基于赋权偏差传递网络的6Dof-RUS并联机构随机误差分析

对于已经完成加工装配高精度并联机构,当出现使用精度无法满足设计要求时,需要对产生误差的源头进行追溯,只修复部分构件提高机构精度。以单点激光测距仪检测方法与六条由转动副(R)虎克铰链(U)球面副(S)构成单支链的6自由度并联机构(6Dof-RUS)随机误差模型之间的映射为研究内容。首先构建了6Dof-RUS并联机构赋权偏差传递网络,其次建立了相机坐标系中光斑与平面约束之间的映射方程,通过结构误差雅可比矩阵将结构参数误差映射为可观测的动平台位姿误差。最后进行了实验验证,实验结果表明,在有限次测量次数的情况下可快速对随机误差进行溯源,验证了所提方法的有效性与可靠性,对其他拓扑构型并联机构精度综合具有一定借鉴意义。

Type Synthesis of Two-Degrees-of-Freedom Rotational Parallel Mechanism with Two Continuous Rotational Axes

The two-rotational-degrees-of-freedom（2R） parallel mechanism（PM） with two continuous rotational axes（CRAs） has a simple kinematic model.It is therefore easy to implement trajectory planning,parameter calibration,and motion control,which allows for a variety of application prospects.However,no systematic analysis on structural constraints of the 2R-PM with two CRAs has been performed,and there are only a few types of 2R-PM with two CRAs.Thus,a theory regarding the type synthesis of the 2R-PM with two CRAs is systematically established.First,combining the theories of reciprocal screw and space geometry,the spatial arrangement relationships of the constraint forces applied to the moving platform by the branches are explored,which give the 2R-PM two CRAs.The different distributions of the constraint forces in each branch are also studied.On the basis of the obtained structural constraints of branches,and considering the geometric relationships of constraint forces in each branch,the appropriate kinematic chains are constructed.Through the reasonable configuration of branch kinematic chains corresponding to every structural constraint,a series of new 2R-PMs with two CRAs are finally obtained.

Flexible Bio-tensegrity Manipulator with Multi-degree of Freedom and Variable Structure

Conventional manipulators with rigid structures and sti ness actuators have poor flexibility,limited obstacle avoidance capability,and constrained workspace.Some developed flexible or soft manipulators in recent years have the characteristics of infinite degrees of freedom,high flexibility,environmental adaptability,and extended manipulation capability.However,these existing manipulators still cannot achieve the shrinking motion and independent control of specified segments like the animals,which hinders their applications.In this paper,a flexible bio-tensegrity manipulator,inspired by the longitudinal and transversal muscles of octopus tentacles,was proposed to mimic the shrinking behavior and achieve the variable motion patterns of each segment.Such proposed manipulator uses the elastic spring as the backbone,which is driven by four cables and has one variable structure mechanism in each segment to achieve the independent control of each segment.The variable structure mechanism innovatively contains seven lock-release states to independently control the bending and shrinking motion of each segment.After the kinematic modeling and analysis,one prototype of such bionic flexible manipulator was built and the open-loop control method was proposed.Some proof-of-concept experiments,including the shrinking motion,bending motion,and variable structure motion,were carried out by controlling the length of four cables and changing the lock-release states of the variable structure mechanism,which validate the feasibility and validity of our proposed prototype.Meanwhile,the experimental results show the flexible manipulator can accomplish the bending and shrinking motion with the relative error less than 6.8%through the simple independent control of each segment using the variable structure mechanism.This proposed manipulator has the features of controllable degree-of-freedom in each segment,which extend their environmental adaptability,and manipulation capability.

新型3-DOF 1T2R并联机构的运动学分析与尺度优化

移动和转动混合运动的并联机构具有很高的研究和应用价值。基于转移混合输出运动的机构适用范围广,但该类机构的设计比较困难。为了研发和推广转移混合运动的1T2R并联机构,基于平面五杆机构和一条无约束支链,设计了一种一平移两转动(1T2R)的并联机构。首先,根据方位特征(POC)方程对机构进行了拓扑结构分析,并计算了该机构的自由度;然后,对该并联机构进行了运动学建模,推导了其位置正反解的解析表达式,并基于雅可比矩阵分析了机构的奇异性,利用三维离散搜索法计算了机构的工作空间,给出了机构在工作空间中的灵巧度分布情况;最后,利用粒子群算法(PSO)对机构的工作空间和灵巧度进行了双重优化,同时探讨了无约束支链的布置角φ对机构工作空间和灵巧度的影响。研究结果表明:所设计的1T2R并联机构结构简单,具有位置解析解;优化后的机构的工作空间和灵巧度分别提升了93.47%,203.42%;当无约束支链的驱动方向与平面(2P-3R)机构垂直布置时,能够获得更好的运动性能。该结果为3-DOF 1T2R机构的实际应用奠定了理论基础。

