Study On Accuracy Design And Kinematic Parameter Calibration Of Optical Mirror Polishing Robot

With the advent of the information age,modern optical systems are rapidly developing in the direction of large-caliber,high-precision,high-resolution.Among them,optical mirror plays an important role in the strategic deployment of national security and scientific development with its superior optical performance.With the increasing demand for the accuracy of optical mirror,the related optical mirror machining equipment is also constantly updated and improved.Combined with the series manipulator on the parallel manipulator,it has the advantages of high stiffness,fast response,small accumulated error and large range of motion,which is more suitable for the machining of large optical mirror.In this paper,a hybrid machining equipment composed of a three degree of freedom parallel manipulator and a two degree of freedom rotating head is used as the main body of the optical mirror polishing robot.Considering that the motion accuracy of the parallel manipulator has an important impact on the mirror machining quality,so this paper studies the error modeling,accuracy design,kinematic parameter calibration and multi-objective dimension optimization design of the parallel part in the robot.The accuracy of the model and the effectiveness of the research methods are verified by numerical simulation and experiment.The main research contents are as follows:(1)The error modeling method of the parallel part in the polishing robot is studied and the error separation is carried out.Firstly,the closed-loop vector method is used to model the kinematics of the serial and parallel parts in the robot and the position of the polishing disk is solved.Secondly,based on the optimization of the ball pair in the parallel part,the geometric error sources in each kinematic pair of the parallel manipulator are analyzed.Finally,the error mapping model is established based on the vector method,and the compensable error sources and the non-compensable error sources in the model are separated.It provides the theoretical basis for the subsequent accuracy analysis of the error sources and the compensation of the end pose error.(2)The accuracy design method of the parallel part in the polishing robot is studied and the numerical simulation is carried out.Firstly,the influence degree of each geometric error sources on the end pose error is analyzed and the main error source is determined.The error sensitivity model is established,and the sensitivity degree of the moving platform motion precision to each error source in the design space is quantitatively analyzed.Secondly,the random sampling of each geometric error is carried out,and the probability of error value distribution of the moving platform under its comprehensive influence is simulated and analyzed.In addition,the maximum error distribution in the design space of the moving platform is simulated and analyzed to provide a theoretical basis for subsequent research and development trajectory planning.Finally,the overall cost model is established,and the accuracy synthesis of the error sources is studied based on the quantum particle swarm optimization algorithm.Monte Carlo simulation was used to verify the rationality of the tolerance distribution of geometric error sources.(3)The kinematic parameter calibration method of the parallel part in the polishing robot is studied and verified by experiments.Firstly,according to the analysis of the geometric error sources and the separation result of the compensable error sources,determine the geometric error parameter to be calibrated and establish a calibration model.Secondly,the poses of the moving platform were measured by experiments,and the Levenberg-Marquardt method and the improved pivot element weighted iterative algorithm were used for parameter identification.On this basis,a comparative analysis is made on the identification error rate.Finally,based on the results of parameter identification,the pose error of the moving platform is compensated,and the error values before and after calibration are simulated and compared by MATLAB software,which verifies the accuracy of error mapping model and the effectiveness of kinematic calibration method.(4)The kinematic and dynamic performance of the polishing robot are studied and the multi-objective dimension optimization is realized.Firstly,performance indexes such as dexterity of motion,pose accuracy,driving moment and inertia coupling strength are defined,and the change rule of each index in the design space is simulated and analyzed.At the same time,the correlation between each performance and manipulator size parameters is determined.Secondly,on the basis of determining the optimal design variables,the constraints are set up according to the workspace analysis results and the size range of each component,and the multi-objective optimization model is established by using the linear weighting method.Then,the genetic algorithm toolbox of MATLAB is used to optimize the objective function,and a set of scale parameters which make the robot's motion performance optimal are obtained.Finally,according to the dimension optimization results of the manipulator,the movement performances before and after optimization are compared and analyzed to verify the accuracy of the optimization results and provide theoretical basis for the design of the polishing robot.There are 55 pictures,14 tables and 99 references in this paper.