Singularity analysis of 5-RPUR parallel mechanisms (3T2R)

Singularities of parallel mechanisms are related to the regularity of certain Jacobian matrices whose rank deficiency makes the mechanisms lose their inherent rigidity. This paper presents the results of a detailed investigation of the singular configurations of 5-degree-of-freedom parallel mechanisms performing all three translations and two independent rotations. The general architecture of the mechanism—arising from the type synthesis of symmetrical 5-degree-of-freedom parallel mechanisms—is comprised of a mobile platform attached to a base through five identical revolute–prismatic–universal revolute-jointed serial kinematic chains. From the results of screw theory, it is demonstrated that the Jacobian matrix of the above mechanism is constituted by six Plücker lines, a special case of Grassmann coordinates. This channels us to use the so-called Grassmann line geometry instead of applying a classical linear algebra approach. Grassmann line geometry can be regarded as a classification of the degeneration of the Plücker line set. Moreover, six simplified designs are proposed for which their singular configurations can be predicted by means of the Grassmann line geometry. The principles of this study can also be applied to other types of symmetrical 5-degree-of-freedom parallel mechanisms.     

A comprehensive analysis of a 3-P (Pa) S spatial parallel manipulator

In this paper, a novel 3-degree of freedom (3-DOF) spatial parallel kinematic machine (PKM) is analyzed. The manipulator owns three main motions (two rotations and one translation) and three concomitant motions (one rotation and two translations). At first, the structure of this spatial PKM is simplified according to the characteristic of each limb. Secondly, the kinematics model of this spatial PKM is set up. In addition, the relationship between the main motions and concomitant motions is studied. The workspaces respectively based on the outputs and inputs are derived and analyzed. Furthermore, the velocity model is put forward. Two indexes based on the velocity model are employed to investigate the performance of this spatial PKM. At last, the output error model can be obtained and simulated. The comprehensive kinematics analysis in this paper is greatly useful for the future applications of this spatial PKM.     

3SPS+1PS四自由度并联仿生平台运动学分析

针对3SPS+1PS对称型并联仿生平台,利用螺旋理论对其进行自由度分析得出该机构具有三转一平4个自由度,当平动自由度固定时可用于模拟人体髋关节的三维运动。基于四元数法建立了机构位姿运动方程。以四元数描述机构运动特性,避免了欧拉角描述刚体位姿存在的奇异问题。将髋关节运动曲线作为机构输出运动,基于逆运动学模型仿真出各驱动支链位移变化曲线为平滑曲线,说明该机构在模拟髋关节运动时其驱动支链易于控制。     

(2-UPS+U)&R串并混联机构工作空间分析

提出了一种新型串并混联机器人,该机器人腿部采用了3自由度(2-UPS+U)R串并混联机构,具有工作空间灵活、能耗低、地形适应性强等特点。同时还对(2-UPS+U)R串并混联机构的自由度进行了分析计算,求解了该机构的工作空间,验证了该机构工作时的灵活性。     

对称4自由度3R1T并联机构雅可比分析

针对对称4自由度3RIT并联机构提出一种雅可比分析方法.首先运用位移群理论分析3RIT并联机构的自由度特性,得到动平台在空间的运动为四维位移流形,然后运用螺旋理论建立单个分支运动链的雅可比矩阵,该矩阵为6×5长方阵:再利用该类并联机构的自由度特性证明6×5的分支雅可比矩阵的第四行和第五行为冗余元素,删除其中之一则可把分支雅可比矩阵简化为5×5方阵,该方阵在机构非奇异位形下满秩.在选定并联机构的驱动副后,对每个分支简化后的5×5雅可比方阵求逆,再分别取出逆阵中对应于驱动副的行矢量构成一个4×5长方阵,由于该长方阵的第四列元素始终与0相乘为冗余信息,删除该列元素后得到一个4×4可逆方阵,对之求逆即得整个4自由度3RIT并联机构的雅可比矩阵.该方法简捷易行,可进一步应用于3R1T并联机构的性能分析和运动学设计.     

Forward kinematic problem of 5-RPUR parallel mechanisms (3T2R) with identical limb structures

This paper investigates the formulation of the forward kinematic problem of the 5-DOF parallel mechanisms performing three translation and two independent rotations with identical limb structures. The mathematical framework used in this paper is based on algebraic geometry where the forward kinematic problem is explored in a seven-dimensional kinematic space by the means of the so-called Study parameters. In this paper, the algorithms proposed for obtaining the forward kinematic expression is based on two approaches which differ by their concept of eliminating passive variables. The first one is based on the application of the so-called resultant method and the second one, as a novel approach referred to as linear implicitization algorithm, uses an elimination procedure based on solving several systems of linear equations. The forward kinematic problem is solved using the homotopy continuation and it is revealed that it has 1680 finite solutions. Moreover, the forward kinematic problem is studied in three-dimensional Euclidean space where a class of simplified designs are proposed which admit a simpler formulation for the forward kinematic problem. Finally, based on the simplified designs, for a nearly general design a univariate expression of degree 220 is obtained.     

