Polymer Optical Fiber-Embedded Force Sensor System for Assistive Devices With Dynamic Compensation
Letícia Avellar, Gabriel Rueda Delgado, Eduardo Rocón, Carlos Marques, Anselmo Frizera, Arnaldo Leal‐Junior
Abstract
This paper presents the development and the performance analysis of a force sensor using a novel high stretchable polymer optical fiber (POF) fabricated using the light polymerization spinning (LPS) fiber. The system consists of an LPS-POF fiber encapsulated in a flexible material polydimethylsiloxane (PDMS), in addition to a light source and a photodetector. The sensor was characterized by using a commercial 3-axis force sensor K3D60a ±500N/VA (ME Systeme, Germany). Since the LPS-POF and PDMS are viscoelastic materials, tests with loading and unloading cycles were performed to evaluate the sensor response. A viscoelasticity compensation model was proposed to decrease the errors and the sensor phase delay provoked by the viscoelastic behavior. In addition, the LPS-POF force sensor was applied on two different applications, as a gait perturbation system for balance assessment and as a walking cane for gait assistance. Results showed that proposed sensor presents a linear response, with determinant coefficient ( R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) of 0.9974, and high sensitivity ( S=40N/V). However, the unload time presented high phase delay and errors, corroborating the viscoelastic behavior. Compensated response presented lower hysteresis, leading to a decrease of the root mean square error (RMSE) of approximately 65%. Moreover, numerical integration was used as performance metric for the results of both applications and presented a decrease of 48% in the first application and up to 46% in the second application when used viscoelasticity compensation. The proposed sensor is small and versatile for different applications, and presents simple fabrication, data acquisition and processing.