Piezoelectric bimorphs' characteristics as in-socket sensors for transfemoral amputees.

Amr El-Sayed,Noor Abu Osman,Nur Hamzaid

doi:10.3390/s141223724

Amr El-Sayed, Noor Abu Osman + Show 1 more

Open Access

https://doi.org/10.3390/s141223724

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Abstract

Alternative sensory systems for the development of prosthetic knees are being increasingly highlighted nowadays, due to the rapid advancements in the field of lower limb prosthetics. This study presents the use of piezoelectric bimorphs as in-socket sensors for transfemoral amputees. An Instron machine was used in the calibration procedure and the corresponding output data were further analyzed to determine the static and dynamic characteristics of the piezoelectric bimorph. The piezoelectric bimorph showed appropriate static operating range, repeatability, hysteresis, and frequency response for application in lower prosthesis, with a force range of 0–100 N. To further validate this finding, an experiment was conducted with a single transfemoral amputee subject to measure the stump/socket pressure using the piezoelectric bimorph embedded inside the socket. The results showed that a maximum interface pressure of about 27 kPa occurred at the anterior proximal site compared to the anterior distal and posterior sites, consistent with values published in other studies. This paper highlighted the capacity of piezoelectric bimorphs to perform as in-socket sensors for transfemoral amputees. However, further experiments are recommended to be conducted with different amputees with different socket types.

Highlights

Advancements in prosthetic knee systems are of increasing importance to assist transfemoral amputees perform their different daily activities [1] such as walking, stair climbing, and running [2,3]more naturally
Different types of sensors are involved in active knee devices, for example, a potentiometer acts as an angle sensor to measure the knee joint angle, a load cell is used to measure the knee torque, a gyroscope sensor to detect the acceleration of the knee joint, and a force sensing resistor (FSR) is utilized as on/off sensor to detect the prosthetic knee phases [6]
The dynamic characteristics basically show the capability of the piezoelectric bimorph under certain dynamic conditions

Summary

Introduction

Advancements in prosthetic knee systems are of increasing importance to assist transfemoral amputees perform their different daily activities [1] such as walking, stair climbing, and running [2,3]more naturally. For example the angle sensor (potentiometer) measures the inclination angle of the knee joint during the stride, while a torque sensor identifies the amount of torque that is needed for the knee to perform the movement [7]. These sensors are called passive sensors [6,8,9], as they are placed around the prosthetic knee joint to identify the knee movement. The direct contact between the amputee subject and the socket device in the presence of the in-socket sensor would be more useful to acquire direct measurements from specific socket locations

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