• 대한인간공학회지
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• 제33권4호
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• pp.281-287
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• 2014

Objective: The objective of the study is to develop a portable assistance device to help elderly users reduce strain on the knee and leg muscle while the elderly are standing up. Background: The pose of standing up from a chair is a basic movement, but the elderly often have difficulty standing up due to their weak muscles. We focus on designing a solution that helps the elderly reduce physical problems and support them standing up. Method: This study consists of three parts. Part I explores the way to reduce the refrain of leg muscle while standing up from a chair. In the process of structural development, we found that the moment is minimized when user pushes down the armrests due to a decrease in the force acting on the center of mass. In part II, a user test of 20 participants was carried out to rank the order of comfort of two stimuli: the chair with fixed armrests and the chair with the four-link mechanism that we created-in three different ways; (1) to stand up without touching armrests, (2) to stand up by pushing down on fixed armrests, and (3) to stand up by pushing down on armrests and being supported by the mechanism. To examine the statistically significant differences among the rank means, a Friedman test was conducted. In part III, we analyze the results of the user test and interview feedbacks, focusing on establishing a design strategy from UPO and visualizing it in 1:1 scale. Results: In part I, we decided to develop the four-link mechanism. The bottom is lifted up as the link rises. In part II, based on the rank data, we empirically found that UPO was assessed as the most comfortable during the stimuli. The thigh angle is smaller and the bottom of UPO is separated from a seat. In part III, after assessing the results and feedbacks, we created a visualization strategy for UPO: light, friendly, and novel. Conclusion: The portable and non-mechanical UPO comprises a four-link system that lifts the user's hips while standing. It can help users avoid knee and leg muscle strain. Its universal design considers the elderly's difficulties. Application: In a future study, combining light and durable material in UPO is expected to increase its usability. And this study is an opportunity to design various types of standing assistance devices.

• 대한치과보철학회지
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• 제41권4호
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• pp.503-518
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• 2003

Statement of problem : There have been previous studies about considerable variations in machining accuracy and consistency in the implant-abutment-screw interfaces. Purpose : The purpose of this study was to evaluate the machining accuracy and consistency of implant/abutment/screw combinations on two randomly selected implants from each of four manufactures. Material and methods : In this study, screws were respectively used to secure a cemented abutment, to a hexlock implant fixture ; teflon coated titanium alloy screw(Torq-Tite) and titanium alloy screw in Steri--Oss system, gold-plated gold-palladium alloy screw(Gold-Tite) and titanium alloy screw in 3i system gild screw ana titanium screw in AVANA Dental Implant system, and titanium screws in Paragon System. The implants were perpendicularly mounted in polymethyl methacrylate autopolymerizing acrylic resin block(Orthodontic resin, Densply International Inc. USA) by use of dental surveyer. Each abutment screw was secured to the implant with recommended torque value using a digital torque controller. Each screw was again tightened after 10 minutes. All samples were cross sectioned with grinder-polisher unit(Omnilap 2000 SBT Inc) after embeded in liquid unsaturated polyester (Epovia, Cray Valley Inc) Results : There were the largest gaps in the neck areas of screws in hexagonal extension implants which were examined in this study. The leading edge of the abutment screw thread (superior surface) was in contact with the implant body thread, and the majority of the contacting surfaces were localized to the middle portion of the mating threads. Considerable variation in the contacting surfaces was noted in the samples evaluated. Amounts of contact in the abutment screw thread were larger for assemblies with Gold-Tite screw, gold alloy screw. Torq-Tite screw than those with titanium screws. The findings of intimate contact between the screw and screw seat were seen in all samples, regardless of manufacturers. However, microgap between the head and lateral neck surface of the screw and the abutment could be dectected in all samples. The findings of intimate contact between the platform of the implant and the bottom of the abutment were consistent in all samples, regardless of manufacturers. However, microgaps between the lateral surface of external hex of the fixture and the abutment could be dectected in all samples. Conclusion : Considerable variations in machining accuracy and consistency were noted in the samples and the implant-abutment-screw interfaces were incomplete. From the results of this study, further development of the system will be required, including improvements in pattern design.

