A Hierarchical Structure Control Strategy Based On MPC For A Six-DOF Manipulator

With the development of technology and social progress,the application of manipulators is becoming more and more extensive.This paper studies the industrial manipulator driven by DC servo motor.In practical applications,not the manipulator need be controlled quickly and accurately,but also the trajectory of the manipulator need to be plan.In this paper,a hierarchical structure control strategy based on model predictive control is designed to make the manipulator reach the target position quickly and accurately.Therefore,this paper has important theoretical significance for the study of manipulator control strategy.The main work of this paper is as follows:Firstly,based on the DH representation,the link coordinate system of the manipulator is determined,the transformation matrix of the end of the manipulator relative to the base is constructed,the equation of the manipulator motion with six degrees-of-freedom(DOF)is established,and the analytical solution of the inverse kinematics of the manipulator is solved using a geometric method.Based on the Lagrange equation,a dynamic model of a six-DOF rigid joint manipulator is established.On this basis,it is assumed that the manipulator is an eccentric cross section,which is a linear spring between the rotor and the connecting rod of motor.The dynamic model of the flexible jo int manipulator is established,and the correctness of the model is verified through simulation.Secondly,taking the optimal time of the manipulator as the optimization index,the 3-5-3 degree polynomial interpolation method is used for trajectory planning,and the genetic algorithm is used to optimize each interpolation time.Aiming at the problem of trajectory planning from one point to another in the joint space,a time-optimal trajectory planning algorithm is designed.The comparison with the particle swarm optimization algorithm proves that the method is stable under the optimal time condition.Finally,referring to the industrial hierarchical structure predictive control system,a six-DOF manipulator hierarchical structure control strategy with model predictive control as the core is designed.The control strategy is divided into three layers:the first is at the trajectory planning layer,the time-optimal trajectory planning algorithm based on genetic algorithm is used to obtain the target trajectory;the second is at the model prediction control layer,the joint trajectory is close to the upper target trajectory and provided to the lower controller Set value;third,the lower layer uses 6 PD controllers to track the trajectory according to the set value to achieve final control.Through three-level interaction,the integration of trajectory planning and trajectory tracking is realized,which make the manipulator can reach the target position quickly and accurately.The simulation results show that,compared with the PD control strategy,the hierarchical control strategy designed in this paper has better control performance and reduces the end tracking error.This paper studies the kinematics,dynamics,trajectory planning and control strategies of the 6-DOF manipulator.The optimal time planning is realized,the tracking error of the end trajectory is reduced,and the inconsistency between the trajectory planning results and the control results in the actual production process of the manipulator is effectively solved.