共查询到20条相似文献,搜索用时 296 毫秒
1.
NURBS surfaces are commonly used in CAD/CAM software systems to represent the complex shapes of mechanical parts. Well-planned tool paths for machining the surfaces can significantly increase cutting efficiency and improve part quality. The steepest ascent tool-path pattern has been proposed for making sculptured surfaces in a 3-axis finish milling operation, and it has been proven that a steepest ascent tool-path is inherently more efficient in removing material to make these surfaces within tolerances than a tool path of any other type. However, the mathematical representation of steepest ascent paths on NURBS surfaces has not been addressed. In our work, simplified formulae of these paths are derived, and a comprehensive, efficient algorithm to plan steepest ascent tool-paths on compound NURBS surfaces is developed. To verify its validity and efficiency, this innovative approach is applied to a complicated compound surface. Furthermore, a comparison between the steepest ascent and CATIA tool-paths on two NURBS surfaces is conducted to demonstrate the advantages of the steepest ascent tool-paths for NURBS surface part production. 相似文献
2.
Chen-Ming Chuang Author Vitae Author Vitae 《Computer aided design》2005,37(10):1039-1051
Precision z-level contour machining is important for various computer-aided manufacturing (CAM) applications such as pocket machining and high-speed machining (HSM). This paper presents a new z-level contour tool-path generation algorithm for NC machining of triangulated surface models. Traditional approaches of z-level machining rely on the creation of accurate CL (cutter location) surfaces by surface offsetting or high-density z-map generation, which is computationally expensive and memory demanding. In contrast, this paper presents a novel approach to the generation of CL data directly from the section polygon of a triangulated surface model. For each polygon vertex of the contour, the offset direction is determined by the normal to the edge, while the offset distance is not fixed but is determined from the cutter shape and the part surface. An interference-free tool-path computation algorithm using fillet endmills is developed. Since there is no need to create a complete CL surface or high-density z-map grids, this proposed method is highly efficient and more flexible, and can be directly applied to triangulated surfaces either tessellated from CAD models, or reconstructed from 3D scanned data for reverse engineering (RE) applications. 相似文献
3.
4.
5.
NURBS (Non-uniform rational B-splines) surfaces are one of the most useful primitives employed for high quality modeling in CAD/CAM tools and graphics software. Since direct evaluation of NURBS surfaces on the GPU is a highly complex task, the usual approach for rendering NURBS is to perform the conversion into Bézier surfaces on the CPU, and then evaluate and tessellate them on the GPU. In this paper we present a new proposal for rendering NURBS surfaces directly on the GPU in order to achieve interactive and real-time rendering. Our proposal, Rendering Pipeline for NURBS Surfaces (RPNS), is based on a new primitive KSQuad that uses a regular and flexible processing of NURBS surfaces, while maintaining their main geometric properties to achieve real-time rendering. RPNS performs an efficient adaptive discretization to fine tune the density of primitives needed to avoid cracks and holes in the final image, applying an efficient non-recursive evaluation of the basis function on the GPU. An implementation of RPNS using current GPUs is presented, achieving real-time rendering rates of complex parametric models. Our experimental tests show a performance several orders of magnitude higher than traditional approximations based on NURBS to Bézier conversion. 相似文献
6.
Georgia N. Koini Sotirios S. Sarakinos Ioannis K. Nikolos 《Advances in Engineering Software》2009,40(1):41-51
This paper presents a software tool for the conceptual design of turbomachinery bladings named “T4T” (Tools for Turbomachinery). It provides the ability to interactively construct parametric 3D blade rows of various types, including for multistage machines. The design procedure is parametric and a variety of different rotating machinery components may be produced. The design parameters used for the blades as well as the hub and shroud surfaces construction correspond to 2D sections. However, the resulting geometries are modeled as NURBS 3D surfaces and can be imported to other CAD or analysis software via standard exchange protocols. The geometry definition is empowered by the object oriented structure of the software and an easy-to-use graphical interface, which makes the design phase a straightforward procedure. The software’s structure and geometric algorithms, the blading design procedure, along with sample designs which demonstrate the capabilities of the software, are presented in this paper. 相似文献
7.
A. C. O. Miranda L. F. Martha P. A. Wawrzynek A. R. Ingraffea 《Engineering with Computers》2009,25(2):207-219
This work describes an automatic algorithm for unstructured mesh regeneration on arbitrarily shaped three-dimensional surfaces.
The arbitrary surface may be: a triangulated mesh, a set of points, or an analytical surface (such as a collection of NURBS
patches). To be generic, the algorithm works directly in Cartesian coordinates, as opposed to generating the mesh in parametric
space, which might not be available in all the cases. In addition, the algorithm requires the implementation of three generic
functions that abstractly represent the supporting surface. The first, given a point location, returns the desired characteristic
size of a triangular element at this position. The second method, given the current edge in the boundary-contraction algorithm,
locates the ideal apex point that forms a triangle with this edge. And the third method, given a point in space and a projection
direction, returns the closest point on the geometrical supporting surface. This work also describes the implementation of
these three methods to re-mesh an existing triangulated mesh that might present regions of high curvature. In this implementation,
the only information about the surface geometry is a set of triangles. In order to test the efficiency of the proposed algorithm
of surface mesh generation and implementation of the three abstract methods, results of performance and quality of generated
triangular element examples are presented. 相似文献
8.
