Visualization of Microvibrations by Mechanical Frequency Tuner

A device to detect and visualize periodic mechanical vibrations is presented. The device is realized by a mechanical resonance frequency tuner, a laser source, and a screen. The mechanical vibration frequency of a target machine can be searched by rotating adjustment screw in the tuner. The tuner except the laser source, consists of leaf spring, magnets, screw, mirror, and cupper plate which are passive and thus is robust to environmental stresses, reliable and explosion proof. The vibration is amplified both by the tuner and an optical system. The laser beam is irradiated to the vibrating mirror in the tuner, the direction of the beam reflected by the mirror changes in synchronization with the vibration, and the laser beam finally draws the magnified laser spot trajectory the on the screen. A small solar cell and phosphorescent tape are set on the screen. The solar cell irradiated by the laser beam generates periodic pulse voltage with the frequency of twice of the vibration frequency. The phosphorescent tape memorizes the maximum amplitude as the afterglow even if the vibration frequency of machine fluctuates around the tuned frequency. A theoretical model of the tuner was built. The tuning frequencies calculated by the model and those experimentally obtained showed good agreement. The frequency was tuned in the range from 31Hz and 115Hz. A laser spot trajectory by vibration velocity of 0.9 mm $/\text{s}$ (peak displacement of 0.013 mm) had the amplitude of 0.74 m. The displacement was 114,000 times magnified. Further magnification is possible by adjusting the laser beam elevation angle.