Yonghyun Lee

Improvement of loading/unloading performance using control input position and considering disk vibration characteristics

Loading/unloading (L/UL) dynamic characteristics are affected by various operating parameters, such as L/UL speed, disk speed, disk vibration, and so on. The effects of these parameters on L/UL performance are investigated experimentally using an acoustic emission (AE) sensor, an in-plane laser Doppler vibrometer (LDV), and a vertical LDV. The experimental data shows that during the loading of the slider, the contact probability is lower for low L/UL speeds. The frequencies of slider-disk contact are lower for low disk rpm during the loading process, whereas in the unloading process the contact probability is lower for high disk rpm. The effects of disk vibration on the L/UL process are also studied, and we have found that the relative gap and slider-disk velocity between the disk and ramp affect the contact events in the L/UL process. During 1000 unloading cycles, most noncontact events occurred near the region of the maximum ramp gap during the loading process. During unloading, most of the contacts between the slider and disk occurred at the minimum relative speed. Slider-disk contact rarely occurred at the maximum relative unloading speed. The noncontact region tends to expand with higher disk speeds during the unloading process. This paper proposes a method to control the unloading input position to improve L/UL performance. By controlling the unloading instant based on the disk vibration characteristics, we can significantly reduce the number of slider-disk contacts.

Numerical Quasi-Static Analysis of Ultralow Flying Slider During Track-Seeking Motion Over Discrete Track Media

It is important to accurately estimate the flying height (FH) of the ultralow flying slider in hard disk drive (HDD). Especially, during the track-seeking motion, the FH can change by the motion from inner diameter (ID) to outer diameter (OD) and vice versa. The FH variation induced by the track-seeking motion happens over discrete track media (DTM). Therefore, the FH variation during track-seeking is an important issue and it certainly should be considered for DTM. In this research, we performed the track-seeking simulation using quasi-static approximation to reduce the computation time. The effects on groove depth, width, and pitch with the effective skew angle taken into account were investigated with the simulation. As a result, we calculated the absolute change in FH as a function of the effective skew angle and groove depth. Finally, we proposed that the model that considers the effective skew angle over DTM should be adopted in the track-seeking motion-studies.

Advanced Unloading Analysis Considering Lateral Velocity and Disk RPM Drop in Emergency Parking

A conventional unloading analysis was carried out in no consideration for fast lateral velocity and disk rpm drop during the emergency parking. However, current hard disk drive (HDD) systems need an improved performance in the portable aspect. Therefore, much faster emergency parking is absolutely necessary to protect the system from sudden power-off or an external shock. In case of fast emergency parking, the fast lateral velocity causes an effective skew, and then there is a flying height (FH) loss which does not occur in a normal unload. Also, the FH loss induced by a disk rpm drop occurs at an unloading point in case that a portable small form factor HDD like 1.8 in is suddenly parking from inner diameter to outer diameter. This means that the unloading performance considering the effective skew becomes lower than one of the conventional unloading analysis. In this paper, we propose the advanced unloading analysis that can be applied to the fast emergency parking velocity. To do so, we investigate the FH loss by the fast lateral velocity and the disk rpm drop, and introduce the result of the advanced unloading analysis.

Effect of Air Bearing Surface on Shock Resistance of Optical Head for Solid Immersion Lens Based Near Field Recording System

A solid immersion lens (SIL)-based near field recording (NFR) device is regarded as the next generation optical storage device that can achieve an areal density over 100 GB/in2 . However, the NFR system is very weak for the external shock due to the extremely small gap between a SIL and a disc. Many researches using a gap servo control were carried out, but the results were too insufficient to satisfy needs of the industry. To solve this problem, we propose a new method using air bearing surface (ABS) to avoid a collision between the SIL and the disc occurred by the external shock. In this paer, we check a feasibility of a ABS on shock resistance in NFR system due to many reasons such as a large mass of moving part, a protrusion of the SIL and a low stiffness of wire. We also design an ABS to avoid effectively the collision between the SIL and the disc and to improve shock resistance of SIL based NFR system. Finally, we investigate the effect of the ABS on shock resistance of optical head for SIL based NFR system.

