• 한국소음진동공학회논문집
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• 제15권10호
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• pp.1148-1159
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• 2005

In this paper, the various uncertainties generated in an optical disk drive (ODD) and the robust servo designs considering the uncertainties are studied. First, the brief introduction an ODD and the servo error tolerance of it are discussed. Then, the classifications of uncertainty and the concept of relative stability are introduced. Considering the uncertainty of an ODD, two robust control approaches are applied: (i) mixed sensitivity approach in H$\infty$ control theory for unstructured uncertainty, (ii) QFT for structured uncertainty Finally, the designed controllers are realized by DSP, and these controllers are applied to a commercial DVD-ROM drive. From these experiments, we prove that the designed robust controllers have more good disturbance rejection performance and robustness when it is compared to the conventional lead-lag controller.

• 대한전기학회논문지:시스템및제어부문D
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• 제54권1호
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• pp.1-10
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• 2005

This paper proposes a new and simple input prediction method for robust servo system. A robust tracking control system for optical disk drives was proposed recently based on both Coprime Factorization (CF) and Zero Phase Error Tracking (ZPET) control. The CF control system can be designed simply and systematically. Moreover, this system has not only stability but also robustness to parameter uncertainties and disturbance rejection capability. Since optical disk tracking servo system can detect only tracking error, it was proposed that the reference input signal for ZPET could be estimated from tracking errors. In this paper, we propose a new control structure for the ZPET controller. It requires less memory than the previously proposed method for the reference signal generation. Numerical simulation results show that the proposed method is effective.

• 대한기계학회논문집B
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• 제26권8호
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• pp.1069-1076
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• 2002

Contamination particles in a hard disk drive can cause serious problems including slider crash and thermal asperities. A recirculation filter is typically installed in the hard disk drive to remove the particles. Measurements and theoretical predictions of particle concentration decay with the filter are carried out for a commercially available HDD. Especially, the effect of disk rotational speed on the particle capture efficiency is investigated. Results show that filter efficiency is higher for higher disk rotational speed.

• 한국정밀공학회지
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• 제17권2호
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• pp.35-42
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• 2000

In recent years the recording density of hard disks has increased significantly largely due to the decreasing flying height. As a result of decreased flying height, the reliability issue become more critical. In this work the relationship between hard disk surface damage and data loss was investigated by using an actual hard disk drive. The purpose of this research was to identify the key factor which leads to data loss. It was shown that data loss is directly related to the physical damage of the Co-magnetic layer and there was no data loss when only carbon protective coating was damaged by the diamond tip.

• Journal of Magnetics
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• 제15권3호
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• pp.143-147
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• 2010

Rotary-type voice coil motors are widely used as actuators in hard disk drives. The recent trend toward higher density and smaller form factors in data storage devices requires performance improvement of the voice coil motor. In this study, we introduce a Halbach magnet array to the voice coil motor in order to increase the force generation. The Halbach magnetic circuit outperforms the conventional magnetic circuit due to the confined magnetic flux. To investigate the performance of the Halbach magnetic circuit, we analyze air gap flux density with the various shapes and thickness of the magnets using 3-dimensional finite element analysis. Consequently the optimum shape of the Halbach magnetic circuit is proposed. Simulations and experimental results proved effectiveness of the proposed magnet array in the voice coil motor for a commercial hard disk drive.

• 대한기계학회논문집B
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• 제29권5호
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• pp.599-608
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• 2005

Controlling particle contamination is important to increase storage capacity as the flying height of a slider in a hard disk drive decreases. Since precise detection and analysis of particles are primary steps of particle control in a HDD, many researchers have used sampling methods. In this paper, we newly designed a particle sampler and conducted performance evaluation of the sampler. Also, we conducted particle sampling from the HDD using the particle sampler and analysis of sampled particles by SEM and AES. Experimental results show that the particles generated by the slide-disk interaction mainly came from the disk surface.

• 한국정밀공학회지
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• 제17권5호
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• pp.154-159
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• 2000

A multi-beam optical disk drive is presented as a method for improving the effective data transfer rate by increasing the beam spot number formed on an optical disk. The beam rotating actuator is necessary for putting multi-beam on more than one track. The beam rotating actuator is made up of piezoelectric material, high stiffness wire hinge and dove prism. The actuator has good frequency response above 1KHz and suitable operational range. The dynamic equation for the actuator is derived.

• Journal of Mechanical Science and Technology
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• 제14권7호
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• pp.744-751
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• 2000

To achieve lower flying height for high areal recording density, the laser zone texturing of the disk needs to be designed to reduce glide height. One problem of the laser bump design is that the regular laser bump pattern often produces glide resonance phenomenon, which leads to failure of the glide height test. However, it was found in this study that glide resonance is an intrinsic problem of the glide head used and resonance phenomenon depends on the type of the head slider, that is, the natural frequency of the slider body. Therefore, higher glide height or glide failure caused by glide resonance does not lead to head/media interface problem in the real drive operating conditions in which the data head is used. Pseudo-random bump pattern greatly reduces the glide resonance. Smaller bump pitch will also help to reduce the glide resonance. However, as bump spacing becomes smaller, glide height will be increased due to increased air pressure developed around the bumps. Lowering bump height is the most effect way to reduce glide avalanche.

• 대한기계학회논문집B
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• 제29권7호
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• pp.795-804
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• 2005

As the flying height of a slider in a hard disk drive decreases, the slider and disk are more likely to come in contact and generate contamination particles. Since particle contamination can cause serious problems including thermal asperity, it must be prevented to increase storage capacity. When particles are generated in a HDD, particles can be charged and have a few number of elementary charges. In this paper, the size distribution of particles and electrical current due to particle according to the disk rotational speed were measured. Also, the average number of elementary charges was calculated from experimental data. SEM images of particles were obtained by using a particle sampler designed in our laboratory.

• 정보저장시스템학회논문집
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• 제1권1호
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• pp.84-92
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• 2005

This work presents the feasibility of shunt damping far vibration suppression of the rotating HDD disk-spindle system using piezoelectric bimorph. A target vibration mode which significantly restricts the recording density increment of the drive is determined through modal analysis and a piezoelectric bimorph is designed to suppress unwanted vibration. After deriving the two-dimensional generalized electromechanical coupling coefficient of the shunted drive, the shunt damping of the system is predicted by simulating the displacement transmissibility using the coefficient. In addition, optimal design process using sensitivity analysis is undertaken in order to improve the shunt damping of the system. The effectiveness of the proposed methodology is verified through experimental implementation by observing the vibration characteristics of the rotating disk-spindle system in frequency domain.