• Korean Journal of Applied Biomechanics
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• v.26 no.2
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• pp.161-166
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• 2016

Objective: The purpose of this study was to determine the knee and ankle joint kinematics and kinetics by comparing downhill walking with valley-shape combined slope walking. Method: Eighteen healthy men participated in this study. A three-dimensional motion capture system equipped with eight infrared cameras and a synchronized force plate, which was embedded in the sloped walkway, was used. Obtained kinematic and kinetic parameters were compared using paired two-tailed Student's t-tests at a significance level of 0.05. Results: The knee flexion angle after the mid-stance phase, the mean peak knee flexion angle in the early swing phase, and the ankle mean peak dorsiflexion angle were greater during downhill walking compared with valley-shape combined slope walking (p < 0.001). Both the mean peak vertical ground reaction force (GRF) in the early stance phase and late stance phase during downhill walking were smaller than those values during valley-shape combined slope walking. (p = 0.007 and p < 0.001, respectively). The mean peak anterior GRF, appearing right after toe-off during downhill walking, was also smaller than that of valley-shape combined slope walking (p = 0.002). The mean peak knee extension moment and ankle plantar flexion moment in late stance phase during downhill walking were significantly smaller than those of valley-shape combined slope walking (p = 0.002 and p = 0.015, respectively). Conclusion: These results suggest that gait strategy was modified during valley-shape combined slope walking when compared with continuous downhill walking in order to gain the propulsion for lifting the body up the incline for foot clearance.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.8
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• pp.1043-1050
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• 2013

Parallel robots used in industry require high stiffness or high speed because of their structural characteristics. Nowadays, the importance of rapid transportation has increased in the distribution industry. In this light, an industrial parallel robot has been developed for high-speed transfer. The developed parallel robot can handle a maximum payload of 3 kg. For a payload of 0.1 kg, the trajectory cycle time is 0.3 s (come and go), and the maximum velocity is 4.5 m/s (pick amp, place work, adept cycle). In this motion, its maximum acceleration is very high and reaches approximately 13g. In this paper, the design, analysis, and performance test results of the developed parallel robot system are introduced.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.2
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• pp.257-263
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• 2013

In this study, dynamic behaviors of a wave energy generation system (WEGS) that converts wave energy into electric energy are analyzed using multibody dynamics techniques. Many studies have focused on reducing the effects of a mooring system on the motion of a WEGS. Several kinematic constraints and force elements are employed in the modeling stage. Three-dimensional wave load equations are used to implement wave loads. The dynamic behaviors of a WEGS are analyzed under several wave conditions by using MSC/ADAMS, and the rotating speed of the generating shaft is investigated for predicting the electricity capacity. The dynamic behaviors of a WEGS with a mooring system are compared with those of a WEGS without a mooring system. Stability evaluation of a WEGS is carried out through simulation under extreme wave load.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.1926-1930
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• 2004

We suggest a turning gait planning of a quadruped walking robot with an articulated spine. Robot developer has tried to implement a gait more similar to that of natural animals with high stability margin. Therefore, so many types of walking robot with reasonable gait have been developed. But there is a big difference with a natural animal walking motion. A key point is the fact that natural animals use their waist-oint(articulated spine) to walk. For example, a crocodile which has short legs relative to a long body uses their waist to walk more quickly and to turn more effectively. The other animals such as tiger, dog and so forth, also use their waist. Therefore, this paper proposes discontinuous turning gait planning for a newly modeled quadruped walking robot with an articulated spine which connects the front and rear parts of the body. Turning gait is very important as same as straight gait. All animals need a turning gait to avoid obstacle or to change walking direction. Turning gait has mainly two types of gaits; circular gait and spinning gait. We apply articulated spine to above two gaits, which shows the majority of an articulated spine more effectively. Firstly, we describe a kinematic relation of a waist-joint, the hip, and the center of gravity of body, and then apply a spinning gait. Next, we apply a waist-joint to a circular gait. We compare a gait stability margin with that of a conventional single rigid body walking robot. Finally, we show the validity of a proposed gait with simulation.

