• Journal of Positioning, Navigation, and Timing
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• v.11 no.1
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• pp.23-28
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• 2022

The eLoran system is a high-power terrestrial navigation system that is recognized as the most appropriate alternative to complement the GNSS's vulnerability to radio frequency interference. Accordingly, Korea has conducted eLoran technology development projects since 2016. The eLoran system developed in Korea provides 20 m positioning accuracy to maritime user in Incheon and Pyeongtaek harbor. To accurately calculate the position with the eLoran signal, it is necessary to apply a compensation method that mitigates the propagation delay. In this paper, we develop the compensation method to mitigate the eLoran signal propagation delay and evaluate the positioning performance in Incheon harbor. The propagation delay due to the terrain characteristics is pre-surveyed and stored in the user receiver. Real-time fluctuations in propagation delay compared to the pre-stored data are mitigated by the temporal correction generated at a nearby differential Loran station. Finally, two performance evaluation tests were performed to verify the positioning accuracy of the Korean eLoran system. The first test took place in December 2020 and the second in April 2021. As a result, the Korean eLoran service has been confirmed to provide 20 m location accuracy without GPS.

• Journal of the Korean Society for Precision Engineering
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• v.34 no.4
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• pp.265-272
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• 2017

Velocity ripple in manufacturing processes reduces productivity and limits the precision of the product. In practice, the frequency and phase of velocity ripples always change minutely, which makes it impossible to compensate for the ripple by simply inserting an opposite feed-forward signal in the system. In this study, an active-phase compensation algorithm was developed to enable the velocity-ripple controller to track the phase change of the ripples in real time. The proposed controller can compensate for the velocity ripple whatever its cause, including disturbance by the torque ripple. The algorithm consists of three functional modules: the velocity-ripple extractor, the synchronized integrator, and the phase shifter. Experimental results showed that the proposed controller clearly reduces velocity ripples with phase variation.

• Proceedings of the KIPE Conference
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• 2000.07a
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• pp.739-743
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• 2000

With significant development of power electronics technology the proliferation of nonlinear loads such as such as static power converters has deteriorated power quality in power transmission distribution systems. Notably voltage harmonics resulting from current harmonies produced by the nonlinear loads have become a serious problem in many systems Moreover momentary interruptions and voltage sags are responsible for many of the power quality problems found in typical industrial plants. Int his paper proposed 3 phase hybrid series active power filter is not only for harmonic compensation but also for harmonic isolation between supply and load and for voltage regulation and imbalance compensation Through computer simulations we have verified the effectiveness of the proposed system.

• Proceedings of the Korean Society of Computer Information Conference
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• 2020.07a
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• pp.375-378
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• 2020

본 연구는 토지 보상비의 추정 모델 개발을 위해서 건설 CALS (Continuous Acquisition & Life-cycle Support) 시스템의 내부데이터와 개별공시지가 및 표준지 공시지가 등의 외부데이터, 그리고 개발된 추정 모델의 고도화를 위한 개별공시가 데이터를 기반으로 생성된 데이터를 활용하였다. 이렇게 수집된 3가지 유형의 데이터를 분석하기 위해서 기존 선형 모델 또는 의사결정나무 (Tree) 기반의 모델상 과적합 오류를 제거할 경우 매우 유용한 알고리즘으로 Decision Tree 기반의 Xgboost 알고리즘을 데이터 분석 방법론으로 토지 보상비 추정 모델 개발에 활용하였다. Xgboost 알고리즘의 고도화를 위해 하이퍼파라미터 튜닝을 적용한 결과, 실제 보상비와 개발된 보상비 추정 모델의 MAPE(Mean Absolute Percentage Error) 범위는 19.5%로 확인하였다.

• Journal of Positioning, Navigation, and Timing
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• v.4 no.4
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• pp.181-186
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• 2015

A High-degree Cubature Kalman Filter (CKF) is proposed to deal with the Strapdown Inertial Navigation System (SDINS) alignment problem. In-flight Alignment (IFA) is an effective method to compensate for attitude errors of the navigation system. While providing precise attitude error compensation, however, the external source aided alignment often creates a nonlinear filtering problem caused by a large misalignment angle. Introduced recently, Cubature Kalman Filter is a suitable technique for various nonlinear problems. In this paper, a higher degree CKF is applied to this accuracy-is-everything SDINS IFA problem. The simulation results show that the proposed technique outperformed a traditional nonlinear filter in terms of precision and alignment time.

