Automation of chamfering by an industrial robot; for the case of hole on free-curved surface

The study deals with the automatic chamfering for the case of hole on free-curved surface on the basis of CAD data, using an industrial robot. As a chamfering tool, a rotary-bar driven by an electric motor is mounted to the arm of the robot having six degrees-of-freedom in order to give an arbitrary position and attitude to the tool. The robot control command converted from the chamfering path is transmitted directly to the robot. From the experimental results, the system is found effective to remove a burr along the edge of a hole on a workpiece with free-curved surface.     

椭圆抛物面/球面求交算法

基于广义特征多项式给出了判断椭圆抛物面与球面是否有交的方法,在有交的条件下,得到了交线为圆的条件以及圆心、半径和法向量等重要几何参数,确保了交线的准确绘制。以平行圆族为基础进行坐标变换,在新坐标系下将椭圆抛物面的一个参数方程代入球面的方程中,得到一个一元四次方程,由方程根的分布情况确定交线的拓扑结构,在每一个有交子区间上,给出所有交曲线段的参数方程。给出了几个具体的实例进行说明。     

有限元网格的孔洞修补算法研究

针对板料成形零件的有限元网格模型提出了一种基于曲面的网格孔洞修补算法,该算法首先建立有限元网格模型的孔洞边界信息,其次利用网格孔洞边界和单元信息确定截面线的方向并生成截面线,然后用蒙皮法构造光滑的蒙皮曲面,最后利用基于边界约束的铺砌算法生成混合网格的孔洞网格,根据此算法获得的孔洞网格可以与原有网格光滑地融为一体,可以很好地满足板料成形CAE分析零件的网格孔洞修补要求,应用实践表明该算法是稳定可靠的。     

Analytical Characteristics of Intersection Curve between a Cylinder anda Cone with Two Obliquely Intersected Axes and Graphical Methodof Locating Special Points

轴线相交的圆柱和圆锥两立体相交时,一般情况下会产生两条相贯线。文章分析 了在圆柱、圆锥正交和圆柱、圆锥斜交情况下,相贯线随圆柱半径变化而形成的不同形状和特 殊点性质。进一步结合解析形式分析,推导了圆柱、圆锥轴线相交并产生左右两条相贯线时, 两条相贯线上最里点的分布规律;相贯线形状与圆柱半径取值范围的精确对应关系;并给出了 确定相贯线上最里点的辅助球半径公式。最后,文章依据以上结果提出了圆柱、圆锥斜交时相 贯线上所有特殊点的图解方法。     

A reliable triangular mesh intersection algorithm and its application in geological modelling

We introduce a reliable intersection algorithm for manifold surface meshes. The proposed algorithm builds conforming surface meshes from a set of intersecting triangulated surfaces. This algorithm effectively handles all degenerate triangle–triangle intersection cases. The key idea of the algorithm is based on an extensive set of triangle–edge intersection cases, combined with an intersection curve tracking method. The intersection operations do not rely on global spatial search operations and no remeshing steps are needed. The intersection curves are introduced into each surface mesh using a unique curve imprinting algorithm. The imprinting algorithm naturally handles degenerate intersection cases of many surfaces at an edge or at a point. The algorithm produces a consistent mesh data structure for subsequent mesh optimization operations. The mesh intersection algorithm is used within a general framework for modelling and meshing of geological formations, which are essential for reliable mathematical modelling of oil reservoirs.     

Stresses in a tensile strip with a large circular hole

This paper considers the determination of the stress concentration factor at the edge of a large circular hole in a flat strip under tension, as the diameter of the hole approaches the width of the strip. It is found that the stress concentration factor decreases as load increases, going from 1.94 to a limiting value of 1.00.     

