Dynamic Modeling And Sliding Mode Control Of 3-RUU Parallel Mechanism Polishing Robot

At present,the grinding of spatial free-form surface parts is mainly completed manually,which has some problems,such as poor working environment,low grinding efficiency,and poor surface quality uniformity of parts.In the field of automatic grinding,the widely used grinding robot is a series robot.Serial robot has the advantages of simple structure and convenient control,but it is not suitable for grinding large-scale precision parts because of its low repeated positioning accuracy and low stiffness.The parallel robot with few degrees of freedom has been widely concerned in the robot processing industry because of its high precision,high stiffness,compact structure and easy control.However,compared with the serial robot,its workspace is small,and it is not suitable for grinding large-size parts.Therefore,a 3-RUU coaxial parallel mechanism polishing robot is designed in this paper.The theoretical research is carried out from the aspects of configuration analysis and design,kinematics analysis,dynamic modeling,robot control and so on,and the prototype control test is carried out.The results show that the coaxial layout parallel robot effectively expands the workspace of the parallel mechanism and provides an effective scheme for the automatic grinding of spatial free-form surface parts.The main research work and results are as follows:(1)The configuration of the coaxial parallel mechanism is analyzed,and the influence of the joint hinge on the workspace of the robot is compared.According to the size requirements of grinding parts,a 3-RUU coaxial parallel mechanism grinding robot with 3 translational degrees of freedom is designed.The influence of the distribution of the branch chains of the robot on the kinematic performance of the parallel mechanism is analyzed.It is concluded that the multi branch chain rod cluster configuration can significantly reduce the accompanying motion of the end moving platform.By comparing and analyzing the influence of the branch chain joint on the robot workspace,the U-shaped joint is selected to obtain a larger workspace.(2)The kinematics model of 3-RUU coaxial parallel mechanism is established.The inverse kinematics model of the robot is established by geometric method.The NURBS curve is used to fit the grinding trajectory of the robot.Because the parallel mechanism has the characteristics of high coupling,in order to clearly describe the motion characteristics of the robot,the Frenet frame method is used to plan the motion trajectory,and the displacement,velocity and acceleration of the end moving platform are obtained.Then the motion parameters of each driving arm are obtained through the inverse kinematics solution,which are calculated by Matlab and compared with the Adams simulation results,The accuracy of the kinematic model is verified.(3)Based on the principle of virtual work,the dynamic model of 3-RUU coaxial parallel robot is established.Using Matlab to solve the dynamic parameters,the calculation results of the driving torque of the three driving arms are consistent with the Adams simulation results,which verifies the correctness of the dynamic model.(4)In order to improve the trajectory tracking accuracy of robot grinding,a sliding mode controller of 3-RUU coaxial parallel mechanism is designed based on the dynamic model.The 3-RUU coaxial parallel mechanism is a strongly coupled nonlinear system.A sliding mode controller based on the improved reaching law of the dynamic model is proposed to achieve accurate motion tracking control.In order to improve the dynamic performance of the robot,a speed regulation controller based on permanent magnet synchronous motor is designed with the trajectory tracking accuracy and convergence speed as the control objectives,and the robot control simulation analysis is carried out by using Matlab/Simulink.Compared with the traditional PID control,the simulation results show that the designed sliding mode controller has high tracking accuracy,good stability and short response time.(5)An experimental prototype of 3-RUU coaxial parallel mechanism polishing robot is constructed.Preset the circular grinding trajectory,carry out the motion control test of the grinding robot,and monitor the actual running state of the robot motor.The results show that the robot controller can achieve good motion tracking,verify the effectiveness of the controller,and provide a theoretical and technical basis for the motion control of the robot prototype.