6-PSS并联机器人操作机平动工作空间解析

提出一种求解6-PSS并联机器人操作机平动工作空 间 边界的解析方法．该方法将平动工作空间问题归结为三类子空间边界求交问题,即分别由六 张球面片交集构成的上、下边界与由六张椭圆柱面交集构成的侧面边界的求交问题．文中还 提出主工作空间的概念和相应的解析表达及工作空间评价指标,并探讨了设计参数对评价指 标的影响规律．     

基于Metropolis遗传算法的并联机器人结构优化设计

以六自由度Stewart并联机器人的灵巧度为目标函数，以设计空间、每条支腿的最大最小长度之比和虎克铰、球铰的极限摆角为约束条件建立了结构优化模型．将模拟退火算法中的Metropolis准则引入到实值编码遗传算法的选择操作中，产生了Metropolis遗传算法，采用该算法进行了并联机器人结构优化问题的求解．通过与采用标准遗传算法得出的结果比较，证实了Metropolis遗传算法在并联机器人结构优化设计中的有效性和优越性．     

基于Simulink的Stewart平台仿真研究

Stewart平台是一种6自由度的并联机器人机构，该文介绍了基于Simulink的SimMechanics模块集对Stewart平台进行仿真研究的方法，在具体分析SimMechanics模块集中各模块的使用及参数设置方法的基础上，运用该模块集对Stewart平台进行了建模。既便于使用SimMechanics模块集建立其他复杂机械系统的模型，又利于对Stewart平台进行深入研究。最后针对某Stewart平台的轨迹跟踪问题进行了仿真研究，获得了满意的结果。     

新型6-HTRT并联机器人工作空间和参数研究

本文介绍了新型6-HTRT并联机器人的机构型式和工作原理，给出了考虑到约束条件的 位置逆解算法和存在多组解时的逆解选取准则．利用逆解算法和三维搜索，得到了确定该类 型机器人工作空间的方法和工作空间体积的计算公式．分析了6-HTRT并联机器人工作空间 的形态特点以及机器人结构参数和运动参数对工作空间体积的影响．     

基于蚁群算法的并联机器人误差补偿方法

提出一种利用蚊群算法补偿Stewart并联机器人位姿误差的方法.基于闭环矢量法建立Stewart并联机器人位姿误差模趔,通过6个驱动杆的长度误差和铰链误差得到并联机器人的位姿误差.在位姿误差模型的基础上,利用基于网格划分策略的连续蚁群算法,通过信息素更新指导蚂蚁反复搜索,对驱动杆杆长误差进行寻优,最终补偿Stewart...     

面向精密调整的6-HTRT并联机器人

为实现光学精密调整,研制出了由交流伺服电机驱动的6-HTRT并联机器人,它具有6个自由度,其结构特点决定了该机器人可以完成高精度定位调整。分析了机器人的位置逆解,并对不同位姿下的工作空间进行了仿真。控制系统采用基于ISA总线的闭环控制方式,测试结果显示:该并联机器人工作空间较大、分辨率高、重复定位精度高,说明机器人结构和控制系统设计的合理性。最后应用此并联机器人成功完成了光学精密装配试验。     

采用SG平滑滤波的Stewart平台主从控制研究

针对并联机器人在未知环境,特别是危险环境中的路径规划难的问题,采用一种相同自由度下的主从控制方式实现并联机器人遥操作。为实现对机器人的控制,运用机构几何学方法对经典Stewart并联平台进行运动学分析,获得平台的运动学反解模型以及工作空间范围。以SpaceMouse通用3D鼠标作为控制主手,采用增量式映射方式,建立了Stewart平台的主从控制模型。考虑到主手存在由于人手抖动导致的控制不平滑问题,采用Savitzky-Golay(SG)平滑滤波法进行处理。通过对SG平滑滤波方法进行原理分析以及仿真试验,验证了该方法具有较好的平滑效果。基于Ethercat和Ethernet技术,组建了相应试验平台。试验结果表明,从手跟随主手运动最大延时约为40 ms。由此可知,该方法具有良好的实时性和平滑度,可以为并联机器人的实际应用提供参考。     

工业用并联机器人位置正解的精确求解

利用工业用6-DOF并联机器人位置反解易于获得这一特性,把较难的六自由度并联机器人位置正解问题转化为应用位置反解结果作为训练样本进行学习,从而实现机械手从关节变量空间到工作变量空间的非线性映射。文中以工业用6-DOF并联机器人为例,采用BP算法对其正解进行了求解,并利用Matlab进行仿真,结果表明该方法计算精度高,克服了数值解法的求解精度受初值影响较大的缺点。经过验证,BP网络的求解精度满足了控制精确的要求。     

