500m口径球面射电望远镜进舱缆线连接机构的设计及其静力学分析

由于500 m口径球面射电望远镜(Five-hundred-meters aperture spherical radio telescope,FAST)的馈源舱与地面之间是柔性连接,其包含动力电缆和信号光缆在内的缆线进舱连接机构的设计较为困难。针对FAST馈源舱是由悬索支撑的特殊结构形式,对3种可能的缆线进舱连接机构的设计方案进行分析比较,并从静力学角度分析悬架于支撑索上的缆线质量对于支撑索张力和舱倾斜角所造成的不利影响。为求解舱-索系统的静力学和工作空间优化问题,从3种设计方案中选择进舱连接通道的支撑索悬链线方程进行分析和求解,建立悬链线参数与舱体静力平衡方程的关系。计算结果表明,3种缆线进舱连接机构的设计方案的不利影响均较小,从力学角度均具备可行性条件。     

大型射电望远镜类Stewart平台的奇异性研究

将大型射电望远镜的悬索馈源舱体系统类比于Stewart平台,对其进行奇异性的研究。考虑柔性悬索只能承受拉力的特点和天文观测的要求,分析了馈源舱的可实现工作空间。基于系统的非线性静力平衡方程,根据力传递Jacobian矩阵的行列式和条件数,剖析了工作空间内部的力奇异性。研究结果为确定系统工作空间提供了依据,为改进系统结构设计,消除奇异性提供了参考。     

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。     

附加被动控制索系的柔索并联机器人的优化设计和振动分析

大射电望远镜馈源支撑系统是一类欠约束型索牵引并联机器人.对附加被动控制索系的此并联机构首次从整个工作空间优化设计的角度建立其优化模型, 并用实验和数值仿真验证其抑振的有效性.首先,基于动平台的非线性静平衡方程提出系统的两层规划模型;其次,在iSIGHT软件平台上对LT5 m被动控制构型的设计参数进行优化求解;最后,通过数值仿真及实验分别比较有无附加被动控制索系结构的振动特性.结果显示,仿真与实验结果的最大振幅基本一致,LT新构型可以显著抑制系统的风振.研究结论为欠约束型WDPR(wire driven parallel robot)系统的减振提供新思路,并对LT500 m工程的结构设计有很好的借鉴作用.     

基于索驱动的大型柔性结构振动抑制策略研究

柔性索并联机构具有工作空间大、能耗低和惯量小等优点,适用于长距离柔性桁架结构的振动主动抑制。首先提出一种四索驱动的柔性体抑振并联机构,根据闭环矢量原理和机构的几何特征,对四索并联机构进行运动学分析。接着建立四索并联机构的静力学模型,并将超长尺度柔性桁架机构的往复振动简化为梁的弯曲振动,利用振型叠加法求解外部激励作用下的强迫响应。最后针对超长尺度柔性桁架机构的振动抑制问题,提出一种基于模糊控制与PID控制相结合的控制策略,通过仿真验证所提控制策略的有效性。结果表明,所设计的柔索并联抑振系统具有明显的抑振效果,柔性桁架的振幅与振动衰减时间大幅降低,且系统的四索索力值能够在合适范围内变化。     

大型射电望远镜悬索馈源支撑系统静刚度分析

针对大射电望远镜(LT)悬索支撑系统特殊的结构形式,对6索组成的馈源支撑系统的静刚度进行分析。首先,对舱索系统静平衡方程沿馈源舱运动方向上求导,同时考虑到悬索刚度随其应力变化而呈现几何非线性的特点,给出了馈源支撑系统静刚度的公式。其次,在上面结果的基础上,分析了一个定点位置下馈源舱在外界扰动下的振动情况,通过与大型射电望远镜50 m室外模型振动试验结果相比较,说明了静刚度求解方法的有效性。最后,给出了大型射电望远镜50m模型馈源舱运动空间边缘的悬索应力与馈源支撑系统刚度的关系。     

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。     

结构参数对大型射电望远镜舱索并联机构奇异性的影响

与Stewart平台机构相似，大型射电望远镜舱索并联机构存在奇异性问题。在舱索机构开环运动控制模型的基础上，探讨了结构参数对奇异性的影响，找到了通过修改结构参数消除奇异性的方法，给出了设计参数可行域。计算机仿真和模型现场实验证明了设计方法的可行性。     

绳索-弹簧机构工作空间分析

对于绳索牵引并联机构,因绳索只能承受拉力而不能承受压力,因此完全约束的n自由度绳索牵引并联机构至少需要由n+1根绳索来驱动,冗余驱动会导致成本增加,绳索拉力求解复杂。绳索牵引并联机构中,在末端执行器与机架之间选择适当位置引入弹簧,构成绳索-弹簧机构,由弹簧来提供被动力,则可以实现绳索驱动器与自由度数目相同的可控绳索-弹簧机构。以平面3根绳索1根弹簧机构为例,建立模型,求解可行工作空间,分析弹簧参数对绳索-弹簧机构可行工作空间的影响,采用遗传算法对机构构型进行优化,并对比分析优化前后的工作空间指标。结果表明,绳索-弹簧机构在构型优化选择适当的弹簧参数后,可以显著改变工作空间及其质量,为后期规划动平台的运动轨迹提供参考。     

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。     

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。     

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。     

Linear quadratic optimal controller for cable-driven parallel robots

In recent years, various cable-driven parallel robots have been investigated for their advantages, such as low structural weight, high acceleration, and large workspace, over serial and conventional parallel systems. However, the use of cables lowers the stiffness of these robots, which in turn may decrease motion accuracy. A linear quadratic (LQ) optimal controller can provide all the states of a system for the feedback, such as position and velocity. Thus, the application of such an optimal controller in cable-driven parallel robots can result in more efficient and accurate motion compared to the performance of classical controllers such as the proportional-integral-derivative controller. This paper presents an approach to apply the LQ optimal controller on cable-driven parallel robots. To employ the optimal control theory, the static and dynamic modeling of a 3-DOF planar cable-driven parallel robot (Feriba-3) is developed. The synthesis of the LQ optimal control is described, and the significant experimental results are presented and discussed.     

