Feedforward Compensation for Suppression of Seam Boundary Error Propagation in Robotic Welding Systems

In this paper, a novel filling control algorithm for suppression of seam boundary error propagation is proposed for robotic multipass welding systems. First, the multipass welding process is formulated as a closed-loop control design problem with a low-gain feedback controller in the baseline loop. Next, a noncausal feedforward controller is designed for compensating the error from previous welding passes. The noncausal feedforward controller is optimized using the H
_∞
loop-shaping technique such that the error caused by nonrepetitive disturbances in one pass is gradually eliminated, while the error caused by repetitive disturbance in every pass is suppressed. Our experimental results on an industrial robotic welding system show that the proposed control algorithms eliminate seam boundary errors caused by nonrepetitive disturbances within five passes, and a reduction of 12.8% in root mean-square-error of seam boundary error when subjected to repetitive disturbances in every filling pass.