基于特征的几何公差实体模型的研究（一）：CAD／CAM中基于特征的几何…

本文对机械工程设计，制造与质量检测中的公并进行了深入的分析，提出了用几何公差愉的自由度来表示ＣＡＤ／ＣＡＭ中３Ｄ几何公差的方法。用该方法的表示的几何公差模型能合理地，有效地定义和解释当今的国家公差标准，它为在ＣＡＤ／ＣＡＭ中建立一个严密的，完善，基于特征的公左实体模型奠定了可靠的理论基础。     

基于特征的公差表示方法与实现

公差的存储表示是公差分析和公差综合的基础 ,提出一种几何公差的计算机辅助表示方法。利用特征的几何公差结构块 ,建立各种公差带的空间表示函数 ,并计算其三维空间中相应自由度的允许变动量。通过图论方法给出公差图的形式化定义 ,设计公差图的数据结构 ,可实现零件公差的计算机存储表示。最后给出零件实例来验证所提出的方法。     

基于特征的几何公差实体模型的研究(一)——CAD/CAM中基于特征的几何公差表示模型

本文对机械工程设计、制造与质量检测中的公差进行了深入的分析,提出了用几何公差结构块（ＧｅｏｍｅｔｒｉｃＴｏｌｅｒａｎｃｅＳｔｒｕｃｔｕｒｅＢｌｏｃｋｓ简称ＧＴＢＳ）的自由度来表示ＣＡＤ／ＣＡＭ中３Ｄ几何公差的方法。用该方法表示的几何公差模型能合理地、有效地定义和解释当今的国家公差标准,它为在ＣＡＤ／ＣＡＭ中建立一个严密的、完善的、基于特征的公差实体模型奠定了可靠的理论基础。     

一种基于数学定义的三维公差语义表示方法

目前三维CAD系统中的几何公差信息只是一种文本符号，缺乏工程语义，如何对其作出合理的解释对于CAD/CAM集成有着十分重要的意义，给出了基于语义的几何公差分类方法及基于自由度变动的基本几何要素数学表示方法，基于公差的数学定义，系统地推导了各种类型公差的三维语义表示方法，准确完整地表示出了其语义；最后给出实例进行应用分析。     

概念设计中的三维公差分析？

根据三维公差分析理论与产品设计和制造之间的公差分配矛盾,提出了在概念设计阶段进行公差设计的思想。应用矢量环公差数学理论在三维公差软件 CETOL 6σ中建模,并用二阶分析理论进行三维公差分析。通过工程实例表明三维公差分析在概念设计中的应用具有重要意义。     

《GB/T1182--2008》简介（续二）

新标准在引言中指出：“本标准提出了几何公差的基础概念和基本原理”。这里所说的基础概念和基本原理就是关于几何公差带的概念和原理。因此．要掌握有关几何公差的标准及其应用。必须深入学习并熟练掌握有关几何公差带的理论。     

基于SDT的三维公差域建模方法研究

以自由度和变动理论为基础,研究了基于SDT的平面特征公差数学模型表示方法。首先研究了三维公差域参数化表示方法,基于新一代产品几何规范标准体系(GPS),将几何偏差分为本质偏差和方位偏差,研究了三维公差域参数化建模方法,并基于运动自由度分析的SDT方法分析了三维公差域建模的一般步骤。最后以平面特征的公差建模为例,对不同类型的平面分别建立了数学模型。     

确定尺寸及位置公差的综合公差带

在机械制造过程中,判断零件是否合格,就是判断零件的各结构要素是否在制造公差范围内,即公差带的范围内。正确理解产品设计所提出的尺寸公差、位置公差所形成的综合公差带,是制定产品零件制造工艺方案和合理选择检验手段的重要条件。对于独立的尺寸公差带或位置公差带不难于理解。但对于尺寸公差和位置公差的综合公差带就容易造成误解。     

浅议形位公差的公差带概念

1　形位公差带概念的形成公差带是公差类标准中常用的概念之一 ,在形位公差标准产生以前 ,公差带还仅用于尺寸公差方面。由于尺寸公差或偏差的数值大小与基本尺寸的数值大小相比 ,相差太大 ,不便用同一个比例画出来表示。但为了清楚说明孔和轴的配合关系 ,就采用一种抽象化的图解方法 ,以便表达尺寸公差、偏差及配合之间的关系 ,图中的上下两条直线之间的区域便是尺寸公差带。因此 ,尺寸公差带实际上是一种用来分析零件制造过程中误差变动情况的图形 ,用它来表明零件极限尺寸的变动范围和孔轴之间的配合关系 ,非常形象直观。形位公差标准把…     

基于几何公差描述逻辑的公差类型的自动生成

为了使公差信息更好地被计算机理解,将描述逻辑引入到对公差设计的研究中.从几何要素之间的基本空间关系出发,提出几何公差描述逻辑GTDL(Df),并给出该逻辑的Tableau判定算法.应用GTDL(Df)的刻画能力,构建几何公差的GTDL(Df)表示模型;在此基础上,借助GTDL(Df)的Tableau判定算法,设计公差类型的自动生成算法.通过工程实例验证了生成算法的有效性.     

尺寸公差与形位公差混合优化分配

为解决尺寸公差与形位公差混合优化分配问题,提出了一种公差优化分配方法.根据成本-公差函数和尺寸公差与形位公差的关系,建立了以最小制造总成本为目标的非线性公差混合优化分配模型.该模型的约束包括装配尺寸链的功能要求和加工能力.求解该模型能同时得到优化的尺寸公差和形位公差.最后,分别用公差混合优化分配法和传统方法对一个实例进行公差分配,结果表明所提方法比传统方法更优越.     