9.
NURBS were introduced into CAD/CAM systems predominantly for the representation of conventional objects, such as conics and quadrics. Among these, the circle played a critical role in representing a myriad of parts used in the every-day practice. Being the most universally used object, the circle has enjoyed the most popularity in science and engineering. It is an essential entity in both design as well as manufacturing and hence, its representation within CAD/CAM systems requires careful attention. Although the circle enjoys both smoothness as well as a uniform parametrization, its de facto mathematical form, the NURBS form, does not provide either sufficient smoothness or uniform parametrization. On top of all this, NURBS are rational forms requiring homogeneous coordinates in the four-dimensional space, whereas the engineering entity is only Euclidean in 3D. This multiple representational glitch, 3D presence and 4D storage, has given rise to enough headache to warrant reconsideration of the validity of the rational form in engineering design. This paper argues that it is time to drop the “R” from NURBS and to switch to integral splines with approximations where necessary. We also argue that it is time to bury dumb algorithms and consider human-based computing, i.e. our algorithms should be biologically inspired and not based on pure number crunching. 相似文献
10.
Triangulation of 3D surfaces 总被引:1,自引:1,他引:1
A simple generator of graded triangular meshes on spatial surfaces is introduced in this paper. The algorithm is based on the approximation of the surface by tensor product polynomial patches which are uniquely mappable on a planar parametric space. Each of the patches is triangulated separately in its parametric space, using modified advancing front technique allowing for generation of pre-stretched elements, and the obtained triangulation is mapped back onto the original surface. Large effort has been devoted to the treatment of singularities arising on surfaces approximated by degenerated patches. 相似文献
11.
12.
Ramon F. Sarraga Author Vitae 《Computer aided design》2004,36(4):343-349
This article presents a method for modifying CAD/CAM surfaces automatically in accordance with displacements prescribed at a finite set of points in R3, such as node displacements predicted by finite-element analysis. The method is based on the ‘morphing’ approach introduced by Sederberg and Parry in 1986. The input to the process consists of (a) a CAD/CAM model containing trimmed polynomial B-spline surfaces and (b) a set of points and associated displacement vectors in R3. These points are assumed to be close to, but not necessarily on, the objects of the CAD/CAM model. A rectangular volume, enclosing the CAD/CAM model and the input points in R3, is represented as a volume spline, i.e. a trivariate tensor-product spline. A modified volume spline is computed using (a) a least-squares fit based on the given point displacements, and (b) a smoothing functional. The modified CAD/CAM objects are defined as compositions of the original parametric functions and the modified volume spline (i.e. a morphing). In order to ensure compatibility with standard commercial CAD/CAM systems, the modified surfaces are fitted with appropriate splines using any standard, reasonably shape-preserving, fitting procedure applied in the parameter domains of the original surfaces. 相似文献
13.
Fernando Camelli Jyh-Ming Lien Dayong Shen David W. Wong Matthew Rice Rainald L?hner Chaowei Yang 《GeoInformatica》2012,16(2):307-327
A standard use of triangulation in GIS is to model terrain surface using TIN. In many simulation models of physical phenomena,
triangulation is often used to depict the entire spatial domain, which may include buildings, landmarks and other surface
objects in addition to the terrain surface. Creating a seamless surface of complex building structures together with the terrain
is challenging and existing approaches are laborious, time-consuming and error-prone. We propose an efficient and robust procedure
using computational geometry techniques to derive triangulated building surfaces from 2D polygon data with a height attribute.
We also propose a new method to merge the resultant building surfaces with the triangulated terrain surface to produce a seamless
surface for the entire study area. Using Oklahoma City data, we demonstrate the proposed method. The resultant surface is
used as the input data for a simulated transport and dispersion event in Oklahoma City. The proposed method can produce the
seamless surface data to be used for various types of physical models in a fraction of the time required by previous methods. 相似文献
14.
Industrial Geometry aims at unifying existing and developing new methods and algorithms for a variety of application areas with a strong geometric component. These include CAD, CAM, Geometric Modelling, Robotics, Computer Vision and Image Processing, Computer Graphics and Scientific Visualization. In this paper, Industrial Geometry is illustrated via the fruitful interplay of the areas indicated above in the context of novel solutions of CAD related, geometric optimization problems involving distance functions: approximation with general B-spline curves and surfaces or with subdivision surfaces, approximation with special surfaces for applications in architecture or manufacturing, approximate conversion from implicit to parametric (NURBS) representation, and registration problems for industrial inspection and 3D model generation from measurement data. Moreover, we describe a ‘feature sensitive’ metric on surfaces, whose definition relies on the concept of an image manifold, introduced into Computer Vision and Image Processing by Kimmel, Malladi and Sochen. This metric is sensitive to features such as smoothed edges, which are characterized by a significant deviation of the two principal curvatures. We illustrate its applications at hand of feature sensitive curve design on surfaces and local neighborhood definition and region growing as an aid in the segmentation process for reverse engineering of geometric objects. 相似文献
15.
