• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.137.4-137
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• 2001

Omni-directional mobile robots have been employed popularly in several application areas. However, the optimal design has not been considered yet. This paper introduces an optimal design methodology for omni-directional mobile robots. Optimal design parameters such as the offset distance and the wheel radius are identified with respect to isotropy. Furthermore, the force transmission ratio and actuator sizing problem are treated. Conclusivel, three cases are compared minimum actuation, two active caster wheel, and three active caster wheel, we claim that the redundantly actuated mobile robot with three active caster wheel has the best performance.

• Fibers and Polymers
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• v.2 no.4
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• pp.178-183
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• 2001

A pitch precursor for a general purpose carbon fiber was prepared by condensation of pyrolized fuel oil (petroleum residual oil) with bromine under nitrogen blowing. such a condensation raised the softening point of the pitch from 4$0^{\circ}C$ to $265^{\circ}$ with a yield of 43%. The pitch precurosr showed an enhanced aromaticity and enlarged molecular size, which led to a reduction in molecular mobility and optical isotropy. The precursor was spun into fibers of $20\mu\textrm{m}$ diameter at a take-up speed of 700m/min. The fiber was stepwise stabilized in air and carbonized in Ar gas to obtain an isotropic carbon fiber. The carbon fiber exhibited tensile strengths of 500-800 ㎫though the fiber was formed via a crude method. The electric conductivity of the carbon fiber was relatively high, 2.2$\times$$10^2$S/cm, sufficient to be used as electrode materials.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1693-1696
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• 2003

In this paper, input-output velocity transmission characteristics of the Casing Oscillator, which is a constructional machine with 4 degree of freedom are examined. After the Jacobian matrix is decomposed into linear part and angular part, the linear and the angular velocity transmission characteristics are analyzed and visualized in easy way even in the case of 3 dimensional task space with 4 variables. Regarding the measure of dexterity of the Casing Oscillator, the kinematic isotropic index and the manipulability measures which are respectively represented the isotropy and the volume of the manipulability ellipsoid are combined. A performance of the Casing Oscillator is evaluated by the combined manipulability measure.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.7
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• pp.904-914
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• 2004

In this paper, input-output velocity and force transmission characteristics of the Casing Oscillator which is a construction machine with 4 degrees of freedom are examined. After the Jacobian matrix is decomposed into the linear part and angular part, the velocity and force transmission characteristics for the linear and angular workspace are easily analyzed and visualized even if the Casing Oscillator has the spatial dimensional workspace with 4 DOF. Regarding the manipulability measure of the Casing Oscillator, the kinematic isotropic index and the manipulability measure which represent the isotropy and volume of the manipulability ellipsoid, respectively, are combined to coincidently consider them with respect to equivalent ranges and fluctuations. A performance of the Casing Oscillator is evaluated by the newly proposed manipulability measures.

• Journal of the Korean Society of Industry Convergence
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• v.4 no.4
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• pp.387-393
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• 2001

The flow characteristics on the centerline in case of free jet, sudden expansion jet and impinging jet have been investigated. Centerline flow behaviors and similaritis with mean velocities, turbulent intensities, shear stresses, isotropic structures and turbulent kinetic energies on the streamwise direction were looked into and compared with three jets, The results show that mean velocities have represented potential core and decayed with similar gradients. The turbulent intensities and shear stresses were presented peak values in the self-preserving region, and then they were in decay. Aeolotropy in the initial region were possible returned to isotropy patterns with asymptotic approach in the downstream region. It has been found that the turbulent kinetic energies for the three cases of jet existed in the similarity and they coincided with Gaussian profile.

• Tunnel and Underground Space
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• v.10 no.3
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• pp.301-308
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• 2000

Non-linear behavior of rock under compression can be predicted by a crack model. Crack growth in rock renders rock anisotropic. The degree of anisotropy is explained in terms of elastic moduli as a function of load level. In this study, we calculate the changes of elastic moduli due to crack growth numerically by using a crack model and compare these values with experimental results obtained from the measurement of ultrasonic wave velocities. Image processing technique is used to obtain the initial crack information needed for the numerical calculation of elastic moduli.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.47-55
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• 2000

Non-linear behavior of rock under compression can be predicted by a crack model. Crack growth in rock renders rock anisotropic. The degree of anisotropy is explained in terms of elastic moduli as a function of load level. In this study, we calculate the changes of elastic moduli due to crack growth numerically by using a crack model and compare these values with experimental results obtained from the measurement of ultrasonic wave velocities. Image processing technique is used to obtain the initial crack information needed for the numerical calculation of elastic moduli.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1450-1454
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• 2000

In order to understand dynamic characteristics of centrifugal compressor supported foil bearing, of which normal operating speed is about 20,000 ${\sim}$ 50,000 rpm, the rotor whirl is measured using gap sensors. Not only critical speeds of rotor system but also stability of rotor whirl, which are main concerns of the turbo compressor system, are measured using gap sensors by varying the rotating speed the rotor. The stiffness characteristics of bearing system is shown to be almost invariant according to speed variation by the measurement of eccentricity. In addition, from the directional power spectral density function of the measured vibration signal, the isotropy stiffness characteristics of foil bearing system is discussed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.257-260
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• 1997

The high precision of the products manufatured by press forming requires the high stiffness of press machines. In this study, the C-frame type press is analyzed to provide the basic idea on the C-frame press design, especially on the frame design. The finite element method is applied for the analysis and the isotropic propertics of the frame material is also considered. The results are summarized in terms of stresses and displacement distributions. Also, the openback angle of the presses is compared with two different models. The CS-150 and ECS-150 models, which are presses model having 150 ton frame capacity relatively and produced by SSangYong precision Co. LTD, are applied for the analysis.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.49-52
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• 1999

Tailored-welded blanks are used for forming of automobile structural and skin components. Its main objective is to achieve weight and production cost reduction in manufacturing of the components. For successful application of tailored-welded blanks design of initial welded blanks and prediction of welding line movement are critical. Here the utilization of the backward tracing scheme of the finite element method shows to be desirable in design of initial welded blanks for net-shape production and in prediction of the welding line movement. First the design of initial blank in forming of welded thick sheet with isotropy is tried and it appears successful in obtaining a net-shape stamping product. Based in the first approach the backward tracing scheme is applied to anisotropic tailored blank. The welding line movement is also discussed.