• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.10a
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• pp.41-46
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• 2003

The important problem in high speed spindles is to reduce and minimize the thermal effect by motor and bail bearings. Thermal characteristics according to the bearing pre-load and cooling condition are studied for the test spindl with grease lubrication and high frequency motor. Bearing and motor we main heat generation, and heat generation by ball bearings as a function of load, viscosity and gyroscopic moment effect are considered. Temperature distribution and thermal displacement according to the speed of spindle are measured by thermocouple and gap sensor. The results show that the fitting pre-load and cooling temperature are very effective to minimize the thermal effect by motor an ball bearings.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.303-306
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• 1997

Magnetic bearings have been adopted to support the rotor by electromagnetic force without mechanical contact and have many advantages. The application of the magnetic bearings have become more and more widespread in recent years. But magnetic bearings require feedback control for stable operation because they are inherently open loop unstable systems. In this study, H infinity controller has been applied for rotor-magnetic bearing system for vibration control. The result showed that H infinity controller has better performance than PID controller through simulations.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.607-610
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• 2002

As machines become smaller and faster multileaf foil bearings are used to overcome the problems with heat, friction and wear Systems with foil bearings do not need a separate system for lubrication. These bearings are self acting and are therefore green systems. Until now, there have been many studies on the structural and dynamical performances. Therefore the object of the present study is to predict the flow and structural characteristics by using the Fluid/structure interaction method. The increase in RPM led to the increase in pressure, temperature difference, maximum velocity, Mach number, shear stress and torque. In the case of 90,000 RPM effects such as choking led to a non-lineararity in the system. Also the effect of eccentricity ratio was observed and showed that eccentricity increased the maximum pressure and the density difference while decreasing the shear stress and torque.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.8
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• pp.1787-1798
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• 1995

Monitoring and diagnosis of the operating machine mean evaluating the condition of a machine such as the detection of the defects and the prediction of the time to failure in the machine elements, while it is running. In this study, a technique of automatic diagnosis using probability concept is studied and the analyses of the pattern comparison are introduced. An expert system, which is able to analyze the automatic identification of the multiple defects in the ball bearings, is also developed. Finally, to confirm the effectiveness of the programmed algorithms, some tests were made with specimens of the ball bearings involving the multiple defects. The proposed system reasonably predicts the defects.

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.1
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• pp.19-24
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• 2008

We propose a new miniature air-bearing stage with a moving-magnet slotless linear motor. This stage was developed to achieve the precise positioning required for submicron-level machining and miniaturization by introducing air bearings and a linear motor sufficient for mesoscale precision machine tools. The linear motor contained two permanent magnets and was designed to generate a preload force for the vertical air bearings and a thrust force for the stage movement. The characteristics of the air bearings, which used porous pads, were analyzed with numerical methods, and a magnetic circuit model was derived for the linear motor to calculate the required preload and thrust forces. A prototype of a single-axis miniature stage with dimensions of $120\;(W)\;{\times}\;120\;(L)\;{\times}\;50\;(H)\;mm$ was designed and fabricated, and its performance was examined, including its vertical stiffness, load capacity, thrust force, and positioning resolution.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.936-941
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• 2001

This paper deals with the design of oil-tree motor-driven two-stage centrifugal compressor supported by air-lubricated multi-leaf foil bearings. The design of this compressor is performed, based upon prediction of critical speeds, load capacity, and stability. It is demonstrated in this paper that multi-leaf foil bearings can be adopted to satisfactorily support this centrifugal compressor.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.7 s.112
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• pp.746-753
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• 2006

This paper proposes a method to calculate the stiffness and the damping coefficients of the coupled journal and thrust bearings. The Reynolds equations and their perturbation equations are transformed to the finite element equations by considering the continuity of pressure and flow at the interface between bearings. The Reynolds boundary condition is used in the numerical analysis to simulate the cavitation phenomena. The dynamic coefficients of the proposed method are compared with those of the numerical differentiation of the loads with respect to finite displacements and velocities of bearing center. It shows that the proposed method is more accurate and efficient than the differentiation method.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.11
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• pp.1102-1111
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• 2007

The theory for a fault-tolerant control of homopolar magnetic bearings is developed. New coil winding law is utilized such that control fluxes are isolated for an 8-pole homopolar magnetic bearing. Decoupling chokes are not required for the fault tolerant magnetic bearing since C-core fluxes are isolated. If some of the coils or power amplifiers suddenly fail, the remaining coil currents change via a distribution matrix such that the same magnetic forces are maintained before and after failure. Lagrange multiplier optimization with equality constraints is utilized to calculate the optimal distribution matrix that maximizes the load capacity of the failed bearing. Some numerical examples of distribution matrices are provided to illustrate the theory. Simulations show that very much the same dynamic responses (orbits or displacements) are maintained throughout failure events while currents and fluxes change significantly.

• Earthquakes and Structures
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• v.7 no.6
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• pp.969-999
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• 2014

Aim of the paper is the definition of optimal design parameters characterizing the isolation system of a bridge, both in the case of elastomeric (VI) and sliding bearings (SI), having viscoelastic or rigid-plastic behavior, respectively, installed between the piers and the deck. The problem is treated by means of an analytical approach. Using the frequency response analysis, a simple procedure is proposed to determine the optimal value of the viscous coefficient or the yield displacement of the isolators. The adequacy of the proposed procedure is finally verified through time-history analyses performed on a practical case under natural earthquakes.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.09a
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• pp.320-328
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• 2001

Base Isolation system is an effective design strategy that provides a practical substitute for the seismic design of bridge. In this study, the dynamic tests were performed on two kinds of aseismic bridge bearings : Hydampot (hysteretic damping bearing) and Dynapot . Then, the dynamic analysis was carried out far a bridge using the experimental results to estimate the seismic performance of the bearings. Analysis was performed for four types oi earthquake loadings. The results of the dynamic test and theoretical analysis indicate that the performance of both bridge bearings is appropriate fur the earthquake loading.