Design And Implementation Of Micro-vibration Measurement System Based On Collinear Optical Heterodyne Interference

As a non-contact non-destructive testing technology,laser heterodyne interferometry has become the main development direction of micro-vibration testing technology because of its high detection accuracy,high sensitivity,fast dynamic response and simple structure and easy integration,and plays an important role in micro-electro-mechanical systems,precision instrument manufacturing and aerospace fields.In this paper,a new collinear optical heterodyne interferometric micro-vibration measurement system is designed and built with a LR-RSP semiconductor laser as the light source and a dual acousto-optical modulator to address the problems of low detection accuracy,weak anti-interference and poor stability of traditional vibration measurement techniques.The signals were collected and analyzed by MATLAB and FPGA.The main research contents can be summarized as follows:The article analyzes the measurement theory based on laser Doppler effect by establishing a model,and improves and optimizes the structure for the shortcomings of the traditional measurement system.A structured symmetrical dual-optical collinear optical heterodyne interferometry system is designed by using dual acousto-optical modulators,which greatly improves the anti-interference power of the system.A precision diaphragm is added to the optical path to filter out stray light and eliminate optical noise to improve the measurement accuracy.The optical isolation system is designed to realize the propagation and isolation of the laser beam.Next,the components of the acousto-optic modulation system are studied,and the drive source circuit of the acousto-optic modulator is designed.The ideal case of heterodyne interference is analyzed,the source of nonlinear error of the complete system is studied,and the specific error is derived.After that,the performance testing and selection of each part of the system’s optical devices are performed for the nonlinear errors.Meanwhile,a dual AD acquisition module controlled by FPGA is designed to complete the acquisition of two signals.Based on the digital phase discrimination method,a high-precision interpolation frequency counting module is designed to process the optical heterodyne interference signal.Finally,the overall system was experimentally verified,and a collinear optical heterodyne interferometric vibration measurement system was built.Static experiments and vibration measurement experiments were conducted using piezoelectric ceramics to simulate vibrations of different frequencies and amplitudes,and the interference signals were collected and analyzed.The experimental results show that the relative error of measured frequency is less than 0.25%,the relative error of measured displacement is not more than 3.05%,and the measurement resolution of the system is 2.1 nm.The results demonstrate that the designed micro-vibration measurement system can achieve high accuracy detection on the nanometer scale.The use of FPGA to process the heterodyne interference signal is of great importance for the integration and miniaturization of the collinear optical heterodyne interference micro-vibration measurement system.