• Journal of Advanced Marine Engineering and Technology
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• 제32권8호
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• pp.1303-1308
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• 2008

Keeping cooling water temperature higher within the allowable range helps marine engines to run in more efficient condition especially when the engine load is low. Temperature control of jacket cooling water in outlet side of main engine has been more widely adopted to ships these days for the purpose to reduce fuel consumption rate. But If the temperature sensor for the control loop is placed at the outlet of engine, it brings more difficulties in attaining stable and desirable properties due to dead times included in pipe length and engine itself comparing to the case where the measuring point is at the inlet side of main engine. In relation with this problem, Feed-forward control could be one of realistic solutions as it reveals good properties and requires less cost for system configuration. This study suggests a forward control system which leads to improved temperature control performances to disturbance signals which could arise from variation of engine load or weather condition. Two dead times in the modelling were described, considering pipe length between the actuator and the engine as well as the thermal process inside the engine. The results of analysis were shown by simulations to confirm responses under different conditions.

• 한국세라믹학회지
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• 제40권4호
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• pp.385-392
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• 2003

Sol-gel preparation technique using a chemical reaction of metal alkoxides has been widely used for the fabrication of various materials including ceramics. However, its mechanism has been studied till now because a number of chemical ways are possible from various alkoxides and additives. In this study, the mechanism of hydrolysis, condensation, and polymerization of alkoxides were investigated from the fabrication of lead-zirconate-titanate (PbZr$\_$x/Ti$\_$l-x/O$_3$; PZT) thin film that is used as various micro-actuator, transducer, and sensor because of its high electro-mechanical coupling factors and thermal stability. Furthermore, the fabrication process and characteristics of self-patternable PZT film using photosensitive stabilizer were studied in order to resolve the problem of physical damage and properties degradation during dry etching for device fabrication. Using an optimum condition to prepare the self-patternable PZT film, more than 5000 ${\AA}$ thick self-patternable PZT film could be fabricated by three times coating. The PZT film showed 28.4 ${\mu}$c/cm$^2$ of remnant polarization (Pr) and 37.0 kV/cm of coercive field (E$\_$c/).

• 한국안전학회지
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• 제24권5호
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• pp.1-5
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• 2009

NiTiCu alloys can produce a large force per unit volume and operate with a simple mechanism. For this reasons, it has been widely studied for application as a micro actuator. So in this study, one-way and two way shape memory effects of Ti-42.5at%Ni-2.0at%Cu alloys are studied. In the case of one-way shape memory effects, shape memory recoverable stress and strain of this alloys were measured by means of tension and compression tests under constant temperature. The strains by tension and compression stress were perfectly recovered by heating at any testing conditions also shape memory recoverable stress increased to 116 MPa in tension tests and to 260 MPa in compression tests. In the case of two-way shape memory effects, transformation temperatures from thermal cycling under constant uniaxial applied tension and compression loads linearly increased by increasing external loads and their maximum recoverable strain is 3.8% at 100MPa tensile condition and 2.2% at 125 MPa compression condition.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.865-868
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• 2001

We designed and fabricated a planner-type thermoelastic microactuator with a latch-up operation for optical switching. Latch-up actuation is prerequisite to implement an optical switch with low power consumption and high reliability. The proposed microactuator consists of four cantilever-shaped thermal actuators, four displacement linkages, two shallow arch-shaped leaf springs, a mobile shuttle mass with a micromirror, and four elastic boundaries. The structural layer of the planar microactuator is phosphorous-doped 12$\mu\textrm{m}$-thick polysilicon, and the sacrificial layer is LTO(Low Temperature Oxide) of 3$\mu\textrm{m}$thickness. The displacement of actuator is as large as 3$\mu\textrm{m}$when the length of actuation bar is 100$\mu\textrm{m}$in length at 5V input voltage. The proposed microactuators have advantages of easy assembly with other optical component by way of fiber alignment in the substrate plane, and its fabrication process features simplicity while retaining batch-fabrication economy.

• 대한기계학회논문집A
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• 제26권9호
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• pp.1874-1881
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• 2002

Heat dissipation technology using the flow resonant phenomenon is a kind of a new concept in the heat transfer area. A vibration exciter is needed to enhance air flow mixing which has the natural shedding frequency of thermal system. A mechanical vibrating device for the air flow oscillation is introduced, which is driven by a moving coil actuator with a displacement estimator using strain gage. An analytical dynamic model for this mechanical vibration exciter is presented and its validity is checked by the comparison with experimental data. Values of some unknown system parameters in the analytic model are estimated through the system identification approach. Based on this mathematical model, the vibration exciter using strain displacement estimator is developed. During the experimental verification phase, it turns out the high modal resonant characteristics of a vibrating plate are a major barrier against obtaining a high bandwidth vibration exciter.

• 한국정밀공학회지
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• 제31권2호
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• pp.99-104
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• 2014

Active vibration control methods are required in the high speed rotor systems supported by magnetic bearings. A prediction control technique is one of the control methods. Gain and phase angle are primarily chosen with analyzing the responses for a certain rotor speed. The feasibility of this technique has been reported for only analytical simulations. Therefore this paper constructs the test rig supported by ball bearings with a magnetic bearing type actuator and develops a prediction control system by using LabVIEW and Compact RIO. Finally as rotating speeds are modulated, the gains and phase angles for the speeds are determined with vibration control of the test rig. This leads that the prediction control technique may be applied to the rotor system with the magnetic bearing.

