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피재환,방효충 한국항공우주학회 2013 International Journal of Aeronautical and Space Sc Vol.14 No.4
The hemispherical resonator gyroscope is a type of vibratory gyroscope, which can measure angle or angular rate, basedon its operating mode. This paper deals with the case when the hemispherical resonator gyroscope is operated in anglemeasurement mode. In angle measurement mode, the resonator pattern angle precesses, with respect to the external rotationinput, by the principle of the Coriolis effect, so that the external rotation can be estimated, by measuring the amount ofprecession angle. However, this pattern angle drifts, due to the manufacturing error of the resonator. Since the drift effectcauses degradation of the angle estimation performance of the resonator, the corresponding drift compensation control shouldbe performed, to enhance the estimation performance. In this paper, a mathematical model of the hemispherical resonatorgyro is first introduced. By using the mathematical model, a nonlinear observer for imperfection parameter estimation, andthe corresponding compensation controller are designed to operate hemispherical resonator gyros, as angle measurementsensors.
위성간 각도정보만을 활용한 상대 항법에서 임펄스 기동을 사용한 가관측성 향상 궤적 설계
피재환,방효충 한국항공우주학회 2014 한국항공우주학회 학술발표회 논문집 Vol.2014 No.4
본 논문에서는 위성간 각도정보를 활용한 상대 항법에서 가관측성 향상을 위한 랑데부 궤적 설계를 다룬다. 소형위성의 경우 무게와 전력 소모량에 제약이 크므로 간편한 카메라 센서를 항법 센서로 사용하였다. 이 경우 상대 거리 정보를 정적인 상황에서 얻을 수 없으므로 이에 따른 적절한 기동 설계가 필수적이다. 궤적 설계를 위하여 상대거리 추정 오차와 위성 위치 사이의 기하학적 관계식을 유도하고 이에 따라 필요한 가관측성을 확보하는 인공위성 상대 궤적을 설계하였다. 수치적 시뮬레이션을 통하여 설계된 궤적으로부터 얻을 수 있는 상대 위치 추정 오차를 계산하여 설계된 궤적을 검증하였다. In this paper, satellite rendezvous trajectory is designed for safe operation of angles-only relative navigation between small satellites. Since small-size satellite has significant limitation on mass and power consumption, vision based camera is selected for relative navigation sensor. In this case, the relative angle information is obtained and the relative range information cannot be obtained in static situation. Therefore, it is necessary to design appropriate relative trajectory to obtain sufficient observability from relative angle measurement only. Geometrical analysis is performed to analyze the effect of observability maneuver on relative range estimation error. By using the analyzed result, rendezvous trajectory is designed to obtain sufficient relative navigation performance. Numerical simulation is performed to verify the designed trajectory.
The Morphology and Crystallography of Isothermal Martensite in Yttria Stabilized Zirconia
피재환,Eui-Seok Choi,Motozo Hayakawa 한국세라믹학회 2006 한국세라믹학회지 Vol.43 No.2
A full retention of the tetragonal phase with coarse grains (50~60μm) was possible with the specimen ZrO2-1.9mol% Y2O3. In these coarse grains, {101}t annealing twins were frequently observed, although they do not exist in the usual fine grained specimens. The morphology and growth rate of the isothermally formed individual products are studied at an optical microscopic level. The habit planes of both products are also identified by performing two-surface trace analysis on the grains whose orientations are determined by the electron back scattering pattern (EBSP) method. The morphologies of isothermal martensite were well-defined thin plates and lenticular types. The growth rate in their longitudinal directions was quite slow and temperature-dependent. A two-surface trace analysis, incorporated with the EBSP method, identified the habit planes near {013}c in agreement with previous reports obtained from TEM works.
