A review of recent advances in the single- and multi-degree-of-freedom ultrasonic piezoelectric motors

•A comprehensive and original review of recent advances (2015–2020) on the ultrasonic piezoelectric motors.•A classification of piezoelectric motors according to vibration types and output motion.•The working principles and performance of different structures.•Summary and future perspectives on ultrasonic piezoelectric motors. In this paper a comprehensive review of recent studies on the ultrasonic piezoelectric motors is presented. The authors focus on research articles published in the last five years mostly. The primary subject of this investigation is the development of piezoelectric ultrasonic motors including analytical, numerical and experimental analysis. In further sections, classification methods of piezoelectric motors, survey criteria and three main groups of ultrasonic piezoelectric motors with examples have been presented and described. Finally, the conclusions and future research perspectives have been proposed.