Fiber Bragg Gratings in CYTOP Fibers Embedded in a 3D-Printed Flexible Support for Assessment of Human⁻Robot Interaction Forces.

Arnaldo Leal-Junior,Kyriacos Kalli,Camilo Díaz,Carlos Marques,Anselmo Frizera-Neto,Maria Pontes,Antreas Theodosiou

doi:10.3390/ma11112305

Abstract

We developed a flexible support with embedded polymer optical fiber (POF) sensors for the assessment of human–robot interaction forces. The supports were fabricated with a three-dimensional (3D) printer, where an acrylonitrile butadiene styrene (ABS) rigid structure was used in the region of the support in which the exoskeleton was attached, whereas a thermoplastic polyurethane (TPU) flexible structure was printed in the region where the users placed 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, were embedded in the TPU structure. In this case, a 2-FBG array was embedded in two supports for human–robot interaction force assessment at two points on the users’ legs. Both FBG sensors were 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%. Such errors were 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.

Highlights

Advances in medicine and improvements to quality of life have led to an increase in the life expectancy of the general population [1]
3D printing on the development of flexible structures and sensors’ embedment, and (iii) the advances in the inscription of long fiber Bragg gratings (FBGs) arrays in CYTOP fibers, this paper presents the development of a flexible support for human–robot interaction force assessment using a FBG array in CYTOP fibers
This paper presented the design and sensors’ characterization of a 3D-printed, FBG-embedded flexible support for human–robot interaction force assessment in a wearable exoskeleton

Summary

Introduction

Advances in medicine and improvements to quality of life have led to an increase in the life expectancy of the general population [1]. An ageing world population has placed demands on the use of assistive technology and in particular towards novel robotic assistance and rehabilitation devices, since increasing neurological injuries and weakness of skeletal muscles inhibit the independent movement and full recovery of the elderly once such injuries are sustained [2]. In these cases, robotic therapy has several advantages over conventional therapy, which include higher repeatability for rehabilitation exercises and quantitative feedback of the patient recovery [3]. The development of flexible structures has been driven by novel manufacturing processes, and three-dimensional (3D) printing may be regarded as one of the manufacturing processes that have enabled the development of complex and custom-made structures and geometries for soft robotics [7]

Methods

Results

Conclusion