Large-Range Polymer Optical-Fiber Strain-Gauge Sensor for Elastic Tendons in Wearable Assistive Robots.

Jonathan Casas,Arnaldo Leal-Junior,Carlos A. Cifuentes,Marcela Múnera,Anselmo Frizera,Camilo R. Díaz

doi:10.3390/ma12091443

Jonathan Casas, Arnaldo Leal-Junior + Show 4 more

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https://doi.org/10.3390/ma12091443

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Abstract

This paper presents the development and validation of a polymer optical-fiber strain-gauge sensor based on the light-coupling principle to measure axial deformation of elastic tendons incorporated in soft actuators for wearable assistive robots. An analytical model was proposed and further validated with experiment tests, showing correlation with a coefficient of R = 0.998 between experiment and theoretical data, and reaching a maximum axial displacement range of 15 mm and no significant hysteresis. Furthermore, experiment tests were carried out attaching the validated sensor to the elastic tendon. Results of three experiment tests show the sensor’s capability to measure the tendon’s response under tensile axial stress, finding 20.45% of hysteresis in the material’s response between the stretching and recovery phase. Based on these results, there is evidence of the potential that the fiber-optical strain sensor presents for future applications in the characterization of such tendons and identification of dynamic models that allow the understanding of the material’s response to the development of more efficient interaction-control strategies.

Highlights

In recent years, wearable robotics has gained significant attention [1]
This paper presents the implementation of a polymer optical fibers (POFs) strain-gauge sensor based on a light-coupling principle, aiming to measure the deformation of elastic tendons under tensile stress implemented in the soft-robotic foot–ankle orthosis
This article presented the development and validation of an optical-fiber strain-gauge sensor based on the light-coupling principle for axial strain measurement in elastic tendons incorporated in wearable assistive robots

Summary

Introduction

Wearable robotics has gained significant attention [1] This field concentrates on the development of devices that are designed and shaped in functions of the human body and the degrees of freedom of specific joints [2]. In the context of rehabilitation and assistance, wearable robots are mainly focused on the fabrication of exoskeletons (e.g., upper- and lower-limb exoskeletons) and orthoses [3]. The aim of these devices is to provide support to users in different ranges of movement by stabilizing their limbs and helping to restore or reinforce weak functions [4,5]. A current limitation in design is the selection of actuators, as they need to be compliant and back-drivable to meet the needs of devices and their users [5], which, at the end, influences the performance and acceptance of the robotic platform [2,6]

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