• Title, Summary, Keyword: NURBS

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Automatic Generation of Finite Element Meshes by Regenerating NURBS Surfaces (NURBS 곡면 재생성을 통한 유한 요소망의 자동 생성)

  • 박정민;채수원
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.784-787
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    • 2002
  • The NURBS surfaces are widely employed for exchanging geometric models between different CAD/CAE systems. However if the input NURBS surfaces are poorly parameterized, most surface meshing algorithms may fail or the constructed meshes can be ill-conditioned. In this paper presents a new method is presented that can generate well conditioned meshes even on poorly parameterized NURBS surfaces by regenerating NURBS surfaces. To begin with, adequate Points are sample on original poorly parameterized surfaces and new surfaces are created by interpolating these points. And then. mesh generation is performed on new surfaces. With this method, models with poorly parameterized NURBS surfaces can be meshed successfully.

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Integration of Shell FEA with Geometric Modeling Based on NURBS Surface Representation (NURBS 곡면기반의 기하학적 모델링과 셀 유한요소해석의 연동)

  • Choi, Jin-Bok;Roh, Hee-Yuel;Cho, Maeng-Hyo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.31 no.1
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    • pp.105-112
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    • 2007
  • The linkage framework of geometric modeling based on NURBS(Non-Uniform Rational B-Spline) surface and shell finite analysis is developed in the present study. For this purpose, geometrically exact shell finite element is implemented. NURBS technology is employed to obtain the exact geometric quantities for the analysis. Especially, because NURBS is the most powerful and wide-spread method to represent general surfaces in the field of computer graphics and CAD(Computer Aided Design) industry, the direct computation of surface geometric quantities from the NURBS surface equation without approximation shows great potential for the integration between geometrically exact shell finite element and geometric modeling in the CAD systems. Some numerical examples are given to verify the performance and accuracy of the developed linkage framework. In additions, trimmed surfaces with some cutouts are considered for more practical applications.

NURBS Interpolator with Recursive Method (재귀적 방법에 의한 NURBS 보간기)

  • Baek Dae Kyun;Ko Tae Jo;Lee Jeh Won;Kim Hee Sool
    • Journal of the Korean Society for Precision Engineering
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    • v.22 no.5
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    • pp.45-54
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    • 2005
  • The purpose of this research is to find a simple and accurate NURBS interpolator for CNC systems such as robot, CMM and CNC machine tools. This paper presents a new design of NURBS interpolator for CNC system. The proposed algorithm used the recursive characteristics of NURBS equation, the previous incremental value and chord length for the sake of a constant chord length. Simulation study was conducted to see the performance of the proposed interpolator with reference-word and reference-pulse method. Consequently, an accurate and simple NURBS interpolator was possible for modem CNC systems.

NURBS Post-Processing of Linear Tool Path (미소직선 공구경로의 NURBS 변환)

  • Kim, Su-Jin;Choi, In-Hugh;Yang, Min-Yang
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.7
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    • pp.1227-1233
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    • 2003
  • NURBS (Non Uniform Rational B-Spline) is widely used in CAD system and NC data for high speed machining. Conventional CAM system changes NURBS surface to tessellated meshes or Z-map model, and produces linear tool path. The linear tool path is not good fur precise machining and high speed machining. In this paper, an algorithm to change linear tool path to NURBS one was studied and the machining result of NURBS tool path was compared with that of linear tool path. The N-post including both a post-processing and a virtual machining software was developed. The N-Post transforms linear tool path to NURBS tool path and quickly shades a machined product on OpenGL view, while comparing a machined surface with a original CAD one. A virtulal machined model of original tool path and post-processed tool path was compared to original CAD model. The machining error and machining time of post-processed NURBS tool path were investigated.

Spline-Based Finite Element Analysis with T-Spline Local Refinement (T-스플라인 국부세분화를 고려한 스플라인 기반 유한요소해석)

  • Seo, Yu-Deok;Kim, Ki-Seung;Youn, Sung-Kie
    • Proceedings of the KSME Conference
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    • pp.366-371
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    • 2007
  • In many CAD systems, NURBS has been employed to construct exact geometries. Recently, NURBS finite element analysis methods were proposed by some authors for convenient connection between CAD and finite element analysis. Additional advantages of NURBS FEA, such as exact geometry and no mesh generation, are obtained. However, NURBS is inefficient in local refinement and merging patches. For refinement of local region in interest, additional control points should be inserted into the entire row or column which contains the local region. There is another inefficiency of NURBS during merging patches into a large structure due to propagation of control points. In order to overcome these inefficiencies of NURBS, T-spline was proposed by Sederberg. In this work, T-spline based finite element method is proposed for efficient local refinement and merging patches. At first, accuracy and efficiency of NURBS FEA is verified and efficiency of T-spline FEA is verified by comparing with NURBS FEA.

