• 한국정밀공학회지
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• 제29권3호
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• pp.279-288
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• 2012

The material removal mechanism in machining is significantly affected by the cutting edge geometry. Its effect becomes even more substantial when the depth of cut is relatively small as compared to the characteristic length which represents the shape and size of the cutting edge. Conventionally, radius or focal length has been employed as the characteristic length with the assumption that the shape of cutting edge is round or parabolic. However, in reality, there could be various ways to determine the radius or focal length even for the same tool edge profile, depending on the region to be considered as cutting edge in the measured profile and the constraints to be set in constructing the best fitted circle or parabola. In this regard, the present study proposes various models to determine the characteristic length in terms of radius or focal length. Their physical compatibility are validated by carrying out 2D orthogonal cutting experiments using inserts with a wide range of characteristic length ($30{\sim}180\;{\mu}m$ in terms of radius) and then by investigating the correlation between the characteristic length and the cutting forces. Such validation is based on the common belief that the larger the characteristic length is, the blunter the cutting edge is and the higher the cutting forces are. Interestingly, the results showed that the correlation is higher for the radius or focal length obtained with a constraint that the center of best fitted circle or the focus of the best fitted parabola should be on the bisectional line of the wedge angle of tool.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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• pp.9-14
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• 2002

Ferrule is widely used as fiber optic connecters. In fiber-optic communications, the shape accuracy such as coaxiality and cylindricity of ferrule affects insertion loss. When coaxial grinding of ferrule supported by two pin, pin alignment and chucking accuracy are very important. In this research, the kinematic behavior of the ferrule center is investigated in the case where cone-shaped center pins and round circle hales which make contact with each other near the edge of the holes, using homeogenous coordinate transformation and numerical analysis. The obtained results are as follows: The alignment errors between center pins alone do not affect the rotation accuracy of ferrule. The alignment errors between center holes cause a sinusoidal displacement of ferrule. And the maximum displacement of ferrule centers increase in proportion to the center pin angle in the case of a fixed alignment errors

• 전자공학회논문지C
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• 제34C권10호
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• pp.51-58
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• 1997

In this paper, a technique ot estimate center positions of the circular parts under noisy condition is presented. The circle chords are segmented from the circle with successively varying angle and weighted to reduce the center estimation errors effected by the orientations of the circle chords. The weighting factors for variable length chords are adaptively detemined according to the error contribution of each chord in center estimation. Robust estimation of the center positions of the circular parts are possible even though the edge informations are partially contaminated by the non-uniform lighting or the background textures. Computer simulations for several images which are obtained for same object under real environment y camera, show that the proposed techniqeu yields 1.85 and 2.77 of estimated error-distribution for center position and radius in mean square error, that the proposed has more robust estimation than those of the conventional methods.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.987-991
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• 2003

Ferrule is widely used as fiber optic connecters. In fiber-optic communications, the shape accuracy such as coaxiality and cylindricity of ferrule affects insertion loss. When coaxial grinding of ferrule supported by two pin, pin alignment and chucking accuracy are very important. In this research, the kinematic behavior of the ferrule center is investigated in the case where cone-shaped center pins and round circle holes which make contact with each other near the edge of the holes, using homeogenous coordinate transformation and numerical analysis. The obtained results are as follows: The alignment errors between center holes cause a sinusoidal displacement of ferrule. And the maximum displacement of ferrule centers increase in proportion to the center pin angle. The relationship between center pins displacement in coaxial grinding and grinding accuracy was explained.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2006년도 6th International Meeting on Information Display
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• pp.1306-1310
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• 2006

We conducted visual perception experiments to determine the perception limits of motion blur based on human visual system at LCD TV's moving pictures. The motion blur can be expressed Blurred Edge Width (BEW). The results showed that the BEW of moving pictures should be below 3.4pixels (visual angle 4.2') at 3H distance in a living room environment.

• 한국의학물리학회:학술대회논문집
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• 한국의학물리학회 2003년도 제27회 추계학술대회
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• pp.67-67
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• 2003

It is crucial to minimize setup errors of a cancer treatment machine using a high energy and to perform precise radiation therapy. Usually, port film has been used for verifying errors. The Korea Cancer Center Hospital (KCCH) has manufactured digital electronic portal imaging device (EPID) system to verify treatment machine errors as a Quality Assurance (Q.A) tool. This EPID was consisted of a metal/fluorescent screen, 45$^{\circ}$ mirror, a camera and an image grabber and could display the portal image with near real time KIRAMS has also made the acrylic phantom that has lead line of 1mm width for ligh/radiation field congruence verification and reference points phantom for using as an isocenter on portal image. We acquired portal images of 10$\times$10cm field size with this phantom by EPID and portal film rotating treatment head by 0.3$^{\circ}$, 0.6$^{\circ}$ and 0.9$^{\circ}$. To check field size, we acquired portal images with 18$\times$18cm, 19$\times$19cm and 20$\times$20cm field size with collimator angle 0$^{\circ}$ and 0.5$^{\circ}$ individually. We have performed Flatness comparison by displaying the line intensity from EPID and film images. The 0.6$^{\circ}$ shift of collimator angle was easily observed by edge detection of irradiated field size on EPID image. To the extent of one pixel (0.76mm) difference could be detected. We also have measured field size by finding optimal threshold value, finding isocenter, finding field edge and gauging distance between isocenter and edge. This EPID system could be used as a Q.A tool for checking field size, light/radiation congruence and flatness with a developed video based EPID.

