Regulation of GMA welding thermal characteristics via a hierarchical MIMO predictive control scheme assuring stability

This paper deals with the regulation of the thermal characteristics of gas metal are welding (GMAW). A complete treatment of the welding control probl em requires the regulation of both the geometrical and thermal characterist ics of the weld. Both classes of characteristics are of critical importance , but the thermal ones have received less attention in the majority of prev ious work. The present paper proposes a hierarchical predictive control sch eme for the metallurgical characteristics of GR GMAW, A previously develope d model for the regulation of the heat-affected zone, the cooling rate, and the nugget cross-sectional area is used for the open-loop predictions. At the first level of the hierarchy, a parameterized generalized predictive co ntrol (GPC) algorithm is selected, among other control techniques, due to t he inherited difficulty of the welding thermal process and the robustness o f this algorithm against modeling errors and parameter variations. The main drawback of GPC is that it does not guarantee stability. The second level of the control hierarchy where a coordinator specifies a set of reliable va lues for the parameters of GPC, so that stability is assured, and transmits them to the controller of the first level overcomes this difficulty. This paper provides a representative set of simulation results obtained by the p resent hierarchical GPC scheme, including a comparison with the classical l inear-quadratic optimal control scheme. These results show the superiority of the GPC scheme.