• 제어로봇시스템학회논문지
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• 제19권1호
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• pp.15-26
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• 2013

This paper proposes a classification method of parallel, vertical parking states and pillars for parking assist system using ultrasonic sensors. Since, in general parking space detection module, the compressed amplitude of ultrasonic data are received, the analysis of them is difficult. To solve these problems, in preprocessing state, symmetric transform and noise removal are performed. In feature extraction process, four features, standard deviation of distance, reconstructed peak, standard deviation of reconstructed signal and sum of width, are proposed. Gaussian fitting model is used to reconstruct saturated peak signal and discriminability of each feature is measured. To find the best combination among these features, multi-class SVM and subset generator are used for more accurate and robust classification. The proposed method shows 92 % classification rate and proves the applicability to parking space detection modules.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2004년도 하계종합학술대회 논문집(2)
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• pp.549-552
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• 2004

The thesis describes the design of 12bit digital-to-analog converter (DAC) which shows the conversion rate of 500MHz and the power supply of 3.3V with 0.35${\mu}m$ CMOS 1-poly 4-metal process for advanced wireless transceiver of high speed and high resolution. The proposed DAC employes segmented structure which consists of 6bit MSB, 3bit mSB, 3bit LSB for area efficiency Also, using a optimized aspect ratio of process and new triple diagonal symmetric centroid sequence for high yield and high linearity. The proposed 12bit current mode DAC was employs new deglitch circuit for the decrement of the glitch energy. Simulation results show the conversion rate of 500MHz, and the power dissipation of 85mW at single 3.3V supply voltage. Both DNL and INL are found to be smaller than ${\pm}0.65LSB/{\pm}0.8LSB$.

• Journal of Magnetics
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• 제21권3호
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• pp.348-355
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• 2016

Precision motion stages used in the manufacturing process of flat-panel displays have inevitably low settling performance due to their huge mass and bulky structures. In order to improve the settling performance, several methods of frame vibration compensation have been developed so far. These methods are used to cancel the vibration by imposing a counter force or modifying the resonance mode of the frame of the stage. To compensate the frame vibration, high force actuators are required. In this paper, a mighty voice coil actuator is proposed to generate the counter force against the frame vibration. The proposed voice coil actuator has an axis-symmetric rectangular structure to achieve a large force with simple and low cost fabrication. Also, the voice coil actuator allows radial clearance up to ${\pm}4mm$. Using an optimized design process and a magnetic circuit model, the power consumption is minimized while the required force is obtained. With a power of 322 W, the VCA has been designed to have a maximum force of 574 N with a force constant of 164 N/A. Experimental results verified the force constant of the fabricated voice coil actuator is well matched with the designed value.

• 한국항공우주학회지
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• 제48권5호
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• pp.373-381
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• 2020

쿼드로터는 대칭적인 구조로 모델링이 간단하지만 외란과 시스템의 불확실성에 민감하다는 단점이 있다. 쿼드로터의 제어를 위해 비교적 간단하게 적용이 가능한 PID 제어가 많이 연구되고 있지만, 비선형 시스템에서는 정밀한 제어가 힘들다는 단점이 있다. 본 논문에서는 이를 해결하기 위하여 외란과 시스템의 불확실성에 강인한 특징을 가지는 슈퍼 트위스팅 알고리즘(Super twisting algorithm)을 이용한 쿼드로터 제어를 제안한다. 이 제어기법을 이용하여 쿼드로터의 자세제어기를 구성하였다. 구성한 제어기의 성능을 검증하기 위해 시뮬레이션 및 실제 비행시험을 진행하였다. 제어기의 보다 객관적인 성능 검증을 위해 PID 제어와 성능 비교를 진행하였다.

• Wind and Structures
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• 제5권2_3_4호
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• pp.329-336
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• 2002

The along-wind response of a surface-mounted elastic fence under the action of wind was investigated numerically. In the computations, two sets of equations, one for the simulation of the unsteady turbulent flow and the other for the calculation of the dynamic motion of the fence, were solved alternatively. The resulting time-series tip response of the fence as well as the flow fields were analyzed to examine the dynamic behaviors of the two. Results show that the flow is unsteady and is dominated by two frequencies: one relates to the shear layer vortices and the other one is subject to vortex shedding. The resulting unsteady wind load causes the fence to vibrate. The tip deflection of the fence is periodic and is symmetric to an equilibrium position, corresponding to the average load. Although the along-wind aerodynamic effect is not significant, the fluctuating quantities of the tip deflection, velocity and acceleration are enhanced as the fundamental frequency of the fence is near the vortex or shedding frequency of the flow due to the occurrence of resonance. In addition, when the fence is relatively soft, higher mode response can be excited, leading to significant increases of the variations of the tip velocity and acceleration.

