• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.05a
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• pp.157-160
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• 2004

We have studied an optically compensated splay (OCS) mode driven by fringe electric field. The OCS LC configuration obtained by applying voltage to vertically aligned LCs shows a dark state when an optic axis of the OCS cell coincides with one of crossed polarizer axis. When the fringe electric field is applied, the LC director rotates in plane above whole electrode surface, giving rise to high transmittance and wide viewing angle simultaneously.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.356.2-356.2
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• 2014

Spin Transfer Torque (STT) is of great interest in data writing scheme for the Magneto-resistive Random Access Memory (MRAM) using Magnetic Tunnel Junction (MTJ). Scalability for high density memory requires ferromagnetic electrodes having the perpendicular magnetic easy axis. We investigated CoZr as the ferromagnetic electrode. It is observed that interfacial magnetic anisotropy is preferred perpendicular to the plane with thickness dependence on the interfaces with Pt layer. The anisotropy energy (Ku) with thickness dependence shows a change of magnetic-easy-axis direction from perpendicular to in-plane around 1.2 nm of CoZr. The interfacial anisotropy (Ki) as the directly related parameters to switching and thermal stability, are estimated as $1.64erg/cm^2$ from CoZr/Pt multilayered system.

• Proceedings of the KIPE Conference
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• 1998.07a
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• pp.234-238
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• 1998

Parameter estimation of induction motor for vector control presented in this paper can be easily implemented and applied to inverters in the industrial field, because it needs no additional hardware such as voltage sensor and measuring equipment. At first, the stator resistance including switching loss of inverter is measured by simple voltage-current equation. Next, in pre-magnetization of machine by imposing the d-axis constant field-current, q-axis torque current is forced to the machine until its speed feedback reachs to pre-defined level of speed limit. At this time, we can measure the rotor time-constant by decreasing the distorted output-voltage of inverter. At last, stator inductance, transient inductance, and moment of inertia can be measured by the relationship of output voltage, output torque and speed feedback. The validity and usufulness of this method is verified by experimental results.

• Proceedings of the KIEE Conference
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• 1998.07f
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• pp.2166-2168
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• 1998

A PWM inverter using power FET is developed to switch the excitation current of 5 phase hybrid stepping motor for the use of driving X, Y table. A micro processor based controller is also developed to control the excitation current switching of X, Y axis stepping motor as well as synchronizing operation of Z-axis servo motor. The developed driving control system is applied to the industrial embroidery sewing machine.

• Journal of Power Electronics
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• v.13 no.1
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• pp.77-85
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• 2013

This paper proposes a new dead time compensation method of independent six-phase permanent magnet synchronous motors (IS-PMSM). The current of the independent phase machines contains odd-numbered harmonics because of the dead time and the nonlinear characteristics of the switching devices. By using the d-q-n three-dimensional vector analysis, these harmonics can be extracted at the n-axis current. Thus, the current distortion can be compensated by controlling the n-axis current of the IS-PMSM to zero. The proposed method is simple and can be easily implemented without additional hardware setup. The validity of the proposed compensation method is verified with simulations and several experiments.

• Proceedings of the KSR Conference
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• 1999.11a
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• pp.288-295
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• 1999

This paper presents an application of vector control strategy for 1.2MVA IGBT traction drive for electric railway vehicle. The vector control requires the control of the phase and amplitude of output voltage vector[5]. But in case of traction system far railway vehicle, the one-pulse mode is used in order to utilize the link voltage fully[8]. So it is impossible to control the flux axis current and the torque axis current instantaneously and independently. So this paper proposes the vector control strategy with slip-frequency control at one-pulse mode. And precise switching technique between the two different control structures has been proposed. And the strategy was verified by experimental result with 1.2MVA IGBT inverter with four 210㎾ induction motors.

• Journal of the Optical Society of Korea
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• v.16 no.4
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• pp.409-413
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• 2012

Off-axis color shift in the dark state and gray scale inversion in an in-plane switching (IPS) liquid crystal display (LCD) device were investigated. Analyses were performed using the Poincar$\acute{e}$ sphere representation. The results show that color shift in the dark state and gray scale inversion in an IPS LCD can be reduced by using a biaxial film. We confirmed the extent of these improvements by measuring the optical performance of a fabricated IPS LCD.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.2160-2170
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• 1991

Three-dimensional turbulent structures in the near field of elliptic jet were experimentally investigated by using a three-color, three-component Laser Doppler Velocimeter. The Reynolds number based on the nozzle exit velocity and nozzle equivalent diameter(De) was about 4*10$^{4}$. The turbulent characteristics of a sharp-edged elliptic nozzle with aspect ratio of 2 were analyzed along major and minor axis at X/De=2,3,5,7 and along the centerline up to X/De=14. Quantities measured at each point with the 3-D LDV system were three orthogonal velocity components, turbulent intensity, skewness, flatness, and Reynolds shear stress. The nondimensional mean velocities coincided well with the Schlichting's empirical curve with going downstream. Elliptic jet of AR=2 had two switching points at about X/De=2 and 16. The turbulent intensity along the minor axis was distributed widely than that along the major axis. In the near field, X/De<5, the Reynolds shear stresses of the inner part of the elliptic jet had negative value, which indicated the enhancement of entrainment toward the inner part.

• Journal of Institute of Control, Robotics and Systems
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• v.14 no.7
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• pp.711-719
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• 2008

Although non-real time simulation and pilot based evaluations are available for the development of flight control computer prior to real flight tests, there are still many risky factors. The control law designed for prototype aircraft often leads to degraded performance from the initial design objectives, therefore, the proper evaluation methods should be applied such that flight control law designed can be verified in real flight environment. The one proposed in this paper is IFS(In-Flight Simulator). Currently, this system has been implemented into the F-18 HARV(High Angle of Attack Research Vehicle), SU-27 and F-16 VISTA(Variable stability. In flight Simulation Test Aircraft) programs. This paper addresses the concept of switching mechanism for FLCC(Flight Control Computer)-SWMC(Switching Mechanism Computer) using 1553B communication based on flight control law of advanced supersonic trainer. And, the fader logic of TFS(Transient Free Switch) and stand-by mode of reset '0' type are designed to reduce abrupt transient and minimize the integrator effect in pitch axis control law. It hans been turned out from the pilot evaluation in real time that the aircraft is controllable during the inter-conversion process through the flight control computer, and level 1 handling qualities are guaranteed. In addition, flight safety is maintained with an acceptable transient response during aggressive maneuver performed in severe flight conditions.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.9
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• pp.179-190
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• 1999

To automate the polishing process, a polishing robot with two axes which is attached to a machining center with three axes has been developed by our previous research. This automatic polishing robot is able to keep the polishing tool normal to the curved surface of die and is able to maintain a constant pneumatic pressure. Therefore, in the case of a curved surface die, the surface roughness to be polished by the system with five axes is improved superior than the surface by a three-axis machining center. However, because the polishing robot was big and heavy, a polishing workspace was limited and then it was difficult to attach the robot to machining center. In this study, the smaller and lighter polishing robot than the previous has been designed to improve defects due to the magnitude and weight of the robot. And the sliding mode control ins applied to polishing robot to improve the tracking performance. To obtain switching parameters of sliding mode control, the signal compression method is used. Code separation program to separate the date for a three-axis machining center and a two-axis polishing robot from a five-axis NC data is improved for users to check conveniently the separated trajectory and to handle many data by using the graphic user interface. To evaluate the polishing performance of the developed robot, the polishing experiment for shadow mask was carried out. The result shows the automatic polishing robot has a good trajectory tracking performance and obtains a good polished workpiece efficiently under recommended polishing conditions.