Research On The Design And Motion Control Of Serial-parallel Robot For HTGR Plugging And Welding

The high temperature gas cooled reactor(HTGR)is currently a mainstream nuclear power technology that many nuclear power countries are actively researching and developing.During the shutdown and overhaul of nuclear power plants,it is necessary to plug the tube plate ends of the feedwater inlet and steam outlet of the steam generator to ensure that maintenance and replacement can be carried out simultaneously,thereby shortening the maintenance time.In this paper,a plugging and welding robot based on a 7DOF serial-parallel mechanism was designed according to the requirements of the HTGR plugging process.The key technologies,such as the structure design and motion control of the robot,were investigated.A novel 7DOF plugging and welding robot composed of a 3-PSP parallel mechanism and a SCARA serial mechanism was proposed.The robot’s body design,selection of important components,and static analysis of critical components were conducted.The robot mainly adjusts its pose in a confined space using the parallel mechanism and installs and welds the plugging head in the desired location using the serial mechanism.The forward and inverse kinematic equations of the SCARA serial mechanism were solved using the D-H method and analytical method,respectively.The forward and inverse kinematic equations of the parallel mechanism were solved by analyzing the structural characteristics of the 3-PSP mechanism and the accompanying motion of the end effector.The robot’s kinematics forward and inverse solutions were verified using Matlab,which laid the theoretical foundation for the robot’s motion control.In addition,the robot’s pose accessibility was analyzed through simulation using the robot kinematics and Monte Carlo method.The position interpolation of spatial lines and spatial arcs in the Cartesian space was achieved using the equal segment and equal radian discrete segmentation method.The robot’s spatial attitude was described using unit quaternions,and the attitude interpolation in Cartesian space was accomplished using spherical linear interpolation.The trajectory planning of joint space was realized using a linear function with a cycloidal transition,which ensured that the joint displacement,velocity,and acceleration were continuous during the motion process and contributed to the robot’s motion stability and extended its lifespan.Furthermore,the correctness of the algorithm was verified by simulating the trajectory planning in both Cartesian and joint spaces using Matlab software.The reliable welding process parameters were determined by conducting mechanical performance testing,liquid penetration testing,and metallographic testing on several welding sample plates,which enabled the plugging and welding robot to have excellent process performance.The repeated positioning accuracy experiment of the plugging robot prototype was conducted at three different speeds using a micrometer and a high-precision attitude sensor,and the robot’s distance accuracy and laser leveling accuracy were tested based on camera monitoring.The error sources of the robot were analyzed,and the main factors affecting the accuracy were identified.The robot’s error compensation was realized using differential evolution algorithm.