• 한국항공우주학회지
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• 제36권7호
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• pp.680-687
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• 2008

본 논문에서는 광학방식 헤드 트랙커를 위한 맵 생성 알고리즘과 초기자세 추정기법을 제안한다. 제안한 광학방식 헤드 트랙커는 적외선 스테레오 카메라와 특징점으로 사용되는 적외선 다이오드가 부착된 헬멧으로 구성된다. 광학방식 헤드 트랙커의 경우 발광된 특징점의 중심점을 추적하여 조종사 머리의 자세 및 위치를 추정하기 때문에 이를 고려한 특징점의 정확한 위치정보가 요구된다. 제안한 맵 생성 알고리즘은 적외선 다이오드의 방사 형태를 고려하여 정밀한 특징점의 위치 정보가 포함된 맵 데이터와 머리 좌표계를 생성한다. 또한 초기자세 추정 기법은 헬멧에 부착된 특징점의 패턴을 이용하여 카메라와 머리 사이의 초기 자세와 위치를 빠르게 추정하며 이를 바탕으로 동체인 전투기를 기준으로 하는 머리 움직임을 정확하게 추정할 수 있다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.894-900
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• 2005

A new approach to the straightforward implementation of the unscented filter in a unit quaternion space is proposed for spacecraft attitude estimation. Since the unscented filter is formulated in a vector space and the unit quaternions do not belong to a vector space but lie on a nonlinear manifold, the weighted sum of quaternion samples does not produce a unit quaternion estimate. To overcome this difficulty, a method of weighted mean computation for quaternions is derived in rotational space, leading to a quaternion with unit norm. A quaternion multiplication is used for predicted covariance computation and quaternion update, which makes a quaternion in a filter lie in the unit quaternion space. Since the quaternion process noise increases the uncertainty in attitude orientation, modeling it either as the vector part of a quaternion or as a rotation vector is considered. Simulation results illustrate that the proposed approach successfully estimates spacecraft attitude for large initial errors and high tip-off rates, and modeling the quaternion process noise as a rotation vector is more optimal than handling it as the vector part of a quaternion.

• International Journal of Aeronautical and Space Sciences
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• 제18권3호
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• pp.565-573
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• 2017

This paper presents a multistage in-flight alignment (MIFA) method for a strapdown inertial navigation system (SDINS) suitable for moving vehicles with no initial attitude references. A SDINS mounted on a moving vehicle frequently loses attitude information for many reasons, and it makes solving navigation equations impossible because the true motion is coupled with an undefined vehicle attitude. To determine the attitude in such a situation, MIFA consists of three stages: a coarse horizontal attitude, coarse heading, and fine attitude with adaptive Kalman navigation filter (AKNF) in order. In the coarse horizontal alignment, the pitch and roll are coarsely estimated from the second order damping loop with an input of acceleration differences between the SDINS and GPS. To enhance estimation accuracy, the acceleration is smoothed by a scalar filter to reflect the true dynamics of a vehicle, and the effects of the scalar filter gains are analyzed. Then the coarse heading is determined from the GPS tracking angle and yaw increment of the SDINS. The attitude from these two stages is fed back to the initial values of the AKNF. To reduce the estimated bias errors of inertial sensors, special emphasis is given to the timing synchronization effects for the measurement of AKNF. With various real flight tests using an UH60 helicopter, it is proved that MIFA provides a dramatic position error improvement compared to the conventional gyro compass alignment.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 D
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• pp.2077-2078
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• 2006

This paper describes the development or a closed-loop Strapdown Attitude Reference System (SARS) algorithm integrated filtering estimator for determining attitude reference for railway and aviation system using fuzzy inference. The SARS consists of 3 single-axis rate gyms in conjunction with 2 single-axis accelerometers. For optimal values of fuzzy systems, we utilize on-line scheduling method for initial values and then use genetic algorithms for fine tuning. Implementation using experimental test data of unmanned aerial vehicle has been performed in order to verify the estimation. The proposed fuzzy inference based SARS demonstrate that more accurate performance can be achieved in comparison with conventional one. The estimation results were compared with the on-board vertical gyro as the reference standard.

