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이정훈(Jeung Hoon Lee),김삼묘(Sam Myo Kim) 한국정보과학회 1996 한국정보과학회 학술발표논문집 Vol.23 No.2A
본 논문은 프랙탈 영상 압축 방식의 속도를 개선하기 위하여 새로운 도메인 분류 및 검색 방안을 제안한다. 도메인 분류는 DCT에 의하여 얻어진 한 개의 DC값과 최상위 두 개의 AC값을 바탕으로 이루어졌으며 도메인을 근접 빈도(nearest frequency neighborhood)에 따라 검색하는 방안을 택하였다. 실험결과 종전의 방법에 비하여 영상의 질을 유지하며 약 5배의 속도 향상을 얻을 수 있었다.
상용 유한요소해석 프로그램을 이용한 공압 스프링 내 다이아프램의 복소강성 산출
이정훈(Lee, Jeung-Hoon),김광준(Kim, Kwang-Joon) 한국소음진동공학회 2006 한국소음진동공학회 논문집 Vol.16 No.9
An accurate mathematical model for complex stiffness of the pneumatic spring would be necessary for an efficient design of a pneumatic spring used in vibration isolation tables for precision instruments such as optical devices or nano-scale equipments. A diaphragm, often employed for prevention of air leakage, plays a significant role of complex stiffness element as well as the pressurized air itself Therefore, effects of the diaphragm need to be included in the dynamic model for a more faithful description of dynamic behavior of pneumatic spring. But the complex stiffness of diaphragm is difficult to predict In an analytical way, since it is a rubber membrane of complicated shape in itself. Moreover, the diaphragm should be expandable in response to pressurization inside a chamber, which makes direct measurement of complex stiffness of diaphragm extremely difficult. In our earlier research, the complex stiffness of diaphragm was indirectly measured, which was just to eliminate the theoretical stiffness of pressurized air from the measured complex stiffness of the pneumatic spring. In order to reflect complex stiffness of inflated diaphragm on the total stiffness at the initial design or design improvement stage, however. it is required to be able to predict beforehand. In this paper, how to predict the complex stiffness of inflated rubber diaphragm by commercial FE codes (e.g. ABAQUS) will be discussed and the results will be compared with the indirectly measured values.
이정훈(Lee, Jeung-Hoon),김광준(Kim, Kwang-Joon) 한국소음진동공학회 2008 한국소음진동공학회 논문집 Vol.18 No.1
Pneumatic vibration isolator typically consisting of dual-chamber pneumatic springs and a rigid table are widely employed for proper operation of precision instruments such as optical devices or nano-scale equipments owing to their low stiffness- and high damping-characteristics. As environmental vibration regulations for precision instruments become more stringent, it is required to improve further the isolation performance. In order to facilitate their design optimization or active control, a more accurate mathematical model or complex stiffness is needed. Experimental results we obtained rigorously for a dual-chamber pneumatic spring exhibit significantly amplitude dependent behavior, which cannot be described by linear models in earlier researches. In this paper, an improvement for the complex stiffness model is presented by taking two major considerations. One is to consider the amplitude dependent complex stiffness of diaphragm necessarily employed for prevention of air leakage. The other is to employ a nonlinear model for the air flow in capillary tube connecting the two pneumatic chambers. The proposed amplitude-dependent complex stiffness model which reflects dependency on both frequency and excitation amplitude is shown to be very valid by comparison with the experimental measurements. Such an accurate nonlinear model for the dual-chamber pneumatic springs would contribute to more effective design or control of vibration isolation systems.
이정훈(Lee, Jeung-Hoon),김광준(Kim, Kwang-Joon) 한국소음진동공학회 2008 한국소음진동공학회 논문집 Vol.18 No.4
Pneumatic vibration isolator has a wide application for ground-vibration isolation of vibration-sensitive equipments. Recent advances In precision machine tools and instruments such as nano-technology or medical devices require a better isolation performance, which can be efficiently done by precise modeling- and design- of the isolation system. This paper will discuss an efficient transmissibility design method for pneumatic vibration isolator by employing the complex stiffness model of dual-chamber pneumatic spring developed in our previous research. Three design parameters of volume ratio between the two pneumatic chambers, the geometry of capillary tube connecting the two pneumatic chambers and finally the stiffness of diaphragm necessarily employed for prevention of air leakage were found to be important factors in transmissibility design. Based on design technique that maximizes damping of dual-chamber pneumatic spring, trade-off among the resonance frequency of transmissibility, peak transmissibility and transmissibility in high frequency range was found, which was not ever stated in previous researches. Furthermore this paper will discuss about negative role of diaphragm in transmissibility design. Then the design method proposed in this paper will be illustrated through experiment at measurements.
인체 머리부 6 자유도 운동 측정의 신뢰성 향상을 위한 가속도계 감도축의 옵셋(offset) 추정
이정훈(Lee, Jeung-Hoon),김광준(Kim, Kwang-Joon),장한기(Jang, Han-Kee) 한국소음진동공학회 2008 한국소음진동공학회 논문집 Vol.18 No.9
Notion sickness is well known to be caused by long time exposure to the very low frequency motion in the multiple axes of human body Since the vestibular system for the perception of low frequency motion is located in the head, accurate measurement of 6 degree of freedom head motion is of great importance. In this study, the measurement system consisting of a safety helmet and 9 translational accelerometers was constructed for the estimation of 3 translational and 3 rotational motions of human head. Since estimation errors of 3 rotational components can be significantly magnified even by small offset of the sensitivity axis from the geometric center of an accelerometer, accurate measurement of sensitivity axis must be preceded. The method for accurate estimation of the offset was proposed, and the effect of offset on the estimation of angular acceleration was investigated.