《Computers & Structures》2002,80(16-17):1399-1408
One of the major difficulties in meshing 3D complex geometries is to deal with non-proper geometrical definitions coming from CAD systems. Typically, CAD systems do not take care of the proper definition of the geometries for the analysis purposes. In addition, the use of standard CAD files (IGES, VDA, …) for the transfer of geometries between different systems introduce some additional difficulties.In this work, a collection of algorithms to repair and/or to improve the geometry definitions are provided. The aim of these algorithms is to make as easy as possible the generation of a mesh over complex geometries given some minimum requirements of quality and correctness. The geometrical model will be considered as composed of a set of NURBS lines and trimmed surfaces.Some examples of application of the algorithms and of the meshes generated from the corrected geometry are also presented in this work. 相似文献
16.
An efficient, robust parametric trimmed surface triangulation method is presented. Efficiency is gained during trimmed curve tracing by minimising the number of cells processed. Key feature is the efficient tracing algorithm, and knowledge of orientation of the trimming curves is not required. The method is applicable to NURBS surfaces and operates on the untrimmed surface, constructing a rectangular parametric grid onto which the trimming curves are traced. This approach also minimises the occurrence of degenerate triangles and copes with holes independently of the grid size. 相似文献
17.
W. D. Henshaw 《Engineering with Computers》2002,18(3):265-273
We are interested in building structured overlap-ping grids for geometries defined by Computer-Aided-Design (CAD) packages.
Geometric information defining the boundary surfaces of a computation domain is often provided in the form of a collection
of possibly hundreds of trimmed patches. The first step in building an overlapping volume grid on such a geometry is to build
overlapping surface grids. A surface grid is typically built using hyperbolic grid generation; starting from a curve on the
surface, a grid is grown by marching over the surface. A given hyperbolic grid will typically cover many of the underlying
CAD surface patches. The fundamental operation needed for building surface grids is that of projecting a point in space onto
the closest point on the CAD surface. We describe a fast and robust algorithm for performing this projection which makes use
of a fairly coarse global triangulation of the CAD geometry. Before the global triangulation is constructed the connectivity
of the model is determined by an edge-matching algorithm which corrects for gaps and overlaps between neighbouring patches.
ID="A1" Correspondence and offprint requests to: Dr. W. D. Henshaw, Center for Applied Scientific Computing, L-661, Lawrence Livermore National Laboratory, Livermore, CA
94551, USA. E-mail: henshaw@llnl.gov 相似文献
18.
This paper addresses an image‐based method for modeling 3D objects with curved surfaces based on the non‐uniform rational B‐splines (NURBS) representation. The user fits the feature curves on a few calibrated images with 2D NURBS curves using the interactive user interface. Then, 3D NURBS curves are constructed by stereo reconstruction of the corresponding feature curves. Using these as building blocks, NURBS surfaces are reconstructed by the known surface building methods including bilinear surfaces, ruled surfaces, generalized cylinders, and surfaces of revolution. In addition to them, we also employ various advanced techniques, including skinned surfaces, swept surfaces, and boundary patches. Based on these surface modeling techniques, it is possible to build various types of 3D shape models with textured curved surfaces without much effort. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
19.
Coefficient formula and matrix of nonuniform B-spline functions 总被引:2,自引:0,他引:2
The paper derives a coefficient formula of nonuniform B-spline functions of arbitrary degree from the Coxde Boor recursive algorithm. An efficient numerical algorithm for the coefficient matrix of nonuniform B-spline functions is also presented that is based on this formula. The results in the paper are useful for the evaluation and conversion of NURBS curves and surfaces in CAD/CAM systems. They will promote the application of product data-exchange standards in industry. 相似文献
20.
It has been widely used in CAD field for many years and gradually applied in CAM area with the prevalence of NURBS interpolator equipped in CNC controllers. But few of them provide the tool radius compensation function. In order to achieve the goal of generating tool-path, an algorithm was presented to offset NURBS curves by an optimum process for CAD/CAM systems in this paper. NURBS format is ideal for HSM applications, but not all NURBS outputs are equal and standard. Basically, there are two different ways to generate NURBS tool-paths; one is to fit a NURBS curve to the conventional tool-path output, the other one is to generate a NURBS tool-path from the start. The main targets for the tool-path of this paper are: (1) To keep a constant distance d between progenitor curve C(t) and offset curve Cd(t) on the normal direction of C(t); (2) to alternate the order k of the basis function in offset curve Cd(t); (3) to oscillate the number of control points of offset curve Cd(t) and compare it with progenitor curve C(t). In order to meet the tolerance requirements as specified by the design, this study offsets the NURBS curves by a pre-described distance d. The principle procedure consists of the following steps: (1) construct an evaluating bound error function; (2) sample offset point-sequenced curves based on first derivatives; (3) give the order of NURBS curve and number of control points to compute all initial conditions and (4) optimize the control points by a path searching algorithm. 相似文献