Research On Dynamic Performance And Kinematic Accuracy Assurance Of Large Optical Mirror Polishing Robot

Modern optical systems are developing towards large diameter,high precision and high resolution.The traditional processing equipment is still inadequate in dynamic performance and other aspects,and it is difficult to adapt to the current demand for large optical mirror applications.The use of serial robots for large optical mirror polishing operations also suffers from deficiencies in rigidity,dynamic performance and positioning accuracy.Thus,the introduction of a parallel manipulator with compact structure,high rigidity and low motion error into the field of optical mirror processing can improve the working performance of the processing equipment to a certain extent.In addition,to avoid the disadvantages of small working space and strong motion coupling of the fully parallel manipulator,a large optical mirror processing equipment using a five-degrees-of-freedom hybrid robot with a dual-rotor grinding system is proposed.The hybrid polishing robot has a multi-closed-loop structure,and the robot’s inertial coupling,component elasticity,gravity field,and geometric errors all have an impact on its dynamic performance and kinematic accuracy.Therefore,in order to improve the working performance of the large optical mirror polishing robot,a combination of theoretical modeling,numerical simulation and prototype experiments is used to study the joint effect,inertia coupling,branched-chain layout,gravity field,branched-chain elasticity and geometric error,and to assure the kinematic accuracy of the polishing robot from two aspects:comprehensive optimization of multiple performance parameters and kinematic error compensation.The main research contents are as follows:1)To establish the explicit dynamics model of the polishing robot and analyze the active branched-chain inertia coupling property,firstly,considering the friction effect of robot motion joints,the polishing robot dynamics model with explicit form is established based on the kinematic model with Newton-Euler method.Secondly,based on the dynamics model under the joint space,the active branched-chain inertia coupling property evaluation model of the polishing robot is proposed.Finally,the validity of the dynamics model is verified by the virtual prototype,and the variation of the inertial coupling strength of the active branched-chain in the workspace is analyzed by numerical simulation.2)To study the effect of the branched-chains’ spatial layout and gravity field on the static stiffness property of the polishing robot,firstly,combined the configuration characteristic of the polishing robot,the static stiffness models of the robot series system and parallel system considering the gravity field are established respectively.Secondly,the static stiffness model of the whole machine for the polishing robot considering the gravity field was formed based on the principle of small deformation superposition.Finally,the effect of the spatial layout of the active branched-chains on the stiffness performance of the polishing robot is studied,and the distribution characteristics of the robot terminal deformation in the workspace considering the gravity field are analyzed by numerical simulation.3)For analyzing the influence of the elasticity and cross-sectional parameters of the kinematic branched-chains of the polishing robot on its dynamic properties,firstly,taking the spatial beam element as the basic model,the elastic dynamic equation for the kinematic branched-chain of the polishing robot is established based on the finite element method.Secondly,combined with the elastic deformation coordination condition,the polishing robot rigid-flexible coupling elastic dynamics model is established.Finally,the distribution law of the low-order natural frequency of the polishing robot in the workspace and the influence of the cross-sectional parameters of the kinematic branched-chain components on the low-order natural frequency are analyzed by numerical simulation,and the validity of the elastic dynamics model is verified by the physical prototype modal experiments.4)To clarify the influence of the geometric errors of the polishing robot on the kinematic accuracy and identify the geometric error source parameters,firstly,based on the D-H matrix method and perturbation theory,the kinematic error model of the polishing robot containing geometric errors in component machining,assembly and positioning is established.Secondly,the geometric error source parameters of the polishing robot are processed singly,and the influence law of each geometric error on the position error of the moving platform is analyzed by numerical simulation.Finally,the geometric error sources of the polishing robot are identified and analyzed based on the L-M algorithm by establishing a kinematic error identification model and experimentally measuring the kinematic parameters of the moving platform.5)For improving the comprehensive working performance of the research and throwing robot and assuring its kinematic accuracy,firstly,the influence law of the structural parameters of the polishing robot on its kinematic performance index and static/dynamic performance index is analyzed.Secondly,a comprehensive optimization model with multiple performance parameters of the polishing robot is established based on hierarchical analysis by selecting the main indexes such as kinematic dexterity,branched-chain acceleration,kinematic error,inertial coupling and stiffness,and the structural parameter of the polishing robot is optimized and the changes of the performance indexes before and after the optimization are compared and analyzed.Finally,the compensation of the kinematic errors of the polishing robot is completed by modifying the robot motion control parameters based on the geometric error identification results,and its endpoint kinematic accuracy is tested by combining with the large optical mirror polishing trajectory.The research on dynamic performance and kinematic accuracy assurance of the large optical mirror polishing robot carried out in this project is of great significance to improve the dynamic performance of the hybrid optical mirror polishing robot,ensure the kinematic accuracy of the robot and enhance the quality of the mirror surface.It can also provide theoretical and experimental references for dynamic performance improvement and motion accuracy assurance of parallel/hybrid manipulators in other engineering backgrounds.The dissertation has 79 figures,18 tables and 178 references.