共查询到20条相似文献,搜索用时 218 毫秒
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一种复杂二次曲面轮廓度评定方法 总被引:1,自引:0,他引:1
为了建立复杂二次曲面轮廓度评定中计算机数据处理的理论模型和实现方法,提出了一种不要求满足小误差假设、不使用微分线形化评定二次曲面轮廓度的方法。该方法首先通过最小二乘法得到一个初始二次曲面,然后用模式搜索对初始二次曲面系数进行调整,直到找到满足最小区域原则的理想二次曲面,其目标函数值作为被测曲面的轮廓度。在计算过程中使用坐标变换将一般型的二次曲面化为标准型,既简化了轮廓度的计算,而且被测曲面可以在测量范围内任意放置。对抛物面轮廓度评定表明目标函数随着模式搜索的进行逐渐减小,模式搜索得到的抛物面轮廓度值比用最小二乘法得到的轮廓度值小得多,因此该方法更好地反映了被测二次曲面表面形状误差。 相似文献
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反求工程中过渡曲面特征提取算法研究 总被引:16,自引:1,他引:16
针对反求工程中常见的过渡曲面特征,提出了一种过渡曲面特征的提取算法。该算法包括数据分块和过渡曲面参数提取两部分,在数据分块算法中,通过数据精简,曲率估算和曲率比较等步骤,将过渡区域的数据点从原努点云数据中分离出来,在过渡曲面参数提取算法中,通过圆柱拟合和过渡区域跟踪算法,计算出一系列过渡曲面的截面线,该算法和已有的过渡曲面特征提取算法相比,无需人工交互,而且适用于等半径过渡曲面特征和变半径过渡曲面特征。 相似文献
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基于无网格局部Petrov-Galerkin法的曲面修复算法 总被引:1,自引:1,他引:0
针对三维残缺数据曲面重构的困难,提出残缺点云或有孔洞网格曲面数据修复的新算法,该方法通过拟合进行曲面重构,大大减小了边界节点误差的影响;同时采用基于板壳理论的无网格法,使孔洞曲面修复更光滑,尤其可以更真实地修补出锻压制造的薄板零件.首先应用移动最小二乘法插值对残缺点云进行边界提取,然后给出逐层节点布置算法,最后应用基于最小势能原理的无网格法进行曲面修复,并将通常无网格法中积分圆域改进为多边形域.编写相应程序,经简单二次曲面缺损网格修补验证算法的有效性,结果分析表明误差很小,曲面修复结果理想.为进一步证明算法实用性,对实际薄壳产品的孔洞进行算法应用,修补效果理想. 相似文献
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《机械科学与技术》2017,(1):114-118
针对车身曲面难以用单张曲面进行表达的情况,提出用光滑拼接多张带形状参数的双三次Q-Bézier曲面技术构造曲面方法,并用多张双三次Q-Bézier曲面拼接描述汽车车身曲面;提出由设计师构建多个单张双三次Q-Bézier曲面,再进行曲面间的光滑拼接,在编辑各组双三次Q-Bézier曲面公共边界的位置及其各形状参数的情况下,得到大量的车身造型方案。该方法基于双三次Q-Bézier曲面的生成及其拼接原理,可以高效调整车身曲面及其公共边界,获得光滑的曲面连接效果,从而快速获得多种汽车车身造型方案。所提方法运算速度快、易于操作,具有良好的可拓展性。 相似文献
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针对单值散乱点云曲面刀具路径规划问题,提出了一种基于最小二乘支持向量机的计算方法。在计算过程中,将点云数据向平面投影,得到二维点集。应用网格划分和边界网格内测量点高斯映射技术,提取平面区域内的边界特征点。用边界特征点定义点云曲面的实际加工区域,在此区域内规划平行等间距刀具路径。应用最小二乘支持向量机拟合点云数据,求得被加工曲面的连续表达模型,经此模型将二维刀具路径数据向三维空间映射,求出刀触点数据。将刀触点经法向偏置计算,求得刀位点。实例验证证明,该方法能较好地解决信息不完备散乱点云曲面刀具路径生成问题。 相似文献
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基于表面法矢的散乱数据分割与几何特征提取 总被引:1,自引:0,他引:1
使用区域增长法进行散乱数据的区域分割以及二次曲面几何特征的提取.算法首先自动地布置种子区域,然后通过迭代/拟合这一循环过程来实现区域的增长.为了提高算法的可靠性,提出基于散乱数据表面法矢的二次曲面直接拟合方法.该方法根据特定类型二次曲面的几何性质,应用线性最小二乘技术求解其几何参数,从根本上解决以往二次曲面拟合算法因几何参数初值的设置精度不高而导致的求解效率低,进而失败的问题.试验结果表明提出的算法实现简单,且稳定可靠. 相似文献
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Measured surface localization (MSL) is one of the key essentials for the assessment of form error in precision manufacturing. Currently, the researches on MSL have focused on the corresponding relation search between two surfaces, the performance improvement of localization algorithms and the uncertainty analysis of localization. However, low efficiency, limitation of localization algorithms and mismatch of multiple similarities of feature points with no prior are the common disadvantages for MSL. In order to match feature points quickly and fulfill MSL efficiently, this paper presents a new localization approach for measured surfaces by extracting the generic umbilics and estimating their single complex variables, describing the match methods of ambiguous relation at umbilics, presenting the initial localization process of one pair matched points, refining MSL on the basis of obtained closet points for some measured points by the improvement directed projection method. In addition, the proposed algorithm is simulated in two different types of surfaces, two different localization types and multiple similar surfaces, also tested with the part of B-spline surface machined and bottle mould with no knowledge, finally the initial and accurate rigid body transformation matrix, localization errors between two surfaces and execution time are got. The experimental results show that the proposed method is feasible, more accurate in localization and high in efficiency. The proposed research can not only improve the accuracy and performance of form error assessment, but also provide an effective guideline for the integration of different types of measured surfaces. 相似文献
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J.M. Selig 《Mechanism and Machine Theory》2011,46(2):156-167
A line symmetric motion is the motion obtained by reflecting a rigid body in the successive generator lines of a ruled surface. In this work we review the dual quaternion approach to rigid body displacements, in particular the representation of the group SE(3) by the Study quadric. Then some classical work on reflections in lines or half-turns is reviewed. Next two new characterisations of line symmetric motions are presented. These are used to study a number of examples one of which is a novel line symmetric motion given by a rational degree five curve in the Study quadric. The rest of the paper investigates the connection between sets of half-turns and linear subspaces of the Study quadric. Line symmetric motions produced by some degenerate ruled surfaces are shown to be restricted to certain 2-planes in the Study quadric. Reflections in the lines of a linear line complex lie in the intersection of the Study quadric with a 4-plane. 相似文献
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Ke YinglinSun QingLu ZhenCollege of Mechanical andEnergy Engineering Zhejiang University Hangzhou China 《机械工程学报(英文版)》2003,16(2):163-166
