• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.3
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• pp.31-40
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• 2017

This paper deals with the high precision of GPS measurement reduction and its implementation on near real-time and kinematic mode for those applications requiring centimeter-level precision of the estimated coordinates, even if target stations are a few hundred kilometers away from their references. We designed the system architecture, data streaming and processing scheme. Intensive investigation was performed to determine the characteristics of the GPS medium-range functional model, IGS infrastructure and some exemplary systems. The designed system consisted of streaming and processing units; the former automatically collects GPS data through Ntrip and IGS ultra-rapid products by FTP connection, whereas the latter handles the reduction of GPS observables on static and kinematic mode to a time series of the target stations' 3D coordinates. The data streaming unit was realized by a DOS batch file, perl script and BKG's BNC program, whereas the processing unit was implemented by definition of a process control file of BPE. To assess the functionality and precision of the positional solutions, an experiment was carried out against a network comprising seven GPS stations with baselines ranging from a few hundred up to a thousand kilometers. The results confirmed that the function of the whole system properly operated as designed, with a precision better than ${\pm}1cm$ in each of the positional component with 95% confidence level.

• Journal of Bio-Environment Control
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• v.23 no.1
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• pp.26-30
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• 2014

Purpose of this study was a development of a sprayer arm auto control system that could be operated according to distance from pear trees for automation of pest control. Auto control system included two parts, hardware and software. First, controller was made with an MCU and relay switches. Two types of ultra-sonic sensors were installed to measure distance from pear trees: one on/off type that detect up to 3 m, and the other continuous type providing 0~5 V output corresponding to distance of 0~3 m. Second, an auto control algorithm was developed to control. Each spraying arm was controlled according to the sensor-based distance from the pear trees. And it could dodge obstacles to protect itself. Max and min signal values were eliminated, when five sensor signals was collected, and then signals were averaged to reduce sensor's noises. According to results of field experiment, auto control test result was better than non auto control test result. Spraying rates were 69.25% (left line) and 98.09% (right line) under non auto control mode, because pear trees were not planted uniformly. But, auto control test's results were 92.66% (left line) and 94.64% (right line). Spraying rate was increased by maintaining distance from tree.

• Journal of Broadcast Engineering
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• v.26 no.4
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• pp.409-418
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• 2021

Conformal coating is a technology that protects PCB(Printed Circuit Board) and minimizes PCB failures. Since the defects in the coating are linked to failure of the PCB, the coating surface is examined for air bubbles to satisfy the successful conditions of the conformal coating. In this paper, we propose an algorithm for detecting problematic bubbles in high-risk groups by applying image signal processing. The algorithm consists of finding candidates for problematic bubbles and verifying candidates. Bubbles do not appear in visible light images, but can be visually distinguished from UV(Ultra Violet) light sources. In particular the center of the problematic bubble is dark in brightness and the border is high in brightness. In the paper, these brightness characteristics are called valley and mountain features, and the areas where both characteristics appear at the same time are candidates for problematic bubbles. However, it is necessary to verify candidates because there may be candidates who are not bubbles. In the candidate verification phase, we used convolutional neural network models, and ResNet performed best compared to other models. The algorithms presented in this paper showed the performance of precision 0.805, recall 0.763, and f1-score 0.767, and these results show sufficient potential for bubble test automation.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.10
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• pp.881-887
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• 2014

Micro-sized Peltier coolers are generally employed for uniformly distributing heat generated in the multi-chip packages. These coolers are commonly classified into vertical and planar devices, depending on the heat flow direction and the arrangement of thermoelectric materials on the used substrate. Owing to the strong need for evaluation of performance of thermoelectric modules, at present an establishment of proper theoretical model has been highly required. The design theory for micro-sized thermoelectric cooler should be considered with contact resistance. Cooling performance of these modules was significantly affected by their contact resistance such as electrical and thermal junction. In this paper, we introduce the useful and optimal design model of small dimension thermoelectric module.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.7
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• pp.734-739
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• 2016

The globe valve is a linear motion valve that is designed primarily to stop, start, and regulate flow. The disk of a globe valve can be removed totally from the flow path or it can completely close the flow path. In this study, numerical analysis using ANSYS-CFX was initially performed to predict the flow coefficient and build a prototype model of a globe valve. The flow coefficient is the volume of water at $15.6^{\circ}C$ that will flow per minute through a valve with a pressure drop of 1 psi across the valve. In other words, it is an important factor for determining the size of the valve. From the analysis results, the fluid flux of water and flow coefficient of the valve were extracted. From the numerical results, a prototype of ultra-fine precision control valve, which can regulate the fluid flow of range 0 ~ 0.1 gal per min, was developed. The experimental results were compared with the numerical results using the flow coefficient ($C_v$) graph. From the comparative results, the flow coefficient ($C_v$) error percentage between the numerical and experimental results was very low, which is acceptable, proving that the proposed prototype model is convincing. In addition, it is possible to predict the flow coefficient using only numerical analysis.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.6
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• pp.169-174
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• 2019

