• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.668-674
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• 2001

An experimental study was performed for two types of co-axial cylindrical shell structures in order to establish the relationship between in-air dynamic characteristics and in-water ones and to observe hydrodynamic mass effects on their mode shapes when submerged. The outer cylinders are prepared with two kinds to get more insights on the fluid-structure interaction phenomena: one is flexible, which means that the outer cylinder has almost same stiffness as the inner one, and the other is a rigid one whose stiffness is more than ten times of the inner one's(it might be regarded as the scaled-down model of the reactor internals). The finite element. analyses were also implemented to support the experimental results. The results show that the natural frequencies of a co-axial cylindrical shell structure in water are remarkably lower than those in air due to the fluid mass effects. In case of the flexible-to-flexible cylinders, there exist in-phase and out-of-phase mode shapes and they are affected by the annular gap between the. co-axial cylinders. For the in-phase mode the in-water natural frequency decreases exponentially as the gap increases, while it slightly increases in case of the out-of-phase mode due to the squeezing effect of the gap fluid. In the flexible-to-rigid case, the normalized natural frequency(in-water frequency/in-air one) of the inner cylinder(core barrel model) ranges between in-phase and out-of-phase mode frequencies of the flexible-to-flexible co-axial cylindrical structure having identical dimensions. Also the normalized natural frequency of the inner cylinder of the flexible-to-rigid one moves from near of the in-phase mode frequency into the out-of-phase mode value of the flexible-to-flexible case as circumferential mode number(n) increases.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.511-516
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• 2000

In order to not only perform as a extreme model under the severe operating condition but also acquire more diverse and advanced control capability utilizing high compliance, active vibration control of a flexible 2-link robot manipulator are investigated. Multi variable-structured frequency shaped optimal sliding mode is proposed for the flexible robot manipulator like control system, whose control variables, an angular motion of joint and vibration of flexible link, have to be controlled simultaneously by one control torque at a driving joint. The control system is divided into two subsystems, a control input related subsystem and an added subsystem. The proposed sliding mode, composed of multi control variables, makes optimized relation between subsystems and a individual control input, thus, the sliding mode controller can compensate whole dynamics of each subsystems simultaneously. And the possibility and effectiveness are verified by vibration control of a manipulator having two flexible links. Simulation and experiment results show that the proposed control scheme achieves the purpose effectively.

• Transactions of the Society of Information Storage Systems
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• v.4 no.1
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• pp.23-28
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• 2008

In this paper we suggested the moving magnet type actuator for optical disc drive which has high frequency of flexible mode. Generally, moving magnet type actuator has the advantage for increase the frequency of flexible mode. But it has low driving sensitivity due to the weight of its moving part. To overcome this shortcoming, we designed the model with the closed electromagnetic circuit for tracking direction. In addition, we improved the driving sensitivity and frequency of flexible mode by using of DOE (design of experiment) procedure for EM circuit. Consequently, it is verified that final designed model satisfied with the desired specifications.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.479-483
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• 2006

As high-definition television(HDTV) broadcasting were generalized, there have been many researches and developments about large storage capacity and fast data transfer rate in optical disk drives(ODD). Pickup actuators must have high flexible mode frequencies and gain margins. Flexible modes are caused by the flexibility of moving parts in the actuator and a servo bandwidth is limited by them. As a result, the system becomes unstable for high-speed operations in high density reading and recording. In this paper, we suggest improved modeling method that considers the bonding layer. And, flexible mode frequency of actuator is improved by Design of Experiment of lens holder. Magnet circuit is designed considering the relation with moving part. Through improving yoke design, the magnetic flux is changed and DC tilt is reduced. Consequently, we designed actuator which has high flexible mode frequency and gain margins.

