Laser interferometry is recognized as an extremely sensitive measurement technique, capable of detecting quantities that conventional sensors usually cannot. However, such advantage also brings a challenge, the interferometer detects, beyond the interest measurements, the environmental disturbances, causing the signal fading which usually leads to a nontrivial process to extract the relevant signal, making the interferometer operation more difficult. Thus, the challenge of interferometry is to be able to measure physical quantities whose values are extremely small, in the presence of external environmental disturbances whose magnitudes are several orders of magnitude higher. Objecting to mitigate this drawback, this work presents the implementation of a digital controller based on variable structures and sliding modes (VS/SM) method, applied to two beams interferometry. The VS/SM technique is a powerful technique in the nonlinear control area because it is simple to implement, presents high performance and provides robustness characteristic. In this work, its digital implementation is made by using the myRI0-1900 (National Instruments) embedded platform, which allows easy configuration and the visualization of system when working online. The results showed that the proposed digital implementation allows the system to log the data from experimental tests, which enables the assembly of an embedded system. As additional advantages, it allows to digitally configure the control gain, allowing high gains, and consequently, a fast response. Applications of this closed loop interferometer to piezoelectric actuators are presented.
In this work, we present the application of a nonlinear control system, based on variable structure control and sliding modes, to a fiber optic Mach-Zehnder interferometer. We showed that this control system is able to keep the interferometer in quadrature, suppress the signal fading, lead to high accuracy control, featuring ease of implementation and high robustness. Thus, the controlled interferometer was employed for the measurement of frequency response and mechanical resonances of a cylindrical piezoelectric actuator. The advantages of an all-fiber interferometric sensor combined with the proposed nonlinear control system features compactness, light weight, alignment free, electromagnetic immunity, high sensitivity, geometric versatility, robustness, real-time high precision measurement, and possibility of operation in harsh environments.