The main purpose of reverse engineering is to convert discrete data points into piecewise smooth, continuous surface models. Before carrying out model reconstruction it is significant to extract geometric features because the quality of modeling greatly depends on the representation of features. Some fitting techniques of natural quadric surfaces with least-squares method are described. And these techniques can be directly used to extract quadric surfaces features during the process of segmentation for point cloud. 相似文献
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X. L. Jin 《Machining Science and Technology》2013,17(2):199-220
This article develops two statistical rough surface models to investigate the material removal rate in surface polishing. Model I implies that the contact between two surfaces is equivalent to that between a composite surface and a plane; but Model II is without the equivalent surface concept. The prediction differences of the two models were first investigated with the aid of contact mechanics. The analysis shows that the relative error of the predictions by the two models could be minimized by considering the interactions between asperities, and that this error increases with the separation of the mean planes, but decreases with the asperity density, asperity radius and standard deviation of the asperity height. By extending the models to study the material removal rate in polishing, it was found that asperity interaction is an important factor in a statistical modelling of polishing, and that with a given separation of the reference planes of the pad and workpiece surfaces, the material removal rate increases with the volume concentration of abrasive particles and varies with the pad roughness. The study also showed that the microstructure of a polishing pad has a significant effect on the material removal rate of a polishing. 相似文献
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This paper studies thin film flows with free surfaces driven by gravity through two types of undulated planes: periodically sinusoidal plane and triangle. The substrate plane is fixed and inclined to a certain angle and the flow with a free surface. Through finite element method (FEM), commenced from Navier-Stokes equations and continuity equation, the exact numerical results of free-surface film flows are obtained through discretization solution to finite equations in flowing areas. Based on the numerical calculations, the streamlines and wall shearing stress during the flowing process are visualized via post-proceeding, and the streamlines separation, the onset and evolution of vortex near the substrate boundary during the flow are also analyzed. The influences from the waviness of the substrate planes profile, height of the triangle plane, and change of the film height on film flow dynamics properties are shown. 相似文献
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Zhaomiao Liu Xin Liu Guobin Wang Hong Liao 《Frontiers of Mechanical Engineering in China》2010,5(2):219-225
This paper studies thin film flows with free surfaces driven by gravity through two types of undulated planes: periodically
sinusoidal plane and triangle. The substrate plane is fixed and inclined to a certain angle and the flow with a free surface.
Through finite element method (FEM), commenced from Navier-Stokes equations and continuity equation, the exact numerical results
of free-surface film flows are obtained through discretization solution to finite equations in flowing areas. Based on the
numerical calculations, the streamlines and wall shearing stress during the flowing process are visualized via post-proceeding,
and the streamlines separation, the onset and evolution of vortex near the substrate boundary during the flow are also analyzed.
The influences from the waviness of the substrate planes profile, height of the triangle plane, and change of the film height
on film flow dynamics properties are shown. 相似文献
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Mohamed R. Rahayem Johan A. P. Kjellander 《The International Journal of Advanced Manufacturing Technology》2011,52(1-4):155-169
Applications like geometric reverse engineering, robot vision and automatic inspection require sets of points to be measured from the surfaces of objects and then processed by segmentation and fitting algorithms to establish shape parameters of interest. In industrial applications where speed, reliability and automatic operation is of interest a measuring system based on a laser profile scanner mounted on an industrial robot can be of interest. In earlier publications we have presented such a system and also a segmentation algorithm for planar surfaces using 2D profile data in combination with robot poses. Due to the data reduction offered by this approach the segmentation algorithm computes faster than algorithms based on 3D point sets alone. Encouraged by the results we have now developed a segmentation algorithm for two different quadric surfaces also based on 2D profiles in combination with robot poses. This paper presents the new algorithm together with test results and also an interesting observation that points to future work. 相似文献