• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.1
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• pp.48-61
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• 1989

In this paper, two-dimensional numerical simulation of GaAs MESFFT with 0.7${\mu}m$ gate length is perfomed. Drift-diffusion model which consider that mobility is a function of local electric field, is used. As a discretization method, instead of FDM (finite difference method) and FEM (finite element method), the Control-Volume Formulation (CVF) is used and as a numerical scheme current hybrid scheme or upwind scheme is replaced by power-law scheme which is very approximate to exponential scheme. In the process of numerical analysis, Peclet number which represents the velocity ratio of drift and diffusion, is introduced. And using this concept a current equation which consider numerical scheme at the interface of control volume, is proposed. The I-V characteristics using the model and numerical method has a good agreement with that of previous paper by others. Therefore, it is confined that it may be useful as a simulator for GaAs MESFET. Besides I-V characteristics, the mechanism of both velocity saturation in drift-diffusion model is described from the view of velocity and electric field distribution at the bottom of the channel. In addition, the relationship between the mechanism and position of dipole and drain current, are described.

• Journal of the Korean Institute of Intelligent Systems
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• v.21 no.3
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• pp.283-289
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• 2011

In this research a controller based on velocity estimator for a Wheeled Inverted Pendulum (WIP) is designed and various numerical simulation studies are carried out. The WIP has stable and unstable equivalent points. To Keep the unstable equilibrium point, a controller should control carefully the wheels persistently. There are angle, angular velocity, displacement, and velocity of the WIP for controller inputs. The velocity is obtained by differentiating the encoder signals from the motor and is subject to the resolution of the encoder. An improved velocity detection method is proposed based on low resolution encoder and velocity estimator. Various numerical simulations are carried out for showing the validation of the velocity estimator in case of the inclined road condition.

• 제어로봇시스템학회:학술대회논문집
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• 1992.10a
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• pp.260-265
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• 1992

This paper presents an adaptive control scheme for flexible joint robot manipulators. This control scheme is based on the Lyapunov direct method with the arm energy-based Lyapunov function. The proposed adaptive control scheme uses only the position and velocity feedback of link and motor shaft. The adaptive control system of flexible joint robots is asymptotically stable regardless of the joint flexibility value. Therefore, the assumption of weak joint ealsticity is not needed. Also, joint flexibility value is unknown. Simulation results are presented to show the feasibility of the proposed adaptive control scheme.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.1
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• pp.51-57
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• 2011

Information of the lateral velocity and the sideslip angle in a vehicle is very useful in many active vehicle safety applications such as yaw stability control and rollover prevention. Because cost-effective sensors to measure the lateral velocity and the sideslip angle are not available, reliable algorithms to estimation them are necessary. In this paper, a sliding mode observer is designed to estimate the lateral velocity. The side slip angle is estimated using the recursive least square with the disturbance observer and the pseudo integral. The estimated parameters from the combined estimation method are updated recursively to minimize the discrepancy between the model and the physical plant, and any possible effects caused by disturbances. The performance of the proposed monitoring system is evaluated through simulations and experiments.

• Structural Engineering and Mechanics
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• v.46 no.3
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• pp.371-385
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• 2013

Vibration isolators and anti-vibration mounts are ideal, for example, in creating floating floors for gymnasiums, or performance spaces. However, it is well-known that there are great difficulties on isolating vibration transmission in structural steel components, especially steel floors. Besides, the selection of inertia blocks, which are usually used by engineers as an effective vibration control measure, is usually based on crude methods or the experience of the engineers. Thus, no simple method or indices have been available for assessing the effect of inertia blocks on vibration isolation or stability of vibratory systems. Thus, the aims of this research are to provide further background description using a FE model and present and implement a modal approach, that was validated experimentally, the latter assisting in providing improved understanding of the vibration transmission phenomenon in steel buildings excited by a velocity-source type of excitation. A better visualization of the mean-square velocity distribution in the frequency domain is presented using the concept of modal expansion. Finally, the variation of the mean-square velocity with frequency, whilst varying mass and/or stiffness of the coupled system, is presented.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.10 no.2
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• pp.64-72
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• 2001

Weld line is one of serious troubles which are observed in a plastic part manufactured by a injection molding process. This is caused by many process factors, which are molding pressure, temperature, velocity, location of a injection gate, mold geometry and material properties. investigation on the effects of these process factors to the appearance of a weld line was carried out using a finite element method. Filling and packing analyses were carried out by modifying both the configuration of the injection gates and cavity thickness. Proper locations of the injection gates could be determined by considering molding pressure, temperature, velocity and frozen layer, and whereby the weld line was controled. In order to make a weak appearance of the weld line, flow velocity and flow front in a cavity were also investigated by modifying a cavity thickness. As a result, flow front was extended around the corner in the cavity by changing the flow velocity and hence the appearance of the weld line was much weakened.

