• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.168-171
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• 2003

Instrumented indentation tests have been used for estimating material properties. In order to analyze deformation characteristics with various factors, the unloading stiffness should be properly determined from the elastic behaviour. In general, the unloading stiffness is obtained from shifted power functions fitting to indentation unloading curves. But, the functions give often a poor representation of actual data. In this study, control conditions for fitting unloading curves by shifted power functions were investigated. The current efforts may provide useful information about unloading process and valid unloading stiffness.

• Journal of Institute of Control, Robotics and Systems
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• v.11 no.8
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• pp.704-708
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• 2005

In this paper, a simple idea is proposed to change the compliance center of the Remote Center Compliance (RCC) by adjusting the elasticity of the Elastomer Shear Pad (ESP). To vary the elasticity of the ESP, a hole is made in the ESP along its stiffness axis, and a stiffness adjusting rod (SAR) is inserted into the hole. By adjusting the insertion depth of the rod, lateral stiffness of the ESP can be varied, and the compliance center of the VRCC can be controlled accordingly. To verify the effectiveness of the proposed idea, a prototype VRCC is designed and, the position of the compliance center with various lengths of the inserted rod are measured.

• Smart Structures and Systems
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• v.18 no.5
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• pp.955-982
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• 2016

Recent studies integrating vibration control and structural health monitoring (SHM) use control devices and control algorithms to enable system identification and damage detection. In this study real-time SHM is used to enhance structural vibration control and reduce damage. A newly proposed control algorithm, including integrated real-time SHM and semi-active control strategy, is presented to mitigate both damage and seismic response of the main structure under strong seismic ground motion. The semi-active independently variable stiffness (SAIVS) device is used as semi-active control device in this investigation. The proper stiffness of SAIVS device is obtained using a new developed semi-active control algorithm based on real-time damage tracking of structure by damage detection algorithm based on identified system Markov parameters (DDA/ISMP) method. A three bay five story steel braced frame structure, which is equipped with one SAIVS device at each story, is employed to illustrate the efficiency of the proposed algorithm. The obtained results show that the proposed control algorithm could significantly decrease damage in most parts of the structure. Also, the dynamic response of the structure is effectively reduced by using the proposed control algorithm during four strong earthquakes. In comparison to passive on and off cases, the results demonstrate that the performance of the proposed control algorithm in decreasing both damage and dynamic responses of structure is significantly enhanced than the passive cases. Furthermore, from the energy consumption point of view the maximum and the cumulative control force in the proposed control algorithm is less than the passive-on case, considerably.

• The Journal of Korea Robotics Society
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• v.12 no.3
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• pp.263-269
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• 2017

Recently, soft robots using soft materials are presented. Thanks to soft materials, soft robots have flexible, highly-stretchable or adaptable features. However, due to the flexibility of soft material, it is hard for soft robots to control accurately or perform high force. To deal with these limitations, variable stiffness technology, which enables the stiffness control of structure, has been developed. In this research, a dual-stiffness structure that is actuated by the assembly of two flexible structures are presented. Each flexible structure consists of flexible film part and rigid parts placed at regular intervals. The flexibility of film between rigid parts allows each structure to move softly. On the other hand, by combining two structures rigid part of each part constrain the degrees of freedom of the other side part. And this causes the stiffness of whole structure to be increased. This paper will cover concepts, design, analysis and experiments of this structure.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.1
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• pp.110-122
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• 2008

Pneumatic vibration isolator typically consisting of dual-chamber pneumatic springs and a rigid table are widely employed for proper operation of precision instruments such as optical devices or nano-scale equipments owing to their low stiffness- and high damping-characteristics. As environmental vibration regulations for precision instruments become more stringent, it is required to improve further the isolation performance. In order to facilitate their design optimization or active control, a more accurate mathematical model or complex stiffness is needed. Experimental results we obtained rigorously for a dual-chamber pneumatic spring exhibit significantly amplitude dependent behavior, which cannot be described by linear models in earlier researches. In this paper, an improvement for the complex stiffness model is presented by taking two major considerations. One is to consider the amplitude dependent complex stiffness of diaphragm necessarily employed for prevention of air leakage. The other is to employ a nonlinear model for the air flow in capillary tube connecting the two pneumatic chambers. The proposed amplitude-dependent complex stiffness model which reflects dependency on both frequency and excitation amplitude is shown to be very valid by comparison with the experimental measurements. Such an accurate nonlinear model for the dual-chamber pneumatic springs would contribute to more effective design or control of vibration isolation systems.

