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Pohang, South Korea

Lee Y.,Hanyang University | Kim S.H.,Hanyang University | Lee S.-H.,Hanyang University | Lee C.W.,Seagate Korea Design Center | Chung C.C.,Hanyang University
IFAC Proceedings Volumes (IFAC-PapersOnline) | Year: 2014

In this paper, we propose a new control scheme, position and velocity profile tracking control for new generation servo track writing (STW). While conventional servo track writers need controllers that perform fast positioning control with fast track seek and regulation, spiral servo track writers require accurate position and velocity profile tracking control for high quality servo patterns on the media disk. Since STW timing eventually renders geometrically accurate servo patterns, in constant velocity region both position and and velocity error signals should be regulated within small bounds. It is known that regulation via integral sliding mode controller (SMC) provides a good tracking performance, but using a high switching gain is not appropriate for a system having resonance modes. In this paper, thus we apply sliding mode control with disturbance observer to STW. To verify utility of the proposed position/velocity profile track control, we conducted some experiments using a state-of-the-art STW system. Comparative study with the conventional control method was made. The performance of proposed method was experimentally validated. © IFAC. Source

Park K.-S.,Yonsei University | Lim S.,Yonsei University | Park Y.-P.,Yonsei University | Chang Y.-B.,Seagate Korea Design Center | Park N.-C.,Yonsei University
Microsystem Technologies | Year: 2012

Hard disk drives (HDDs) in laptop personal computers (PCs) are subject to impact-induced failure, as well as to operational vibrations. Elastic mounts with cushioning materials are often used to minimize the likelihood of failure in such cases. In this paper, we analyze the dynamic characteristics and shock response of the vibration isolation systems supporting HDDs. Anti-vibration performance is investigated via position error signal and acceleration transmissibility. Shock response is obtained from a lumped parameter model, based on the nonlinearity of the rubber mounts. Based on the results, we propose guidelines for shock and vibration isolation systems, including a dual rubber mount design. © Springer-Verlag 2012. Source

Park K.-S.,Yonsei University | Lim G.,Yonsei University | Park Y.-P.,Yonsei University | Hong E.-J.,Seagate Korea Design Center | Park N.-C.,Yonsei University
Microsystem Technologies | Year: 2012

Currently, almost all hard disk drives (HDDs) have adopted a loading/unloading mechanism that increases their recording capacity and improves their reliability. However, these mechanisms still create a few scratches or defects in the loading/unloading zone. Slipping at the dimple-flexure interface was recently reported as one of the causes. In this research, we first analyzed the relative behavior of dimple-flexure based on fretting wear marks. We determined that the dimple-flexure behavior included both slipping and rotating motion simultaneously. We then verified the distinct slipping and rolling phenomenon at the moment of ramp contact using finite-element method (FEM) analysis. An experimental setup was constructed, and an unloading experiment was carried out to obtain the ramp contact characteristics corresponding to various unloading velocities. Based on the verified FEM, the characteristics of dimple-flexure relative behavior were investigated for various suspension design parameters, ramp contact characteristics, and unloading velocities. A higher ramp contact force and shorter contact duration resulted in larger slip displacements and roll angles between the dimple and the flexure. Finally, we analyzed the unloading performance of an HDD for various design parameters using quasi-static approximation while considering the relative behavior between the dimple and flexure. The quasi-static analysis indicated a change of approximately 15 % in the flying height at an unloading velocity of 40 in. per second when the relative motion between the dimple and flexure was considered during the unloading process. Even, slider-disk contact occurred at an unloading velocity of 50 ISP. © Springer-Verlag 2012. Source

Lim G.,Yonsei University | Park K.-S.,Gachon University | Park N.-C.,Yonsei University | Park Y.-P.,Yonsei University | And 3 more authors.
Microsystem Technologies | Year: 2016

Recently, the number of disks in hard disk drives has increased, and the gap between the slider and disk has decreased. These changes make the contact between the ramp and disk easily. External shock and ramp–disk contact can cause change in disk curvature. Such a change in disk curvature affects the air bearing pressure between the slider and disk. However, disk curvature has not been considered in the previous research. Thus, in this study, we investigated the influence of disk curvature on slider dynamics. Disk curvature was calculated from a transient shock analysis, and was then applied to slider dynamic analysis. As a result, disk curvature reduced the shock performance, by decreasing the minimum flying height and increasing the pitch and roll angle of the slider. © 2015, Springer-Verlag Berlin Heidelberg. Source

Lee Y.,Seagate Korea Design Center | Hong E.-J.,Seagate Korea Design Center | Kim C.-S.,Seagate Korea Design Center
IEEE Transactions on Magnetics | Year: 2013

Ramp load/unload (L/UL) technology becomes core technology in mobile hard disk drive (HDD) because it enables higher areal density and stronger shock robustness. However, ramp L/UL has some instability because of the structural limit that a head should repeatedly move between a ramp and a disk. Among much instability, the slider-disk contact generated during L/UL process mainly affects the drive reliability. In particular, the slider-disk contact during the loading process has a critical effect on head-disk interface (HDI) failure due to difference of impact force by much higher height level despite of low frequency. Therefore, this paper mainly focused on the loading contact and instability. At first, we defined the loading contact, scratch and instability generated by the slider-disk contact. To do so, we verified the contact location considering the interaction of the air bearing surface (ABS) and the disk, and we analyzed the relations for the loading contact between the ABS and the slider motions. After definition for the loading contact and instability, we evaluated the effects of the head stack assembly (HSA) height, the ramp height and the disk height based on the ABS performance. The relations among the HSA, ramp, and disk height affected the main parameters related to the loading contact and instability such as the Z-height, the pitch/roll slider attitude, and the gramload. We focused on the effect of the mechanical parameters according to the loading contact and instability. Finally, we measured the height differences for passed and failed drive samples. We could find out how the height differences cause the loading contact and instability through the relation among mechanical parameters such as the height of the HSA, the ramp and the disk. Based on these results, this paper proposed that the mechanical parameters such as the height relations should also be considered in order to avoid the loading contact and instability and to improve the loading performance. © 1965-2012 IEEE. Source

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