Vibration measurement of ultrasonic motor using stroboscopic interferometry

In this paper, we propose a stroboscopic interferometric method to measure small vibrations of an ultrasonic motor. The Fizeau interferometer in the optical microscope is used to obtain stroboscopic interference images of a vibrating surface. The measured interferograms are analyzed by the fringe scanning method. The stator of an ultrasonic motor is excited at a resonant frequency of 30 kHz. As the laser irradiation time is sufficiently short compared with the vibration period of the sample, interferometric images with a high contrast are obtained. By changing the delay time of the laser irradiation, vibrations of the surface at different phases are obtained. The distribution of the vibration is visualized sequentially. The stator is vibrated at an amplitude of 3.7 μm peak to peak, so the measurement error is evaluated to be 1/20 of the laser wavelength approximately. This method is useful for designing an optimal ultrasonic motor.