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Optimization of Pivot Obliquity for a Foldable Bicycle
형준호,노종련,김사엽 한국정밀공학회 2016 International Journal of Precision Engineering and Vol.17 No.7
The folding technology which enables bicycle to be carried and stored easily is divided into various folding mechanism according to the number of hinges and the direction of pivot axis. The single lateral pivot type foldable bicycle is considered a promising personal mobility since it allows quick and easy folding motion and access to public transit system. However, there are significant troubles in folding dimensions that both the front and rear wheels are arranged in a slanted way, and the folding width increases at the bottom. It is because the pivot axis is slanted from the exact lateral axis so that the interference between the front and rear wheel in the course of folding could be prevented. This study aims at designing the optimal pivot obliquity of a lateral pivot type of foldable bicycles to align both the front and rear wheels in parallel. The variables of the pivot axis obliquity were set as the azimuthal angle (ϕ) and polar angle (θ), and a parametric simulation was carried out. It is revealed that the azimuthal angle affect the alignment angle between the front and rear wheels, and optimal azimuthal angle could be derived which makes the alignment angle to 0o. The findings from this study will contribute to the popularization of foldable bicycles with excellent usability and smaller folding width.
Influence of a Gait-Pattern-Based Crank Drive System on Knee Joint Load During Stand-Up Cycling
형준호,Jongryun Roh,김사엽 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.20 No.5
This study proposes a crank drive system that considers gait characteristics and is without dead points (GP-crank) to decrease the knee joint load for stand-up bicycles. A comparative experiment was conducted from the perspective of cycling kinematics to investigate the differences between the proposed GP-crank and conventional crank drive systems. The pedaling motion was analyzed by measuring the three-dimensional movements and pedal reaction forces of 16 subjects driving cranks in a standing posture. Although no significant differences were found in the peak pedal reaction force, flexion angle of the lower limb joints, and joint flexion moments between the drive systems, the vertical displacement of the center of body mass was significantly smaller for the GP-crank. In addition, the knee joint was extended for the GP-crank at the time the knee moment reached its maximum. Consequently, decreased knee joint stress of the GP-crank was demonstrated by its comparatively reduced vertical displacement of the center of body mass and stress on the knee joint. This study shows that the disadvantages of existing stand-up bicycles can be addressed by using the proposed GP-crank.
사이클링 시 페달각도와 족관절 각도의 관계에 대한 시뮬레이션 연구
형준호,김사엽,정경렬 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.4
사이클링 시 족관절각도의 운동학적 연구는 많이 진행되지 않았다. 사이클링시 족관절각도 변화는 정량적으로 통제하기가 어려워 실험적인 연구가 어렵다는 한계가 있다. 이에 본 연구에서는 인체모델을 이용하여 페달이 일회전하는 동안 페달각도의 변화폭이 족관절각도 변화폭과 경기에 미치는 영향을 고찰해 보았다. 페달각도 변화폭을 20°부터 60°까지 5단계로 설정하고 시뮬레이션을 수행하여 족관절각도의 변화폭을 측정하였다. 시뮬레이션 결과 페달각도 변화폭이 작아질수록 족관절각도 변화폭은 커지고 동시에 발목신전근인 가자미근에 작용하는 텐션은 작아져 효과적인 근육 동원이 이루어졌다. 이 같은 결과는 성적이 우수한 선수일수록 사이클링 시 족관절각도 변화폭이 크게 나타난다는 기존연구와 일치하여 인체모델을 이용한 시뮬레이션 연구의 유용성을 보여주었다. There have been few researches on cycling postures particularly concerning with the variation of ankle angle. It is difficult to control the ankle joint of cyclist so the experimental study has its limitation. In this study mathematical human model was used to simulating the relationship between the variation of pedal angle and the variation of ankle angle during cycling. Five steps of variation of pedal angle were set up from 20 to 60 degree and the variation of ankle angle was calculated during cycling simulation. The results say that the smaller variation of pedal angle is, the greater variation of ankle angle was shown. And also the tension of soleus muscle which is ankle extensor was small. This result was corresponding to the existing study and this means human model was effective in cycling study.
형준호,노종련,최준호 대한기계학회 2022 大韓機械學會論文集A Vol.46 No.10
Swing beds to improve human sleep are emerging as promising commercial products. The crank device inducing the reciprocating swing motion in the existing products has a mechanical problem that makes it difficult to commercialize. In this study, a swing mechanism with a circular translational motion without dead-point was adopted. An over-constrained crank system was applied. A double-cone-shaped special roller whose rolling behavior matches with the circular translational motion of the crank was designed to diminish friction at high axial loads. Finally, the degree of smoothness of motion was numerically confirmed by measuring the rotation torque of a manufactured prototype. Clinical research on the effect of the developed swing bed on human sleep will be conducted in the future.
Hot Filament CVD에 의해서 증착된 다이아몬드 박막의 표면형상에 미치는 기판온도의 영향
형준호,조해석 한국결정학회 1995 韓國結晶學會誌 Vol.6 No.1
Hot Filament CVD법에 의해 증착된 다이아몬드 박막의 기판온도와 증착시간 변화에 따르는 표면형상 변화를 관찰함으로써 그 증착기구를 규명하고자 하였다. 기판온도가 낮을 경우에는 비정질 탄소 및 DLC(diamond like carbon)가 증착되고 기판온도가 증가함에 따라 사가형의 (100)명으로 구성된 입자를 가지는 다이아몬드 박막이 증착되었으며 매우 높은 기판온도에서는 (100)명과 (111)명으로 이루어진 결정외형을 가지는 입자들로 구성되는 다이아몬드 박막이 증착되었다. 다이아몬드 박막의 (100) 우선배향성은 증착시의 비교적 높은 과포화도에 기인하는 것으로 생각되며, 이러한 (100) 우선배향성을 가지는 박막은 결정면내에 twin을 함유하지 않으므로 단결정박막으로의 성장가능성이 크다. 기판온도가 증가해도 다이아몬드 박막의 입자크기는 증가하지 않았으며 시간에 따른 증가양상도 온도에 관계없이 비슷한 경향을 보였다. 그러나 필라멘트 온도가 일정할 때 다이아몬드 박막의 핵 밀도는 기판온도가 높을수록 증가하였으며 시간에 따른 증가폭도 기판온도가 높을수록 더 크게 나타났다. The growth mechanism of diamond thin films, deposited by Hot Filament CVD, was investigated through observation of changes in their surface morphology as a function of the substance temperature and deposition time. Amorphous carbon or DLC thin films were deposited at low substrate temperature. Diamond films consisting of square-shaped particles, whose surfaces are (100) planes, were deposited at an intermedate temperature. At high substrate temperatures, diamond films consisting of the particles showing both (100) and (111) plane were deposited. The (100) proferred orientation of the diamond films are believed to be due to a relatively high supersaturation during deposition, and the growth condition for the diamond films having (100) preferred orientation can be applied to the single crystal growth since no twins are generated on the (100) plane. The grain size of the diamond films did not change with increasing temperature and its increasing rate with increasing deposition time was the same irrespective of the substrate temperature. However, the nucleation density increased with substrate temperature and its increasing rate with deposition time was much higher for the films deposited at higher substrate temperature.