State-of-the-art ultrasonic micromotors and their future applications

Piezoelectric actuators and ultrasonic motors have advanced enormously since their beginnings over 25 years ago. They offer advantages of low speed, low inertia and high torque operation without the need for gearboxes. They are now successfully competing with conventional electromagnetic motors in applications requiring small positioning motors. Ultrasonic stepper motors and piezoactuators have not competitors in the field of ultraprecision positioning drives. Ultrasonic motors convert high frequency vibrations of a structure excited by piezoelectric elements into rotor or slider motion by a frictional drive. This principle has been configured into many embodiments, giving rapid response times, holding torque without power applied and potentially silent motion. Their miniaturization for use in MEMS (microelectromechanical systems), microrobotics and the watch industry is particularly exciting, since they have a simple construction and excellent performance for their size. Ultrasonic motors have the potential to meet space research needs as actuators for telerobotics applications. The current difficulties in designing high performance ultrasonic motors are associated with the lack of complete models and general design rules, especially in the analysis of the frictional drive between the rotor and stator. The technical problems associated with required tolerances in construction, bonding piezoelectric materials to a stator structure and the performance of different friction layer materials are not completely solved. This work discusses the state-of -the-art ultrasonic miniature motor's research, commercial application and future trends.