• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 D
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• pp.2092-2095
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• 2001

In this paper, the performance of a new alternative form of three-axis attitude estimation algorithm for a rigid body is evaluated via simulation for the situation where the observed vectors are the estimated baselines of a GPS antenna array. This method is derived based on a simple iterative nonlinear least-squares with four elements of quaternion parameter. The representation of quaternion parameters for three-axis attitude of a rigid body is free from singularity problem. The performance of the proposed algorithm is compared with other eight existing methods, such as, Transformation Method (TM), Vector Observation Method (VOM), TRIAD algorithm, two versions of QUaternion ESTimator (QUEST), Singular Value Decomposition (SVD) method, Fast Optimal Attitude Matrix (FOAM), Slower Optimal Matrix Algorithm (SOMA).

• 한국항공우주학회지
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• 제38권3호
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• pp.243-248
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• 2010

본 연구에서는 인공위성의 관성 모멘트 추정을 위해 MRP(Modified Rodrigues Parameter) 자세 변수기반의 추정기를 설계하였다. MRP는 인공위성 자세 결정시 쿼터니 언(Quaternion) 파라미터의 구속 조건으로부터 발생하는 필터의 오차 공분산 행렬의 특이(Singularity) 현상을 피할 수 있는 장점이 있다. 한편 MRP의 경우 자세각 변위가 클 경우에 역시 특이현상이 발생할 수 있어 이를 피하기 위해 적절한 자세각 범위에서 인위적인 기준 운동을 생성하여 필터 설계에 적용하였다. 쿼터니언 파라미터의 단점을 극복하여 보다 안정된 오차 공분산 갱신 결과의 필터의 개선된 성능을 예상할 수 있다.

• Transactions on Control, Automation and Systems Engineering
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• 제4권2호
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• pp.169-175
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• 2002

A sliding mode control of spacecraft attitude tracking with actuator, especially reaction wheel, is presented. The sliding mode controller is derived based on quaternion parameterization for the kinematic equations of motion. The reaction wheel dynamic equations represented by wheel input voltage are presented. The input voltage to wheel is calculated from the sliding mode controller and reaction wheel dynamics. The global asymptotic stability is shown using a Lyapunov analysis. In addition the robustness analysis is performed for nonlinear system with parameter variations and disturbances. It is shown that the controller ensures control objectives for the spacecraft with reaction wheels.

• Journal of Mechanical Science and Technology
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• 제18권2호
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• pp.203-210
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• 2004

Attitude control law design for spacecraft large angle maneuvers is investigated in this paper. The feedback linearization technique is applied to the design of a nonlinear tracking control law. The output function to be tracked is the quaternion attitude parameter. The designed control law turns out to be a combination of attitude and attitude rate tracking commands. The attitude-only output function, therefore, leads to a stable closed-loop system following the given reference trajectory. The principal advantage of the proposed method is that it is relatively easy to produce reference trajectories and associated controller.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2001년도 ICCAS
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• pp.92.1-92
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• 2001

Sliding mode control of spacecraft attitude tracking with actuator, especially reaction wheel, is presented. The sliding mode controller is derived based on quaternion parameterization for the kinematic equations of motion. The reaction wheel dynamic equations represented by wheel input voltage are presented. The input voltage to wheel is calculated from the sliding mode controller and reaction wheel dynamics. The global asymptotic stability is shown using a Lyapunov analysis. In addition the robustness analysis is taken for nonlinear system with parameter variations and disturbances. It is shown that the controller ensures control objectives for the spacecraft with reaction wheels.

• 한국측량학회지
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• 제36권2호
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• pp.43-50
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• 2018

영상을 기반으로 하는 3차원 위치결정에서 카메라는 핵심적인 요소이며 이러한 카메라의 내부적인 특성을 제대로 결정하는 카메라 캘리브레이션 작업은 대상물의 3차원 좌표를 결정하기 위해서 필수적으로 선행되어야 할 과정이다. 본 연구에서는 캘리브레이션을 위한 체크보드의 크기와 형태에 영향을 받지 않고 반자동으로 카메라의 내부표정요소를 결정하는 방법론을 제안하였다. 제안한 방법론은 쿼터니언을 이용한 외부표정요소 추정, 캘리브레이션 타겟의 인식, 번들블록조정을 통한 내부표정요소 매개변수 결정으로 구성되어 있다. 체스보드 형태의 캘리브레이션 타겟을 이용하여 내부표정요소를 결정한 후 소규모 3차원 모형에 대한 3차원 위치를 결정하였으며 검사점을 이용한 정확도 평가를 통해서 수평위치와 수직위치 오차는 각각 약 ${\pm}0.006m$와 ${\pm}0.007m$를 얻을 수 있었다.

