High-speed microscopic observation of the elliptical motion in an ultrasonic motor

We show the elliptical motion that is the key driving principle of travelling wave ultrasonic motors. The use of a high-speed camera with a microscope enables observation of the elliptical motion with ultrasonic frequencies and few micron amplitudes. How the elliptical motion is related to the motor outputs, such as torque and rotational speed, is interesting in the view of the principle. In this paper, we examine how the elliptical motion changes by the frequency of applied AC voltages that depend on the motor output. Both the elliptical motion and motor output is simultaneously measured in experiment.