• 한국정밀공학회지
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• 제33권2호
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• pp.139-147
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• 2016

Performances of urethane packing in the hydraulic breaker were analyzed using a finite element method. Because of high temperature and high pressure in the hydraulic breaker, it is better to use urethane rather than rubber as a packing material. We obtained the physical properties of urethane at elevated temperature by the tensile test. We analyzed buffer seal and U-packing maintaining the pressure and preventing oil leakage. Deformation, stress distribution, contact length, contact pressure of packing at each pressure step were obtained using finite element analysis. As the temperature increases, stress and contact force tend to decrease at low pressure. As the gap between piston and cylinder increases, contact length and contact forces decrease. Consequently, it is possible to design the packing section using these analyses, and construct a system to predict the possibility of oil leakage in the hydraulic breaker.

• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2009년도 추계학술발표논문집
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• pp.640-644
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• 2009

현재 태양광 산업에서는 고정식 태양광 발전장치보다 발전 효율이 우수한 추적식 태양광 발전장치를 개발하는 연구가 활발하게 진행되고 있다. 추적식 태양광 발전장치는 고정식에 대비하여 단위면적당 일사량을 최대로 유지할 수 있을 뿐만 아니라, 일조시간을 최대로 하여 태양전지의 발전효율을 극대화할 수 있다. 따라서 정밀하면서도 저렴한 태양위치 추적장치는 태양광 발전사업의 경제성을 높이고, 성능 대비 투자비용을 낮춰 태양광 발전설비의 보급을 촉진시켜줄 수 있는 중요한 기술이다. 본 연구는 태양위치를 감지하는데 센서를 사용하지 않고 천문학과 수학을 이용하여 정밀도 1분($0.016^{\circ}$)이내의 태양위치를 계산하는 알고리즘에 관한 것이다. 본 연구에서 제안하는 알고리즘은 장치의 제작비용을 낮추어 줄 뿐 아니라, 발전효율도 높여준다. 구현된 알고리즘을 적용시킨 추적식 태양광 발전장치를 운용 실측한 결과, 최대 30초($0.0038^{\circ}$)의 오차를 보여 추적식 발전장치의 경제성을 높일 수 있고, 시간복잡도(Time Complexity)와 공간복잡도(Spatial Complexity)가 낮아 실시간 태양 추적장치에 최적임을 확인하였다.

• 한국정밀공학회지
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• 제34권2호
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• pp.145-150
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• 2017

Air brake valves are widely used in automotive braking systems and the Korean automobile industry depends on importing them. Therefore, we should develop the technical expertise for their domestic production. In this study, air brake valves were analyzed that can be used in a variety of automobiles. Computational fluid dynamics analysis, static structural analysis, and hyper-elastic analysis were carried out. Before production of an air brake valve system, the performance of different parts has to be evaluated, for instance by using finite element analysis. The structural stability of the product can be determined using static dynamics. The compression behavior of the O-ring is predictable by nonlinear hyper elastic analysis, although errors are possible due to one-way loading. This simulation study can both save time and reduce costs compared to the development of experimental prototypes.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.487-488
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• 2006

Picosecond (ps) laser micro-machining has emerged as an attractive method of fabricating high-precision microstructures, especially in metals. In this paper, a metallic mold for diffraction gratings is fabricated with a mode-locked 12 Ps $Nd:YVO_4$ laser. Laser pulses with a wavelength of 355nm are irradiated on the surface of NOK 80, a mold material, to generate line patterns. In order to minimize the line width, laser power is set just above the ablation threshold of NOK 80. Results show that the spectrum from the fabricated mold is good enough for some industrial application.

• 한국정밀공학회지
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• 제27권2호
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• pp.13-19
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• 2010

Due to the rapid spread of mobile handheld devices, industrial demands for micro-scale holes with a diameter of even smaller than $10{\mu}m$ in sapphire/silicon wafers have been increasing. Holes in sapphire wafers are for heat dissipation from LEDs; and those in silicon wafers for interlayer communication in three-dimensional integrated circuit (IC). We have developed a sapphire wafer driller equipped with a 532nm laser in which a cooling chuck is employed to minimize local heat accumulation in wafer. Through the optimization of process parameters (pulse energy, repetition rate, number of pulses), quality holes with a diameter of $30{\mu}m$ and a depth of $100{\mu}m$ can be drilled at a rate of 30holes/sec. We also have developed a silicon wafer driller equipped with a 355nm laser. It is able to drill quality through-holes of $15{\mu}m$ in diameter and $150{\mu}m$ in depth at a rate of 100holes/sec.