一种基于截距的圆形窗口线裁剪算法

在圆形窗口圆心为坐标原点的前提下,确定两端点同时在外切正方形某边 界之外或至少有一端点在圆形窗口之内的线段之后,当线段两端点都在圆形窗口之外时：如 果线段所在直线在x 或y 任意坐标轴上截距的绝对值小于或等于圆半径r,则可快速判断线 段与圆形窗口是否相交;否则,再根据点-线位置关系以及所引切线与线段分别相交外切正 方形边的交点坐标相比较判断线段与圆形窗口是否相交。该方法可以加快线段与圆形窗口的 求交进程,避免复杂的辅助操作,显著提高裁剪效率。     

基于矢量游走的任意非自交图形合并算法

图形处理软件中,常常需要将许多非自交图形合并成一个图形,提出一种基于矢量游走的任意非自交多边形合并算法,提出了适合于多边形合并运算的改进矢量游走规则及交点转移条件.通过将交点和两相交矢量边联合处理,对交点分类,有效地去除了“伪交点”,进而简化了重合交点处理.提出用带凸度线段的方式来表示圆和舍圆弧边的多边形,成功地将矢量游走规则运用到这些复杂多边形的快速合并当中.     

基于圆形窗口的简单多边形裁剪算法

提出了一种新颖而实用的圆形窗口Ｖ对多边形Ｐ的裁剪算法。它将多边形Ｐ的边视为有向线段，通过引入多边形顶点的入边和出边交点的概念，深入研究了Ｐ被Ｖ裁剪后的区域确定问题，给出了作出Ｐ在Ｖ内部分的定理     

三角网格上的代数曲面重建

提出一种用分片代数曲面构造三角曲面片的方法,利用具有公共边的2个三角形区域的4个顶点的函数值以及公共边2个端点的外法向量来构造一个二次曲面V(g)和一个截面V(h),其交V(g,h)即为2个三角曲面片的公共边界曲线.对每个已确定了边界条件的三角片内部进一步划分成3部分,每部分各自定义一个三次代数曲面.这3个三次代数曲面不仅在其交线处光滑拼接,而且分别沿三角形的边界与V(g)光滑拼接,从而构成一个具有GC1连续性的分片代数曲面.对于只属于一个三角片的边界留有一个自由度,可对曲面形状加以控制.     

Dual-edge robotic gear chamfering with registration error compensation

This paper describes a novel method for robotic gear chamfering called dual-edge chamfering which can facilitate simultaneous chamfering of the two edges of adjacent gear teeth and overcome typical registration errors arising due to the placement of the workpiece in the robot workspace. Deviations of the robot end-effector trajectory when compared to the nominal trajectory due to registration errors are discussed first; such trajectory deviations caused by typical registration errors due to gear center translation and rotation are quantified. Dual-edge chamfering process is described and an efficient trajectory design strategy is developed by considering the kinematic constraints imposed by the profiles of the gear edge and the abrasive tool. The dual-edge chamfering robot trajectory is facilitated by a simple procedure for identifying the gear and gear root centers by employing the robot. To execute the dual-edge chamfering trajectory, an efficient motion/force control strategy that includes active compliance from the tool mounted on the robot is proposed. A number of real-time experiments are conducted to evaluate the proposed method by employing a commercial six degree-of-freedom robot. Two types of large cylindrical metal gears are utilized for testing, an external gear with teeth on the outside and an internal gear with teeth on the inside. In addition to these, two different robotic compliant tools with axial and radial compliance are tested. A representative sample of the experimental results are presented and discussed.     

变壁厚涡轮叶片参数化设计

提出管道交线投影法的中弧线算法,通过圆形管道创建、管道求交和交线投影来计算中弧线.基于中弧线提出涡轮叶片变壁厚算法,通过定义每条截面线上壁厚标志点处的壁厚参数来定义壁厚,将壁厚设计变量从数十个减少至6个,便于参数化设计和优化设计;根据壁厚定义公式,可以设计工程中常见的4种壁厚分布的叶片.最后开发了变壁厚涡轮叶片参数化设计系统,给出设计实例.     

Three-dimensional finite element analysis of interlaminar stresses in thick composite laminates

The three-dimensional finite element computer program has been developed to investigate interlaminar stresses in thick composite laminates. The finite element analysis is based on displacement formulation employing curved isoparametric 16-node elements. By using substructure technique, the program developed is capable of handling any composite laminates which consist of any number of orthotropic laminae and any orientations. In this paper, solid laminates and laminates with a circular hole were taken to study interlaminar stresses at the straight edge and the curved edge, respectively. Various solid laminates such as [45_n/0_n − 45_n/90_n]_s, [45/0/ − 45/90]_ns, and [45/0/ − 45/90]_sn (n = 1˜4) were analyzed. Also, [45/0/ − 45/90]_sn laminates with a circular hole were studied for n = 1 ˜ 20. The effect of laminate thickness and stacking sequence on the interlaminar stresses near the free edge was investigated. Interlaminar stresses were governed by stacking sequence rather than laminate thickness. The boundary layer width did not increase with laminate thickness but with the number of plies in the repeating unit.     

