• Korean Journal of Applied Biomechanics
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• v.19 no.4
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• pp.749-759
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• 2009

The purpose of this study was to provide basic information for improving a soft tennis forehand middle volley technique based on kinematic and kinetic analyses of volleys performed by four male national tennis players($33.3{\pm}2.16$ years). The results are as follows. The first phase of the stroke was the longest, covering 64.7% of the stroke time. The displacement of the center of gravity was 48.1% to the right and 54% to the front in the first phase. When impacted, the elbow joint showed the highest average velocity, 3.67m/s, and the upper arm segment displayed the highest angular velocity, $201^{\circ}/s$. The average of the elbow angle and the ball velocity were $149^{\circ}$ and 18.9m/s, respectively. In the ground reaction force, the left and right foot forces in both the x and y directions showed a statistically significant difference. This result seems to indicate that when the left foot is pushed to the right, the force of the right foot is proportional and symmetrical to the left, serving as a supporter.

• Proceedings of the KIEE Conference
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• 2007.10a
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• pp.315-316
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• 2007

This paper presents a new methodology to improve movement database for a humanoid robot. The database is initially full of human motions so that the kinetics characteristics of human movement are immanent in it. then, the database is updated to the pseudo-optimal motions for the humanoid robot to perform more natural motions, which contain the kinetics characteristics of robot. for this, we use the evolutionary algorithm. the methodology consists of two processes : (1) the offline imitation learning of human movement and (2) the online generation of natural motion. The offline process improve the initial human motion database using the evolutionary algorithm and inverse dynamics-based optimization. The optimization procedure generate new motions using the movement primitive database, minimizing the joint torque. This learning process produces a new database that can endow the humanoid robot with natural motions, which requires minimal torques. In online process, using the linear combination of the motion primitive in this updated database, the humanoid robot can generate the natural motions in real time. The proposed framework gives a systematic methodology for a humanoid robot to learn natural motions from human motions considering dynamics of the robot. The experiment of catching a ball thrown by a man is performed to show the feasibility of the proposed framework.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.4
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• pp.89-94
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• 2019

Glass base sealant is required as a ceramic-ceramic joining material between α-alumina insulation cap and β-alumina electrolyte tube in the development of NaS battery cell package for electrical energy storage system. The fabrication of glass frit by thermal quenching method, phase analysis, particle size analysis, coefficient of thermal expansion and surface roughness according to the glass compositions were analyzed for the fabrication of glass sealing paste for ceramic-ceramic joining. Also, a new evaluation method of the adhesion strength of glass sealant at the small area in ceramic-ceramic joining component was proposed using conventional Dage bond tester that was used to measure the adhesion of solder ball joint.

• Korean Journal of Applied Biomechanics
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• v.23 no.2
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• pp.117-123
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• 2013

The purpose of this study was to provide data to increase the success rate of penalty kicks through quantifying the shape of skilled kicks by performing a kinematic analysis on the change of movement during the kicking phase which the goalkeeper uses as a vital clue. Three high definition video cameras(GR-HD1KR, JVC, Japan) were used for the study and 18 reflective markers were attached to the body joints. Corners of the goal, difficult for goalkeepers to block, were set as aims and 1 m by 1.2 m targets were installed. Each subject had five sets of kicks at random, and the analysis was done on the movements that hit the target. Time, speed of the right lower limb's center of mass, joint angle, and angular velocity were chosen as factors and the results of the analysis showed statistical significance. The player taking a penalty kick should train to avoid leaning one's body towards the kicking direction and change the angle of the right foot right before the impact to decide the direction of the ball. The goalkeeper can increase the save success rate by studying the angle of the kicker's body and the right foot as well as the timing of the kick.

• Journal of Drive and Control
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• v.11 no.2
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• pp.30-35
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• 2014

The pumps of electro-hydrostatic actuators operate most frequently in boundary lubrication speed range, as they compensate for the position control errors as a control element. When conventional swash plate type piston pumps are applied to electro-hydrostatic actuators, the frictional power losses as well as the wear rate of sliding components, such as piston shoes can increase drastically under the boundary friction condition. In this paper, the power losses of the piston shoes were investigated which were engendered by a frictional solid-to-solid contact and leakage flow rate of their hydrostatic bearing. In order to reduce them, DLC-coating was applied to the swash plate and the ball joint of pistons along with its effects were demonstrated. In addition, it was also shown that the wear rate of the piston shoes could be markedly reduced using the DLC-coated swash plate.

• Journal of the Korean Society of Physical Medicine
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• v.13 no.4
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• pp.85-94
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• 2018

PURPOSE: This study was conducted to determine the effects of therapeutic exercise on range of motion (ROM), the manual muscle test (MMT), functional movement screen (FMS) and radiological evaluation in a youth football player with football-specific anterior pelvic tilt (APT). METHODS: The subject of this case report was a 12-year-old youth football player, who presented with football-specific APT. Therapeutic exercise consisted of hamstring stretch, prone hip extension, abdominal crunch, bridging with isometric hip abduction, plank exercise with posterior tilt and posterior pelvic tilting exercise using a swiss-ball for 40 min/day, twice a week for 8-weeks. ROM, MMT, FMS (deep squat, hurdle step, inline lunge, shoulder mobility, active straight-leg raise, rotary stability and trunk stability push-up) and radiographs (lumbar lordotic and sacral horizontal angle) were analyzed before and after week 8 of therapeutic exercise. RESULTS: The ROM, MMT, and FMS increased and the lumbar lordotic angle and sacral horizontal angle improved after 8-weeks of therapeutic exercise. CONCLUSION: The results of this case report suggest that therapeutic exercise improves ROM, MMT and radiography associated parameters in youth football players with football-specific APT. These findings have clinical implications for therapeutic exercise in youth football players with football-specific APT.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.6_3
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• pp.1239-1246
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• 2022

