【作者】 张刚；

【导师】 段学超；

【作者基本信息】 西安电子科技大学 ， 机械电子工程， 2014， 硕士

【摘要】 为了保证大口径天线的性能达到设计要求和天线副面能够及时进行局部调整并使其拟合的拋物面焦距在空间平滑曲线上运动,解决方案之一就是通过安装六轴并联机器人调整机构(Stewart平台)来实现天线副面在空间的运动,其关键技术之一就是天线副面的高精度定位、定姿技术。本文针对精调Stewart平台的结构参数误差和球铰间隙误差辨识进行了研究,旨在经过运动学双重标定后使天线副面精调Stewart平台实现高精度定位、定姿,并为多自由度并联机器人的精确建模以及高精度控制提供理论参考,本文所取得的主要研究成果为:归纳了与Stewart平台位姿相关的基本知识,包括整体平台的自由度计算、运动平台位姿的运动学正逆解等;推导分析了球铰间隙误差对于Stewart平台运动平台运行精度的影响,并建立了球铰间隙简化模型;基于运动平台位置正、逆解算法,针对结构参数误差和球铰间隙误差对平台位姿运行精度的影响进行了仿真分析,分析主要模拟运动平台沿设定的三个坐标轴直线运动和在初始位置绕三个坐标轴进行旋转运动,分析结果表明较小的结构参数误差和球铰间隙误差可以对运动平台运行精度造成较大的影响。根据运动学位置逆解算法,构建了Stewart平台矢量链法双重标定模型;依据设定的结构参数的理论值和运动平台运行位姿误差,基于标定模型对平台结构参数误差和球铰间隙误差进行了辨识;为了检验球铰间隙误差对于运动平台运行精度的影响,区分考虑球铰间隙和未考虑球铰间隙两种情况,对运动学标定后运动平台运行位姿误差进行了仿真分析,分析同样模拟运动平台沿设定的三个坐标轴直线运动和在初始位置绕三个坐标轴进行旋转运动,结果表明,考虑球铰间隙比未考虑球铰间隙时,运动平台的运行精度将会提升一个数量级,由此证明了Stewart平台矢量链法双重标定模型可以有效辨识出Stewart平台的结构参数误差和球铰间隙误差从而使运动精度有数量级的提高。最后对课题样机进行了误差标定实验。通过激光跟踪仪获取驱动支腿伸缩量与运动平台位姿的对应数据对,利用Stewart平台矢量链法双重标定模型对结构参数误差和球铰间隙误差进行了辨识,而后对平台的结构参数进行了修正并在平台运行过程中对球铰间隙误差进行了补偿,根据对运动平台标定前相同位姿的重新测量获得的运动平台实际位姿,通过与运动平台期望位姿的对比,验证了Stewart平台矢量链法双重标定模型的可行性和有效性。更多还原

【Abstract】 In order to ensure the performance of large caliber antenna that achieves the design requirements, timely conduct local adjustment of the secondary reflector of antenna and make its fitting paraboloid focus moving on spatial smoothing curve, one solution is that hexapod parallel manipulator adjustment mechanism(Stewart platform) is fixed to realize the motion of the secondary reflector in space. One of the key techniques is to determinate the high precision position-and-orientation of the antenna’s secondary reflector which is realized by the double kinematic calibration.This thesis studies on the error identification of the accurate adjusting Stewart platform’s structure parameters and ball joint clearances. This study aims to make the accurate adjusting Stewart platform of the antenna’s secondary reflector to realize the high precision position-and-orientation after the kinematic bi-calibration, and provide the theory reference for multi degree of freedom parallel manipulator’s accurate modeling and high precision control. The main achievements of this thesis are as:The related basic knowledge of Stewart platform’s position-and-orientation is summarizes, including to calculate the degree of freedom(DOF) of the manipulator and solute the motion-platform’s positive-and-inverse kinematic algorithm. The influence is deduced and analyzed that ball joint clearance error made for the motion platform running accuracy of Stewart platform. The simply model about ball joint clearance error is established. Simulation analysis is carried on the impact that of structural parameter errors and ball joint clearance errors to position-and- orientation’s errors, which is based on the algorithm of positive-and-inverse kinematics. The analysis mainly simulate that the motion platform make liner motion along three setting axes and initial-position rotation around three axes. The analysis results show that the smaller error of structural parameters and the ball joint clearance can greatly affect the accuracy of platform motion.According to the inverse kinematics algorithm of position, the bi-calibration model is established for Stewart platform using the vector chain method. According to the setting structure parameters’ theoretic value and the position-and- orientation’s errors of the motion platform, the identification of the structural parameters’ and the ball joint clearances’ errors is carried out that based on the bi-calibration. For checking the impact that the ball joint clearances’ errors make for the motion platform’s operation accuracy, the simulation analysis is made about the position-and- orientation’s errors of the motion platform that is calibrated, which is distanced between considering with ball joint clearance and considering without ball joint clearance. The analysis also simulate that the motion platform make liner motion along three setting axes and initial-position rotation around three axes. The result shows that the operation precision of the motion platform will be made up an order of magnitude, when considering with ball joint clearance. The result also show that Stewart platform bi-calibration model based on vector chain method can effectively identify the structural parameters’ and the ball joint clearances’ errors of Stewart platform, so that the motion accuracy is improved by orders of magnitude.Finally, the calibration experiment is conducted on the project prototype. Driving leg stretching amount and the motion platform’s position-and- orientation can get by laser tracker. The structural parameters’ and the ball joint clearances’ errors are identified using Stewart platform bi-calibration model based on vector chain method. The structural parameters’ errors are revised and the ball joint clearances’ errors are compensated in operating process. According to the motion platform’s practical position-and- orientations which are measured on the same position. Stewart platform bi-calibration model based on vector chain method is verified to be feasible and effective by contrast between the expectation value and the practical value after bi-calibration.更多还原