直角柔性铰链的力学特性

为了深入分析精密传动用柔性铰链的机械性能,在研究常用结构形式柔性铰链力学特性的基础上,对变形敏感的直角柔性铰链的力学特性进行了分析．建立了直角柔性铰链空间力学模型,推导了空间刚度矩阵表达式．在此基础上。从柔性铰链基本结构尺寸等方面研究了影响柔性铰链刚度性能的因素,研究发现影响柔性铰链变形性能的刚度系数与柔性铰链几何尺寸参数和构成柔性铰链材料的弹性模量密切相关．研究表明,当柔性铰链的有效长度增加或材料的弹性模量降低时,其各方面的刚度系数均有不同程度的降低．研究工作对深入分析柔性铰链力学特性、优化设计压电驱动器结构,提高其综合性能具有一定的意义．     

考虑温度效应的微操作平台的建模与性能分析

微操作平台处于温度变化的工作环境中会产生热误差、断裂或疲劳破坏等意外情况.为了提高基于直梁式柔性铰链的微操作平台的精度,采用有限元方法建立考虑温度效应的平台热响应模型,并基于该模型对其热误差和热应力进行分析.采用欧拉-伯努利梁模拟直梁式柔性铰链和杆件的力学行为,采用最小势能原理得到计入温度效应的微操作平台的力学方程.采用模态截断技术推导出温度变化与热误差、热应力之间的传递函数.以桥式微操作平台为算例分析温度变化对其性能的影响.分析结果表明:热误差对温度变化的灵敏度为0.192μm/℃,温度变化会产生较大的静态热误差;通过选择合理的结构参数可减小热误差;当单位温度变化时会产生0~0.21μm振动和11.6 MPa的热应力,在动态热载荷作用下会产生较大的热振动和热应力.所以,不能忽略温度效应对微操作平台的影响,需要通过优化设计和热误差补偿策略减小其影响.     

新型柔性铰链的柔度计算

在力或力矩作用下,柔性铰链将会产生相应的微弹性变形,其柔度性能是表征载荷与形变关系的量度,直接影响着柔性铰链的运动精度和综合性能.目前柔性铰链的设计一般基于繁琐的数值积分方法和有限元技术来计算柔性铰链的性能指标.在提出一种新型柔性铰链的基础上,基于弹性静力学基本公式和微积分理论,推导出一种新型柔性铰链的柔度计算公式,为新型柔性铰链的设计提供了理论依据;严格推导出柔性铰链中心轴线上任意位置的变形公式,实现了柔性铰链的精确设计计算.采用ANSYS软件对理论公式的准确性进行验证,两种结果十分吻合.     

压电陶瓷驱动的精密微操作平台特性与优化

设计一种结构紧凑、具有大运动空间和响应快的微操作平台,并对其静态和动态特性进行分析和优化.利用杠杆机构和连杆机构设计一种能实现两级放大的微操作平台,结构对称地设计在同一平面,并采用导向机构实现精确的导向运动.利用功能原理,采用伪刚体方法建立反映平台的静态和动态特性封闭形式的理论模型.由理论模型与有限元分析的结果比较分析可知,两者所得的结果误差范围为6.0%~7.2%,说明所推导模型的正确性.基于理论模型分析构型参数和柔性铰链尺寸参数对放大倍数、输出刚度、应力和固有频率的影响.结果表明,结构参数变化对输出刚度与固有频率的影响是矛盾的,对放大倍数和应力的影响也相互矛盾,需要通过优化结构参数以综合平衡其性能指标.提出一种以综合平衡平台的静态和动态特性为目标,并考虑应力、放大倍数和几何尺寸为约束的优化模型.结果表明优化后的固有频率和放大倍数比优化前均提高,而输出刚度降低,说明优化后的平台性能更好.     

