Research On Model Prediction Motion Control Of Parallel Mechanism Multibody System

Under the background of made in China 2025,China's manufacturing industry is gradually developing towards high precision.The parallel mechanism multi-body system has been widely used for its characteristics of fast motion,large acceleration and high payload.However,because of the complexity of the system,the uncertainty of the model parameters,the nonlinear factors and the coupling of the parameters,the motion control of the parallel mechanism multi-body system has become a hot and difficult research point.In this thesis,taking a 3-TPT parallel mechanism multi-body system as the research object,and its kinematics modeling,workspace analysis and dynamics modeling are completed,controller based on PID(proportion,integral,differential)and model predictive control(MPC)are also designed to realizes the trajectory tracking control of the end-point of the system actuator.(1)The structure and working principle of the 3-TPT parallel mechanism multi-body system were analyzed.Based on the robotics theory,the kinematics model of the 3-TPT parallel mechanism multi-body system was established by means of coordinate transformation,and the inverse and positive kinematics solutions of the parallel mechanism were solved.At the same time,according to the constraint conditions such as the length of branch chain,the workspace of the mechanism was studied based on the analytical method,and the 3d simulation diagram of the workspace was drawn by MATLAB software.(2)The mechanism was decomposed into two major systems,namely,the moving platform and the branch chain,according to the Lagrange method,the dynamic model of the multi-body system of 3-TPT parallel mechanism was established.The state space equation of the control system was established by using the matrix transformation method,and it was linearized by Taylor expansion.According to the dynamics equation of the system,MATLAB software was used for simulation and calculation of dynamics,and the change law of branch chain position,speed and driving force with time was analyzed.(3)The physical model of parallel mechanism multi-body system was built by the Sim mechanics toolbox of MATLAB.According to the SimMechanics physical model,the PID controller of the parallel mechanism was established,and the model prediction controller of the parallel mechanism was established according to the state space equation of the system.The spatial trajectory,coordinate position tracking curve,and the tracking error curve of the two control methods were respectively obtained and analyzed.(4)The simulation results of the two controllers were compared.The results showed that the motion control system based on model predictive algorithm,can better meet the requirements of the 3-TPT parallel mechanism multi-input multi-output nonlinear control system,reduce the modeling errors of controlled objects and the influence of uncertain factors such as structure,parameters and environment,and has better control performance.To sum up,in this thesis,a multi-body model of a 3-TPT parallel mechanism was used as the research objective,the motion control of a multi-body system of 3-TPT parallel mechanism was studied,and PID and model predictive control were applied to realize the trajectory tracking of the central point of the actuator at the end of the mechanism.In the research work of this thesis,a new idea for the control of parallel mechanism was provided and a foundation for the further application of model predictive control in the precise control of parallel mechanism was also laid.