• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 추계학술대회 논문집
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• pp.528-533
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• 1995

An analyical method is proposed to construct a clamp jointed structure as an equivalent stiffness matrix element in the finite element modal analysis of a complex beam structure. Static structural analysis was first made for the detail finite element model of the clamp joint. Utilizing the results of this analysis, the equivalent stiffness matrix element was buildup by using the flexibility influence coefficient method and Guyan condensation. The proposed method was applied to finite element modal analysis of a clamp jointed cantilever beam. And the finite element analysis results were compared to those experimental modal analysis. Comparison shows doog agreement each other Furthermore the effects of normal contact(or clamping) load on the equivalent stiffness matrix was also examined. The equivalent stiffness matrix showed little change in spite of the remakable increase in the contact load on the clamp joint.

• 한국철도학회:학술대회논문집
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• 한국철도학회 1998년도 창립기념 춘계학술대회 논문집
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• pp.525-532
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• 1998

In this study, dynamic characteristics of catenary that supplies electrical power to high-speed trains is investigated. A particular emphasis is placed on the effect of droppers on the dynamic response of the contact wire, a dropper is an element that connects the contact wire with the messenger wire so as to maintain near uniform compliance, Finite element model compressing 3 spans is constructed. For the linear model, droppers are modeled as linear springs with various stiffness values. Modal analysis is performed to obtain the natural frequencies and modes and the variation in the modal density distribution for changing stiffness values are noted. Impulse response is also obtained through computer simulation. In practice, dropper is a nonlinear element with low stiffness in compression and high stiffness in tension. Hence, dropper can be modeled as a nonlinear spring with hi-directional stiffness values. Impulse and harmonic responses are obtained for the nonlinear model through simulation. The responses aye also compared with the linear cases.

• 한국생산제조학회지
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• 제20권6호
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• pp.756-760
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• 2011

This paper proposed an alignment stage driven by piezo actuators for alignment process of a contact-type lithography. Among contact-type lithography processes, an UV-curable nanoimprint process is an unique process to be able to align patterns on upper and lower layers. An alignment stage of the UV-curable nanoimprint process requires nano-level resolution as well as high stiffness to overcome friction force due to contact moving. In this paper, the alignment stage consists of a compliant mechanism using flexure hinges, piezo actuators for high force generation, and capacitive sensors for high-resolution measurement. The compliant mechanism is implemented by four prismatic-prismatic compliant chains for two degree-of-freedom translations. The compliant mechanism is composed of flexure hinges with high stiffness, and it is directly actuated by the piezo actuators which increases the stiffness of the mechanism, also. The performance of the ultra-precision stage is demonstrated by experiments.

• 대한기계학회논문집
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• 제18권12호
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• pp.3185-3194
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• 1994

In this study, an impact model and impact response analysis method was suggested for the impacts between arbitrary shaped bodies. Unlike the impacts between geometrically simple structures, there is no rules to analyze the impacts between general elastic structures First of all, it has been attempted to explain the impoot between arbitrary elastic structures as the elastic deformation of a virtual contact spring in the vicinity of contact points. The contact stiffness and the exponent are determined from the Hertz's contact theory and F. E. analysis. In order to evaluate the validities and limitations of the proposed methods, an impact tester and the miniature of container, missile and isolators have been provided and tested experimentally. All the experiments were performed with various impact conditions. The results obtained by the proposed methods were directly compared with the measured values in terms of maximum contract force, contact duration, the shape of contact force and the structure responses. The computed contact force and responses, using this proposed methods, were very close to the measured results, unless any plastic deformations were presented.

• 비파괴검사학회지
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• 제31권1호
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• pp.40-46
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• 2011

닫힘균열과 같은 고체-고체의 접촉계면에서 접촉 음향 비선형성을 평가하기 위해 벌크 투과파를 이용하는 기존의 전통적인 음향 비선형 기술의 경우 현장 적용하는데 있어서 송수신 탐촉자를 장착하기 위해 구조물 내부로 접근하는 것은 접근한계성의 어려움이 있다. 본 연구에서, 고체-고체의 접촉계면에서 음향 비선형성을 측정하기 위해 새로운 반사기법을 제안하였고 이는 대상재료의 동일한 면에서 송신과 수신을 하여 현장 적용성에 매우 편리한 기법이다. 이를 위해, 접촉압력에 대한 멱함수 모델를 통한 선형 그리고 비선형 강성을 추정하고 이를 기반으로 계면에서 반사된 초음파의 비선형 파라미터를 이론적으로 계산하였다. A16061-T6 시편에 대한 접촉압력에 따른 접촉계면 실험 결과들은 이론적인 예측과 매우 잘 일치하였으며 따라서 본 연구에서 제안된 반사모드 기술의 유효성을 검증하였다.

