| Generally speaking welding manipulator has three rotate joint, high flexibility, it can apply to most welding occasion, but the price of it is always high and the adaptability is poor. Especially, under the circumstances of pipeline welding for pressure vessel nozzle, ordinary welding manipulator cannot complete the task in these narrow places. This special motion path lead to the complex control. As a result, we design a control system for pipeline welding based on the research on kinematics/dynamics.First of all we introduced the demand analysis for pipeline welding in pressure vessel, while upon the analysis of mechanism we designed the structure of the mechanical arm. Then, based on D-H theory, we built a kinetic model for the welding robot, solved the function of forward kinematics and the inverse kinematics. At the same time we carry on a study of trajectory planning method, it proved that the error of spline fitting is smaller than that in cubic polynomial fitting and the spline fitting is smoother than another one. So we chose the method of spline to fit the velocity.On the other hand, we make a dynamics analysis for the mechanical arm. On the foundation of Euler’s formula we built a dynamic model of the manipulator and make a simulation in ADAMS, as a result, we get the parameters of joint velocity and joint torque, and researched the variation characteristic. The research said that the torque in the joint is stable, but when it start or stop the torque changed rapidly, it cans influent the accuracy greatly. Further, based on the research on the dynamic model, we put out a nonlinear PID method, that matched the dynamic model, to control the robot then we make a simulation in MATLAB to compare it to the ordinary PID method and it can improve control accuracy greatly.Finally, based on the motion control card and servo motor we make the welding robot and control system, and programed a software for the control system. |
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