• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.4
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• pp.1154-1163
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• 1996

This paper presents a three dimensional modeling and dynamic anlaysis of a hydraulic excavator. An excavator is composed of a ground, an under-frame, two idlers, two spockets, an upper-frame, a boom, an arm, a bucket two yokes, two connecting rods, two boom cylinders, an arm cylinder, and a bucket cylinder. Each cylinder is modeled with two separate bodies which are linked to each other by a translational joint. The three dimensioanl model of the excavator consists of 22 bodies and each body is assumed as rigid. This paper suggested the maximum lifting capability, a critical load and reaction forces at joints form the DADS simulation. It was presumed that the reaction forces due to a critical load are three times bigger than those due to the maximum lifting capacity.

• Korean Journal of Applied Biomechanics
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• v.25 no.1
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• pp.85-94
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• 2015

Purpose : The purpose of this study was to investigate the influence on the ground reaction force parameters according to wearing positions of backpack for during stair ascending and descending. Methods : Participants selected as subject were consisted of young female(n=10) and performed stairs walks(ascending and descending) with 2 types of wearing position(front of trunk[FT], rear of trunk[RT]). Passive(Fz 1) and active(Fz 2) forces of the vertical GRF were determined from time function and frequency domain. Also shear forces(Fx, Fy 1, Fy 2), dynamic postural stability index(MLSI, APSI, VSI, DPSI), loading rate and center of pressure (${\Delta}COPx$, ${\Delta}COPy$, COP area) were calculated from time function and frequency domain. Results : Fx, Fy 1, Fy 2, and Fz 1 in GRF didn't show significant differences statistically according to the wearing positions of backpack(p>.05), but stair descending showed higher forces than that of stair ascending. Particularly, Fz 2 of stair ascending showed higher forces than that of stair descending(p<.001), RT types showed higher than that of FT types(p<.05). MLSI, APSI, VSI, and DPSI of stair descending showed the increased stability index than that of stair ascending(p<.05), MLSI of RT types showed the decreased stability index than that of FT types(p<.05). Loading rate didn't show significant differences statistically according to the wearing positions of backpack(p>.05), but stair descending showed higher loading rate than that of stair ascending(p<.001). Also, ${\Delta}COPx$ in stair descending showed the increased movement than that of stair ascending(p<.05). Conclusions : A backpack of 10 kg(10 kg(ratio of body weights $17.61{\pm}1.17%$) showed significantly change GRF parameters according to wearing positions during stair ascending and descending. If possible, we suggest that the dynamic stability, in case of stairs walking with a smaller weights can be further improved.

• Korean Journal of Applied Biomechanics
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• v.18 no.4
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• pp.49-57
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• 2008

The purpose of this study was to determine the effects of 12-week elastic resistance exercise for the elderly on the magnitude of frequency and variability of ground reaction force signals. To this aim, total 12 elderly women aged in their 70 were participated in this study and asked to do a 12-week elastic resistance exercise program. FFT(fast Fourier Transform) was used to analyze the frequency domain analysis of the ground reaction forces's signals and an accumulative PSD (power spectrum density) normalized by support phase of walking was calculated to reconstruct the certain signals. To estimate the gait stability between the before and after exercise, values of variability were determined in a coefficient of variance. The magnitude of frequency and variability analysis for media-lateral signal revealed significantly less after exercise (p<.05). In contrast, variability of this signal's frequency that have used to evaluate the local stability during walking exhibited significantly greater after exercise(p<.05). In summary, magnitude frequency and variability of media-lateral ground reaction force's signal were significantly changed after a 12-week elastic resistance exercise.

• Korean Journal of Applied Biomechanics
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• v.23 no.3
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• pp.245-252
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• 2013

The purpose of this study was to analyze the effect that various loads have on the lower limb biomechanics. The following variables were measured and analyzed; performance time for each phase, lower limb moments and joint angles, and ground reaction forces. The kinematic and kinetic data was recorded by 2 force platforms and a motion capture system while 12 healthy adults in their twenties stepped down three steps under loads of 0%, 10%, 20% BW. Results are as follows. First, the different loading conditions did not seem to significantly affect the performance times and the joint angles. Second, the largest ground reaction forces were observed at the 1 step at the 10% BW condition. Finally, at the 0% BW loading condition the right hip extension moment was the smallest and the left hip flexion moment was the largest. The results show that there are not any significant changes in the biomechanics of the lower limbs under loading conditions up to 20% BW. Further investigations including more loading conditions with more weights and more additional steps analyzed are needed.