• 대한치과보철학회지
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• 제42권2호
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• pp.192-209
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• 2004

Purpose : The purpose of this study was to evaluate the machining accuracy and consistency of implant/abutment/screw combination or internal connection type. Material and methods: In this study, each two randomly selected internal implant fixtures from ITI, 3i, Avana, Bicon, Friadent, Astra, and Paragon system were used. Each abutment was connected to the implant with 32Ncm torque value using a digital torque controller or tapping. All samples were cross-sectioned with grinder-polisher unit (Omnilap 2000 SBT Inc) after embeded in liquid unsaturated polyester (Epovia, Cray Valley Inc). Then optical microscopic and scanning electron microscopic(SEM) evaluations of the implant-abutment interfaces were conducted to assess quality of fit between the mating components. Results : 1) Generally, the geometry of the internal connection system provided for a precision fit of the implant/abutment into interface. 2) The most precision fit of the implant/abutment interface was provided in the case of Bicon System which has not screw. 3) The fit of the implant/abutment interface was usually good in the case of ITI, 3I and Avana system and the amount of fit of the implant/abutment interface was similar to each other. 4) The fit of the implant/abutment interface was usually good in the case of Friadent, Astra and Paragon system. The case of Astra system with the inclined contacting surface had the most Intimate contact among them. 5) Amount of intimate contact in the abutment screw thread to the mating fixture was larger in assembly with two-piece type which is separated screw from abutment such as Friadent, Astra and Paragon system than in that with one-piece type which is not seperated screw from abutment such as ITI, 3I and Avana system. 6) Amount of contact in the screw and the screw seat of abutment was larger in assembly of Friadent system than in asembly of Astra system of Paragon system. Conclusion: Although a little variation in machining accuracy and consistency was noted in the samples, important features of all internal connection systems were the deep, internal implant-abutment connections which provides intimate contact with the implant walls to resist micro-movement, resulting in a strong stable interface. From the results of this study, further research of the stress distribution according to the design of internal connection system will be required.

• Journal of Biosystems Engineering
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• 제33권4호
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• pp.224-229
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• 2008

This study was aimed to minimize the impact force and vibration transmitted to the transporting materials from the trailer and wheel shaft by installing the leaf spring suspension device at the space between the wheel shaft and frame of power tiller trailer. The developed trailer equipped with leaf spring suspension device was compared to the existing trailer without suspension device, in order to identify the vibration absorption effect of the leaf spring. The results of this study could be summarized as follows; (1) The length and the maximum bending amount of the leaf spring were designed as 1,000 mm and 42 mm, respectively, considering the possible space for installing at below the trailer. When 4 leaf springs were installed on both wheel shafts, the allowable maximum load was identified as 9,418 N. (2) The average vibration accelerations for the frequency less than 20 Hz, where the severe transporting loss could be represented, were $0.017\;m/s^2$ and $0.133\;m/s^2$ for the developed and the existing trailer, respectively, showing the vibration absorption effect of about 87%. And the average vibration accelerations on the driver's seat for the frequency less than 20 Hz were $0.01\;m/s^2$ and $0.20\;m/s^2$ for the developed and the existing trailer, respectively, which showed the similar vibration absorption effect. (3) The change of the average vibration accelerations for the frequency from 20 Hz to 80 Hz showed the similar tendency with the result for the frequency less than 20 Hz, but the effect for developed trailer was reduced slightly. And the effect of vibration absorption for the above 80 Hz was reduced highly. However, by installing the leaf spring suspension device at the trailer, the low frequency below 40 Hz, which could affect on transporting loss severely, could be reduced highly. (4) The maximum vibration acceleration for the frequency less than 20 Hz were $0.027\;m/s^2$ and $1.267\;m/s^2$ for the developed and the existing trailer, respectively. And the change of maximum acceleration between 20 Hz and 120 Hz was showed similar tendency with the result for the frequency less than 20 Hz, but the width of change was reduced highly.

