• Journal of Astronomy and Space Sciences
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• 제35권4호
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• pp.263-277
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• 2018

This paper presents a vision-based relative pose estimation algorithm and its validation through both numerical and hardware experiments. The algorithm and the hardware system were simultaneously designed considering actual experimental conditions. Two estimation techniques were utilized to estimate relative pose; one was a nonlinear least square method for initial estimation, and the other was an extended Kalman Filter for subsequent on-line estimation. A measurement model of the vision sensor and equations of motion including nonlinear perturbations were utilized in the estimation process. Numerical simulations were performed and analyzed for both the autonomous docking and formation flying scenarios. A configuration of LED-based beacons was designed to avoid measurement singularity, and its structural information was implemented in the estimation algorithm. The proposed algorithm was verified again in the experimental environment by using the Autonomous Spacecraft Test Environment for Rendezvous In proXimity (ASTERIX) facility. Additionally, a laser distance meter was added to the estimation algorithm to improve the relative position estimation accuracy. Throughout this study, the performance required for autonomous docking could be presented by confirming the change in estimation accuracy with respect to the level of measurement error. In addition, hardware experiments confirmed the effectiveness of the suggested algorithm and its applicability to actual tasks in the real world.

• 한국산학기술학회논문지
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• 제16권3호
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• pp.2172-2177
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• 2015

상수 모듈러스 오차의 확률을 영으로 줄이는 등화 알고리듬에 결정 궤환 방식이 도입된 DF-MZEP-CME (decision feedback - maximum zero-error probability for constant modulus errors) 알고리듬은 채널 왜곡 보상에서 보다 향상된 성능을 보인다. 그러나 이 DF-MZEP-CME 알고리듬은 기울기 계산에서 샘플 사이즈에 비례하는 계산량을 가지게 되어 구현상 장애요인으로 작용한다. 이 논문에서는 DF-MZEP-CME 알고리듬의 기울기를 반복적으로 추정하도록 하여 계산량이 샘플 사이즈와 무관하게 함으로서 계산량 문제를 해결한다. 샘플 사이즈 N 에 대해 기존 알고리듬이 10N 의 곱셈량을 가지지만 제안한 방식은 샘플 사이즈와 무관하게 단지 20 번의 곱셈을 수행한다. 또한 제안한 방식의 기울기 계산이 초기상태로부터 안정 상태로 넘어갈 때 연속성을 유지하는 것으로 나타나 오차 전파에 예민한 결정 궤환 방식에 매우 적합한 알고리듬으로 판단된다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2002년도 ICCAS
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• pp.45.5-45
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• 2002

In this paper, a quasi-deadbeat minimax estimation (QME) is proposed as a new class of time-domain parameter estimations for deterministic generic linear models. Linearity, quasi-deadbeat property, FIR structure, and independency of the initial parameter information will be required in advance, in addition to a new performance criterion of a worst case gain between the disturbances and the current estimation error. The proposed QME is obtained in a closed form by directly solving an optimization problem. The QME is represented in both a batch form and an iterative form. A fast algorithm for the suggested estimation is also presented, which is remarkable in view...

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2001년도 ICCAS
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• pp.156.4-156
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• 2001

The uncertainties of an atmospheric re-entry flight with respect to stability and controllability are aerodynamic error, measurement error of the angle of attack, variation of dynamic pressure, wind, and trim position of the control surfaces, etc. During hypersonic flight, a future angle of attack is biased from a nominal schedule. In order words, because the angle of attack is estimated from the navigation data, estimation error occurs due to wind, atmospheric density variation, etc. Error models used in this study, include a standard deviation of +-3 sigma, and are the normal distribution of statistics. This paper shows the appraisement of tracking performance onto the reference trajectory, satisfaction of the initial condition of TAEM about the re-entry system.

• Journal of Electrical Engineering and Technology
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• 제13권2호
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• pp.752-760
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• 2018

In this paper, interior permanent magnet synchronous motor (IPMSM) design for sensorless drive, considering magnetic neutral point shift according to magnetic saturation, has been proposed. Sensorless control was divided into a method based on inductance and a method based on back induced voltage. Because induced voltage is very small at zero or low speed, error in rotor initial position estimation may occur. Using the ratio of saliency addresses this problem. When using high-frequency injections at low speed, the rotor's initial position is estimated at the smallest portion of the inductance. IPMSM has the minimum inductance at the d-axis. However, if magnetic saturation leads to magnetic neutral point variation, following the load current change, there is a change in the minimum point of inductance. In this case, it can lead to failure of initial rotor position estimation. As a result, it is essential that the blocking design has an inductance minimum point shift. As such, in this study, an IPMSM design method, by blocking magnetic neutral point change, has been proposed. After determining the inductance profile based on the finite element analysis (FEA), the results of proposed method were verified.

