基于载荷作用的柔性体三维公差建模及精度影响分析

传统精度设计仅考虑零部件几何公差的影响,未涉及装配载荷作用下零部件变形的影响。为了保证机械系统在工作过程中的可靠性与稳定性,不仅要求在产品设计与制造环节中要严格保证零部件具有良好的设计性能与制造质量,更重要的是保证装配过程中各零部件间的配合性能。以具体的卧式加工中心为例,通过有限元法获取零部件载荷效应下的变形数据信息,结合小位移旋量理论、齐次坐标变换理论及表面认证思想,建立零件载荷变形偏差的综合三维数学模型。分析结果表明:装配载荷作用下的零件变形偏差总体上呈现出传递和累积的趋势,系统末端变形偏差累积量达到-0.024 9 mm。因此,零件载荷变形偏差对机械系统精度的影响不容忽视,设计阶段的三维公差分析应该综合考虑尺寸、形位公差及载荷作用下的变形偏差对机械系统装配精度的影响,才能形成一种面向整机精度的协调与保障机制,为提高复杂精密机械系统的整机性能提供理论与技术支撑。     

组合式动态汽车衡测量误差修正方法研究

针对现有方法误差修正效果不佳的问题,提出组合式动态汽车衡测量误差修正方法研究。该方法以原始的变异函数为基础,对其进行拓展处理,构建了汽车衡表面协变异函数模型,以此来实现车辆通过汽车衡时条件因素与汽车衡表面不同位置的空间关系构建。在误差修正阶段,将汽车衡的秤台面分为若干等分,并设置各区域的中心位置为标准载荷单元,根据其载荷值与误差的定量关系,确定测量误差的修正强度。测试结果表明：设计方法对于不同测量状态下的测量结果误差始终稳定在单位分度值范围内,具有较高的准确性。     

基于刚体位移的天线反射面拟合新算法

射电望远镜和雷达天线的反射面的加工误差和变形直接影响系统的工作性能.为准确计算反射面的实际误差,一般须对变形后的反射面进行最佳抛物面拟合.基于刚体空间运动原理,提出一种利用确定刚体位移的6自由度及抛物面的焦距共7个广义自由度来拟合空间抛物面的新方法.通过该方法可直接求得最佳抛物面的顶点空间位置、轴线方向及其焦距.回顾传统的由一般二次曲面推出特征值的抛物面拟合法和小变形下基于法向偏差的抛物面拟合方法,并通过计算实例与之进行比较.验证了方法的稳定性和精确性.同时还集成了一种简便的拟合误差求解方法.     

过盈配合接触界面的研究

通过W-M函数建立具有分形特征的等效粗糙表面与刚性平面的接触模型,模拟压缩机叶轮与轴过盈配合下界面的接触。将接触模型导入到有限元软件Ansys中,分析接触模型接触面积、接触压力、滑移面积、粘着面积与变载荷的关系和表面路径上的应力与变形。结果表明,接触时只有个别较高的微凸体发生接触,微凸体肩部区域的应力较大,微凸体中心位置变形量最大,接触界面在一定的法向载荷下接触面积减小,粘着面积增大,配合件发生了宏观的变形。     

数字图像相关法在WC/Cu复合材料线膨胀系数测量中的应用

为了提高数字图像相关曲面拟合法在实际应用中的亚像素定位精度,对曲面拟合法进行了修正,并用修正后的曲面拟合法研究了WC颗粒大小和含量对WC/Cu复合材料线膨胀系数的影响.首先,分析了曲面相关拟合法在实际应用中的测量误差来源,并对其进行了修正.然后,用粉末冶金法制备出WC/Cu复合材料,对表面制备有耐高温散斑的试件进行热膨胀实验,并利用修正后的曲面拟合法测量了不同温度下WC/Cu复合材料的热变形场.最后,通过一元二次多项式拟合建立了WC/Cu复合材料热膨胀系数真值.结果表明:修正后的曲面拟合法有效地改善了传统方法的亚像素位移在0.5像素左右位移场不连续的问题,减小了亚像素定位误差,获得了更为准确的测量数据.     

