并联六自由度机构运动学与动力学标定对比

为了研究并联六自由度机构不同标定方法的适用性,依据运动学标定和动力学标定,分别建立了并联六自由度机构的标定模型,并通过数值仿真对标定效果进行对比分析。结果表明：运动学标定方法对提高机构运动正解精度更为有效,正解误差比动力学标定的结果小4．9％,有利于传统的基于关节空间的并联机构控制策略;动力学标定方法对提高机构动力学模型精度更为有效,关节驱动力误差比运动学标定的结果小5～25 N,更适合基于工作空间的并联机构控制策略。     

Nonlinearity for a parallel kinematic machine tool and its application to interpolation accuracy analysis

This paper is concerned with the kinematic nonlinearity measure of parallel kinematic machine tool (PKM), which depends upon differential geometry curvature. The nonlinearity can be described by the curve of the solution locus and the equal interval input of joints mapping into inequable interval output of the end-effectors. Such curing and inequation can be measured by BW curvature. So the curvature can measure the nonlinearity of PKM indirectly. Then the distribution of BW curvature in the local area and the whole workspace are also discussed. An example of application to the interpolation accuracy analysis of PKM is given to illustrate the effectiveness of this approach.     

Stiffness estimation of a parallel kinematic machine

This paper presents a simple yet comprehensive approach to quickly estimating the stiffness of a tripod-based parallel kinematic machine. This approach can be implemented in two steps. In the first step, the machine structure is decomposed into two substructures associated with the machine frame and parallel mechanism. The stiffness models of these two substructures are formulated by means of virtual work principle. This is followed by the second step that enables the stiffness model of the machine structure as a whole to be achieved by linear superposition. The 3D representations of the machine stiffness within the usable workspace are depicted and the contributions of different component rigidities to the machine stiffness are discussed. The result is compared with that obtained through finite element analysis.     

Kinematic calibration of a class of parallel kinematic machines (PKM) with fewer than six degrees of freedom

The accuracy of parallel kinematic machines (PKM), particularly machine tools is an important performance index. It has been acknowledged that kinematic calibration is a practical and economical way for enhancing the accuracy of PKM systems. The procedure usually involves four steps, i.e. error modeling, measurement, identification and implementation[1,2]. So far, most work on the kinematic calibration of PKM systems has focused upon the objects with six degrees of freedom (DOF)[3—13]. A…     

Error modeling,sensitivity analysis and assembly process of a class of 3-DOF parallel kinematic machines with parallelogram struts

This paper presents an error modeling methodology that enables the tolerance design, assembly and kinematic calibration of a class of 3-DOF parallel kinematic machines with parallelogram struts to be integrated into a unified framework. The error mapping function is formulated to identify the source errors affecting the uncompensable pose error. The sensitivity analysis in the sense of statistics is also carried out to investigate the influences of source errors on the pose accuracy. An assembly process that can effectively minimize the uncompensable pose error is proposed as one of the results of this investigation.     

Inverse dynamics and servomotor parameter estimation of a 2-DOF spherical parallel mechanism

A novel reconfigurable 5-DOF hybrid manipulator—TriVariant-B is composed of a 2-DOF spherical parallel mechanism which is serially connected with a 3-DOF open-loop kinematic chain undergoing one translation and two rotations by a prismatic joint. The merit of this design is that a relatively large workspace/limb-stroke ratio can be achieved thanks to the decomposition of the fixed point rotation and the relative translation. In this paper, on the basis of inverse dynamic formulation of the 2-DOF spherical parallel mechanism, an approach is proposed for estimating the servomotor parameters including moment of inertia, rated speed and the maximum torque in a quick manner. The approach has been employed for the development of a prototype for frame cutting process. Supported by the National Natural Science Foundation of China (Grant Nos. 50535010 and 50510488)     