Design and Analysis of a Novel Compliant Mechanism with RPR Degrees of Freedom

A novel compliant mechanism with RPR degrees of freedom(DOF)is proposed where R and P represent rotation and translation DOFs,respectively.The proposed compliant mechanism is obtained from dimension synthesizing a 2-RPU-UPR rigid parallel mechanism with the method of optimization of motion/force transfer characteristic.R,P and U represent rotation,translation and universal pairs,respectively.Firstly,inverse kinematics and Jacobian matrix are analyzed for the dimensional synthesis.Then,output transmission indexes of branches in the parallel mechanism are given.Dimensional synthesis is completed based on the normalized design parameter.And optimization of flexure joints based on constrained energy is carried out.Afterwards,the novel compliant mechanism is obtained by direct replacing method.Mechanical model of the compliant mechanism including static stiffness and input stiffness is built based on the pseudo-rigid body modeling method and virtual work principle.Finally,FEA simulation by Ansys Workbench is carried out to verify DOF,effectiveness of the dimension synthesis,and compliant model.Optimization of motion/force transfer characteristic is first applied for the design of compliant mechanisms to suppress drift of rotation axis in the paper.

Evaluation on Configuration Stiffness of Overconstrained 2R1T Parallel Mechanisms

Currently,two rotations and one translation(2R1T)three-degree-of-freedom(DOF)parallel mechanisms(PMs)are widely applied in five-DOF hybrid machining robots.However,there is a lack of an effective method to evaluate the configuration stiffness of mechanisms during the mechanism design stage.It is a challenge to select appropriate 2R1T PMs with excellent stiffness performance during the design stage.Considering the operational status of 2R1T PMs,the bending and torsional stiffness are considered as indices to evaluate PMs'configuration stiffness.Subsequently,a specific method is proposed to calculate these stiffness indices.Initially,the various types of structural and driving stiffness for each branch are assessed and their specific values defined.Subsequently,a rigid-flexible coupled force model for the over-constrained 2R1T PM is established,and the proposed evaluation method is used to analyze the configuration stiffness of the five 2R1T PMs in the entire workspace.Finally,the driving force and constraint force of each branch in the whole working space are calculated to further elucidate the stiffness evaluating results by using the proposed method above.The obtained results demonstrate that the bending and torsional stiffness of the 2RPU/UPR/RPR mechanism along the x and y-directions are larger than the other four mechanisms.

5-DOF混联机器人设计与运动学分析

针对现有2R1T并联机构并不能很好地满足航空航天工业制孔稳定性的问题,设计了一种全新的两转一移并联机构3SPU-PU,并基于此并联机构设计了2-DOF转头,构造了5-DOF混联机器人,可用于某型飞机座舱盖制孔。首先,利用修正的G-K公式计算了3SPU-PU并联机构的自由度;其次,利用子结构综合的方法对所设计的五自由度混联机器人进行了逆运动学分析;运用ADAMS仿真分析与MATLAB理论计算对运动学分析理论模型进行了验证;最后,利用有限元分析方法对混联机器人进行了静力学分析。结果表明,所设计的混联机器人刚度大、质量轻,能更好地满足制孔稳定性的需求,研究结果也为混联机器人的样机研制、动力学分析及实时控制打下了理论基础。

Type Synthesis of 1T2R Parallel Mechanisms Using Structure Coupling-Reducing Method

Direct kinematics with analytic solutions is critical to the real-time control of parallel mechanisms.Therefore,the type synthesis of a mechanism having explicit form of forward kinematics has become a topic of interest.Based on this purpose,this paper deals with the type synthesis of 1T2R parallel mechanisms by investigating the topological structure coupling-reducing of the 3UPS&UP parallel mechanism.With the aid of the theory of mechanism topology,the analysis of the topological characteristics of the 3UPS&UP parallel mechanism is presented,which shows that there are highly coupled motions and constraints amongst the limbs of the mechanism.Three methods for structure coupling-reducing of the 3UPS&UP parallel mechanism are proposed,resulting in eight new types of 1T2R parallel mechanisms with one or zero coupling degree.One obtained parallel mechanism is taken as an example to demonstrate that a mechanism with zero coupling degree has an explicit form for forward kinematics.The process of type synthesis is in the order of permutation and combination;therefore,there are no omissions.This method is also appli cable to other configurations,and novel topological structures having simple forward kinematics can be obtained from an original mechanism via this method.

