• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.1942_1943
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• 2009

무선통신 시스템의 소형화와 저가격, 고품질, 다기능 재료 및 첨단 가공 기술과 연계된 필터설계 및 제작 기술에 대한 연구가 활발히 진행 중이다. 그러나 무선통신 시스템은 주파수라는 한정된 자원을 사용하기 때문에 주파수 자원의 효율적 관리를 위한 규제나 방안이 필요하고. 이에 따라서 여러 가지 대책과 방안이 필요로 하고 있다. 그래서 필터의 성능개선을 위한 연구가 본질 적으로 중요하게 되었다. 본 논문은 체비세프(Chebyshev)필터와 버터워스(Butterworth)필터를 이용한 대역통과(band pass) 필터를 제안한다. 이 필터는 안정화된 통과대역과 빠른 주파수 응답을 얻기위해 6차 체비세프필터와 8차 버터워스필터를 결합 하였다. 측정된 대역통과 필터는, 차단 영역을 구분하는 스커트(skirt)특성은 날카롭게(sharp) 되었고 통과대역의 평탄도 또한 개선되어짐을 볼 수 있다. 제안된 필터의 중심주파수는 2.5GHz, 대역폭은 200MHz이고, 대역내 평탄도는 0.5dB, 경사도는 오차가 60dB일때 체비세프는 210MHz, 버터워스는 340MHz, 체비세프-버터워스는 290MHz가 되어 버터워스 보다 좋게 되었으며 극점의 배치도 안정적인 결과를 얻었다.

• 대한기계학회논문집A
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• 제35권12호
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• pp.1647-1653
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• 2011

일반적으로 사출금형의 사출주기는 플라스틱 제품의 냉각 시간에 크게 좌우되는 데, 냉각회로를 적용하여 조절할 수 있다. 금형의 냉각회로는 전통적으로 기계가공을 통하여, 직선형상만을 생성할 수 있었지만, 최근 적층조형 방법의 개발로 코어 형상을 따라가는 형상적응형 냉각회로를 생성할 수 있게 되었다. 한편 금형의 다이 재질로 열저항력이 크고, 치수변화가 적은 H13 스틸이 널리 사용되고 있지만, 열전도율이 낮기 때문에 냉각효율은 높지 않다. 이러한 점에서 열전달 효율을 극대화 시킬 수 있는 방법으로 H13 스틸과 구리(Cu)를 기능적으로 혼합한 기능성 경사 복합재(FGM)를 적층조형을 이용하여 냉각회로에 적용하는 방안이 검토되고 있다. 이러한 시도로서 본 논문에서는 H13 스틸과 Cu 간의 FGM을 이용한 형상적응형 냉각회로의 모델링 방법을 제안하고자 한다.

• Journal of the Korean Wood Science and Technology
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• 제41권1호
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• pp.42-50
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• 2013

1980년대 중반 이후 국내 생산이 시작된 온돌마루(이하 합판마루)는 종전의 주택용 바닥재(PVC 바닥재)의 대체재로서 일반 소비자들의 폭발적인 수요를 얻어왔다. 그러나 최근 마루판 산업은 건축경기 악화 및 산업 환경의 변화로 인한 수요의 감소와 그에 따른 생산율의 저하 등의 근본적인 문제점이 있다. 최근 마루판용 합판의 원재료로 주로 사용된 동남아산 수종의 고갈 및 변화로 인한 양질의 합판원재료 확보가 어려워졌다. 이에 대한 대응책으로 중국산 유칼립투스를 원재료로 부분적으로 이용한 마루판용 합판의 대체이용이 시도되고 있다. 본 연구에서는 유칼립투스 단판을 부심판으로 제조한 복합합판의 마루판용 합판의 원재료로서의 사용 가능성을 실험을 통해 비교분석하였으며, 모든 단판이 동남아산 Meranti로 구성된 합판을 대조군으로 설정했다. 변형에 영향을 미치는 인자로 단판 간 밀도차이와 합판의 밀도경사를 이용하였다. 본 연구의 실험결과는 다음과 같다. 1) 남양재 시험편은 병판의 밀도가 다른 단판의 밀도보다 큰 M자형의 밀도경사, 유칼립투스 시험편은 반대성향의 W자형의 밀도경사를 나타내었다. 2) 종류에 따른 마루판의 변형은 마루 가공 시험편이 합판상태로 가공을 한 경우보다 최소 0.1~최대 6.25 mm 적게 나타났으며, Density Profile 측정 결과 단판 간의 밀도차가 클수록 변형이 많이 발생하였다.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2001년도 추계학술대회(한국공작기계학회)
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• pp.393-398
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• 2001

The technique of high speed machining is widely studied in machining fields, because the high efficiency and accuracy in machining can be obtained in high speed machining. Unfortunately the development of tool for high speed machining in not close behind that of machine tool. In this study, several types flat endmill is prepared for obtaining data according to tool shape. Especially, we concentrated in helix angle, number of cutting edge, rake angle and relief angle. Machinability is measured by cutting force, tool life, tool wear, chip shape and surface roughness according to cutting length. 3-axis cutting forces are acquired from the invented tool dynamometer for high speed machining. Particularly, we found out that the axial cutting force waveform has a good relation with tool wear features. By above results, it is suggested the endmill tool with $45^{\circ}$ helix angle, 6 cutting edge, $-15^{\circ}$ rake angle and $12^{\circ}$ relief angle be suitable for high speed machining

