• 제어로봇시스템학회논문지
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• 제15권8호
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• pp.772-777
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• 2009

The geometric distortion of image is one of the most important parameters that take effect on the accuracy of optical inspection systems. We propose a new correction method of the image distortion to increase the accuracy of PCB inspection systems. The model-free method is applied to correct the randomly distorted image that cannot be represented by mathematical model. To reduce the correction time of inspection system, we newly propose a grid reduction algorithm that minimize the number of grids by the quad-tree approach. We apply the proposed method to a PCB inspection system, and verify its usefulness through experiments using actual inspection images.

• 방송공학회논문지
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• 제18권3호
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• pp.455-462
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• 2013

본 논문에서는 여러 개의 마이크를 이용하여 잡음을 제거하는 방법인 공간 필터로 전처리된 신호를 입력으로 하는 음성 왜곡 가중 다채널 위너 필터 (Spatially Preprocessed Speech Distortion Weighted Multi-channel Wiener Filter: SP-SDW-MWF)에 대해 소개하고, 가중치를 결정하는 방법을 제안한다. SP-SDW-MWF는 마이크로폰 어레이를 이용한 잡음 제거 알고리즘으로서 마이크로폰 불일치와 같은 오차에 강인한 것으로 알려져 있다. SP-SDW-MWF는 필터 계수를 최적화할 때 음성 왜곡과 잡음 제거에 대한 기준으로 나누어 가중치를 두고 있다. 이러한 가중치를 결정하기 위해, 본 논문에서는 전력 스펙트럼 밀도 오차를 평가 척도로 사용하여 마이크로폰으로부터 입력된 음성 신호와 잡음의 전력 스펙트럼 밀도의 비 (a priori SNR)를 이용하는 방법을 제안한다. 실험결과에서 나타난 바와 같이 a priori SNR에 따라 가변적인 가중치를 사용하는 것이 고정된 값을 가중치로 사용하는 것보다 향상된 성능을 보임을 알 수 있다.

• Journal of Welding and Joining
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• 제28권4호
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• pp.41-48
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• 2010

The purpose of this study is to establish the control method of the global bending distortion caused by fabrication process of hatch-cover in a container ship. In order to do it, the transitional behavior of global bending distortion in the deck of hatch-cover during fabrication process was measured by 3-dimensional measuring instrument. From the results, the principal factor controlling the global bending distortion was identified as the bending moment associated with the longitudinal shrinkage force and transverse shrinkage caused by welding and flame heating and the change of the centroid axis of hatch-cover in each fabrication process. Therefore, in this study, with the predictive equations of the longitudinal shrinkage force and transverse shrinkage caused by welding and flame heating and the simplified thermo elastic method, the predictive method for the global bending distortion was established and verified by comparing with the measured result. Based on the results, the amount of reverse bending distortion of main stiffeners was determined to prevent the global bending distortion of hatch-cover.

• Journal of Welding and Joining
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• 제25권5호
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• pp.72-77
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• 2007

Prediction and control of the thermal distortion is particularly important for the design and manufacture of welded thin metal structure. In this study, numerical computations are performed to analyze effect of structure section shape and weld line location on distortion. In addition, this study aims to develop a thermal elasto-plastic simulation using finite element method to predict distortion, with particular emphasis on bending deformation generated in outline welding of a thin box structure. From the numerical analysis, it was revealed that the section shape and weld line location play an important role on the welding distortion. Among 3 types of section shape design proposed in this study, the least deformation remained in the two path welded structure.

• Journal of Welding and Joining
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• 제34권6호
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• pp.20-27
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• 2016

This study deals with the proper conditions of the trail rolling method (TRM) for the prevention of the buckling welding distortion at the AA5083 GMA butt weldment. For it, the effect of the working conditions of TRM including the rolling depth and the rolling distance between the welding torch and the roller on the longitudinal welding shrinkage force of the weldment was evaluated by using 3 dimensional thermo-mechanical FE analyses. The longitudinal welding shrinkage force inducing the buckling welding distortion at the GMA butt weldment was mitigated with an increase in the rolling depth and the rolling distance between the welding torch and the roller. Based on the results, the proper conditions of trail rolling method were established to reduce the longitudinal welding shrinkage force of the GMA butt weldment to below the critical value corresponding to the bucking distortion.

