| dc.description.abstract | Shield metal arc welding (SMAW) is the most common type of an arc welding process that melts and joins metals, but its research is less than inert gas metal arc welding (GMAW) or inert gas tungsten arc welding (GTAW). This thesis describes an automatic SMAW control system which has replaced manual operations required a well-trained technician. Robotic welders have replaced manual human operations in many welding applications, but the automated process control systems have not been fully developed due to the complexity of the process.
A numerical procedure is first developed to derive a second-order mathematical model of the welding control system, which consists primarily of an electrode feed-rate mechanism driven by an AC servomotor. The automatic welding control system can be considered an electrode feed-rate velocity control system. To be able to develop nonlinear controllers for the SMAW system and also for enabling numerical simulation to analyze an industrial welding process, a second-order mathematical model of the welding control system has been derived and the parameters of the system have been identified. The electrode feed-rate mechanism for our proposed controllers is driven an AC servomotor that can both compensate for the molted part of the consumed electrode and for the undesirable fluctuations of the arc length during automated welding operation.
An adaptive fuzzy sliding mode controller (AFSMC) consists of an equivalent control part and a hitting control part. An adaptive law derived from a Lyapunov function is used to obtain the FLC’s parameters, and is applied to approximate the equivalent control part of the sliding mode control (SMC), so that the system states can be forced to zero. By using three rules FLC, the hitting control part that satisfies the hitting conditions of the SMC can force the system’s states to reach and remain on the sliding surface. Therefore, the stability of the AFSMC can be guaranteed and can be used to modulate the rate of the electrode feeding mechanism that regulates the arc current of the SMAW. The simulation and the experimental results both show that this automatic welding control system, based on the AFSMC, can perform effectively.
Finally, in this thesis, a nominal nonlinear mathematical model containing uncertainties such as dead-zone, welding control system saturation, and the identified system parameters is derived. A novel variable structure model reference control scheme is designed to modulate the rate of the electrode feed mechanism thereby regulating the arc current, the developed controller assures the global reaching condition of the sliding mode of the controlled welding system. In the sliding mode, the electric current error between the plant and the model approaches zero asymptotically. Moreover, the welding system remains insensitive to uncertainties and disturbance as the systems with friction. The simulation and experimental results confirm that the automatic welding control system, based on the proposed model-following variable structure controller, successfully maintains the magnitude of the arc current at the desired value and preserves the stability of the arc length, thereby ensuring an excellent welding performance. | en_US |