Vibration transmission of an USM rotor observed by phase-shift interferometry

We evaluate performance of vibration-type microdevices. Stroboscopic phase-shift interferometry is capable of imaging high speed (∼MHz) and small (∼10nm) vibration and is applied to displacement measurement of the microdevices. A laser diode, which is used as a light source of the interferometry, is irradiated stroboscopically in order to observe an object vibrating at high frequency. Phase-shift algorithm is used to obtain high contrast images. An optical system is a Fizeau-type interferometer which eliminates optical noises. An ultrasonic motor (USM), which consists of a rotor and a stator, is used as a test object. The vibration frequency of the stator is about 50 kHz. In our previous work, several vibration distributions of the stator with different vibration phases were measured. A vibration state on the stator surface has been obtained by some vibration distributions. In this paper, we measure the vibration state of the rotor surface of the USM. When the rotor of the USM is driven by small vibration of the stator, the rotor surface is deformed. Therefore, some vibration distributions on the rotor surface with different vibration phases are measured according to the phase of the driving signal. The vibration distributions are compared with each other. As a result, the change of the vibration distribution proves the movement of the surface of the rotor.