A ZPET-Repetitive Speed Controller for Ultrasonic Motors. - H. Rodríguez; José Luis Pons Rovira; Ramón Ceres Ruíz (ICRA, 2000)

An Evaluation of Ultrasonic Motors as Driving Technology in Impedance Controlled Robots. - José Luis Pons Rovira; H. Rodríguez; Eduardo Rocon de Lima (ICRA, 2004)