Design of an estimator for the prediction of drying curves

Drying processes are mostly performed on an empirical basis in industrial applications. In order to develop controllers for optimal drying, a model that predicts the moisture concentration is required. Most models can only be solved numerically as they incorporate distributed parameters which are not directly measurable; moreover, these models complicate the design of controllers. The use of an estimator, which approximates the model behaviour by estimating the states, is, however, very convenient for nonlinear control purposes. In this research a sliding mode observer is developed for the drying process of pasta. The observer is based on the estimation of the time derivative of the diffusivity, which is the most determining key factor during the drying of pasta. The sliding mode estimator not only permits the model states to be calculated analytically, it also assures convergence of the predicted model output towards the actual process output. The convergence of the predicted model output towards the actual process output is proved in this study and illustrated for several drying conditions.