CAD／CAM系统中圆柱形零件几何参数公差的辅助确定

本文从机械精加工中常用的外圆磨削着手,寻求圆柱形零件的尺寸误差、圆度误差、表面粗糙度之间的内在联系。同时,考虑零件的功能要求,加工成本,加工方法,建立计算机辅助确定几何参数公差的数学模型,为CAD/CAM系统及其它机械设计中合理选择零件几何参数公差提供依据。     

统计圆度公差及其误差评定的研究

在分析几何圆度公差及其误差评定方法存在问题的基础上,指出现有圆度误差的各种测量评定方法都是基于几何公差的概念。提出应以统计圆度公差作为几何圆度公差的补充与发展。论述了统计圆度误差的意义及其测量评定方法。     

链槽类零件公差设计一致性的评价工具——软件量规

通过对漂移模型、虚拟边界要求及条件公差理论的剖析,在ＩＳＯ和国家标准的公差原则基础上,给出与标准相一致的,可用于键槽类零件公差一致性验证的软件量规数学等效式。它为基于约束的参数化ＣＡＤ系统中,计算机辅助公差设计的评价提供了理论依据,对于促进ＣＡＤ／ＣＡＭ集成,特别是并行工程的发展具有重要的科学意义和应用价值。     

浅谈如何提高机械加工的质量

1机械加工精度 机械加工精度是指零件加工后的实际几何参数（尺寸、形状和位置）与理想几何参数相符合的程度。它们之间的差异称为加工误差。加工误差的大小反映了加工精度的高低。误差越大加工精度越低,误差越小加工精度越高。加工精度包括三个方面内容：尺寸精度指加工后零件的实际尺寸与零件尺寸的公差带中心的相符合程度;形状精度指加工后的零件表面的实际几何形状与理想的几何形状的相符合程度;位置精度指加工后零件有关表面之间的实际位置与理想。在机械加工中总是存在一定的加工误差,误差都包括哪些方面以及怎样提高加工精度昵？     

基于特征的参数化CAD建模

介绍了一种基于特征的参数化ＣＡＤ建模方法，该方法根据ＣＡＰＰ／ＣＡＭ所需要的几何特征信息，工艺特征信息及制造特征信息建立特征库，通过参数化设计过程完成零件设计，并为后续ＣＡＰＰ／ＣＡＭ的信息提取建立基础。     

基于虚拟仪器的圆度仪的研究

在总结国内外圆度检测技术的发展及研究现状的基础上,提出了基于虚拟仪器采用CCD摄像方式来获取机械零件圆度检测信息的方法。对采集到的零件图片进行图像处理,得到零件的圆度特征信息,从而精确快速的检测出零件圆度误差和相关几何尺寸和形位公差,通过与标准件或设计要求的比较,判断出被测零件的圆度是否合格。实验表明本虚拟圆度仪,非接触测量,速度快,准确度高。     

确定圆周分布孔组位置度误差最小包容圆的新方法

孔组位置度误差值用最小包容圆的直径φf表示。根据圆周分布孔组位置度的特性,各孔的公差带可集中在任一孔的理想位置上,最小包容圆的圆心必须与公差圆的圆心重合,所以最小包容圆是指以孔的理想位置为中心,包容孔组中各孔的实际位置的最小圆。而孔组各孔的理想位置取决于孔组几何框图相对于基准的位置。几何框图相对于基准固定与否,直接影响到φf的取值问题。本文就确定圆周分布孔组位置度误差最小包容圆作些探讨。一、基准圆心如图1所示零件,6孔圆周均布,以φT孔为基准A。用极坐标法测量能得出被测要素的径向误差△R和角向弧长误差△S。如果测得的角向误差△θ为角度值时,可根据△S=△θ×0.0029×R求出△S。其中△θ角向误差     

参数化特征造型工具系统FMT

介绍了参数化特征造型工具系统ＦＭＴ，该系统具有特征造型、参数化设计、公差分析与综合、有限元建模等功能，初步实现了ＣＩＭＳ环境下的ＣＡＤ／ＣＡＭ集成。     

基于参数化特征建模的信息集成系统—FVCAD

本系统在自行开发的二维参数化绘图系统ＶＣＡＤ基础上，建立一个三维特征征库，在零件的二维设计过程中采取以零件的方位面为单元建立机械零件的特征模型，实现ＣＡＤ／ＣＡＰＰ／ＣＡＭ的信息集成。     