巨型柔性Stewart平台解空间的研究

本文针对大型射电天文望远镜FAST中馈源系统的柔索结构及运动要求，提出了巨型柔 性Stewart平台的概念，并由馈源舱的非线性静平衡方程给出了解空间的定义．通过计算发 现六悬索巨型柔性Stewart平台的工作空间中存在六个解空间为零的面，不能保证馈源舱连 续平稳地做空间扫描．在综合考虑馈源舱运行规律及悬索受力特点的基础上，本文通过增加 两根向下拉的冗余悬索，设计了八悬索巨型柔性Stewart平台．计算结果表明八悬索巨型柔 性Stewart平台消除了解空间为零的位置，为大型射电天文望远镜FAST中采用八悬索而不是 六悬索巨型柔性Stewart平台提供理论基础和数值依据．     

Stewart并联机器人力敏感性分析及实验验证

研究了Stewart并联机器人的人机交互安全性问题．首先建立机器人的静力学方程,提取关节力敏感度和关节力敏感方向指标,度量关节力对操作力的感知敏感性．采用解析法和数值法结合的方法求算关节全局力敏感度．接着分析关节力敏感度在笛卡儿工作空间和位姿工作空间中的分布,以及构型参数对关节全局和局部力敏感度的影响．然后通过限制工作空间和调节末端执行器在工作过程中的位姿,在设计阶段合理选取构型参数,改善关节力敏感度的方法提高人机交互安全性．最后通过实验测试证明了,关节力敏感度能有效度量关节对交互力的敏感性,末端执行器的位置和姿态能直接改变关节力敏感度．     

Dimensional optimization of 6-DOF 3-CCC type asymmetric parallel manipulator

In this paper, dimensional optimization of a six-degrees-of-freedom (DOF) 3-CCC (C: cylindrical joint) type asymmetric parallel manipulator (APM) is performed by using particle swarm optimization (PSO). The 3-CCC APM constructed by defining three angle and three distance constraints between base and moving platforms is a member of 3D3A generalized Stewart–Gough platform (GSP) type parallel manipulators. The dimensional optimization purposes to find the optimum limb lengths, lengths of line segments on the base and moving platforms, attachment points of the line segments on the base platform, the orientation angles of the moving platform, and position of the end-effector in the reachable workspace in order to maximize the translational and orientational dexterous workspaces of the 3-CCC APM, separately. The dexterous workspaces are obtained by applying condition number and minimum singular values of the Jacobian matrix. The optimization results are compared with the traditional GSP manipulator for illustrating the kinematic performance of 3-CCC APM. Optimizations show that 3-CCC APM have superior dexterous workspace characteristics than the traditional GSP manipulator.     

The synthesis of planar parallel manipulators with prismatic joints for an optimal,singularity‐free workspace

The synthesis of three‐degree‐of‐freedom planar parallel manipulators is performed using a genetic algorithm. The architecture of a manipulator and its position and orientation with respect to a prescribed workspace are determined. The architectural parameters are optimized so that the manipulator's constant‐orientation workspace is as close as possible to a prescribed workspace. The manipulator's workspace is discretized and its dexterity is computed as a global property of the manipulator. An analytical expression of the singularity loci (local null dexterity) can be obtained from the Jacobian matrix determinant, and its intersection with the manipulator's workspace may be verified and avoided. Results are shown for different conditions. First, the manipulators' workspaces are optimized for a prescribed workspace, without considering whether the singularity loci intersect it or not. Then the same type of optimization is performed, taking intersections with the singularity loci into account. In the following results, the optimization of the manipulator's dexterity is also included in an objective function, along with the workspace optimization and the avoidance of singularity loci. Results show that the end‐effector's location has a significant effect on the manipulator's dexterity. © 2002 John Wiley & Sons, Inc.     

Software Tool to Compute,Analyze and Visualize Workspaces of Parallel Kinematics Robots

The aim of this paper is to present a new software tool designed to compute and allow visualization of the different types of workspaces of parallel manipulators in the most user-friendly and efficient way. The graphical interface of this program makes it possible to define the geometrical scheme of the robot. All required parameters of the kinematic model can be set easily and quickly. Given that the workspace of a parallel manipulator is a complex entity, this CAD tool has implemented all the controls needed to visually define all the complicated parameters required to launch a workspace computation. Once the calculations are performed, the challenging task of visualizing the results has been optimized. Due to the circumstance that a workspace can be a higher than three-dimensional (3-D) mathematical entity, which cannot be graphically represented, the user can choose the specific variables (two or three) onto which to project the workspace obtained (2-D or 3-D representations). Within these surfaces and volumes, several color maps, associated with kinematic indicators, can be traced to enable the most efficient path planning of the manipulator analyzed.     

