基于能量法的大型叶片毛坯曲面重构

针对大型叶片毛坯曲面测量数据的特点，提出了一种基于能量法的毛坯曲面重构算法。该算法由2个主要步骤构成；基于参数域同构的毛坯曲面拟合，基于加工余量分布均匀的毛坯曲面匹配。实践证明，该算法构造的毛坯曲面不仅拟合精度高、光顺性能好，而且可以大大简化大型叶片五坐标数控加工贵州的辅助定位及进给速度优化等问题的计算。     

飞机结构件组合曲面侧铣加工刀轨生成方法

针对目前五轴侧铣刀轨生成方法生成组合曲面侧铣加工刀轨困难的问题,通过分析飞机结构件中组合曲面的类型,提出了一种基于曲面拟合的精度可控、刀轴摆动均匀且无干涉的飞机结构件组合曲面侧铣加工刀轨生成方法.该方法通过迭代拟合使曲面拟合精度可控,通过角度扇形离散控制刀轴摆角,通过局部微调以减少干涉.经实例验证,该方法精度可控、效率高、刀轨生成算法稳定、加工质量高.基于该方法开发的系统已在某大型航空企业得到应用.     

基于设计公差约束的螺旋桨配准问题

针对螺旋桨加工过程中叶面和叶背加工余量分布不均匀的问题,提出了一种公差约束条件下螺旋桨毛坯与设计曲面快速配准的方法,用以保证螺旋桨叶面和叶背加工余量均匀。在螺旋桨设计过程中,分析了半径、纵斜、轴向位置和桨叶夹角对设计曲面空间位置的影响,确定了基于设计公差变动范围的螺旋桨形貌变化约束条件。建立了约束条件下螺旋桨曲面配准数学模型,并基于模拟退火算法快速求解得到全局最优解。螺旋桨毛坯曲面与设计曲面的匹配验证结果表明,该算法能实现螺旋桨毛坯曲面和设计曲面的快速匹配。     

点云特征型面的边界曲线拟合及曲面裁剪算法

点云特征型面边界曲线的拟合质量直接决定了对应曲面裁剪的质量。以机械零件点云模型为研究对象,针对点云分割型面的边界点识别、排序、拟合和曲面裁剪问题展开研究。基于场力法提取的边界点集,提出了基于最短距离法的边界点集排序和方向夹角阈值限定的边界点集去噪等预处理算法;采用局部二次多项式函数拟合估算边界点集曲率,提出了基于曲率突变点归属性判断的边界点集分段和拟合算法;通过控制点投影变换求取二维裁剪边界,提出了基于特征点集多边形凹凸性的二维边界曲线方向判断法。使用机械零件模型典型型面进行实验,验证了各阶段算法。该算法具有很好的适用性,可进一步扩展应用至复杂曲面边界裁剪。     

大型复杂曲面的荒加工研究

提出了大型曲面的荒加工概念 ,它是对加工余量较大的区域进行的局部加工 ,是粗加工的预处理。其关键之处在于如何求取“荒岛”的边界 ,由此确定荒加工区域 ,安排走刀路径。利用基于 Herm ite离散点曲面造型的新算法构造了余量分布曲面 ,避开了毛坯面与零件曲面等距面的求交问题 ,求取余量分布曲面的等高线即可获得“荒岛”的边界。荒加工能减少大量空行程 ,大幅度提高加工效率。     

大型叶片五坐标数控加工进给速度优化

针对大型叶片数控加工中存在加工余量分布不均匀的现象 ,本文在建立叶片毛坯曲面模型的基础上 ,提出了一种基于恒切削量的进给速度优化算法 ,在计算刀位轨迹、生成 NC代码的过程中实现了进给速度的优化。实践表明 ,这种方法能够提高大型叶片的五坐标数控加工效率 ,降低刀具磨损 ,改善叶片表面加工质量。     

采用正交函数优化三维自由曲面

自由曲面重建时,一般采用增加控制点个数来提高曲面拟合精度,但控制点的增加会引起曲面连续阶数变低.通过分析传统算法在曲面拟合中的不足,提出采用正交函数的曲面拟合方法,该算法避开不规则数据点进行拟合,保证了曲面的光顺性.当采用3×3阶曲面,36个控制点进行曲面拟合时,曲面重构最大误差仅为0.077 0mm,曲面满足G2曲率连续.实验结果表明,所提出的曲面优化算法,实现了曲面控制点数与曲面光顺和重构精度的最佳匹配,提高了曲面拟合的品质.     

