实例推理技术在机床夹具CAD中的应用

本文以机床夹具为研究对象，分析了机床夹具的特征，指出机床夹具特征相似可描述为结构相似和功能相似两个方面。根据基于实例推理方法，研究了机床夹具设计中的实例库设计、检索方法、检索算法等关键技术。介绍了我所与南航联合开发的基于UG平台的专用机床夹具CAD系统基于实例推理的设计向导技术特点与应用情况。     

隨行夹具的几种夹紧机构

随行夹具的夹紧机构,不同于普通机床夹具的夹紧机构。普通机床夹具的夹紧机构,是将工件牢固地压紧在夹具的定位面上,而随行夹具的夹紧机构,为了要保证夹具的随行动作,不能将工件夹紧固牢,其夹紧件和定位支承件对工件来讲,应是如图1所示的弹性夹紧和弹性支承(有时也采用固定支承)。笔者从所经过的几代产品夹具设计资料中,选择了几种夹紧机构,仅供参改。     

国家质量技术监督局废止89项国家标准

现将国家质量技术监督局 2 0 0 0年 5月 2 5日以质技监标函 [2 0 0 0 ]0 76号文批复国家机械工业局废止的 89项国家标准中与航空工业有关的标准刊登如下。废止的国家标准项目序号标准编号标准名称1ＧＢ/Ｔ 34 65-1 983长柄机用丝锥2ＧＢ/Ｔ 34 66-1 983长柄螺母丝锥3ＧＢ/Ｔ 1 2 868-1 991 机床夹具零件及部件Ｔ形　槽用螺母4ＧＢ/Ｔ 1 2 869-1 991 机床夹具零件及部件　双头　螺栓5ＧＢ/Ｔ 1 2 870 -1 991 机床夹具零件及部件　槽用　螺栓6ＧＢ/Ｔ 1 2 871 -1 991 机床夹具零件及部件　快换　垫圈7ＧＢ/Ｔ 1 2 872 -1 991 机床夹具零件及部…     

三机部关于颁发《通用零件》等部标准的通知

为适应生产、科研发展的需要,现颁发经修订的《通用零件》、《机床夹具零件》、《通用零件、机床夹具零件技术条件》部标准,于一九七四年四月一日开始实施。     

采用机床夹具的经济分析方法之探讨

本文对采用机床夹具的经济效益进行了较为全面的分析,并对采用机床夹具经济评价中的临界产量计算公式进行了修改和对比分析,从理论和实践方面阐明了修改临界产量计算公式的必要性及现实意义。     

HB3201-79《气液泵》简介

气液泵是以压缩空气为能源,通过气控自动换向阀操纵差动式气液缸活塞自动往复运动,获得排出高压油的增压动力装置。它适用于断续供油状态的液压装备。如用于机床液压夹具(可以同时供给数台机床上液压夹具用的     

《通用零件》等部标准延期执行

《通用零件》、《机床夹具零件》、《通用零件、机床夹具零件技术条件》部标准,原规定自一九七四年一月一日开始实施。由于印刷、出版、发行等原因,将原规定的实施日期改为一九七四年九月一日。     

薄膜卡盘的设计和制造

在精磨夹具的设计过程中,经常会碰到一些精度要求高,形状特殊而且刚性差的零件。常用的液塑、滚针、蛇形管衬套结构的定心夹具,对这些特殊情况难以满足要求,因为这些结构虽然都可消除零件定位误差,但由于夹具装上机床后,夹持零件的表面不能修整,而达不到非常理想的精度。因此人们都在寻求夹具在机床上修整后,不用移动夹爪而利用固定膜片的弹性变形来定位夹紧零件,以消除夹具的安装误差和零件的定位误     

飞机结构件机械加工柔性夹具系统

飞机制造业中的工艺装备一般指机械加工夹具、装配型架、钣金模具、焊接夹具、测量检验夹具等.机械加工是获得飞机零件最终形状和精度的最主要方法,而机床夹具在保证飞机零件机械加工质量和工装加工效率方面起到重要作用.     