Kinetics of Athermal Martensitic Transformation in Yttria Doped Zirconia
피재환,Eui-Seok Choi,Motozo Hayakawa 한국세라믹학회 2005 한국세라믹학회지 Vol.42 No.11
The high temperature tetragonal phase of zirconia containing 1.40~1.60mol% of yttria can be fully retained at room temperature by rapid cooling. The metastable tetragonal phase transforms into the monoclinic phase athermally upon subzero cooling. The transformation exhibited an athermal burst transformation. The effects of yttria content and grain size on the athermal martensitic transformation were studied in detail. The burst temperature linearly decreased with increasing yttria content or decreasing grain size. To consider the distribution of martensite nuclei, the Weibull modulus of the athermal martensitic transformation was evaluated from the distribution of the burst transformation temperature. From the Weibull analysis, the distribution of embryos appears to be more homogeneous than that of the defects responsible for the fracture of similar material.
피재환,박종철,김유진,황광택,김수룡,Pee, Jae-Hwan,Park, Jong-Chul,Kim, Yoo-Jin,Hwang, Kwang-Taek,Kim, So-Ryong 한국분말야금학회 2008 한국분말재료학회지 (KPMI) Vol.15 No.6
Aluminum nitride (AlN) powders were prepared by the chemical vapor synthesis (CVS) process in the $AlCl_{3}-NH_{3}-N_{2}$ system. Aluminum chloride ($AlCl_3$) as the starting material was gasified in the heating chamber of $300^{\circ}C$. Aluminum chloride gas transported to the furnace in $NH_{3}-N_{2}$ atmosphere at the gas flow rate of 200-400ml/min. For samples synthesized between 700 and $1200^{\circ}C$, the XRD peaks corresponding to AlN were comparatively sharp and also showed an improvement of crystallinity with increasing the reaction temperature. In additions, the average particle size of the AlN powders decreased from 250 to 40 nm, as the reaction temperature increased.
회전각 측정 모드를 위한 반구형 공진 자이로의 오차 요소 추정
피재환,방효충 한국항공우주학회 2013 한국항공우주학회 학술발표회 논문집 Vol.2013 No.11
반구형 공진 자이로는 공진 상태에서 코리올리 힘에 의해 세차 운동하는 물리적 특성을 이용하여 각속도 또는 각도를 측정한다. 본 논문에서는 공진자이로가 회전각 측정 모드로 운영될 시의 제어 방법에 대하여 다루도록 한다. 특히 회전각 측정 모드에서는 패턴각을 외부각속도 입력에 따라 자유롭게 세차 운동할 수 있도록 하는데, 이때 공진기의 제작 오차에 따라 패턴각의 표류현상이 발생한다. 이는 회전각 측정 성능을 저하시키므로 표류현상을 제거하기 위하여 공진기의 오차 요소 추정이 필요하다. 오차 요소에 따른 패턴각의 표류현상 분석 및 공진기의 오차 요소 추정을 위한 관측기 설계를 수행하였다. Hemispherical resonator gyro can measure the angular rate or angle based on the principle of Coriolis effect. This paper considers the case when the resonator gyro works as angle measurement sensor. Especially for the angle measurement mode, the pattern angle is allowed to precess freely with respect to the external rotation. However, the angle measurement performance is affected by pattern angle drift effect due to the manufacturing error of the resonator. In this paper, pattern angle drift effect due to the manufacturing error is analyzed and the error parameter observer is designed.
ZDP(Zinc Decomposition Process)를 이용한 폐 초경합금의 분해기구
피재환,김유진,성남의,황광택,조우석,김경자 한국세라믹학회 2011 한국세라믹학회지 Vol.48 No.2
Decomposition promoting factors and decomposition mechanism in the zinc decomposition process of waste hard metals which are composed mostly of tungsten carbide and cobalt were evaluated. Zinc volatility amount was suppressed and zinc valatilization pressure was produced in the reaction graphite crucible inside an electric furnace for ZDP. Reaction was done for 2 h at 650℃, which 100 % decomposed the waste hard metals that were over 30 mm thick. As for the separation-decomposition of waste hard metals, zinc melted alloy formed a liquid composed of a mixture of γ-β1 phase from the cobalt binder layer (reaction interface). The volume of reacted zone was expanded and the waste hard metal layer was decomposed-separated horizontally from the hard metal. Zinc used in the ZDP process was almost completely removed-collected by decantation and volatilization-collection process at 1000℃.