Seam tracking and welding speed control of mobile robot for lattice type welding

This paper presents the seam tracking and motion control of a mobile robot for lattice type welding. Its dynamic equation and motion control methods for welding speed and seam tracking are described. The motion control is realized in the view of keeping constant welding speed and precise target line even though the robot is driven along the straight line or curve. The mobile robot is modeled based on Lagrange equation under nonholonomic constraints and the model is represented in state space form. The motion control of the mobile robot is separated into three driving motions of straight locomotion, turning locomotion and torch slider control. For the torch slider control, the proportional integral derivative (PID) control method is designed. For the straight locomotion, a concept of decoupling method between input and output is adopted and for the turning locomotion, the turning speed is controlled according to the angular velocity value at each point of the corner with range of 90 degrees constrained to the welding speed. The experiment has been done to verify the effectiveness of the proposed controllers. These results are shown to fit well by the simulation results.