3-RPS并联机床的标定建模及振动分析

并联机床在标定时所建立的位置参考系与运动参考系不一致产生系统误差,从而影响机床的结构性能。通过改进标定建模方式,将两个参考系统一,并用数值模拟该并联机床的标定过程,对比结果发现,改进后的模型可以完全消除测量时的系统误差对并联机床标定精度的影响。把标定过的模型导入ADAMS进行振动仿真分析,通过对比可以发现标定过模型的各项振动指标明显优于未标定的模型,从而进一步提高并联机床的结构性能。直接提高机械加工精度及安装精度能够提高并联机床的结构参数的精度,但其代价将是极大地增加加工成本,采用运动学标定并联机床的运动学建模的方法则只需要按普通精度要求进行机械加工,这种标定建模方式具有很高的实用价值。     

Step kinematic calibration of a 3-DOF planar parallel kinematic machine tool

This paper presents a novel step kinematic calibration method for a 3 degree-of-freedom (DOF) planar parallel kinematic machine tool, based on the minimal linear combinations (MLCs) of error parameters. The method using mapping of linear combinations of parameters in error transfer multi-parameters coupling system changes the modeling, identification and error compensation of geometric parameters in the general kinematic calibration into those of linear combinations of parameters. By using the four theorems of the MLCs, the sets of the MLCs that are respectively related to the relative precision and absolute precision are determined. All simple and feasible measurement methods in practice are given, and identification analysis of the set of the MLCs for each measurement is carried out. According to the identification analysis results, a step calibration including step measurement, step identification and step error compensation is determined by taking into account both measurement costs and observability. The experiment shows that the proposed method has the following merits: (1) the parameter errors that cannot influence precision are completely avoided; (2) it reflects the mapping of linear combinations of parameters more accurately and enhances the precision of identification; and (3) the method is robust, efficient and effective, so that the errors in position and orientation are kept at the same order of the measurement noise. Due to these merits, the present method is attractive for the 3-DOF planar parallel kinematic machine tool and can be also applied to other parallel kinematic machine tools with weakly nonlinear kinematics. Supported by the “863” High-Tech Program of China (Grant Nos. 2006AA04Z204 and 2006AA04Z227), National Natural Science Foundation of China (Grant Nos. 50775118 and 50605041), the “973” Basic Research Project of China (Grant Nos. 2006CB705406 and 2007CB714000), and Tsinghua Basic Research Foundation (Grant No. JC200701)     

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.     

基于元动作单元的数控机床运动精度映射

为使数控机床精度设计有定量的理论数值供参考,从运动的角度出发,建立了基于元动作单元的数控机床运动精度映射模型. 采用“功能(Function)-运动(Motion)-动作(Action), FMA”的结构化分解方法得到元动作单元,并结合多体系统理论对数控机床拓扑结构进行了描述；运用旋量理论对数控机床误差建模,建立数控机床空间运动误差模型,并用螺旋理论得到空间运动误差综合值；以制造成本、空间运动误差螺距及其大小为设计准则,构建了运动精度映射模型,并应用NSGA-Ⅱ遗传算法对数控机床运动精度进行映射. 对某国产加工中心进行运动精度映射求解,说明了该模型的可行性和有效性.     

Calibration of parallel kinematics machine using generalized distance error model

This paper focus on the accuracy enhancement of parallel kinematics machine through kinematics calibration. In the calibration processing, well-structured identification Jacobian matrix construction and end-effector position and orientation measurement are two main difficulties. In this paper, the identification Jacobian matrix is constructed easily by numerical calculation utilizing the unit virtual velocity method. The generalized distance errors model is presented for avoiding measuring the position and orientation directly which is difficult to be measured. At last, a measurement tool is given for acquiring the data points in the calibration processing. Experimental studies confirmed the effectiveness of method. It is also shown in the paper that the proposed approach can be applied to other typed parallel manipulators.     

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.     

Delta并联机械手几何误差建模及灵敏度分析

以一类含平行四边形支链的Delta并联机械手为对象,利用空间矢量链分析方法,构造出机构末端位置和姿态误差与几何误差之间的映射关系,明确揭示出影响机构末端不可补偿误差的几何误差源,并借助灵敏度分析定量揭示几何误差对末端位姿误差的影响.研究成果对指导同类装备的设计与制造具有普遍的意义.     

并联机床虚拟设计的理论方法

针对并联机床,从自由度数定理出发,确保了并联机床概念设计的可靠性;运用多体系统运动学理论,推导出并联机床运动学模型及加工空间与结构尺寸关系的模型,进而,通过并联机床相对运动约束方程,推导出并联机床刀具运动与驱动杆系参数的关系方程．这一整套研究思路,对指导并联机床的设计与控制,减小设计的盲目性提供了有力的理论依据．     

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。     

滚齿机传动链运动误差的频谱分析

用山东工业大学研制的圆感应同步器式运动精度测量仪配以TP801B—Z80单板计算机,完成了传动链运动误差的数据采集和处理工作。从数据采集开始,经十多分钟时间即可直接从数据处理结果找出机床传动链的薄弱环节,作出诊断结论,从而进行修理或调整机器,以提高机器的传动精度。     

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.     

