• 한국정밀공학회지
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• 제25권3호
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• pp.157-164
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• 2008

While developing physical prototype from CAD model, rapid prototyping mainly focuses on two key points reducing time and material consumption. So, we have to change from a traditional solid model to building a hollowed prototype. In this paper, a new method is presented to hollow out solid objects with uniform wall thickness to increase RP efficiency. To achieve uniform wall thickness, it is necessary to generate internal contour by slicing the offset model of an STL model. Due to many difficulties in this method, this paper proposes a new algorithm that computes internal contours computing offset model which is generated from external contour using wall thickness. Proposed method can easily compute the internal contour by slicing the offset surface defined by the sum of circle swept volumes of external contours without actual offset and the circle wept volumes. Internal contour existences are confirmed by using the external point. Presented algorithm uses the 2D geometric algorithm allowing RP implementation more efficient. Various examples have been tested with implementation of the algorithm, and some examples are presented for illustration.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.2195_2196
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• 2009

DC-offset is a very important subject in power systems protection, since DC-offset causes mal-operation of the distance relay. This paper deals with the influence of a FIR filter used for removing the DC-offset upon the convergence characteristics of distance relaying algorithm based on Fourier Transform.

• 대한전기학회논문지
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• 제41권9호
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• pp.973-983
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• 1992

A very fast algorithm, using fast Haar transformation with half a cycle dc-offset free data, to extract the power frequency components and to detect faults in power systems is proposed. For the speed-up, two important techniques are used. First, according to the symmetric characteristics of sine and cosine functions, fundamental frequency components are calculated with only half a cycle sample data. For using these characteristics, post-fault de-offset components must be removed beforehand. Therefore, secondly, a newly designed digital filter is used to remove exponentially decaying dc-offset from the post-fault signal. In accordance with series simulations, transmission line faults can be detected in around half a cycle after faults.

• 조명전기설비학회논문지
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• 제28권11호
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• pp.68-76
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• 2014

This paper presents an offset error compensation algorithm for the accurate phase angle of the grid voltage in single-phase grid-connected inverters. The offset error generated from the grid voltage measurement process cause the fundamental harmonic component with grid frequency in the synchronous reference frame phase lock loop (PLL). As a result, the grid angle is distorted and the power quality in power systems is degraded. In addition, the dq-axis currents in the synchronous reference frame and phase current have the dc component, first and second order ripples compared with the grid frequency under the distorted grid angle. In this paper, the effects of the offset and scaling errors are analyzed based on the synchronous reference frame PLL. Particularly, the offset error can be estimated from the integrator output of the synchronous reference frame PLL and compensated by using proportional-integral controller. Moreover, the RMS (Root Mean Square) function is proposed to detect the offset error component. The effectiveness of the proposed algorithm is verified through simulation and experiment results.

• 대한전자공학회논문지TC
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• 제45권5호
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• pp.21-29
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• 2008

본 논문은 IEEE802.11n 시스템의 반송파 주파수 옵셋 추정 알고리즘을 제안한다. IEEE802.11n 시스템은 다중 송수신 안테나 시스템이므로 종래의 단일 송수신 안테나 시스템에 적용되는 알고리즘과는 다르게 다중 수신부에서 적용 가능한 결합 기법을 고려하여 적용하여야 한다. 따라서 본 논문에서는 IEEE802.11n 과 같은 다중 수신 안테나 시스템에서 적용 가능한 수신기 결합 구조의 반송파 주파수 옵셋 추정 알고리즘을 제안하고, 제안하는 선택적 결합 반송파 주파수 옵셋 추정 알고리즘이 종래의 알고리즘보다 SNR 10dB에서 채널 B 인 경우에 1/10, 채널 D 인 경우에 1/2 의 MSE 오류로 추정이 가능함을 확인하였다.

• 한국CDE학회논문집
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• 제5권3호
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• pp.242-254
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• 2000

This paper describes an efficient solid modeling method for thin-walled plastic or sheet metal parts, based on the non-manifold offsetting operations. Since the previous methods for modeling and converting a sheet into a solid have adopted the boundary representations for solid object as their topological framework, it is difficult to represent the exact adjacency relationship between topological entities of a sheet model and a mixture of wireframe and sheet models that can appear in the meantime of modeling procedure, and it is hard to implement topological operations for sheet modeling and transformation of a sheet into a solid. To solve these problems, we introduce a non-manifold B-rep and propose a sheet conversion method based on a non-manifold offset algorithm. Because the non-manifold offset aigorithm based on mathematical definitions results in an offset solid with tubular and spherical thickness-faces we modify it to generate the ruled or planar thickness-faces that are mostly shown in actual plastic or sheet metal parts. In addition, in order to accelerate the Boolean operations used the offset algorithm, we also develope an efficient face-face intersection algorithm using topological adjacency information.