• Transactions of the Society of Information Storage Systems
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• v.2 no.4
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• pp.240-244
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• 2006

As high-definition television(HDTV) broadcasting becoming more generalized, there have been many researches and developments about a large storage capacity and a fast data transfer rate in optical disk drives (ODD). Pickup actuators must have high flexible mode frequencies and large gain margins. Flexible modes are caused by the flexibility of moving parts in the actuator and a servo bandwidth is limited by them. As a result, the system becomes unstable for high-speed operations in high density reading and recording. In this paper, we suggest improved modeling method in considering of the bonding layer. And, the flexible mode frequency of actuator is improved by Design of Experiments of lens holder. The Magnet circuit is designed considering the relation with the moving part. Through improving the yoke design, the magnetic flux is changed and the DC tilt is reduced. Consequently, we designed an actuator which has a high flexible mode frequency and a large gain margins.

• Journal of Mechanical Science and Technology
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• v.19 no.10
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• pp.1846-1855
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• 2005

This paper presents a new stochastic controller applied on the vibration control system under irregular disturbances based on the mode selection scheme. Measured displacement and frequency characteristics are simultaneously used in designing a mode selecting controller. This technique is validated by applying to the suppression problem of a flexible beam with randomly vibrated circumstances. The presented method, called Mode Selecting Stochastic Controller, uses the frequency measurement of the flexible system based on a Fast-Fourier transformation algorithm. This controller is constructed by combining mode selection method with previous known Stochastic Controller in real time: Numerical simulations and several experiments are conducted to validate the proposed method. The performance of the proposed method is compared with a stochastic controller developed recently. This method was improved compared with previous one.

• 정보저장시스템학회:학술대회논문집
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• 2005.10a
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• pp.69-70
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• 2005

In this paper, slim type optical pickup actuator was fabricated and its FE model was tuned to experimental results through precise coil models. In order to widen its control bandwidth, stiffness of moving parts was increased by changing shape of coil section. Finally, we checked that flexible mode frequency and gain margin was increased.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.1054-1057
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• 2003

A Real Time Mode Selecting Stochastic Controller (RTMSSC) is developed as a new control strategy for a vibrating system under irregular disturbance. Displacement information and frequency characteristics obtained from me::id analysis of the system are used to design a Mode Selecting Controller. This Paper explains design technique of RTNSSC by applying it to the suppression of a flexible beam experiencing random vibration. The RTMSSC is designed by stochastic control from the modal information. The frequency information of the flexible system is utilized from the Mode Selecting Unit (MSU) based on a Fast-Fourier Transformation algorithm. The performance of the proposed technique, RTMSSC, is compared with that of Real Time Stochastic Controller developed recently, which show quite promising results.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.11
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• pp.204-212
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• 1999

In this paper, the vibrational motion of a flexible beam clamped on a translating base and carrying a moving mass is investigated. The equations of motion which describe the total dynamics of the beam-mass-cart system are derived and the coupled dynamic equations are solved by unconstrained modal analysis. In modal analysis, the exact normal mode solutions corresponding to the eigenfrequencies for the position of the moving mass and the ratios of the mass of the flexible beam, the moving mass and the base cart are used. Proper transformations of the time solutions between the normal modes for a position and those for the next position of the moving mass are also adopted. Numerical simulations are carried out to obtain the open-loop responses of the system in tracking the pre-designed path of the moving mass.

• International Journal of Aeronautical and Space Sciences
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• v.15 no.2
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• pp.113-122
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• 2014

The objective of the paper is to clarify a methodology based on the use of the existing component mode synthesis methods for the case of two damped substructures which are coupled through a linking viscoelastic flexible substructure and for which the structural modes with free geometrical interface are used for each main substructure. The proposed methodology corresponds to a convenient alternative to the direct use either of the Craig-Bampton method applied to the three substructures (using the fixed geometric interface modes) or of the flexibility residual approaches initiated by MacNeal (using the free geometric interface modes). In opposite to a geometrical interface which is a topological interface on which there is a direct linkage between the degrees of freedom of substructures, we consider a physical flexible interface which exists in certain present technologies and for which the general framework linear viscoelasticity is used and yields a frequency-dependent damping and stiffness matrices of the physical flexible interface.