• 대한기계학회논문집A
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• 제32권9호
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• pp.761-769
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• 2008

The majority of mechanical parts are manufactured by milling machines. Hence, geometrically efficient algorithms for tool path generation and physical considerations for better machining productivity with guarantee of machining safety are the most important issues in milling tasks. In this paper, an optimized path generation algorithm for direction parallel milling which is commonly used in the roughing stage is presented. First of all, a geometrically efficient tool path generation algorithm using an intersection points-graph is introduced. Although the direction parallel tool path obtained from geometric information have been successful to make desirable shape, it seldom consider physical process concerns like cutting forces and chatters. In order to cope with these problems, an optimized tool path, which maintains constant MRR in order to achieve constant cutting forces and to avoid chatter vibrations at all time, is introduced and the result is verified. Additional tool path segments are appended to the basic tool path by using a pixel based simulation technique. The algorithm has been implemented for two dimensional contiguous end milling operations, and cutting tests are conducted by measuring spindle current, which reflects machining situations, to verify the significance of the proposed method.

• 반도체디스플레이기술학회지
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• 제12권2호
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• pp.79-84
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• 2013

Nanoimprint lithography (NIL) is the next generation photolithography process in which the photoresist is dispensed onto the substrate in its liquid form and then imprinted and cured into a desired pattern instead of using traditional optical system. There have been considerable attentions on NIL due to its potential abilities that enable cost-effective and high-throughput nanofabrication to the display device and semiconductor industry. Although one of the current major research trends of NIL is large-area patterning, the technical difficulties to keep the uniformity of the residual layer become severer as the imprinting area increases more and more. In this paper, with the rolling type imprinting process, a mold, placed upon the $2^{nd}$ generation TFT-LCD glass sized substrate($370{\times}470mm^2$), is rolled by a rubber roller to achieve a uniform residual layer. The prediction of residual layer thickness of the photoresist by rolling of the rubber roller is crucial to design the rolling type imprinting process, determine the rubber roller operation conditions-mpressing force & feeding speed, operate smoothly the following etching process, and so forth. First, using the elasticity theory of contact problem and the empirical equation of rubber hardness, the contact length between rubber roller and mold is calculated with consideration of the shape and hardness of rubber roller and the pressing force to rubber roller. Next, using the squeeze flow theory to photoresist flow, the residual layer thickness of the photoresist is calculated with information of the viscosity and initial layer thickness of photoresist, the shape of mold pattern, feeding speed of rubber roller, and the contact length between rubber roller and mold previously calculated. Last, the effects of rubber roller operation conditions, impressing force & feeding speed, on the residual layer thickness are analyzed with consideration of the shape and hardness of rubber roller.

• 한국전기전자재료학회논문지
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• 제27권11호
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• pp.740-745
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• 2014

ZnO nanowires were grown by hydrothermal synthesis process and piezoelectric poly vinylidene fluoride (PVDF) was then coated on top of the ZnO-nanowires by spray-coating technique. The composite layer of ZnO-nanowires/PVDF was applied to an energy harvesting device based on piezoelectric-conversion mechanism. A defined mechanical force was given to the nanogenerator device to evaluate their electric power generation characteristics, where output current density and voltage were examined. Electric power generation property of the ZnO-nanowires/PVDF based nanogenerator device was compared to that of the nanogenerator device with ZnO-nanowires as single active layer. Effect of the ZnO-nanowires on improvement of power generation was discussed to examine its feasibility for the nanogenerator device.

• Journal of Welding and Joining
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• 제21권2호
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• pp.70-75
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• 2003

Spot welding is a process that sheet metals are joined in one or more spot by heating at the faying interface. In this process, the spatter is dispersed from melted area. It has been reported that spatter generation has adverse effects on weld quality. However, no systematic study has been carried out to find out its effect on weld quality in resistance spot welding processes. In this study, specially designed specimen are used to perform experimental investigation of spatter generation and its effect. Major finding of this study show trends in tensile-shear strength for various amounts of spatter generated during spot welding process. Thus, optimum welding conditions are proposed in view of spatter generation and tensile-shear strength. (Received December 11, 2002)

• 한국군사과학기술학회지
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• 제10권3호
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• pp.189-199
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• 2007

The present survey paper introduces the research history, characteristics of body and fin shapes, basic principles of various locomotions and propulsion-generation mechanism of aquatic animals in nature, which utilize unsteady flow through a noble mechanism that is different in paradigm from the propulsion generation mechanism of man-made marine vehicles, and so have excellent performance and efficiency. The authors hope that the present paper helps to activate the domestic research interest on the fields of swimming in nature, which is expected to provide great ideas for improvement and innovation of today's marine vehicles.