Flexure joints are recently used in the ultra-precision mechanism for a telecommunication mirror stage. Flexure joints have several advantages coming from their monolithic characteristics. They can be used to reduce the size of manipulators or to increase the precision of motion. In our research, 6 dof(degree of freedom) mechanism is suggested for micrometer repeatability using a flexure mechanism. To design the 6-dof motion, the 2-dof planar mechanism are designed and assembled to make the 6-dof motion. To achieve a certain performance, it is necessary to define the performance of mechanism that quantifies the characteristics of flexure joints. This paper addresses the analysis and design of the 6-dof parallel manipulator with a flexure joint using a finite element analysis tool. To obtain experimental result, CCD laser displacement sensor is used for the total displacement and the stiffness for the 6-dof flexure mechanism.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.12
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• pp.5412-5419
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• 2011

The need is growing for high-speed spindle because various equipment are becoming more precise, miniaturization and high speed with the development of industries. Air-lubricated dynamic bearings are widely used in the optical lithographic manufacturing of wafers to realize nearly zero friction for the motion of the stage. Air-lubricated dynamic bearing can be used in high-speed, high-precision spindle system and hard disk drive(HDD) because of its advantages such as low frictional loss, low heat generation, averaging effect leading better running accuracy. In the paper, numerical analysis is undertaken to calculate the performance of air-lubricated dynamic bearing with herringbone groove. The static performances of herringbone groove bearings which can be used to support the thrust load are calculated. Electrochemical micro machining($EC{\mu}M$) which is non-contact ultra precision machining method has been developed to fabricate the air-lubricated dynamic bearing and optimum parameters which are inter electrode gap size, concentration of electrolyte, machining time are simulated using numerical analysis program.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.14 no.3
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• pp.36-42
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• 2015

The aspherical lens was designed to be able to array a focal point. For this reason, it has very curved surface. The aspherical lens is fabricated by injection molding or diamond turning machine. With the aspherical lens, tool marks and surface roughness affect the optical characteristics, such as transmissivity. However, it is difficult to polish free form surface shapes uniformly with conventional methods. Therefore, in this paper, the ultra-precision polishing method with MR fluid was used to polish an aspherical lens with 4-axis position control systems. A Tool path and polishing mechanism were developed to polish the aspherical lens shape. An MR polishing experiment was performed using a generated tool path with a PMMA aspherical lens after the turning process. As a result, surface roughness was improved from $R_a=40.99nm$, $R_{max}=357.1nm$ to $R_a=4.54nm$, $R_{max}=35.72nm$. Finally, the MR polishing system can be applied to the finishing process of fabrication of the aspherical lens.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2000.04a
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• pp.151-156
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• 2000

Ultra precision progressive die have used for above one million's lot size of production part. In the field of design and making tool for press working, the progressive die for sheet metal (STS 304, thickness : 0.5mm) is a specific division. In order to prevent the defects, the optimum design of the production part, strip layout, die design, die making and tryout etc. are necessary. They require analysis of many kinds of important factors, i.e. theory and practice of metal press working and its phenomena, die structure, machining condition for die making, die materials, heat treatment of die component, know-how and so on. In this study, we designed and constructed a progressive die of multi-stage and performed try out. Out of these processes the die development could be taken for advance. Especially the result of tryout and its analysis become the characteristics of this paper (part 1 and part 2) that nothing might be ever seen before such as this type of research method on all the processes. In the part 2 of this study we treated die making and tryout mostly.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.9
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• pp.914-923
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• 2009

Helix antennas have been widely applied to satellite TT&C, data communication and GPS receiver systems onboard military, remote sensing and communication purpose satellites. The helix antennas are known to be convenient to control impedance and radiation coverage characteristics with a maximum directivity in satellite z-axis. Waveguide horn is commonly used for radar system that needs ultra-wideband pulse for exploration ground radar and electromagnetic disability measurement etc. It has high efficiency and low reflection characteristics provided by the low-profile shape and suppressed radiation distortion. In this paper, a waveguide horn structure incorporated with helix antenna design is proposed for satellite applications that require ultra-wideband pulse radar and high rate RF data communication link to ground station over wide coverage area. The main design concern is to synthesize variable beam forming pattern based on modified horn-helix combination helicone structure such that multi-mission antenna is implemented applicable for TT&C, earth observation, high data rate transmission. Waveguide horn helps to reduce the overall antenna structure size by introduction fold type reflector connected to the tapered helix antenna. The next generation KOMPSAT satellite currently under development requires high-performance precision attitude control system. We present an initial design of a hybrid hern-helix antenna structure suitable for efficient RF communication module design of multi-purpose satellite systems.