• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.6
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• pp.1203-1211
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• 2017

This paper proposes a robust controller for flexible joint robots to achieve tracking performance and to improve robustness against both matched and mismatched disturbances. The proposed controller consists of a disturbance observer(DOB), passivity-based controller, and integral sliding mode controller(ISMC) in a backstepping manner. The DOB compensates the mismatched disturbance in the link-side and formulates the reference input for the motor-side controller. Interconnection and damping assignment passivity-based controller (IDA-PBC) performs tracking control of motor-side, and it is integrated to nominal control of ISMC to guarantee the over-all stability of the nominal system, while, matched disturbances are decoupled by the discontinuous control of ISMC. In the design of the link-side controller, PD type impedance controller is designed with DOB and this leads the continuous control input which is suitable to the reference input for the motor-side.

• Structural Engineering and Mechanics
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• v.63 no.3
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• pp.329-345
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• 2017

This paper devoted to study dynamic interaction between crack and inclusion or void by developing the eXtended Finite Element Methods (XFEM). A novel XFEM approximation is presented for these structures containing multi discontinuities (void, inclusion, and crack). The level set methods are used so that elements that include a crack segment, the boundary of a void, or the boundary of an inclusion are not required to conform to discontinuous edges. The investigation covers the effects of a single circular or elliptical void / stiff inclusion, and multi stiff inclusions on the crack propagation path under dynamic loads. Both the void and the inclusion have a significant effect on the dynamic crack propagation path. The crack initially curves towards into the void, then, the crack moves round the void and propagates away the void. If a large void lies in front of crack tip, the crack may propagate into the void. If an enough small void lies in front of crack tip, the void may have a slight or no influence on the crack propagation path. For a stiff inclusion, the crack initially propagates away the inclusion, then, after the crack moves round the inclusion, it starts to propagate along its original path. As ${\delta}$ (the ratio of the elastic modulus of the inclusion to that of the matrix) increases, a larger curvature of the crack path deflection can be observed. However, as ${\delta}$ increases from 2 to 10, the curvature has an evident increase. By comparison, the curvature has a slight increase, as ${\delta}$ increases from 10 to 1000.

• Journal of Satellite, Information and Communications
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• v.9 no.3
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• pp.86-90
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• 2014

A DC-DC Converter operates in CCM(Continuous Coundcution Mode), DCM(Discontinuous Conduction Mode), CRM(Critical Conduction Mode). The CRM is boundary between CCM and DCM. If a DC-DC converter is designed to operate in CRM, its inductor volume can decrease and power loss which caused by switch and diode can decrease. In this paper, the DC-DC converter which operates in CRM is applied to a solar array regulator(SAR) for the satellite. The switching frequency of the CRM boost SAR changes according to input and output condition. The switching frequency limit logic is applied to limit the maximum switching frequency. Meanwhile, the small signal transfer function of the CRM boost SAR is simple, so the controller design is also simple. In this paper, the small signal transfer function from control reference to solar array voltage is induced. And the voltage controller is designed based on the small signal transfer function. Finally, the CRM boost SAR is verified by simulation.

• Korean Journal of Materials Research
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• v.24 no.11
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• pp.585-590
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• 2014

Microstructural evolution in the thickness direction of an oxygen free copper processed by accumulative rollbonding (ARB) is investigated by electron back scatter diffraction (EBSD) measurement. For the ARB, two copper alloy sheets 1 mm thick, 30 mm wide and 300 mm long are first degreased and wire-brushed for sound bonding. The sheets are then stacked and roll-bonded by about 50% reduction rolling without lubrication at an ambient temperature. The bonded sheet is then cut to the two pieces of the same dimensions and the same procedure was repeated on the sheets up to eight cycles. The specimen after 1 cycle showed inhomogeneous microstructure in the thickness direction so that the grains near the surface were finer than those near the center. This inhomogeneity decreased with an increasing number of ARB cycles, and the grain sizes of the specimens after 3 cycles were almost identical. In addition, the aspect ratio of the grains decreased with an increasing number of ARB cycles due to the subdivision of the grains by shear deformation. The fraction of grains with high angle grain boundaries also increased with continuing process of the ARB so that it was higher than that of the low angle grain boundaries in specimens after 3 cycles. A discontinuous dynamic recrystallization occurred partially in specimens after 5 cycles.

• Journal of Digital Contents Society
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• v.2 no.2
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• pp.179-189
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• 2001

This paper aims at faster processing and retrieval in fingerprint identification systems by reducing the amount of preprocessing and the size of the feature vector. The distribution of fingerprint directions is a set of local directions of ridges and furrows in small overlapped blocks in a fingerprint image. It is extracted initially as a set of 8-direction components through the Gabor filter bank. The discontinuous distribution of directions is smoothed to a continuous one and visualized as a direction image. Then the center of the distribution is selected as a reference point. A feature vector is composed of 192 sine values of the ridge angles at 32-equiangular positions with 6 different distances from the reference point in the direction image. Experiments show that the proposed algorithm performs the same level of correct identification as a conventional algorithm does, while speeding up the overall processing significantly by reducing the length of the feature vector.

