• 로봇학회논문지
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• 제11권2호
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• pp.73-82
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• 2016

This paper focuses on the vibration analysis of planar cable-driven parallel robots on their configurations. Despite of many advantages of the cable robots, elasticity of the cables may cause the vibration at the existence of external disturbance, resulting in deterioration of positioning accuracy. According to the vibration theory, having high first order natural frequency can prevent resonance with low frequency disturbance from the surrounding environment. A series of simulations showed that choosing frame / end-effector shape and cable connection method affects robots' natural frequency. For the precise simulation, the cables are modeled as linear springs and axial vibration of cables is mainly considered. Aspect ratios of the frame and end-effector are defined as non-dimensional parameters while their areas are fixed. It was shown that vibration analysis guides to design a planar cable robot in terms of high capacity to reduce vibration.

• Earthquakes and Structures
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• 제13권1호
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• pp.51-58
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• 2017

Passive dynamic vibration absorbers (DVAs) are often used to suppress the excessive vibration of a large structure due to their simple construction and low maintenance cost compared to other vibration control techniques. A new type of passive DVA consists of two pendulums connected with spring and dashpot element is investigated. This research evaluated the performance of the DVA in reducing the vibration response of a two degree of freedom shear structure. A model for the two DOF vibration system with the absorber is developed. The nominal absorber parameters are calculated using a Genetic Algorithm(GA) procedure. A parametric study is performed to evaluate the effect of each absorber parameter on performance. The simulation results show that the optimum condition for the absorber frequencies and damping ratios is mainly affected by pendulum length, mass, and the damping coefficient of the pendulum's hinge joint. An experimental model validates the theoretical results. The simulation and experimental results show that the proposed technique is able be used as an effective alternative solution for reducing the vibration response of a multi degree of freedom vibration system.

• Journal of Mechanical Science and Technology
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• 제16권11호
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• pp.1395-1403
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• 2002

The characteristics of gear meshing vibration undesgo change as the vibration is transmitted from the gear to the housing. Therefore, vibration transmission characteristics of helical gear systems must be understood before the effective methods of reducing gear noise can be found. In this work, using a helical gear with different lead errors, the gear vibration in the rotational direction and the bearing vibration are measured. The frequency characteristics of gear and bearing vibration are investigated and a comparson is also provided.

• International Journal of Vascular Biomedical Engineering
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• 제1권2호
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• pp.4-12
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• 2003

The present study investigated the effect of transverse vibration on the hemorheological characteristics of blood using a newly designed pressure-scanning capillary viscometer. As vibration was applied, aggregated blood cells (rouleaux) were disaggregated. The range of vibration frequency and amplitude are $0{\sim}100\;Hz$ and $0{\sim}0.8\;mm$, respectively for a capillary diameter 0.84 mm. As vibration increased, blood viscosity initially increased and tended to decrease. In order to delineate the unexpected results, the present study proposed two counteracting mechanisms of vibration related with red blood cell (RBC) aggregation affecting hemo-rheological properties. One is the reduction of RBC aggregation due to vibration causing an increase of blood viscosity. The other is forced cell migration due to the transverse vibration, which in turn forms a cell-free layer near the tube wall and causes a decrease of flow resistance.

• 대한기계학회논문집A
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• 제39권7호
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• pp.665-671
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• 2015

유성 기어박스의 진동기반 고장진단 기법은 조립 및 제작공차와 하중조건에 의해 결정되는 진동 변조특성에 따라 성능을 달리하는 특성을 갖는다. 이 논문에서는 풍력발전기에 장착되어 있는 유성 기어박스의 고장을 효과적으로 진단하기 위해 진동 변조특성을 고려한 고장진단기법을 제안하고자 한다. 리샘플링된 진동신호에 대한 대역 필터링을 사용함으로써 유성기어박스의 진동 변조특성을 규명하고자 하였으며, 진동추출 윈도우함수의 최적위치를 선정하여 활용함으로써 가변적 진동 변조현상에서도 강건한 고장진단을 수행할 수 있도록 하였다. 제안된 고장진단기법의 검증을 위해 2kW 급 풍력발전기 테스트베드가 설계되었으며 기어 치 부분파손이 모사 제작되어 기어박스에 장착되었다.

