Abstract
Doppler self-mixing laser probing techniques are often used for vibration measurement with very high accuracy. A novel optoelectronic probe solution is proposed, based on off-the-shelf components, with a direct reflection optical scheme for contactless characterization of the target’s movement. This probe was tested with two test bench apparatus that enhance its precision performance, with a linear actuator at low frequency (35 µm, 5–60 Hz), and its dynamics, with disc shaped transducers for small amplitude and high frequency (0.6 µm, 100–2500 Hz). The results, obtained from well-established signal processing methods for self-mixing Doppler signals, allowed the evaluation of vibration velocity and amplitudes with an average error of less than 10%. The impedance spectrum of piezoelectric (PZ) disc target revealed a maximum of impedance (around 1 kHz) for minimal Doppler shift. A bidimensional scan over the PZ disc surface allowed the categorization of the vibration mode (0, 1) and explained its deflection directions. The feasibility of a laser vibrometer based on self-mixing principles and supported by tailored electronics able to accurately measure submicron displacements was, thus, successfully demonstrated.
Highlights
Laser Doppler velocimetry is a well-known measurement technique, widely used for accurate and remote measurement of fluid velocity and objects’ displacement, velocity, and acceleration
In order to measure the Doppler signal produced by a vibrating moving target, an optical probe based on a laser diode (LD) with self-mixing interference capabilities was used
One test bench was composed by a linear actuator (35 μm of amplitude) at low frequency (5–60 Hz), other with disc shaped transducers with small amplitude (0.6 μm) and high frequency (100– 2500 Hz)
Summary
Laser Doppler velocimetry is a well-known measurement technique, widely used for accurate and remote measurement of fluid velocity and objects’ displacement, velocity, and acceleration. The use of a laser diode (LD), both as an emitter and as a receiver of coherent light, allows for the capability to measure the velocity and displacement of a moving target surface These optoelectronic elements, LDs, have been widely used in many different areas due to these remarkable features such as high sensitivity and accuracy, contactless operation, and a simplified optical scheme, when compared with most of the alternative sensors [1,2,3,4]. In order to measure the Doppler signal produced by a vibrating moving target, an optical probe based on a LD with self-mixing interference capabilities was used This probe was tested with two different test benches in order to determine its ability to accurately measure velocity and other movement characteristics of a moving target. One test bench was composed by a linear actuator (35 μm of amplitude) at low frequency (5–60 Hz), other with disc shaped transducers with small amplitude (0.6 μm) and high frequency (100– 2500 Hz)
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