Monitoring of mechatronic systems is one of the essential issues in the industries. In this context, we firstly deal with the modeling of an electro-mechanical system obtained by assembling a mechanical model, which is a single stage of a gear element and an electrical model that is an asynchronous motor. Secondly, we use homogeneous sliding mode observers in order to supervise the gear dynamical behavior. The observers' parameters are suitably chosen to ensure rapid and accurate convergence between the real and the estimated system states. Finally, a comparative study between three simulations is presented in order to illustrate the observers performances and the influence of the mechanical dynamics on the electrical states.