The Mechanism And Control Scheme Design Of Valve Welding Robot

With the gradual improvement of the level of industrial automation, more and more manual welding fields are gradually replaced by the welding robot. Using welding robot can not only reduce the labor cost, but also improve the efficiency and precision of welding.This paper is aimed at the welding of a specific valve body sealing surface. Through the research of the mechanism and control scheme of the welding robot, it could be applied to the valve body sealing surface of the welding task. The work is as the following:(1) Through the methods of reference and comparison, we choose the motor drive mode of the six joints and six degree of freedom robot, and its assembly model is established by using Solidworks software. Then the kinematic analysis of the robot system is carried out by using D-H method, including the kinematic modeling and the solution of the positive and inverse kinematics of the robot and the position changing machine. In addition, the working space of the welding robot is analyzed based on the kinematic analysis of the welding robot, and it also shows the projection of the working space.(2) We do a research on the dynamics of robot by using the method of Lagrange, and we solve the welding robot’s dynamics equation through constructing the robot’s Lagrange equation. Then, the expressions of the driving force and driving torque for each member of the welding robot is derived and calculated out based on expressions of the inertia force and inertia torque of the Newton-Euler equation.(3) We import a model of robot into ADAMS to do a kinematics and dynamics simulation. Through the kinematics simulation, it is concluded that the joint angle, the center displacement of each bar and angular velocity and angular acceleration are all within the range of their own. In addition, based on the robot and position collaborative welding kinematics model and the method for solving the parameters of kinematics simulation, the results show that the joint angles of the robot and position changing machine are also in their reasonable range. The robot’s joint angle curves are cyclical changed and smooth process so that it can ensure the smooth tracking motion of thewelding gun. Torch end point trajectory fitting of ellipse curve, indicating that the torch end could track to real-time tracking to elliptical weld the inner wall of the valve body real-time and with high accuracy of fitting. Through the ADAMS dynamics simulation of each joint driving force and driving torque with the time changes, it could be concluded that: driving force and driving torque are within the range, robot system in welding process has stable operation, and it has no interference or body wall collision and other undesirable phenomena so that it could confirm that the robot could weld well in narrow space of the valve body.(4) We propose a welding robot control system overall scheme which has communication between main controller and servo motion control based on EtherCAT,which mainly to solve the problems of communication and control algorithms. In addition,we also research the composition of the welding work station and the overall layout, and then introducing the welding process requirements and giving the results of welding test.The results show that the welding process is smooth, the shape of the elliptical weld trajectory is smooth and has high precision so that it can achieve welding requirements of the actual production of the valve sealing surface.