Manufacturing-Oriented Tolerance Design of Parallel Machine Tools

精度设计是机床误差避免技术的重要手段,涉及在工作空间中给定刀具的最大位姿允差后,合理地制定零部件制造公差及装配工艺的问题。以3—HSS型并联机床为对象,利用空间矢量链模型建立零部件制造误差与动平台位姿误差的映射关系。给定零部件制造公差后,利用该模型即可预估出动平台的位姿误差。在此基础上,根据灵敏度分析结果,提出一种在给定刀具位姿允差条件下,以零部件制造公差加权欧氏范数最大为目标,以角性公差和线性公差在同一精度等级下达到均衡为约束条件的精度设计方法。研究成果已成功地应用于一台并联机床样机的开发。     

数控机床几何精度设计指标确定方法研究

针对数控机床几何精度设计过程中整机精度设计指标难于合理确定的问题,提出一种基于待加工试件公差指标反演机床刀具工件间相对位姿误差允许变动范围的方法。该方法首先建立试件单一公差项与机床位姿误差之间的约束关系模型,即为满足试件单一公差要求,机床刀具工件间相对位姿误差需要被控制在何种范围内,然后将所有公差项对应的变动范围求交集即可得到机床位姿误差的允许变动范围,并作为整机精度设计的设计指标,用于机床零部件公差分配。推导了常用公差项对应的位姿误差变动范围的求解方法,并以机床精度检验标准中轮廓加工试件为例,阐述了所提方法的应用过程。     

6-UPS并联机床误差分布特性

为确定6-UPS交叉杆式Stewart型并联机床BJ-04-02(A)的加工精度特性,运用逆向思维方式,从刀具平台发生给定位置误差、姿态误差时驱动杆长度的变化中获得机床精度信息。计算了工作空间内各位置点、各姿态下刀具平台发生给定位置误差、姿态误差时驱动杆长度的变化量;通过极值、倒数等运算,获得了单位杆长误差引起的刀具平台位置、姿态误差的上下限,并给出了位姿误差在工作空间内的分布特性。     

基于自适应遗传算法的新型6自由度并联机器人精度综合

精度设计是机器人误差标定技术的重要手段,精度综合是精度分析的逆问题,涉及在工作空间中给定末端操作器的最大位姿误差后,合理地制定出零部件的制造公差及各关节的装配误差的问题.文中在精度分析的基础上,基于误差独立作用原理和原始误差等效作用原则,考虑运动副配合间隙误差和杆长误差,利用自适应遗传算法,以制造成本最小为优化目标,对6-DOF并联平台机构进行精度综合.该方法的求解结果能满足精度要求,具有实用价值.     

基于模糊遗传算法的新型6自由度并联机器人精度综合

精度设计是机器人误差标定技术的重要手段，精度综合是精度分析的逆问题，涉及在工作空间中给定末端操作器的最大位姿误差后，合理地制定出零部件的制造公差及各关节的装配误差的问题。在精度分析的基础上，基于误差独立作用原理和原始误差等效作用原则，考虑运动副配合间隙误差和杆长误差，利用模糊遗传算法，以制造成本最小为优化目标，对6-DOF并联平台机构进行精度综合。该方法的求解结果能满足精度要求，具有实用价值。     

载荷不确定性的机床支承件公差优化设计

为降低不确定因素对机床支承件精度的影响,提高支承件精度稳健性,针对机床支承件安装基准面,提出一种考虑载荷不确定性的机床支承件公差优化设计方法。首先建立机床支承件精度稳健性优化模型;其次,考虑载荷不确定性求解与支承件所联接零部件的位姿误差分布,利用响应面法构建支承件安装基准面公差、载荷不确定变量与支承件误差分布参数间的近似模型;再次,结合现有的加工成本函数,利用粒子群嵌套优化算法求解优化问题。以某龙门式加工中心横梁为例,利用不确定性优化方法优化基准面公差。最后,通过与确定性优化结果对比,发现提出的稳健性公差优化设计方法在保证加工成本较低的同时,可以有效提升设计产品的稳健性。     

