On The Kinematic Bi-calibration Of The Parallel Manipulator For The Secondary Reflector Of High Precision Antenna

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.