magnetic recording (HAMR) has improved the storage density of hard disc drives. The PFPE molecules of lubricant layer adhered on the disc can transfer from the lubricant layer and form the lubricant bridge which can deteriorate the stability of read/write process. In this paper, the formation and breaking of lubricant bridge at the head–disc interface (HDI) affects HAMR stability and deserves to be investigated. Using molecular dynamic simulation, a full-atom model was built to evaluate the behaviour of the lubricant bridge. Moreover, the effects of lubricant temperature, heating-up time, disc rotation speed and bearing pressure on the HDI were studied. It has been found that the amount of transferring atoms sharply increased when the lubricant temperature was above 700 K. The loss rate of lubricant layer decreased gradually during the heating process and it took about 2.2 ns for the remaining lubricant to reach stability. Furthermore, transferring PFPE molecules can form the lubricant bridge. A shorter heating-up time makes the lubricant bridge thicker and more robust. And the duration of lubricant bridge is notably affected by heating-up time, rotation speed and bearing pressure. A shorter heating-up time leads to a longer duration of lubricant bridge, whereas a higher rotation speed and bearing pressure reduces the duration of lubricant bridge.

Simulation of aerodynamic noise and vibration noise in hard disk drives

Due to the difficulty to separate the aerodynamic noise and vibration noise in hard disk drives (HDDs), it is hard to identify the contribution of each noise to the total noise by the experimental measurement. In this paper, both the aerodynamic noise and the vibration noise inside drives are studied. Two operation states are considered, including that the arm is at a fixed location and the arm is swinging over the disk. The investigated gases include the air and helium.

Simulation of temperature distribution around media heat spot in heat assisted magnetic recording

The super-fast growth in recording areal density and the correlative decrease of the exterior dimension has been greatly beneficial to the widespread use of hard disk drives (HDDs). In the pursuit of high areal recording density, the heat assisted magnetic recording (HAMR) has been promised to be a new and feasible technology for the next generation of HDDs. In this paper, the temperature distribution around media heat spot in HAMR drive is studied. Firstly, a three-dimensional HAMR drive finite element model consisting of the disk, voice coil motor (VCM), suspension, slider, and filter is built. Then, the flow characteristics and temperature distributions in HAMR drives filled with air and helium are investigated respectively. Finally, the cooling effects of the high speed disk rotation and the heat convection in head-disk interface (HDI) are analyzed and compared.

TPC Heater-Slit Design to Reduce Crosstalk Effects on Flying Height Control

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.