Research On Dynamic Parameter Identification And Control Strategy Of 3-PPR Parallel Servo Platform

During the experiment of a large laser device,a large number of bottom loading optical mechanical modules need to be installed in the optical path of laser device.According to the characteristics of the module,a set of 6-DOF precision alignment system is designed,and the 3-ppr parallel servo platform is the core component to realize the plane pose adjustment.In order to successfully complete the task of installation and calibration and ensure the installation accuracy of the module,the plane pose tracking performance of the 3-ppr parallel servo platform needs to meet higher requirements.However,the uncertainty of system parameters and the external interference in the process of installation and calibration bring challenges to the high-precision control of the platform.In addition,the parallel servo platform is a kind of multi-axis control system,and the cooperation of each joint motion is also an important factor affecting the pose tracking accuracy of the platform.This paper takes3-ppr parallel servo platform as the research object,and studies its dynamic parameter identification and control strategy.The main contents are summarized as follows:Firstly,the kinematics and dynamics model of 3-ppr parallel servo platform is established.On the basis of kinematic analysis and Lagrange equation,the dynamic model of the mechanism body is deduced,and the dynamic model of the driving system is given.The dynamic model of the platform including the driving system is established.Secondly,based on the weighted least square method,the parameter identification of the dynamic model of the 3-PPR parallel servo platform including the drive system is studied.The linearization form of the model about the parameters to be identified is obtained by mathematical derivation;the Fourier series improved by quintic polynomial form is used as the excitation trajectory at the end effector on the moving platform,and the genetic algorithm is used to optimize the coefficient with the minimum condition number of the observation matrix as the index.The parameters identification simulation and experimental model is built,which not only identifies the inertia parameters and joint friction parameters of the mechanism body,but also identifies some parameters of the drive system.Thirdly,a robust controller based on synchronization error is designed to solve the problem that the movement of joints is uncoordinated after being disturbed and the trajectory tracking precision is reduced.Based on the idea of "virtual motor",the motion error information of the three real axes is connected through the virtual axis,and the synchronization error of each axis is defined.Based on this,a robust controller is designed to make the tracking error and synchronization error of the three axes converge asymptotically.Through the simulation analysis,it is found that the control strategy can improve the nonlinear synchronization performance of each axis and effectively improve the system coordination.Finally,based on the Beckhoff motion controller using the Ether CAT field bus,a3-PPR parallel servo platform verification prototype is built,and two sets of trajectory tracking experiments are designed to compare the trajectory tracking performance of robust controllers based on synchronization errors with that of the traditional computed torque controller.Experiments show that the robust control strategy based on synchronization error has smaller tracking error,stronger robustness,and makes the system work in a more collaborative state.The control strategy can meet the control requirements in the actual installation and calibration process.