• Korean Journal of Applied Biomechanics
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• v.23 no.2
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• pp.131-139
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• 2013

Naejirgi is one of the fastest, most forceful and most often being used kicks in Taekkyon games, The purpose of this study was to investigate kinetic factors on two types of Naejirgi kick, one of which uses knee bending of supporting leg and the other uses little it. 12 taekkyoners (11 males and one female) who are the students of Y University participated in this study. They have been practicing on Taekkyon for five years or more. Positions of CoM, the elapsed time of each phase, vertical ground reaction forces, joint moments and impulses of supporting leg were analyzed for this study. The results were as follows; in Naejirgi with knee bending of supporting leg than without knee bending of supporting leg, the vertical motion range of whole body CoM was larger during phase 2 and 3, the elapsed time of phase 4 were longer, players stayed longer in the nearest location to opponent, during phase 4 the vertical ground reaction forces of supporting foot were larger, and joint extension moments and angular impulses of supporting leg (especially knee) were larger. In conclusion supporting knee bending is not a useful strategy for Naejirgi, because players stay longer in the nearest position to opponent and consumed more muscle force and energy for producing the vertical momentum which is unnecessary for pushing down the opponent.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.5
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• pp.142-149
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• 2009

This paper proposes and demonstrates novel flexible contact force sensing devices for 3-dimensional force measurement. To realize the sensor, polyimide and polydimethylsiloxane are used as a substrate, which makes it flexible. Thin-film metal strain gauges, which are incorporated into the polymer, are used for measuring the three-dimensional contact forces. The force sensor characteristics are evaluated against normal and shear load. The fabricated force sensor can measure normal loads up to 4N. The sensor output signals are saturated against load over 4N. Shear loads can be detected by different voltage drops in strain gauges. The device has no fragile structures; therefore, it can be used as a ground reaction force sensor for balance control in humanoid robots. Four force sensors are assembled and placed in the four corners of the robot's sole. By increasing bump dimensions, the force sensor can measure load up to 20N. When loads are exerted on the sole, the ground reaction force can be measured by these four sensors. The measured forces can be used in the balance control of biped locomotion system.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1288-1293
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• 2003

This study predicts muscle forces acting on the lower extremity when the knee joint is in deep flexion. The whole bodies were approximated as a link model, and then the moment equilibrium equations at the lower extremity joints were derived for given reaction forces against the ground. Measurement of deep flexion was carried out by placing ten markers on the body. This study calculated the moment acting at each joint from the equations of force and moment, classified the complicated muscles around the knee joint. and then predicted the muscle forces to balance the joint moment. Two models were proposed in this study: the simpler one that consists of three groups of muscle and the more detailed one of nine groups of muscle.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.103-108
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• 2003

In the construction of mountain tunnels, reaction forces of the legs of steel arch supports against the ground are often expected to support the ground being excavated. In these cases, a stress concentration occurs in the ground directly under the support legs. If the bearing capacity of the ground is insufficient or displacement is not effectively constrained, the local failure of the ground under the support legs or settlement of the tunnel supports due to large deformation could result. It is therefore necessary to reinforce the support legs to reduce settlement. As a means of reducing settlement, wing-ribbed steel arch supports are well used. In this study, with the aim of finding a way to quickly reduce the settlement of steel arch support legs, effectiveness of a new type of wing ribs to reinforce steel arch supports was investigated through laboratory testing.

• Proceedings of the KIEE Conference
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• 2000.07d
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• pp.2804-2807
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• 2000

This paper suggests a method of the forward dynamic analysis for the computer simulation on the analysis of the dynamic behavior for biped walking robot. The equations f motion of the system or the simulation are constructed by using the Method of the multibody dynamics which is powerful method for modeling of the complex biped system. For the simplicity of simulation, we consider that the sole of the contacting foot is affected by the reaction forces for tree structure system topology instead of the addition or deletion of the kinematic constraints. The ground reaction forces can be modeled using the simple spring and damper model at the three contacting points on the sole of the foot. For minimizing the errors of numerical integration, the number of equations of motion is minimized by adding the driving constraints or a controller instead of the direct driving torques.

• Proceedings of the KIEE Conference
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• 2006.10c
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• pp.205-207
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• 2006

Since a humanoid robot inherently suffers from instability and always risks tipping itself over, or topping to the ground, it is necessary to ensure high stability and reliability of walk. An unexpected ground condition is one of the principal factors of instability. This paper proposes a walk stabilization method consisting of a Fuzzy algorithm and geometry under uneven terrain. The ground reaction forces that are measured by the FSR sensors on the sole are used to check the ground condition and the robot posture. The effectiveness of proposed method is verified by computer simulations.