革命性的装夹方式--电控永磁夹具

在中国的机床工具制造与消费市场中,品质与性能各异的机床、数控系统、刀具、功能配套件和辅助设备琳琅满目,然而,绝大多数高精、高速、高效的数控机床仍然在使用最为传统的夹具,即螺丝压板和虎钳,这严重地影响了一流机床和刀具效能的充分发挥,而更为严重的是目前很多人没有认识到夹具系统在整个切削过程中的重要性,一味地提高机床和刀     

一种鼻锥钝化高超声速轴对称进气道流动特性实验

前缘钝化尺度是高超声速进气道设计中的关键参数。针对一种前体锥加弯曲压缩面的高超声速轴对称进气道,选取最大尺度为3.2mm(5%唇缘半径)的几种典型鼻锥钝化半径,在马赫数Ma=6来流,及模型安装攻角为0°、4°、7°的条件下开展鼻锥钝化尺度对进气道流动性能影响的实验研究。采用纹影拍摄及压力测量记录各来流条件下进气道前体流场结构及壁面压强分布,并在无攻角来流条件下利用微型扰流器进行边界层强制转捩研究。结果表明,对无攻角来流而言,即使是尺度高达3.2mm的钝化半径对进气道前体流场结构及壁面静压分布也基本没有影响。此来流条件下,几种不同鼻锥钝化半径的前体压缩面均出现小范围流动分离,而添加扰流器后该分离区均消失。钝化尺度的影响随着攻角的增加而显现,尽管不同鼻锥钝化尺度下迎风面流场及壁面压强分布几乎没有差别,但背风面随钝化尺度增大表现为边界层明显增厚、流动趋于不稳定。其中最大钝化尺度R=3.2mm的构型在4°攻角来流时背风面即出现明显的分离区,而7°攻角来流时背风面更是出现大范围流动分离、进气道背风侧不起动,并导致进气道内部壁面压强显著下降。     

Adaptive Sliding Control of Six-DOF Flight Simulator Motion Platform

本文使用Newton-Euler法推导了六自由度飞行模拟器运动平台完整的线性化形式的动力学方程,并以此为基础,提出了一种在任务空间中的非线性自适应滑模控制方法。这种控制方法将系统中的不确定性分为定常不确定参数和时变不确定参数,利用非线性自适应控制对定常不确定参数进行辨识,同时结合滑模控制对时变不确定参数和外部扰动进行补偿。通过数值仿真分析表明,该控制策略能准确识别运动平台的载荷、惯量、重心等参数,同时又能有效地提高系统的鲁棒性能。     

航天器返回地球的气动特性综述

航天器返回地球的飞行过程中,气动特性是实现将宇宙飞行速度减到落地前速度、保证再入飞行得到有效控制以及再入防热安全可靠的关键因素。针对简单旋成体气动外形、半弹道式再入控制、烧蚀防热类返回航天器,综述了返回地球过程中变化的空气流域特性、航天器周围的气体绕流环境、空气与航天器作用产生的动力学与热效应等。系统地给出了该类航天器的再入气动特性参数与飞行性能的共性规律,包括:气动阻力与再入减速、气动升力与再入轨迹控制、配平攻角与飞行稳定性、气动加热与防热,以及再入过程中不同气动特性航天器、气象条件变化等对再入飞行性能的影响规律。为航天器开展返回飞行过程的跨流域气动性能工程研制提供设计参考。     

Nonlinear Adaptive Slewing Motion Control of Spacecraft Truss Driven by Synchronous V-gimbaled CMG Precession

The slewing motion control of a truss arm driven by a V-gimbaled control-moment-gyro (CMG) is a nonlinear control problem. The V-gimbaled CMG consists of a pair of gyros that must precess synchronously. The moment of inertia of the system, the angular momentum of the gyros and the external disturbances are not exactly known. With the help of feedback linearization and recursive Lyapunov design method, an adaptive nonlinear controller is designed to deal with the unknown items. Performance of the proposed controller is verified by simulation.     