• 전력전자학회논문지
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• 제11권3호
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• pp.274-283
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• 2006

Permanent Magnet Synchronous Motor(PMSM)는 볼스크류, 기어 및 타이밍 벨트를 이용하여 NC, 가공기, 로봇 및 공장 자동화를 포함하여 산업 시스템 전반에 널리 사용되고 있다. 이러한 PMSM과 부하의 결합으로 구성된 시스템은 동력의 전달에 있어서, 고유의 공진 주파수를 가지며 공진 주파수 대역에서의 기계계의 응답 특성은 매우 불안정하고, 기계 시스템의 손상을 일으키게 된다. 본 논문에서는 PMSM을 이용한 직선 운동 시스템에서 기계적인 결합에 의한 기구부의 진동을 억제하기 위하여 진동 주파수를 자동으로 검출하여, 진동의 원인이 되는 토크 지령 신호를 억제하는 적응형 노치 필터를 포함하는 속도 제어 시스템을 제안한다. 하지만, 기계적인 진동 주파수와 주파수의 대역은 전동기에 결합된 결합 기구 및 부하에 따라서 변동하는 특성을 가지고 기계적인 진동의 크기도 진동원이 되는 신호에 따라 변동하므로, 이를 적응형 노치 필터부에서 이를 진단하여 진동 주파수를 자동으로 억제함으로써 안정적인 운전이 가능하도록 설계된다. 본 논문에서 제안된 기계적인 진동을 억제하기 위한 적응형 노치 필터의 성능은 시뮬레이션 및 실험을 통하여 검증하였다.

• Journal of Mechanical Science and Technology
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• 제18권12호
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• pp.2258-2264
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• 2004

This article described the numerical investigation of shear-thinning blood flow characteristics when subjected to longitudinal and transverse vibrations and delineated the underlying mechanisms of the flow rate enhancements, respectively. In order to fully consider the mechanical vibrations of the capillary, a moving wall boundary condition was adopted. The present numerical results showed that the longitudinal vibration caused a significant increase of wall shear rates, which resulted in a decrease of viscosity and the subsequent increase of flow rates. However, the shear rate for the transverse vibration was slightly increased and the calculated flow rate was underestimated comparing with the previous experimental results.

• 대한기계학회논문집A
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• 제22권2호
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• pp.437-443
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• 1998

Automobile company tries to reduce the inertia of powertrain to increase the fuel efficiency and increase the engine power every year to make the high speed driving possible at full load condition. These cause the torsional vibration of powertrain. But the demand about ride comfort improvement is increased constantly, so torsional vibration of powertrain become an emergency problem to be cured. This study is a basic research to reduce the torsional vibration of powertrain at driving condition. First, the heavy duty powertrain is characterized as a vibrating system. Its natural frequencies and mode shapes are reviewed. Second, by comparison of simulation results and experiment results, validity of developed model is verified. Finally, the couterplan which can reduce the torsional vibration by mode analysis and parameter modification is suggested.

• 대한기계학회논문집A
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• 제20권5호
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• pp.1534-1542
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• 1996

Gear vibration is caused by the mesh stiffness, gear accuracy, and assembling errors. For these reasons, helical gear has the azial, radial, and rotational vibrations. In this study, the mesh stiffness is calculated by considering the tooth bending, contact, and foundation deformations. Rotational vibration of helical gear with tooth error is modeled by the nonlidear equation of motion with single degree of freedom and is anlyzed numerically. Also, by a specially designed experimental set-up, the analysis are cross-checked and the vibration characteristics of helical gear are discussed.

• Structural Engineering and Mechanics
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• 제57권1호
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• pp.161-178
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• 2016

This research is aimed to design and analyze the performance of double dynamic vibration absorber (DVA) using a pendulum and a spring-mass type absorber for reducing vibration of two-DOF vibration system. The conventional fixed-points method and genetics algorithm (GA) optimization procedure are utilized in designing the optimal parameter of DVA. The frequency and damping ratio are optimized to determine the optimal absorber parameters. The simulation results show that GA optimization procedure is more effective in designing the double DVA in comparison to the fixed-points method. The experimental study is conducted to verify the numerical result.