自由曲面特征造型及其有效性维护的研究

对HUST-CAID（哈尔滨理工大学计算机辅助工业造型设计）系统研究的基础之上,引入自由曲面特征,运用自由曲面特征定义点构建几何形状轮廓曲线,实现特征参数化。其次,根据特征的分类和参数化,结合HUST-CAID系统的自身特点,完成特征类的定义,并在所构建的几何形状轮廓曲线的基础之上,使用扫掠法和蒙皮法技术构造出几何形状原型和最终的特征实例形状。最后,建立了一套自由曲面特征有效性维护机制。     

自由特征模型约束求解研究*

在对自由特征模型参数化基础上,提出一种约束求解的新方法。该方法对自由特征形体定义点进行参数化,建立几何约束图,将约束问题分解为三角形约束和四面体约束两大类,分别进行求解,定义手向性规则,利用该规则将子问题组合为全局解。在自主开发的HUST-CAIDS（哈尔滨理工大学计算机辅助工业设计系统）中实现了本算法,并得到满足设计者需求的模型。     

密集标志点集的拓扑保持变换方法*

在对自由特征模型参数化基础上,提出一种约束求解的新方法。该方法对自由特征形体定义点进行参数化,建立几何约束图,将约束问题分解为三角形约束和四面体约束两大类,分别进行求解,定义手向性规则,利用该规则将子问题组合为全局解。在自主开发的HUST-CAIDS（哈尔滨理工大学计算机辅助工业设计系统）中实现了本算法,并得到满足设计者需求的模型。     

层次参数化的自由曲面特征表示与实现

为了解决自由曲面特征参数化问题,提出一种自由曲面特征参数分层实现框架.采用从高层到底层、从整体到局部的分层思想,将自由曲面特征的参数及映射关系划分为"3层参数和2级映射"结构来定义曲面特征,即高层语义参数表示整体形状,中间层参数表示特征线和底层参数表示细节形状,并在各层参数间建立映射和约束关系;同时支持设计者用Scheme命令快速实例化曲面特征.该方法避免了传统方式中由高层特征参数到底层数据间直接的复杂映射关系,且方便了曲面特征的实例化.实验结果表明,文中方法使得设计者能够从特征语义层直观地编辑修改自由曲面特征,是一种有效的自由曲面特征参数化表示和实现方法.     

附加自由曲面构造框架及其有效性维护的研究*

在对HUST-CAID(哈尔滨理工大学计算机辅助工业造型设计)系统进行研究的基础上,首先引入了自由曲面特征,然后结合HUST-CAID系统定义了自由曲面特征的分类和参数化,应用这种分类和参数化的方法创建了一个自由曲面特征,提出了一种基于FFDP配置的附加自由曲面特征的构造框架。此框架可以使自由曲面整体模型的构造完全参数化。最后建立了基于这个框架构造的自由曲面附加特征的有效性维护机制,从而达到对自由曲面附加特征进行有效性维护的目的。     

点云的形状与曲线重建算法

针对平面无序带噪点云的曲线重建问题,给出了点云形状的定义并提出了构造点云形状的算法.该算法基于Delaunay三角剖分,在构造好点云的Delaunay三角剖分后对三角剖分进行细化,使得在点云中的点周围形成空间上的局部均匀采样;基于集合论中的基本概念定义点云中内点、外点和边界点,并且明确地定义了点云的形状,根据Delaunay三角剖分细化时,选择不同的参数得到不同层次的点云的形状;选择合适的参数得到相应形状后,通过薄化过程得到具有流形结构的曲线.实验结果表明,采用文中算法得到的重建曲线很好地反映了点云的形状,验证了该算法的有效性.     

基于曲率流的点模型编辑方法*

为了对点模型表面进行保细节的自由形状编辑,提出了一种基于曲率流的点模型形状编辑方法。该方法定义了基于平均曲率流的光顺算子,通过此光顺算子获得点模型不同光滑程度的曲面表示。运用对应曲面上点之间的向量差进行相应几何细节的抽取,在相邻的曲面表示之间将几何细节剥离出来。用户可以在不同的曲面上进行自由形状编辑,而无须关心几何细节。在变形后的曲面上再将相应的几何细节映射回去,实现对模型保细节的变形。实验结果表明该方法是一种有效的点模型造型算法,在变形的同时,有效地保持了模型表面的细节特征。     

基于曲率流的点模型编辑方法*

为了对点模型表面进行保细节的自由形状编辑,提出了一种基于曲率流的点模型形状编辑方法。该方法定义了基于平均曲率流的光顺算子,通过此光顺算子获得点模型不同光滑程度的曲面表示。运用对应曲面上点之间的向量差进行相应几何细节的抽取,在相邻的曲面表示之间将几何细节剥离出来。用户可以在不同的曲面上进行自由形状编辑,而无须关心几何细节。在变形后的曲面上再将相应的几何细节映射回去,实现对模型保细节的变形。实验结果表明该方法是一种有效的点模型造型算法,在变形的同时,有效地保持了模型表面的细节特征。     

