• Smart Structures and Systems
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• 제24권5호
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• pp.649-657
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• 2019

Recently, an advanced video deflectometer based on the principle of off-axis digital image correlation was presented and advocated for remote and real-time deflection monitoring of large engineering structures. In engineering practice, measurement accuracy is one of the most important technical indicators of the video deflectometer. However, it has been observed in many outdoor experiments that data drift often presents in the measured deflection-time curves, which is caused by the instability of imaging system and the unavoidable influences of ambient interferences (e.g., ambient light changes, ambient temperature variations as well as ambient vibrations) in non-laboratory conditions. The non-ideal unstable imaging conditions seriously deteriorate the measurement accuracy of the video deflectometer. In this work, to perform high-accuracy deflection monitoring, potential sources for the drift error are analyzed, and a drift error model is established by considering these error sources. Based on this model, a simple, easy-to-implement yet effective reference point compensation method is proposed for real-time removal of the drift error in measured deflections. The practicality and effectiveness of the proposed method are demonstrated by in-situ deflection monitoring of railway and highway bridges.

• Journal of Positioning, Navigation, and Timing
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• 제12권1호
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• pp.23-35
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• 2023

Korea Augmentation Satellite System (KASS) is a satellite-based augmentation system (SBAS) that provides approach procedure with vertical guidance-I (APV-I) level corrections and integrity information to Korea territory. KASS is used to monitor navigation performance in real-time, and this paper introduces the design, implementation, and verification process of mission monitoring (MIMO) in KASS. MIMO was developed in compliance with the Minimum Operational Performance Standards of the Radio Technical Commission for Aeronautics for Global Positioning System (GPS)/SBAS airborne equipment. In this study, the MIMO system was verified by comparing and analyzing the outputs of reference tools. Additionally, the definition and derivation method of accuracy, integrity, continuity, and availability subject to MIMO were examined. The internal and external interfaces and functions were then designed and implemented. The GPS data pre-processing was minimized during the implementation to evaluate the navigation performance experienced by general users. Subsequently, tests and verification methods were used to compare the obtained results based on reference tools. The test was performed using the KASS dataset, which included GPS and SBAS observations. The decoding performance of the developed MIMO was identical to that of the reference tools. Additionally, the navigation performance was verified by confirming the similarity in trends. As MIMO is a component of KASS used for real-time monitoring of the navigation performance of SBAS, the KASS operator can identify whether an abnormality exists in the navigation performance in real-time. Moreover, the preliminary identification of the abnormal point during the post-processing of data can improve operational efficiency.

• Proceedings of the KIEE Conference
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• 대한전기학회 2001년도 합동 추계학술대회 논문집 정보 및 제어부문
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• pp.53-56
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• 2001

In this paper we discuss a direct satellite broadcasting system for vehicle. The proposed satellite-steering algorithm and controller based on it are designed for a communication and broadcasting system which uses the Mugungwha satellite. The Mugungwha satellite that the proposed system should steer is a geostationary orbit device. The satellite-steering algorithm computes azimuth and elevation with reference to a stationary point on earth. This is extended to a real satellite steering algorithm that considers position and attitude. Real moving position and attitude are represented by latitude, longitude, roll, pitch and yaw. To apply these five pieces of information to the reference satellite steering algorithm, we introduce Euler's degree coordinates that express independently the rotation of each axis relative to an axis. There are two ways a basic algorithm of the antenna of a vehicle can track and orient to satellite. One way is a feedback loop method for broadcasting gain, while the other is a feedback loop method for position and attitude of a vehicle. In the present paper, we design a controller of satellite broadcasting system for a vehicle using an algorithm that combines the two methods. We performed a simulation and experiment to prove effectiveness.

• Journal of Welding and Joining
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• 제8권3호
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• pp.60-69
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• 1990

Plasma arc cutting is a fusion cutting process in which a gas-constricted arc is employed to produce a high-temperature, high-velocity plasma jet on the workpiece. This process provides some advantages such as increased cutting velocity, excellent working accuracy and the ability to cut special materials (widely used stainless steels and Al-alloys, for example), when compared with iconventional oxyfuel gas cutting. From the view point of price and reliability of the power source, plasma arc cutting has also some distinct advantages over laser beam cutting. High-speed machines with NC or CNC systems are needed for the plasma arc or laser beam cutting process, while for oxyfuel gas cutting, low-speed machines with copying templates or optical-shape tracking sensors can be applied. The low price and high flexibility of the microprocessor arc contributing more and more the application of CNC system in the plasma arc cutting process, as in other manufacturing fields. From these points of view, a microprocessor-based plasma arc cutting system was developed by using a reference-pulse system, and its performance was tested. The interpolating routines were programmed in the assembly language for saving the memory volume and improving the compouting speed, which has an intimate relationship with the available cutting velocity.

