• Tribology and Lubricants
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• v.15 no.4
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• pp.335-342
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• 1999

Corrosion of the disk has been an ongoing concern for the manufacturers of hard disk drives. With the advent of magnetoresistive (MR) head, very low levels of corrosion and contamination become more critical since the raised defects and corrosion products on the disk surface-anything that heats the MR sensor due to the contact-can distort the output signal of the head. This phenomenon is called as thermal asperity. In this paper, the effect of corrosion as a form of Co migration on the occurrence of thermal asperity in MR drives was investigated. The corrosion test at high temperature (60$^{\circ}C$) and high relative humidity (80%) was emphasized in this study and the testing results at ambient condition were compared. The corrosion on the disks was characterized as the amount of Co ion migration using an ion chromatography (IC) and a time-of-flight secondary ion mass spectroscopy (TOF-SIMS). It is proved that corrosion on the disk surface after storage testing is closely correlated to the amount of Co ions migration from the magnetic layer to disk surfaces and higher Co migration causes more thermal asperities in the drive. In order to reduce Co migration, several methods such as burnishing process and structure of the carbon overcoat were investigated. It is found that the hydrogenated carbon overcoat shows the least Co migration among different types of overcoat layer. However, the most effective way to reduce Co migration is the application of Cr layer between the overcoat and the magnetic alloy layer.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.06a
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• pp.53-60
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• 1999

As the flying height decreased, it is essential that hard disk drives perform reliable under various environmental conditions. In this paper the tribological characteristics of a head/disk interface are investigated under various temperature, relative humidity, altitude and outgas conditions. Specially, Contact-Start-Stop(CSS) tests were performed to assess the stiction, acoustic emission, slider take-off behavior, and track average amplitude(TAA). It is shown that the surface damage and head failure are accelerated by high temperature and humidity as well as low ambient pressure.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.286-289
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• 1996

Two servo control algorithms are suggested to reduce the tracking error of a computer hard disk drive. One is the repetitive control to reduce the repeatable tracking error which is not explicitly taken into account in the design of a conventional controller. This algorithm was successfully applied to a commercial disk using a fixed point DSP. The other is the multi-rate sampling control which generates the control output between each sampling times since the sampling time of hard disk drives is limited. These algorithms were shown effectively to reduce tracking errors.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1998.10a
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• pp.131-138
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• 1998

It is essential that hard disk drives perform reliable under various temperature, humidity, and ambient pressure conditions. In this paper the tribological characteristics of a head/disk interface are investigated under various environmental conditions. Specially, Contact-Start-Stop(CSS) tests were performed to assess the stiction and slider take-off behavior. It is shown that the surface damage is accelerated by high temperature and humidity as well as low ambient pressure.

• Journal of Mechanical Science and Technology
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• v.15 no.3
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• pp.281-290
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• 2001

Particle contamination has been an ongoing problem affecting the reliability of the magnetic hard disk drives. Especially the recent use of MR head requires much tighter control of particle contamination due to thermal asperity (TA) phenomenon. In this study, the effects of slider air bearing surface design of TA reduction capability were investigated by manufacturing two types of sliders. Numerical methods were used to simulate the motion of particles in the head/media interface. Experiments were conducted to verify the results predicted by the numerical simulation. Drives were built and exposed to particle contamination using a particle injection chamber, which turned out to be a very simple and reliable particle generation method over conventional aerosol technique. Then the number of TA generated in the drives was recorded and compared. Also the contacts between slider and particles were investigated by acoustic emission study. It was found that a new ABS design, which has aerodynamic U-shaped rail and central flow passage, was beneficial in reducing the particle contamination on the slider.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.438-444
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• 1997