新型并联机床动力学研究

新型并联机床是空间多环机构在机床业的创造性应用,考虑组成该机床各构件的弹性影响,建立了机床的弹性动力学有限元分析模型,同时针对几种典型结构工况对该机床进行了固有特性和动力响应分析,得出了结构工况与机床动态特性的关系,这些研究为该机床进行动态设计提供了基础。     

Inverse kinematic optimal design of 6-DOF parallel manipulators

To obtain the required articular velocities as lower as possible for the given kinematics of the moving platform, this paper focuses on this kind of articular velocities optimization of 6-DOF parallel manipulators. Based on the inverse kinematic analysis, the H∞ norm of the weighted Jacobian matrix was adopted as the performance index to minimize the articular velocities, and then the optimal design problem was formulated to find a manipulator geometry that minimized the global performance index with the constraints of the workspace and structural parameters limits. Since the optimal design problem is a constrained nonlinear optimization problem without explicit analytical expressions, the genetic algorithm was applied to numerically solve the problem. Simulation results indicate that the articular velocities of the optimal manipulators can be the minimum while the kinematic reauirements of the moving platform are satisfied.     

2-DOF平面并联机器人结构参数优化的研究

提出了一种新颖的高速高精度机器人机构采用高速精密直线电机驱动-2-DOF平面并联杆机构.在杆机构的设计中,以结构紧凑和抑振为目标,分别采用模拟退火算法和有限元动力仿真进行了几何尺寸和截面尺寸的优化,并提出了一种基于本模型特点的新解产生机制.实验测试结果表明经优化设计后的平面并联杆机构刚度大,高速运动下的残余振动＜1 μm,直线电机的稳定时间成为决定机器人稳定时间的关键因素.     

3-PRS并联机构位置正解分析

根据3-PRS并联机构具有2个转动自由度和1个移动自由度的结构特点,利用封闭矢量方法和简化坐标转换矩阵,得到该机构运动平台中心的运动方程,然后运用遗传算法并结合其运动方程给出并联机构运动学位置正解适应度函数和目标函数,将计算结果代入运动方程求出杆长,其误差小、精度高,为3-PRS并联机构的控制策略奠定了基础．该解法既不需要选取迭代初值,也不需要复杂的数学推导,容易实现而且通用性强．     

6DOF并联机床的运动学解耦

如何解决6DOF并联机床的强耦合,一直是6DOF并联机床伺服控制上的一个难题,为此,在对Jacobian矩阵进行改造的基础上,提出了一种新的解耦方法,得到了准对解耦矩阵,实现了对6DOF并联机庆的平均和转动之间的解耦。     

一种5轴混联铣床运动学的矢量法分析

介绍一种由3自由度并联机构和2自由度串联机构组成的5轴混联铣床.采用矢量分析的方法,引入单位矩阵和四元素向量对运动学分析中的高阶转换矩阵进行降阶处理,实现机构输入参数与机构独立运动参数之间的矩阵转化,解决了机构运动参数耦合的问题;详细推导出铣床的并联部分驱动输入速度、加速度与机构动平台输出速度、加速度之间的数学关系,借助于运动学仿真分析软件验证了算法的正确性.该算法对于具有运动参数耦合的并联机构或混联机构的运动学分析、动力学分析以及机构的运动控制具有一定的参考价值.     

Calibration of a Parallel Kinematic Machine Tool

The parallel kinematic machinetool(PKMT)is anew-style machine tool[1].Though it has an advan-tage over traditional NC machine tool due to a seriesof characteristics such as si mple structure,fast re-sponse speed and non cumulative errors[2,3],its abso-lute accuracy is not sufficient for a machine tool re-quiring high accuracy.A mainfactor reducingthe ac-curacy is kinematic parameter errors caused by ma-chining and assembling errors[4].Calibration is a solution to this problem.It ismore prac…     

