Real-time self-mixing sensor for vibration measurements

摘要

This paper shows the development of an optical instrument for vibrations measurements, without contact. The device is based on self-mixing interferometry, realized with very low optical complexity and cost. As any interferometer, it detects the power modulation of the beam laser, due to the remote target displacement. The signal is acquired by a Digital Signal Processor that provides to reconstruct the target movements, in real-time. Two different algorithms were developed to cover a great range of optical conditions. The best focus point is determined by an embedded autofocus system that moves the collimating lens driving a step-by-step engine. The measured distance ranges from 5 cm to 2 m, with a resolution of about 50 nm.