基于RBF神经网络的虚拟轴机床末端刀具运动位姿实时检测研究

实现虚拟轴机床末端刀具位姿的实时检测目前仍然是虚拟轴机床在数控加工领域实现高精度控制和产业化的障碍之一。针对六自由度虚拟轴机床的末端刀具位姿检测进行研究。首先对虚拟轴机床进行运动学分析,然后以虚拟轴机床末端刀具的位姿逆解作为神经网络的训练样本,构建结构自适应确定的RBF神经网络,实现虚拟轴机床从关节变量空间到工作变量空间的映射,最后利用已训练好的RBF神经网络实现虚拟轴机床末端刀具位姿的实时检测。实验结果表明:利用该方法实现虚拟轴机床末端刀具运动位姿的检测不仅具有可行性,而且具有较高的检测精度,为虚拟轴机床末端刀具的直接闭环高精度控制奠定了基础。     

3-RRR型数控回转台的精度分析

研究３－ＲＲＲ数控回转台的精度分析问题。利用空间矢量链分析法构造零部件制造误差与动角台位姿误差的映射关系,建立相应的精度分析概率模型;在此基础上对设定零部件加工精度等级后的动角台位姿进行误差估计和灵敏度分析。研究成果为合理确定零部件尺寸和形位公差及其加工装配工艺的制定提供了理论依据。     

一种少自由度飞行模拟运动平台误差分析

将一种少自由度并联机构3-PRS用作飞行模拟运动平台,为使该平台运动精度满足系统要求,对其进行误差分离与灵敏度分析。通过研究平台运动学逆解模型获得驱动雅克比矩阵与约束雅克比矩阵,采用空间闭环误差矢量链的误差建模方法,对运动平台进行误差建模,获得各个几何误差源与终端输出位姿误差之间的映射函数,在所建立的全误差源模型的基础上,利用解析法去除冗余误差源后,借助驱动雅克比矩阵与约束雅克比矩阵将影响该平台末端可补偿位姿误差的误差源和不可补偿位姿误差的误差源分离。最后,在整个运动空间内,借助灵敏度分析,获得影响末端不可补偿位姿误差源的全局灵敏度影响系数。根据灵敏度影响系数可指导前期设计阶段各零部件公差等级的选择以及装配阶段装配公差的确定,研究结果对同类少自由度并联机构具有指导意义。     

基于D-H矩阵的Stewart型并联机床位姿误差计算模型

针对6自由度Stewart型并联机床,以D-H变换矩阵为建模工具,建立起包含铰座位姿参数、杆件D-H参数的机床动平台位姿方程.采用矩阵微分方法推导出一个机床位姿误差线性化计算模型.该模型不仅使铰座位姿参数误差、杆件D-H参数误差等几何误差全部进入机床位姿误差计算方程,而且将机床位姿误差与几何误差之间的非线性隐式函数关系简化为线性显式函数关系.基于支链杆长方程建立起一个能描述机床位姿误差与几何误差之间实际映射关系的非线性计算模型,以其作为参考模型对线性化计算模型的有效性进行检验.仿真表明:在小误差条件下,线性化模型可以很好地逼近非线性模型,由于具有形式简洁、分析与计算方便等特点,基于D-H变换矩阵的位姿误差线性化计算模型可用于Stewart型并联机床的精度分析、精度综合及运动学标定.仿真结果还表明:当对机床位姿精度要求较高时,需要考虑杆件的全部D-H参数误差对机床位姿的影响.     

