• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.127-130
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• 2003

4-bit 강유전체 위상변위기를 이용하여 10 GHz, 상온에서 작동하는 위상배열 안테나를 설계 및 제작하였다. 이 안테나는 빔 스캔을 위하여 전압에 대한 비선형특성을 보이는 강유전체 Bal-xSrxTiO3 (BST)를 기본으로 하는 위상변위기를 이용하였다. 우리는 펄스레이져 증착법으로 MgO (001) 기판위에 걸맞게 증착된 BST 박막을 일반적인 사진공정과 식각법을 이용하여 동일평판형 전극을 가진 위상변위기를 만들었다. 일반적인 동일평판형 강유전체 위상변위기의 경우 연결 전송선로의 임피던스와의 차이로 인해 반사손실과 이로 인한 부가적인 삽입손실이 발생한다. 이런 손실들을 줄이기 위해 입력과 출력 포트에 임피던스 매칭을 하였다. 이렇게 테이퍼링되어 만들어진 동일평판형 위상변위기는 이전의 구조에 비해 반사 손실과 삽입 손실 값에서 각각 약 10, 2 dB 정도씩의 개선을 보였다. 이 구조로 전송선로의 길이를 길게하여 만든 1-bit 강유전체 위상변위기는 10 GHz, 150 V의 전압변화에서 180도의 차등위상변위를 보였으며 최대 삽입손실과 최대 반사손실은 각각 약 10 dB, 20 dB 이다. 안테나 모듈은 4개의 마이크로스트림 패치 안테나와 4개의 강유전체 위상변위기로 이루어졌는데 10 GHz, 150 V의 전압변화에서 약 15도의 빔 스캔을 확인하였다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.3
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• pp.432-437
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• 2016

The behavior of a bellows for an electromagnetic control valve was investigated. The bellows consists of an outer metal bellows, inner spring, and metal caps. The bellows needs to have sensitive and precise motion against external loads and pressure loads in order to control the position of the valve accurately. The spring constant of the inner spring and load-displacement curve of the bellows set were measured using a test machine. The inner spring showed a linear relation between load and displacement. The bellows set showed small stiffness at small displacement, and then the stiffness slightly increased upon subsequent displacement. Based on the measured data, finite element analysis was performed. Axisymmetric conditions were applied, and shell elements were used. The effective material properties of the outer bellows material were extracted. Additional analysis was performed, and the behavior of the bellows was analyzed using the finite element model.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.89-89
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• 2011

반도체 공정 등에서 $10^{-6}{\sim}10^{-8}$ mbar의 고진공 환경을 제공하기 위하여 사용되는 고진공 터보분자펌프 (Turbomolecular Pump, TMP)는 다층의 회전깃을 갖는 로터를 회전시켜 분자를 배출시키는 방식을 사용하는 진공펌프이다. 또한 최근에는 디스플레이 및 반도체 공정에서 높은 진공도뿐만 아니라, 높은 배기속도를 요구하는 추세에 따라, 터보 펌프와 드래그 펌프부분을 동시에 가지고 있어 상대적으로 작동 진공도 영역이 넓은 복합 분자펌프(Compound Turbomolecular Pump, CMP)의 활용도가 넓어지고 있다. 이러한 분자펌프가 장시간의 고속회전에 적합하도록 비접촉 방식인 자기부상 방식의 적용이 최근 거의 표준화 되어 있다. 자기베어링 시스템은 전자기력을 이용하여 자성체인 회전축을 부상지지 함으로써 비접촉 고속 회전이 가능하여 윤활이 용이하지 않은 진공 환경 등 가혹한 환경에 적합하며, 터보분자펌프는 자기베어링이 가장 널리 사용되고 있는 분야이기도 하다. 자기베어링 시스템의 설계는 크게 하드웨어와 소프트웨어로 나누어질 수 있는데, 하드웨어의 경우 전체 로터 시스템의 특성을 고려하여 설계되어야 하며, 주로 자기베어링 코어와 코일, 변위센서 및 전력 증폭 시스템 등의 기전적인 요소들이 이루어져 있다. 하드웨어 설계와 함께 제어시스템의 설계도 매우 중요하며, 이는 자기베어링 시스템이 불안정한 특성을 갖는 개루프계를 갖고 있으므로 안정화를 위한 능동제어 시스템이 필수적이며 진동제어 등 여러 가지 기능이 요구되기 때문이다. 본 논문에서는 이러한 자기부상형 고진공 복합분자펌프의 제어를 위한 선형제어시스템의 구성을 실제 시스템의 적용을 통하여 설명하였다. 각 제어기는 DSP 를 이용한 디지털 제어시스템으로 구성되었으며, 2,500 l/s 급의 복합 분자펌프 시작품에 적용하여 25,000 rpm 까지의 기본 성능시험을 수행하였으며, 발열 특성의 개선을 위한 비선형 제어기의 설계 사례에 대한 시뮬레이션 결과를 나타내었다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.9
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• pp.1679-1687
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• 2016

Mobile robots are effectively used in industrial fields that require flexible manufacturing systems. Mobile robots have to move with mechanical loads such as product parts along the specified paths, and are usually equipped with kinematic controllers. When the loads and nonlinear frictions are too high, satisfactory control performances can not be expected with the kinematic controllers, so some dynamic controllers have been developed. Conventional dynamic controllers require the exact weights and locations of the loads; however, the loads are frequently changed and unknown so that the control performances of the conventional controllers are limited. This paper proposes an adaptive PD control method using gradient descent learning to have sufficient dynamic control performance for unknown loads. Simulation studies have been conducted for various load conditions to verify that the adaptive PD control method have much broader convergence region than the convention method.