轮廓度误差的精密测量和评定

对具有复杂、不规则轮廓的零件进行精密测量和误差评定，是当前几何量计量领域中后个重要课题。本文针对在坐标测量机上进行轮廓测量提出了对曲线和曲面轮廓的数学描述方法、对曲线和曲面的等距平移以得到实测轮廓、以及引入矢量积运算对实际轮廓误差进行法向评定，从而实现了对零件复杂形面的精密测量和误差评定，对国家和国际标准中轮廓度公差标准的贯彻实施可起到推动作用，并最终达到提高产品质量的目的。     

在坐标测量机上检测复杂曲面形状误差的理论与方法研究

 介绍了在三坐标测量机上测量和评定面轮廓度误差的数学模型,和应用最优化方法用Ｔｕｒｂｏ  Ｃ语言编制的计算机程序,经校核验证,该算法符合形位公差国家标准的有关规定.     

精密工程中的“免形状测量模式”

为测量未知名义几何模型和参数的零件,提出了“免形状测量模式”．该测量模式通过高精度获取被测轮廓的“数据微粒”,建立典型几何要素及其内在不变量的理论模型,作为识别被测要素几何形状的准则;根据识别准则识别被测轮廓的名义几何形状;利用数据处理与误差分析软件,确定几何参数进而完成误差评定．论述了两个关键问题,即几何信息获取和几何形状识别．分析了几何信息获取的关键技术,阐述了对测量仪器的要求,介绍了结合内插和外插技术的自适应采样策略;提出了用于几何形状快速识别的6个算子;研制了测量仪器FormFree300,实现了“免形状测量”．     

Economic tolerance design for quality

This paper provides a few general mathematical models for determining product tolerances which minimize the combined manufacturing costs and quality loss. The models contain quality cost with a quadratic loss function and represent manufacturing costs with geometrical decay functions. The models are also formulated with multiple variables which represent the set of characteristics in a part. Applications of these models include minimizing the total cost with effective tolerance allocation in product design.     

Analysis of geometrical error in the stereolithography process using a stochastic approach

The geometrical error in the stereolithography process is analysed using a stochastic approach. This approach is based on a unified methodology, developed by the authors, for studying the mechanical error in different rapid prototyping processes. The tolerances and clearances have been assumed to be random variables. The coordinates of a point on the resin surface, traced by the laser beam, are expressed as a function of random variables. In a numerical example, the geometrical error has been found for a grid of points traced by the laser beam. The three-sigma error bands are plotted when tracing example curves. This is the band in which the laser beams of 99.73% of machines, produced on a mass scale, lie on the work surface for the given tolerances and clearances. Stringent values of tolerances and clearances reduce the error at the tool tip, but the cost of manufacturing and assembling the machines may become prohibitive.     

Tolerance transfer in sheet metal forming

A literature review of sheet metal forming errors as well as geometrical dimensions and tolerances (GD&T) shows that the theoretical means for the allocation of process tolerances with respect to GD&T are insufficient. In order to judge the influence of geometrical process errors (e.g., angular errors of bends), two typical sheet metal designs with parallelism and a position tolerance are studied. These case studies comprise a detailed analysis of tolerance chains including angular errors of bends and their positions. The resulting errors are compared with those resulting from length dimensional process errors and conclusions are drawn.     

A method for selecting dimensions,tolerances and precisions for alignment

A method is developed for selecting the dimensions and tolerances of mating parts and the precision of the process equipment with regard to the performance of the alignment phase of many processes, for example assembly. A formula is presented which expresses the performance as a function of the size ratio and tolerances of the objects being mated and the precision of the equipment. Non-dimensional tolerances and precisions provide a means to present graphically the underlying relationships in a useful yet general form. In situations where the equipment precision is given a priori, maximum allowable size ratio tables provide a method for determining the part dimensions and tolerances that will enable the equipment to mate the parts successfully. Assembly process application examples are given.     

Adaptive beam steering implemented in a ferroelectric liquid-crystal spatial-light-modulator free-space,fiber-optic switch

Active alignment of a 1 x 8 free-space optical switch was studied experimentally. Optical signals, carried on single-mode fibers, were switched by a ferroelectric liquid-crystal-on-silicon spatial light modulator. Continuous measurement of the in-coupled power to the fibers provided feedback for the switch control. The switch automatically located and locked to the output fibers. An advantage with adaptive switches of a similar kind is relaxed geometrical tolerances in the switch assembly. Further, such switches can adapt to possible geometrical changes and light wavelength drift during operation.