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Noise Covariance Adaptation of Doppler Velocity Log Considering Vehicle’s Attitude
Jaehyuck Cha,Hojin Ju,Chan Gook Park,Kijeong Yoo,Chanju Park 제어로봇시스템학회 2018 제어로봇시스템학회 국제학술대회 논문집 Vol.2018 No.10
Doppler velocity Log (DVL) is a sensor offering velocity information. This paper analyzes the error characteristics of DVL measurements and proposes a noise covariance adaptation method by using the vehicle’s attitude information. For the successful operation of various marine vehicles, proper navigation systems are required. Inertial navigation system (INS) is usually adopted as a main navigation system in many applications, but it has a characteristic of cumulatively increasing error with time. However, the errors can be suppressed by using another sensor such as DVL. The accuracy of DVL measurements is dependent to the distances to the sea floor along the transducer axes, and each distance is a function of the vehicle’s attitude. The analysis is verified by computer simulations, and the result shows that the proposed method decreases the navigation errors.
Jaehyuck Cha,Jeong Ho Hwang,Chan Gook Park 제어로봇시스템학회 2021 제어로봇시스템학회 국제학술대회 논문집 Vol.2021 No.10
This paper proposes an invariant extended Kalman filter (IEKF) to which an adaptive fading scheme is applied as an initial alignment technique for marine vehicles in mooring condition. In the presence of wave disturbance, the coarse alignment accuracy decreases, which affects the initial attitude estimation error of the fine alignment. Accordingly, the IEKF robust to the large initial errors is applied during the fine alignment process. Moreover, the accuracy of zero velocity updates (ZUPT) decreases because they have non-zero translational velocity under the influence of waves. Thus, the performance of the conventional EKF using a fixed measurement covariance is degraded. In this paper, the adaptive fading scheme adjusting Kalman gain is applied to the IEKF to accelerate the convergence rate. The proposed method is verified by numerical simulation.
Coarse Alignment of Lunar Exploration Rover Using Accelerometer and Sun Sensor
Jaehyuck Cha,Sejong Heo,Chan Gook Park 제어로봇시스템학회 2017 제어로봇시스템학회 국제학술대회 논문집 Vol.2017 No.10
Lunar rover plays a key role in lunar exploration based on its maneuverability. For the successful operation of the lunar rover, a high-accuracy navigation technique has to be obtained. In order to perform high-accuracy inertial navigation, the accuracy of initial alignment is important. In general, initial alignment can be divided into two processes, coarse and fine alignment. In the general coarse alignment process, the acceleration and rotation rate of the stationary rover are used as reference vectors. However, the acceleration and rotation rate of the Moon are 1/6 and 1/27 times smaller than those of the Earth, respectively. As a result, even though the same sensors are used, the performance of initial coarse alignment gets worse on the Moon. In this paper, three coarse alignment methods using accelerometers and sun sensor, instead of accelerometers and gyros, are proposed and the associated errors are analyzed. For comparison, the existing general coarse alignment algorithms are summarized. The analyses are verified by appropriate computer simulations, and it shows that the proposed algorithms greatly improve the performance of coarse alignment, outperforming the existing algorithms at least on the Moon. Therefore, the proposed algorithm is suitable for lunar rover application, and can also be applied to other planetary explorations.
고 해상도 버퍼 설계를 통한 전달 정렬의 측정치 시간 지연 보상 기법
차재혁(Jaehyuck Cha),박찬국(Chan Gook Park),김광훈(Kwanghoon Kim),권승복(Seungbok Kwon) 제어로봇시스템학회 2022 제어·로봇·시스템학회 논문지 Vol.28 No.4
In this paper, we propose a time delay compensation method for transfer alignment using a high-resolution buffer design. Time delay degrades the performance of transfer alignment, resulting in subsequent mission failure. The value of such a time delay may not be constant and varies indefinitely depending on the system configuration or operating environment, which reduces the time delay estimation performance using general Kalman filtering. Using a state buffer is one of the methods to solve this problem. This paper presents a new time delay estimation method using a time delay candidate buffer. The proposed scheme can finely set the interval of time delay candidates and does not require a separate memory. In addition, a method for designing an appropriate time delay candidate buffer interval according to the activation of a vehicle and the performance of the MINS is presented. Simulations verified that the proposed technique could reduce the memory requirement and improve the transfer alignment performance for finely changing the time delay.
차재혁(Jaehyuck Cha),허세종(Sejong Heo),박찬국(Chan-Gook Park) 한국항공우주학회 2017 韓國航空宇宙學會誌 Vol.45 No.10
달 탐사에 있어 로버 활용의 필요성은 (구)소련과 중국의 사례와 미국의 수차례에 걸친 화성 탐사로 인해 입증되었다. 달 탐사 로버의 성공적인 운용을 위해서는 높은 정밀도의 항법 성능이 요구되며, 이를 위해서는 높은 정밀도의 초기 정렬이 필수적이다. 일반적으로는 단일 위치 정렬을 수행하나, 높은 수준의 초기 정렬 성능이 필요한 경우 다중위치 정렬을 수행한다. 하지만, 달 환경의 제약으로 인해 달 탐사 로버의 초기 정렬 성능은 지구환경에 비하여 떨어지게 되며, 이는 다중위치 정렬을 수행하여도 극복할 수 없다. 따라서 본 논문에서는 태양 센서를 보조로 활용한 달 환경에서의 다중위치 정렬 기법을 제안한다. 태양 벡터의 측정치 모델을 구성하고, 이에 대한 가관측성 분석을 수행하였다. 컴퓨터 시뮬레이션을 통해 제안한 알고리즘의 성능을 분석하였고, 그 결과 초기 자세 추정 성능이 크게 향상되었음을 확인하였다. In lunar exploration, the necessity of utilizing rover is verified by the examples of the Soviet Union and China and the similar Mars missions of the United States. In order to achieve the successful management of a lunar rover, a high precision navigation technique is required, and accordingly, high precision initial alignment is essential. Even though it is general to perform initial alignment in a steady state, a multiposition alignment technique is applied when high performance is needed. On the lunar surface, however, the performance of initial alignment decreases from that on Earth, and it cannot be improved by applying multiposition alignment method owing to certain constraints of lunar environment. In this paper, a sun sensor aided multiposition alignment technique is proposed. The measurement model for a sun vector is established, and its observability analysis is performed. The performance of the proposed algorithm is verified through computer simulations, and the results show the estimation performance is improved dramatically.
Bacterial Cell Manipulation Inside an Evaporating Droplet Using Dielectrophoresis
유재혁(Jaehyuck Yoo),이수진(Sujin Lee),차미선(Misun Cha),이정훈(Junghoon Lee) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Concentration of Escherichia coli (E. coli) cells in 1 ㎕ droplet of water was detected by depositing them on an array of electrodes using dielectrophoresis (DEP). Electrowetting was used to effectively concentrate the E. coli in a droplet of water which dried out during the DEP deposition, enabling a simple but powerful system without complicated microfluidic components. By measuring the capacitance after the deposition and evaporation, it was possible to quantitatively evaluate the cell population correlated with the concentration.