3-UPU并联机床关于3D自由曲面刻字的计算机辅助几何法

基于一种新的计算机辅助变量几何法,以新型3-dof（3自由度）3-UPU并联机床为对象,加工具有任意复杂形状的工件以及在任意3D自由曲面或平面上刻字。通过几何约束和尺寸驱动技术,先建立3-UPU并联模拟机构,再构造任意3D自由曲面和刀具轨迹的引导平面,与3-UPU模拟并联机构合成,得到用于加工任意3D自由曲面的模拟并联机床。给定加工路径,各驱动杆长和动平台的位置能自动求解出来。通过解析的方法验证对比,得出计算机辅助变量几何法不仅简单直观,而且省去了大量的编程计算。     

一种5轴混联加工中心的位姿正逆解分析

为了解决目前纯并联机床存在的问题,研究了一种新型5轴混联加工中心结构,该新型结构具有工作空间大、静动态刚度好的优点.针对其运动参数间存在较强的耦合性,给出了运动平台姿态参数与位置参数间的数学解耦关系,将解析法和数值法相结合,对其位姿逆解进行了详细的推导,同时借助改进的杆长逼近法,进行了位姿正解的推导.实例验证结果表明算法正确、有效.该算法对混联机构的运动分析具有一定的参考意义.     

Stewart型并联机床直线插补步长的研究

为了提高Stewart型并联机床运动学精度,文章研究并联机床末端运动轨迹的直线插补步长和非线性插补误差的关系.提出了采用曲率法度量非线性运动误差和插补步长之间的关系,基于以上方法,建立了度量并联机床非线性强度的曲率模型.通过数值仿真的方法,得出并联机床工作空间内非线性误差的分布规律,并得出整个机床工作空间内的最大曲率为0.0016.利用以上结论,在满足插补精度的前提下,选取较大的直线插补步长,提高了并联机床的加工效率.     

Optimal measurement configurations for kinematic calibration of six-DOF serial robot

An optimal measurement pose number searching method was designed to improve the pose selection method. Several optimal robot measurement configurations were added to an initial pre-selected optimal configuration set to establish a new configuration set for robot calibration one by one. The root mean squares (RMS) of the errors of each end-effector poses after being calibrated by these configuration sets were calculated. The optimal number of the configuration set corresponding to the least RMS of pose error was then obtained. Calibration based on those poses selected by this algorithm can get higher end-effector accuracy, meanwhile consumes less time. An optimal pose set including optimal 25 measurement configurations is found during the simulation. Tracking errors after calibration by using these poses are 1.54, 1.61 and 0.86 mm, and better than those before calibration which are 7.79, 7.62 and 8.29 mm, even better than those calibrated by the random method which are 2.22, 2.35 and 1.69 mm in directions X, Y and Z, respectively.     

并联机床构型及其设计方法初探

在对现有各种并联构型分析的基础上，从联接型式、驱动方式和自由度数三方面对并联机床构型进行了分类．结合典型并联机床分析了不同类型并联构型的特点，并对并联机床构型设计的目标、步骤和具体方法进行了研究．提出了可以采用型数综合法、构型衍生法和运动约束法完成并联构型的具体设计。     

三自由度并联姿态测量机构及其位姿显式解

考虑到串联结构的六自由度位姿仪在对被测物体进行位姿综合测量时存在的误差累积，影响测量精度，提出并联结构的三自由度姿态测量装置，将其连接到三自由度串联结构位置测量仪的末端来实现被测物体六个自由度的综合测量。通过机构综合来克服并联机构正解困难，经推导得出被测物体姿态的显式解，从而缩短了计算时间，大大提高了测量效率。测量精度分析为三自由度并联结构姿态测量机构设计奠定了基础。     

Optimal measurement configurations for kinematic calibration of six-DOF serial robot

An optimal measurement pose number searching method was designed to improve the pose selection method.Several optimal robot measurement configurations were added to an initial pre-selected optimal configuration set to establish a new configuration set for robot calibration one by one.The root mean squares (RMS) of the errors of each end-effector poses after being calibrated by these configuration sets were calculated.The optimal number of the configuration set corresponding to the least RMS of pose error wa...