Control of Droplet Detachment Frequency in a GMAW Process by a Hybrid Model Predictive Control

Efficient control of a gas metal arc welding (GMAW) process enables one to obtain high quality products as a consequence of achieving a high quality weld. Although control of the droplet detachment frequency in the welding process would play a great role in improving the welding quality, measuring this variable is difficult and expensive. In this paper, we attempt to control the frequency of droplet detachments without directly measuring it. To this end, we utilize the hybrid property of the GMAW process to indirectly control the frequency. Specifically, a mixed logical dynamical (MLD) model is obtained by considering the hybrid act of the process during droplet detachment. Then, a nonlinear model predictive controller with variable control and prediction horizons is designed incorporating the hybrid behavior of the process. The controller regulates the droplet detachment frequency without measuring this variable directly. Computer simulation results show that the proposed controller leads to a higher quality weld compared to the present approaches.