Weld seam tracking method of root pass welding with variable gap based on magnetically controlled arc sensor

Real-time tracking and alignment of the welding torch with the center of the weld seam are critical for automatic root pass welding of medium-thick plates. However, assembly errors, heat input, and interference from droplets on the arc signal cause real-time changes in the weld seam and gap, making real-time tracking of root pass welding with a variable gap highly challenging. In this study, we propose a tracking method of root pass welding with variable gap based on the magnetically controlled arc sensor. First, a coded magnetically controlled arc sensor was developed for the acquisition of weld seam information. Secondly, combined with the simplified model of arc scanning welds, an arc signal compensation method of selectively taking the average based on the Ransac algorithm was proposed. Finally, we proposed an optimized weld deviation detection method by combining the mathematical model of magnetically controlled arc oscillation with the mathematical model of droplet transition size and frequency under the influence of an alternating magnetic field. Weld deviation detection was performed using the compensated arc signal combined with the positioning information provided by the excitation current coding sequence. The experiment results showed that the maximum detection errors in the Y-axis and Z-axis directions do not exceed 0.40 mm and 0.23 mm, respectively. Our proposed method can effectively track the weld seam of root pass welding with a variable gap.