• 한국정밀공학회지
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• 제21권6호
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• pp.160-166
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• 2004

In this study, a new algorithm, named as Contour Offset Algorithm(COA) is developed to fabricate precise features or patterns in the range of several micrometers by nano replication printing(nRP) process. In the nRP process, a femto-second laser is scanned on a photosensitive monomer resin in order to induce polymerization of the liquid monomer according to a voxel matrix which is transformed from the bitmap format file. After polymerization, a droplet of ethanol is dropped to remove the unnecessary remaining liquid resin and then only the polymerized figures with nano-scaled precision are remaining on the glass plate. To obtain more precise replicated features, the contour lines in voxel matrix should be modified considering a voxel size. In this study, the efficiency of the proposed method is shown through two examples in view of accuracy.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2004년도 하계종합학술대회 논문집(1)
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• pp.43-46
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• 2004

In this paper, we present a carrier phase estimation algorithm for LDPC coded systems. LDPC coded system can not achieve the ideal performance if phase offset is introduced by channel. However, the estimation of phase offset is very hard since the operating point of LDPC is very low SNR. To solve this problem, the algorithm using the tentative soft decision value and based on Maximum Likelihood (ML), was proposed in [2]. But this algorithm has problem which works only under constant phase offset. If phase offset is time variant, it has a severe degradation in performance. To solve this problem. we propose two types of estimators. symbol by symbol estimator: Unidirectional estimator (UDE) and hi-directional estimator (BDE), and sub-block estimator (SBE).

• 한국통신학회논문지
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• 제30권4A호
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• pp.250-258
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• 2005

본 논문에서는 다중사용자 주파수 도약 OFDMA(frequency hopping orthogonal frequency division modulation-requency division multiple access, FH-OFDMA) 시스템에서 단일 프리엠블 심볼을 이용하여 정확하고 신속한 주파수 동기를 획득할 수 있는 프리엠블 구조와 동기 알고리듬을 제안한다. 서로 다른 주파수 옵셋을 갖는 다중 사용자 신호가 수신되면, 부반송파간 직교성이 훼손되어 간섭이 발생한다. 제안한 알고리듬은 각 사용자에게 할당되는 부채널을 대략적 주파수 옵셋 추정 영역과 미세 주파수 옵셋 추정 채널 영역으로 분할하여 프리엠블을 생성한다. 미세 주파수 옵셋은 전력밀도 함수를 이용한 NAH (non-data aided)방식을 이용하여 추정하곡 짧은 심볼을 얻은 후 심볼간의 상관을 이용하여 추정한다. 두 추정치를 조합하면 한 개의 프리엠블 신호로 정확한 주파수 옵셋을 측정할 수 있다. 모의 실험에서는 일반적인 상관을 이용한 방식과 본 알고리듬의 주파수 옵셋 추정 성능을 상향 FH-OFDMA 시스템을 구성하여 비교 평가한다.

• 한국인터넷방송통신학회논문지
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• 제9권2호
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• pp.111-116
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• 2009

본 논문은 차세대 고속무선 DTV(Digital Television)를 위한 터보복호기반의 위상 옵셋 추정 기법이 대해 연구하였다. 위상 추정기법은 터보 복호기 외부에 추정기를 두어 다음 상태의 위상을 추정하기 위해 LMS (Least Mean Square) 방식을 사용하였다. 기존의 LMS 방식은 구현이 간결하지만 고정의 스텝 사이즈를 가지고 있으므로 시간에 따라 변화하는 다중 경로 환경에서는 채널 추정이 힘들며 트래킹 능력이 떨어지는 단점을 가지고 있다. 따라서 본 논문에서는 고정 스텝 사이즈가 아닌 채널의 상태에 따라 스텝 사이즈를 변화 시키는 가변 스텝사이즈를 갖는 LMS 방식을 제안한다. 모의실험은 임의의 위상 옵셋에 대하여 수행되었으며, 제안한 방식이 기존의 방식에 비해 개선된 성능을 보임을 알 수 있었다.