• Journal of Institute of Control, Robotics and Systems
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• v.18 no.2
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• pp.103-109
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• 2012

Fish generates large thrust through an oscillating motion with a compliant joint of caudal fin. The compliance of caudal fin affects the thrust generated by the fish. Due to the flexibility of the fish, the fish can generate a travelling wave motion which is known to increase the efficiency of the fish. However, a detailed research on the relationship between the flexible joint and the thrust generation is needed. In this paper, the compliant joint of a caudal fin is implemented in the driving mechanism of a robotic fish. By varying the driving frequency and stiffness of the compliant joint, the relationship between the thrust generation and the stiffness of the flexible joint is investigated. In general, as the frequency increases, the thrust increases. When higher driving frequency is applied, higher stiffness of the flexible joint is needed to maximize the thrust. The bending angles between the compliant joint and the caudal fin are compared with the changes of the thrust in one cycle. This result can be used to design the robotic fish which can be operated at the maximum thrust condition using the appropriate stiffness of the compliant joint.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.11a
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• pp.651-652
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• 2010

• Journal of Institute of Control, Robotics and Systems
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• v.6 no.7
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• pp.568-577
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• 2000

In this paper for an object grasped by a robot hand to work in stiffness control domain we first investigate the number of fingers for successful stiffness modulation in the object operational space. Next we propose a new compliance control method for robot hands which consist of two steps. RIFDS(Resolved Inter-Finger Decoupling Solver) is to decompose the desired compliance characteristic specified in the op-erational space into the compliance characteristic in the fingertip space without inter-finger coupling and RIJDS(Resolved Inter-Joint Decoupling Solver) is to decompose the fingertip space without inter-finger coupling and RIJDS(Resolved inter-Joint Decoupling Solver) is to decompose the compliance characteristic in the finger-tip space into the compliance characteristic given in the joint space without inter-joint coupling. Based on the analysis results the finger structure should be biominetic in the sense that either kniematic redundancy or force redundancy are required to implement the proposed compliance control scheme, Five-bar fingered robot hands are used as an illustrative example to implement the proposed compliance control method. To show the effectiveness of the proposed compliance control method simulations are performed for two-fingered and three-fingered robot hands.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2001.10a
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• pp.337-344
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• 2001

This paper is concerned with the change of joint rigidity in estimating the degree of semi-rigidity of connections and the buckling load in a single layer latticed dome. The estimations are based on information about the ratio for the rotational stiffness of the connection to the flexural stiffness of the member and the minimum eigenvalue of a structure for pinned, semi-rigid and completely rigid cases, respectively. Connection characteristics are reflected in the ratio control of joint rigidity for the DOFs to be related using the spring element by FEM.

• Journal of Institute of Control, Robotics and Systems
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• v.13 no.4
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• pp.320-328
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• 2007

This paper presents a stiffness modeling of a low-DOF parallel robot, which takes into account of elastic deformations of joints and links, A low-DOF parallel robot is defined as a spatial parallel robot which has less than six degrees of freedom. Differently from serial chains in a full 6-DOF parallel robot, some of those in a low-DOF parallel robot may be subject to constraint forces as well as actuation forces. The reaction forces due to actuations and constraints in each serial chain can be determined by making use of the theory of reciprocal screws. It is shown that the stiffness of an F-DOF parallel robot can be modeled such that the moving platform is supported by 6 springs related to the reciprocal screws of actuations (F) and constraints (6-F). A general $6{\times}6$ stiffness matrix is derived, which is the sum of the stiffness matrices of actuations and constraints, The compliance of each spring can be precisely determined by modeling the compliance of joints and links in a serial chain as follows; a link is modeled as an Euler beam and the compliance matrix of rotational or prismatic joint is modeled as a $6{\times}6$ diagonal matrix, where one diagonal element about the rotation axis or along the sliding direction is infinite. By summing joint and link compliance matrices with respect to a reference frame and applying unit reciprocal screw to the resulting compliance matrix of a serial chain, the compliance of a spring is determined by the resulting infinitesimal displacement. In order to illustrate this methodology, the stiffness of a Tricept parallel robot has been analyzed. Finally, a numerical example of the optimal design to maximize stiffness in a specified box-shape workspace is presented.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.1
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• pp.102-111
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• 2017

An automobile ball joint is the element for connecting the control arm and the knuckle arm, allowing rotational motion. The ball joint consists of the stud, plug, socket, and seat. These components are assembled through the caulking process that consists of plugging and spinning. In the existing research, the pull-out strength and gap stiffness were calculated, but we did not consider the uncertainties due to the numerical analysis and production. In this study, the uncertainties of material property and tolerance are considered to predict the distributions of pull-out strength and gap stiffness. Also, pull-out strength and gap stiffness are predicted as the a distribution rather than one deterministic value. Furthermore, a robust design applying the Taguchi method is suggested.

