Hiroyuki Kubotera

Unsteady analysis and experimental verification of the aerodynamic vibration mechanism of HDD arms

The authors investigate the flow structure in 3.5-in hard disk drives with a rotation speed of 10033 rpm, especially the unsteady flow around actuator arms with and without a weight-saving hole, and clarify the unsteady flow in detail. In the method of approach utilized in this investigation, they used: 1) a direct numerical simulation of the Navier-Stokes equations to analyze the flow field; 2) a laser Doppler velocimeter to measure the velocity field; and 3) a laser Doppler vibrometer to monitor unsteady displacement of the actuator arm. The authors find a three-dimensional spiral vortex in the wake region of the arm and the flow spilled from the weight-saving hole. These flows can be considered to be an excitation source for the actuator arm. The power spectrum of the arm torque generated by calculated wind disturbance agrees with that of measured wind disturbance. This verifies the existence of the predicted vortices and the flow spilled from the weight-saving hole.

Effect of various physical factors on thin lubricant film migration on the flying head slider at the head-disk interface of hard disk drives

The mechanism of lubricant migration on a flying slider’s air bearing surface in magnetic hard disk drives is examined in this paper. As the head-disk spacing diminishes, the lubricant contamination from the disk and its migration behavior on the flying head slider becomes an increasing concern. The spatiotemporal behavior of the thin lubricant film on a slider surface is complicated, and it is affected by many physical factors. We investigate the contributions and functionalities of the potentially related physical factors and parameters on the lubricant film dynamics by numerical simulation. The analysis results show that the air bearing shear stress is the primary driving force in the lubricant migration, while the air bearing pressure makes only a minor contribution. The relative strength and direction of the Couette and Poiseuille flow components of the air bearing shear stress govern the lubricant migration direction and the points of lubricant stagnation. The lubricant surface free energy plays an ...

Lubricant Migration Simulations on the Flying Head Slider Air-Bearing Surface in a Hard Disk Drive

In this paper, we numerically study the lubricant migration on a flying slider air-bearing surface in a hard disk drive. The lubricant dynamics is based on a continuum thin film lubrication theory with inter-molecular forces and a precursor film model. It includes air-bearing pressure, air-bearing shear stress, the Laplace pressure, the disjoining pressure, and the shear stress caused by the surface free energy gradient. Using this model we investigate the lubricant migration behavior on a modern negative pressure type slider surface. We also reveal the correlation between the lubricant migration behavior and the air-bearing shear stress. We further perform the lubricant migration analysis for various different slider designs, radii, and skew angles.

Aerodynamic vibration mechanism of HDD arms predicted by unsteady numerical simulations

With increases in recording density and higher rotation speeds, the aerodynamic aspect of hard disk drives (HDDs) is now quite significant. We studied the internal airflow of HDDs using a direct numerical simulation. We simulated two cases: the first had an arm with no weight-saving hole (no-hole case), while the second had an arm with a weight-saving hole (hole case). We observed periodic vortices (Karman type) for which the frequency was about 4 kHz in the downstream of the arm in both cases. The scale of the vortex in the hole case was larger than that in the no-hole case. In the hole case, the spectrum of the arm torque had sharp peaks that would directly affect the head positioning accuracy. Moreover, we found that there was no remarkable peak in the no-hole case.

Effects of Track-Seeking Motion on the Flying Attitudes of Ultralow Flying Sliders

The flying height (FH) change during a track-seeking motion becomes of significant concern for ultralow flying sliders. The presence of nanoscale adhesion forces, such as intermolecular and electrostatic forces, can adversely decrease the FH and even cause head-disk impact. A quasi-static approximation of track-seeking motion is proposed here, which if sufficiently accurate can substantially decrease the computation time over that required for a dynamic analysis. The track-seeking performances of four different air bearing surface (ABS) designs are numerically investigated by the quasi-static approximation, and the results are compared with those computed by the CML Dynamic Simulator. The former gives good agreements with the latter but with much less computation effort. The effects of various factors causing FH changes are presented and compared quantitatively. The effective skew angle is found to be the dominant factor, but the inertia effect is also not negligible. Two designs, called Scorpion III and IV, designed previously as active FH control sliders, are found to exhibit an enhancement in track-seeking performance, compared with two other conventional ABS designs

Dynamic Numerical Simulation of Lubricant Behavior at the Head Disk Interface

The lubricant contamination and migration on the flying head slider surface in hard disk drives are studied in this paper. The lubricant dynamics is modeled based on the continuum thin film lubrication theory with inter-molecular forces. We investigate the detailed lubricant behavior on a modern negative-pressure type flying slider. We find distinct lubricant migration speeds depending on the etch depth of the slider surface and the accumulation of lubricant at specific regions. We also find that lubricant behavior largely correlates with the magnitude and direction of the air bearing shear stress.

Study of aerodynamic vibration mechanism of HDD arms with unsteady analysis and its experimental verification

In this paper, we investigate aerodynamic phenomena occurring around the actuator arm of a hard disk drive using direct numerical simulation (DNS) and an experiment using laser Doppler vibrometer. Through numerical simulation we found a three-dimensional periodic spiral vortex in wake region of the actuator arm and that the weight-saving hole of an arm excites the vortex in contrast to an arm that has no hole. By experiment, we confirmed the presence of some peaks in the spectrum of arm torque.