Accuracy analysis and design of A3 parallel spindle head

As functional components of machine tools, parallel mechanisms are widely used in high efficiency machining of aviation components, and accuracy is one of the critical technical indexes. Lots of researchers have focused on the accuracy problem of parallel mechanisms, but in terms of controlling the errors and improving the accuracy in the stage of design and manufacturing, further efforts are required. Aiming at the accuracy design of a 3-DOF parallel spindle head(A3 head), its error model, sensitivity analysis and tolerance allocation are investigated. Based on the inverse kinematic analysis, the error model of A3 head is established by using the first-order perturbation theory and vector chain method. According to the mapping property of motion and constraint Jacobian matrix, the compensatable and uncompensatable error sources which affect the accuracy in the end-effector are separated. Furthermore, sensitivity analysis is performed on the uncompensatable error sources. The sensitivity probabilistic model is established and the global sensitivity index is proposed to analyze the influence of the uncompensatable error sources on the accuracy in the end-effector of the mechanism. The results show that orientation error sources have bigger effect on the accuracy in the end-effector. Based upon the sensitivity analysis results, the tolerance design is converted into the issue of nonlinearly constrained optimization with the manufacturing cost minimum being the optimization objective. By utilizing the genetic algorithm, the allocation of the tolerances on each component is finally determined. According to the tolerance allocation results, the tolerance ranges of ten kinds of geometric error sources are obtained. These research achievements can provide fundamental guidelines for component manufacturing and assembly of this kind of parallel mechanisms.     

一种含平行四边形支链的3自由度并联机构姿态精度综合与装配工艺设计

以含平行四边形支链的3平动自由度并联机构主模块为对象,通过误差建模揭示出影响这种机构末端姿态精度因素。利用灵敏度分析结果,将精度综合归结为一类有约束线性规划问题,并据此提出两种可以有效抑制末端姿态误差的装配工艺方案。     

Design and accuracy analysis of a metamorphic CNC flame cutting machine for ship manufacturing

The current research of processing large size fabrication holes on complex spatial curved surface mainly focuses on the CNC flame cutting machines design for ship hull of ship manufacturing. However, the existing machines cannot meet the continuous cutting requirements with variable pass conditions through their fixed configuration, and cannot realize high-precision processing as the accuracy theory is not studied adequately. This paper deals with structure design and accuracy prediction technology of novel machine tools for solving the problem of continuous and high-precision cutting. The needed variable trajectory and variable pose kinematic characteristics of non-contact cutting tool are figured out and a metamorphic CNC flame cutting machine designed through metamorphic principle is presented. To analyze kinematic accuracy of the machine, models of joint clearances, manufacturing tolerances and errors in the input variables and error models considering the combined effects are derived based on screw theory after establishing ideal kinematic models. Numerical simulations, processing experiment and trajectory tracking experiment are conducted relative to an eccentric hole with bevels on cylindrical surface respectively. The results of cutting pass contour and kinematic error interval which the position error is from –0.975 mm to +0.628 mm and orientation error is from –0.01 rad to +0.01 rad indicate that the developed machine can complete cutting process continuously and effectively, and the established kinematic error models are effective although the interval is within a ‘large' range. It also shows the matching property between metamorphic principle and variable working tasks, and the mapping correlation between original designing parameters and kinematic errors of machines. This research develops a metamorphic CNC flame cutting machine and establishes kinematic error models for accuracy analysis of machine tools.     

一种串并联型机床及其误差分析

多杆件并联及串并联型机床是正在致力研究和开发的新型加工设备,分析了一种新研制的串联型机床的结构及空间误差,推导并验证了主轴平台空间运动误差的数学模型,通过示例计算探讨了连杆的制造误差和滑座的进给误差给刀具空间运动位置精度和平台姿态的影响。     

Surface error decomposition for fixture development

As an integrated element of the manufacturing system of components, the machining fixture is a major contributing factor of the profile and orientation errors of component features. An effective way to control the accuracy of components is to decompose error sources and evaluate individual influential factors. This paper proposed a systematic method of error identification and calculation, in which locating error and machining error were studied. The locating error, which is the surface error generated before machining, is obtained from the calculation of the surface error based on tolerances of the locating positions and the decomposition of clamping deformation using finite element analysis (FEA). The machining error, the surface error generated from machining operations, is gained mainly from the coordinate measurement machine’s (CMMs) measurements. The surface error of multi-machining operations is investigated and the resultant surface error is evaluated against tolerance. The analysis of a sample feature of a turbine blade is provided as an example.     