• Archives of design research
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• v.13 no.3
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• pp.245-252
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• 2000

The facade in the street is a unfixed type, thus it is not easy to investigate the characteristic of structures. In addition, a color mainly depends on sensitivity, therefore, it is very difficult to provide the solution of the problems. The purpose of this study is to investigate the relationship between a form of the facade and a color, and to introduce the methodology and the direction of the color scheme for the facade in the street. for the purpose of this study, 47 facades are empirically analyzed. Based upon the results of research analysis, this study try to find out the relationship among the formative continuity of the facade in the street, a color, and the quality of the material. From the results, it suggests the new direction for the image formation of the facade in the street centering around a color. This study concludes that the characteristics of the facade in the street is discontinuous, and the color scheme is not based on the formative continuity. Moreover, the whole street is composed of each strong individual character. In order to harmonious creation of the facade in the street, primary colors and painting colors should be constrained. Finally, the color scheme based on the formative continuity of the facade in the street should be carefully considered.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.10
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• pp.77-82
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• 2004

This paper presents polar converting logic(PCL) of BTT missiles against slowly moving or stationary targets. A guidance commands expressed in rectangular coordinates must be converted in the form of polar coordinates for BTT control. Since conventional PCL has nonlinear and discontinuous function, the missiles may lose controllability when pitch acceleration command equals to zero. Further, roll coupling may have a serious unstabilizing influence on homing guidance with two gimbals seeker. In this paper, a linear homotopy equation is introduced to improve the controllability and a command following performance at midcourse phase. We also design a PCL which is less sensitive to pitch acceleration command so that it may improve the stability of the homing loop. To substantiate our conclusion, results of the computer simulation have been illustrated.

• Proceedings of the KIEE Conference
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• 2006.04b
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• pp.310-312
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• 2006

Maglev using EMS becomes unstable by unexpected big air-gap disturbance. The main causes of the unexpected air-gap disturbance are step-wise rail joint and large distance between rail splices. For the stable operation of the Maglev, the conventional system uses the threshold method, which selects one gap sensor among two gap sensors installed on the magnet to read the gap between magnet and guide rail. But the threshold method with a wide bandwidth makes the discontinuous air-gap signal at the rail joints because of the offset in air gap sensors and/or the step-wise rail joins. Further more, in the case of the one with a narrow bend-width, it makes Maglev system unstable because of frequent alternation. In this paper, a new method using fuzzy rule to reduce air-gap disturbances proposed to improve the stability of Maglev system. It treats the air-gap signal from dual gap sensors effectively to make continuous signal without air gap disturbance. Simulation and experiment results proved that the proposed scheme was effective to reduce air-gap disturbance from dual gap sensors in rail joints.

• Journal of Welding and Joining
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• v.15 no.4
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• pp.143-153
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• 1997

In this study, bending test was performed on the real-scale, built-up beam test model fabricated by the $CO_2$ arc spot welding to evaluate the applicability of the welding method to the production of the stiffened plate in car-carrying ship. The built-up beam models which were fixed at both ends in longitudinal direction or simply supported to the rigid foundation, depending on the restraint condition of the corresponding car decks considered, were subjected to simulated design vehicle loads or concentrated point loads. During the test, the central deflection and the longitudinal bending stresses were measured from several points on the longitudinal flange face to predict the section properties of the built-up beams. The longitudinal bending stress on each spot weld were also measured to calculate the average horizontal shear force subjected to spot welds. Test results revealed that the shear strength of spot welds with their current weld nugget size and welding pitch was adequate enough to withstand the horizontal shear forces under the design vehicle loads. Although the built-up beam fabricated by the arc spot welding was a discontinuous beam, its mechanical behavior was well explained by the continuous beam theory using the effective breadth of plate. Based on test results, the criterion for the size of spot weld of which the average shear stress might meet the allowable stress requirement of AWS Code could be established.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.1
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• pp.67-81
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• 2000

An accurate and efficient numerical method for two-dimensional nonlinear radiation problem has been developed. The wave motion due to a moving body is described by the assumption of ideal fluid flow, and the governing Laplace equation can be effectively solved by the higher-order boundary element method with the help of the GMRES (Generalized Minimal RESidual) algorithm. The intersection or corner problem is resolved by utilizing the so-called discontinuous elements. The implicit trapezoidal rule is used in updating solutions at new time steps by considering stability and accuracy. Traveling waves caused by the oscillating body are absorbed downstream by the damping zone technique. It is demonstrated that the present method for time marching and radiation condition works efficiently for nonlinear radiation problem. To avoid the numerical instability enhanced by the local gathering of grid points, the regriding technique is employed so that all the grids on the free surface may be distributed with an equal distance. This makes it possible to reduce time interval and improve numerical stability. Special attention is paid to the local flow around the body during time integration. The nonlinear radiation force is calculated by the "acceleration potential technique". Present results show good agreement with other numerical computations and experiments.