6自由度含弹簧被动支链的绳牵引并联机构工作空间分析

为分析含弹簧被动支链的绳牵引并联机构工作空间特性,建立机构静力学模型,提出一种能直观反映绳牵引并联机构姿态空间大小的评价指标,以含2根弹簧支链的6索6自由度绳牵引并联机构为例,分析弹簧支链参数对机构工作空间性能和工作空间形状的影响。针对引入弹簧支链后出现的工作空间形状缺陷,建立缺陷部分混合位置因子-范围因子罚函数模型,并通过理想点法与遗传算法结合的方法实现了机构工作空间性能多目标优化。结果表明：通过罚函数法在优化中有效消除了可能出现的机构工作空间形状缺陷;含弹簧支链的绳牵引并联机构优化中选择适当弹簧参数,可以显著提高工作空间体积与动平台转动范围。     

面向在轨装配的八索并联机构构型设计与工作空间分析

针对大型空间结构的在轨装配任务,提出了由八根绳索驱动的索并联机构,具有结构简单、质量轻、工作空间大的特点;针对绳索并联机构的构型综合问题,定义了出线点和绳索与中心执行器连接点的关联矩阵,在此基础上考虑约束条件综合出了八索并联机构的18种有效构型;计算了不同构型的力封闭工作空间以及针对在轨装配任务时的力螺旋可行工作空间,以工作空间体积为指标筛选出了最佳构型;分析了绳索拉力范围以及绳索与中心执行器连接点的位置变化对机构力螺旋可行工作空间的影响,并且对连接点的位置参数进行了优化。     

绳索驱动腕部并联康复机构设计与逆运动学分析

针对现有腕部康复机构运动范围小,存在柔顺性和舒适性差等问题,提出一种新型绳索驱动、压缩弹簧支撑的柔性并联腕部康复机构。机构定平台、动平台由三根绳索和压缩弹簧连接,弹簧用来模拟腕骨与韧带复合体,起支撑并限制与掌骨相对应的动平台运动;动平台模拟掌骨末端,定平台模拟桡骨和尺骨末端;三根绳索模拟肌肉来驱动并联机构。考虑弹簧轴向位移以及柔性问题,基于有限转动张量法和力与力矩平衡分析方法,构建系统逆运动学数学模型,得到运动学和静力学联合求解的非线性方程组。通过对机构模型分析,完成0～75°下各绳索长度和拉力的数值求解。通过仿真与试验得到人体腕部生理运动空间和机构有效工作空间,验证了机构的合理性和分析方法的正确性。所提出的求解方法对康复机器人和绳索驱动并联机构设计具有积极的促进作用。     

基于工作空间最大化的平面柔索驱动并联机构优化设计

工作空间是并联机构的重要指标,柔索驱动并联机构与杆支撑并联机构相比,其突出的优点是具有较大的工作空间.从平面柔索驱动并联机构出发,探讨柔索与动平台的连接位置对定姿态工作空间大小的影响.建立柔索驱动并联机构静力模型,并对4根柔索驱动的3自由度平面机构的定姿态工作空间进行分析,对此类机构的柔索与动平台的连接位置参数进行建模,通过直接搜索的优化算法对这些位置参数进行优化,得到了最优的结构参数.与常用的平面构型相对比,优化后的机构构型具有更大的定姿态工作空间.     

6自由度绳牵引并联机构的运动学分析

在分析总结前人研究成果的基础上,提出了一种由7根绳牵引的结构紧凑的6自由度并联机构首先对机构构型进行了描述;接着建立了机构静力学模型,总结了前人关于绳牵引并联机构的可控工作空间、具有拉力条件的工作空间和具有刚度条件的工作空间分析方法;并针对提出的6自由度绳牵引并联机构,采用Monte-Carlo技术在Matlab环境下编程进行仿真,验证所采用的工作空间分析方法的可行性.仿真结果表明机构平动可控工作空间大而转动工作空间小;在主位姿附近机构的刚度性能好;但许可的绳拉力范围小;工作空间的边界问题仍待解决.后续工作还将进行机构的运动学综合.该构型的6自由度绳牵引并联机构在超大工作空间的机器人领域有潜在的应用前景.     

面向自动仓储的绳索牵引并联机器人构型选择与参数优化

针对自动仓储领域的应用需求,研究了冗余驱动绳索牵引并联机器人的构型选择和参数优化问题。分析了自动仓储应用中冗余驱动绳索牵引并联机器人的结构特点,建立了静力学模型和力可行条件。基于动平台在需求力矩下力可行条件的分析,提出了一种最大负载优化指标。设计了完整的优化方法,并对所有构型的最大负载进行优化,最终得到了最优的构型及其动平台参数。通过仿真测试,将优化结果与其他构型以及随机选取的动平台参数进行了对比。结果表明最优构型的最大负载性能最佳,并且经过优化后,最大负载有明显提高。     