• Transactions of the Korean Society of Mechanical Engineers A
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• 제20권1호
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• pp.115-126
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• 1996

In the time optimal control problem, bang-bang control has been used becaese it is the theoretical time minimum solution. However, to improve tracking speed performance in the time optimal control, it is important to select a switching point accurately which makes the velocity zero near the target track. But it is not easy to select the swiching point accurately because of the damping coefficient variation and uncertainties of modeling an actual system. The Adaptive model following control(AMFC) is implemented to relieve the difficulty and inconvenience of this task. The AMFC and make the controlled plant follow as closely as possible to a desired reference model whose switching point can be calculated easily and accurately, assuring the error between the states of the reference model and those of the controlled plant appoaches zero. The hybrid control method composed of AMFC and PID is applied to a tracking actuator of the magneto optical disk drive(MODD) in random access devices to improve its slow tracking performance. According to the simulaion and experimental results, the average tracking time as small as 20ms is obtained for a 3.5 magneto-optical disk drive. The AMFC also can be applied for other random access devices to improve the average tracking performance.

• Journal of Korean Society for Geospatial Information Science
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• 제18권2호
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• pp.13-20
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• 2010

Currently, NGII(National Geographic Information Institute) provides VRS(Virtual Reference System) service using 44 CORS(Continuously Operating Reference Stations). Since the VRS provides high-precision coordinate in a short time, the users and applications are expected to be rapidly increasing. The accuracy analysis on the VRS service, however, was not sufficiently performed yet. Therefore, in this study, the VRS data is acquired from various circumstances and its accuracy is analyzed. According to analysis, it was concluded that the VRS could be applied to public control point survey. Furthermore, it was found that the PQ(Position Quality) which represents variance of estimated coordinates rather than GDOP(Geometric Dilution of Precision) is more relevant as a factor to determine the accuracy of coordinates. Based on the analysis of data from four manufacturers (TRIMBLE, MAGELLAN, LECIA, TOPCON), it was confirmed that the standard deviations better than 3cm. Therefore, VRS Survey apply to public control point survey.

• Proceedings of the KSRS Conference
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• 대한원격탐사학회 2005년도 Proceedings of ISRS 2005
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• pp.586-588
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• 2005

The MSC (Multi Spectral Camera) system is a remote sensing payload to obtain high resolution ground image. This system uses lossy image compression method for &Direct mission& that transmit whole image during one contact. But some image degradation occurred especially at high compression ratio. To reduce this degradation, the MSC uses NUC (Non-uniformity Correction) Unit. This unit correct CCD (Charge Coupled Device)'s high-frequency non-uniformity. So high frequency contents of image can be minimized and whole system SNR can be maximized. But NUC has some disadvantage either. It decreases entire system reliability by adding one electronic system. Adding NUC also led to difficulty of electronic design, assembly and testability. In this paper, the comparison is performed between on-orbit non-uniform correction and on ground correction. by evaluating NUC advantage for the point of view of image quality. Using real MSC parameter and proper model, considerable reference point for the system design came to possible.

• Journal of Electrical Engineering and Technology
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• 제11권1호
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• pp.117-124
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• 2016

Solar photovoltaic pumping system is one of most important of renewable energy applications especially in rural areas. Besides, the control strategy for standalone solar pumping system based on induction motor and without DC/DC converter has been widely studied and discussed in the literature. This topology is of great concern due its economic issues, especially when a standard frequency converter (SFCs) with scalar control is used instead of a dedicated PV inverter. This paper proposes an external control module to generate SFCs frequency reference in order to ensure both maximum power point tracking (MPPT). We present method of modeling and control of photovoltaic pumping system based centrifugal pump controlled by new improved incremental conductance in order to optimize the price and operation of pumping system this MPPT algorithm have many advantages like can be eliminate proportional integral controller It is a low cost solution since it requires no additional power equipment. The induction motor driven pump that is powered by a solar array is controlled by the indirect field oriented control (IFOC). The effectiveness of the proposed approach is illustrated by simulations carried out under Matlab Software. The experimental results are compared with simulation results.

• The Transactions of the Korean Institute of Power Electronics
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• 제16권6호
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• pp.594-601
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• 2011

In this paper, a new current controller with the compensation of an unbalance and distorted grid voltages has been proposed. Generally, in the three-phase power system, single phase or nonlinear loads can be connected with the 3 phase linear load simultaneously on the same point of common coupling. Therefore, The source voltage unbalance and distortion problem can be occurred. Under these unbalance and distorted grid voltage conditions, the input current of 3 phase PWM rectifiers also have unbalance and distortion. In this paper, a current controller with the simple Model Reference Adaptive System based unbalance and distorted voltages observer is proposed to get a sinusoidal input current. The performance of the proposed algorithm is verified through the simulation and the experiment.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• 제40권12호
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• pp.1086-1092
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• 2012

It has been studied for DGPS/INS(Differential Global Positioning System/Inertial Navigation System) to offer the more precise and reliable navigation data with the aviation industry development. The flight performance evaluation of navigation system is very significant because the reliability of navigation data directly affect the safety of aircraft. Especially, the high-level navigation system, as DGPS/INS, need more precise flight performance evaluation method. The performance analysis is performed by comparing between the DGPS/INS navigation data and reference trajectory which is more precise than DGPS/INS. The GPS receiver, which is capable of post-processed CDGPS(Carrier-phase DGPS) method, can be used as reference system. Generally, the DGPS/INS is estimated the CG(Center of Gravity) point of aircraft while the reference system is output the position of GPS antenna which is mounted on the outside of aircraft. For this reason, estimated error between DGPS/INS and reference system will include the error due to lever arm. In order to more precise performance evaluation, it is needed to compensate the lever arm. This paper presents procedure and result of flight test which includes lever arm compensation in order to verify reliability and performance of DGPS/INS more precisely.