【作者】 刘晓明；

【导师】 孙家广；

【作者基本信息】 清华大学 ， 计算机科学与技术， 2011， 博士

【摘要】 圆环面是机械零件设计中常见的一种曲面，数控机床刀具的有效工作面有时也设计成圆环面，CAD/CAM系统中经常面临着圆环面和曲面的求交与距离计算问题。本文研究了两个圆环面的求交和距离计算以及基于圆环面片逼近的点投影算法，论文的主要工作如下：提出了一种两圆环面的求交检测和距离计算的方法。首先证明了空间两圆的Hausdorf距离可以通过计算共线法向点获得。通过解一个一元八次方程，求出两圆的共线法向点，然后对共线法向点进行分类比较，得到两圆之间的最近距离和Hausdorf距离。接着，给出了两圆环相交、分离和包含三种位置关系的充分必要条件，证明了两个圆环面间的位置关系不仅与其大圆的最近距离有关，还与其大圆的单向Hausdorf距离有关，进而解决了两圆环面之间的最近距离计算问题，所有的计算过程都可实时完成。和已有的算法相比，本文算法的优点在于能够正确判断出一圆环完全被另一圆环包含的情形，并计算出它们的最近距离。提出了一种两圆环面求交的算法。首先用隐式方程表示交线在一个圆环面参数空间的原像曲线，然后用特征点将原像曲线分割成多段单值函数曲线。接着对特征点进行拓扑分析，求得原像曲线的拓扑结构，最后用自适应的剖分方法求得满足给定精度要求的交线。和传统的跟踪法求交相比较，本文算法可以克服跟踪法的分支跳跃和小环遗漏的问题；生成的交线上的交点是解析法求得，精度高于跟踪法的数值迭代求精方法；传统的跟踪法只能用步长粗略控制交线的精度，而本文的自适应算法可以较准确地控制交线精度。提出了一种用圆环面片逼近法求点到曲面投影的算法。研究了用圆环面片在局部逼近曲面的方法，在此基础上设计了一个二阶几何迭代算法求点到曲面的投影，每次迭代时，在曲面上的投影初值点处构建一个与原曲面二阶密切的圆环面片，将测试点投影到该圆环面片上，以求得下一次迭代初值。该方法既适用于参数曲面，也适用于隐式曲面，稳定性和效率都优于现有方法。更多还原

【Abstract】 A torus is often used in the design of mechanical parts and the cutter heads ofnumerically controlled machine tools. It is needed to compute the intersection curvesor the minimum distance of a torus and a surface in CAD/CAM systems. This dis-sertation focuses on the computation of intersection and the minimum distance of twotori and point projection on surfaces based on torus patch approximation. The maincontributions are summarized as follows.A method for the collision detection and the minimum distance computation be-tween two tori is presented. This dissertation proves that the Hausdorf distance be-tween two circles in three-dimensional space can be obtained by computing theircollinear normal points, which can be calculated by solving an equation of degreeeight. With classification and comparison of the collinear normal points, the minimumdistance and the Hausdorf distance between these two circles are obtained. This dis-sertation gives the sufcient and necessary conditions of the three types of positionrelationship (i.e. inclusion, disjunction and intersection) between two tori and provesthat position relationship between two tori relates to not only the minimum distancebut also the two directed Hausdorf distances between their major circles. And then theminimum distance between two tori is calculated. The method can be carried out inreal time. Compared with existing methods, the method has the advantage that it canmake correct judgement in the case of that a torus completely includes another torusand compute the distance between them.An algorithm for torus/torus intersection is presented. The pre-image of the inter-section in the parametric space of one torus is represented by an implicit equation. Thepre-image is divided into one-valued function curve segments by characteristic points.The topological feature of these characteristic points is analyzed and the structure of thepre-image is obtained. Intersection curves satisfying required precision are generatedby a self-adaptive refinement method. Compared with the tracing method, the algo- rithm can overcome the drawbacks of straying and loop missing of the tracing method.Additionally, the points on the intersection curves obtained by the algorithm are com-puted by the analytic method, whose precision is higher than the points obtained byiteration when using the tracing method. The tracing method can only control theprecision roughly by estimating the advance step, while the algorithm can control theprecision accurately.An algorithm for point projection on surfaces is presented. This dissertation pro-poses a local surface approximation method with a torus patch. Based on it, a secondorder geometric iteration algorithm for point projection on surfaces is proposed. Ineach iteration, a second order osculating torus patch to the surface at the previous pro-jection is constructed. Then the test point is projected onto the torus patch to computethe next projection. The algorithm can apply to not only parametric surfaces but alsoimplicit surfaces, and its stability and efciency are better than the existing methods.更多还原