平面柔索驱动并联机构的灵活工作空间及构型优化

灵活工作空间是并联机构的一个重要指标,文中以平面三自由度柔索驱动并联机构为研究对象,讨论如何获得灵活工作空间较优的构型。首先建立平面柔索驱动并联机构的静力学模型,然后给出了灵活工作空间的计算方法和数值算例。最后以灵活工作空间为目标,以柔索驱动静平台连接点的位置为优化参数,利用遗传优化算法对构型参数进行优化。通过比较优化前后两种构型发现,优化后构型的灵活工作空间的面积大为提高。     

基于凸集理论的绳牵引串并联机器人工作空间算法

为求解m≥n（m为绳索数目,n为机构自由度）绳牵引串并联机器人的力旋量可行工作空间,提出一种基于凸集理论的非迭代求解算法。该算法利用闵可夫斯基之和的性质构造绳索的旋量集,借助非迭代的数学思想验证该旋量集是否完全包含外部旋量集。首先,通过确定初始超平面找出凸集所有的边界超平面,根据初始超平面偏移的距离确定边界超平面投影位置; 然后推导出旋量平衡的判定表达式,并采用数值分析的方法得到绳牵引机器人的力旋量可行工作空间;最后,采用该算法对两种典型的绳牵引串并联机器人进行工作空间求解,结果验证了所提出的基于凸集理论工作空间求解方法的有效性。     

大型射电望远镜馈源定位3T索牵引并联机构分析与设计

在新一代大型射电望远镜的机构设计中,由于馈源质量的大幅降低,在馈源定位的设计中,提出采用四绳索牵引并联机构,牵引馈源舱实现三个方向的平动运动,达到加大馈源工作空间的目的.为了研究非线性绳索控制机构中的尺度优化设计问题,在已知馈源舱位置的情况下,为解决由于绳索自重导致的悬链线问题,通过将悬链线简化成抛物线的方法,解决悬链线带来的高度非线性静力平衡方程组的求解问题,得到简化的静力学平衡方程.通过建立的简化静力学平衡方程,求解出四绳索牵引并联系统的工作空间与设计参数间的关系,并使用一种以力优化为目标的优化算法得到工作空间中四绳索静力平衡下的精确索拉力和伸长量.通过综合考虑满足条件的参数,最终给出满足设计要求的机构优化尺度参数.     

线性驱动并联机构基于有效工作空间比的尺度优化

提出了1种并联机构工作空间的几何求解及尺度优化方法。首先,借助闭环矢量法构造了线性驱动6自由度并联机构的位置逆解模型;推导得出并联机构定姿态可达工作空间的边界曲面方程,获得精确的3维可达空间;提出"有效工作空间比"概念,以刻画可达工作空间的有效尺度域;最后,在考察归纳机构关键尺度参数对有效工作空间比的影响规律的基础上,以包络已知任务空间的可达空间体积最小作为目标函数,结合有效工作空间比取值范围、驱动关节位移范围、构件干涉及尺度约束等约束条件,联合应用模拟退火+模式搜索算法进行了机构关键尺度参数的优化设计。研究成果可为并联机构的结构设计奠定必要理论基础。     

Workspace quality analysis and application for a completely restrained 3-Dof planar cable-driven parallel manipulator

With the advantage of large workspace, low energy consumption and small inertia, the cable-driven parallel manipulator (CDPM) is suitable for heavy workpieces in rapid velocity and acceleration. We present a workspace analysis approach to solve force and torque equilibriums of completely restrained CDPMs. By this approach, not only the distribution but also the value of tensions driven by cables is investigated together. Two new indices, all cable tension distribution index (ACTDI) and area of the global quality workspace (AG) are proposed to evaluate the quality of the workspace. By concentrating on the workspace and its quality combined with the tension characteristics, these criteria are used to determine the optimal workspace in CDPMs. To verify the capacity of the proposed method, simulation examples are presented and the results demonstrate the approach’s effectiveness. In the end, the dimensional design for a planar CDPM is discussed with the indices of workspace quality.     

Optimal Design and Force Control of a Nine-Cable-Driven Parallel Mechanism for Lunar Takeoff Simulation

Traditional simulation methods are unable to meet the requirements of lunar takeo simulations, such as high force output precision, low cost, and repeated use. Considering that cable-driven parallel mechanisms have the advantages of high payload to weight ratio, potentially large workspace, and high-speed motion, these mechanisms have the potential to be used for lunar takeo simulations. Thus, this paper presents a parallel mechanism driven by nine cables. The purpose of this study is to optimize the dimensions of the cable-driven parallel mechanism to meet dynamic workspace requirements under cable tension constraints. The dynamic workspace requirements are derived from the kinematical function requests of the lunar takeo simulation equipment. Experimental design and response surface methods are adopted for building the surrogate mathematical model linking the optimal variables and the optimization indices. A set of dimensional parameters are determined by analyzing the surrogate mathematical model. The volume of the dynamic workspace increased by 46% after optimization. Besides, a force control method is proposed for calculating output vector and sinusoidal forces. A force control loop is introduced into the traditional position control loop to adjust the cable force precisely, while controlling the cable length. The e ectiveness of the proposed control method is verified through experiments. A 5% vector output accuracy and 12 Hz undulation force output can be realized. This paper proposes a cable-driven parallel mechanism which can be used for lunar takeo simulation.     