The polygon package

The polygon package is a set of procedures which manipulate geometric objects in the 2D plane. The operations that can be performed on these objects, regarded as polygons, include intersection, union, asymmetric difference, inflation and deflation. Polygons may have both straight and circular arc edges and include holes within their boundaries. Using a binary tree of bounding boxes as a sorting aid in the centrally important procedure for calculating edge intersections results in a fast, efficient package.     

材料塑性应变对某钢制车轮残余应力测试的影响

针对车轮轮辋与轮辐组合焊缝附近结构的残余应力测试通常采用盲孔法,孔边由于应力集中易产生塑性变形的问题,采用有限元仿真与测试相结合的方法分析在钢制车轮加工的不同阶段,轮辋焊缝区残余应力测试时材料塑性变形对应变释放因数和残余应力测试结果的影响,并分析由Kirsch解析解确定的应变释放因数A和B计算车轮焊缝区残余应力测试所带来的误差.发现当孔边塑性变形较大时,用Kirsch解析解确定的应变释放因数计算残余应力会产生很大误差.     

中水浮拱浮力舱的结构强度分析

针对浅水动态柔性管/缆系统的附件——中水浮拱的浮力舱,介绍其结构特点和功能等,并给出其基本参数;用ANSYS分析浮力舱结构强度,得到壁厚变化对浮力舱的强度和质量影响的一般规律;研究浮力舱在破舱后对中水浮拱整体功能的影响;总结内部隔板与外舱体连接处的倒角半径和浮力舱应力变化曲线,给出最佳倒角半径范围.研究结果可以提高中水浮拱的安全可靠性和设计水平.     

曲面交线的B样条优化逼近

目前，在比较成熟的商业几何核心系统中，曲面的交线是一种基于位置算子的“精确”表示或称为“过程”表示．这样的交线如果用在几何建模操作中，必须输出为系统支持的曲线表示(如B样条表示)．现有的几何核心系统中曲面交线的B样条逼近算法存在控制点数目过多和连续性偏低(C^1)的缺点，导致下游操作结果太复杂且连续性低．基于此，提出了一种曲面交线的B样条逼近算法，使控制点数目减少为原来的三分之一，而连续阶上升为C^2．该算法已经在SolidWorks系统中得到应用，效果良好．     

Computing medial axes of generic 3D regions bounded by B-spline surfaces

A new approach is presented for computing the interior medial axes of generic regions in R³ bounded by C⁽⁴⁾-smooth parametric B-spline surfaces. The generic structure of the 3D medial axis is a set of smooth surfaces along with a singular set consisting of edge curves, branch curves, fin points and six junction points. In this work, the medial axis singular set is first computed directly from the B-spline representation using a collection of robust higher order techniques. Medial axis surfaces are computed as a time trace of the evolving self-intersection set of the boundary under the the eikonal (grassfire) flow, where the bounding surfaces are dynamically offset along the inward normal direction. The eikonal flow results in special transition points that create, modify or annihilate evolving curve fronts of the (self-) intersection set. The transition points are explicitly identified using the B-spline representation. Evolution of the (self-) intersection set is computed by adapting a method for tracking intersection curves of two different surfaces deforming over generalized offset vector fields. The proposed algorithm accurately computes connected surfaces of the medial axis as well its singular set. This presents a complete solution along with accurate topological structure.     

三维桁架结构图分拆与相贯线数据提取方法研究

针对多管相贯线切割的需要,提出了一种三维桁架结构设计图分拆和管件数据提取方法。该方法首先将三维曲面表示的整体实体图细分成一系列基本图元,然后通过对基本图元的识别分析获得各管件的参数,并给出了相贯线切割所需要的管件各种相贯参数的计算方法。最后通过在6轴数控管切割机上的试验, 验证了该方法的可行性和有效性。