Sg. Tzafestas et Ej. Kyriannakis, Regulation of GMA welding thermal characteristics via a hierarchical MIMO predictive control scheme assuring stability, IEEE IND E, 47(3), 2000, pp. 668-678
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.