基于NURBS方法的复杂叶片形状设计

探讨工程曲线、曲面设计中的NURBS方法,介绍NURBS曲线、曲面的数学表达,采用NURBS方法建立了叶片的数学模型,并用该方法进行了曲面的拟合与显示.     

基于高斯曲面拟合的亚像素边缘检测算法

提出了一种基于高斯曲面拟合的亚像素边缘检测算法.该算法首先使用传统Canny算子进行边缘像素级的粗定位,再以粗定位边缘像素为中心取5x5窗口获取梯度幅值,对其进行高斯曲面拟合,在梯度方向上寻找局部极值点,从而达到边缘亚像素级的精细定位的效果.文中介绍了算法的理论依据,给出推导过程,并用螺旋测微器的标准间隙进行实例分析,...     

基于曲面迭代的离心泵数值叶片模型

针对传统的泵CAD软件存在的缺陷,依据泵的水力设计用Bezier曲线来拟合各轴面流线,依据轴面流线、叶片安放角沿流线的分布函数及叶片的型线方程得到叶片表面上离散点集,提出用一种基于盈亏修正思想的迭代非均匀B-spline曲面算法来拟合叶片型面;利用调节轴面流线的控制点及叶片安放角的分布规律来调节叶片表面的各型值点,从而达到调控叶片曲面的目的;建立数值叶片模型与泵的设计参数间的关系,实现叶片的参数化设计,摒弃繁琐的二维木模图。实例表明提出的数值叶片模型是合理的,具有重要的理论意义和工程应用价值。     

粗糙表面弹性微动接触数值研究

由于实际工程表面多为粗糙表面,这里研究了粗糙表面对微动接触中压力和切向应力的影响。研究接触过程中法向载荷保持不变,切向载荷为周期性的交变载荷。首先,建立接触算法和模型,其算法核心是利用共轭梯度法(CGM)计算微动接触中的表面压力及切向应力并使用快速傅里叶变换(FFT)加快计算速度。然后,在验证算法正确的基础上,分析正弦和非高斯粗糙表面接触的压力和切向应力的分布,通过对光滑与粗糙表面的研究对比,表明:(1)在正弦表面接触切向应力分布呈现尺寸效应;(2)在非高斯表面接触中,切向应力分布跟光滑表面形状类似;同时由于粗糙峰存在,粗糙表面下的切向应力比光滑表面下的要大,研究粗糙表面微动接触对实际工程具有重要意义。     

A new free-form surface fitting method for precision coordinate metrology

Free-form surfaces are widely used in advanced optical and mechanical devices. In order to assess the form accuracy of free-form surfaces, it is needed to fit the measurement surface with the design template. To improve the fitting efficiency and accuracy, the fitting procedure is divided into two stages, rough fitting and final fitting. A new rough fitting method, called structured region signature is proposed. Structured region signature is a generalised global feature which represents the surface shape by a one-dimensional function. The template location occupying the best fitting signature is considered to be the correct initial position of the measurement surface. In the final fitting, the motion parameters are calculated iteratively using the Levenberg-Marquardt algorithm. Simulation and experiments are given to identify the validity of this method. It is demonstrated that the fitting accuracy is as high as 1:10⁶.     

Application of the lifting wavelet to rough surfaces

This paper proposes a lifting wavelet model for enhancement of accuracy of surface roughness characterisation. In this work, the theory and fast algorithm of the lifting wavelet are briefly introduced and a lifting wavelet model for extraction of roughness of surfaces has been developed. The rough surface recovered has good refinement accuracy in contrast to the least squares polynomial fitting. Applications are conducted by using a series of typical surfaces, planes and curves, measured by contact (stylus) and non-contact (phase-shifting interferometry) instruments, to demonstrate the feasibility and applicability of using the lifting wavelet model in the analysis of these surfaces.     

基于表面法矢的散乱数据分割与几何特征提取

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.     

