• 한국산학기술학회논문지
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• 제19권12호
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• pp.47-53
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• 2018

산업용으로 다양한 형태의 로봇팔이 사용되고 있으며, 특히, 다품종 소량생산으로 생산방식의 변화가 이루어지면서 산업현장에서 다양하게 사용이 가능한 그리퍼에 대한 중요성이 높아지고 있다. 이러한 중요성에 기반을 두어 본 연구진은 기존에 연성재질의 비선형성을 이용하여 강성을 변화시킬 수 있는 가변강성 메커니즘 그리퍼를 연구하였다. 시제품을 제작하고 실험을 통해 강성의 변화와 그 유용성을 확인하였다. 그러나 세 개의 가변강성 메커니즘을 배치하여 그리퍼를 설계 및 제작함으로써 물체를 파지하는 상황에 따라 파지를 제대로 하지 못하는 현상이 발생하였다. 또한, 그리퍼 간의 균형이 맞지 않아 물체 파지 시에 파지할 물체가 회전하면서 미끄러지는 경우가 드물게 발생하는 문제가 있었다. 이러한 문제점을 보완하기 위하여 새로운 형태의 그리퍼가 필요하게 되었다. 새로운 형태의 그리퍼를 설계하기 위하여 생체모사기술을 적용하였다. 사람의 손바닥과 파리지옥의 움직임을 통해 영감을 얻어 새롭게 가변강성 소프트 로봇 핸드를 설계하였다. 손바닥이 접히는 메커니즘을 가변강성 그리퍼에 장착된 텐던을 당기는 것과 연동하여 파지 성능을 높일 수 있었다. 가변강성 메커니즘에 파리지옥과 손바닥 형태의 메커니즘을 결합하여 파지 안전성을 높인 소프트 로봇 핸드는 기존의 가변강성 메커니즘 그리퍼보다 다양한 형태와 무게를 가진 물체를 안정적으로 파지하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2011년도 춘계학술대회 논문집
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• pp.1373-1374
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• 2011

• 한국정밀공학회지
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• 제32권12호
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• pp.1049-1054
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• 2015

Nowadays, there are many researches involving structural actuators, which have adjustable stiffness; they are also called variable stiffness actuators (VSA). The VSAs can adjust the characteristics of actuators for various functions and human-machine safety. This paper describes the design and analysis of two types of VSAs. To adjust stiffness, the actuators are controlled by a principle of lever ratio mechanism, by changing a pivot position or a spring position in the structure with springs. To make the principle workable, the designs are simplified by using a ball screw system with a motor. Each structure shows different static properties with variable rates of stiffness. We have also shown the experimental verification of the dynamic performance of the two types of VSAs. This research can be applied to various industrial fields, where humans work in conjunction with robots.

• Journal of the Korean Wood Science and Technology
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• 제17권4호
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• pp.35-43
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• 1989

Nailed joints, which are commonly used in Wooden structures, transmit loads from one member to another and induce partial composite actions between members. Long-term loads induce creep slip in nailed joints and affect load sharing and partial composite action, which may reduce joint stiffness. Two theoretical viscous-viscoelastic models were developed for nailed joints to predict creep behavior under long-term variable loads. Those models were also used to predict stiffness changes under long-term variable loads. The stiffness of nailed joint is defined as a Secant modulus which is called the joint modulus or slip modulus. Input data for the models are the results of constant load tests under three different load levels. To verify the models, nailed joints were also tested under two long-term variable load functions. The predictions of the models were very close to the experimental data. Therefore, the theoretical viscous-viscoelastic models and procedures developed in this study can be applied to predict creep slip and the changes in joint moduli of nailed joints under long-term variable loads.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2003년도 춘계 학술발표회논문집
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• pp.449-456
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• 2003

Hybrid semi-active control system is applied to improve the seismic peformance of the building structure against earthquake excitation and the LQR-based semi-active control algorithm is developed to tune the integrated stiffness/damping characteristics of the hybrid system complementarily. Numerical simulation for a 8-story shear building has been carried out to verify the applicability and effectiveness of the proposed method. Analysis results showed that the hybrid system can be a compromising solution to the seismic response control problem, compared with conventional variable stiffness or variable damping systems. Comparison results proved that the proposed algorithm can perform refined tuning of the stiffness and damping coefficients of the hybrid semi-active control system better than sliding mode control algorithm.

