Design of feedforward filling control for joining thick materials using robotic welding systems

In this paper, a filling control strategy is proposed for robotic welding of thick materials which requires multipass welding. The multi-pass welding process is formulated as a closed-loop control design problem. A PI controller is used in the baseline loop for regulating the seam boundary error in the current pass; a non-causal feedforward controller is designed using the H∞ loop shaping technique for regulating the error from previous welding passes. Simulation results show that as compared to without using a feedforward controller, error propagation on the seam boundary will be eliminated within six passes for disturbances occurring only in the first filling pass, and error amplification is contained within four passes for disturbances occurring at the same position in every filling pass.