• 한국정밀공학회지
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• 제26권10호
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• pp.108-115
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• 2009

Although nanosecond pulsed laser drilling and milling are rapid and non-wear processes in micromachining, the quality cannot meet the precision standard due to the recast layer and heat affected zone. On the other hand, electrical discharge machining (EDM) is a well-known high precision machining process in micro scale; however, the low material removal rate (MRR) and tool wear remain as drawbacks. In this paper, hybrid process of laser beam machining (LBM) using nanosecond pulsed laser and micro EDM was studied for micro drilling and milling. While the quality of the micro structure fabricated by this hybrid process remains as high as direct EDM, the machining time and tool wear can be reduced. In addition, variable depth of layer was introduced as an effective method improving efficiency of hybrid milling.

• 한국전자통신학회논문지
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• 제13권1호
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• pp.101-106
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• 2018

본 연구는 산업현장에서 많이 사용되는 솔레노이드의 사용함에 있어서, 정밀한 위치 제어를 위한 제어기 설계의 방법을 제안한다. 먼저 관측기는 외란을 적극 반영하여 상태추정을 할 수 있는 루엔버거 관측기를 설계하고 적절한 이득을 설정한다. 관측된 상태를 바탕으로 분수차수 PD제어기를 설계하여, 위치제어에 적용한 결과 분수차수제어기는 목표량이 다르더라도 거의 동일한 제어성능을 얻을 수 있었다. 또한, 정상상태의 위치 오차가 0.1[%]이내이고, 기동시간이 약 0.05초 이내의 정밀한 위치제어성능 가짐을 확인할 수 있었다.

• 한국광학회지
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• 제18권1호
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• pp.31-36
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• 2007

직경과 초점거리가 수 mm인 카메라폰 렌즈의 성능을 평가하는 변조전달함수(Modulation Transfer Function: MTF) 측정장치를 개발 하였다. 전체 측정장치는 물체부, 상분석부, 렌즈 마운터로 구성되며, 물체부는 비축상 측정을 위하여 회전한다. 렌즈의 정밀한 정렬을 위하여 정밀한 수평형 거치대를 제작하였으며 광축 조정과 렌즈의 기울어짐 등의 문제를 매우 효과적으로 개선하였다. 시험렌즈의 초기정렬이 끝나면 자동으로 MTF를 측정하며 측정시간은 10초 이내이다.

• 한국정밀공학회지
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• 제30권10호
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• pp.1009-1015
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• 2013

Ultra-short laser pulses are effective, when high requirements concerning accuracy, surface roughness and heat affected zone are demanded for surface structuring. In particular, picosecond laser systems that are suited to be operated in industrial environments are of great interest for many practical applications. This paper focused on inducing optimum process parameters for higher volume ablation rate by analyzing a relationship between crater diameter and optical spot size. In detail, the dependency of the volume ablation rate, penetration depth and threshold fluence on the pulse duration 8 ps and wavelength of 515 nm was discussed. The experimental results showed that wavelength of 515 nm resulted in less threshold fluence ($0.075J/cm^2$) on copper than IR wavelength ($0.3J/cm^2$). As a result, it was possible that optimum fluence for higher volume ablation rate was achieved with $0.28J/cm^2$.

• 한국정밀공학회지
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• 제15권9호
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• pp.117-126
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• 1998

For investigating rubber pad sheet metal forming process, the rubber pad deformation characteristics as well as the contact problem of rubber pad-sheet metal has been analyzed. In this paper, the behavior of the rubber deformation is represented by hyper-elastic constitutive relations based on a generalized Mooney-Rivlin model. Finite element procedures for the two-dimensional responses, employing total Lagrangian formulations are implemented in an implicit form. The volumetric incompressibility condition of the rubber deformation is included in the formulation by using penalty method. The sheet metal is characterized by elasto-plastic material with strain hardening effect and analyzed by a commercial code. The contact procedure and interface program between rubber pad and sheet metal are implemented. Inflation experiment of circular rubber pad identifies the behaviour of the rubber pad deformation during the process. The various form dies and scaled down apparatus of the rubber-pad forming process are fabricated for simulating realistic forming process. The obtaining experimental data and FEM solutions were compared. The numerical solutions illustrate fair agreement with experimental results. The forming pressure distribution according to the dimensions of sheet metal and rubber pads, various rubber models and rubber material are also compared and discussed.