Structural Characteristics and Mechanical Properties of Rock Mass in the Field of Tianwan Nuclear Power Plant, China

The structural characteristics and mechanical properties of the rock mass are important parts of the feasibility study on the nuclear power engineering field. In this study, by means of in situ investigation and statistics, the structural plane and joint fissure features of the rock mass were analyzed and discussed at different plots and different depth scopes in the Tianwan Nuclear Power engineering field, the rock mass integrality and its weathered degree were evaluated respectively, and especially, the unfavorable geological phenomena of strongly-weathered cystid existing in the field were studied. According to the results of indoor rock mechanical tests, in combination with drilling, the shallow seismic prospecting, sonic logging and point load tests, the statistical results of physical and mechanical indices of rocks at key plots of the field were analyzed, and the design parameters of the field were calculated. It provided scientific basis for the foundation design of the nuclear power plant.

NUMERICAL ANALYSIS OF BIFURCATION BUCKLING FOR ROTATIONALLY PERIODIC STRUCTURES UNDER ROTATIONALLY PERIODIC LOADS

By considering the characteristics of deformation of rotationally periodic structures under rotationally periodic loads, the periodic structure is divided into some identical substructures in this study. The degrees-of-freedom (DOFs) of joint nodes between the neighboring substructures are classified as master and slave ones. The stress and strain conditions of the whole structure are obtained by solving the elastic static equations for only one substructure by introducing the displacement constraints between master and slave DOFs. The complex constraint method is used to get the bifurcation buckling load and mode for the whole rotationally periodic structure by solving the eigenvalue problem for only one substructure without introducing any additional approximation. The finite element (FE) formulation of shell element of relative degrees of freedom (SERDF) in the buckling analysis is derived. Different measures of tackling internal degrees of freedom for different kinds of buckling problems and different stages of numerical analysis are presented. Some numerical examples are given to illustrate the high efficiency and validity of this method.

NEW CRITERION OF DEGREE OF FREEDOM FOR PLANE MECHANISM

A new criterion of degree of freedom for planar mechanism was presented. Compared with Gruebler's equation, this criterion possesses some characteristics. On one hand, this equation needs no modifying to the complex hinges, degrees of local freedom, and the case of mechanism with all sliding pairs. On the other hand, synthesing the concepts of substitution higher pair for kinematically equivalent lower pair, DOF determination and evolution. which benefits the students in learning. Hence, the authors suggest the formula be recommended, since its briefness, easiness to grasp.

结构动力学应用中若干基本概念的研究

结构动力特性被广泛应用于结构振动控制、结构可靠性设计和健康监测,由此涉及到一些动力学基本概念的理解问题尚待深入探讨。采用一简支梁横向振动算例以及分别通过模态位移法和模态加速度法对多自由度系统的响应振幅进行分析计算,探讨结构位移响应与第一阶固有频率的关系、结构各阶位移模态的贡献与模态应变能的关系。基于模态正交性,通过分析多自由度振动系统的位移响应,论述了系统共振的必要条件,即在保证系统振动频率(某阶固有频率)等于激励频率的同时,其位移响应还应呈现出相应模态的形态;实现多自由度系统纯模态共振,可用于精确识别结构的模态参数。

波长可调的量子点纠缠光源(特邀)

可按需产生纠缠光子对的量子光源是光量子网络中的重要组成部分。半导体量子点可确定性地产生高纠缠保真度的光子对。基于量子点构建量子网络所需的量子中继单元时,需要多个发光波长一致的高质量纠缠光源。然而量子点形貌、组分和应力的不均一性严重限制了基于量子点的量子中继器的可扩展性。国内外研究团队发展了多种量子点生长后调节技术,成功调节量子点精细结构劈裂并通过联合多个调节自由度实现多维度的调节。本文综述了目前联合多个调节自由度实现发光波长和精细结构劈裂均能调控的实验方案,总结了不同方案的调节方法和研究现状,并介绍了将量子点与光学微腔相结合通过Purcell效应能进一步提升纠缠光源的性能。最后,对该领域的未来发展进行展望。

基于等效单自由度的涡轮扫频振动研究

针对有限元方法对扫频工况下涡轮振动求解出现的困难,提出了基于等效单自由度的涡轮结构振动扫频算法,并对涡轮扫频振动特征进行分析.建立了涡轮流固耦合计算模型,使用非线性谐波法得到了涡轮表面的气动激励,使用谐响应方法分析了涡轮的稳态振动特性.基于能量原理,建立了涡轮等效单自由度计算模型,通过与稳态振动结果的对比,验证了方法的可行性与正确性,并利用所建立模型分析了涡轮的扫频振动特征.结果表明,涡轮在扫频工况下响应峰值、半功率带宽以及响应曲线形状等特征与稳态工况存在差异.等效单自由度算法与有限元方法计算得到的涡轮响应误差小于10%,共振峰偏移率小于1%.