Synthesis of branched chains with actuation redundancy for eliminating interior singularities of 3T1R parallel mechanisms

Although it is common to eliminate the singularity of parallel mechanism by adding the branched chain with actuation redundancy, there is no theory and method for the configuration synthesis of the branched chain with actuation redundancy in parallel mechanism. Branched chains with actuation redundancy are synthesized for eliminating interior singularity of 3-translational and 1- rotational(3T1R) parallel mechanisms. Guided by the discriminance method of hybrid screw group according to Grassmann line geometry, all the possibilities are listed for the occurrence of interior singularities in 3T1R parallel mechanism. Based on the linear relevance of screw system and the principles of eliminating parallel mechanism singularity with actuation redundancy, different types of branched chains with actuation redundancy are synthesized systematically to indicate the layout and the number of the branched chainsinterior with actuation redundancy. A general method is proposed for the configuration synthesis of the branched chains with actuation redundancy of the redundant parallel mechanism, and it builds a solid foundation for the subsequent performance optimization of the redundant actuation parallel mechanism.     

一种新型半对称三平移一转动(3T1R)并联操作手的运动学研究

基于方位特征(POC)方程的并联机构拓扑结构设计理论与方法,提出了一种能实现三平移一转动(3T1R)的2RRPaR+2RSS并联操作手机构.对该机构进行了结构特性分析,计算了其自由度及POC集,并得出其耦合度为2;依据该机构的结构特性及几何约束条件,采用二维搜索法对该机构的位置正解进行了求解,推导出了其位置逆解,并验证...     

基于PSO-SVM的3SPS+1PS并联髋关节试验机正运动学研究

为了克服传统髋关节试验机在模拟复杂运动轨迹和变载荷动力加载时存在的不足,提出一种以3SPS+1PS并联机构为核心运动模块的髋关节试验机。该试验机有三个转动和一个移动自由度。该试验机的位置正解是其应用的前提,采用粒子群优化(PSO)的支持向量机(SVM),利用位姿逆解结果,通过训练学习,建立正运动学求解模型,进而求得该髋关节试验机的运动学正解。数值仿真结果表明,粒子群优化的支持向量机求解该试验机正运动学的精度满足精确控制的要求。     

A systematic approach to identify the error motion of anN-degree of freedom manipulator

A generalised calibration technique for identifying the joint geometric parameters of an N-degrees-of-freedom (d.o.f.) robot manipulator model is presented. The technique is analogous to the synthesising calibration method applied in the calibration of coordinate measuring, machines. It describes the state of each joint by six d.o.f. and assumes rigid-body motion. The initial step in the calibration involves locating the axis of motion of each joint; the axes are then used to extract the kinematic parameters, introduced by Denavit-Hartenberg (D-H). In order to derive the generalised manipulator kinematic equation, the robot model is modified to include the six error motion components associated with each axis. The paper also addresses the problem of identifying the error motion components of each joint, on the basis of a set of measurement of three noncollinear points at the robot end-effector at various joint configurations. Because the technique is based on axis-by-axis calibration, other non-geometric errors such as joint backlash and gear transmission error may also be revealed.     

一种用于球面阵T/ R 组件安装的新型支架

大型球面相控阵雷达安装的T/R组件数量众多,所用线缆数量更是T/R组件的数倍,导致雷达总体制造成本居高不下。为了降低雷达的总体成本,文中设计了一种用于球面相控阵雷达T/R组件安装的新型支架,并通过3D软件对新型T/R组件支架进行了仿真设计。新型支架能够很好地解决球面相控阵雷达T/R组件安装复杂、走线困难的问题,能有效降低结构加工成本和电缆成本,对后续工程实施有很大的启发。文中首先介绍了相控阵雷达的发展现状和面临的成本问题以及传统T/R组件支架存在的安装问题,然后阐述了新型T/R组件支架的组成和优势,最后探讨了球面相控阵雷达的发展趋势。     

基于单开链单元的三平移一转动并联机器人机构型综合及分类

以单开链支路为单元,揭示了欠秩并联机器人机构结构组成的某些规律,提出了输出运动为三平移及一定向转动的并联机器人机构型综合的一种系统,有效的新方法,型综合共得到50个新机构,并对其进行了分类,提出的4d.o.f,并联机器人机构型综合方法具有普遍性意义,并已用于其它运动输出类型的欠秩并联机器人机构的型综合。     

Simulation solving/modifying velocity and acceleration of a 4UPS+SPR type parallel machine tool during normal machining of a 3D free-form surface