一种结合部法向刚度的预估方法

提出一种结合部法向刚度的预估方法.通过表面形貌测量仪获取粗糙表面的轮廓数据,拟合生成粗糙表面轮廓曲线,在此基础上建立考虑摩擦的二维粗糙表面的有限元弹塑性接触模型,用罚函数法计算压力在0～0.8 MPa的加载过程中接触层的应力、位移和接触面积.计算结果表明,粗糙表面真实的接触面积在低载荷下快速增大,高载荷下的增大速度很缓...     

新的粗糙表面弹塑性接触模型

提出一种新型的粗糙表面弹塑性微观接触模型.该模型的建立基于接触力学理论和接触微凸体由弹性变形向弹塑性变形及最终向完全塑性变形的转化皆是连续和光滑的假设.研究单个微凸体在载荷逐渐增加时的变形规律,并重点推出弹塑性变形区间的接触方程.在此基础上应用概率统计理论导出了粗糙表面的接触载荷、平均分离和实际接触面积之间的数学关系式.在不同的塑性指数和载荷条件下,该模型与GW弹性模型和CEB弹塑性模型就实际接触面积和法向距离的预测结果进行了对比.结果表明,在同样塑性指数和载荷条件下比GW模型预测的实际接触面积大但法向距离小,且两者的差距随塑性指数和载荷的增加而增大.因此该模型的预测结果更加符合人们的试验观察和直觉,能够更加科学和合理地描述两个粗糙表面的微观和宏观接触状态.     

具有连续光滑特性的结合面接触刚度模型

结合面接触刚度直接影响着机械系统的静、动态力学性能和精度保持性水平.基于微凸体在弹性、弹塑性以及完全塑性接触变形过程中,接触刚度具有连续、光滑特性的思想,首先提出利用Hermite多项式插值函数,来弥补单一微凸体接触刚度建模时存在的不连续等缺陷,建立了具有连续光滑特性的单一微凸体接触刚度新模型;然后基于统计学方法,建立了结合面的法向接触刚度模型;最后将所建模型与GW、ZMC、KE和BRAKE模型进行对比分析.结果表明:本文模型实现了单一微凸体接触刚度在不同接触状态之间连续且光滑地转变;对于光滑表面形貌,基于GW、ZMC、KE以及BRAKE模型预测的接触刚度与本文模型结果的差异较小,其中本文模型最接近于纯弹性的GW模型;当表面粗糙度增大时,GW模型与其他几种模型的差异逐渐增大,此时本文模型与考虑微凸体多种变形阶段的ZMC模型吻合较好;再次表明载荷与表面粗糙度是影响刚度的两个主要因素,即随着载荷的增大或表面粗糙度的减小,接触刚度递增.     

多源不确定性下平面变胞机构运动可靠性分析

变胞机构可根据环境和工况的变化及需求,进行重组和重构,在机器人领域得到广泛应用.变胞机构可变拓扑结构特性,使得分析多源不确定性下变胞机构全构态运动可靠性更为困难.以多源不确定性下平面五杆变胞机构为研究对象,提出一种适应交变温度工况的变胞机构全构态运动可靠性分析方法.建立温度载荷下连杆制造公差-热变形、关节配合公差-热变形的耦合模型,采用服从截断正态分布的随机参数和区间参数描述连杆尺寸、转动副和移动副间隙的不确定性,基于变胞特性建立变胞机构全构态运动误差传递模型,结合区间优化算法和蒙特卡洛算法建立多源不确定性下变胞机构全构态运动可靠性模型.基于提出的方法,分析了交变温度工况下变胞机构全构态运动可靠性分布规律,并分析了不同孔轴配合、连杆公差等级及其热膨胀系数对变胞机构全构态运动可靠性的影响规律.     

计入套圈变形和润滑影响的球轴承动刚度研究

针对传统拟静力学分析方法未考虑轴承套圈热变形、离心力变形和弹流润滑作用引起轴承内部沟道曲率中心与滚动体中心几何位置关系的变化,难以准确反映轴承动刚度不足的现状,建立了计入套圈变形和弹流润滑影响的轴承拟静力学修正模型。采用所建立的模型研究了轴承不同工作转速和预紧力条件下轴承热变形、离心力变形和润滑油膜对动刚度的影响规律,通过与Gupta等典型算例及实验的对比验证,证实了所建立模型及分析结果的有效性。     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.     

Short-Term Relay Quality Prediction Algorithm Based on Long and Short-Term Memory

The fraction defective of semi-finished products is predicted to optimize the process of relay production lines, by which production quality and productivity ar...     

