Development of active displacement detector for slight vibration measurement

摘要

Vibration inspection is an important consideration in maintaining device stability and precision during system operation. Although many methods for vibration measurement have been presented, most of them focus on inspecting violent vibrations, whose displacement variations are larger than hundreds of micrometers. In this study, an active displacement detector is proposed for slight vibration measurement based on the astigmatic theory. The detector is composed of an astigmatic lens, an objective lens, a folding mirror, quarter wave plate, and a polarized beam splitter (PBS). An external control box controls the system's power supply and signal communication between the detector and computer. Instead of traditional passive methods, an active laser beam behaves as a shape indication influenced by the surface deformation of a vibration target. A four-quadrant photodiode (QPD) detects the energy change ratio of a laser beam and translates the signal into the corresponding displacement. It was confirmed by experiment that the displacement detector was able to measure the patterns of different vibration models, including amplitude and frequency information. Even a slight vibration less than few micrometers could be measured successfully by the detector.