典型柔性铰链回转精度性能计算与分析

针对柔性铰链转动中心偏移引起的误差,推导了柔性铰链回转精度计算的数学模型,以力学卡氏第二定理和微积分为理论基础,通过建立恰当的坐标系,推导出典型柔性铰链转动中心精度的统一解析形式,并用推导的解析式计算了单边直圆、单边抛物线和单边正割曲线形柔性铰链的转动精度．利用有限元方法对柔性铰链的转动中心的柔度解析式进行校验,结果表明有限元与闭环解析式的偏差小于9％;通过定义转动中心的柔度比函数,分析了柔性铰链的结构参数对其转动精度的影响,并比较了这几种柔性铰链的转动精度性能,为柔性铰链的工程设计提供了理论依据．     

压电陶瓷驱动三自由度精密定位系统的弹性动力学与输入调理特性研究

对压电陶瓷驱动三自由度精密定位系统的动力学性能进行了研究。首先建立了系统的弹性动力学模型，采用变截面框架单元描述柔性铰链，给出了其单元刚度矩阵和质量矩阵。通过实验获得了系统的低阶模态参数，并和分析结果进行了比较，验证了所建动力学分析模型的正确性。提出了基于动力学特性分析的驱动输入调理概念。分别采用正弦曲线和五次多项式作为调理函数对系统驱动的动态性能进行了研究。研究结果表明：对驱动输入进行必要的调理是十分必要的，所采用的两种调理方法均有效改善了系统的驱动特性，但由于采用五次多项式作为调理函数完全避免了驱动开始和结束时的加速度冲击，因而可获得更好的驱动效果。     

考虑构件弹性的电动Stewart并联机构刚度建模与仿真

基于集总解析建模方法和构件有限元分析建立包含驱动副、被动万向铰链和运动杆件弹性变形以及预载作用下的Stewart机构刚度矩阵模型。采用添加虚拟铰链等效构件弹性的方式,将分支等效为一系列刚性构件经由主、被动副以及虚拟铰链连接的形式,给出了运动关节和虚拟铰链变量对机构末端位姿的运动学Jacobian矩阵的数值计算方法,应用虚功原理得到静平衡方程,最终建立了机构无预载以及预载下的刚度矩阵模型。该模型不仅考虑了控制环路刚度,还将构件柔性的有限元分析结果与解析建模相结合,在降低计算成本的同时保证了精度。通过一机构分析实例,考察了两种模型下刚度分布的差异。     

LET柔性铰链的等效刚度分析及其参数优化

分析了表示LET柔性铰链转动能力的扭转等效刚度,为确保铰链的转动精度提出了拉压等效刚度的概念并推导出其计算公式。以LET柔性铰链的结构参数为设计变量,提高转动能力和转动精度为目标,建立了铰链的优化模型;采用模拟退火法实现了LET柔性铰链的参数优化,并对优化前后铰链的转动性能进行了分析比较。结果表明,优化后铰链的转动能力和转动精度比优化前都有了明显提高。     

基于动态等效刚度的平面柔性铰链建模与分析

提出一种能够实现虎克铰功能的平面柔性铰链。在分析平面柔性铰链自由度的基础上扩展铰链的运动形式,对铰链的两种位姿建立一种动态等效刚度计算的理论模型,借助Gauss拟合探究大变形位姿下刚度的非线性变化规律,并在有限元平台上验证了模型的正确性。根据理论模型对铰链整体的刚度变化特点进行了分析,探讨了铰链的性能特性。最后将该平面柔性铰链引入6DOF并联隔振平台,采用ADAMS、ANSYS联合仿真对所建新平台进行刚柔耦合动力学分析。结果表明,该平面柔性铰链在满足虎克铰运动要求的同时还能够有效避免虎克铰间隙引起的振动传递率突变问题。     

柔性铰链可倾瓦轴承动静态特性研究

针对一种新型的椭圆型柔性铰链可倾瓦轴承,在柔性铰链刚度建模的基础上,通过建立轴瓦油膜厚度模型及轴颈和轴瓦的平衡模型,采用有限差分法及牛顿迭代法,研究了柔性铰链可倾瓦轴承中柔性铰链的旋转刚度对轴承的动静态性能的影响规律。研究结果表明:柔性铰链旋转刚度越小,轴承越接近普通可倾瓦轴承,稳定性越好;并得出了适于柔性铰链可倾瓦轴承应用的柔性铰链旋转刚度参考范围,为这类轴承的应用设计提供了参考。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...