• Journal of Digital Convergence
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• v.13 no.11
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• pp.441-448
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• 2015

The purpose of the study was to perform a comparative analysis of the success and failure cases to increase the completeness of vault "Shirai-Kim Hee Hoon" technique. The subject of the study was "K" a male gymnast from Korean Artistic Gymnastic National team. The results obtained through the three-dimensional analysis during international as well as practice session are as follows: Firstly, excluding BC, the lead time in each PrF, HC and PoF phases were shorter during successful trials than in failure trials. Secondly, during successful trials, the horizontal and vertical velocity appeared to be higher during taking off, which contributed positively to the leaping motion in the horizontal direction. Thirdly, when compared with successful and failure trials, the body's angular rotation was highly maintained during the takeoff from the spring board followed by larger thigh angular displacement at the vault before actually attempting the backward rotation.

• Korean Journal of Applied Biomechanics
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• v.27 no.3
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• pp.171-179
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• 2017

Objective: The purpose of this study was to perform a kinematic and kinetic analysis of double-under jump rope technique according to skill level and sex. Method: Participants comprised a skilled group of 16 (9 males, 7 females), and an unskilled group of 16 with 6 months or less of experience (9 males, 7 females). Five consecutive double-under successes were regarded as 1 trial, and all participants were asked to complete 3 successful trials. The data for these 3 trials were averaged and analyzed after collecting the stable third jump in each trial. The variables used in the analysis included phase duration, total duration, flight time, vertical toe height, stance width, vertical center of mass displacement, and right lower limb ankle, knee, and hip joint angles in the sagittal plane during all events. Results: The skilled group had a shorter phase and total duration and a shorter flight time than the unskilled group. The vertical center of mass displacement and ankle dorsiflexion angle were significantly smaller in the skilled group. The male group had a shorter phase duration than the female group. The vertical toe height was greater, the stance width was smaller, and the ankle and hip flexion angles were smaller in the male group. Conclusion: Variables that can be used to distinguish between skill levels are phase and total duration, flight time, vertical center of mass displacement, and ankle dorsiflexion angle. Differences between sexes in double-under jump rope technique may be related to lower limb flexion angle control.

• Korean Journal of Applied Biomechanics
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• v.27 no.3
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• pp.189-195
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• 2017

Objective: The aim of this study was to examine the effect of foot landing type (forefoot vs. rearfoot landing) on kinematics, kinetics, and energy absorption of hip, knee, and ankle joints. Method: Twenty-five healthy men performed single-leg landings with two different foot landing types: forefoot and rearfoot landing. A motion-capture system equipped with eight infrared cameras and a synchronized force plate embedded in the floor was used. Three-dimensional kinematic and kinetic parameters were compared using paired two-tailed Student's t-tests at a significance level of .05. Results: On initial contact, a greater knee flexion angle was shown during rearfoot landing (p < .001), but the lower knee flexion angle was found at peak vertical ground reaction force (GRF) (p < .001). On initial contact, ankles showed plantarflexion, inversion, and external rotation during forefoot landing, while dorsiflexion, eversion, and internal rotation were shown during rearfoot landing (p < .001, all). At peak vertical GRF, the knee extension moment and ankle plantarflexion moment were lower in rearfoot landing than in forefoot landing (p = .003 and p < .001, respectively). From initial contact to peak vertical GRF, the negative work of the hip, knee, and ankle joint was significantly reduced during rearfoot landing (p < .001, all). The contribution to the total work of the ankle joint was the greatest during forefoot landing, whereas the contribution to the total work of the hip joint was the greatest during rearfoot landing. Conclusion: These results suggest that the energy absorption strategy was changed during rearfoot landing compared with forefoot landing according to lower-extremity joint kinematics and kinetics.

