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인간의 보행 패턴 분석을 통한 최적의 보행 제어 인자 추출에 대한 연구
하승석,한영준,한헌수 한국지능시스템학회 2007 한국지능시스템학회 학술발표 논문집 Vol.17 No.1
본 논문은 인간의 보행에 대한 에너지 분석을 통해 biped robot의 설계 단계에서 최적의 보행제어인자를 추출하기 위한 연구이다. 에너지 효율이 높은 보행인자 값을 얻기 위해 인간의 보행영상을 획득하고, 획득된 영상을 5-link biped robot model로 근사화하여 dynamics와 energy를 분석한다. 또한 link의 길이 비율과 link의 무게, link의 관성의 변화를 통해 5-link로 근사화된 인간의 보행 효율과 기구적 요소 사이의 민감도를 판단할 수 있다. 인간과 자유도가 다른 biped robot이 인간과 같은 보행을 위하여 설계단계에서 고려되어야할 중요한 기구적 요소가 이러한 민감도를 통해 구해진다.
하승석(Seung-Seok Ha),유천열(Chun-Yeol You) 한국자기학회 2006 韓國磁氣學會誌 Vol.16 No.2
We theoretically demonstrate that the interlayer exchange coupling (IEC) energy can be manipulated by means of an external bias voltage in a F₁/NM/F₂/S (F₁: ferromagnetic, NM: nonmagnetic metallic, F₂: ferromagnetic, S: semiconductor layers) four-layer system. It is well known that the IEC energy between two ferromagnetic layers separated by nanometer thick nonmagnetic layer depends on the spin-dependence of reflectivity to the F₁/NM/F₂/S four-layer system, where the reflectivities at the interface in NM/F₂ interface also depends on F₂/S interface due to the multiple reflection of an electron-like optics. Finally, the IEC energy depends on the spindependent electron reflectivity not only at the interfaces of F₁/NM/F₂, but also at the interface of F₂/S. Naturally the Schottky barrier is formed at the interface between metallic ferromagnetic layer and semiconductor, the Schottky barrier height and thickness can be tailored by an external bias voltage, which causes the change of the spin-dependent reflectivity at F₂/S interface. We show that the IEC energy between two ferromagnetic layers can be controlled by an external bias voltage due ti the electron-optics nature using a simple free-electron-like one-dimensional model.
인간 관절 에너지 분석을 통한 이족로봇의 자연스러운 보행 제어
하승석(Seungsuk Ha),한영준(Youngjoon Han),한헌수(Hernsoo Hahn) 제어로봇시스템학회 2008 제어·로봇·시스템학회 논문지 Vol.14 No.2
This paper proposes a method of adaptively generating a gait pattern of biped robot. The gait synthesis is based on human"s gait pattern analysis. The proposed method can easily be applied to generate the natural and stable gait pattern of any biped robot. To analyze the human"s gait pattern, sequential images of the human"s gait on the sagittal plane are acquired from which the gait control values are extracted. The gait pattern of biped robot on the sagittal plane is adaptively generated by a genetic algorithm using the human"s gait control values. However, gait trajectories of the biped robot on the sagittal plane are not enough to construct the complete gait pattern because the biped robot moves on 3-dimension space. Therefore, the gait pattern on the frontal plane, generated from Zero Moment Point (ZMP), is added to the gait one acquired on the sagittal plane. Consequently, the natural and stable walking pattern for the biped robot is obtained, as proved by the experiments.
인간의 보행 회전력의 주파수 특징 분석을 이용한 이족로봇의 적응적 보행 패턴 생성
하승석(Seung-Suk Ha),한영준(Young-Joon Han),한헌수(Hernsoo Hahn) 한국지능시스템학회 2008 한국지능시스템학회논문지 Vol.18 No.1
본 논문에서는 이족로봇의 자연스러운 보행 패턴을 생성하기 위해 인간의 보행 회전력(torque)을 주파수 영역에서 분석하고 분석된 데이터를 이용하여 적응적으로 이족로봇의 보행패턴을 생성하는 기법을 제안한다. 인간의 보행 회전력은 시간영역에서 복잡한 형태를 가지므로 DCT(Discrete Cosine Transform)를 이용하여 주파수영역으로 변환시켜 분석한다. 주파수 영역에서 얻어진 보행 회전력의 특징을 이용하여 이족로봇의 sagittal plane에서의 보행패턴을 생성한다. 또한 이족로봇의 안정적인 보행 패턴을 생성하기 위하여 동적 평형 상태임을 판단할 수 있는 Zero Moment Point(ZMP)해석을 통해 frontal plane상의 보행패턴을 생성하여 3차원 공간상의 안정적이고 인간과 같이 자연스러운 보행 패턴을 생성했다. This paper proposes a method of adaptively generating a gait pattern of biped robot. The gait synthesis is based on human's gait pattern analysis. The proposed method can easily be applied to generate the natural and stable gait pattern of any biped robot. To analyze the human's gait pattern, sequential images of the human's gait on the sagittal plane are acquired from which the gait control values are extracted. The gait pattern of biped robot on the sagittal plane is adaptively generated by a genetic algorithm using the human's gait control values. However, gait trajectories of the biped robot on the sagittal plane are not enough to construct the complete gait pattern because the biped robot moves on 3-dimension space. Therefore, the gait pattern on the frontal plane, generated from Zero Moment Point (ZMP), is added to the gait one acquired on the sagittal plane. Consequently, the natural and stable walking pattern for the biped robot is obtained.
Brillouin Light Scattering을 이용한 GaAs/Fe/Au 구조의 자기이방성
하승석(Seung-Seok Ha),유천열(Chun-Yeol You),이석목(Sukmock Lee),Kenta Ohta,Takayuk Nozaki,Yoshishige Suzuki,W. Van Roy 한국자기학회 2008 韓國磁氣學會誌 Vol.18 No.4
It has been well-known that the Fe/GaAs heterostructure has a small lattice mismatch of 1.4 % between Fe and GaAs, and the Fe layer is grown epitaxially on the the GaAs substrate. There are rich physics are observed in the GaAs/Fe interface, and the spininjection is actively studied due to its potential applications for spintronics devices. We fabricated Fe wedge layer in the thickness range 0~3.4 ㎚ on the GaAs (100) surface with 5-㎚ thick Au capping layer. The magnetic anisotropy of the Fe/GaAs system was investigated by employing Brillouin light scattering (BLS) measurements in this study. The spin wave excitation of Fe layer was studied as the function of intensity and the in-plane angle of external magnetic field, and thickness of Fe layer. Also these various dependences were analyzed with analytic expression of spin wave surface mode in order to determine the magnetic anisotropies. It has been found that the GaAs/Fe/Au system has additional uniaxial magnetic anisotropy, while the bulk Fe has biaxial anisotropy. The uniaxial anisotropy shows increasing dependency respected to decreasing thickness of Fe layer while biaxial anisotropy is reduced with Fe film thickness. This result allows the analysis that the uniaxial anisotropy is originated from interface between GaAs surface and Fe layer.