Composite Planar Tolerance Allocation with Dimensional and Geometric Specifications

A new optimal approach for planar tolerance allocation is proposed in which dimensional and orientation geometric specifications are included. To deal with the increased complexity of planar tolerance analysis, a special relevance graph (SRG) is used to represent the relationships between manufactured elements and their size and tolerance information. In addition, the SRG is also applied for the geometric dimensions and tolerances. Using a suitable algorithm, planar tolerance chains that include geometric specifications can be generated automatically during process planning. Through a graph based analysis, stacks of tolerance zones are obtained. The resultant tolerance zone contains all of the composite links of the tolerance zones. The links are assigned according to the process capacities, which can be considered as constraints. A linear optimal model is established to solve the tolerance allocation problem. A practical example is used to demonstrate the feasibility and effectiveness of the proposed method.     

基于工序加工能力的并行公差优化设计

提出一种基于工序加工能力的并行工序公差优化设计方法。在产品的初步结构设计阶段，通过相配零件的加工工艺规划把装配功能公差表示为零件的工序公差，建立以加权制造总成本最小为目标，以并行公差链、标准化的工序公差系数、机床最大经济极限公差为约束的非线性并行公差优化设计模型，求解该模型得到最佳的工序公差。最后给出了并行公差优化设计的一个工程实例，结果表明，所提的方法具有比传统串行等精度方法更合理、工序公差数值更大的优点。     

尺寸链中形位公差的判别与解算

从零件形位公差要素所采用的公差原则入手,讨论了在尺寸链计算中,是否应该考虑形位公差的影响以及形位公差组成环性质的判别方法,并通过实例加以说明。     

棱柱公差一致性验证技术的研究

分别按照国际中的包容要求、最大实体要求及最小实体要求 ,分析了棱柱形零件尺寸公差和形位公差一致性准则 ,给出了判别一致性的数学等效式 ,举例说明了棱柱公差一致性验证的过程 ,为棱柱形零件计算机辅助公差设计的一致性验证提供了理论方法。     

Dimensional and geometrical tolerance balancing in concurrent design

In conventional design, tolerancing is divided into two separated sequential stages, i.e., product tolerancing and process tolerancing. In product tolerancing stage, the assembly functional tolerances are allocated to BP component tolerances. In the process tolerancing stage, the obtained BP tolerances are further allocated to the process tolerances in terms of the given process planning. As a result, tolerance design often results in conflict and redesign. An optimal design methodology for both dimensional and geometrical tolerances (DGTs) is presented and validated in a concurrent design environment. We directly allocate the required functional assembly DGTs to the pertinent process DGTs by using the given process planning of the related components. Geometrical tolerances are treated as the equivalent bilateral dimensional tolerances or the additional tolerance constraints according to their functional roles and engineering semantics in manufacturing. When the process sequences of the related components have been determined in the assembly structure design stage, we formulate the concurrent tolerance chains to express the relations between the assembly DGTs and the related component process DGTs by using the integrated tolerance charts. Concurrent tolerancing which simultaneously optimizes the process tolerance based on the constraints of concurrent DGTs and the process accuracy is implemented by a linear programming approach. In the optimization model the objective is to maximize the total weight process DGTs while weight factor is used to evaluate the different manufacturing costs between different means of manufacturing operations corresponding to the same tolerance value. Economical tolerance bounds of related operations are given as constraints. Finally, an example is included to demonstrate the proposed methodology.     

Tolerance analysis of mechanical assemblies based on modal interval and small degrees of freedom (MI-SDOF) concepts

Tolerance analysis is a key analytical tool for estimation of accumulating effects of the individual part tolerances on the design specifications of a mechanical assembly. This paper presents a new feature-based approach to tolerance analysis for mechanical assemblies with geometrical and dimensional tolerances. In this approach, geometrical and dimensional tolerances are expressed by small degrees of freedom (SDOF) of geometric entities (faces, feature axes, edges, and features of size) that are described by tolerance zones. The uncertainty of dimensions and geometrical form of features due to tolerances is mathematically described using modal interval arithmetic. The two concepts of modal interval analysis and SDOF are combined to describe the tolerance specifications. The algorithm is presented which explains the steps and the procedure of tolerance analysis. The proposed method is compatible with the current GD&T standards and can incorporate GD&T concepts such as various material modifiers (maximum material condition, least material condition, and regardless of feature size), envelope requirement, and bonus tolerances. This method can take into account multidimensional effects due to geometrical tolerances in tolerance analysis. The application of the proposed method is illustrated through presenting an example problem and comparing results with tolerance charting method.     

Fuzzy-small degrees of freedom representation of linear and angular variations in mechanical assemblies for tolerance analysis and allocation

Tolerances naturally generate an uncertain environment for design and manufacturing. In this paper, a novel fuzzy based tolerance representation approach for modeling the variations of geometric features due to dimensional tolerances is presented. The two concepts of fuzzy theory and small degrees of freedom are combined to introduce the fuzzy-small degrees of freedom model (F-SDOF). This model is suitable for tolerance analysis of mechanical assemblies with linear and angular tolerances. Based on the fuzzy concept, a new index (called the assemblability index) is introduced which signifies the fitting quality of parts in the assembly. Graphical and numerical representations of tolerance allocation by this method are presented. The goal of tolerance allocation is to adjust the tolerances assigned at the design stage so as to meet a functional requirement at the assembly stage. The presented method is compatible with the current dimensioning and tolerancing standards. The application of the proposed methodology is illustrated through presenting an example problem.