自由曲面特征的定义与识别技术的研究

结合自主开发的HUST-CAID（哈尔滨理工大学计算机辅助工业造型设计）系统的特点,引入自由曲面特征,给出了自由曲面特征的参数化定义,并在此基础上对自由曲面特征识别进行研究,先是给出自由曲面特征识别的定义,接着提出了基于曲线的特征识别的算法。该方法将基于曲线的特征以二维参数的形式给出定义,使其能在二维平面上研究,通过重构特征的剖面模板库,从而利用目标特征与模板特征匹配实现了特征识别。     

基于机器视觉的形状尺寸检测方法研究

基于机器视觉技术的产品自动检测、分类和测量系统,由于非接触性和快速、精度高等优点在实际生产中得到广泛关注.论文研究并建立了目标体几何形状和尺寸检测机器视觉系统.原始图像经过预处理、获取图像轮廓特征后,采用一个基于不变矩、相对矩和提取角点特征的新方法自动识别目标体的形状.根据工业应用实际情况,线性模型标定获取摄像机内外参数,计算目标体形状特征的真实尺寸.实验证明该方法计算复杂度相对于带佣的Hough变换大大降低,适合实时处理,实验结果较为理想.     

Numeric and curve parameters for freeform surface feature models

The success of feature modelling systems depends to a large extent on offering user-friendly ways for specifying and varying feature models. In this paper, several new facilities are introduced for this.Numeric and curve parameters are presented for specification and variation of freeform surface feature models. Several properties of the parameters can be defined, such as the direction of evaluation for a curve parameter. In addition to parameters present in features, other parameters can be added to a feature model, including intersection curves between features.To provide these facilities, a new three-level structure is introduced, which includes a partially evaluated model that can capture new generic model entities, including feature intersection curves. The work has been implemented in a prototype surface feature modelling system with functionality for feature class definition, feature model creation, and advanced feature model variation through the new types of parameters.     

Local parameterization of freeform shapes using freeform feature recognition

Form feature modeling is a much used shape modeling technique that offers high-level control over a shape. When a feature-based interpretation of shape data is not available, e.g. when a shape is obtained by a laser range scanner or from a database of shapes, then the features must be reconstructed through feature recognition. Many methods for the recognition of machining features exist, but these methods cannot be used for freeform feature recognition, of which the complexity is much larger. In this paper, a new freeform feature recognition method is presented that is based on a new definition of the freeform feature concept. The method uses a three-step approach to feature recognition, in which first the global shape of a feature is matched to the target shape model. In a second step, this global shape is locally adapted to the target shape by adapting the definition of the feature. Finally, if the desired configuration of the feature has been determined, it can be used to reconstruct the target’s shape. In the first two steps, an evolutionary approach is taken to maximizing the similarity between the feature and the target shape. Finally, the target shape is reconstructed to incorporate the recognized feature. An extensive application example is given and the method is validated by applying it to a large number of artificially created test cases.     

Creation of user-defined freeform feature from surface models based on characteristic curves

This paper proposes a novel method for the creation of user-defined freeform feature (UDFFF) from existing surface model. The developed methodology has four major steps: selecting the region of interest (ROI), obtaining the characteristic curves from the surface model, reconstructing the ROI surface, and parameterizing the UDFFF. To quickly create UDFFF on the ROI, the representation of freeform feature based on characteristic curves is proposed. First, the characteristic curves of ROI are obtained automatically or by a small amount of human–computer interaction. In particular, user can directly and easily draw the curves on surface to satisfy the designer's requirements. Second, from the set of characteristic curves that is obtained, freeform surface is reconstructed by a suitable surface generation method, e.g., sweeping, revolving, skinning, and filling. Finally, parameterization of the freeform feature is configured, which primarily involves establishing parameters and building the mappings between feature parameters and shape data. Moreover, according to the degrees of freedom, two types of parameterization of freeform features may be described: one (low degrees of freedom) can be accurately described by the characteristic curves and the other (high degrees of freedom) can be approximated with these curves. The proposed UDFFF creation method has been tested with examples based on the surface models. Experience with our prototype system indicates that it allows untrained users to create UDFFFs from the surface models.     

流线型结构特征造型方法及其在高速列车设计中的应用

提出了一种基于自由曲面的流线型结构特征造型方法,并将其应用于200km／h电动车组“先锋号”的流线型结构设计之中,流线型结构特征所描述的实体模型对自由曲面外形的变化具有自适应性,该方法便于流线型结构数据存取和修改,可在自由曲面外形和流线型结构各种参数多次修改的情况下自动生成流线型结构实体;大幅度地减少了人机交互时间,解决了高速列车流线型结构实体造型过程中设计周期过长的问题。     

混合加工特征识别方法

介绍一种集成了自动特征识别和用户交互特征定义的混合特征识别方法，该方法采用基于广义痕迹的特征识别建立零件的加工特征模型，通过交互特征定义对已建立的加工特征模型进行局部修改和再解释，在交互特征定义中，用户只需通过选取要修改的特征面定义自己的特征，剩余的面则调用自动特征识别算法处理，特征参数由系统提供的统一算法计算，从而减少了交互的工作量，这种混合特征识别方法有助于提高加工特征识别系统的实用性和健壮性。     

基于特征参数模型的对话框生成

本文介绍特征参数模型中的语义规定，使特征参数按预先设定受表达式、表格约束。系统可根据特征参数模型自动生成对话框，通过参数的调整可自动改变对话框显示外观。