End-to-End Multiview Gesture Recognition for Autonomous Car Parking System

The use of hand gestures can be the most intuitive human-machine interaction medium.The early approaches for hand gesture recognition used device-based methods....     

Application of Feature Extraction through Convolution Neural Networks and SVM Classifier for Robust Grading of Apples

This paper proposes a novel grading method of apples,in an automated grading device that uses convolutional neural networks to extract the size,color,texture,an...     

分布动态载荷识别的抗噪处理

针对正交多项式频域法在用多种响应对矩形薄板进行载荷识别中抗噪性较差的问题,综合运用平均法、矩阵预处理和奇异值截断法等方法对之进行改善,并引入空间映射的思想,将该方法的应用范围拓展为复杂的模型.利用仿真算例,证实了该方法具有较好的抗噪性.     

基于MELTAC-N平台的核电厂安全级DCS环网研究与测试

针对工程实践中环网通讯相关问题的处理缺乏理论基础及国产化安全级DCS平台的开发缺乏成熟经验借鉴问题,对基于MELTAC-N平台核电厂安全级DCS环网的软硬件实现进行了研究。提出了安全级DCS环网双环网冗余设计、光切换开关设计等硬件设计方法,以及以RPR协议为基础,采用全数据收发策略的软件设计方法。在CPR1000安全级DCS平台上对安全级DCS环网的可靠性及实时性进行了评价,并进行了容错能力、响应时间及响应时间稳定性测试验证实验。结果表明,基于MELTAC-N平台安全级DCS环网软硬件设计具有较好的容错能力及响应时间稳定性。     

The laboratory simulation of abrasive wear

Abrasive wear has long been recognised as one of the most potentially serious tribological problems facing the operators of many types of plant and machinery; several industrial surveys have indicated that wear by abrasion can be responsible for more than 50% of unscheduled machine and plant stoppages. Locating the operating point of a tribological contact in an appropriate operational ‚map’︁ can provide a useful guide to the likely nature and origins of the surface degradation experienced in use, though care must be exercised in choosing the most suitable parameters for the axes of the plot. Laboratory testing of materials and simulations of machine contacts are carried out for a number of purposes; at one level for the very practical aims of ranking candidate materials or surface hardening treatments in order of their wear resistance, or in an attempt to predict wear lives under field conditions. More fundamentally, tests may be aimed at elucidating the essential physical mechanisms of surface damage and loss, with the longer term aim of building an analytical and predictive model of the wear process itself. In many cases, component surface damage is brought about by the ingress of hard, particulate matter into machine bearing or sealing clearances. These may be running dry although, more usually, a lubricant or service fluid is present at the interface. A number of standardised wear test geometries and procedures have been established for both two- and three-body wear situations, and these are briefly described. Although abrasive wear is often modelled as following an ‚Archard’︁ equation (i.e. a linear increase in material loss with both load and time, and an inverse dependence on specimen hardness) both industrial experience and laboratory tests of particularly lubricated contacts show that this is not always the case: increasing the hardness differential in an abrasively contaminated lubricated pair may not always reduce the rate of damage to the harder surface.     

ANGULAR DISTORTION ALLOWABLE VALUE AND ASSESS METHOD OF WELD ON COKE TOWER

A graph as the new engineering method for estimate the safety of bulging deformation of coke tower is proposed. Through stresses analysis of circumferential weld of coke tower and comparing the stresses produced by pressure with heat stress of steady state, residual stress, bending stress produced by both itself weight and wind loads, it showed that the stresses produced by pressure on the angle distortion are the main factor of equivalent stress of the combined stress. After comparing four kinds of stress controlling conditions, the relation to stress with depth of angular distortion, grade of curvature of angular distortion and half of region of angular distortion has been inferred. Graph of deformation allowable value of coke tower for different condition by angular distortion and half of region of angular distortion has been plotted. The five steps for its engineering use have been explained. The lighter the grade of curvature is, the larger of bulge allowance, may be, and the bigger of depth of angular distortion may pose too. For the coke tower with a popular structure of Dg 5 400 mm×28 mm, the result by graph is nearly more than the result of two formulas formed by other research, the error is less than 7.0%. But, the graph can be easily applied to different size of angular distortion.