| With the wide application of optical mirrors in observation systems,aerospace,optical instruments and other fields,modern optical systems are becoming ultra-precision,large-diameter,aspherical,and high-resolution.The development of optical mirrors in these directions also puts forward higher requirements on the processing equipments.The parallel manipulator has the advantages of large rigidity,great dynamic characteristics,and no accumulated error.Combining it with the series manipulator can better adapt to modern optical processing technology.In this thesis,a five-degree-of-freedom hybrid optical mirror processing robot is used as the research object,and the research is carried out from the perspective of control system.The robot is a multi-axis system.In the process of trajectory tracking control,the end error is coupled by a single joint tracking error.The traditional control method aimed at reducing the single joint tracking error cannot directly compensate for the end contour error.Considering that high-precision contour control is an important guarantee for the realization of precision processing of optical mirrors,the research is carried out from trajectory error analysis,kinematics closed-loop control system,single-joint feedforward compensation control,multi axis cross-coupling contour control,physical prototype experiment.The main contents are as follows:(1)In the research of trajectory error analysis.Firstly,starting from the definition of trajectory tracking error and contour error in trajectory motion control,conduct theoretical analysis.Secondly,taking advantage of the characteristics that joint tracking error is easy to measure but contour error is not easy to measure,and the trajectory tracking error is coupled by the single joint tracking error,a plane 2D contour error model is established based on the trajectory tracking error.Thirdly,on the basis of above,the Frenet coordinate system is established according to the principle of differential geometry,basing on the tangential approximation method and circular approximation method to derive 3D contour error model.Finally,the trajectory error is randomly given in the MATLAB,and numerical simulation is performed.The trajectory tracking error is compared with the contour error to verify the trajectory error analysis result,and the contour error calculated by the model is compared with the real contour error to verify the deduced mathematical model.And the design goal of the contour control system of the optical mirror processing robot is determined to improve the tracking accuracy of the single-joint control system and compensate the end contour error.(2)In the research of kinematics closed-loop control system.Firstly,according to the actual working environment of the optical mirror processing robot,the pose inverse solution model of the series module is established by the geometric method,the rotation angle of the series rotor and the end position of the parallel module under a given end trajectory are obtained.Secondly,the closed-loop vector method is used to establish the kinematics model of the parallel module,and the movement law of each joint of the parallel module is obtained.Thirdly,according to the principle of servo control,a mathematical model of the current loop,speed loop,position loop is established,and the parameters are adjusted to obtain a single-joint servo controller.Finally,under the given end trajectory,the solved joint motion laws are used as the input of the servo control system to obtain the kinematics closed-loop control system of the whole machine with five inputs and five outputs,and the simulation test is carried out based on MATLAB/Simulink to realize the preliminary contour control function of the end,which provides ideas for the following feedforward compensation and contour compensation strategies.(3)In the research of single-joint feedforward compensation control.Firstly,according to the feedforward control principle,combined with the kinematics closed-loop control system,the speed and acceleration feedforward compensation is introduced.The system transfer function,the feedforward compensation coefficient,and theoretically analyzed of the error before and after compensation are studied.Secondly,establish a parallel module dynamic model based on the Kane equation to decouple the driving force and disturbance forces,such as inertial force,coupling force in the end motion process.A dynamic feedforward controller is established to obtain transfer function,and determine the dynamic feedforward coefficient.Finally,a simulation experiment based on MATLAB/Simulink verifies the effects of velocity,acceleration feedforward compensation and dynamics feedforward compensation.The results show that single-joint feedforward compensation can effectively improve the tracking accuracy of the system.(4)In the research of multi axis cross-coupling control.Firstly,according to the respective functions and characteristics of the parallel module and the serial module,a contour control strategy for the whole machine is proposed.Secondly,establishing a parallel module cross-coupling contour control system,including converting the contour error model to the parallel module task space,establishing forward channel cross-coupling gain model and compensation channel cross-coupling gain model to realize direct compensation of contour error on the basis of single-joint feedforward compensation.Thirdly,the stability analysis of the cross-coupled control system based on the contour error transfer function is studied.Finally,based on the MATLAB/Simulink simulation experiment,kinematics closed-loop control + the single-joint feedforward compensation + cross-coupling contour compensation method used in this thesis can greatly reduce the system contour error,and the system's contour control performance is also verified.(5)In the research of experimental on physical prototypes.Building the "PC+PMAC" open control system based on the methods and processes which are mentioned above.Compiling control programs and algorithm programs,debuging the control system,and extracting multiple sets of related experimental data to analyze.The whole machine contour control strategy proposed in this thesis and the conclusions put forward in the research process are verified by experiments.This thesis has 82 figures,5 tables,and 95 references. |
PDF Full Text Request