共查询到20条相似文献,搜索用时 15 毫秒
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Lin Zhu Shuang-Shuang Peng Cheng-Long Yin Tien-Chien Jen Xi Cheng Yi-Hsin Yen 《The International Journal of Advanced Manufacturing Technology》2014,70(5-8):995-1007
In this paper, using the specifications of nodal points on a nonuniform rational B-spline (NURBS) curve of three degrees with respect to NURBS curve parameter and defining the coefficients for the velocity and acceleration vectors on these points, a new method is presented to design a tool path via C2 PH spline curves. Values of the velocity/acceleration vector coefficients corresponding to the nodal points on the original NURBS curve are computed by pattern search algorithm. To this end, the normal distance between the constructed C2 PH spline curve and its corresponding original NURBS curve is considered as the objective function. Using combination of the time-dependent feed rate interpolation in the acceleration/deceleration phase of the motion and the constant feed rate interpolation in the middle region of the motion, the position commands of the designed NURBS-based C2 PH spline curve are generated. Several improved NURBS-based C2 PH spline curve following tasks were implemented with pseudo-derivative feedback feed forward (PDFF) controller. The experimental and simulation results confirm that the devised interpolator with designed PDFF controller is not only feasible for machining the complicated tool path represented in the improved NURBS-based C2 PH spline form but also yields satisfactory contouring performance under variable feed rate. 相似文献
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Yuan-Lung Lai James Shih-Shyn Wu Jui-Pin Hung Jian-Hong Chen 《The International Journal of Advanced Manufacturing Technology》2006,27(11-12):1124-1131
Higher degree curves are used in applications because they are easier to manipulate interactively but require heavy computation. Most of the equations for curves used popularly in CAD software are of degree 2 and 3, because two curves of degree 3 can guarantee 2nd derivative continuity at the connection point. This study proposes a different but simpler method than any put forward before to deal with degree reduction of free-form curves. The reduced curves use the simplest knot vector type, i.e., the open uniform knot vector. Unlike other methods, this study does not modify or refine the knot vectors but perturb the control points globally. After obtaining an initial condition, a radiating web-like search algorithm is applied to detect the optimum positions. These NURBS curve formats reach basic industrial standards for CAD/CAM/CNC applications. By defining a global bound error function, this algorithm can achieve an optimum solution not only for NURBS curves but also Bézier/B-spline curves. 相似文献
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J.-L. Shih S.-H. Frank Chuang 《The International Journal of Advanced Manufacturing Technology》2006,29(7-8):714-721
A robust method is proposed to generate tool paths for NURBS-based machining of arbitrarily shaped freeform pockets with islands.
Although the input and output are all of higher-degree NURBS curves, only one simple category of geometric entities, i.e.,
line segments, is required for initial offsetting and for detecting and removing self-intersecting loops. Furthermore, using
those linear non-self-intersecting offsets as the legs of NURBS control polygons, NURBS-format tool paths can be smoothly
reconstructed with G1-continuity, no overcutting, no cusps, and global error control. Since all operations involved in computing tool path curves
are linear geometric calculations, the method is robust and simple. Examples with integrated rough and finish cutting tool
paths of pockets demonstrate the usefulness and effectiveness of this method. 相似文献
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Hyung Bae Jung Kwangsoo Kim 《The International Journal of Advanced Manufacturing Technology》2011,57(1-4):265-270
This paper proposes a new formula of B-spline curve. The new formula generates exact same shape as that of the original B-spline curve formula but has different basic functions and knot vector. This formula requires the number of knots to be the same as the number of control points. This property of the new formula enables us to select the knot vector automatically even in case of nonuniform and to generate spline with relative constant speed. Some experimental results demonstrate its usefulness and quality. 相似文献
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C.-W. Cheng M.-C. Tsai 《The International Journal of Advanced Manufacturing Technology》2004,23(11-12):865-873