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A complete S-shape feed rate scheduling approach for NURBS interpolator

  • Du, Xu;Huang, Jie;Zhu, Li-Min
    • Journal of Computational Design and Engineering
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    • v.2 no.4
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    • pp.206-217
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    • 2015
  • This paper presents a complete S-shape feed rate scheduling approach (CSFA) with confined jerk, acceleration and command feed rate for parametric tool path. For a Non-Uniform Rational B-Spline (NURBS) tool path, the critical points of the tool path where the radius of curvature reaches extreme values are found firstly. Then, the NURBS curve is split into several NURBS sub-curves or blocks by the critical points. A bidirectional scanning strategy with the limitations of chord error, normal/tangential acceleration/jerk and command feed rate is employed to make the feed rate at the junctions between different NURBS blocks continuous. To improve the efficiency of the feed rate scheduling, the NURBS block is classified into three types: short block, medium block and long block. The feed rate profile corresponding to each NURBS block is generated according to the start/end feed rates and the arc length of the block and the limitations of tangential acceleration/jerk. In addition, two compensation strategies are proposed to make the feed rate more continuous and the arc increment more precise. Once the feed rate profile is determined, a second-order Taylor's expansion interpolation method is applied to generate the position commands. Finally, experiments with two free-form NURBS curves are conducted to verify the applicability and accuracy of the proposed method.

Development of the Real-Time 3D NURBS Interpolator for CNC Machines (CNC 공작기계의 실시간 3차원 NURBS 보간기 개발)

  • 홍원표;양민양
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.1032-1035
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    • 2000
  • Increasing demands on precision machining with computerized numerical control (CNC) machines have necessitated that the tool to move not only position error as small as possible, but also with smoothly varying feedrates in space. This paper presents a new high precision interpolation algorithm for 3-dimensional (3D) Non-Uniform Rational B-Spline (NURBS) curve in the reference-pulse CNC technique. Based on the minimum path error strategy, real-time NURBS interpolator was developed in software and this was implemented with a PC-NC milling machine. The several experimental results have shown that the proposed NURBS interpolator is useful for the high precision machining of complex shapes. It is expected that this algorithm can be applied to the CNC machines for the machining of 3D free-form surfaces.

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NURBS Interpolation Algorithm for CNC Machines (CNC 공작기계의 NURBS 보간 알고리즘에 관한 연구)

  • Hong, Won-Pyo;Yang, Min-Yang
    • Journal of the Korean Society for Precision Engineering
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    • v.17 no.12
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    • pp.115-120
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    • 2000
  • Increasing demands on precision machining of free-form surface have necessitated that the tool to move not only position error as small as possible, but also with smoothly varying feedrates. This paper presents new algorithm for high precision 3D(3-dimensional) NURBS(Non-Uniform Rational B-Spline) interpolation in the reference-pulse technique. Based o the minimum path error strategy, interpolation algorithm was designed to follow the NURBS curve. Using this algorithm a real-time 3D NURBS interpolator was developed in software. The algorithm implemented in a PC showed promising results in interpolation error and speed performance. It is expected that this can be applied to the CNC systems for the high precision machining of complex shapes.

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An universal NURBS interpolator for an architectured CNC controller (개방형 수치제어 장치를 위한 범용 NURBS 보간기)

  • 강성균
    • 제어로봇시스템학회:학술대회논문집
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    • pp.656-659
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    • 1996
  • An universal NURBS interpolation for an open architectured CNC controller is proposed in order to unify internal data structure and algorithm of different interpolations such as linear, circular and spline, and to intelligently interface CAD database of the various workpiece contour. Furthermore, NURBS interpolation may result in better surface roughness and high speed machining due to the continuous generation of cutter movement. The mathematical manipulation of NURBS is presented and the practical implementation on the CNC controller of a lathe is discussed for real machining. The comparison between a computer design and workpieces machined on a lathe shows the feasibility of the NURBS interpolation format as an universal interpolation scheme.

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Structured Surface Grid Generation on Body Surfaces defined by NURBS (NURBS로 정의된 표면상에서의 정렬격자 생성 기법)

  • Kim Byoungsoo;Lee Eun-Hee
    • 한국전산유체공학회:학술대회논문집
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    • pp.144-151
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    • 2001
  • NURBS 곡면식으로 정의된 물체 표면상에서 표면 정렬 격자를 생성할 수 있는 방법을 소개하였다. 공학 응용분야에서의 물체 표면 정의는 여러 개의 패치들로 표현되는 것이 일반적이고, 여기서 소개하는 표면격자 생성기법은 이러한 여러 패치들에 걸쳐서 분포되는 정렬격자를 쉽게 생성할 수 있도록 한다 이 기법은 매개변수 형태의 타원형 격자생성 방정식의 해를 구하되, 여러 NURBS 패치에 걸쳐서 투영/분포된 초기 격자계를 타원형 방정식 반복계산 과정의 매개변수형 표면 정의식으로 임시 활용한다. 매개변수형 타원형 방정식의 해가 얻어지고 나면, 그 결과 격자계를 다시 NURBS 패치에 투영을 시키고 타원형 방정식의 해를 구하는 과정이 반복된다. 이러한 반복과정이 전체적으로 수렴이 이루어질 때까지 반복된다. 이 방법에 의해서 얻어지는 표면 정렬 격자계들은 타원형 격자생성기법의 특징인 완만성을 가지면서 정의된 물체표면에서 벗어나지 않는 격자점들이 된다. 소개된 방법은 간단하면서도 하나의 NURBS 곡면만이 아니라 여러 개의 NURBS 곡면에 걸쳐있는 정렬격자계를 효율적으로 생성할 수 있도록 해주며, 그 기본적인 접근법은 NURBS 곡면식 만이 아니라 다른 형태의 매개변수형 형상 정의식에도 적용이 가능하다.

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