• 전기학회논문지
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• 제60권10호
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• pp.1915-1923
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• 2011

For automated guidance control of a magnetically guided-all wheel steered vehicle, it is necessary to have information about position and orientation of the vehicle, and deviations from the reference path in real time. The magnet reference system considered here consists of three magnetic sensors mounted on the vehicle and magnetic markers, which are non-equidistantly buried in the road. This paper presents an observer to estimate such position and orientation at the center of gravity of the vehicle. This algorithm is based on the simple kinematic model of vehicle and uses the data of wheel velocity, steering angle, and the discrete measurements of marker positions. Since this algorithm requires the exact values of initial states, we have also proposed an algorithm of determining the initial position and orientation from the 16 successive magnet pole data, which are given by the magnetic measurement system(MMS). The proposed algorithm is capable of continuing to estimate for the case that the magnetic sensor fail to measure up to three successive magnets. It is shown through experimental data that the proposed algorithm works well within permissible error range.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 추계학술대회 논문집
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• pp.550-554
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• 2007

A one-dimensional heat transfer model coupled with parameter estimation is developed in this study to predict the effective thermal conductivities of soil formation and borehole resistances from in situ field test data. In this application a new method of using initial ignoring time(IIT) obtained from error estimation is tried and turned out to be successful in determining soil thermal conductivities. The validity of this model is accomplished through comparison of the predicted temperature profiles of the model with the data from laboratory scale experimental setting. Eleven test boreholes were constructed in Ochang, Chungcheong Buk Do, and thermal response test was carried out with each borehole. The results of the in situ tests were analyzed with our 1-D numerical model and compared with the results of line source method. The comparison shows that the thermal properties from line source method is a little lower (${\sim}95%$)than those from numerical method. The reason of such result seems to be the lower thermal conductivity of grout material, which is not counted in line source method.

• Journal of information and communication convergence engineering
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• 제9권3호
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• pp.319-324
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• 2011

In computing the optical flow. Horn and Schunck's method which is a representative algorithm is based on differentiation. But it is difficult to estimate the velocity for a large displacement by this algorithm. To cope with this problem multigrid method has been proposed. In this paper, we have proposed a scaled multigrid algorithm which the initial flow for a level is calculated by the summation of the optimally scaled flow and error flow. The optimally scaled flow is the scaled expanded flow of the previous level, which can generate an estimated second image having the least RMS error with respect to the original second image, and the error flow is the flow between the estimated second image (generated by the optimally scaled flow) and the original second image. The flow for this level is then estimated using the original first and second images and the initial flow for that level. From among the various coarsest starting levels of the multigrid algorithm, we select the one that finally gives the best estimated flow. Better results were achieved using our proposed method compared with Horn and Schunck's method and a conventional multigrid algorithm.

• 제어로봇시스템학회논문지
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• 제14권12호
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• pp.1294-1301
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• 2008

Under passive RFID environment, this paper presents a new localization of a mobile robot traversing over the floor covered with tags, which is superior to existing methods in terms of estimation performance and cost effectiveness. Basically, it is assumed that a mobile robot is traveling along a series of straight line segments, each segment at a certain constant velocity, and that the number of tags sensed by a mobile robot at each sampling instant is at most one. First, for a given line segment with known starting point, the velocity and position of a mobile robot is estimated using the spatial and temporal information acquired from the traversed tag. Some discussions are made on the validity of the basic assumptions and the localization for the initial segment with unknown starting point. Second, for a given tag distribution density, the optimal tag arrangement is considered to reduce the position estimation error as well as to make easy the tag attachment on the floor. After reviewing typical tag arrangements, the pseudorandom tag arrangement is devised inspired from the Sudoku puzzle, a number placement puzzle. Third, through experiments using our passive RFID localization system, the validity and performance of the mobile robot localization proposed in this paper is demonstrated.

• 한국통신학회논문지
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• 제40권2호
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• pp.247-252
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• 2015

영확률을 성능기준으로 하는 적응 알고리듬은 충격성 잡음에 강인함을 나타내며 그 결정 궤환 알고리듬은 심각한 다경로 채널 왜곡을 효과적으로 보상하는 것으로 알려져 있다. 그러나 이러한 결정 궤환 영확률 알고리듬은 각 필터 구역에 대해 매 샘플시간마다 여러 합산 동작을 계산해야하는데 이것이 실제 구현에 장애가 되고 있다. 이 논문에서는 반복적 기울기 추정 방식을 가진 결정 궤환 영확률 알고리듬을 제안하며 이 알고리듬은 기존 계산량 O(N)을 샘플 사이즈 N에 무관한 상수량으로 줄일 수 있음을 보인다. 또한 초기상태와 안정상태의 가중치 갱신이 연속적인 과정으로 이루어져 결정 궤환에서 어떤 기울기 추정 오류 전파도 일으키지 않음을 보인다.