• International Journal of Control, Automation, and Systems
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• 제1권4호
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• pp.520-526
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• 2003

In the case of a strapdown inertial navigation system (SDINS) with sizeable attitude errors, the uncertainty caused by linearization of the system degrades the performance of the filter. In this paper, a robust filter and various error models for the uncertainty are presented. The analytical characteristics of the proposed filter are also investigated. The results show that the filter does not require the statistical property of the system disturbance and that the region of the estimation error depends on a freedom parameter in the worst case. Then, the uncertainty of the SDINS is derived. Depending on the choice of the reference frame and the attitude error state, several error models are presented. Finally, various in-flight alignment methods are proposed by combining the robust filter with the error models. Simulation results demonstrate that the proposed filter effectively improves the performance.

• 한국전산구조공학회논문집
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• 제18권2호
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• pp.141-149
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• 2005

본 논문에서는 유연체 동역학해석을 위하여 유한회전을 표현하는데 있어, 4원법의 대수학적인 표현을 도입하여 운동방정식이 에너지보존 조건을 만족하도록 이산화된 에너지 평형식으로 정식화되었다. 여기서 사용된 유한회전의 4원법은 로드리게스 매개변수를 이용하도록 하였으며, 구속력에 대한 일이 제거되도록 하였다. 수치해석의 예를 통하여 제안된 방법이 사다리꼴 방법과 비교할 때 비선형 문제에서도 무조건적으로 안정조건을 보장함을 검증하였으며, 향후 유연한 관절로 연결된 3차원 유연다물체에 대한 동역학 해석을 확장할 수 있는 토대를 마련하였다.

• 제어로봇시스템학회논문지
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• 제7권8호
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• pp.703-710
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• 2001

The nonlinear observers are proposed for a nonlinear system. To improve the characteristics such as stability, convergence, and $H^{\infty}$ filter performance criterion, we utilize an $H^{\infty}$ filter Riccati equation or a modified $H^{\infty}$ filter Riccati equation with a freedom parameter. Using the Lyapunov function method, the characteristics of the observers are analyzed. Then the in-flight alignment for a strapdown inertial navigation system(SDINS) is designed using the proposed observer. And the additive quaternion error model is especially used to reduce the uncertainty of the SDINS error model. Simulation results show that the observer with the modified $H^{\infty}$ filter Riccati equation effectively improves the performance of the in-flight alignment.

• Journal of Astronomy and Space Sciences
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• 제26권1호
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• pp.31-46
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• 2009

An Unscented Kalman Filter (UKF) for estimation of the attitude and rate of a spacecraft using only magnetometer vector measurement is developed. The attitude dynamics used in the estimation is the nonlinear Euler's rotational equation which is augmented with the quaternion kinematics to construct a process model. The filter is designed for small satellite in low Earth orbit, so the disturbance torques include gravity-gradient torque, magnetic disturbance torque, and aerodynamic drag torque. The magnetometer measurements are simulated based on time-varying position of the spacecraft. The filter has been tested not only in the standby mode but also in the detumbling mode. Two types of actuators have been modeled and applied in the simulation. The PD controller is used for the two types of actuators (reaction wheels and thrusters) to detumble the spacecraft. The estimation error converged to within 5 deg for attitude and 0.1 deg/s for rate respectively when the two types of actuators were used. A joint state parameter estimation has been tested and the effect of the process noise covariance on the parameter estimation has been indicated. Also, Monte-Carlo simulations have been performed to test the capability of the filter to converge with the initial conditions sampled from a uniform distribution. Finally, the UKF performance has been compared to that of the EKF and it demonstrates that UKF slightly outperforms EKF. The developed algorithm can be applied to any type of small satellites that are actuated by magnetic torquers, reaction wheels or thrusters with a capability of magnetometer vector measurements for attitude and rate estimation.