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

摘要

Laser interferometry is recognized as an extremely sensitive measurement technique, capable of detecting quantitiesthat conventional sensors usually cannot. However, such advantage also brings a challenge, the interferometerdetects, beyond the interest measurements, the environmental disturbances, causing the signal fading which usuallyleads 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 extremelysmall, in the presence of external environmental disturbances whose magnitudes are several orders of magnitudehigher. Objecting to mitigate this drawback, this work presents the implementation of a digital controller basedon variable structures and sliding modes (VS/SM) method, applied to two beams interferometry. The VS/SMtechnique is a powerful technique in the nonlinear control area because it is simple to implement, presents highperformance and provides robustness characteristic. In this work, its digital implementation is made by using themyRI0-1900 (National Instruments) embedded platform, which allows easy conguration and the visualizationof system when working online. The results showed that the proposed digital implementation allows the systemto 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.