• Wind and Structures
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• 제7권4호
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• pp.265-280
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• 2004

This paper presents some fundamental results on the dynamics of the periodic Karman wake behind a circular cylinder. The wake is treated like a dynamical system. External forcing is then introduced and its effect investigated. The main result obtained is the following. Perturbation of the wake, by controlled cylinder oscillations in the flow direction at a frequency equal to the Karman vortex shedding frequency, leads to instability of the Karman vortex structure. The resulting wake structure oscillates at half the original Karman vortex shedding frequency. For higher frequency excitation the primary pattern involves symmetry breaking of the initially shed symmetric vortex pairs. The Karman shedding phenomenon can be modeled by a nonlinear oscillator. The symmetrical flow perturbations resulting from the periodic cylinder excitation can also be similarly represented by a nonlinear oscillator. The oscillators represent two flow modes. By considering these two nonlinear oscillators, one having inline shedding symmetry and the other having the Karman wake spatio-temporal symmetry, the possible symmetries of subsequent flow perturbations resulting from the modal interaction are determined. A theoretical analysis based on symmetry (group) theory is presented. The analysis confirms the occurrence of a period-doubling instability, which is responsible for the frequency halving phenomenon observed in the experiments. Finally it is remarked that the present findings have important implications for vortex shedding control. Perturbations in the inflow direction introduce 'control' of the Karman wake by inducing a bifurcation which forces the transfer of energy to a lower frequency which is far from the original Karman frequency.

• Steel and Composite Structures
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• 제23권3호
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• pp.285-302
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• 2017

Buckling-restrained braced frames (BRBFs) are commonly used as the lateral force-resisting systems in building structures in the seismic regions. The nearly-symmetric hysteretic response and the delayed brace core fracture of buckling-restrained braces (BRBs) under the axial cyclic loading provide the adequate lateral force and deformation capacity to BRBFs under the earthquake excitation. However, the smaller axial stiffness of BRBs result in the undesirable higher residual drift response of BRBFs in the post-earthquake scenario. Two alternative approaches are investigated in this study to improve the elastic axial stiffness of BRBs, namely, (i) by shortening the yielding cores of BRBs; and (ii) by reducing the BRB assemblies and adding the elastic brace segments in series. In order to obtain the limiting yielding core lengths of BRBs, a modified approach based on Coffin-Manson relationship and the higher mode compression buckling criteria has been proposed in this study. Both non-linear static and dynamic analyses are carried out to analytically evaluate the seismic response of BRBFs fitted with short-core BRBs of two medium-rise building frames. Analysis results showed that the proposed brace systems are effective in reducing the inter-story and residual drift response of braced frames without any significant change in the story shear and the displacement ductility demands.

• Journal of Welding and Joining
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• 제27권3호
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• pp.60-66
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• 2009

The structures distorted by welding have to be corrected. Since the correcting work needs a lot of costs and time, it is very important to minimize the buckling distortion due to welding of thin plate structure. Therefore the aim of this study is to investigate the effect of single bead on plate welding and fillet welding on the buckling distortion. In the single bead on plate welding, it was found that the welding speed and welding sequence were the most dominant factors on distortion. In the fillet welding, there were four typical buckling modes observed, and the welding sequence was the most influential factor on the buckling distortion. However typical distortion measuring method is not considered for the distortion correcting process costs of each buckling modes, therefore, in this study, the measuring method is developed to classify the buckling modes for torsion of specimen and buckling distortion depend on nodal point for the bead on plate welding specimen and fillet welds.

• 한국공간구조학회:학술대회논문집
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• 한국공간구조학회 2008년도 춘계 학술발표회 논문집
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• pp.127-132
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• 2008

최근, 지진하중에 대한 대공간구조무의 응답특성에 관한 연구가 다수 수행되었으며, 라이즈/스팬비가 큰 지붕구조에 대하여서는, 수평지진입력에 대한 역대칭모드의 증폭이 지배적으로 됨이 지적되었다. 본 연구에서 제안하는 정적지진하중평가법에서는, 라이즈가 있는 지붕구조의 내진설계를 수행함에 있어, 허용응력도설계법을 따르며, 그림1과 같이 설계용전단력를 지붕면에 따라 부가하는 정적평가법을 채용하고 이를 정적지진하중평가법이라 부르기로 한다. 본 논문의 구성으로서는, 정적평가법의 개념 및 정적설계식의 유도과정을 나타내고, 라이즈/스팬비가 서로 다른 지붕구조물을 대상으로 하여, 본 평가법에 의한 결과와 정적응답해석을 수행한 결과를 비교하고, 정적평가법의 타당성에 대하여 검토한다.

• Bulletin of the Korean Chemical Society
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• 제31권9호
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• pp.2598-2602
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• 2010

Two 3-D zinc framework compounds, $[Zn_6(BTB)_4(4,4'-bipy)_4(H_2O)_4]{\cdot}9H_2O$ (1) and $[Zn_3(BTB)_2(4,4'-bipy)_2(H_2O)_2]{\cdot}5H_2O$ (2) ($H_3BTB$ = 1,2,3-benzenetricarboxylic acid, 4,4'-bipy = 4,4'-bipyridine), are obtained from the diffusion method and hydrothermal reaction respectively. Though 1 and 2 has the same coordination geometries of zinc atoms and coordination mode of $BTB^{3-}$, their 2-D layers are different: mirror symmetric layers in 1; parallel ones in 2, further connecting by 4,4'-bipy into 3-D frameworks. The hydrothermal reaction of 2 results in a more stable 3-D framework than the one in 1, which is supported by the single point energy calculations. 1 and 2 show similar blue fluorescence at 417 nm, which can be assigned to LMCT.