• Journal of The Korean Society of Integrative Medicine
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• v.7 no.4
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• pp.301-309
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• 2019

Purpose : The purpose of this study was to provide an effective method of exercise therapy for patients with cervicogenic headache. Methods : The subjects were divided into the following two groups according to the intervention received: cervical stretch exercise (n=15, control group) cervix-stabilizing exercise (n=15, experimental group) tone (Hz) and stiffness (N/m) of the suboccipital and upper trapezius muscles were measured. T1 slope angle and neck tilt angle were measured. After the exercise program intervention, a greater amount of change in muscle tone and stiffness of suboccipital and upper trapezius muscles was found in the experimental group, as compared to the control group. Greater amount of change in posture was found in the experimental group, as compared to the control group (p<0.05). Results : After the exercise program intervention, a greater amount of change in muscle tone and stiffness of suboccipital and upper trapezius muscles was found in the experimental group, as compared to the control group. Greater amount of change in posture was found in the experimental group, as compared to the control group (p<0.05). Conclusion : The neck-stabilizing exercise were shown to be effective in decreasing the tone of the cervical muscles by stabilizing the cervical bone and improving muscle activity, and in improving the posture by decreasing muscle tone and stiffness.

• Earthquakes and Structures
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• v.3 no.5
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• pp.749-766
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• 2012

Structural control through integration of passive damping devices within the building structure has been increasingly implemented internationally in the last years and has proven to be a most promising strategy for earthquake safety. In the present paper an alternative configuration of an innovative energy dissipation mechanism that consists of slender tension only bracing members with closed loop and a hysteretic damper is investigated in its dynamic behavior. The implementation of the adaptable dual control system, ADCS, in frame structures enables a dual function of the component members, leading to two practically uncoupled systems, i.e., the primary frame, responsible for the normal vertical and horizontal forces and the closed bracing-damper mechanism, for the earthquake forces and the necessary energy dissipation. Three representative international earthquake motions of differing frequency contents, duration and peak ground acceleration have been considered for the numerical verification of the effectiveness and properties of the SDOF systems with the proposed ADCS-configuration. The control mechanism may result in significant energy dissipation, when the geometrical and mechanical properties, i.e., stiffness and yield force of the integrated damper, are predefined. An optimum damper ratio, DR, defined as the ratio of the stiffness to the yield force of the hysteretic damper, is proposed to be used along with the stiffness factor of the damper's- to the primary frame's stiffness, in order for the control mechanism to achieve high energy dissipation and at the same time to prevent any increase of the system's maximum base shear and relative displacements. The results are summarized in a preliminary design methodology for ADCS.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.11 no.6
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• pp.193-199
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• 2001

Active control of forced vibration of the cantilevered laminated composite plates using collocated piezoceramic sensor/actuator is analyzed numerically and verified experimentally for various fiber orientations. Impact on the stiffness and the damping properties is studied by varying stacking sequence of [$\theta$$_{4}$O$_{2}$90$_{2}$]s for the laminated composite plate. For the forced vibration control, the plate is excited by one pair of collocated PZT exciters in resonance and its vibrational response is suppressed by the other collocated PZT sensor/actuator using direct negative velocity feedback. It is shown that the active control of forced vibration is more effective for the smart laminated plate with higher modal damped stiffness(2ζ$\omega$/aup 2/) .

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.48-51
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• 1996

A 5-bar structure with redundant actuators is proposed as a finger mechanism. It is shown that one additional redundant actuator greatly enhances the load handling capacity of the system. The actuator location should be carefully decided to maximize the performance enhancement. Furthermore, we develop stiffness and frequency control algorithms based on the internal loading created by redundant actuation. The effectiveness of these algorithms have been demonstrated by simulations.

• Journal of Korean Society of Steel Construction
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• v.10 no.1 s.34
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• pp.63-72
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• 1998

The stiffness design method is presented as a drift control model of steel structures and applied to design of space trusses subjected to stress and displacement constraints. The stiffness design method is developed by integrating the resizing techniques for an effective drift control algorithm with the strength design process according to the commonly used design specifications such as allowable stress design. In the resizing technique the amount of material to be modified depends on the member displacement participation factors and is determined by an optimization technique. Using the stiffness design method, a structural design model for steel structures is proposed and applied to two verifying examples. As demonstrated in the examples, the displacement of the structures can be effectively controlled without expensive computational cost.