基于木质异型材的两自由度工作台研究

设计了一种两自由度可旋转工作台,用于辅助普通三轴数控机床对木质异型材进行复杂曲面加工。该工作台可通过两台电机控制工作台同时或分别进行X轴和Y轴方向上的旋转,左侧电机驱动蜗轮蜗杆传动实现工作台X轴向旋转,右侧电机驱动齿轮副传动实现工作台Y轴向旋转,通过互相配合实现多平面、多角度加工。通过对工作台关键支撑结构进行静力学分析与模态分析,确定工作台整体支撑结构合理性,为两自由度工作台结构设计提供参考。

4自由度番茄采摘机软体机械臂运动学分析

综合考虑番茄采摘机软体机械臂在复杂环境中的使用需求,以此来确定番茄采摘机械的4自由度模型。对番茄采摘软体机械臂进行正运动和逆运动分析,同时确定机械臂结构、关节长度、自由度选择等参数,并绘制出三维模型,从而为下一步选择控制系统硬件及软件编程奠定基础。

基于灰色关联熵的冻融作用下混凝土力学性能与孔隙结构模型研究

为研究混凝土在冻融循环过程中孔隙结构对力学性能的影响,对不同冻融循环次数的混凝土进行力学性能、扫描电子显微镜(SEM)、低场核磁共振(NMR)等试验,并利用灰色关联熵方法建立冻融循环过程中抗压强度与孔隙结构之间的数学模型。结果表明:随着冻融循环次数的增加,混凝土力学性能下降明显,孔隙度增加且T_(2)谱总面积逐渐增加;冻融循环过程中对力学性能影响最大的两个因素分别为少害孔孔隙占比以及自由流体饱和度(FFS),对应的灰熵关联度分别为0.989 3和0.995 2。以抗压强度为参考,以自由流体饱和度和少害孔孔隙占比为比较序列建立GM(1,3)模型,模型预测值与试验平均值相对误差仅为0.29%,表明预测模型可以为混凝土冻融循环过程中力学性能提供公式依据。研究成果有助于加深对冻融循环过程中混凝土结构损伤演化规律的认识。

2-DOF平面并联机器人结构参数优化的研究

提出了一种新颖的高速高精度机器人机构:采用高速精密直线电机驱动-2-DOF平面并联杆机构.在杆机构的设计中,以结构紧凑和抑振为目标,分别采用模拟退火算法和有限元动力仿真进行了几何尺寸和截面尺寸的优化,并提出了一种基于本模型特点的新解产生机制.实验测试结果表明:经优化设计后的平面并联杆机构刚度大,高速运动下的残余振动<1 μm,直线电机的稳定时间成为决定机器人稳定时间的关键因素.

一种变自由度单回路机构的变拓扑结构设计及拓扑分析

特殊单回路机构通过一些特殊位置后会发生自由度变化,从而使其拓扑学、运动学/动力学性能发生变化,并适用于不同的应用背景。研究设计了一种由8个转动副(R)组成的单回路并联机构,它有3种运动模式,分别为2自由度、4自由度以及3自由度驱动,对应3个机构;然后,分析计算了3种运动模式下机构的方位特征集、自由度、耦合度3个主要拓扑特性,并分析了3种机构变拓扑结构的稳定性及可转变性;同时,对运动模式1、模式3下机构的位置正反解进行了分析。为基于这种变自由度单回路机构单元的可重构并联机构的研究提供了基础。

基于传感器的6-DOF并联机构运动学正解

6 -DOF (DegreesofFreedom)并联机构的位姿正解问题复杂而且多解.讨论了处理正解问题的各种不同方法,其中数值迭代法和使用附加传感器的两种方法可以直接找到正解.重点研究了使用附加传感器获取并联机构正解的方法及传感器的类型,并对采用直线位移传感器和旋转传感器及其配置方法进行了比较,不同的配置会影响到正解的计算精度与计算过程.讨论了采用直线位移传感器与旋转传感器联合求解时合理的传感器数量及相应的配置,并针对一种相对通用的配置方法,推导了获得位姿正解的计算过程.根据计算分析,采用4个旋转传感器或者3个直线传感器,经过适当的配置,可以获得并联机构的正解.