Naozumi Tsuda

An analysis of disk flutter in hard disk drives in an aerodynamic simulation

We performed a numerical simulation using a three-disk model with shrouds to evaluate the effect of air flows in the axial direction in a hard disk drive. And to clarify the relationships between disk surface pressure and disk flutter that have been a matter of conjecture, we performed a response analysis using the unsteady hydrodynamic force that was obtained as the excitation force by our numerical simulation.

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.

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.

Two-axis pointing mechanism for Earth observation system using heterodyne interferometry positioning sensor

The 2-Axis pointing mechanism which we developed is designed for earth observation system. This pointing mechanism is expected to work on the geostationary orbit with high resolution compare with former one. To achieve high resolution, we adopted optical heterodyne technique to mirror angle detecting sensor instead of rotary encoder. The angle of the mirror is calculated from the distance between mirror base and a certain point of reverse side of the mirror. We can get the resolution of 0.029 (mu) rad. For mirror driving mechanism, we adopted a crank mechanism because a pointing mechanism working on the geostationary orbit is not necessary to rotate whole angle. We can get about 1:10 reduction ratio with a crank mechanism in addition to the reduction gear attached to the motor shaft. We have made experimental model and validated its performance.

HDD SLIDER AIR BEARING DESIGN OPTIMIZATION USING A SURROGATE MODEL

This report addresses a new optimization method in which the DIRECT algorithm is used in conjunction with a surrogate model. The DIRECT algorithm itself can find the global optimum with a high convergence rate. However the convergence rate can be much improved by coupling DIRECT with a surrogate model. The surrogate model known as the Kriging model is used in this research. It is determined by using sampling points generated by the DIRECT algorithm. This model expresses the shape of a hyper surface approximation of the cost function over the entire search space. Finding the optimum point on this hyper surface is very fast because it is not necessary to solve the time consuming air bearing equations. By using this optimum candidate as one of the DIRECT sampling points, we can eliminate many cost function evaluations. To illustrate the power of this approach we first present some simple optimization examples using known difficult functions. Then we determine the optimum design of a slider with 5nm flying height (FH) starting with a design that has a 7nm FH.Copyright

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.