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.

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.

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。

Novel Mobility Formula for Parallel Mechanisms Expressed with Mobility of General Link Group

The determination of virtual constraints is always one of the key and difficult problems in traditional mobility calculation. To make mobility calculation simple, considering avoiding virtual constraints, some new formulae have been presented, however these formulae can hardly intuitively reflect general link group＇s restrictions on output member and its influences on independence of output parameters, which is premise to the judgment of the properties of mobility. Towards the problem to reveal the intrinsic relationship between the degree of freedom（DOF） of a mechanism, the link group, and the dimension of output parameters, also to avoid determination of virtual constraint, based on the new concepts of the ＂DOF of general link group＂ and ＂node parameters＂, a new formula in the calculation of the mobility of mechanisms is presented that is expressed with DOFs of the general link groups and rank of motion parameters of base point of the output link. It is named GOM（mobility of groups and output parameter） formula. On the basis of new concepts of＂effective parameters＂ and ＂invalid parameters＂, a rule is put forward for solving the DOF of mechanisms with invalid parameters by GOM formula, that is, the base point parameters are the subset of effective parameters of link group. Thereafter, several examples are enumerated and the results coincide with the prototype data, which proves the validity of the proposed formula. Meanwhile, it is obtained that the necessary and sufficient condition for the judgment of output parameters independence is that each of the DOF of the link group is not less than zero. The proposed formula which is simple in calculation provides theoretical basis for the judgment of independence of output parameters and provides references for type synthesis of novel parallel mechanisms with independence requirements of their output parameters.

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。

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.

Determination of the workspace of a new coordinate-measuring machine using parallel-link mechanism

Presents the detailed algorithm established for determination of workspace for a 3-DOF coordinate measuring machine using parallel link mechanism by constructing the inverse kinematic model first and then reviewing the physical and kinematical constraints from the structural characteristics of the parallel link mechanism, and discusses the actual geometries of workspace and the factors having effect on workspace through computer simulation thereby providing necessary theoretical basis for the research and development of coordinate measuring machines using parallel link mechanism.

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。

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.

INCREASING PROPERTY OF SPECTRUM IN THE VIBRATIONS OF A CYCLIC CHAIN OF MASSES DISTRIBUTED ACCORDING TO THE GTM SEQUENCE

Generalized Thue-Morse sequences were introduced into the vibrational problem of a chain of masses linked by springs of constant strength, and the increasing property of spectrum of linear operator about the vibrational model was proved.

Topological Configuration and Rotation Analysis of the Three⁃Order Rubik􀆳s Cube

The mechanism of three⁃order Rubik􀆳s Cube(RC)has the characteristics of recombination and variable degree of freedom,and it is difficult to accurately describe the degree of its freedom.This paper takes RC as the research object,and the adjacency matrix is constructed based on topology and graph theory in order to describe the variation rule of topological configuration in the single layer rotation of RC.In this paper,the degree of freedom of the RC in any shape can be described by defining the concept of entanglement degree of freedom,establishing a set of adjacency matrix,and determining the degree of freedom of the RC which is attributed to the number of non⁃zero elements in the set of adjacent matrix.The prime number is proposed to describe the rotation of the RC combined with the rotation recognition of RC,which is simple and convenient for computer processing.The research contents in this paper are beneficial to the study of RC from the perspective of mechanism science.Meanwhile,it is of great significance to the study of other complex mechanisms with variable degrees of freedom.

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。

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。

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.

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.

并联坐标测量机研究进展

并联机构具有刚度大、承载力强、动力性能好、支链间误差平均效应等优势,在机器人、机床、微动器件等领域得到了广泛应用。然而,传统直角式坐标测量机和关节式坐标测量机采用串联结构,存在误差累积的固有缺陷。鉴于并联机构具有的互补优势,近二十年来并联坐标测量机得到了快速的发展。结合国内外技术现状和团队的研究成果,对并联坐标测量机机构学、运动学、动力学、机构性能和控制策略等方面进行了系统的回顾和分析,总结了目前并联坐标测量机研究中存在的主要问题,提出了进一步的解决方法与思路,并展望了未来的发展趋势。

3-DOF转动柔索驱动风洞机构的力雅可比矩阵

简要概述了柔索牵引并联机器人在国内外的研究和发展现状,提出一种新颖的基于5根柔索牵引并联机器人的三自由度转动角度机构及测力一体化风洞试验装置。应用并联机构基本理论研究了机构的运动学逆解。依据空间解析几何理论,直接推导出在各柔索安装单分量力传感器时模型的感、测力变换雅可比矩阵。最后给出了数值算例,验证了该装置应用于风洞测力试验的有效性,为该测力装置应用于风洞试验奠定了基础。

双模式可重构并联机构的构型及其在酒盒产线中的应用

目的为实现酒盒生产线上酒盒胶线点胶和酒盒底座清废环节的自动化,提出一种双模式可重构并联机构。方法基于螺旋理论分析该机构在2种模式下的自由度,利用闭环矢量法和D-H法求得对应模式下的位置逆解,采用数值法求解机构工作空间、灵巧度和转动能力指标,给出该机构的应用实例。结果该机构在2-URU/RRC模式下具有3T自由度,2-URU/URC模式下具有3T1R自由度,工作空间连续且无空洞,获得2-URU/RRC模式下灵巧度指标分布规律和2-URU/URC模式下动平台转动能力。结论该机构在2-URU/RRC模式下可满足胶线点胶作业需求,在2-URU/URC模式下可满足底座清废作业需求,提高了酒盒生产线自动化程度。

基于ADAMS六自由度矿用液压机械臂的动力学仿真

为保障煤矿井下运输安全,减少井下人工搬运,进一步提升搬运机器人的井下运输效率至关重要。针对该现状提出一个具有六自由度液压机械臂的搬运机器人机械结构设计方案。利用SolidWorks软件建立液压机械臂的仿真模型,并采用ADAMS软件对机械臂关节角速度进行动力学仿真,最后进行计算对比。由仿真结果总结得出该方案机械臂结构设计具有合理性。