• Tribology and Lubricants
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• 제6권1호
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• pp.52-56
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• 1990

The Lubrication Mode of line contacts between the vane and camring in an oil hydraulic vane pump with intravanes has been investigated. Variations of the radial acting force of a vane were calculated from previously measured results of dynamic internal pressure in four chambers surrounding a vane, and variations of the lubrication mode were estimated in both the rotational speed range from 500 to 1500 rpm and in the delivery pressure range from 1 to14 Mpa. The results indicate the variations of the radial acting force. It is found that the regimes of lubrication in the vane tip contacts cover rigid-isoviscous to rigid-variable viscosities.

• Journal of Power Electronics
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• 제15권3호
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• pp.634-643
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• 2015

This paper presents a high frequency design approach for improving efficiency over a wide load range in the self-driven phase-shifted full-bridge converters for server power systems. In the proposed approach, a detailed ZVS analysis of the lagging leg switches in both the continuous conduction mode (CCM) and the discontinuous conduction mode (DCM) is presented. The optimum dead time and the determination of the appropriate operation mode are given for high efficiency according to the load conditions. Finally, the optimum operation conditions are defined to achieve a high-efficiency. A laboratory prototype operating at 80 kHz, rated 1 kW (12 V-83.3 A), is built to verify proposed theoretical analysis and evaluations. The experimental results show that the maximum efficiency is achieved as 95% and 83.5% at full load and 5% load conditions, respectively.

• 제어로봇시스템학회논문지
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• 제7권5호
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• pp.393-398
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• 2001

This paper presents a new method with time-varying boundary layer and input gain, variated by Fuzzy Logic Control(FLC) by means of the system state in Sliding Mode Control (SMC). In addition to the time-varying boundary layer, the time-varying range of the fuzzy membership function has an effect on not only chattering reduction but also fast response characteristics. On the basis of SMC with time-varying boundary and FLC with time-varying input and output range, a computer simulation for inverted pendulum results in elimination of the chattering phenomenon and fast response.

• 한국전기전자재료학회논문지
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• 제15권8호
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• pp.671-677
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• 2002

In this study, the high frequency SMD ceramic resonators with the size of $3.7{\times}3.1{\times}0.385\textrm{mm}^3$ were fabricated using $Pb_{0.88}(La_{0.6}Nd_{0.4})_{0.08}(Mn_{1/3}Sb_{2/3})_{0.02}Ti_{0.98}O_3$ ceramics with the variations of electrode radius size. With increasing the electrode radius size, resonant resistance in third overtone mode was decreased and electromechanical coupling factor($k_{t3}$) in third overtone mode was showed constant values. Taking into consideration mechanical quality factor($Qm_{t3}$) of 5,552 and dynamic range(D.R) of 60.72dB in third overtone mode, the ceramic resonator with the electrode radius size of $\theta$1.13mm was suitable for 20MHz resonator application.

• 한국정밀공학회지
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• 제24권2호
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• pp.86-94
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• 2007

In this paper, a dual stage servo mechanism has been developed for image tracking system to improve control performances such as small rise time, small overshoot, small settling time, small stabilization error etc. A secondary stage, a platform, actuated by a pair of electro-magnets is mounted on a conventional elevation gimbal. In this mechanism, the gimbal provides large range but slow motion and the platform provides small range but fast positioning. A sliding mode control is applied to the platform positioning to attain robust performances and stability in the presence of the disturbance related to dynamic coupling of the gimbal and the platform. Results from experiments illustrate that the suggested dual stage mechanism controlled by the sliding mode control is effective in improving responses and attenuating the disturbance response related with dynamic coupling.

• JSTS:Journal of Semiconductor Technology and Science
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• 제13권4호
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• pp.361-366
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• 2013

A full-range analytic drain current model for depletion-mode long-channel surrounding-gate nanowire field-effect transistor (SGNWFET) is proposed. The model is derived from the solution of the 1-D cylindrical Poisson equation which includes dopant and mobile charges, by using the Pao-Sah gradual channel approximation and the full-depletion approximation. The proposed model captures the phenomenon of the bulk conduction mechanism in all regions of device operation (subthreshold, linear, and saturation regions). It has been shown that the continuous model is in complete agreement with the numerical simulations.

• 동력기계공학회지
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• 제19권4호
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• pp.89-96
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• 2015

This paper investigates some strategies to overcome the chattering problem of the conventional sliding mode observer (SMO) and to improve the rotor position estimation performance for full range sensorless control of a PMSM. An adaptive observer gain based on the Lyapunov's stability criterion and a cascade low pass filter with advanced phase delay compensation were proposed to reduce the chattering problem and to strengthen the filtering capability of the SMO. Several cases studies through experiments were carried out to confirm conventional SMO's problems and effectiveness of the proposed strategies. The experimental results show that the proposed method gives precise estimation on speed and rotor position when the motor rotates on 2% of its rated speed.

• 한국소음진동공학회논문집
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• 제21권4호
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• pp.374-383
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• 2011

A numerical model based on a mode method coupling beams and a rectangular plate is proposed to estimate radiation characteristics of an edge-clamped rectangular plate. The radiation efficiency and radiation power in the audio frequency range including the critical frequency can be predicted. The proposed model is rather simple and straightforward and gives reliable results comparing to the previous studies. The estimated radiation characteristics are compared to those of the pinned condition plates and also to those based on the formulae proposed by Maidanik. The radiation efficiency of the clamped plate seems a little higher than that of the pinned plate in the frequency range of corner and edge modes. It is explicitly shown that the power as well as efficiency at high frequencies is not influenced by these edge boundary conditions.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 F
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• pp.1940-1943
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• 1998

A new PWM rectifier which offers a unity power factor is proposed. The circuit has same inductance as the conventional boosting type PWM rectifier in powering mode, but the inductance is splitted to 2 part in freewheeling mode. So the period of freewheeling mode is shorter than that of conventional boosting type PWM rectifier, and discontinuous input current is obtained in wide duty range. Therefore the proposed PWM rectifier accomplishs a unity power factor in wide range of duty ratio and boosting factor. And the conventional boosting type PWM rectifier has poor power factor near the unity boosting ratio, the proposed PWM rectifier improves this problem. The mathmatical analysis are presented and experimental results are given.

• Journal of Power Electronics
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• 제9권4호
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• pp.582-592
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• 2009

This paper proposes a new speed sensorless direct torque and flux controlled interior permanent magnet synchronous motor (IPMSM) drive. Closed-loop control of both the torque and stator flux linkage are achieved by using two proportional-integral (PI) controllers. The reference voltage vectors are generated by a SVM unit. The drive uses an adaptive sliding mode observer for joint stator flux and rotor speed estimation. Global asymptotic stability of the observer is achieved via Lyapunov analysis. At low speeds, the observer is combined with the high frequency signal injection technique for stable operation down to standstill. Hence, the sensorless drive is capable of exhibiting high dynamic and steady-state performances over a wide speed range. The operating range of the direct torque and flux controlled (DTFC) drive is extended into the high speed region by incorporating field weakening. Experimental results confirm the effectiveness of the proposed method.