【作者】 刘琦；

【导师】 杨将新； 吴昭同；

【作者基本信息】 浙江大学 ， 机械制造及其自动化， 2002， 硕士

【摘要】 本文结合国家自然科学基金项目“综合公差计算机辅助设计系统研究”(59705022)，研究了基于MDT的装配尺寸链自动生成与公差分析技术，开发了计算机辅助公差分析系统的原型系统。论文的主要研究内容如下： 第一章：本章在分析尺寸链自动生成技术、计算机辅助公差分析与设计系统的研究现状的基础上，提出了本论文研究的主要内容和结构安排。 第二章：研究了MDT的约束机制，分析了MDT支持的三种约束：尺寸约束、几何约束和装配约束的特点。结合ISO／TC213的特征类型研究了各实际特征和拟合派生特征，从而将变动几何约束分为自参考、互参考和配合变动几何约束三类。 第三章：在研究机械装配关系信息要求基础上，分析了几种常用的装配信息模型；引入了对象的概念，采用了自上而下的装配数据库方式，结合公差系统的特点对装配信息模型加以改进，提出了面向尺寸链的装配数据库这一概念，并软件实现之，最后给出了该数据库中的零件类、装配类和约束链类的定义。 第四章：提出了基于装配图约束关系的尺寸链自动生成原理。其原理为在装配图上指定封闭环后，系统在该装配图中提取该次装配的装配约束，并自动查找与该封闭环属于同一装配尺寸链的各零件，获得它们的相关尺寸信息，从而进一步自动生成尺寸链。装配尺寸链的自动生成是后续公差分析和公差综合的基础。 第五章：研究了尺寸链组成环和封闭环的尺寸分布模型，提出依据不同装配特点可将封闭环尺寸模型分为正态分布和β分布两种，最后应用β分布模型进行了尺寸公差分析研究。 第六章：开发了基于MDT的三维公差分析系统的原型系统。 第七章：对全文进行总结；对计算机辅助公差分析系统需进一步开展的工作进行了探讨和展望。更多还原

【Abstract】 Based on the "Study on Computer Aided Tolerancing System" (National Nature Science Fund Project, No: 59705022), the technology of the automatic generation of assembly dimension chain and tolerance analysis based on MDT is presented. The prototype system for computer aided tolerance analysis is developed and proved by examples.In the first chapter, State-of-the-arts of computer aided tolerancing (CAT) system at home and abroad are summarized. The technology of the automatic generation of assembly dimension chain is also analyzed. Main contents and general structure scheme of this dissertation are present.In the second chapter, the constraints mechanism of MDT is studied. Dimension constraints, geometric constraints and assembly constraints of MDT are analyzed. Combined with new feature type defined by ISO/TC 213 and based on the feature of spacial movement-pair, seven features are analyzed. Variational geometric constraints (VGC) are classified as self-referenced VGC, cross-referenced VGC and mating VGC. Seven kinds of self-referenced VGC, and six kinds lower-pair mating VGC are classified.In the third chapter, the relationship of mechanical assembly and information request is studied. Several common assembly information models are analyzed. The concept and feature of object are imported. Top-down assembly database way is adopted and the assembly information model is improved with the concern of the character of the CAT. The concept of assembly database faced to dimension chain is put forward and realized. At last, the definition of the part class, assembly class and constraint class of the assemble database are given.In the fourth chapter, the automatic generation theory of the dimension chain based on assemble drawing is put forward. First, the closing loop is specified in the assembly drawing by the user. Then system can get the assembly constraints from the drawing and find all the parts joined in this assemble relation. The parts’ related dimension information is also obtained. The dimension chain is generated later.In the fifth chapter, the dimension distributing models of the buildup loop and closing loop are studied. Putting forward that closing loop can be divided into normal distribution model and beta distribution model. At the end, tolerance analysis is studied based on the beta distribution model.In the sixth chapter, the prototype system for three-dimensional tolerance design based on MDT is studied.In the seventh chapter, all of the work in this dissertation is summed up. The future research of computer-aided tolerancing is prospected.更多还原