Ultrasonic micro-motors stator evaluation

Due to their high-torque low-speed piezo-electric motors, using traveling waves, are candidate for the future micro-motors. Nevertheless the importance of asymmetry and flatness defects increases as the motor dimension decreases. Therefore it is very useful to study the behavior of micromotors stators and to evaluate the relative importance of different losses. We jointly use two methods. An optical one, using an heterodyne interferometer, gives a picture for both amplitude and phase of the vibration. This result allows one to obtain an identification of vibrations modes, an evaluation of vibration energy, a comparison of two standing waves used to produce the traveling wave and the analysis of the structure holding the stator. Furthermore a precise measurement of electrical impedance of the piezo-electric ceramics as a function of frequency gives the dielectric and mechanical losses. The electrical measurements are also used to follow the behavior of different modes with the presence of rotor on the stator. Together electrical and optical methods give powerful tools for the stator evaluation. Precise examples will be given for stator with a diameter in the millimeter range