• 한국구조물진단유지관리공학회 논문집
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• 제17권6호
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• pp.145-152
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• 2013

콘크리트는 대표적인 건설재료로서 지난 19세기 후반 이후 각종 구조물의 축조에 활용되고 있다. 콘크리트는 일반적으로 적절한 설계 및 시공 규정을 준수한다면 내구성을 확보하는 것으로 인식되었으나, 구조물의 사용 과정 중에 겪게 되는 각 종 외적 작용으로 인해 수명단축 및 성능저하 현상이 빈번히 나타나고 있으며 더욱이 노후화에 따른 콘크리트 구조물의 성능 저하는 억제할 수 없으며 결국 콘크리트 구조물의 유지관리 측면에서 보수 및 보강은 필요한 실정이다. 본 연구에서는 기존의 보수 및 보강공법의 성능을 개선하고자 콘크리트 표면의 강화 및 특히 내화학 성능의 향상을 위하여 개발되어진 내화학성적층보강공법 (Chemical Resistance of Laminating Reinforcement Method : CRM)을 적용하였다. 따라서 본 연구에서는 콘크리트 시험체에 대한 다양한 내구성 시험을 통하여 일반적인 보수 및 보강공법을 적용한 시험체 와의 비교분석을 통하여 결과를 도출하였으며 시험결과, 기존 보수 및 보강공법보다 CRM을 적용한 콘크리트 시험체의 내구성능이 향상되었는데 이는 에폭시계의 내산섬유보강 및 2중의 섬유계의 보강시트로 인한 적층효과로 판단된다.

• Journal of Welding and Joining
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• 제34권2호
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• pp.1-10
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• 2016

The use of materials for modern lightweight auto-bodies is becoming more complex than hitherto assemblies. The high strength materials nowadays frequently used for more specific fields such as the front and rear sub frames, seat belts and seats are mounted to the assembled body structure using bolt joints. It is desirable to use nuts attached to the assembled sheets by projection welding to decrease the number of loose parts which improves the quality. In this study, nut projection welding was carried out between a nut of both boron steel and carbon steel and ultra-high strength hot-stamped steel sheets. Then, the joints were characterized by optical and scanning electron microscope. The mechanical properties of the joints were evaluated by microhardness measurements and pullout tests. An indigenously designed sample fixture set-up was used for the pull-out tests to induce a tensile load in the weld. The fractography analysis revealed the dominant interfacial fracture between boron steel nut weld which is related to the shrinkage cavity and small size fusion zone. A non-interfacial fracture was observed in carbon steel nut weld, the lower hardness of HAZ caused the initiation of failure and allowed the pull-out failure which have higher in tensile strengths and superior weldability. Hence, the fracture load and failure mode characteristics can be considered as an indication of the weldability of materials in nut projection welding.

• 자원리싸이클링
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• 제26권3호
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• pp.79-91
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• 2017

수소연료전지자동차(FCV)의 핵심은 고분자고체형연료전지(Polymer Solid Fuell Cell: PEFC)이고 전지 중에서 전기화학적 전기를 발생하는 핵심 소재는 백금촉매이다. 백금은 남아프리카와 러시아 등에 편재되어있고, 백금의 세계생산량은 연간 약 178톤이고 고가이므로 리싸이클링 한다. 현재 PEFC에 Pt를 사용하는 양은 $0.2{\sim}0.1mg/cm^2$인데, 전지의 가격을 줄여서 FCV보급을 확대하기 위하여 사용하는 Pt양을 $0.05{\sim}0.03mg/cm^2$까지 감소시키는 것을 목표로 하여 각국이 연구 개발하고 있다. 나노배금 제조기술은 건식법과 습식법으로 크게 나누며 습식환원법을 중심으로 제조하는 방식이 Pt를 제조하는데 유리하다. 나노Pt를 이용하여 폴리올법, 개량형 Cu-UPD/Pt 치환법 및 나노캡슐법 등에 의해 $Pt-Pd/Al_2O_3$, Pt/C, Pt/GCB, Pt/Au/C, PtCo/C, PtPd/C 등의 Pt촉매가 연구 개발되고 있으며, Pt촉매의 활성향상 및 안정화 기술 등이 보고되고 있다. 본고는 나노Pt와 나노Pt촉매의 제조기술 및 폐 촉매의 리사이클링 및 Pt촉매의 응용기술 경향을 조사 분석하였다.