• 한국전자파학회논문지
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• 제19권11호
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• pp.1223-1232
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• 2008

본 논문에서는 비공진형 협벽 도파관 슬롯 배열 설계를 위해 필요한 기준이 되는 단위 슬롯 어드미턴스를 해석적으로 추출하는 방법을 제시하였다. 충분한 개수의 동일 기울임 각을 가지는 교번 슬롯 구조에 대해, 도파관 협벽의 단위 슬롯과 단위 슬롯 양쪽에 이웃한 전송선 부분을 균일한 손실 전송선으로 근사하고, 이로부터 손쉽게 전체의 ABCD 행렬을 계산하여 전체의 시뮬레이션 또는 측정값과 비교함으로써, 손실 전송선의 복소 특성 임피던스와 복소 전파 상수를 구하고 해석 적으로 정규화 된 슬롯 어드미턴스를 추출하였다. 제안한 방법의 타당성을 입증하기 위해, 대역 협벽 도파관 슬롯 배열 설계용으로 제작된 기준 슬롯 도파관 샘플의 정규화 된 슬롯 어드미턴스를 구하고 기존의 방법으로 얻은 값과 비교하여 잘 일치함을 보였다.

• 한국공작기계학회논문집
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• 제10권4호
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• pp.55-64
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• 2001

In this study, hemisphere and cylindrical shapes were machined for different tool paths and machining conditions with ball endmill cutters. Tool deflection, cutting forces and shape accuracy were measured according to the inclination position of the sculptured surface. As the decreasing of inclination position angle, the tool deflection was increased due to the decreased cutting speed when the cutting edge is approaching toward the center. Tool deflection when upward cutting is obtained less than that of downward cutting and down-milling in upward cutting showed the least tool deflection for the sculptured surface. Roundness values were found in least roundness error when down-milling in upward cutting. It is obtained the very little difference between 90。and 45。 of inclination position angle. The best surface roughness value was obtained in upward up-milling and showed different tendency with tool deflection and cutting force. For down-milling, the cutting resistance of the side wall direction is larger than that of feed direction. Therefore, this phenomenon which is received over cutting resistance can be caused of chatter.

• Wind and Structures
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• 제35권3호
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• pp.177-191
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• 2022

Trains emerging on a streamlined bridge-girder may have salient interference effects on the aerodynamic properties of the bridge. The present paper aims at investigating these interferences by wind tunnel measurements, covering surface pressure distributions, near wake profiles, and flow visualizations. Experimental results show that the above interferences can be categorized into two primary effects, i.e., an additional angle of attack (AoA) and an enhancement in flow separation. The additional AoA effect is demonstrated by the upward-moved stagnation point of the oncoming flow, the up-shifted global symmetrical axis of flow around the bridge-girder, and the clockwise-deflected orientation of flow approaching the bridge-girder. Due to this additional AoA effect, the two critical AoAs, where flow around the bridge-girder transits from trailing-edge vortex shedding (TEVS) to impinging leading-edge vortices (ILEV) and from ILEV to leading-edge vortex shedding (LEVS) of the bridge-girder are increased by 4° with respect to the same bridge-girder without trains. On the other hand, the underlying flow physics of the enhancement in flow separation is the large-scale vortices shedding from trains instead of TEVS, ILEV, and LEVS governed the upper half bridge-girder without trains in different ranges of AoA. Because of this enhancement, the mean lift and moment force coefficients, all the three fluctuating force coefficients (drag, lift, and moment), and the aerodynamic span-wise correlation of the bridge-girder are more significant than those without trains.

• 대한족부족관절학회지
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• 제15권3호
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• pp.139-143
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• 2011

Purpose: The purpose of this study was to introduce the 'Matrixplasty' for the treatment of a severely incurved toenail with growth plate deformity and to report our results treating this disease entity. Materials and Methods: Between January 2010 and May 2010, 48 consecutive patients (62 cases) underwent treatment of symptomatic incurved toenails with the 'matrixplasty'. The mean period of time at last follow-up was $14.0{\pm}1.3$ months. The recurrence rate and complication rate were evaluated. An American Orthopedic Foot and Ankle Society (AOFAS) forefoot hallux score was assigned and patients were evaluated at pretreatment and the last follow-up meeting. For evaluation of improvement in toenail shape, the center to edge angle of the toenail was measured at pretreatment and last follow-up. Results: All ingrown toenails healed and the nail deformity was corrected within 3 weeks after the procedure. Among the 62 cases, four cases had recurred by the last follow-up. The mean pretreatment AOFAS forefoot hallux score was $73.1{\pm}12.8$, and it improved to $98.7{\pm}1.1$ by the last follow-up (p<0.01). The mean center to edge angle of the toenail improved from $53.3{\pm}12.9$ degrees to $18.2{\pm}7.4$ degrees by the last follow-up (p<0.01). Minor paronychia, which was managed with local wound dressing and oral antibiotics, was identified in eight cases. Conclusion: Matrixplasty showed excellent clinical results in the treatment of severe incurved toenail (pincer nail) and this procedure also showed great improvement of the deformed toenail and its growth plate.