A novel model reduction method for sheet forming processes using wavelet packets

Cross-directional control of sheet forming processes, such as a paper machine, can involve up to 600 inputs and 3000 outputs. For such large-scale systems, it is necessary to find proper model reduction strategies before starting controller design. The paper introduces a model reduction method for such processes based on an efficient modified wavelet packet algorithm. The large dimensional signals in the spatial domain can be transformed into a small number of scaling and wavelet coefficients in the wavelet domain, thus the dimension of the original input-output model is reduced without losing any significant information. Two additional benefits are obtained: (1) the system's controllability can be significantly improved because the system's condition number is greatly decreased, (2) the physical limits of the actuators can be directly transformed from the original model to the reduced model.