Singularity analysis and detection of 6-UCU parallel manipulator

6-UCU kind Gough–Stewart platform (GSP) has been used extensively in practice. The singularity of GSP has been studied by many scholars, but their works mainly focused on finding the methods to divide the cases of singularity or searching the solutions with Jacobian matrices. On the other hand, this paper studies the singularities of 6-UCU parallel manipulator caused by not only the active joints but also passive universal joints. Two types of singularity are derived based on a degree of freedom method by using screw theory. Singularity detection is essential to certify the absence of singularity within a prescribed workspace or a reachable workspace for a practical use of the 6-UCU parallel manipulator. Algorithms are proposed by using evolutionary strategy to detect the singularity in the desired or reachable workspace of the 6-UCU parallel manipulator. Case studies are presented to demonstrate the effectiveness of the proposed singularity detection methods.     

Dexterous Workspace Optimization of a Tricept Parallel Manipulator

The growing interest in the use of parallel manipulators in machining applications requires clear determination of the workspace and dexterity. In this paper, the workspace optimization of a Tricept parallel manipulator under joint constraints is performed. This parallel manipulator has complex degrees of freedom and, therefore, leads to dimensionally inhomogeneous Jacobian matrices. Here, we divide the Jacobian entries by units of length, thereby producing a new Jacobian that is dimensionally homogeneous. By multiplying the associated entries of the twist array to the same length, we made this array homogeneous as well. The workspace of the manipulator is parameterized using several design parameters and is optimized using a genetic algorithm. For the workspace of the manipulator, local conditioning indices and minimum singular values are calculated. For the optimal design, it is shown that by introducing the local conditioning indices and minimum singular values, the quality of the parallel manipulator is improved at the cost of workspace reduction.     

Robotic Workspaces after a Free-Swinging Failure

A robotic manipulator can fail in many different ways, and its capabilities after a failure are a major concern, especially for manipulators used in hazardous and remote environments, where the cost of repair or replacement is high. This article presents a study of the workspaces of robotic arms after a free-swinging failure, defined as a hardware or software failure that prevents the application of actuator torque on a joint. Two analytical methods are discussed. The first is for planar arms only and is based on a positional inverse-kinematic algorithm that uses polynomial roots, guaranteeing that all solutions, and therefore the postfailure workspace, can be found. The second method has no such guarantee, but is applicable to general spatial manipulators. It is based on a differential technique for tracing the postfailure workspace boundary.     

Kinematic analysis of a 3-PRS parallel manipulator

Although the current 3-PRS parallel manipulators have different methods on the arrangement of actuators, they may be considered as the same kind of mechanism since they can be treated with the same kinematic algorithm. A 3-PRS parallel manipulator with adjustable layout angle of actuators has been proposed in this paper. The key issues of how the kinematic characteristics in terms of workspace and dexterity vary with differences in the arrangement of actuators are investigated in detail. The mobility of the manipulator is analyzed by resorting to reciprocal screw theory. Then the inverse, forward, and velocity kinematics problems are solved, which can be applied to a 3-PRS parallel manipulator regardless of the arrangement of actuators. The reachable workspace features and dexterity characteristics including kinematic manipulability and global dexterity index are derived by the changing of layout angle of actuators. Simulation results illustrate that different tasks should be taken into consideration when the layout angles of actuators of a 3-PRS parallel manipulator are designed.     

Method for kinematic calibration of stewart platforms

A Stewart platform is a six degrees of freedom parallel manipulator composed of six variable-length legs connecting a fixed base to a movable plate. Like all parallel manipulators, Stewart platforms offer high force/torque capability and high structural rigidity in exchange for small workspace and reduced dexterity. Because the solution for parallel manipulators' forward kinematics is in general much harder than their inverse kinematics, a typical control strategy for such manipulators is to specify the plate's pose in world coordinates and then solve the individual leg lengths. The accuracy of the robot critically depends on accurate knowledge of the device's kinematic parameters. This article focuses on the accuracy improvement of Stewart platforms by means of calibration. Calibration of Stewart platforms consists of construction of a kinematic model, measurement of the position and orientation of the platform in a reference coordinate frame, identification of the kinematic parameters, and accuracy compensation. A measurement procedure proposed in this article allows a great simplification of the kinematic identification. The idea is to keep the length of the particular leg, whose parameters are to be identified, fixed while the other legs change their lengths during the measurement phase. By that, redundant parameters can be eliminated systematically in the identification phase. The method also shows the estimation of each leg's parameters separately because the measurement equations are fully decoupled, which results in a drastical reduction of the computational effort in the parameter identification. Simulation results assess the performance of the proposed approach. © 1993 John Wiley & Sons, Inc.     

On the dynamic model and kinematic analysis of a class of Stewart platforms

In this paper, a dynamic model for a class of Stewart platform (six degrees of freedom parallel link robotic manipulators) is derived by using tensor representation. A set of six Lagrange's equations are obtained. The kinematics analysis for a class of Stewart platform is conducted and a sixteenth order polynomial equation corresponding to the forward kinematic solution of the Stewart platform is obtained, which gives all possible global solutions of a manipulator configuration for a given set of six leg lengths.