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.     

Typical gait analysis of a six-legged robot in the context of metamorphic mechanism theory

The equivalent mechanism of the system is often considered as one specific mechanism in most existing studies of multi-legged robots, however the equivalent mechanism is varying while the robot moves on the ground. Four typical tripod period gaits of a radial symmetrical six-legged robot are analyzed. Similar to the metamorphic mechanism, the locomotion of multi-legged robot is considered as a series of varying hybrid serial-parallel mechanisms by assuming the constraints of the feet on the ground with hinges. One gait cycle is divided into several periods, and in different walking period there is a specific equivalent mechanism corresponding to it, and the walking process of multi-legged robot is composed by these series of equivalent mechanisms. Walking performance can be got by analyzing these series of equivalent mechanisms. Kinematics model of the equivalent mechanism is established, workspaces of equivalent mechanisms are illustrated by simulation and a concept of static stability workspace is proposed to evaluate the static stability of these four gaits. A new method to calculate the stride length of multi-legged robots is presented by analyzing the relationship between the workspace of two adjacent equivalent parallel mechanisms in one gait cycle. The stride lengths of four gaits are given by simulations. Comparison of stride length and static stability among these four typical tripod gaits are given. It has been proved that mixed gait and insect-wave gait II have better static stability than mammal kick-off gait and insect-wave gait I. Insect-wave gait II displays its advantage on stride length while the height of robot body lower than 87 mm, mammal kick-off gait has superiority on stride length while the height of robot body higher than 115 mm, and insect-wave gait I shows its shortcoming in stride length. The proposed method based on metamorphic theory and combining the footholds and body height of robot provides a new method to comprehensive analyze the performance of multi-legged robot.     

State-of-the-art on theories and applications of cable-driven parallel robots

Cable-driven parallel robot (CDPR) is a type of high-performance robot that integrates cable-driven kinematic chains and parallel mechanism theory. It inherits the high dynamics and heavy load capacities of the parallel mechanism and significantly improves the workspace, cost and energy efficiency simultaneously. As a result, CDPRs have had irreplaceable roles in industrial and technological fields, such as astronomy, aerospace, logistics, simulators, and rehabilitation. CDPRs follow the cutting-edge trend of rigid–flexible fusion, reflect advanced lightweight design concepts, and have become a frontier topic in robotics research. This paper summarizes the kernel theories and developments of CDPRs, covering configuration design, cable-force distribution, workspace and stiffness, performance evaluation, optimization, and motion control. Kinematic modeling, workspace analysis, and cable-force solution are illustrated. Stiffness and dynamic modeling methods are discussed. To further promote the development, researchers should strengthen the investigation in configuration innovation, rapid calculation of workspace, performance evaluation, stiffness control, and rigid–flexible coupling dynamics. In addition, engineering problems such as cable materials, reliability design, and a unified control framework require attention.     

Dimensional Synthesis of a 3-DOF Parallel Manipulator with Full Circle Rotation

Parallel robots are widely used in the academic and industrial fields. In spite of the numerous achievements in the design and dimensional synthesis of the low-mobility parallel robots, few research ef...     

5自由度大工作空间/支链行程比混联机械手的概念设计与尺度综合

研究一类新型5自由度可重构混联机械手的创新设计和尺度综合问题,该机械手模块由-2自由度球面并联机构和一条通过滑移副与之串接的两转动-移动串联运动链组成.该混联机械手由于将定点转动与相对滑移运动解耦,因此具有工作空间/支链行程比大的特点,适合高速轻载作业,可作为即插即用模块用于搭建不同类型的加工制造装备.在建立2自由度球面并联机构的速度映射模型的基础上,分析该机构的奇异性和各向同性问题,并以速度雅可比矩阵最小奇异值的全域均值为操作性能指标,研究2自由度球面并联机构的尺度综合问题.通过单调性分析揭示出尺度参数对该指标的影响规律,进而将尺度综合问题简化为求解杆长等式约束问题.最后给出一组算例,使该尺度综合方法的有效性得到验证.     

3-RUU微动并联机构的尺寸型模型及性能图谱

基于伪刚体模型及运动学参数的量纲一化,建立了3-RUU微动并联机构的尺寸型模型,该模型在有限区间内给出了3-RUU微动并联机构所有可能的尺寸参数组合,模型空间内的任意一点代表具有相同或相似运动性能的同一族机构。结合对微操作运动性质的分析,提出了作业空间体积值、作业空间形状值及常值雅克比矩阵条件数等三种描述微动机构运动学性能的评价指标,并根据尺寸型模型及定义的性能指标绘制了反映机构性能与尺寸参数关系的性能图谱。