• 한국전산구조공학회논문집
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• 제26권2호
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• pp.139-146
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• 2013

본 논문에서는 페러데이 법칙을 이용한 진동발전 장치를 지하철의 자갈도상과 콘크리트 도상의 분류에 따른 기전력 량을 분석 하였다. 지하철 2호선 서초~방배 구간의 자갈도상에서 콘크리트 도상 변경으로 동일한 전동차 운행속도로 동일 구간에서 차량운행에 의한 동특성을 분석하고 진동력발전 장치를 이용해 얻어질 수 있는 기전력 량을 분석하였다. 또한 페러데이의 법칙에 의한 유도 기전력 식에 의한 계산 기전력 량과 발전 장치에 의한 관측 기전력 량을 베이지안 회귀 분석 및 상관분석을 통하여 철도에 적용되는 모델에 대한 신뢰구간과 모델식을 각 도상별로 업데이팅하였다. 수정된 식을 이용한 기전력은 한 개의 진동발전 장치 당 콘크리트 도상에서 4mV, 자갈도상에서는 40mV의 전력을 얻을 수 있다.

• 한국철도학회논문집
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• 제19권4호
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• pp.409-416
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• 2016

팬터그래프와 전차선간의 접촉력 특성은 열차의 집전성능을 나타내는 중요한 특성으로서 국제규격에 따른 엄격한 관리가 필요한 항목이다. 최근에는 소음저감 커버가 고속열차의 팬터그래프 주위에 설치가 되고 있으나 팬터그래프 커버에 의한 접촉력 특성에 대한 연구는 거의 수행되지 않았다. 본 연구에서는 차세대고속열차(HEMU-430X)를 이용하여 팬터그래프 커버가 팬터그래프의 집전성능에 미치는 영향을 동적 접촉력 측정을 통하여 분석하였다. 그 결과 팬터그래프 커버가 부착이 되면 300km/h 주행 시 평균접촉력이 약 50N 낮아짐을 확인하였다. 또한 정적압상력을 제외한 순수한 팬터그래프 커버 유무에 의한 평균접촉력의 차이는 300km/h에서 최대 110N까지 측정되었다. 한편 팬터그래프 커버에 의하여 접촉력 표준편차가 약 3~5N 변화하는 것도 확인하였다.

• 전기학회논문지
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• 제65권5호
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• pp.811-818
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• 2016

This paper suggests a structure of power control system in floating wave-offshore wind hybrid power generation system. We have developed an unified SCADA(Supervisory Control and Data Acquisition) system which can be used to monitor and control PCS(Power Conversion System) based on IEC61850. The SCADA system is essential to perform the algorithm like proportional distribution and data acquisition, monitoring, active power, reactive power control in hybrid power generation system. IEC61850 is an international standard for electrical substation automation systems. It was made to compensate the limitations of the legacy industrial protocols such as Modbus. In order to test the proposed SCADA system and algorithm, we have developed the wind-wave simulator based Modbus. We have designed a protocol conversion device based on real-time Linux for the communication between Modbus and IEC61850. In this study, SCADA system consists of four 3MW class wind turbines and twenty-four 100kW class wave force generator.

• Journal of Mechanical Science and Technology
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• 제19권spc1호
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• pp.395-402
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• 2005

This paper deals with modeling and computer simulation of a full multibody vehicle model for a driving simulator. The multibody vehicle model is based on the recursive formulation and a corresponding simulation code is generated automatically from AUTOCODE, which is a symbolic computation package developed by the authors using MAPLE. The paper describes a procedure for automatically generating a highly efficient simulation code for the full vehicle model, while incorporating realistically modeled components. The following issues have been accounted for in the procedure, including software design for representing a mechanical system in symbolic form as a set of computer data objects, a multibody formulation for systems with various types of connections between bodies, automatic manipulation of symbolic expressions in the multibody formulation, interface design for allowing users to describe unconventional force-and torque-producing components, and a method for accommodating external computer subroutines that may have already been developed. The effectiveness and efficiency of the proposed method have been demonstrated by the simulation code developed and implemented for driving simulation.

• Transactions on Electrical and Electronic Materials
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• 제16권1호
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• pp.37-41
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• 2015

The most common structure of the current transformer (CT) consists of a length of wire wrapped many times around a silicon steel ring passed over the circuit being measured. Therefore, the primary circuit of CT consists of a single turn of the conductor, with a secondary circuit of many tens or hundreds of turns. The primary winding may be a permanent part of the current transformer, with a heavy copper bar to carry the current through the magnetic core. However, when the large current flows into a wire, it is difficult to measure its magnitude of current because the core is saturated and the core shows magnetic nonlinear characteristics. Therefore, we proposed a newly designed CT which has an air gap in the core to decrease the generated magnetic flux. Adding the air gap in the magnetic path increases the total magnetic reluctance against the same magnetic motive force (MMF). Using a ferrite core instead of steel also causes the generation of low magnetic flux. These features can protect the magnetic saturation of the CT core compared with the steel core. This technique can help the design of the CT to obtain a special shape and size.