Wearable Detection of Trunk Flexions: Capacitive Elastomeric Sensors Compared to Inertial Sensors.

Gabriele Frediani,Leonardo Bocchi,Federico Carpi,Giovanni Zonfrillo,Federica Vannetti

doi:10.3390/s21165453

Abstract

Continuous monitoring of flexions of the trunk via wearable sensors could help various types of workers to reduce risks associated with incorrect postures and movements. Stretchable piezo-capacitive elastomeric sensors based on dielectric elastomers have recently been described as a wearable, lightweight and cost-effective technology to monitor human kinematics. Their stretching causes an increase of capacitance, which can be related to angular movements. Here, we describe a wearable wireless system to detect flexions of the trunk, based on such sensors. In particular, we present: (i) a comparison of different calibration strategies for the capacitive sensors, using either an accelerometer or a gyroscope as an inclinometer; (ii) a comparison of the capacitive sensors’ performance with those of the accelerometer and gyroscope; to that aim, the three types of sensors were evaluated relative to stereophotogrammetry. Compared to the gyroscope, the capacitive sensors showed a higher accuracy. Compared to the accelerometer, their performance was lower when used as quasi-static inclinometers but also higher in case of highly dynamic accelerations. This makes the capacitive sensors attractive as a complementary, rather than alternative, technology to inertial sensors.

Highlights

Many types of workers have to deal with tiring, incorrect, and even risky body postures and movements, which involve excessive and/or repeated flexions of the trunk while accomplishing duties
The gold standard to measure human body kinematics is represented by stereophotogrammetry, which uses external cameras to track the position of markers arranged on the subject [5]
The sensors had at rest a length of

Summary

Introduction

Many types of workers have to deal with tiring, incorrect, and even risky body postures and movements, which involve excessive and/or repeated flexions of the trunk while accomplishing duties. This can cause pain and increase the risk of musculoskeletal injuries, such that the trunk’s flexion is a key variable to assess risks associated with incorrect and dangerous postures in occupational health management [1,2,3,4]. The gold standard to measure human body kinematics is represented by stereophotogrammetry, which uses external cameras to track the position of markers arranged on the subject [5] This technique has a high accuracy, it is not always applicable to monitor workers. Does it require bulky, complex-to-use, and expensive equipment, but it requires the subject to be confined within an empty space, so as to enable continuous tracking by the cameras

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Conclusion