Trajectory Tracking Control Of 3-PRR Parallel Mechanism

This topic is based on a major national special project,and takes a 3-PRR parallel mechanism that can realize posture adjustment as the research object.Through theoretical research,simulation analysis and experiment,it conducts research on its kinematics,dynamics,and control strategy.The main research is The content is as follows:First,a 3-PRR parallel mechanism is proposed,and the mechanical structure model is introduced and simplified.The closed vector chain method is used to solve the inverse kinematics;the dynamic equation of the 3-PRR configuration is established based on the principle of virtual work;the inverse dynamics and dynamics simulation of the mechanism are carried out.Then,the mathematical model of the electro-hydraulic servo system is established,the joint space-based control structure is adopted,the position-based PID control strategy is designed,and the influence of PID parameters on the control effect is analyzed through simulation.In order to improve the safety and compliance of the parallel mechanism,a position-based impedance controller is designed for the tracking error caused by the parallel mechanism and the uncertain internal stress caused by the instability of the hydraulic system.The controller compensates the position by designing the disturbance force observed by the nonlinear disturbance observer;The simulation shows that the position-based PID control strategy can basically complete the trajectory tracking,and the position-based impedance control can well meet the requirements of the compliance control without affecting the position tracking accuracy.Next,in order to further improve the control accuracy and enhance the synergy of the parallel mechanism,a cascade control method based on the disturbance observer is proposed.The cascade control adopts inner loop force control,so that the hydraulic cylinder has the function of a force generator,and the outer loop adopts sliding film control.Aiming at the problem of the coordination of parallel mechanisms,the joint coupling error that integrates the joint space tracking error and different sets of coordination errors is defined.Simulations and experiments show that the cascade control strategy not only greatly improves the trajectory tracking accuracy of the driving slider,but also allows the parallel mechanism to have better synergy.The research content of this paper has certain reference significance for the kinematics,dynamics modeling,control strategy improvement and engineering application of parallel mechanism.