This paper presents a real-time control algorithm based on Taylor’s expansion for implementing variable feed rate non-uniform rational B-spline (NURBS) curve interpolators using a digital signal processor for precision CNC machining. To efficiently compute the NURBS curve and its derivatives in real-time, an effective method is proposed. The variable feed rate NURBS curve interpolator can be used to realise the ACC/DEC before feed rate interpolation in which the ACC/DEC (acceleration/deceleration) planning on the feed rate command executes before the interpolation takes place, so that the path command errors caused by conventional ACC/DEC planning using the post feed rate interpolation can be effectively eliminated. To demonstrate the performance of the proposed algorithm, an X-Y table driven by two servomotors is controlled to track command paths represented by multiple blocks of NURBS curves. Experimental results verify the effectiveness of the proposed method. 相似文献
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节点矢量影响NURBS曲线的规律研究与应用 总被引:3,自引:0,他引:3
以非均匀有理B样条(Non uniform rational B-spline, NURBS)曲线理论为基础,证明修改节点矢量对NURBS曲线的影响具有局部性,推导修改节点矢量引起的NURBS曲线变化量的计算式,提出修改节点矢量影响NURBS曲线的一般规律。对计算机辅助图形设计(Computer aided geometric design, CAGD)中曲线局部修改的实例进行试验研究,证明了修改节点矢量可以实现对NURBS曲线的局部修改,实现曲线交互式设计。对NURBS插值曲线节点因子调节法中航空压气机叶片边缘测量的实例进行了试验研究,证明可以获得拟合误差最小的叶片型面测量点NURBS插值曲线。试验研究证明所提出的“节点矢量影响NURBS曲线的一般规律”是正确的和可行的。 相似文献
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数控刀位点的B样条精确拟合 总被引:1,自引:0,他引:1
为了满足现代NURBS曲线加工的要求,提出了把数控刀位点进行分段并按照用户设定精度进行快速拟合的一种算法。在拟合的过程中,通过不断地分析逼近误差,调整节点矢量,进行最小二乘拟合,直至使生成曲线达到规定的精度。利用上述方法进行最小二乘拟合时,建立的矩阵方程存在大量的零元素,采用了新的数据结构来存储矩阵方程,节省了内存空间,简化了求解步骤,获得了较快的计算速度。 相似文献
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Adam Gąska Marcin Krawczyk Robert Kupiec Ksenia Ostrowska Piotr Gąska Jerzy Sładek 《The International Journal of Advanced Manufacturing Technology》2014,71(1-4):497-507
It is complex and divergent for the conventional motion controllers to process various G codes using different interpolation algorithms. This impairs programming efficiency and robustness of the controller. In this paper, we propose the universal non-uniform rational B-splines (NURBS)-based interpolator which can simplify the architecture of interpolation in spite of interpreting different kinds of inputs. Direct conversion of long G01 and G02/G03 numerical control (NC) segments to NURBS segment is first implemented. The fitting of multiple short segments into a continuous and smooth NURBS segment is then carried out. More importantly, the universal NURBS-based interpolator utilizes the Cox–de Boor algorithm which is highly efficient and can take advantage of the parallel computing scheme to accelerate the processing speed. Furthermore, due to the construction of real-time environment, the proposed algorithm enables interpretation, look-ahead functions, and motion control to work simultaneously. A 2D NC program possessing hundreds of short G01 segments and long segments (i.e., G02, G03, and long G01) is tested on an in-house developed XY-table with a PC-based motion controller. The results have shown the effectiveness and feasibility of the proposed real-time NURBS-based interpolator. 相似文献
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运用NURBS曲线拟合算法将节点插入算法应用到动叶片截面型线造型中,采用UG软件中的NURBS样条曲线构造器功能在多个截面上准确绘制出动叶片的截面曲线造型,并利用NURBS曲面造型模块生成烟气轮机动叶片的实体模型。对零件结构特点进行工艺分析,运用UG的加工模块进行加工仿真,生成刀具轨迹并进行试验加工,为后续烟气轮机动叶片的数控加工提供依据。 相似文献
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Kuan-Yuan Lin Wen-Der Ueng Jiing-Yih Lai 《The International Journal of Advanced Manufacturing Technology》2008,39(7-8):760-773
A novel approach is proposed for converting NC files of G01/G02/G03 codes into NURBS curves. The NC points are first acquired from an NC file composed of lines and arcs. A segmentation algorithm based on the angles and lengths evaluated from adjacent points is then used to subdivide the entire group of points into segments. An error-bounded constrained curve fitting algorithm is implemented to fit each segment of points into a curve, maintaining the accuracy, smoothness and boundary continuity between the curves. The chord errors between the NC points and the fitted curves are controlled, which ensures the accurate recovery of NC paths. Also, a knot insertion algorithm is proposed to determine the appropriate number of control points automatically, allowing effective fitting of all segments. Several examples are presented to demonstrate the feasibility of the proposed approach. 相似文献
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Behnam Moetakef Imani Amirmohammad Ghandehariun 《The International Journal of Advanced Manufacturing Technology》2011,56(5-8):619-629