• 한국정보기술학회 영문논문지
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• 제8권2호
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• pp.101-110
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• 2018

This paper introduces feedback linearization (FL) based adaptive sliding mode control (ASMC) effective against ground effects of the quadrotor UAV. The proposed control has the capability of estimation and effective rejection of those effects by adaptive mechanism, which resulting stable attitude and positioning of the quadrotor. As output variables of quadrotor, x-y-z position and yaw angle are chosen. Dynamic extension of the quadrotor dynamics is obtained for terms of roll and pitch control input to be appeared explicitly in x-y-z dynamics, and then linear feedback control including a ground effect is designed. A sliding mode control (SMC) is designed with a class of FL including higher derivative terms, sliding surfaces for which is designed as a class of integral type of resulting closed loop dynamics. The asymptotic stability of the overall system was assured, based on Lyapunov stability methods. It was evaluated through some simulation that attitude control capability is stable under excessive estimation error for unknown ground effect and initial attitude of roll, pitch, and yaw angle of $30^{\circ}$ in all. Effectiveness of the proposed method was shown for quadrotor system with ground effects.

• 한국측량학회지
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• 제37권6호
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• pp.465-472
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• 2019

사진 촬영 당시의 외부표정요소 추정 방법에는 공선조건식 기반 후방교회법이 널리 사용되지만 초기값을 필요로 하고, 그 값에 민감하다는 단점이 있다. 본 연구에서는 초기값을 필요로 하지 않는 외부표정요소 알고리즘인 쿼터니언 기반 공간후방교회법과 PnP (Perspective-n-Point algorithm)을 소개하고 그 결과를 비교하였다. 두 결과를 비교하기 위하여 일반 스마트폰으로 취득한 영상을 사용하였고, 지상기준점 취득은 본 연구진이 보유하고 있는 하이브리드 MMS (Mobile Mapping System) 점군 자료를 이용하였다. 그 결과, 공선조건식 기반 SPR (Single Photo Resection)을 참값으로 할 때, 쿼터니언 기반 SPR이 PnP 알고리즘에 비해 자세각 추정 정확도가 높았다. 카메라 위치추정의 경우에는 두 알고리즘 모두 지상기준점과 비교했을 때 0.8m 내의 정확도를 보임을 확인하였다.

• International Journal of Control, Automation, and Systems
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• 제5권4호
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• pp.388-396
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• 2007

This paper describes a multipath estimation method for Global Positioning System (GPS) dual frequency carrier phase measurements. Multipath is a major error source in high precision GPS applications, i.e., carrier phase measurements for precise positioning and attitude determinations. In order to estimate and remove multipath at carrier phase measurements, an array GPS antenna system has been used. The known geometry between the antennas is used to estimate multipath parameters. Dual frequency carrier phase measurements increase the redundancy of measurements, so it can reduce the number of antennas. The unscented Kalman filter (UKF) is recently applied to many areas to overcome some of the limitations of the extended Kalman filter (EKF) such as weakness to severe nonlinearity. This paper uses the UKF for estimating multipath parameters. A series of simulations were performed with GPS antenna arrays located on a straight line with one reflector. The geometry information of the antenna array reduces the number of estimated multipath parameters from four to three. Both the EKF and the UKF are used as estimation algorithms and the results of the EKF and the UKF are compared. When the initial parameters are far from true parameters, the UKF shows better performance than the EKF.

• 대한공간정보학회지
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• 제18권2호
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• pp.93-97
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• 2010

본 연구에서는 카메라 자세 정보가 없는 무인헬기에 탑재된 카메라로부터 취득된 연속영상을 등록하기 위한 개량형 KLT기법을 제시하였으며 그 절차는 다음과 같이 구성된다. 초기 특징점은 연속영상에서 모서리점을 검출하고 동적프로그래밍에 의한 특성곡선매칭에 의해 특징점을 추적하였다. 추적된 특징점 중 오류점은 RANSAC추정법에 의해 제거되며 호모그래피이론에 의해 나머지점은 정확한 정합점으로 분류되었다. 영상등록에 의한 편위보정영상모자이크생성은 쌍일차보간법에 의해 생성하였으며, 결과분석을 통해 제시된 방법이 흔들림이 있는 연속영상을 등록하는데 적합한 방법임을 제시하였다.