并联机构不同正解间无奇异转换问题探讨

并联机构的正解具有多解性，以一种平面三自由度并联机构为例，研究了不同正解之间的无奇异连接路径问题．结合Innocenti发现的第一条无奇异路径，采用基于奇异曲面的图形化方法分析了正解构型在工作空间中的分布．发现了两个正解间的多条类似路径，这些路径形成了连接两个正解位形的近似于螺旋状的管道空间．首次发现了在其它的正解之间也存在着这样的非奇异路径．这些结果表明并联机构的奇异曲面及正解分布异常复杂，如果两个正解对应的雅可比矩阵行列式值异号，则一定不存在无奇异路径；如果同号，则还要根据奇异曲面来定．两个正解构型间无奇异路径的判定还最终依赖于对奇异曲面更为清楚的描述．     

基于性能驱动的船载稳定平台尺度参数优化设计

为提升船载稳定平台的运动学性能,针对■并联机构的尺度参数优化问题,以机构的工作空间体积和全域力传递率为综合评价指标,采用小生境遗传算法优化得到稳定平台的最佳几何构形。具体地,采用数值法与解析法相结合的方式判断支链长度、关节转角、奇异位形等约束条件的生效情况,求解出并联稳定平台的工作空间;基于力雅可比矩阵逆矩阵的最小奇异值定义机构的局部力传递性能,以工作空间内局部力传递率的平均值作为全域力传递性能评价指标;以工作空间体积和全域力传递率的加权和为优化目标,采用小生境自适应遗传算法完成优化求解,获得最优尺度参数。与初始构形的性能对比分析表明,优化构形在力传递性能方面有35%的提升,具有更好的综合运动学性能。制作试验样机并完成相关实验,验证了所提尺度参数优化方法的有效性。最后探讨了多目标优化过程中不同的权重系数取值对优化结果的作用规律,发现选用均衡的权重可获得更佳的综合性能。     

三自由度手指机构分析及其优化设计

本文引进工作空间和可达空间来描述多关节柔性手指机构的工作范围.采用空间解析几何法,推导出空间3R手指机构工作空间的体积和奇异面的面积,提出手指机构工作姿态最佳的评价方法并推出其与工作空间体积最大的等价关系。分析手指机构各向同性点存在条件并作为优化设计的约束函数、以A3型手指机构的工作空间容积比最大、位置奇异而密度比最小和工作姿态最佳作为优化目标进行数值计算.     

3-RRRT并联机器人位置正向求解研究

研究一种3-RRRT型并联机器人机构的运动学正向求解方法。根据3-RRRT型并联机器人机构特点以及关节运动的取值范围，提出了以并联机器人支链中支杆的方向余弦和动平台绝对位置坐标为系统的广义坐标的方法，并详细地推导了3-RRRT型并联机器人运动学模型，通过进一步消除中间变量的方法最终获得了易于正、逆运动学求解的只包含3个驱动关节坐标与动平台3个绝对位置坐标的约束方程组。最后，运用基于Moore—Penwse广义逆的牛顿迭代格式编制了MATLAB运动学正向求解程序，并进行了运动学正向求解数值仿真，结果表明求解程序快速有效。     

机器人工作空间的界限面及其位置奇异曲面的代数求解方法

本文提出了一个求解运动副转角或移动有限制的任意机械手的工作空间界限面及其位置奇异曲面的代数方法。得出了手部参考点在固定坐标系中的一系列位置奇异曲面方程。并以5R,6R和5R-P机器人为例,使用计算机绘制出其工作空间上述各种曲面的子午截面曲线图。结果与其它方法相比,具有精度高,运算快的特点,不仅具有理论意义,而且还有实用价值。     

基于3-UPS/RRR的并联踝关节康复机构及其性能分析

基于踝关节的生理解剖结构和运动特性分析,提出了一种适用于踝关节康复的3自由度3-UPS/RRR并联机构.该机构采用三个主动支链倾斜布置避开了机构的奇异位形,能满足踝关节康复运动需要,同时约束支链和动平台的设计使机构的转动中心与患者的踝关节转动中心重合.应用解析法得到了机构的位置反解,建立了速度雅可比矩阵和静力雅可比矩阵,求解了机构的工作空间.基于雅可比矩阵,仿真分析了机构的运动学性能和静力学性能.结果表明在规定的工作空间内机构具有良好的可操作性、运动灵活性、刚度特性和力矩传递性能.最后运用牛顿-欧拉法建立了机构的逆动力学方程,得到了驱动力、约束力与运动参数的关系,并给出了仿真实例.     