Various methods for parametric interpolation of non-uniform rational B-spline (NURBS) curves have been proposed in the past. However, the errors caused by the approximate nature of the NURBS interpolator were rarely taken into account. This paper proposes an integrated look-ahead algorithm for parametric interpolation along NURBS curves. The algorithm interpolates the sharp corners on the curve with the Pythagorean-hodograph (PH) interpolation. This will minimize the geometric and interpolator approximation errors simultaneously. The algorithm consists of four different modules: a sharp corner detection module, a PH construction module, a feedrate planning module, and a dynamics module. Simulations are performed to show correctness of the proposed algorithm. Experiments on an X?CY table confirm that the developed method improves tracking and contour accuracies significantly compared to previously proposed algorithms. 相似文献
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Sun YuwenSchool of Mechanical Engineering Dalian University of Technology Dalian ChinaWang Yuechao Liu WeijunRobotics Laboratory Shenyang Institute of Automation Chinese Academy of Science Shenyang China 《机械工程学报(英文版)》2003,16(4):420-423
A new method for recovering shape from cross-sectional contours with complex branchingstructures is presented. First, each branching problem by providing an intermediate contour using dis-tance function and image processing technology is solved. Then, all contours are divided into severalgroups of simple contours. For each group, a NURBS curve is fitted to contour points in each sectionwithin a given accuracy on a common knot vector.Finally, the NURBS surface skinning of these con-tours is performed for providing a smooth geometric model. The method is suitable to reproduce theobject by NC machining or rapid prototyping. Some results demonstrate its usefulness and feasibility. 相似文献
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S.-H.F. Chuang J.-L. Shih 《The International Journal of Advanced Manufacturing Technology》2006,29(1-2):151-158
Computing offset curves is an important geometric operation in areas of CAD/CAM, robotics, cam design and many industrial
applications. In this paper, an algorithm for computing offsets of NURBS curves using C2-continuous B-spline curves is presented. The progenitor curve in database is initially approximated by a line-fitting curve,
and then the exact offset of this line-fitting curve is introduced as an initial offset. Based on the initial offset and a
set of selected knots, an intended C2-continuous B-spline curve is subsequently constructed. The method uses a new error-measuring scheme, which is based on the
convex hull property of Bézier curves and the idea of cumulative errors, to calculate the global error bound of offset approximation.
The method obtains offset curves with C2 continuity and guarantees that the actual error bound is precisely within the prescribed tolerance. In addition, it also
allows one to selectively parametrize the offset curve. 相似文献
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利用非均匀有理B样条(NURBS),对弧面凸轮的运动特征曲线进行了修正计算.就型值点与节点矢量的确定方法、权因子的选取与优化、控制顶点的反算等修正中的关键问题,进行了较为详细地分析.通过比较B样条和NURBS修正曲线的位移误差,表明用NURBS修正后的误差明显小于用B样条修正后的误差. 相似文献
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Fast NURBS interpolation based on the biarc guide curve 总被引:2,自引:2,他引:0
Jichun Wu Huicheng Zhou Xiaoqi Tang Jihong Chen 《The International Journal of Advanced Manufacturing Technology》2012,58(5-8):597-605
In parametric spline interpolation, the real-time parameter update is a crucial step which will directly affect the processing performance such as the feed rate fluctuation, the contour error, the online computational effort, etc. The use of Taylor approximation interpolation method to identify the next interpolate point will cause large feed rate fluctuation due to the accumulation error and the truncation error, which will affect the machining quality. As there is no accurate analytic expression between the parameter u and arc length S and the mapping between them is nonlinear, and in order to reduce the feed rate fluctuation and light computation requirement for online interpolation, the paper first samples the tool path with step parameter and Gauss integration, with the sampled points being in the coordinate system defined by parameter u and arc length S. Then, the sampled points are fitted into the guide curve with the use of the biarc fitting method, and the analytic expression between parameter u and arc length S is established. The biarc so derived can be used to realize a fast NURBS interpolation and the simulation results validate the reliability and effectiveness of the proposed method. 相似文献