The effect of inlet conditions on the flow and heat transfer in multiple rotating cavity with axial throughflow

This paper discusses experimental results from two different build configurations of a heated multiple rotating cavity test rig.Measurements of heat transfer from the discs and tangential velocities are presented.The test rig is a 70% full scale version of a high pressure compressor stack of an axial gas turbine engine.Of particular interest are the internal cylindrical cavities formed by adjacent discs and the interaction of these with a central axial throughflow of cooling air.Tests were carried out for a range of non-dimensional parameters representative of high pressure compressor internal air system flows(Re up to 5×106 and Rez up to 2×105).Two different builds have been tested.The most significant difference between these two build configurations is the size of the annular gap between the(non-rotating) drive shaft and the bores of the discs.The heat transfer data were obtained from thermocouple measurements of surface temperature and a conduction solution method.The velocity measurements were made using a two component,LDA system.The heat transfer results from the discs show differences between the two builds.This is attributed to the wider annular gap allowing more of the throughflow to penetrate into the cavity.There are also significant differences between the radial distributions of tangential velocity in the two builds of the test rig.For the narrow annular gap,there is an increase of non-dimensional tangential velocity V/Ωr with radial location to solid body rotation V/Ωr=1.For the wider annular gap,the non-dimensional velocities show a decrease with radial location to solid body rotation.      

Investigation of Formation Process of the Chrome-free Passivation Film of Electrodeposited Zinc

The feasibility was investigated to substitute chrome-free passivation treatment of electrodeposited zinc in a titanium bath for chromate passivation treatment. The formation mechanism of the chrome-free passivation film was further analyzed. The surface mor- phologies and the elemental compositions of the treated samples with varied immersion times were observed by scanning electron mi- croscopy (SEM) and determined by energy dispersion spectrometry (EDS), respectively. The electrode potential of the sample surface was recorded in the film formation process. The changes of the electrode potential are in accordance with that of SEM and EDS of the sample surface. The results of X-ray photoelectron spectroscopy (XPS) show the chrome-free passivation film composed of ZnO, SiO2, TiO2, Zn4Si2O7(OH)2, and SrF2. The anode zinc dissolution and the local pH value increase due to the cathode hydrogen ion reduction process result in the formation of the chrome-free passivation film. The macro-images of the chrome-free passivation films formed on electrodeposited zinc show that the color of the film changes from blue to iridescence with the increase of the immersion times.     

基于H∞性能指标的质量矩拦截弹鲁棒控制

 以所建立的质量矩拦截弹数学模型为基础，利用微分几何的反馈线性化理论，得到一个解耦线性系统，考虑到拦截弹的鲁棒性要求和3个滑块的协调控制问题，提出采用双回路的设计方法，内回路采用线性二次调节器（LQR），外回路采用考虑混合灵敏度问题的H_∞控制设计。仿真结果证明了该方法动态性能满足设计要求，同时对系统参数的不确定性具有较强的鲁棒性。     

复合固体推进剂和胶粘剂的固化剂交联范围

固化剂的当量比为反应初始时总固化剂基团数对总粘合剂基团数之比,它是决定复合固体推进剂和胶粘剂性能的重要参数.本文根据聚合物结构的网络理论导得了固化剂交联范围预测关系式.大量实践结果表明:当固化聚合物形成网络结构时,所有的当量值均在交联范围内,该范围比预聚物粘合剂的凝胶化范围要窄.     

微型扑翼飞行器风洞试验初步研究

 为了对微型扑翼飞行器空气动力学基本特性进行定量研究，利用西北工业大学微型飞行器专用风洞对微型扑翼飞行器机翼进行初步风洞吹风试验。试验中进行了扑动频率、风速、迎角、机翼平面形状、翼型弯度对机翼气动特性影响的研究。通过试验得出了微型扑翼飞行器升力、推力产生的基本规律，为微型扑翼飞行器总体设计和气动设计提供了参考。     

On Nonlinear Evolution of C-type Instability in Nonparallel Boundary Layers

The process of evolution, especially that of nonlinear evolution, of C-type instability of laminar-turbulent flow transition in nonparallel boundary layers are studied by means of a newly developed method called parabolic stability equations （PSE）. Initial conditions, which are very important for the nonlinear problem, are investigated by computing initial solution of the harmonic waves, modifying the mean-flow-distortion, and giving initial value of TS wave and its subharmonic waves at initial station by solving linear PSE. A numerical method with high-order accuracy are developed in the text, the key normalization conditions in the PSE are satisfied, and nonlinear PSE are solved efficiently and implemented stably by the spatial marching. It has been shown that the computed process of nonlinear evolution of C-type instability in Blasius boundary layer is in good agreement with the experimental results.