Design of a nonlinear observer for mechanical systems with unknown inputs

This paper deals with the design of nonlinear observers for a class of nonlinear mechanical systems in presence of uncertainties (or unknown inputs). Based on sliding-mode technique, a novel observer structure is developed in order to reconstruct the unmeasured velocity variable. The proposed observer guarantees an asymptotic velocity observation also in presence of uncertainties. Simulation results are included to show the effectiveness of our method.