A CAD variation geometry approach is proposed for solving/modifying the inverse velocity/acceleration of the active legs and the forward velocity/acceleration of a 5-dof 4UPS + SPR parallel machine tool (PMT) during its simulation normal machining of a 3D free-form surface. First, the twin simulation mechanisms of this PMT with the same base are created for normal machining the same 3D free-form surface. Second, a velocity simulation mechanism of this PMT is created from the twin simulation mechanisms. Third, an acceleration simulation mechanism of this PMT is created from the three similar simulation mechanisms with the same base. Finally, the extension, the velocity and acceleration of the active legs, and the velocity and acceleration of the PMT are solved and modified during the simulation normal machining of the 3D free-form surface. The simulation solutions are verified by an analytic approach.     

NEURON(○R)3150TM芯片与串行数模/模数转换器的接口设计

基于NEURON○R 3150TM神经元芯片的LONWORKS现场总线技术已广泛应用于各个领域,为开发新型LONWORKS智能节点,满足不同应用需求,这里介绍NEURON○R 3150TM神经元芯片与串行数模/模数转换器(TLC5615C/TLC2543C)的接口方法     

加氢反应器用3Cr-1Mo-1/4V-Ti-B钢的回火脆化研究

本文对加氢反应器用３Ｃｒ－１Ｍｏ－１／４Ｖ－Ｔｉ－Ｂ钢母材与焊缝金属的化学成分,力学脆性转变温度进行了测定,结果表明该材料与常Ｃｒ－Ｍｏ相比其综合性能优越,抗回火脆化性能好,能满足高温高压大型热壁加氢反应器制造要求。     

A simple approach to the determination of the crystallographic orientation: applications and accuracy

A simple analytical solution for the crystallographic orientation is described. This method is based on one indexed Kikuchi pair in a known zone rather than the corresponding diffraction spots. The accuracy of this method is shown to be better than 0.1° even for cases in which a zone axis deviates by a large angle (e.g. 10°) from the centre of the beam direction. This approach simplifies experiments beacuse only one pair of Kikuchi lines and a zone axis are needed, and is especially suited when it is difficult or cumbersome to resolve a second pair of Kikuchi lines with sufficient accuracy.     

高效液相色谱-大气压化学电离串联质谱法研究4-(甲基亚硝胺基)-1-(3-吡啶基)-1-丁酮体外模拟代谢作用

烟草特异亚硝胺4-(甲基亚硝胺基)-1-(3-吡啶基)-1-丁酮(NNK)是一种存在于烟草烟气及烟草制品中的强致癌物,其致癌机理是通过细胞色素P450酶的代谢活化生成活泼亲电试剂,导致DNA损伤,因此,建立NNK体外模拟代谢产物的定量分析方法对于研究烟草致癌物具有重要意义。本实验利用高效液相色谱-大气压化学电离串联质谱法（HPLC-APCI-MS/MS）对NNK代谢产物4-羟基-1-(3-吡啶基)-1-丁酮(HPB)进行定量分析。使用选择反应扫描（SRM）模式监测了HPB和内标[3,3,4,4-D₄]HPB,分析方法在0.2~400 nmol/L范围内线性关系良好,线性相关系数R²=0.999 9,检出限(LOD)为0.025 nmol/L (S/N=3),定量限(LOQ)为0.05 nmol/L(S/N=10)。方法的日内和日间准确度为96.6%~101.8%,回收率为98.1%~102.6%。所建立的NNK体外模拟代谢模型可用于烟草特异亚硝胺代谢活化分子机制的研究,为定量分析吸烟致癌相关生物标志物奠定基础。     

MELLT3 protects against cerebral ischemia-reperfusion (I/R) injury through up-regulation of m6A modification

Ischemic cerebrovascular disease is a leading cause of death globally and is often exacerbated by cerebral ischemic/reperfusion injury (CIRI). The exact mechanisms underlying I/R injury are unclear. In this study, we aimed to determine the role of m⁶A-modified methylase complex methyltransferase-like 3 (METTL3) in cerebral ischemia-reperfusion (I/R) injury. We found that m6A and METTL3 levels increased in OGD/RX-induced mouse astrocytes-cerebellar (MA-C) and the brain of middle cerebral artery occlusion (MCAO) model mice. METTL3 siRNA treatment reduced OGD-RX-induced MAC cell viability and proliferation, which increased with METTL3 over-expression. Flow cytometry analysis showed that silencing METTL3 significantly enhanced OGD/RX-induced MAC apoptosis, which was significantly reduced with METTL3 up-regulation. In an MCAO model, METTL3 overexpression significantly reduced cerebral infarction area and decreased brain cell apoptosis, indicating that METTL3 OE treatment could ameliorate brain edema and injury. Thus, METTL3 could be used as a target to treat I/R injury.