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Quasi-Distributed Torque and Displacement Sensing on a Series Elastic Actuator’s Spring using FBG arrays inscribed in CYTOP Fibers

LEAL-JUNIOR, A. ; Theodosiou, A. ; Casas, J. ; Rodriguez, C. ; Santos, W. ; Pontes, M. J. ; Siqueira, A. ; Kalli, K. ; Marques, C. ; Min, R. ; Frizera-Neto, A. Frizera-Neto

IEEE Sensors Journal Vol. 19, Nº 6, pp. - , April, 2019.

ISSN (print): 1530-437X
ISSN (online):

Journal Impact Factor: 1,762 (in 2014)

Digital Object Identifier: 10.1109/JSEN.2019.2898722

Abstract
—We report the application of fiber Bragg grating
(FBG) arrays in polymer optical fibers (POFs) for the quasidistributed displacement and torque sensing in a series elastic
actuator’s spring. The arrays were inscribed in cyclic
transparent optical polymer (CYTOP) fiber through the direct
write, plane-by-plane inscription method using a femtosecond
laser. Two arrays with 4 FBGs each were positioned on a rotary
spring and a numerical analysis using the finite element method
was performed to evaluate the sensors’ behavior under different
loading conditions. Experimental tests were performed on the
spring and results show the FBGs responses follow the predicted
numerical simulations. In addition, a Kalman filter was applied
on the response of the FBGs for sensor fusion, leading to a more
accurate torque estimation, where the relative error for the
torque estimation was improved by a factor of 7. Furthermore,
transverse forces were applied on predefined points of the spring
in order to show the ability of the quasi-distributed sensor
approach to identify external mechanical disturbances on the
spring.