Vision sensing and feedback control of weld penetration in helium arc welding process

Consistent joint penetration is essential to mechanical properties of weldments, yet difficult to realize in gas tungsten arc welding due to heat accumulation, varying welding conditions, and uncertain disturbance, especially for manufacturing large-scale structural components. The solution is to monitor welding penetration in real-time and implement closed-loop control. In this paper a directional light-assisted vision sensing scheme is proposed to measure the transient profile of the backside weld pool/bead for monitoring and further controlling the joint penetration state. The developing zone and the developed zone of the backside weld bead are recognized, helping determining its final width. And the relationship between the transient backside bead width and the corresponding final width is established. Furthermore, the backside bead profile is employed as a feedback signal and the closed-loop control of weld formation is implemented to achieve full penetration and a constant backside bead width. A multiple-input single-output model predictive controller is utilized in the control system, creatively combined with an anti-windup integrator eliminating the steady-state error caused by nonlinearity in welding. Experimental results have proved that the developed control system is effective in keeping a consistent backside bead width with a rapid response, a small overshoot and robustness against varying heat transfer conditions.