Research On Several Problems Of A 6-DOF Parallel Platform

The six-degree-of-freedom parallel platform has the advantages of reasonable structure,high rigidity,and good reliability,and has broad application prospects in the fields of industry,national defense,and entertainment.The six-degree-of-freedom parallel platform has the characteristics of high nonlinearity and strong coupling in dynamics,making the motion control of the six-degree-of-freedom parallel platform one of the theoretical and technical difficulties in the research.The six-degree-of-freedom parallel platform is divided into many types,among which the Stewart-type parallel platform is the most typical,which is widely used in the field of motion simulators,and the six-degree-of-freedom parallel platform is the core component of the motion simulator.The motion simulator has obvious advantages.In terms of vehicle driving simulation,it has the advantages of saving driving training costs and creating a safe driving environment.In terms of entertainment driving simulation,it has the advantages of enhancing entertainment characteristics,improving driving pleasure,and experiencing virtual reality driving.However,motion simulators also have some shortcomings.For example,the fidelity of motion simulators is not high enough and the problem of limited motion space still exists.In this thesis,the structure design,kinematics and dynamics analysis,control strategy design,and somatosensory algorithm improvement of the six-degree-of-freedom parallel platform are studied.The main research contents are as follows:Firstly,the Stewart parallel platform is designed according to the design requirements.The designed structure includes the upper platform,lower platform and Hooke hinge of the six-degree-of-freedom parallel platform.According to the load parameters and using the kinematics inverse solution knowledge,the servo electric cylinder is calculated and selected.The strength of the Hooke hinge with weaker bearing capacity is analyzed using the finite element analysis method.Finally,it is concluded that the Hooke hinge fully meets the strength requirements.Secondly,the kinematics and dynamics of the six-degree-of-freedom parallel platform are studied.Aiming at the difficult problem of kinematics positive solution,a method combining dichotomy and random value method is proposed.This method can quickly and effectively determine the pose of the upper platform,and the calculated value obtained by this method can be better close to the actual value.Aiming at the problem of dynamic modeling,the Lagrangian method is used to establish a dynamic model of a six-degree-of-freedom parallel platform.Then,the position control problem of the six-degree-of-freedom parallel platform is studied.Aiming at the problem of position tracking,a robust control algorithm based on PID control is proposed.Based on the Lyapunov stability theory,the control law and adaptive law of the controller are designed.And the stability analysis and joint simulation test of the proposed control algorithm are carried out.The simulation results verify that the proposed control algorithm has good adaptability and robustness.Finally,the somatosensory algorithm of the six-degree-of-freedom parallel platform is studied.Aiming at the problem of limited movement space of the 6-DOF parallel platform,the classic washout algorithm is introduced to improve the space utilization of the 6-DOF parallel platform.Aiming at the problem of fixed parameters of the classic washout algorithm,an improved method combining the classic washout algorithm and RBF neural network is proposed.The improved washout algorithm improves the fidelity of the six-degree-of-freedom parallel platform.The effectiveness of the proposed improved algorithm is verified by MATLAB simulation.