• Journal of Institute of Control, Robotics and Systems
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• v.22 no.11
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• pp.919-924
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• 2016

This paper proposes a robust control design method for improving the cornering stability of a personal electric vehicle equipped with in-wheel motors. In general, vehicles undergo severe parameter variations and unpredictable disturbances with respect to a wide range of driving conditions (e.g., road surface conditions and vehicle velocity conditions). For this reason, robust control design techniques are required to guarantee consistent driving performances and robustness against various driving conditions. In this paper, an adaptive sliding mode control method is employed to enhance cornering stability by controlling the direct-drive in-wheel motors independently. Additionally, in order to confirm the effectiveness of a proposed control method, real driving tests with an experimental personal electric vehicle are performed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.5
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• pp.383-388
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• 2021

Air-breathing engines used in aircraft have a performance limit as the altitude increases, and this determines the service and absolute ceiling altitude. The method of maintaining altitude and speed in a fixed-wing aircraft in level flight using classical control method is generally using thrust for speed increase/deceleration and pitch attitude for altitude increase/decrease. If this method is used near the service ceiling altitude, increasing the pitch to reduce the altitude error results in a speed reduction. Therefore, it is necessary to use a control method that maintains the speed first using the pitch attitude. Especially in the case of unmanned aerial vehicles, these two methods should be automatically available at the right time. In this paper, we propose a method of switching the speed and altitude maintenance algorithm near service ceiling altitude.

• Journal of Animal Reproduction and Biotechnology
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• v.36 no.2
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• pp.82-90
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• 2021

In the present study, we examined if deep uterine artificial insemination (DUAI) can improve the pregnancy rate of artificial insemination (AI) using epididymal spermatozoa (ES) in Hanwoo cattle. The estrus cycles of 88 Hanwoo cows were synchronized, and 17 cows were artificially inseminated using the DUAI method with ES, 20 cows were artificially inseminated via the uterine body (BUAI) method with ES, and as a control, 51 cows were inseminated by using the BUAI method with ejaculated spermatozoa from 1 proven bull after frozen thawing. The pregnancy rate of the DUAI method (58.8%) was higher than that of the BUAI method (25.0%, p = 0.0498). The motility of ES was examined immediately after thawing and after 3 and 6 h of incubation. The rapid progressive sperm motility of the control group was significantly higher than that of the ES group immediately after thawing and after 3 and 6 h of incubation (p < 0.05). The straight line velocity and average path velocity of the ES group after 6 h of incubation were significantly lower than those in the control group (p < 0.05). The linearity and amplitude of lateral head of ES were lower than those at 6 h (p < 0.05). The flagellar beat cross frequency and hyperactivation of ES were lower than the control spermatozoa immediately after thawing and at 3 h (p < 0.05). These motility parameters suggested that ES had a low motility and fertilization ability compared to the control spermatozoa. After frozen-thawing and 3 h of incubation, the percentage of live spermatozoa with intact acrosomes in the ES was significantly lower than that in ejaculated spermatozoa (p < 0.05). Our findings suggested that the DUAI method can overcome the low pregnancy rate of ES, despite the low motility, viability, and fertilization ability of ES.

• Journal of Institute of Control, Robotics and Systems
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• v.10 no.5
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• pp.395-401
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• 2004

We present an AILC(Adaptive Iterative Learning Control) scheme and a sufficient condition for system parameter identification for uncertain robotic systems that perform the same tasks repetitively. It is guaranteed that the joint velocity and position asymptotically converge to the reference joint velocity and position, respectively. In addition, it is proved that a sufficient condition for parameter identification is the PE(Persistent Excitation) condition on the regressor matrix evaluated at the reference trajectory during the operation period. Since the regressor matrix on the reference trajectory can be easily computed prior to the real robot operation, the proposed algorithm provides a useful method to verify whether the parameter error converges to zero or not.