离散数据曲面的三轴数控粗加工代码生成算法

介绍一种用于离散数据的三轴数控粗加工代码生成算法。该算法以离散数据点为输入信息,先构建一个网格曲面,然后通过一系列的计算步骤,最终得到用于实现离散数据曲面粗加工的数控代码。详细阐述该算法的推导过程,并给出算法的实现细节。该算法被证明具有良好的使用价值。     

一种基于曲线拟合与采样的点云数据压缩方法

在反求工程中,从样件表面采集得到的通常是数量非常庞大的点云数据,严重影响了曲面重建算法的效率;另外,基于四边域曲面的重建算法通常要求型值点数据呈拓扑矩形排列,而采样得到的散乱点云通常不满足这一拓扑要求。文中提出了一种新的数据压缩技术路线,用于把海量散乱点云数据合理地压缩到四边域曲面重建所要求的数据量和拓扑形式。该方法的核心是B样条曲线的拟合和采样。为使采样点更好地反映原始模型的外形特征,给出了一种基于曲率的自由曲线自适应采样算法。应用实例表明本文提出的方法达到了预期的效果。     

曲面笔式加工刀位点曲线的实时拟合

针对曲面高速高精度加工问题,给出一种刀位点轨迹实时生成算法。该方法的实现包括曲面上离散刀触点的生成和基于三次非均匀B样条曲线的刀位点轨迹实时高精度拟合两部分。第一部分,由导动曲线和刀触点轨迹的运动学关系,通过计算导动曲线参数,间接得到投影在曲面上的离散刀触点;第二部分,通过合理参数化、构建模长因子等实现刀位点参数曲线的分段实时拟合。仿真实例表明该算法简单易于编程,曲线拟合精度高,适用于自由曲面笔式加工中刀具路径计算与生成,从而满足复杂曲面高性能数控加工需求。     

Reverse engineering of composite sculptured surfaces

A reverse engineering technique is proposed in this study for modelling composite sculptured surfaces. The proposed technique includes a surface fitting algorithm and a surface blending algorithm. The former is formulated as the least-squares minimisation problem for which an error expression was minimised which yields the optimised position of control points and parameter values for the non-uniform rational B-spline patch. Cubic spline and bicubic surface algorithms are developed for two-patch and four-patch blending, respectively. Computer simulation results clearly demonstrate that the proposed technique is useful for composite surfaces modelling applications. Factors affecting the convergence speed and surface accuracy in the optimisation process are also discussed.     

Complete 3D surface reconstruction from unstructured point cloud

In this study, a complete 3D surface reconstruction method is proposed based on the concept that the vertices of surface model can be completely matched to the unstructured point cloud. In order to generate the initial mesh model from the point cloud, the mesh subdivision of bounding box and shrink-wrapping algorithm are introduced. The control mesh model for well representing the topology of point cloud is derived from the initial mesh model by using the mesh simplification technique based on the original QEM algorithm, and the parametric surface model for approximately representing the geometry of point cloud is derived by applying the local subdivision surface fitting scheme on the control mesh model. And, to reconstruct the complete matching surface model, the insertion of isolated points on the parametric surface model and the mesh optimization are carried out. Especially, the fast 3D surface reconstruction is realized by introducing the voxel-based nearest-point search algorithm, and the simulation results reveal the availability of the proposed surface reconstruction method.     

A novel machining of multi irregular surface using improved noncircular turning method

The backplane processing is an important part of the manufacture of electronic communication equipment; the current processing of backplane surface, especially the rough machining, is still using milling; and the production efficiency is quite low. This paper presents a new method to turn with a cylinder for the rough machining of multi backplane surfaces, which is based on a conventional horizontal lathe and uses the improved method of noncircular machining. The performance requirements of fast tool servo (FTS) device and control model for the machining of noncircular surface are analyzed firstly; the position following control strategy is used instead of traditional position interpolation, according to the multi backplane surfaces machining technology and control strategy; and a novel algorithm, which is combined UG (Unigraphics NX) software surface fitting with cubic spline curve fitting of multi backplanes’ space, is proposed for computer-aided manufacturing (CAM) software design. Finally, the proposed processing method and CAM model algorithm are proved to be effective through the simulation and actual verifications, the products meet the processing requirements and the processing time of each piece is reduced from 8 to 2 min, and they also greatly improve the production automation and achieve energy saving and emission reduction.