Performance of micro ultrasonic motor using one cubic millimeter stator

We present the performance of a micro ultrasonic motor using a stator with a volume of approximately one cubic millimeter, which is one of the smallest ultrasonic motors. The stator consists of a metallic cube with through-hole, a rotor shaft is inserted to the hole, and piezoelectric elements adhered to its four sides. When voltages are applied to the piezoelectric elements, the stator generates travelling wave and spins the rotor. In this paper, we examine how the clearance and preload between the stator and rotor relate to the motor performance. The motor torque and rotational speed are measured by changing the clearance and preload.