• Smart Structures and Systems
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• 제13권4호
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• pp.711-730
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• 2014

In this paper the system dynamic influences in actuators with variable stiffness as contemporary used in robotics for safety and efficiency reasons are investigated. Therefore, different configurations of serial and parallel elasticities are modeled by dynamic equations and linearized transfer functions. The latter ones are used to identify the characteristic behavior of the different systems and to study the effect of the different elasticities. As such actuation concepts are often used to reach energy-efficient operation, a power consumption analysis of the configurations is performed. From the comparison of this with the system dynamics, strategies to select and control stiffness are derived. Those are based on matching the natural frequencies or antiresonance modes of the actuation system to the frequency of the trajectory. Results show that exclusive serial and parallel elasticity can minimize power consumption when tuning the system to the natural frequencies. Antiresonance modes are an additional possibility for stiffness control in the series elastic setup. Configurations combining both types of elasticities do not provide further advantages regarding power reduction but an input parallel elasticity might enable for more versatile stiffness selection. Yet, design and control effort increase in such solutions. Topologies incorporating output parallel elasticity showed not to be beneficial in the chosen example but might do so in specific applications.

• 한국정밀공학회지
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• 제26권5호
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• pp.128-134
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• 2009

This paper aims to design a variable-stiffness type economical safety joint for service robots. The safety joint was designed to have a passive shock absorbing mechanism for protecting human from a catastrophic collision under service condition of robots. A simple mechanism composed of two action disks for switching the load transfer, a spring and a screw for pre-load was proposed. In order to evaluate the performance of the safety joint a testing platform which can carry out the static and impact tests was also designed and fabricated. From the test results, the designed safety joint was proved to have a variable load-carrying capacity and about 42% impact absorption capacity with simple manipulation of the control screw.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2007년도 추계학술대회 논문집
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• pp.449-450
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• 2007

• 로봇학회논문지
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• 제14권2호
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• pp.131-138
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• 2019

In this study, we developed an FSEA(Force-sensing Series Elastic Actuator) composed of a spring and an actuator has been developed to compensate for external disturbance forced. The FSEA has a simple structure in which the spring and the actuator are connected in series, and the external force can be easily measured through the displacement of the spring. And the characteristic of the spring absorbs the shock to the small disturbance and increases the sense of stability. It is designed and constructed to control the stiffness of such springs more flexibly according to the situation. The conventional FSEA uses a fixed stiffness spring and the actuator is not compensated properly when it receives large or small external force. Through this experiment, it is confirmed that FSEA compensates the external force through the proposed algorithm that the variable stiffness compensates well for large and small external forces.

• Structural Engineering and Mechanics
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• 제47권3호
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• pp.345-359
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• 2013

For the purpose of investigating the free vibration response of the spatial curved beams, the governing equations are derived in matrix formats, considering the variable curvature and torsion. The theory includes all the effects of rotary inertia, shear and axial deformations. Frobenius' scheme and the dynamic stiffness method are then applied to solve these equations. A computer program is coded in Mathematica according to the proposed method. As a special case, the dynamic stiffness and further the natural frequencies of a cylindrical helical spring under fixed-fixed boundary condition are carried out. Comparison of the present results with the FEM results using body elements in I-DEAS shows good accuracy in computation and validity of the model. Further, the present model is used for reciprocal spiral rods with different boundary conditions, and the comparison with FEM results shows that only a limited number of terms in the resultant provide a relatively accurate solution.