六自由度并联机器人的支链选取

提出了六自由度并联机器人的支链选取的系统方法． 并联机器人中有多种类型的支链可以用来实现末端执行器的6自由度运动， 每个支链的驱动关节应当在基座上或靠近基座的地方， 由支链所构成的整个并联机构的自由度应当为6．利用这些条件对并联机器人的支链形式进行筛选可以获得可行的支链形式． 通过这种方法可以去除很多不可行的支链形式, 得到可行的支链形式供后续设计使用．     

基于锚球交域投影质心的WSNs三维定位算法

针对无线传感器网络(WSNs)在三维空间的应用场景中,基于质心算法提出了一种基于锚球交汇区域投影质心的WSNs三维定位算法。该算法通过求得锚球空间交汇区域在XOY平面和YOZ平面的投影的质心,从而确定未知节点可能的空间坐标。算法将三维空间位置求解问题通过投影的方法转换成二维平面位置问题求解降低了算法的计算量,锚球在平面上的投影为与锚球同心同半径的圆。因此,通过计算投影区域质心可以得到高精度的未知节点的空间坐标。理论分析与仿真实验结果均表明:该算法具有计算量小、定位精度高、稳定性好等特性。     

求解并联机床工作空间的算法分析和研究

本文针对三自由度并联机床的机构进行了分析，并求出了其位置逆解。在此基础上对求解其工作空间所采用的算法进行了研究和分析，重点给出了边界搜索法的设计方法，并进行了相关算法的分析。结果表明，在机构没有空洞的情况下，边界搜索法是一种理想的求解工作空间的算法     

4-RP(RR)R并联机器人运动仿真

该文给出一个新型的少自由度并联机器人机构4-RP（RR）R的动态仿真。文中对此机构进行了反解分析,确立了此机构运动平台的位置输出与移动副输入及各空间顶点位置的关系。在此基础上,利用Matlab软件模拟出实物动态图,并对利用几何分析法做出的速度曲线、加速度曲线与利用虚设影响系数法求出的速度曲线、加速度曲线进行分析比较,进一步说明了机构本身的运动特性,以及虚设影响系数法对少自由度并联机器人机构4-RP（RR）R求解的正确性。     

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.     

Analysis of the wrench-closure workspace of planar parallel cable-driven mechanisms

The mobile platform of a parallel cable-driven mechanism is connected in parallel to a base by lightweight links, such as cables. Since the cables can only work in tension, the set of poses of the mobile platform for which the cables can balance any external wrench, i.e., for which the platform of the mechanism is fully constrained, is often limited or even nonexistent. Thus, the study and determination of this set of poses, called the wrench-closure workspace (WCW), is an important issue for parallel cable-driven mechanisms. In this paper, the case of planar parallel cable-driven mechanisms is addressed. Theorems that characterize the poses of the WCW are proposed. Then, these theorems are used to disclose the parts of the reachable workspace which belong to the WCW. Finally, an efficient algorithm that determines the constant-orientation cross-sections of these parts is introduced.     

Enlarging parallel robot workspace through Type-2 singularity crossing

In order to increase the reachable workspace of parallel robots, a promising solution consists of the definition of optimal trajectories that ensure the non-degeneracy of the dynamic model in the Type 2 (or parallel) singularity. However, this assumes that the control law can perfectly track the desired trajectory, which is impossible due to modeling errors.This paper proposes a robust multi-model approach allowing parallel robots to cross Type 2 singularities. The main idea is to shift near singularities to a simplified dynamic model that can never degenerate. The two main contributions are the definition of an optimal trajectory crossing Type 2 singularities and the multi-model control law allowing to track this trajectory. The proposed control law is validated experimentally through a Five-bar planar mechanism.     

基于参数优化的球面并联机构仿生眼设计

首先确定仿生眼的目标工作空间,根据其结构的特殊要求,将目标工作空间内最差性能指标作为优化 对象,选取球面并联机构的结构参数．避免了将平均性能指标作为优化对象时可能出现某些姿态的性能较差甚至出 现病态雅可比矩阵的情况;同时,只在目标工作空间而不是可达工作空间进行优化,既体现了优化范围的针对性, 也避免了可达工作空间的计算．最终采用优化后参数设计的仿生眼实物符合设计要求．     

Architecture Selection and Singularity Analysis of a Three-Degree-of-Freedom Planar Parallel Manipulator

A three degree-of-freedom planar parallel manipulator, intended for high-speed, high-precision wire-bonding and electronic-component placement tasks, has been developed in our laboratory. In this paper, the work related to the kinematic manipulator-architecture selection is presented. The reachable workspace and effective base area metrics of the parallel manipulator were utilized for selecting the best possible architecture amongst six potential configurations. Constant platform-orientation regions, within the reachable workspace of the selected manipulator, were identified based on the manipulator task requirements. Simulation results for the workspace analyses (reachable workspace, effective base areas, and constant-orientation regions) are presented in this paper. Once the optimal-workspace architecture was selected, both workspace-boundary and internal singularities were further investigated in order to have a clear view of the set of uncontrollable poses of the manipulator. Singularity analyses examples are also included herein.     