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.206-209
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• 2005

It was investigated that two rods of aluminium can be welded by hot extru-pressure welding method with stepped welding dies, and that the welding pressure on the welding surface were analyzed by computer simulation according to the stepped shapes of welding dies. It was known by computer simulation that welding pressure on the welding section of rods welded using stepped welding dies without eccentricity is lowerer than the welding pressure of rods welded using stepped welding dies with eccentricity of welding surface, and that the welding pressure on the welding section of rods using eccentric-inclined stepped welding dies is higher than the welding pressure of rods using stepped welding dies without eccentricity. And it was known by experiments that two rods of aluminium can be welded on the end sections by hot pressure welding method using eccentric-inclined stepped welding dies without relative rotational movement of contacted aluminium rods needed for the purpose of friction heating and pressure.

• 한국염색가공학회지
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• 제29권3호
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• pp.139-147
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• 2017

In this study, interesting area of development is retro-reflective thin film and then slitting to form retro-reflective material to be conbined with other fibers to form having retro-reflective characteristics, which slitting yarn can then be to provide fabrics. Glass beads are microscopic spherical size with diameters ranging from several microns to several millimeters. Applying the effects of optical property, glass beads are consumed for road safety used to make traffic signs, safety clothing and others. Glass beads retro-reflective films can be turned into slit yarns through slitting yarn process. The slit yarns can be combined into textiles using diverse methods such as weaving to provide a fabric having retro-reflective characteristics. Lightness and Luminance was increased with decreasing of interval of slit yarn in the fabric. Also, the hue is shifted greenish and bluish with interval of slit yarn.

• 대한기계학회논문집
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• 제19권9호
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• pp.2089-2104
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• 1995

A novel and efficient cutter path planning method for machining intricately shaped curved surfaces, called the steepest directed tree method, is presented. The curved surface is defined by triangular facets, the density and structure of which are determined by the intricacy and form accuracy of the surface. Geometrical form definition and recognition of the topological features are used to connect the nodes of the triangulated surface meshes for the successive and interconnected steepest pathways, which makes good use of end milling characteristics. The planetary cutter centers are determined to locate along smoothly changing paths and then the height values of the cutter are adjusted to avoid surface interference. Several machined examples of intersecting and intricate surfaces are presented to illustrate the benefits of the new approach. It is shown that due to more consistent geometry matching between cutter and surface(in comparison with the current CC Cartesian method) surface finish can be typically improved. Moreover, the material in concave fillets which is difficult to be removed by ball mills can be removed efficiently. The built-in positioning of cutter to avoid interference runs minutely in the sharp and discontinuous regions. The steepest upward movement of the cutter gives a stable dynamic cutting state and allows increase in the feedrate and spindle speed while remaining the stable cutting state.

• 한국기계가공학회지
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• 제13권6호
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• pp.88-98
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• 2014

A moving mass on a skewed linear guideway model to analyze the friction-induced stick-slip behavior of ball-screw-driven slides is proposed. To describe the friction force, a friction coefficient function is modelled as a third-order polynomial of the relative velocity between the slide mass and a guideway. A nonlinear differential equation of motion is derived and an approximate solution is obtained using a perturbation method for the amplitudes and base frequencies of both pure-slip and stick-slip oscillations. The results are presented with time responses, phase plots, and amplitude plots, which are compared adequately with those obtained by Runge Kutta 4th-order numerical integration, as long as the difference between the static and kinematic friction coefficients is small. However, errors in the results by the approximate solution increase and are not negligible if the difference between the friction coefficients exceeds approximately 40% of the static friction coefficient.

• 한국기계가공학회지
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• 제12권6호
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• pp.77-83
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• 2013

Orthodontics is a branch of dentistry that is concerned with the study and treatment of malocclusion, which may result from tooth irregularities, disproportionate jaw relationships, or both. Orthodontic devices consist of brackets, archwire connected to each bracket, and bends and hooks for auxiliary functions. Basically, orthodontics involves the interaction of brackets and archwire. It should be noted that uncontrolled tipping can occur due to unwanted movement of the teeth. The bending of an archwire can control the angle of an archwire and the rotation of a tooth. In this study, we predict the relationship between the bending angle of an archwire and the rotation of a tooth using the Kriging interpolation method. Also, we calculate the angle of an archwire that occurs at the minimum value of tooth rotation.

• 소성∙가공
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• 제23권5호
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• pp.303-310
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• 2014

Functionally graded properties are characterized by the gradual variation in composition and structure through the volume of the material, resulting in corresponding gradation in properties of the material. Direct laser melting (DLM) is a prototyping process whereby a 3-D part is built layer-wise by melting metal powder with laser scanning. Studies have been performed on the functionally graded properties induced by direct laser melting of compositionally selected metallic powders. For the current study, quadrangle structures were fabricated by DLM using Fe-Ni-Cr powders having variable compositions. Hardness and EDX analysis were conducted on cross-sections of the fabricated structure to characterize the properties. From the analysis, it is shown that functionally graded properties can be successfully obtained by DLM of selected metallic powders with varying compositions.