Digital control system for two-beam optical interferometry using variable structure and sliding modes method

Abstract

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.