Adaptive end-effector pose control for tomato harvesting robots

This paper investigates the development of a tomato-harvesting robot operating on a plant factory and primarily studies the reachable pose of tomatoes in the nondexterous workspace of manipulator. The end-effector can only reach the tomatoes with reachable poses when the tomatoes are within the nondexterous workspace. If the grasping pose is not reachable, it will lead to grasping failure. An adaptive end-effector pose control method based on a genetic algorithm (GA) is proposed to find a reachable pose. The inverse kinematic solution based on analysis method of the manipulator is analyzed and the objective function of whether the manipulator has a solution or not is obtained. The grasping pose is set as an individual owing to the position of the tomatoes is fixed and the grasping pose is variable. The GA is used to solve until a pose that can make the inverse kinematics have a solution is generated. This pose is the reachable grasping pose of the tomato at this position. The quintic interpolation polynomial is used to plan the trajectory to avoid damage to tomatoes owing to fast approaching speed and a distance based background filtering method is proposed. Experiments were performed to verify the effectiveness of the proposed method. The radius of the workspace of the UR3e manipulator with the end-effector increased from 550 to 800 mm and the grasping range expanded by 208%. The harvesting success rate using the adaptive end-effector pose control method and trajectory planning method was 88%. The cycle of harvesting a tomato was 20 s. The experimental results indicated that the proposed tomato-recognition and end-effector pose control method are feasible and effective.     

Singularity loci of planar parallel manipulators with revolute actuators

The determination of the singularity loci of planar parallel manipulators is addressed in this paper. The inverse kinematics of two kinds of planar parallel manipulators (a two-degree-of-freedom manipulator and a three-degree-of-freedom manipulator) are first computed and their velocity equations are then derived. At the same time, the branches of the manipulators are distinguished by the introduction of a branch index K_i. Using the velocity equations, the singularity analysis of the manipulators is completed and expressions which represent the singularity of the manipulators are obtained. A polynomial form of the singularity loci is also derived. For the first type of singularity of parallel manipulators, the singularity locus is obtained by finding the workspace limits of the manipulators. For the second type of singularity, the loci are obtained through the solution of nonlinear algebraic equations obtained from the velocity analysis. Finally, the graphical representation of the complete singularity loci of the manipulators is illustrated with examples. The algorithm introduced in this paper allows the determination of the singularity loci of planar parallel manipulators with revolute actuators, which has been elusive to previous approaches.     

A unified algorithm to determine the reachable and dexterous workspace of parallel manipulators

This paper presents a novel idea for determining the reachable and dexterous workspace of parallel manipulators. Both the reachable workspace and dexterous workspace are utmost important for optimal design and performance comparison of manipulators, because each configuration or point in this region has specified kinematic dexterity by the designer. We propose a uniform algorithm, called stratified workspace boundary determining algorithm (SWBDA), which considers various physical and contrived constraints. The problems of determining the reachable and dexterous workspace boundaries are defined and the unified method is applied to solve all the problems of this kind. The validity and efficiency of the proposed method are verified with two kinds of representative parallel manipulator, since their relational results were studied in literatures. Finally, the advantages of the proposed method are summarized by comparing with other methods.     

The Synthesis of Three‐Degree‐of‐Freedom Planar Parallel Mechanisms with Revolute Joints (3‐RRR) for an Optimal Singularity‐Free Workspace

In this paper, a method is presented for the synthesis of 3‐R RR planar parallel mechanisms. The method uses a genetic algorithm while considering three different design criteria: the optimization of the mechanism workspace to approach a prescribed workspace, the maximization of the mechanism's dexterity, and the avoidance of singularities inside the mechanism workspace. It is shown that, for a given mechanism, some working modes do not have any corresponding singularity curves located inside the mechanism workspace. Furthermore, a case is presented where, for a given orientation range of the mechanism's end‐effector, there are no parallel singularities located inside the workspace. Finally, two methods are described and compared to deal with the nonuniform units of the mechanism's Jacobian matrix during the dexterity computation. © 2004 Wiley Periodicals, Inc.