基于约束的装配体位置描述及求解

装配体设计是计算机辅助设计(CAD)的一个重要组成部分,本文就装配体设计中装 配体位置的描述及自动求解这两个关键问题进行了深入的探讨,提出了基于约束的装配体 相互位置关系的描述方法及自动求解算法.同时本文首次引入奇异矩阵的方法,较好地解决 了装配体位置的约束冗余、约束不足以及病态矩阵的问题.     

一种基于配合约束的装配顺序产生算法

结合配合约束在装配中的应用,在分析装配零件的配合约束及其特点的基础上,得到零件之间的空间位置关系和零件的局部自由度,充分利用这些信息,引入优先装配方向和局部自由度表的概念,提出了一种基于最少装配方向的装配顺序自动生成算法。     

基于自由度分析的三维几何约束推理求解

三维几何约束求解对于装配设计、装配工艺规划和并行工程等多个领域的研究具有重要意义。以自由度分析为基础，对冗余约束和约束冲突的情况进行判断。采用几何推理的方法，直接从零件上的点、线、面、圆柱面、球面等基本几何元素出发，对这些基本几何元素之间的位置关系进行分析，求解三维几何约束。避免了数值解法中对初始值的依赖和迭代过程的不稳定，提高了三维几何约束求解的速度和稳定性。     

基于装配约束动态管理的虚拟拆卸

装配约束是虚拟拆卸环境下必须考虑的装配体的重要信息，提出虚拟拆卸过程中装配约束的动态管理机制，并实现了基于装配约束导航的虚拟拆卸。装配约束的动态管理包括虚拟环境下装配约束的获取、表达以及拆卸过程中装配约束的动态维护，即装配约束的动态解除和产生，文中用装配约束图表达零件间的装配约束，提出装配约束的间接解除方法，并实现了基于装配约束推理的零件可拆卸方向的推导。最后，通过一个简单装配体的拆卸实例，对文中方法进行了验证。     

装配零件位置关系求解新方法

本文研究装配零件之间内在的几何连接关系，提出一种求解相对位置关系新方法。该方法不用求解方程组，引入虚实体概念，通过动态的虚实体逐步把相对位置关系求解出来，极大地提高了求解速度，降低了装配求解的复杂性．为实现装配ＣＡＤ提供了一种简捷的方法。     

雅克比矩阵近似更新的三维装配约束求解研究

提出了三维装配约束求解中雅克比矩阵近似更新的方法。该方法通过对 迭代过程中满秩以及行秩秩亏雅克比矩阵进行近似更新,提高了约束求解的效率。首先在非 线性迭代求解过程中添加雅克比矩阵及其逆矩阵近似更新的公式;然后给出使用近似更新公 式需要满足的限制条件;最后通过对奇异点扰动算法的描述介绍迭代求解过程中雅克比矩阵 发生行秩秩亏的处理办法。文中提出的策略与算法已在三维装配约束求解引擎CBABench 中实现,给出的实例表明本文提出的方法效果显著。     

用户关注度相关的装配模型动态可视化

为了方便地展示复杂模型各零件之间的三维结构,并清楚地揭示出它们之间的层次装配约束关系,提出一个面向用户交互的装配模型浏览系统.通过构造层次有向拆卸图来保存各零件的拆卸顺序,并采用递归法创建其干涉矩阵和拆卸有向图;装配约束图中的各顶点均用相应零件的图像来表示,以便于用户直观地选择所关注零件.由于采用了focus+context的方式来生成装配约束图,用户所关注零件的局部邻域被自动调整到视图的中心,并且放大显示.另外还提出了一种基于用户关注度的零件颜色自动选取算法,通过鲜明的颜色对比进一步突出用户所关注的装配关系.实验结果证明,该系统有效地提高了用户交互以及装配效率.     

基于约束的装配体技术

本文首先给出了装配体的数学模型与表示模型。系统采用二叉树来表示一个装配体，接着提出了基于约束表示的装配体位置关系的描述方法，约束通过转化以方程的形式求解，并对Ｎｅｗｔｏｎ迭代法提出了改进算法。     

基于装配自由度分析解决欠约束问题

装配是机械制造过程中的一个重要环节,在装配过程中,经常会遇到欠 约束问题。在复杂装配环境下,某个装配零件的欠约束会对其他零件的装配产生意想不到的 结果。装配时,约束条件和零件自由度之间存在一种内在联系,通过建立基体和目标零件的 自由度空间坐标系,对约束条件和自由度关系分析,得到约束条件和自由度关系的逻辑值, 通过逻辑值判断剩余自由度的个数和类型,从而为快速解决欠约束问题提供了一种途径。     

VRML环境下基于语义的产品装配设计技术研究

装配语义是零件间装配约束的抽象与概括，研究基于语义的产品装配设计可有效地提高装配设计的直观性与装配效率。文中给出了基于语义的产品装配设计系统的总体框架结构，将装配语义分为常用语义与特殊语义，并建立了装配语义的层次表达；通过装配语义与几何约束的映射，形成几何约束的代数表达；借助零部件间的运动自由度的求解，实现了装配语义的驱动，有助于将装配设计从几何层发展到语义层进行操作。     

