• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1992년도 가을 학술발표회 논문집
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• pp.133-138
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• 1992

The three dimensional analysis of Framed-Tube structures is neither easy nor efficient because of longer computational time, large memory requirement, tedious input preparation and bulky output. An efficient analysis model for framed-tube structure is proposed in this study. The proposed model can save the computational effort by using the assumption of the rigid floor diaphragm effect and matrix condensation technique. Moreover, it is develpoed by assembling two dimensional frames using the link degrees of freedom which are temporary used to satisfy the vertical displacement compatibility at the corners of a framed-tube. The accuracy and the efficiency of this analytical model is established by comparing with the results using the computer code SAPIV which is based on the three dimensional finite element model.

• International Journal of Control, Automation, and Systems
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• 제6권1호
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• pp.76-85
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• 2008

Motivated by the fact that in many industrial robots the joint velocity is estimated from position measurements, the trajectory tracking of robot manipulators with output feedback is addressed in this paper. The fact that robot actuators have limited power is also taken into account. Let us notice that few solutions for the torque-bounded output feedback tracking control problem have been proposed. In this paper we contribute to this subject by presenting a theoretical reexamination of a known controller, by using the theory of singularly perturbed systems. Motivated by this analysis, a redesign of that controller is introduced. As another contribution, we present an experimental evaluation in a two degrees-of-freedom revolute-joint direct-drive robot, confirming the practical feasibility of the proposed approach.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.568-571
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• 2005

This paper introduces a correlation-based surface matching algorithm that can be used to reconstruct the surface topography of an object that is scanned from multiple overlapping regions by an AFM. The image matching technique is applied to two neighboring images intentionally overlapped with each other. To account for the inaccuracy of the coarse stage implemented in AFM, all the six axes including the rotational degrees of freedom are successively matched to maximize the correlation coefficient. The results show that the proposed 6-axes image matching method is useful for expanding the measurement range of AFM.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 추계학술대회논문집
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• pp.527-533
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• 2000

It is investigated that the characteristics of rotating cantilevered composite beam with a breathing crack. In the present study, the crack is modeled as a breathing crack which opens and closes with the motion of the unidirectional graphite-fiber reinforced polyimide beam. For the finite element analysis, the cracked element is modelled by the local flexibility matrix calculated on the basis of fracture mechanics using Castiligano theorem. Rotating beam is considered only transverse bending motion so that the element includes two degrees of freedom per node such as the transverse deflection and slope. The time history and frequency response function of the beam with a breathing crack are studied by Newmark direct time integration method and FFT(Fast Fourier Transform)simulation. Effects of various parameters such as the crack depths, crack locations, ply angles, volume fraction ratios, and rotating speeds of the beam are also studied. Numerical results indicate that it is more reliable to be modelled as a breathing crack than an open crack.

• 전자공학회논문지B
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• 제33B권4호
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• pp.27-40
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• 1996

This paper proposed a kinematic modeling methodlogy and feedback control system based on kinematics for 2 degrees of freedom of 4-wheeled mobile robot. We assigned coordinate systems to specify the transformation matirx and write the kinematic equation of motion. We derived the actuated inverse and sensed forwared solution for the calculation of actual robot orientation and the desired robot orientation. It is the most significant error and has the largest impact on the motion accuracy. To calculate the WMR position in real time, we introduced the dead-reckoning algorithm and composed two feedback control system that is based on kinematics. Through the simulation result, we compare with the ffedback control system for position control.

• Tribology and Lubricants
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• 제20권4호
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• pp.209-217
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• 2004

Lubrication characteristics between a cylinder block and a valve plate for high speed bent-axis type hydraulic pump play an important role in volumetric efficiency and durability of pump. In this paper, a finite element method is presented for the computation of the pressure distribution between a cylinder block and a valve plate for high speed bent-axis type hydraulic pump. Also, a Runge-Kutta method is applied to simulate the cylinder block dynamics of three-degrees of freedom motion. From the results of computation, we can draw two major conclusions. One is related to the fluid film characteristics between a cylinder block and a valve plate and the other is related to the average leakage that is determined by the pressure gradient and the clearance near the discharge port. The numerical results of cylinder block dynamics were compared with the experimental results using eddy-current type gap sensors those are fixed at a pump housing.

• 대한기계학회논문집A
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• 제25권11호
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• pp.1697-1704
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• 2001

A finite element model for polarization switching in electro-mechanically coupled materials is proposed and applied to predict the switching behavior of a two-dimensional ferroelectric ceramic. A complicated micro-structure existing in the material is modeled as il continuum body and a simple 3 node triangle finite element with nodal displacement and voltage degrees of freedom is used for a finite element analysis. The elements use nonlinear constitutive equations, switching criterion and kinetic relation, fur representation of material response at strong electric and stress fields. The polarization state of the material is represented by internal variables in each element, which are updated at each simulation step based on the proposed constitutive equations. The model reproduces strain and electric displacement hysteresis loops observed in the material.

• 한국정밀공학회지
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• 제22권8호
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• pp.118-127
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• 2005

A spatial 3 degrees-of-freedom mechanism employing Stewart Platform structure is proposed: the mechanism maintains the 3- RRPS structure of Stewart Platform but has an additional passive PRR serial sub-chain at the center area of the mechanism in order to constrain the output motion of the mechanism within the output motion space of the added PRR serial subchain. The forward and reverse position analyses of the mechanism are performed. Then the mechanism having both the forward and the reverse closed-form solutions is suggested and its closed form solutions are derived. It is confirmed, through the kinematic analysis of those two proposed mechanisms via kinematic isotropic index, that both the proposed mechanisms have fairly good kinematic characteristics compared to the existing spatial 3-DOF mechanisms in literature.

• 한국CDE학회논문집
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• 제5권4호
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• pp.393-402
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• 2000

Recently 5-axis NC machines are widely used in Korea. Since 5-axis machines have two more degrees of freedom than 3-axis machines, it is very important to find desirable tool positions(locations and orientations) in order to make an efficient use of expensive 5-axis NC machines. In this research an algorithm to determine “optimal” tool positions for 5-axis machining of sculptured surfaces is developed. For given CC(Cutter Contact) points, this algorithm determines the cutter axis vectors which minimize cusp heights and satisfy constraints. To solve the optimal problem, we deal with following major issues: (1) an approximation method of a cusp height as a measure of optimality (2) Identifying some properties of the optimal problem (3) a search method for the optimal points using the properties. By using a polyhedral model as a machining surface, this algorithm applies to sculptured surfaces covering: overhanged surface.

• 제어로봇시스템학회논문지
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• 제13권8호
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• pp.769-776
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• 2007

This paper proposes the human arm motion tracking algorithm based on the signal processing for surface EMG (electromyogram) sensors attached on both upper arm and shoulder. The signals acquired by using surface EMG sensors are processed with choosing the maximum in a short period, taking the absolute value, and filtering noises out with a low-pass filter. The processed signals are directly used for the motion generation of virtual arm in real time simulator. The virtual arm of simulator has two degrees of freedom and complies with the flexion and extension motions of elbow and shoulder. Also, we show the validity of the suggested algorithms through the experiments.