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Fiber Bragg Gratings in CYTOP Fiber Embedded in a 3D-printed Flexible Support for Human-Robot Interaction Forces Assessment

LEAL-JUNIOR, A. ; Theodosiou, A. ; Rodriguez, C. ; Marques, C. ; Pontes, M. J. ; Kalli, K. ; Frizera-Neto, A. Frizera-Neto

Materials Vol. 11, Nº 11, pp. 2305 - 2305-15, November, 2018.

ISSN (print): 1996-1944
ISSN (online):

Journal Impact Factor: 2,467 (in )

Digital Object Identifier: 10.3390/ma11112305

Abstract
We develop a flexible support with embedded polymer optical fiber (POF) sensors for human-robot interaction force assessment. The supports are fabricated with a 3D printer, where an acrylonitrile butadiene styrene (ABS) rigid structure is used in the region of the support in which the exoskeleton is attached, whereas a thermoplastic polyurethane (TPU) flexible structure is printed in the region where the users place their legs. In addition, fiber Bragg gratings (FBGs) inscribed in low-loss, cyclic transparent optical polymer (CYTOP) using the direct-write, plane-by-plane femtosecond laser inscription method are embedded in the TPU structure. In this case, a 2-FBG array is embedded in two supports for human-robot interaction force assessment at two points of the user’s leg. Both FBG sensors are characterized with respect to temperature and force, additionally the creep response of the polymer, where temperature influences the force sensitivity, was analyzed. Following the characterization, a compensation method for the creep and temperature influence was derived, showing relative errors below 4.5%, where such errors are lower than the ones obtained with similar sensors in previously published works. The instrumented support was attached to an exoskeleton for knee rehabilitation exercises, where the human-robot interaction forces were measured in flexion and extension cycles.