6-UCU并联平台的固有频率和固有振型分析

Stewart平台是一种六自由度的并联机构,特别适用于工作范围不大但负载却很大的工作场合中。众多学者对Stewart平台性能、结构、优化以及控制等方面展开了大量基础研究。为了得到Stewart平台自由振动方程,需要对其固有频率和固有振型进行求解。利用Kane方法建立了Stewart平台的动力学方程,基于该模型求出Stewart平台质量矩阵和刚度矩阵,并进一步得到Stewart平台固有频率方程;最后并利用虚拟样机技术对其进行仿真分析,验真了模型准确性,为下一步振动研究提供理论依据。     

考虑液压缸影响的Stewart平台动力学分析

由于液压系统的特点及Stewart平台的结构特性,液压驱动Stewart平台得到越来越广泛的应用.针对负载小的情况,在对Stewart平台进行运动学分析时,考虑了缸铰点的速度和加速度.详细分析液压缸缸筒、活塞杆两体由于重力和惯性力的作用,在平动和转动时对Stewart平台动力学分析时产生的影响.建立包括液压缸影响的、详细的Stewart平台动力学模型,为Stewart平台的准确设计、分析和控制奠定基础.     

液压驱动Stewart平台位姿控制仿真

由于液压系统的特点以及Stewart平台的结构特性，使液压驱动Stewart平台得到越来越广泛的应用。针对液压驱动Stewart平台，联合平台的运动学和动力学，构建了整个位姿系统的模型；研究了平台的位姿控制策略，并进行了频率特性分析和仿真分析，验证了控制策略的有效性。     

基于神经网络PID控制的液压驱动Stewart平台稳定性研究

Stewart平台运动轨迹容易受到外界波形的干扰,导致其运动轨迹输出误差较大,稳定性较差。对此,创建了液压驱动Stewart平台简图模型,推导了连杆动力学方程式。设计了液压驱动机构,给出了液压流量控制方程式。引用PID控制器并进行改进,设计了神经网络PID控制器。采用Matlab软件对Stewart平台两种控制方法进行仿真,将仿真结果进行对比和分析。结果显示:在无干扰环境中,两种控制器都能较好地实现Stewart平台运动轨迹的跟踪任务,差别不大;在有干扰环境中,采用PID控制器的Stewart平台运动轨迹输出误差较大,稳定性较差,而采用神经网络PID控制器,Stewart平台运动轨迹输出误差较小,稳定性较好。采用神经网络PID控制器,Stewart平台能够自适应调节控制参数,降低外界波形对平台运动轨迹的影响,提高Stewart平台运动的稳定性。     

Stewart平台的综合谐振频率研究

载人的大惯量Stewart平台,多采用液压伺服系统驱动,其必然存在液压-机械综合谐振问题。这是由于油液的可压缩性、传动铰链的弹性及负载惯性等引起的。本文首先根据力-变形关系推导出Stewart平台的刚度矩阵,然后分别根据铰链和液压缸各自组成构件的串并联关系,推导出三维万向铰链和液压弹簧刚度的数学模型。进而建立了液压Stewart平台的无阻尼动力学方程,并据此研究了系统的综合谐振频率。理论计算与实验结果表明,平台的位姿、油液与铰链的刚度等因素决定了系统的综合谐振频率。     

六自由度Stewart平台液压油路的改进设计

相比六自由度Stewart平台的电动缸或者滚珠丝杠传动驱动型式,以液压缸作为驱动元件的液压传动方式有着无法比拟的优势。但是,该种驱动方式需要进行专门的液压油路设计。文中针对六自由度Stewart平台的特点,对在实验研究过程中产生的系统安全性问题进行了分析,提出了一种改进油路的方案。     

Stewart平台运动学仿真分析

Stewart平台的运动学分析是确定系统结构参数、设计液压动力机构、确定系统流量、选择伺服阀的基础和前提。根据Stewart平台机构学原理,在ADAMS/View模块下建立了系统的虚拟样机模型,并对其添加约束和驱动后进行了运动学仿真,得到了各作动器运动参数在不同运动姿态时的变化规律。该方法避免了大量的数学计算与计算机编程工作,通过CAE方法实现了对Stewart平台的运动学仿真。     

大型液压Stewart平台动态耦合特性

耦合现象在液压Stewart平台中普遍存在,以大型液压Stewart平台为目标,采用AMESim和SimMechanics对液压部分及平台机构部分分别建模。通过软件接口建立联合仿真体系对平台动态耦合进行定量分析,数值模拟6缸动态特性在一致和有差异的情况下动态耦合的强度和规律,该仿真体系针对液压与并联机构进行分布式建模,改善了建模精度。建立大型液压Stewart平台通用联合仿真模型,为Stewart平台的耦合研究提供了有效的理论研究手段,能够针对平台进行前期耦合预测,保证设计方案的准确性与可靠性。     

液压Stewart平台柔性换向控制

液压Stewart平台在运动模拟器中的应用日益广泛,其换向平滑是保证模拟器逼真度的重要因素。采用动态Lugre摩擦力模型和Stribeck负斜率效应研究了Stewart平台分支液压缸的最大静摩擦力和动摩擦力;推导了Stewart平台液压系统在换向时因运动惯性产生的增压压力和因结构非对称导致的压力跃变;从控制方法和结构设计等方面提出了柔性换向策略,并进行了实验验证。     

六自由度微重力模拟平台研究

太空环境与地面环境有着很大的不同,根据地面环境下动力学特性设计而成的机械系统在太空零重力环境下作业时会产生"动力过冲"的现象,因此太空机械系统在进入太空工作之前需要进行严格的地面微重力模拟实验以对系统的设计进行验证。针对大型昂贵空间实验目标的地面测试问题,提出了一种基于Stewart机构的混合驱动的六自由度微重力模拟实验平台,基于Kane方法建立了该实验平台的动力学方程,据此设计了面向该平台运动控制的计算力矩控制方法,并利用MATLAB/Simulink与ADAMS进行联合仿真,验证了所提出的控制方法的正确性。     

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.