凸轮评定公差标准及评定方法

建立了几何公差国家标准之后,一般仍用尺寸公差或者用线轮廓度公差评定凸轮。用径向圆跳动公差评定凸轮的方法优于前两者,径向圆跳动公差更适合于凸轮的评定。进行径向圆跳动动公差评定时,凸轮的误差(测量)值和公差(评定)值都要是径向值,便于测量、处理、评定,方法简便、直观。     

用跳动公差评定凸轮方法的探讨

在建立了形位公差标准之后,一般用线(面)轮廓度或者尺寸公差评定凸轮.笔者认为用跳动公差评定的方法优于前两者,跳动公差更适合凸轮测量数据的评定.径向跳动公差评定时,凸轮的误差(测量)值和公差(评定)值都是径向值,便于测量、评定,方法简便、直观.     

推荐采用径向圆跳动公差 控制凸轮的升程误差

在建立了形位公差标准之后,凸轮的评定究竟庆采用什么公差标准,在认识上并不一致,有的认为,即使在建立了形位公差概念之后,亦应采用尺寸公差,有的认为应用用轮廓公差,笔者认为应采用跳动公差概念控制方法,并希望该论点能引起共鸣。     

Matlab在形位公差评定中的应用

本文介绍了Matlab在形位公差评定中的几例应用     

统计公差与表面粗糙度的统计评定

系统分析了现行几何公差标准及其体系的缺点,提出统计公差的特征及其合理性,明确提出了“统计公差即统计参数的公差”,指出“统计公差是几何公差的发展方向”,并以表现粗糙度统计评定的发展说明统计公差的优越性。     

配气凸轮升程与相互角的统筹评定

统筹评定是把内燃机凸轮升程与夹角两者兼顾评定的意思。即在按常规分别对其评定时,若某项略有超差,而另一项不仅合格,而且还有调整余地时,则应将两者兼顾,进行统筹评定。笔者认为:其评定原则是先窄后宽(即先升程后相互角),估算统筹效果。若统筹可改变原不合格状态,则再进行具体统筹,并尽可能使升程与夹角均留有适当的余地。例:一次常规测量EQ140进气凸轮,得升程误差数据如表1。此时键槽与桃尖夹角情     

弧面分度凸轮轮廓的精密测量与误差评定

本文论述了采用三坐标测量机利用其扫描功能以径向、旋向两各方式实现地凸轮轮廓面数据的采集来检测凸轮廓面的方法，并运用ＥＢ样条建立了轮廓的误差评定理论。     

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。     

我国国家标准采用国际国外标准的合规情况分析

根据截至2013年底的国标明细库调查研究发现,我国的国家标准在采用国际国外标准的过程中,存在合规风险。本文指出我国国家标准采用国际国外标准可能面临的合规问题,并针对各个问题给出了政策建议。     

对三例GB标准中未于定义的形位公差的探讨

在引进Ｇ公司的产品图样中 ,碰到三个ＧＢ标准未于定义的形位公差代号。撰文阐述个人的理解。实例一 :螺孔的 ○Ｐ ○Ｍ 公差图 1为一简化了的机油泵体。图 1图中 4×Ｍ6螺孔对平面Ｆ位置度代号框格内公差值的后面标注了符号 ○Ｍ 。ＧＢ中 ○Ｍ 的意思是要求被测要素实际轮廓不越出形位公差的最大实体实效边界。螺孔是复杂曲面 ,其形状 (中径、螺距、半角 )误差由螺纹公差控制。对螺孔而言 ,小于塞规通端的“最大实体实效边界”也毫无意义。鉴于此 ,图1位置度代号框格下方标注了符号 ○Ｐ ,表示被测要素不是螺孔本身 ,而是它的指定延伸部分…     

中央空调噪声超标原因浅析

针对中央空调由于设计安装和强制性规范的实施、管理审查、监督检验等问题而引起的噪声提出意见和建议。     

Simplified design and evaluation of cam surfaces

A method is presented to determine the location and magnitude of cam profile errors. The impact of this method centers around the simplification of the design and evaluation of cam surfaces. The proposed technique can evaluate errors in newly machined or worn cams. Inputs are cam rotational speed and a set of theoretical data points, which lists cam radial displacement and acceleration versus angular position. A recursion formula for the cam profile errors is derived using a finite-difference scheme. Application of the method is discussed. A. H. Soni. Professor of Mechanical & Aerospace Engineering,David L. Smith, Research Associate at the Oklahoma State University, Still-water, Oklahoma.     

What is the appropriate length of the publication period over which to assess research performance?

National research assessment exercises are conducted in different nations over varying periods. The choice of the publication period to be observed has to address often contrasting needs: it has to ensure the reliability of the results issuing from the evaluation, but also reach the achievement of frequent assessments. In this work we attempt to identify which is the most appropriate or optimal publication period to be observed. For this, we analyze the variation of individual researchers’ productivity rankings with the length of the publication period within the period 2003–2008, by the over 30,000 Italian university scientists in the hard sciences. First we analyze the variation in rankings referring to pairs of contiguous and overlapping publication periods, and show that the variations reduce markedly with periods above 3 years. Then we will show the strong randomness of performance rankings over publication periods under 3 years. We conclude that the choice of a 3 year publication period would seem reliable, particularly for physics, chemistry, biology and medicine.     

滚子摆动从动件盘形凸轮的设计及优化

 针对某光学系统要求,对滚子摆动从动件盘形凸轮的设计和凸轮滚子间接触应力与机构体积的综合优化方法进行了研究.根据设计要求,通过Matlab软件,用解析法获得凸轮理论廓形曲线,采用赫兹公式对得到的凸轮曲线进行接触应力分析,建立接触应力和机构体积综合优化的数学模型,通过优化使得最大接触应力由198 MPa降至176 MPa,下降了11%,同时机构体积下降了50%,使机构更好地满足了使用要求和小型化的要求.     

Bidirectional repeaterless transmission of 8 x 10 GE over 210 km of standard single mode fibre

Experimental results on error-free bidirectional transmission of 8times10 Gigabit Ethernet channels over 210 km of standard single mode fibre are presented here. Inexpensive XENPAKs transceivers, conventional unidirectional 1530-1560 nm (C-band) erbium-doped fibre amplifiers and fibre Bragg grating dispersion compensating modules have been used. The results are very promising, especially for operators of national research and educational networks     

A durability model incorporating safe life methodology and damage tolerance approach to assess first inspection and maintenance period for structures

This paper outlines a new durability model to assess the first inspection and maintenance period for structures. Practical scatter factor formulae are presented to determine the safe fatigue crack initiation and propagation lives from the results of a single full-scale test of a complete structure. New theoretical solutions are proposed to determine the s_a−s_m−N surfaces of fatigue crack initiation and propagation. Prediction techniques are then developed to establish the relationship equation between safe fatigue crack initiation and propagation lives with a specific reliability level using a two-stage fatigue damage cumulative rule. A new durability model incorporating safe life and damage tolerance design approaches is derived to assess the first inspection and maintenance period. Finally, the proposed models are applied to assess the first inspection and maintenance period of a fastening structure at the root of helicopter blade.     

谈示波器的修理

本文由示波器的一例故障,介绍示波器的修理方法。