Two robot arms in assembly by using impulsive information

When two robot arms execute coordinated motions in assembly, collision between the two end-effectors cannot be avoided. The collision effects on the two coordinating robots include two aspects: abrupt velocity changes of the robot joints and impulsive forces exerting on the contact point as well as on robot joints. Since the direction of the impulsive force exerting on the contact point is related to the relative position and orientation of the two mating parts, the impulsive force can be used to detect the alignment errors of the two end-effectors. Thus a new assembly method is proposed in this article. The new method uses impulsive information to adjust the position and orientation errors of the two robot arms in assembly, rather than employing a compliance mechanism. The advantage of the new method is that the jamming problem, which is usually associated with compliance methods, never takes place. To make the method practically useful, wrist force sensors are suggested to installed at the wrist of each robot. Dynamic relations between the sensed information and the impulsive force at the contact point are then established. The sensed information thus becomes useful in analyzing the alignment situation. Finally, practical cases are studied to illustrate the use of the new assembly method.     

Adaptive robotic assembly of compliant aero-structure components

The application of robotics to the assembly of large aero-structures has been limited by the large size and inherent compliance of the components involved. The compliance of the components is significant and simple ‘pick and place’ approaches cannot be used due to the inherent dimensional variability between mating parts. The research described in this paper aims to solve this problem by using a non-contact sensing system to measure part deformation and misalignment in real time. The acquired data can then be processed through a mathematical algorithm to calculate the relative component positions required for optimal assembly. The data can also be used to check gross distortion of components and to reject those outside the specification limits. Existing part-to-part holes were used to provide alignment for individual components within the structure. A series of experiments were performed to investigate the feasibility of the method. Results are presented along with a discussion of the problems that may be encountered during robotic assembly. The experimental results show that robots when combined with non-contact metrology can be used for the assembly of compliant aero-structure components within required tolerance limits.     

装配配合约束自动获取技术研究

装配配合约束获取对于装配设计、装配工艺规划等多个领域的研究具有重要意义;现有的装配配合约束获取方法容易产生约束的遗漏和约束无效性;通过对自动获取配合约束技术进行研究,在充分利用CAD模型几何拓扑信息的基础上。提出了几何约束识别和配合验证相结合的装配配合约束自动获取箅法;实践证明,该方法可以显著地提高约束信息的获取效率、正确性和有效性。     

CAD mesh model simplification with assembly features preservation

This paper aims to investigate a CAD mesh model simplification method with assembly features preservation, in order to satisfy the requirement of assembly field for the information of 3D model. The proposed method simplifies a CAD mesh model as follows. Firstly, the notion of ＂conjugation＂ is incorporated into the definition of assembly features, with the purpose of benefitting the downstream applications such as assembly features recognition and preservation. Subsequently, the attributed adjacency graphs （AAGs） of the region- level-represented parts are established. The assembly features are automatically recognized by searching for conjugated subgraphs of every two AAGs based on subgraph isomorphism algorithm. In order to improve the efficiency of assembly features recognition, the characteristics of conjugated subgraphs are adopted to initialize the mapping matrix, and the ＂verifying while matching strategy＂ is used to verify the validity of every two newly founded vertices which are correspondingly matched. Then, simplified CAD mesh model with assembly features preserved is constructed after suppressing the common form features. The method is applied successfully to simplify the CAD mesh model with assembly features well preserved. Moreover, the tradeoff between the cost of time for conjugated subgraphs matching and the complexity of the to-be-matched parts is proven to be almost linear.     

基于模板的自顶向下并行装配设计

在分析产品设计系统的装配功能的基础上,提出了一个并行装配设计模式及装配模板与模板实例化的概念;在处理装配约束的虚拟表示与实例表示概念,使得系统具有了支持自顶向下和自底向上２种设计方法的能力。该方法已被成功地应用于参数化特征造型系统ＺＤ－ＭＣＡＤＩＩ中,证明了基于装配模板基础上的装配设计方法法能在零件设计级上有效地支持并行设计。     

Generating assembly features onto split solid models

A large model can be split into smaller components where by assembly features can be created and attached onto the components so that they can be reassembled to form the original model. The assembly features may function as positioning or interlocking purposes depending on the mating requirement. This paper describes a method for creating assembly features onto the solid components automatically. The main idea of the method is to construct spatial rectangular assembly cells inside the original model. This is done by ray tracing the tool surface that is used to split the model, provided that there is no undercut on the split surface along the assembly direction. The spatial cells represent solid regions in which assembly features can be attached. Different kinds of assembly features can be mapped to the spatial cells, which are then attached to the split components. The split surface can be planar, quadrics or higher order freeform surfaces, thus allowing a high degree of flexibility in creating the assembly feature shapes.     

Graph-based extraction of two-connected morphological features from boundary representations

In this paper a feature extraction technique to isolate two-connected features from a boundary model is discussed. The technique involves identification of faces with multiple edge loops and faces sharing multiple edges as candidates for entrance faces of such features. It is observed that the two-connected features constitute tri connected components in the edge-face graphs of the boundary models. Heuristics are used to enhance an algorithm to decompose the edge-face graph of a boundary representation into its triconnected components. Pros and cons of this method are compared with the classic graph theoretic algorithm used to obtain triconnected components from a graph.