A method of verifying force-closure condition for general cable manipulators with seven cables

This paper introduces a systematic method of verifying the force-closure condition for general 6-DOF cable-driven manipulators with seven cables. Force-closure is defined as that the inverse dynamics problem has a feasible solution for any external wrench exerted on the end-effector. For any given configuration of a 7-cable manipulator, the method can easily determine, by examining the Jacobian matrix of the manipulator, whether a solution of all-positive cable forces exists. The necessary and sufficient conditions of the proposed method are mathematically proven. The paper also addresses the application of the proposed method for determination of the force-closure workspace. As a numerical example, the shape, boundary, dimensions, and volume of the force-closure workspace of a 6-DOF, 7-cable manipulator are discussed.     

Optimal design of a 3-leg 6-DOF parallel manipulator for a specific workspace

Researchers seldom study optimum design of a six-degree-of-freedom(DOF) parallel manipulator with three legs based upon the given workspace. An optimal design method of a novel three-leg six-DOF parallel manipulator(TLPM) is presented. The mechanical structure of this robot is introduced, with this structure the kinematic constrain equations is decoupled. Analytical solutions of the forward kinematics are worked out, one configuration of this robot, including position and orientation of the end-effector are graphically displayed. Then, on the basis of several extreme positions of the kinematic performances, the task workspace is given. An algorithm of optimal designing is introduced to find the smallest dimensional parameters of the proposed robot. Examples illustrate the design results, and a design stability index is introduced, which ensures that the robot remains a safe distance from the boundary of sits actual workspace. Finally, one prototype of the robot is developed based on this method. This method can easily find appropriate kinematic parameters that can size a robot having the smallest workspace enclosing a predefined task workspace. It improves the design efficiency, ensures that the robot has a small mechanical size possesses a large given workspace volume, and meets the lightweight design requirements.     

Optimization design and dynamic stability analysis of 3-DOF cable-driven parallel robot with an elastic telescopic rod

This paper proposes a three degree-of-freedoms (DOFs) cable-driven parallel robot (CDPR), which is actuated by three groups of parallel cables and tensioned by an elastic telescopic rod with a passive spring. Firstly, the architecture of the robot is briefly illustrated with emphasis on the three parallelogram arrangements of the cables and composition of elastic telescopic rod structure. This robot has larger workspace and greater tension than previous under-constrained CDPRs. Secondly, the kinematic and dynamic models of the robot are established. On this basis, the parameters of the spring installed in the telescopic rod are optimized and determined considering both the acceleration and cable force through using the differential evolution (DE) algorithm. Thirdly, dynamic stability analysis of the robot under impulsive disturbances is performed according to the Gauss principle of least constraint (GPLC). The results of a simulation case show that this robot has better dynamic stability in comparison with conventional under-constraint CDPR because of the presence of the elastic telescopic rod. The measurement results in the workspace are obtained through dynamic simulation. Finally, the experiments are performed based on numerical simulation. The feasibility of the CDPR is verified via the experiments and simulations.

     

可重构柔索并联机器人协同避障方法研究

针对可重构索驱动机器人自身结构与环境障碍物间高碰撞风险问题,设计了一种基于临界支撑线及多指抓握的可重构柔索机器人协同避障方法。通过简化环境障碍物与机器人结构得到一类可重构柔索机器人在复杂环境下的一般模型,在此模型基础上利用其结构的拓扑约束及障碍物间的临界支撑线求取机器人的无碰撞运动区域;通过凸包算法及凸包映射算法求取不同构型及障碍物分布下可重构柔索并联机器人的力封闭工作空间,并分析不同构型及障碍物分布对机器人无碰撞力封闭工作空间的影响;随后,通过优化算法求取指定运动轨迹上最优索分布;最后在重构索驱动机器人实验平台对所得优化结果进行验证。实验结果显示,所设计的可重构柔索机器人协同避障方法能有效避免重构索驱动机器人运动过程中的碰撞。     

七索并联对接机构作业空间分析及索力优化设计

柔性索并联机构具有工作空间大、能耗低和惯量小等优点,适合于重载及长径比大的工件吊装对接。提出一种七索驱动的6自由度柔性并联对接机构。借助静力学方程推导出该七索柔性并联机构的结构矩阵,并根据结构矩阵的零空间,计算得到设计参数下的可控工作空间和可行工作空间。通过比较工作空间大小,确定出动平台铰接点角度、动平台半径和下拉索分布半径3个设计参数。以下拉索索力均匀为优化目标,计算出下拉索索力变化情况,并结合工作空间分析和索力变化特点,给出一组满足设计要求的尺度参数。