• Korean Journal of Applied Biomechanics
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• v.25 no.1
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• pp.39-47
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• 2015

Objective : The purpose of this study was to investigate the velocity conversion coefficient and invariance for the optimal phase ratio on the performance of the women's triple jump. Methods : Three-dimensional kinematic data were obtained from the three finalists of the women's triple jumper competition at the 2011 Daegu IAAF World Championships. Computer simulations were performed using the biomechanical model of the triple jump to optimize the phase ratio for the longest actual distance for all athletes with altered velocity conversion coefficients. Results : Top elite triple jumpers showed better technical consistency at the phase ratio. Also, no consistent relationship was observed between the loss in horizontal velocity and the gain in vertical velocity across supporting the three phase. In addition, regardless of the magnitude A1, all athletes were optimized with jump-dominated technique. Finally, as the magnitude of A1 increased, the athletes showed better performance. The obtained overall distance jumped showed the longest actual distance when the optimal phase ratio was transferred from hop-dominated to jump-dominated(the step ratio was 30%~31%), and when the optimal phase ratio was transferred from balanced to jump-dominated(the step ratio was 27%~29%). Conclusion : Future studies need to be conducted in order to explore the active landing motion and the inclination angle of the body with the velocity conversion coefficient simultaneously at each supporting phase.

• Physical Therapy Rehabilitation Science
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• v.6 no.4
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• pp.208-213
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• 2017

Objective: Despite reliable evidence of abnormal scapular motions increases, there is not yet sufficient evidence of abnormal humeral translations. This study aims to analyze the motion of the humeral head toward the scapula when the shoulder is actively abducted using the C-arm. Design: A case report. Methods: The participant was a healthy man without any limitation and pain during shoulder movement. The participant's shoulder was abducted; this movement in the frontal plane was measured using a C-arm (anterior-posterior view) and was analyzed with computer-aided design. The starting posture was $15^{\circ}$, and as the participant abducted his shoulder measurements were taken and analyzed at $30^{\circ}$, $60^{\circ}$, $90^{\circ}$, $120^{\circ}$, $150^{\circ}$, and ending at $165^{\circ}$. A line was drawn perpendicularly to the line connecting the humeral head axis to the glenoid, and another line was drawn perpendiculary to the line connecting the scapular axis to the glenoid. The distance between the two lines measured is defined as the e value. Results: At the starting posture ($15^{\circ}$), the central axis of the humeral head was located 1.92 mm inferior to the central axis of the scapula. The humeral head was superiorly translated from the starting posture to $120^{\circ}$, and then, showed an inferior translation to the ending posture ($165^{\circ}$). Conclusions: The results of this study showed that the humeral head moved upward from the starting posture ($15^{\circ}$) up to $120^{\circ}$ indicating, superior translation, and it moved downward when the posture was past $120^{\circ}$, indicating inferior translation.

• Journal of Biomedical Engineering Research
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• v.28 no.6
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• pp.811-816
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• 2007

The social activities of the elderly have been increasing as our society progresses toward an aging society. As their activities are increased, the occurrence of falls that could lead to fractures are increased. Falls are serious health hazards to the elderly and we need more thorough understanding of falls including the progress of falls and the impact area in various fall directions. Many of the traditional methods of falls research dealt with voluntary falls by younger subject since older subject can easily get fracture from voluntary falls. So, it has been difficult to get exact data about falls of the elderly. Here, we tried to capture the characteristics of the movements of major joints using three dimensional motion capture system during falls experiments using a moving mattress that can safely induce unexpected falls. Healthy younger subjects participated in the actual falls experiment and the moving mattress was actuated by a pneumatic system. The kinematic parameters such as velocities and accelerations of major segments were imported to a computer simulation environment and falls to hard surfaces were simulated in a computational environment using a realistic human model of aged persons. The simulation was able to give approximations to contact forces which can occur during actual falls.