• The Journal of Korea Robotics Society
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• v.1 no.1
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• pp.81-88
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• 2006

Control of a robot manipulator in contact with the environment is usually conducted by the direct feedback control using a force-torque sensor or the indirect impedance control. In these methods, however, the control algorithms become complicated and the performance of position and force control cannot be improved because of the mechanical properties of the passive components. To cope with such problems, redundant actuation has been used to enhance the performance of position control and force control. In this research, a Double Actuator Unit (DAU) is proposed, with which the force control algorithm can be simplified and can make the robot ensure the safety during the external collision. The DAU is composed of two actuators; one controls the position and the other modulates the joint stiffness. Using this unit, it is possible to independently control the position and stiffness. The DAU based on the planetary gears is investigated in this paper. Performance using the DAU is also verified by various experiments. It is shown that the manipulator using this mechanism provides better safety during the impact with the environment by reducing the joint stiffness appropriately on detecting the collision of a manipulator.

• Journal of East-West Nursing Research
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• v.11 no.1
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• pp.42-50
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• 2005

Purpose: The purpose this research was to provide with basic data in the control of the fatiguer found in the patients with fibromyalgia by analysing the factors that predict that. Method: At three university medical center, appointed 245 out-patients diagnosed of fibromyalgia according to the conditions by American College of Rheumatology (1990). The research instruments used in this study were graphic rating scale(Anxiety, sleep disturbance, pain, joint stiffness and depression), physical activity, the number of tender points, life satisfaction and Self-efficacy scale. In data analysis, SPSS 12.0 program was utilized and data were analyzed using descriptive statistics, Pearson's correlation coefficient and multiple regression. Result: The factors that predict the fatigue of patients with fibromyalgia were sleep disturbance, life satisfaction, pain, joint stiffness, illness duration, and anxiety which explained 50.1% of the fatigue. Conclusion: It has been confirmed that the regression equation model of this research may serve as a fatigue prediction factors in patients with fibromyalgia.

• 제어로봇시스템학회:학술대회논문집
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• 1992.10b
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• pp.618-623
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• 1992

In this paper robotic manipulators in which the joints exhibit a certain amount of elasticity are considered. Based on a feedback linearized model, sliding mode control system is designed. In the control system design, weak joint stiffness assumption does not needed. Simulation results are presented to verify the validity of the control scheme. A robustness analysis for a feedback linearized model is also given with respect to uncertainties on the robot parameters.

• Journal of Korean Academy of Nursing
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• v.38 no.1
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• pp.11-18
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• 2008

Purpose: This study was to determine whether the Sun-style 24 forms of Tai Chi exercise improve pain, stiffness, disability, knee joint motion, mobility, balance or falling. Method: Forty-six community-dwelling elderly subjects (mean age, $75.46{\pm}6.28$) voluntarily participated in an intervention group of either 24 forms of Sun-style T ai Chi for 60 min, 2 times per week for 12 weeks or a control group. A non-equivalent pretest-posttest design was used. Independent t-test and ANCOVA were used to examine group differences by using SPSS12.0. Result: The experimental group had significantly less pain (F=7.60, p=.008) and stiffness (t=-3.19, p=.003) than the control group. Also there were significant improvements in knee joint motion on the right knee (t=2.44, p=.019), left knee (t=2.30, p=.026), rising time (F=8.03, p=.07), balance on the left single leg test (t=2.20, p=.033), and fear of falling (t=-2.33, p=.024) in the Tai Chi exercise group. No significant group differences were found in disability and falls efficacy. Conclusion: The Sun-style 24 forms Tai Chi exercise is effective in decreasing pain, stiffness, fear of falling and it improves balance, rising time, and knee joint motion. We suggest a continuing long term intervention to decrease disability and increase efficacy concerning falls.