Tae-Sik Kang

Optimal Design of HDD Air-Lubricated Slider Bearings for Improving Dynamic Characteristics and Operating Performance

Flying attitudes of the slider, which are flying height, pitch, and roll, are affected by air-flow velocity, skew angle, and manufacturing tolerances. In the traditional design process of air-bearing surfaces, we have considered only the steady state flying attitude over the recording band. To reduce the flying height variation during track seek as well as in steady state, we design a new shape for air-bearing surfaces. An optimization technique is used to improve the dynamic characteristics and operating performance of the new air-bearing surface shapes. The quasistatic approach is used in the numerical simulation of the track seek operation because the skew angle effect dominates the inertial effect even at high seek velocities. The perturbation method is applied to the lubrication equation to obtain the air-bearing stiffness. We employ the method of modified feasible directions and use the weighting method to solve the multicriteria optimization problem. The optimally designed sliders show enhanced flying and dynamic characteristics. The steady state flying heights are closer to the target values and the flying height variations during track seek operation are smaller than those for the original ones. The pitch and roll angles are kept within suitable ranges over the recording band during track seek operation as well as in steady state. The air-bearing stiffnesses of the optimally designed sliders are larger than those of the original ones.

An Optimization Method for Design of Subambient Pressure Shaped Rail Sliders

This study proposes a design methodology for determining configurations of subamient pressure shaped rail sliders by using a nonlinear programming technique in order to meet the desired flying characteristics over the entire recording band. The desired flying characteristics considered in this study are to minimize the variation in flying height from a target value, to keep the pitch angle within a suitable range, and to ensure that the outside rail flies lower than the inside rail even with the roll distribution due to manufacturing process. The design variables selected are recess depth, geometry of the air bearing surface, and pivot location in the transverse direction of the slider. The method of feasible directions in Automated Design Synthesis (ADS) is utilized to automatically find the optimum design variables which simultaneously meet all the desired flying characteristics. To validate the suggested design methodology, a computer program is developed and applied to a 30 percent/15 nm twin rail slider and a 30 percent/15 nm tri-rail slider. Simulation results for both sliders demonstrated the effectiveness of the proposed design methodology by showing that the flying characteristics of the optimally designed sliders are enhanced in comparison with those of the initial ones.

An optimum design of the sub-ambient pressure shaped rail sliders on flying characteristics considering the high altitude condition

We present optimum results of the two sub-ambient pressure shaped rail sliders. The goal of optimization is to meet the desired flying characteristics over the entire data zone at sea level as well as at the 5000 ft. Altitude condition. The design variables are the geometry of the air bearing slider (ABS), the recess depth, and the location of the pivot. The method of feasible direction is utilized to find the optimum designs. The optimally designed sliders show the enhanced flying characteristics along with the less deviation at the high altitude condition.

Design and Performance Test of Comb-Shaped Clamp/Spacer for Improvement of Recirculation Filter Efficacy in a Hard Disk Drive

With the recent increase of the rotational speed of hard disk drives, nanoparticle contamination can cause serious problems including thermal asperity. We designed a comb-shaped clamp and spacer to improve the efficacy of the recirculation filter in the operation of the hard disk drive (HDD). We calculated flow characteristics by a commercial computational fluid dynamics (CFD) code for six cases of the comb-shaped clamp and spacer. The calculation results showed that the outward velocity was the highest when the comb-shape angle was 45deg. We measured temporal variations of particle concentration during the operation of the HDD by experiments. Considering the decay rate and the percent clean-up of particle concentration, we found the case of 45deg to be the best design.

Comb-shape Patterned Clamp/Spacer for Improvement of Recirculation Filter Efficiency in Hard Disk Drive

Increased disk rotational speed of hard disk drive and contamination by nanoparticles can cause serious problems including thermal asperity (TA). In this study, the filtration efficiency of recirculation filter system in the hard disk drive was investigated with various particle contamination locations and disk rotational speeds. In result, the filtration efficiency was clearly affected by the particle-generated location. The filter efficiency of nanoparticles generated at the center side of disk surface was lower than that at the edge side of the disk. For improving the filter efficiency, we added a comb-shape pattern to hard disk clamp and spacer. And improved filter efficiency was observed with various comb angles and disk rotational speeds

Ramp Load/Unload Velocity Control of VCM Using BEMF in HDD

Since most of small form-factor drives have a load/unload mechanism and the flying height of the head is getting lower as the capacity of disk drives increases, the load/unload velocity becomes one of the important factors to ensure the reliability of the load/unload mechanism. To control the load/unload velocity accurately, velocity sensing is essential. In this paper, we introduce a very practical method that acquires the load/unload velocity from the back electromotive force (BEMF) of a voice coil motor (VCM) and propose a calibration method for measuring the BEMF from a given circuit. Moreover, the effect of calibration error and temperature variation on the measurement of BEMF is shown by simulation. Then, this present method is applied to the load/unload velocity controller and is verified from the experimental result.

An Optimization of Air-Lubricated Slider Bearings Using the Reduced Basis Concept

In this study, optimum designs of the air-bearing surface (ABS) are achieved using the reduced basis concept which can effectively reduce the number of design variables without cutting down on the design space. Even though the optimization method is easier and more applicable to handle than the trial-and-error method, its efficiency is largely dependent on the number of the design variables. Hence, the reduced basis concept is applied, by which the desired design can be defined as a linear combination of basis designs. The simulation results show the effectiveness of the proposed approach by obtaining the optimum solutions of the sliders whose target flying heights are 25, 20, and 15nm.