【作者】 周志明；

【导师】 程远雄；

【作者基本信息】 华中科技大学 ， 机械工程， 2021， 硕士

【摘要】 由于以航空叶片为代表的精密加工需求的增加,对定位装置的性能要求也越来越高。传统精密定位台由于其结构特性、驱动器性能的原因往往只能达到微米级定位精度,随着近年来智能材料驱动器的应用、柔性机构技术及机器学习算法的发展,为解决超精密工作台超精密、大行程和高刚度的问题,提供了技术途径。论文针对航空叶片加工过程中超精密定位的需要,提出一种基于压电陶瓷作动器及柔性放大机构驱动的空间六自由度柔性并联机构工作台,并对其性能及其运动控制方法开展了系统研究。论文针对现有的精密定位台定位精度不足的问题,提出基于6-PSS并联机构构型的空间六自由度柔性并联定位台的设计方案。采用双轴直圆型柔性铰链克服了传统刚性铰链存在的运动间隙、摩擦磨损等现象引起的精度不足的问题,利用压电陶瓷的微纳驱动能力为定位台获得微纳精度奠定技术基础。首先开展了定位台的空间六自由度柔性并联执行机构的设计,以定位台工作空间、承载能力的要求分析设计执行机构的主要结构尺寸,基于Workbench有限元仿真平台建立定位台执行机构的结构静力学仿真模型,对机构进行运动学分析,获得机构的运动雅可比矩阵,并验证雅可比矩阵的准确性。为增大定位台的工作空间,设计二级级联柔性杠杆位移驱动放大机构,利用有限元模型分析位移放大机构的放大倍数,能将驱动器的行程有效放大。完成定位台总体结构设计。基于有限元模型对空间六自由度柔性并联机构性能进行研究。开展了机构有限元刚度分析,研究动平台在不同载荷条件下的刚度,通过分别在定位台各自由度方向添加载荷计算机构的弹性变形;对驱动力进行计算分析,为驱动器选型提供依据。对平台的可达工作空间进行分析,通过机构有限元模型得到的雅可比矩阵进行机构运动学逆解,考虑了压电陶瓷驱动系统的行程范围限制,采用极限边界搜索法计算出定位台的可达工作空间。计算并分析了定位台执行机构结构尺寸对工作空间、承载刚度和驱动力的影响。为了实现空间六自由度柔性并联机构的运动控制,开展机构的运动建模。基于伪刚体法对机构进行运动学分析,获得机构的数学模型,结果与机构有限元模型比较发现其精度较低,不能用于机构的运动控制。为获得机构精确的运动解析模型,采用卡氏第二定理推导出柔性支链的柔度矩阵的计算式;应用有限元分析验证柔度矩阵结果的准确性。建立空间六自由度柔性并联机构的运动平衡方程和静力平衡方程并联立求解,得到机构的雅可比矩阵解析模型。与雅可比矩阵有限元模型对比,验证解析模型的精度。考虑到定位台在承载变形引起的定位误差,基于机构运动学解析模型,采用多项式回归的机器学习算法实现由于刚度引起的运动误差的补偿,进一步提高定位台的定位精度。本文研究为航空叶片等超精密定位台的开发提供理论与技术基础。更多还原

【Abstract】 With the increase in demand for precision machining represented by aviation blades,the performance requirements for positioning devices are also getting higher and higher.The traditional precision positioning platform can only achieve micron-level positioning accuracy due to its structural characteristics and drive performance.With the application of smart material drives in recent years,the development of flexible mechanism technology and machine learning algorithms,a technical approach has been provided to solve the problems of ultra-precision,large stroke and high rigidity of ultra-precision worktables.Aiming at the need for ultra-precision positioning platform during the machining of aviation blades,this thesis proposes a spatial six-degree-of-freedom flexible parallel mechanism workbench based on PZT and flexible amplification mechanisms,and carry out systematic research on its performance and its motion control methods.Aiming at the problem of insufficient positioning accuracy of the existing precision positioning platform,this thesis proposes a design scheme of a spatial six-degree-offreedom flexible parallel motion platform based on the 6-PSS parallel mechanism.The use of two-axis straight round flexible hinges overcomes the lack of precision caused by the movement gap,friction and wear in the traditional rigid hinges,and the micro-nano drive capability of PZT lays the technical foundation for the movement platform to obtain micronano precision.Firstly,carry out the design of the six-degree-of-freedom flexible parallel actuator of the positioning table.The main structural dimensions of the actuator are analyzed and designed based on the requirements of the working space and bearing capacity of the positioning platform.The static structure of the positioning platform actuator is established based on the Workbench finite element simulation platform.The mechanics simulation model is used to analyze the kinematics of the mechanism,obtain the kinematic Jacobi matrix of the mechanism,and verify the accuracy of the Jacobi matrix.In order to increase the working space of the motion platform,design a two-stage cascaded flexible lever displacement drive magnification mechanism,and the finite element model is used to analyze the magnification of the displacement magnification mechanism,which can effectively magnify the stroke of the driver.Complete the overall structure design of the sports platform.Based on the finite element model,study the performance of the spatial six-degree-offreedom flexible parallel mechanism.The finite element stiffness analysis of the mechanism is carried out to study the stiffness of the moving platform under different load conditions.The elastic deformation of the mechanism is calculated by adding loads in the respective directions of the positioning table;the driving force is calculated and analyzed by providing a basis for the selection of the driver.Analyze the reachable working space of the platform,perform the inverse kinematics solution of the mechanism through the Jacobi matrix obtained by the finite element model of the mechanism,considering the limit of the stroke range of the piezoelectric ceramic drive system,the limit boundary search method is used to calculate the reachable working space of the positioning platform.The influence of the structure size of the positioning table actuator on the working space,bearing stiffness and driving force is calculated and analyzed.In order to realize the motion control of the spatial six-degree-of-freedom flexible parallel mechanism,carry out the motion modeling of the mechanism.Based on the pseudo-rigid body method,carry out the kinematics analysis of the mechanism,and the mathematical model of the mechanism is obtained.The result is compared with the finite element model of the mechanism,and find that its accuracy is low and cannot be used for the motion control of the mechanism.In order to obtain an accurate motion analysis model of the mechanism,use the Karnofsky’s second theorem to derive the calculation formula of the flexibility matrix of the flexible branch chain;the finite element analysis is used to verify the accuracy of the flexibility matrix results.The motion balance equation and static balance equation of the spatial six-degree-of-freedom flexible parallel mechanism are solved in parallel,and obtain the Jacobi matrix of the kinematics analysis model of the mechanism.Compare with the Jacobi matrix of the finite element model to verify the accuracy of the analytical model.Taking into account the positioning error caused by the bearing deformation of the positioning table,based on the kinematics analysis model of the mechanism,the machine learning algorithm of polynomial regression is used to realize the compensation of the motion error caused by the stiffness,and further improve the positioning accuracy of the motion platform.The research in this paper provides a theoretical and technical basis for the development of ultra-precision positioning tables such as aviation blades.更多还原