Improving Hard Disk Drive Unloading Performance With a Disk Bump

Most hard disk drives use ramp load/unload (L/UL) technology because of its many advantages. However, L/UL does have some unresolved drawbacks, such as slider-disk contact during fast unloading. The main objective of our research is to examine the use of a bump on the outer edge of the disk to prevent contact with the disk by the rebounding slider and to improve ramp unloading performance. In particular, this paper focuses on experimental verification of the design of the disk bump that resulted from our previous research. We formed the disk bump on the disk surface using mechanical pressing with tungsten tips and tested the effect of the bump in unloading experiments. An investigation of the acoustic emission burst signal and its power spectrum confirmed that the optimal disk bump prevented slider-disk contact. This improves the ramp unloading performance.

Ramp Tolerance Analysis Considering Geometric Errors

Load/Unload (L/UL) system has many components such as ramp, limiter, lift-tab and so on. In this paper, we focus on ramp and ramp tolerance analysis considering geometric errors such as assembling and manufacturing errors because the large ramp geometric errors bring about unloading fail that means unloading process does not occur. Specially, we numerically investigated the effects of ramp tolerance because a ramp has both upper and lower sides. From the analytic method, unloading point, air-bearing breaking point, maximum ramp translation length (TL) and maximum tilt angle (TA) were investigated. Also, we proposed the maximum ramp tolerances such as translation and rotation.

Design and Analysis of Disk Bump to Improve the Unloading Performance in Hard Disk Drives

Most hard disk drives that apply the ramp load/unload technology unload the heads at the outer edge of the disk while the disk is rotating. During the unloading process, slider-disk contacts may occur by lift-off force and rebound of the slider. The main issue of this paper is to prevent the slider-disk contact by rebound, and we apply a disk bump to the unloading process. To do so, first, the ranges of bump dimension are determined. Second, the stability of each bump is checked by dynamic simulation. Finally, unload analyses are performed for stable bump designs. As a result of these analyses, we investigate proper bump design and position for the unloading process. Through this research, we propose the optimal bump design to improve the unloading performance. We can also identify to remove rebound contact by applying a bump on disk to the unloading process.

Analysis of Thermal Flying-Height Control System About Humid Air Condition in Hard Disk Drive

This research investigates to analyze the effect of humid air on TFC system. Required parameters of humid air and flying attitude of slider are calculated. Condensation of air bearing at over the saturation vapor pressure is considered. Heat transfer coefficient for humid air condition is calculated. TFC simulation about humid air is conducted.Copyright

Opto-Mechatronics Issues in Solid Immersion Lens Based Near-Field Recording

Current developments in the solid immersion lens (SIL) based near-field recording technology are briefly introduced and research results including design, analysis, and experiments in CISD are reported. Also, the concept and performance of the novel optics using SIL is described throughout this paper. To increase the center thickness tolerance of SIL and decrease chromatic aberration, we add the replicated lens on SIL and the diffractive optical element (DOE). As a result of this design, it is confirmed that the SIL thickness tolerance of the replicated SIL optics is from -15 up to 7 mum at 0.035lambda rms, and wavefront aberration is less than 0.035lambda rms through variation of wavelength from 401 up to 412 nm

Analysis of Pitch Static Attitude in Thermally Assisted Magnetic Recording Suspension

This paper presents the analysis of pitch static attitude(PSA) in thermally assisted magnetic recording(TAMR) suspension. The TAMR suspension using an optical fiber has high stiffness such as vertical, pitch and roll. Therefore, P-torque is greatly increased by the optical fiber. Also, flying height(FH) of the slider with TAMR suspension can be largely changed by PSA. In this paper, we focus on the FH by PSA of TAMR suspension. The FH is investigated using various PSA and proper PSA is proposed.