A Kinematic Model and Identification of Geometric Parameters of Robots

0INTRODUCTIONConsiderableattentionhasbeenpaidintherecentyearstotheproblemofrobotaccuracy,whichdependsontheprecisionofmotioncontrolandtherepresentationaceuracyofmanipulator'sgeometricparameters.Inordertoupgradetheaccuracyofrobotwemayidentifyrobotgeometricparametersbyacalibrationprocessandusetheseparametersinthecontrolsystem.TherearealotofpapersdedicatedthecalibrationofrobotsandidentificationOftheirparamet.rs["'].IthasbeenshownthatsmallvariationsinkinematicparametersofthemodelscanpIDducesu…     

解决约束平面偏移问题的机械臂闭环标定

基于平面约束的工业机械臂闭环标定,拟合平面与实际约束平面之间存在一定偏差,直接影响标定精度.针对此问题提出消除偏差的方法及误差模型.建立平面坐标系,得到约束平面的准确方程,通过接触式测量头对约束平面进行测量,在平面坐标系中描述测量点的位置;建立最小完整连续运动学模型,从而减少冗余参数的影响;利用双目视觉定位约束平面并规划理论测量点位置,实现自动化测量;通过改进的最小二乘法对参数误差进行辨识.实验结果表明,修正运动学参数后,机械臂绝对位置精度由1.234 mm提高到0.405 mm.该方法成本低、精度高、效率高,且简化了误差模型,适用于工业机械臂的现场标定,为机械臂生产厂家实现批量化标定及后期设备维护提供了思路.     

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。     

精密机械热误差校正机理及参数遗传优化

在研究精密机械热误差校正机理基础上，提出了主动热校正控制变形误差的精度指标，并研究了减少与增加热控制源对控制精度指标的影响．研究表明主动热校正的控制精度与热控制源数目、控制源位置及控制源的幅值有关，优化的目的是获得最佳的控制源组合及幅值参数，使热误差控制精度指标最小．由于热控制源幅值必须满足一定的设计约束，针对其幅值参数确定的困难性，引入遗传优化算法，该算法具有简单实用的特点，有较强的通用性．实例研究表明，热误差校正控制机理对变形校正控制系统的设计具有指导作用，遗传优化热控制源幅值参数具有快速全局收敛的优点．     

基于并联机构的加工机的工作空间仿真研究

介绍一种基于 6 PSS (P代表移动副 ,S代表球面副 )并联机构的并联加工机工作空间三维仿真新方法———数值分析法 .该法把对工作空间的研究转化成为对一系列剖面内边界点的研究 ,即在某一剖面内采用极坐标表示法 ,其极径上的最远点必满足某个约束条件 (如最大位移约束、最小位移约束或球铰副最大摆角约束 ) ,而这些约束条件中至少有一个不等式可以转化为等式 .用约束不等式转化为等式的方法分别求满足等式条件的极径值 .该仿真方法大大简化了工作空间的计算 .利用该方法对并联加工机工作空间的各个截面进行了分析 ,为该加工机的结构设计提供了理论依据     

Enhancing pose accuracy of space robot by improved differential evolution

Due to the intense vibration during launching and rigorous orbital temperature environment, the kinematic parameters of space robot may be largely deviated from their nominal parameters. The disparity will cause the real pose (including position and orientation) of the end effector not to match the desired one, and further hinder the space robot from performing the scheduled mission. To improve pose accuracy of space robot, a new self-calibration method using the distance measurement provided by a laser-ranger fixed on the end-effector is proposed. A distance-measurement model of the space robot is built according to the distance from the starting point of the laser beam to the intersection point at the declining plane. Based on the model, the cost function about the pose error is derived. The kinematic calibration is transferred to a non-linear system optimization problem, which is solved by the improved differential evolution (DE) algorithm. A six-degree of freedom (6-DOF) robot is used as a practical simulation example, and the simulation results show: 1) A significant improvement of pose accuracy of space robot can be obtained by distance measurement only; 2) Search efficiency is increased by improved DE; 3) More calibration configurations may make calibration results better.     

Kineto-static analysis of a novel high-speed parallel manipulator with rigid-flexible coupled links

A novel high-speed parallel kinematic machine (PKM) named Delta-S parallel manipulator is proposed,which consists of a fixed base connected to a moving platform through three limbs with identical topology.Each limb is composed of one driving arm and one follower arm,herein,the latter includes two strings and one middle rod,all located in a same plane.Compared with similar manipulators with uniform parameters,the novel and unique topology as well as the addition of two strings of Delta-S manipulator can remo...     

对接机构运动模拟器的精度分析

为了探讨对接机构运动模拟器的机构原始误差和对接过程误差引起的位姿偏差,根据对接机构运动模拟器的结构求出运动学方程,依据矩阵全微分理论,建立了机构原始误差与对接机构运动模拟器的位姿误差模型.利用蒙特卡洛方法模拟具有任意概率分布的机构原始误差,抽样计算对接机构运动模拟器的位姿误差,然后对对接机构运动模拟器的位姿精度进行了分析,给出了在其可达工作空间内的概率等高线、概率密度函数和统计数字特征.这些分析结果为对接机构运动模拟器的精度设计、标定和误差补偿提供了方向性的指导.     

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…