Micro ultrasonic motor using a one cubic millimeter stator

Ultrasonic motors are expected to be used as micro-actuators, and the miniaturization of these devices is an interesting subject. We present a micro ultrasonic motor using a stator with a volume of approximately 1 mm³, which is one of the smallest ultrasonic motors. The stator consists of a metallic cube with a through-hole and piezoelectric elements adhered to its sides; the simplicity of the stator allows it to be miniaturized without special machining processes. The vibration mode that the stator generates for rotation is three waves around the circumference of the hole. This vibration mode can generate certain vibration amplitudes and driving torques even when the stator is miniaturized. In this paper, we build a prototype micro ultrasonic motor and examine its basic characteristics, including impedances and vibration amplitudes. The basic motor performance, such as its torque and rotational speed, is demonstrated experimentally.