• 한국자기학회지
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• 제4권4호
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• pp.303-306
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• 1994

본 논문에서는 초자왜소자 $Terfenol-D(Tb_{0.3}Dy_{0.7}Fe_{1.9~1.95})$의 인가자장에 따른 자왜의 변화를 측정하였고, 잔류 자왜 및 초자왜소자의 온도 상승에 의한 열팽창 변형의 영향을 조사 하였다. 또한 초자왜소자에 3.5~14 MPa의 압축 응력을 인가하면서 자왜의 변화를 조사하였다. 그 결과는 인 가 압축 응력이 7 MPa인 경우 1500 Oe의 자장에서의 자왜는 1000 ppm이었으나 압축 응력을 가하지 않은 경 우는 400 ppm이었다. 또한 인가 압축 응력이 커짐에 따라서 자왜가 포화되는 자장의 크기도 커졌다. 잔류 변형과 히스테리시스가 관측되었으며, 따라서 액츄에이터로 이용할 때는 이를 보상하는 기구가 필요하며 또 한 열팽창에 의한 변형도 액츄에이터 응용시에는 고려하여야 한다.

• 한국신뢰성학회지:신뢰성응용연구
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• 제17권3호
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• pp.224-235
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• 2017

Purpose: Reliability is the most important factor to detect defects as wind turbines are deployed in large blades. The methods of detecting defects are various, such as non-destructive inspection and thermal imaging inspection. We propose the phased array ultrasonic testing method of non-destructive testing. Methods: We propose the active pressure mechanism for wind power blade. The phase array ultrasonic inspection method is used for fault detection inner blade surface. Controlled pressure of mechanism with respect to z-axis is important for guarantee the result of phase array ultrasonic inspection. The model based control and proposed mechanism are utilized for overall system stability and effectiveness of system. Result: The result of proposed pressure mechanism B is more stable than A. Convergence speed is also faster than A. Conclusion: We confirmed the performance of the proposed constant pressure mechanism through experiments. Non-destructive testing was applied to the specimen to confirm the reliability of detecting defects.

• 한국전기전자재료학회논문지
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• 제24권10호
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• pp.803-806
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• 2011

1 mol% $Li_2O$ excess $0.9(Na_{0.52}K_{0.48})NbO_3-0.1LiTaO_3$ lead-free piezoelectric multilayer ceramic actuators were investigated to determine their aging properties. To reduce the thermal aging behavior, we applied a rectified unipolar electric field of 5 kV/mm to the specimen to accelerate the electric aging behavior. By employing a rectified unipolar electric field for the piezoelectric actuators, we could remove undesirable heating from the relaxation current in the motion of the ferroelectric domain. To accelerate the aging test, the applied electric fields had a frequency of 900 Hz. To have enough time for charging and discharging, we employed an accurate time constant to design the equivalent circuit model for the aging tester. To extract exact aging behavior, we measured the pseudo-piezoelectric coefficient before and after the aging process. We also measured the electro-mechanical coupling coefficient, the frequency-dependent dielectric permittivity, and the impedance to compare with fresh and aged specimen.

• 한국화재소방학회논문지
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• 제28권4호
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• pp.21-28
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• 2014

단상 2선식 MCCB의 관련 기준을 분석하고, 내열 특성을 평가하여 다음과 같은 결과를 얻었다. KS C 8321은 IEC 60947-2의 규격을 부합화되어 관련 규정 대부분이 유사하다. NFPA는 사용자 중심의 안전 규정을 제시한 것으로 시험 또는 검사 등의 세부 사항은 없으나 안전에 직접 관련이 있는 규정이 구체적으로 명시되어 있다. KS C 8321은 시험과 검사에 대한 항목이 세부적으로 분류되어 있는 것을 알 수 있다. 그러나 IEC 60947-2와 IEEE C37.51의 경우 시험 및 검사 항목을 간소화하거나 일부 생략되어 있다. 내열 실험 장치를 이용하여 MCCB를 $180^{\circ}C$에서 6 hr 동안 열적 스트레스를 인가하였을 때 작동 손잡이의 변형이 확인되었고, 트립 상태로 이동한 것이 확인되었다. 또한 고정걸이의 대부분은 녹아서 기능이 상실되었다. $90^{\circ}C$에서 MCCB가 열적 스트레스를 받았을 때 특이 사항이 없었고, $105^{\circ}C$ 및 $120^{\circ}C$의 온도에서는 고정걸이가 일부 변형되었다. $150^{\circ}C$에서는 고정걸이의 변형 및 명판의 변색 등을 확인할 수 있었다. MCCB의 내부 분석에서 트립바가 녹아서 없어진 것을 알 수 있었고, 상하 가동편은 상부로 이동한 것이 확인되었다. 내전압 6 kV를 60 s 동안 5회 인가한 실험에서 모든 항목이 안전하였다. 또한 절연저항계로 직류 500 V를 인가한 절연 성능 평가 역시 양호하였다.