• 한국음향학회지
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• 제36권4호
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• pp.254-260
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• 2017

본 연구는 만석 객석의자 등의 흡음특성 시 활용될 수 있는 표준더미 개발을 위한 기초연구로서 착의량에 따른 인체의 흡음특성을 잔향실법 측정방법을 이용하여 평가하였다. 측정방법은 기존 연구(Conti et al., 2004)에 따라 잔향실 중앙에 1인의 피험자가 서 있는 조건에서, 다양한 소재의 의복착용에 따른 주파수 대역별 흡음면적을 측정하였다. 측정 결과, 겉옷을 제외한 상하의를 착용하였을 때 전주파수대역 평균 흡음면적은 피험자에 따라 $0.25m^2-0.48m^2$의 분포를 보였고, 외투 착용에 따라 $0.38m^2-0.98m^2$의 분포를 보였다. 섬유소재에 따라 폴리에스터 류의 겉옷은 800 Hz - 1 kHz 대역에서 피크 특성을 보였고, 모나 면 소재의 겉옷은 고주파수 대역으로 갈수록 흡음면적이 높아지는 특성을 보였다. 착의량에 따른 흡음면적의 변화는 착용한 의복의 열저항(clo)과 체표면적당 무게로 구분하여 비교하였다.

• 한국항공우주학회지
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• 제40권12호
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• pp.1070-1079
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• 2012

항공기 사고 시 항공기 구조물의 충돌에너지 흡수 특성은 탑승자 생존성 향상을 위해 매우 중요한 요소이다. 일반적으로 항공기의 비상착륙 시 충돌에너지는 착륙장치, 동체 하부 구조물(Subfloor), 좌석을 통해 탑승자에게 흡수/전달되며, 이 세 가지 구성품은 항공기 내추락성에 매우 중요한 구성품이다. 이 구성품들 중 동체 하부 구조물의 충돌 에너지 흡수 특성은 항공기 형식, 구조물의 형태 및 적용된 재료에 따라 결정된다. 따라서 항공기 동체 하부 구조물의 내추락 특성에 관한 연구는 항공기 안전성 향상을 위해 매우 중요한 분야이다. 본 연구에서는 상대적으로 내추락 특성이 취약한 80~90 인승급 리저널항공기 Narrow Body 동체의 내추락 유한요소 모델 구성과 외연적 유한요소해석을 통한 내추락 해석이 수행되었다. 동체 구조의 충돌에너지 흡수 및 좌석 장착점의 가속도 응답 등의 해석 결과 분석을 통해, 내추락 특성 및 성능 평가 과정을 수행하였다.

• 예술인문사회 융합 멀티미디어 논문지
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• 제7권2호
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• pp.437-444
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• 2017

기계구조물 부재의 단면에 구멍이나 또는 단면이 급격히 변화할 경우, 불연속 부분 주위에서 응력집중이 일어나며 파손이 발생하는 주요 원인이 된다. 그 이유는 부재에 작용하는 평균 응력보다 응력집중 부분에서 훨씬 큰 응력이 작용하기 때문이다. 본 논문에서는 시편의 부분 관통 구멍 주위에서 응력해석을 수행하여 구멍을 통과하는 선상의 주응력 차 값을 구하였다. 광탄성에서 최대주응력과 최소주응력의 차이는 등색프린지 차수와 재료의 프린지 상수를 곱한 값을 빛이 통과한 거리 즉, 시편의 두께로 나눈 값과 같다. 즉, 주응력의 차이는 광탄성 프린지 차수와 비례관계가 있으므로 유한요소해석에 의한 주응력 차이의 분포를 광탄성 실험결과에 비교할 수 있다. 유한요소 범용 소프트웨어인 ANSYS Workbench를 이용하였으며 유한요소법으로 해석된 값을 광탄성 실험으로부터 측정된 값과 비교한 결과 유사한 결과를 얻었다. 이로서 유한요소해석 결과는 실험결과와의 비교를 통해 타당성이 입증될 수 있었다. 또한 구멍깊이 변화에 따라 나타나는 응력분포를 사용하여 응력집중계수를 구하였다. 구멍깊이가 증가할수록 응력집중계수는 증가함을 나타냈다.