• Journal of Institute of Control, Robotics and Systems
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• v.18 no.5
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• pp.502-508
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• 2012

Heliostat, as a concentrator to reflect the incident solar energy to the receiver, is the most important system in the tower-type solar thermal power plant since it determines the efficiency and ultimately the overall performance of solar thermal power plant. Thus, a good sun tracking ability as well as a good optical property of it are required. Heliostat sun tracking system uses usually an open loop control system. Thus the sun tracking error caused by heliostat's geometrical error, optical error and computational error cannot be compensated. Recently use of sun tracking error model to compensate the sun tracking error has been proposed, where the error model is obtained from the measured ones. This work is a development of heliostat sun tracking error measurement and compensation method using BCS (Beam Characterization System). We first developed an image processing system to measure the sun tracking error optically. Then the measured error is modeled in linear polynomial form and neural network form trained by the extended Kalman filter respectively. Finally error models are used to compensate the sun tracking error. We also developed the necessary image processing algorithms so that the heliostat optical properties such as maximum heat flux intensity, heat flux distribution and total reflected heat energy could be analyzed. Experimentally obtained data shows that the heliostat sun tracking accuracy could be dramatically improved using either linear polynomial type error model or neural network type error model. Neural network type error model is somewhat better in improving the sun tracking performance. Nevertheless, since the difference between two error models in compensation of sun tracking error is small, a linear error model is preferred in actual implementation due to its simplicity.

• Journal of Information Management
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• v.38 no.4
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• pp.166-180
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• 2007

The impact of technical innovation upon technical development and production stage in small and medium industry was analyzed through a survey. 54.0% of the respondents answered that employee invention compensation system was 'highly helpful' to technical innovation, while 23% 'important'. 170 of the respondents answered that technical innovation due to employee invention compensation system took place at the stage of 'technical development', while 138 'idea gathering'. That explains that many innovative activities are taking place in the course of idea gathering from customers, competitors and experts; and production stage also requires innovative activities.

• Journal of Mechanical Science and Technology
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• v.15 no.11
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• pp.1482-1489
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• 2001

Thermally-induced errors originating from machine tool errors have received significant attention recently because high speed and precise machining is now the principal trend in manufacturing proce sses using CNC machine tools. Since the thermal error model is generally a function of temperature, the thermal error compensation system contains temperature sensors with the same number of temperature variables. The minimization of the number of variables in the thermal error model can affect the economical efficiency and the possibility of unexpected sensor fault in a error compensation system. This paper presents a thermal error model with minimum number of variables using a fuzzy logic strategy. The proposed method using a fuzzy logic strategy does not require any information about the characteristics of the plant contrary to numerical analysis techniques, but the developed thermal error model guarantees good prediction performance. The proposed modeling method can also be applied to any type of CNC machine tool if a combination of the possible input variables is determined because the error model parameters are only calculated mathematically-based on the number of temperature variables.

• Korean Journal of Construction Engineering and Management
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• v.19 no.3
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• pp.79-88
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• 2018

Construction business VE is classified into design stage VE and construction stage VE. The faster the application, the better the effect. Therefore, the design stage VE was legislated in 2000 and actively applied. However, it is urgent to activate the construction VE, which is complementary to the design VE system. In the meantime, we have made a lot of efforts to activate construction VE by suggesting the necessity of construction VE system, improvement of technology development compensation system, concrete implementation method of construction VE, but it was not effective due to lack of related laws. This study compares and analyzes construction VE system in Korea and abroad for the activation of construction VE after recognizing such domestic reality. A survey of experts in each field of the construction industry was conducted and suggestions for improvement of construction VE system suitable for domestic construction industry were suggested.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.12
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• pp.1067-1076
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• 2016

This paper describes the development of a hybrid-powered wheelchair (HPW) for the elderly. The proposed HPW has novel mechanical and control features compared with conventional powered wheelchairs. An ergonomic back-braking mechanism was designed in order to stop the wheels easily. In terms of control features, the HPW remarkably reduces the muscle power required by combining various assistive functions, such as wheel torque assistance, friction/inertia compensation, gravity compensation, and the one-hand driving algorithm. For wheel torque assistance, strain gauges were attached to the hand-rim in order to measure the wheel torque applied by a human. Gyroscopes and an accelerometer were attached to the wheel and chair respectively for friction and inertia compensation. An inclinometer was attached for gravity compensation and the one-hand driving algorithm was included for patients who can only use one hand. The one-hand driving algorithm controls the angular velocity of the uncontrolled wheel by using a gyroscope and pressure sensors attached to the bottom of the seat. Finally, the performance of the proposed motion assisted algorithm was verified through various experiments.