• Journal of rehabilitation welfare engineering & assistive technology
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• v.6 no.2
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• pp.9-14
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• 2012

In this study, an advanced knee joint for active prosthesis leg driven by a linear actuator is suggested. The structure of knee joints of existing active prosthesis legs consists of three links. This kind of linkage requires large torque to drive the active prosthesis legs. Thus a new linkage structure is suggested to solve such problem in this paper. Motion characteristics of the suggested linkage are examined in the simulation. The motion simulation results show that the proposed linkage is able to imitate human gait cycles with the half of linear actuator speed in existing linkages.

• Journal of the Korean Society of Mechanical Technology
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• v.13 no.2
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• pp.45-54
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• 2011

A vehicle suspension system performs two functions, the ride quality and the stability, which conflict with each other. Among the various suspension systems, an active suspension system has an external energy source, from which energy is always supplied to the system for continuous control of vehicle motion. In the process of the linearization for the nonlinear active suspension system, the frequency dependent damping method is used for the exact modelling to the real model. The pressure control valve which is controlled by proportional solenoid is the most important component in the active suspension system. The pressure control valve has the dynamic characteristics with 1st order delay. Therefore, It's necessary to adopt the lead compensator to compensate the dynamics of the pressure control valve. The sampling time is also important factor for the control performances. The sampling time value is proposed to satisfy the system performances. After the modelling and simulation for the pressure control valve and vehicle dynamic, the performances of the vehicle ride quality and the stability are enhanced.

• Transactions of the Korean hydrogen and new energy society
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• v.26 no.6
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• pp.638-644
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• 2015

This paper describes the continuing effort to analysis and design on dynamic and electrical behavior of gamma-type free piston Stirling engine/generator with dual-opposed linear generator for domestic micro-CHP (Combined Heat and Power) system. The double acting Stirling engine/generator has one displacer and two power piston which are supported by flexure springs. Two power pistons oscillate with symmetric sinusoidal displacement and are connected with moving magnet type linear generators for power generation. To operate Stirling engine/generator, combustion heat of natural gas is supplied to hot-end and heat is rejected from cold-end by cooling water. The temperature difference across the displacer induces the oscillating motion, and it can be explained with mass-spring vibration system. The purpose of this paper is to describe the design process of linear generator for the double acting free-piston Stirling engine.

• Radiation Oncology Journal
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• v.24 no.4
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• pp.300-308
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• 2006

$\underline{Purpose}$: To develop a wireless CCTV system in semi-beam's eye view (BEV) to monitor daily patient setup in radiation therapy. $\underline{Materials\;and\;Methods}$: In order to get patient images in semi-BEV, CCTV cameras are installed in a custom-made acrylic applicator below the treatment head of a linear accelerator. The images from the cameras are transmitted via radio frequency signal (${\sim}2.4\;GHz$ and 10 mW RF output). An expected problem with this system is radio frequency interference, which is solved utilizing RF shielding with Cu foils and median filtering software. The images are analyzed by our custom-made software. In the software, three anatomical landmarks in the patient surface are indicated by a user, then automatically the 3 dimensional structures are obtained and registered by utilizing a localization procedure consisting mainly of stereo matching algorithm and Gauss-Newton optimization. This algorithm is applied to phantom images to investigate the setup accuracy. Respiratory gating system is also researched with real-time image processing. A line-laser marker projected on a patient's surface is extracted by binary image processing and the breath pattern is calculated and displayed in real-time. $\underline{Results}$: More than 80% of the camera noises from the linear accelerator are eliminated by wrapping the camera with copper foils. The accuracy of the localization procedure is found to be on the order of $1.5{\pm}0.7\;mm$ with a point phantom and sub-millimeters and degrees with a custom-made head/neck phantom. With line-laser marker, real-time respiratory monitoring is possible in the delay time of ${\sim}0.17\;sec$. $\underline{Conclusion}$: The wireless CCTV camera system is the novel tool which can monitor daily patient setups. The feasibility of respiratory gating system with the wireless CCTV is hopeful.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.1
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• pp.39-45
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• 2016

Thermal management of a fuel cell is important to satisfy the requirements of durability and efficiency under varying load conditions. In this study, a linear state feedback controller was designed to maintain the temperature within operating conditions. Due to the nonlinearity of automotive fuel cell system, the state feedback controller results in marginal stable under load condition from $0.5A/cm^2$ to $0.7A/cm^2$. A PWM (Pulse Width Modulation) and the modified state feedback controller are applied to control the temperature under the load condition from $0.5A/cm^2$ to $0.7A/cm^2$. The cooling system model is composed of a reservoir, radiator, bypass valve, fan, and a water pump. The performance of the control algorithm was evaluated in terms of the integral time weighted absolute error (ITAE). Additionally, MATLAB/SIMULINK$^{(R)}$ was used for the development of the system models and controllers. The modified state feedback controller was found to be more effective for controlling temperature than other algorithms when tested under low load conditions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.11
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• pp.6446-6451
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• 2014

Pneumatic motors are quite attractive for many applications because of their competitive price, light-weight, easy assembly, safety in hazardous areas as well as other features, such as a good force/weight ratio and operation in exceptionally harsh environments. In contrast to these advantages, pneumatic motors have limited use in applications, particularly those requiring a fast and precise response. These undesirable characteristics are due to the high compressibility of air and from the nonlinearities in pneumatic systems. This paper presents the sliding mode controller based on 3-loop(SMCB3L), which increases the load stiffness to control the rotation angle of a pneumatic motor. The characteristics for the step responses and load disturbances of the proposed controller were compared with the conventional PID controller. The experimental results showed that a properly designed SMCB3L is capable of high positioning accuracy within ${\pm}0.05mm$. Furthermore, the load stiffness of the SMCB3L can be improved 3.5 fold compared to that of PID controllers.