Calibration Technology Of Antenna Vice-reflector Parallel Adjustment Mechanism

In the working process of large-diameter reflector antenna,the pointing accuracy will be affected by environmental load and other factors,resulting in the deviation of pointing accuracy and poor efficiency.Therefore,it is necessary to compensate the posture of vice-reflector by the parallel adjustment mechanism of vice-reflector and according to the motion state of the main-reflector of the antenna,so as to meet the requirements of the antenna pointing accuracy.Due to the limitation of the practical situation,and the vice-reflector parallel adjustment mechanism is in the open or half-open working state.Therefore,it is necessary to identify its actual structural parameters by kinematic calibration and improve its positioning accuracy.In this thesis,the parallel adjustment mechanism of vice-reflector of the antenna is taken as the research object.Based on the forward and inverse solutions of the parallel mechanism kinematics,the external calibration,self-calibration,and coefficient matrix ill-conditioned problems of the parallel mechanism are studied.Finally,experimental verification is performed.The main work of the paper is as follows:1.Research the external calibration technology of Stewart platform.The external calibration method is based on the inverse kinematics of the parallel mechanism,and the vector differential method is used to establish a calibration model.Then,it uses the least squares algorithm to implement the calibration algorithm after multiple iterations to complete the identification of the structural parameters.The improper choice of posture resulting ill-conditioned coefficient matrix is solved using the Liu estimation method during the calibration process,and the solution of the correction factor d is described in detail.Finally,four simulation examples are used to verify the numerical efficiency,robustness,and validity of Liu estimation.2.Research on self-calibration technology of parallel mechanism.On the basis of overcoming the defects of existing external calibration methods and traditional self-calibration methods,a new 4-DOF self-calibration system with redundant legs of a displacement sensor is proposed.Then the calibration model and calibration algorithm of the calibration system are derived in detail using forward and inverse kinematics solutions,and the partial derivative and observability of the calibration algorithm are analyzed.Finally,four simulation examples are used to verify the accuracy,robustness and validity of Liu estimation.3.Experimental verification.First of all,the working principle of the laser tracker of external measuring equipment and the posture measuring system independently developed by the laboratory is briefly introduced.Then the external calibration method and the accuracy of Liu estimation are validated by the calibration experiment under the experimental conditions.