• 한국CDE학회논문집
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• 제9권4호
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• pp.397-405
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• 2004

Texture mapping is the process of covering 3D models with texture images in order to increase the visual realism of the models. For proper mapping the coordinates of texture images need to coincide with those of the 3D models. When projective images from the camera are used as texture images, the texture image coordinates are defined by a camera calibration method. The texture image coordinates are determined by the relation between the coordinate systems of the camera image and the 3D object. With the projective camera images, the distortion effect caused by the camera lenses should be compensated in order to get accurate texture coordinates. The distortion effect problem has been dealt with iterative methods, where the camera calibration coefficients are computed first without considering the distortion effect and then modified properly. The methods not only cause to change the position of the camera perspective line in the image plane, but also require more control points. In this paper, a new iterative method is suggested for reducing the error by fixing the principal points in the image plane. The method considers the image distortion effect independently and fixes the values of correction coefficients, with which the distortion coefficients can be computed with fewer control points. It is shown that the camera distortion effects are compensated with fewer numbers of control points than the previous methods and the projective texture mapping results in more realistic image.

• Transactions on Control, Automation and Systems Engineering
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• 제4권1호
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• pp.38-42
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• 2002

Conditions are discussed for operating a dissymmetric human master-small (or micro) slave system in best (large position gain-small velocity gain) conditions allowing higher operator dexterity when real effects (joint compliance, link flexion delay and transmission distortion) are taken into account. It is shown that position PD feedback law advantage for ideal case no longer holds, and that more complicated feedback law depending on real effects has to be implemented with adapted transmission line. Drawback is slowdown of master slave interaction, suggesting to use more advanced predictive methods for the master and more intelligent control law for the slave.

• Journal of Power Electronics
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• 제19권6호
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• pp.1575-1581
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• 2019

Due to the mismatched line impedance among distributed generation units (DGs) and uncontrolled harmonic current, the droop controller has a number of problems such as inaccurate reactive power sharing and voltage distortion at the point of common coupling (PCC). To solve these problems, this paper proposes a resistive-capacitive virtual impedance control method. The proposed control method modifies the DG output impedance at the fundamental and harmonic frequencies to compensate the mismatched line impedance among DGs and to regulate the harmonic current. Finally, reactive power sharing is accurately achieved, and the PCC voltage distortion is compensated. In addition, adaptively controlling the virtual impedance guarantees compensation performance in spite of load changes. The effectiveness of the proposed control method was verified by experimental results.

• 한국통신학회논문지
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• 제23권8호
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• pp.2010-2024
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• 1998

비디오 부호화에 있어서 평균화질의 향상뿐만 아니라 이웃한 영상들간에 일관된 화질을 유지하는 것은 매우 중요하다. 본 논문에서는 MPEG-2 비디오에 대한 왜곡-비트율 추정방식과 이 추정결과를 이용히여 일정 비트율(CBR)로 부호화되는 MPEG-2 비디오가 일관된 화질을 유지하면서도 향상된 평균화질을 얻도록 하는 순방향 비트율 제어방식을 제안한다. 본 논문에서 제안하는 왜곡-비트율 추정은 부호화에 사용되는 양자화 스텝 크기에 따라한 영상에서 발생하는 비트량과 왜곡을 예측하거나, 역으로 발생하는 비트량이나 왜곡에 대한 양자화 스텝 크기를 예측할 수 있다. 제안된 추정 방식의 장점은 실제의 비디오 부호화 응용에 적용할 수 있을 만큼 계산량이 적고 정확하다는 것이다. 한편 제안된 비트율 제어는 프레임 단위로 왜곡-비트율 추정, 목표 비트 할당, 왜곡 제한 그리고 VBV(Video B Buffer Verification) 제한 절차에 의해서 부호화에 적용할 양자화 파라메터를 결정하고, 이 양자화 파라메터를 적용하여 영상을 부호화 함으로써 일관되고도 향상된 화질을 유지한다. 또한 화면전환이나 기준영상의 화질열화 등에 의하여 화질저하가 오래 지속되는 문제를 B-picture 제거와 기준영상에 대하여 최소 비트량 할당을 보장함으로써 해결한다. 그리고 제안된 순방향 비트율 제어방식과 MPEG-2의 TM5(Test Model 5)에서 제안한 비트율 제어를 비교한 실험 결과들을 통하여 제안된 방식이 영상들 간에 일관된 화질을 유지할 뿐만 아니라 평균화질도 향상 됨을 확인한다.

• Journal of Welding and Joining
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• 제25권1호
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• pp.49-56
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• 2007

Prediction and control of the thermal distortion is particularly important for the design and manufacture of welded thin plate panel. In this study, experiments and computations are performed to analyze effect of a hole configuration and a specimen size on distortion. In addition, this study aims to develop a thermal elasto-plastic simulation using finite element method to predict distortion, with particular emphasis on buckling deformation generated in plates welded around hole. From the experiments, the severe distortion appeared in the weldments by the laser welding process, in which the specimen size plays an important role on the distortion but the hole configuration showed little effect. And the results of numerical analysis were corresponded well with the experiment ones. Thus, a thermal elasto-plastic analysis model for predicting the weld distortion of thin plate panel was successfully developed through this study.