Recently, optical disk drives are increasingly demanded to have higher speed as well as high information density, especially for applications like CD-ROM drives. To this end, improvement of their optical pick-up structure and control is recognized the very challenging issue. In this paper, the 2-D motion of the pick-up is first analytically modelled to identify the cause and effect of the troublesome cross coupling between auto-focusing and tracking directions. Subsequently, the overall system equations are derived to include the dynamics of the related components in the auto-focusing servo system. While its unmeasurable parameters being estimated by the least square error method, a simple but decent linear model can be obtained within its operating frequency range. To design the high speed and robust positional servo controller, the design specifications are detailed and H$\sub$.inf./ control method is employed based on the simple model. Using the pickup in a commercial 8 fold speed CD-ROM drive as an example, performance of the designed controller is verified by realtime experiments.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.12
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• pp.1347-1353
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• 2004

With respect to the researches of the optical flying head(OFH) , the head-gimbal assembly should be analyzed to guarantee the stable fabrication and the characteristics of shock resistance. The suitable design is proved through the Probabilistic analysis of the design parameters and material properties of the model. Probabilistic analysis is a technique that be used to assess the effect of uncertain input parameters and assumptions on your analysis model. Using a probabilistic analysis you can find out how much the results of a finite elements analysis are affected by uncertainties in the model. Another factor is analysis of the dynamic shock analysis. For the mobile application, one of the important requirements is durability under severe environmental condition, especially, resistance to mechanical shock. An important challenge in the disk recording is to improve disk drive robustness in shock environments. If the system comes in contact with outer shock disturbance. the system gets critical damage in head-gimbal assembly or disk. This paper describes probabilistic and dynamic shock analysis of head-gimbal assembly in micro MO drives using OFH slider.

• Journal of Institute of Control, Robotics and Systems
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• v.8 no.8
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• pp.682-690
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• 2002

This paper presents an output feedback controller design method for uncertain linear systems with sinusoidal disturbance of uncertain frequencies. The controller needs to compensate for the performance deterioration due to the uncertain frequencies of sinusoidal disturbance. To this end, we introduce a virtual system including the dynamics corresponding to the uncertain frequencies and design a controller which minimizes the output difference between the virtual system and the closed-loop system. In other words, the controller is designed so that the closed-loop system approximates the virtual system. The feedback controller is achieved by solving an LMI optimization problem involving a robust $H_{\infty}$ constraint. The advantages of the proposed design method are examined by comparing it with a design method that only minimizes the $H_{\infty}$ norm of the transfer function between the sinusoidal disturbance and the output. The proposed design method is applied to the track-following system of rewritable optical disk drives and is evaluated through an experiment.

• Journal of the Korean Institute of Intelligent Systems
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• v.15 no.2
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• pp.135-142
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• 2005

This paper presents an adaptive repetitive control scheme for optical disk drives to track a variable periodic reference signal. Periodic disturbances can be adequately attenuated using the concept of repetitive control, provided the period is known. Because optical disk drives support various speeds, they have the varying periodic disturbances. Based on repetitive control to change sampling frequency to follow the change of reference period, an adaptive repetitive control is proposed in order to deal with such disturbances. The proposed control consists of the repetitive controller and the frequency generator. The former uses a varying sampler operating at fixed multiple times of the disturbance frequency and the latter generates the changeable sampling frequency based on the disturbance frequency. The experimental results on the control of an optical disk drive demonstrate the effectiveness of the proposed schemes and the improvement of random access time as well.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.44 no.4 s.316
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• pp.67-73
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• 2007

An optical pick up generally has coupled dynamics between focusing and tracking servos. The coupled dynamics reduces tracking performance of optical disk drives. A conventional control method is holding the previous tracking control command in the presence of surface defect. The method has a long settling time. If the defective area is getting larger, objective lens will get away from the following track. In order to overcome this problem, this paper proposed a new control method for optical disk drives based on a prediction of tracking error and focusing error. We present how to compensate the coupled dynamics so that reduced setting time is achieved. It is verified by experiments that the proposed method brings an improved performance in the presence of surface defect as well as in the normal operating condition.