Development of an Optical Fiber-Based Insole for Gait Parameters Detection in Rehabilitation Processes in the Population with Lower Limb Disabilities
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Fandiño Rangel, Laura Daniela | 2021
Introduction: As several diseases are reflected in the human foot as plantar pressures, divers gait assessment technologies have been developed. Some of them include force plataforms, IMUs (inertial measurement units) and instrumented insoles. Instrumented insoles have advantages over the other mentioned technologies, for instance, they do not limit the gait assessment to few steps and, they do not require a repetitive process of calibration. Different sensors have been used to develop these instrumented insoles, some examples are capacitive sensors, FSR, piezoresistive sensors and optical sensors. In literature optical sensors have been identified as an attractive option on account of their mechanical properties and the electromagnetic noise immunity. Taking into account the state of the art in this work, an instrumented insole based on polymeric optical fiber sensors is developed and characterized.
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\textbf{Objective:} The objective of the present work is to develop an instrumented insole, with a POF sensor and, an acquisition and transmission module for gait assessment.
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\textbf{Methodology:} To develop the instrumented insole the project was divided in three main components which are the insole, the sensor and the acquisition and transmission module. The sensor was made with a Polymeric optical fiber and the operation principle of the sensor was developed based on a multiplexing technique.
The described components were assembled and a characterization protocol was implemented. This protocol contemplated intervals of time to measure the sensor response to different loads and time intervals for the sensor recovery.
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\textbf{Results:} In this section the characterization protocol outcomes were showed. The response to loads of the four sensitive zones were no-homogeneous among them. The majority of the sensitive zones presented s linear behavior with some exception. On the other hand, some of the sensitive zones presented $R^2$ values lower than $0.8$ and others reached $R^2$ values higher than $0.9$ in their linear trend.
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\textbf{Discussion:} Several factors affected the optical fiber sensors response whereby they have to be consider, otherwise, this factors would affect the developed measuring system, resulting in non-repeatability and in linear response to load decreasing as could be observed in the characterization outcomes.
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\textbf{Conclusions:} An instrumented insole and its acquisition and transmission modules were developed using the microcontroller of the FRDM KL25Z board; additionally an optical fiber coupling board was use to integrate the light sources and the optical fiber for the sensor to work correctly. The operation principle of the instrumented insole is based on a multiplexing technique.
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