Modeling And Control Of 6-DOD Microgravity Simulation Platform

It is necessary to carry out sufficient ground microgravity simulation experiments in the development and testing phase of aerospace equipment to ensure the reliability and safety of aerospace equipment.The development of low-cost and high-scalability ground microgravity simulation experimental platform has become an important part of the aerospace technology development plan.Based on the research work of the microgravity simulation platform structure design,the microgravity simulation implementation strategy,and the 1-DOF microgravity simulation experiment.the key technologies such as modeling,parameter identification and control methods of 6-UPS parallel manipulator used in the 6-DOF microgravity simulation platform is studied in this paper.The research content is divided into four parts.The first part is the kinematic calibration of the 6-UPS parallel manipulator.The error model of 6-UPS parallel manipulator is derived by differential method,and the main kinematic parameters affecting the positioning accuracy of the robot are analyzed.Then the experimental scheme of kinematic calibration of the robot with laser tracker was designed.The Levenberg-Marquardt algorithm is used to identify the kinematic parameters of the parallel manipulator.Finally,the parameter error is compensated.It has been verified that the kinematic accuracy of the parallel manipulator is significantly improved after calibration.In the second part,the dynamics model of 6-UPS parallel manipulator is established by NewtonEuler method.Combined with the symmetry of the parallel mechanism and the repeatability of each branch,the dynamic model of the robot is expressed as a linear form with respect to the base parameter set.decoupling of dynamic parameters and motion state variables.It lays the foundation for the dynamic parameter identification of 6-UPS parallel manipulator.In the third part,the dynamic parameters of the 6-UPS parallel manipulator is studied.An experimental strategy for stepwise identification of inertial parameters and friction parameters is proposed.This scheme can improve the identification accuracy of robot dynamic parameters.The artificial bee colony algorithm is used to identify the nonlinear friction model parameters of the parallel manipulator.The verification results show that the nonlinear Deami-Heimann friction model can effectively reduce the friction prediction error compared with the Coulomb-viscous friction model.The fourth part designs the PID controller with gravity compensation for 6-UPS parallel manipulator.The stability and robustness of the designed controller are verified by theoretical and simulation experiments.The simulation results show that the PID controller with gravity compensation can achieve more accurate trajectory tracking control than the traditional PID controller,especially the steady-state error of Z-axis is reduced from 1.01 mm to 0.21 mm.This controller is used to simulate the microgravity simulation experiment and achieved good simulation results.