This paper introduces the effect of grease on the degradation characteristics of bearings used as key components of packaging equipment and automation systems. Bearings parts are installed to fix and support the rotating body of the system, and performance degradation of the bearings has a great effect on the life of the system too. When bearings are used in various devices and systems, the grease is applied to reduce friction and improve fatigue life. Determining the type of lubricant (grease) is important because it has a great influence on the operating environment and lifespan and ensures long lifespan of systems and facilities. However, studies that simultaneously compared and analyzed the change in mechanical degradation characteristics and the comparison of chemical degradation characteristics according to grease types under actual operating conditions are insufficient. In this paper, three types of small harmonic drive, high-load reducer, and low-load reducer grease used in power transmission joint modules are experimentally selected and finally injected into ball bearings with a load (19,500N) to improve bearing durability. Degradation characteristics were tested by attaching to test equipment. At this time, after the durability test under the same load conditions, the mechanical degradation characteristics, that is temperature, vibration according to the three greases types. In addition, the chemical degradation characteristics of the corresponding grease was compared to present the results of mutual correlation analysis.

• Journal of Korean Orthopaedic Sports Medicine
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• v.1 no.1
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• pp.43-48
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• 2002

Purpose : We evaluated radiographic changes and clinical manifestations of the elbow joint to identify the effects of the throwing between dominant and non-dominant arms. Materials and Methods : A hundred and five little leaguer’s baseball player in 5 elementary school and 2 middle school were evaluated for clinical symptoms and radiographic changes about elbow joint. Mean age was 12 years old and average periods of exercise were 32 months. Elbow functions were evaluated using ASES standardized assessment form and radiographic changes of medial epicondyle were examinated for enlargement, separation of the apophyses, fragmentation and irregularity. Results : Thirty seven players (35$\%$) were complained pain with throwing and the average score was 4.8 using visual analog scale. There were no significant differences in range of motion except flexion angle, valgus angle, and strength between dominant arm and non-dominant arm. Valgus laxity was more prominent in dominant arm. Ulnohumeral tenderness, radiocapitellar tenderness and medial flexor origin tenderness were in 18, 6, and 17 cases respectively in dominant arm. Medial epicondyle was enlarged in dominant arm with 13.0 by 6.3 mm compared to non-dominant arm with 11.7 by 6.1 mm. Apophyseal separation was 0.8 mm in dominant arm and 0.5 mm in non-dominant arm. Fragmentation and irregularity were 14 (13$\%$) and 25 (24$\%$) cases respectively in dominant arm. Conclusion : In little league baseball player, it needs usage of ball and bat with appropriate weight, and careful conditioning programs through throwing exercise in order to avoid elbow injuries.

• Journal of Korean Orthopaedic Sports Medicine
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• v.2 no.1
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• pp.62-70
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• 2003

Purpose: We examined the kinematics and kinetics of the shoulder in youth baseball pitchers in light of the mechanisms of development of little league shoulder and humeral retrotorsion. Materials and Methods: The joint kinematics and the net force and torque acting on the humerus were calculated in fourteen youth pitchers throwing in a simulated game. Results: The major force component acting on the humerus was a tensile force of 378$\pm$81 N that peaked just after ball release. The predominant torque on the humerus was an external rotation torque about the long axis of the humerus. This torque reached a peak value of 35.3$\pm$6.7 Nm about 73$\%$through the pitching motion. This torque is approximately 66$\%$ of the torque required to fracture of the adult humerus. Conclusions: The direction of the humeral torque was consistent with the development of increased humeral retrotorsion in the throwing arm. Shear stress arising from the high torque during the late cocking phase likely leads to deformation the relatively weak proximal humeral epiphysis. The external rotation torque applied to the humerus during the pitch also agrees with the proposed mechanism for development little league shoulder, which has been hypothesized to be due to rotational stresses acting on the epiphysis during the throwing motion.

• Journal of the Microelectronics and Packaging Society
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• v.19 no.4
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• pp.57-64
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• 2012

Ball shear test was performed by test variables such as loading speed and annealing time in order to investigate the effect of surface finishes on the bonding strength of Sn-1.2Ag-0.7Cu-0.4In Pb-free solder. The shear strength increased and the ductility decreased with increasing shear speed. With increasing shear speed, the electroless nickel immersion gold (ENIG) finish showed dominant brittle fracture mode, while organic solderability preservative (OSP) finish showed pad open fracture mode. The shear strength and toughness for both surface finishes decreased with increasing annealing time under the high-speed shear test of 500 mm/s. Typically, the thickness of intermetallic compound increased with increasing annealing time, which means that exposure of brittle fracture became much easier. With increasing annealing time, the both ENIG and OSP finishes exhibited the pad open fracture mode. Overall, ENIG finish showed higher shear strength rather than OSP finish due to its superior barrier stability.