Robust control strategies for an electric motor driven accumulator with elastic webs
Continuous process lines increase the productivity of the plant. Accumulators are used to permit rewind or unwind core changes while the process continues at a constant velocity. Accu-mulators are composed of many free rollers and of a carriage moved to store or release web during the production phases.
This paper concerns the modelling of an accumulator used in industrial elastic web processing plant to allow changing material roll while the rest of the line remains at a constant web velocity. A detailed non linear model of a motor actuated accumulator, programmed in Matlab/Simulink software environment enables a model-based optimization of PI controllers. This model is derived from the physical relationships describing web tension and velocity dynamics in each web span of this accumulator. A linear model is deduced from the non linear one around a working point for frequency domain analysis. Thus the effect of some mechanical accumulator parameter variations are analyzed. The linear model is used to study the effect of some mechanical parameters on the accumulator, with the help of Bode diagrams, and enables to synthesize H1 controllers. In a second part, multi-model industrial PI controllers, adjusted with evolutionary algorithm (modeFRONTIER) on our realistic non linear model are compared with multi-model H1 controllers. Both controllers allow good robustness against mechanical parameter variations. As expected, multi-model control strategy improves significantly the performances.