Tolerance design optimization of machine elements using genetic algorithm

An important problem that faces design engineers is how to assign tolerance limits. In practical applications, tolerances are most often assigned as an informal compromise between functionality, quality and manufacturing cost. Frequently, the compromise is obtained iteratively by trial and error. A more scientific approach is often desirable for better performance. In this paper, a genetic algorithm (GA) is used for the design of tolerances of machine elements to obtain the global optimal solution. The objective is to design the optimum tolerances of the individual components to achieve the required assembly tolerance, zero percentage rejection of the components and minimum cost of manufacturing. The proposed procedure using GA is described in this paper for two tolerance design optimization problems: gear train and overrunning clutch assemblies. Results are compared with conventional techniques and the performances are analyzed.     

Effect of manufacturing tolerances on indexing accuracy and synthesis of the Geneva Mechanism

Machine tools used for batch and mass production are generally equipped with the Geneva Mechanism for indexing. One of the factors affecting the machining accuracy in these machine tools is the positional accuracy of the tools with respect to the work which, in turn, is affected by the indexing accuracy of the indexing mechanism. This paper discusses the effect of manufacturing tolerances on indexing accuracy. It is observed that indexing accuracy is different for constrained and unconstrained designs corresponding to the same value of tolerance. Results regarding indexing accuracy for different values of tolerances in constrained designs are recorded and suggest that, in the case of constrained designs, careful allocation of tolerances on design parameters is needed. The method of tolerance allocation suggested by Choubey and Atluri⁸ is followed. Synthesis of a six-slot Geneva Mechanism incorporating manufacturing tolerances and following stochastic non-linear programming and the exterior penalty function method is carried out to study these effects. Practical implications of the effects of manufacturing tolerances on indexing accuracy and synthesis of Geneva drives are discussed, giving suitable examples     

机器人机构的优化综合

应用最优化技术进行机器人的精度综合，确定能满足绝对位姿精度和重复位姿精度要求，并可使公差制造成本最低的最优连杆参数公差和关节伺服定位精度。在误差概率分析的基础上，建立了机器人机构精度概率优化综合的数学模型。     

新型4自由度并联机器人位姿误差分析

将一种新型四自由度并联机器人等效为由串联机构构成的空间闭环机构 ,运用 Denavit- Hartenberg方法提出了运动平台位姿误差的一种分析算法。利用这个算法可以分析各种构件加工、安装误差对运动平台位姿精度的影响。进行了数值仿真验证了算法的正确性。最后分析出对位姿精度影响较大的因素 ,通过重视这些因素可提高实际机构的操作精度     

Design of a low-cost, precision belt-drive machine for high-throughput nanomanufacturing

The creation of new technology for high-throughput nanomanufacturing is necessary to realize the full potential of some nano-technological products. Here, we present the preliminary design and manufacture of a precision machine for enabling high-throughput nanomanufacturing processes in a laboratory environment. An error analysis and rate analysis for implementing Dip Pen Nanolithography (DPN), a scanning-probe-based nanomanufacturing process, are used to generate detailed machine functional requirements. A deterministic process is then used to design or select each machine element; standard machine elements and easily manufactured components are used when possible to achieve a low-cost design. The machine is capable of operating with an accuracy and repeatability in the range of hundreds of nanometers, with a thermal stability in the tens of nanometers, thus exceeding the performance requirements for DPN as well as the capabilities of current technology. In a manufacturing environment, the machine could implement DPN at a rate which is almost two orders of magnitude faster than current technology. Multiple machines could also be used for parallel processing and increased production rate to make a nanomanufacturing process economically viable.