Nonlinear Identification of Weld Penetration Control System in Pulsed Gas Metal Arc Welding

Abstract

Weld penetration plays an important role in the joint strength and its control has always been the focus of study. The paper established a single-input–single-output (SISO) weld penetration control system in pulsed gas metal arc welding (GMAW-P), where the base current (Ib) was taken as system input and the change in arc voltage during peak current period (ΔU) was taken as the system output. According to the nonlinear relationship between Ib and ΔU, a Hammerstein model with disturbances, composed of nonlinear static model and linear dynamic model, was proposed to describe the nonlinear control system. The nonlinear static system was determined based on the model of Ib and ΔU in steady state, and the parameters of linear dynamic system were identified by the recursive least square algorithm. Pseudo-random ternary signals (PRTS) were designed for the system identification. The identified results showed the Hammerstein model with disturbances can represent the penetration control system in GMAW-P within an acceptable range, which was validated by the step experiments data.