• 항공우주시스템공학회지
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• 제4권2호
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• pp.1-9
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• 2010

An airless tire has advantages over the conventional pneumatic tire in terms of flat proof and maintenance free. According to the recently disclosed inventions on the airless tire, non-pneumatic tire (NPT) consists of the flexible polygon spokes. Considering the NPT structure, the spokes undergo the tension-compression cyclic loading while the tire rolls. Therefore the spokes of NPT are required to have both stiffness and resilience under the cyclic tensile-compressible loading. In general, if a material has a high stiffness, it shows a low elastic strain limit. In this paper, using the auxetic honeycomb structure with negative poissons's ratio, the spokes of NPT tire are designed to have both stiffness and resilience. Finite element based numerical simulation of the contact pressure of a NPT is carried out with ABAQUS.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1998년도 제13차 학술회의논문집
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• pp.20-25
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• 1998

This paper proposes a new compliant contact control strategy for the robot manipulators accidentally interacting with an unknown environment. The main features of the proposed method are summarized as follows: First, each entry in the diagonal stiffness matrix corresponding to the task coordinate in Cartesian space is adaptively adjusted during con-tact along the corresponding axis based on the contact force with its environment. Second, it can be used for both unconstrained and constrained motions without any switching mechanism which often causes undesirable instability and/or vibrational motion of the end effector. Third, the adjusted stiffness gains are automatically recovered to initially specified stiffness gains when the task is changed from constrained motion to unconstrained motion. The simulation results show the effectiveness of the proposed method by employing a two-link direct drive manipulator interacting with an unknown environment.

• Journal of Mechanical Science and Technology
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• 제15권12호
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• pp.1630-1638
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• 2001

Partial rotor rub occurs when an obstacle on the stator of a rotating machinery disturbs the free whirling motion of the rotor, which is more common than full annular rub among the cases of rubbing in rotating machinery. The intermittent contacts and friction during partial rotor rub makes the phenomenon complex. The several nonlinear phenomena of superharmonics, subharmonics, and jump phenomenon are demonstrated for the partial rub using an experimental apparatus in this study. The orbit patterns are also measured experimentally. In order to explain the phenomena of partial rotor rub, the analytical model for the contact between the rotor and stator should be chosen carefully. In this respect, a piecewise-linear model and a rebound model using the coefficient of restitution are investigated on the basis of the experimental observations. Also, Numerical simulations for the two models of contact are done for the various system parameters of clearance, contact stiffness, and friction coefficient. The results show that the piecewise-linear model for partial rotor rub is more plausible to explain the experimental observgations.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.277-282
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• 2001

Partial rotor rub occurs when an obstacle on the stator of a rotating machinery disturbs the free whirling motion of a rotor, which is more common than full annular rub for the cases of rubbing in rotating machinery. The nonlinearity due to the intermittent contacts and friction during partial rotor rub makes the phenomenon complex. The several nonlinear phenomena of superharmonics, subharmonics, and jump phenomenon are demonstrated for the partial rub using an experimental apparatus in this study. A piecewise-linear model and a rebound model using the coefficient of restitution are investigated on the basis of experimental observations in order to adopt as an analytical model of the contact between the rotor and stator during whirling motion. The contact stiffness, coefficient of restitution, and friction coefficient for the contact during partial rub are calculated from the comparison between the numerical simulation and the experimental results. Also, the numerical simulations for the model of partial rub are done for the various system parameters of clearance, contact stiffness, and friction coefficient in order to find the nonlinear behavior of partial rotor rub.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.1391-1395
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• 2006

In non-contact mode atomic force microscopy, the response of a resonating tip is used to measure the nanoscale topography and other properties of a sample surface. However, the tip-surface interactions can affect the tip response and destabilize the non-contact mode control. Especially it is difficult to obtain a good scanned image of high adhesion surfaces such as polymers using conventional hard NCHR tip and non-contact mode control. In this study, experimental investigation is made on the non-contact mode imaging and we report the microcantilever having low stiffness (OMCL) is useful to measure the properties of samples such as elasticity. In addition, we proved that it was adequate to use low stiffness microcantilever to obtain a good scanned image in AFM for the soft and high adhesion sample.