A Low-Cost Flex Sensor Gait Phase Gating Method for Powered Ankle Prostheses

Abstract

Powered ankle prostheses restore the active push-off that passive prosthetic feet cannot provide, yet their cost places them beyond reach for most lower-limb amputees in low- and middle-income countries. This work presents a low-cost knee motion sensing and gait phase gating method for a powered ankle prosthesis using a single resistive flex sensor costing about one thousand seven hundred Pakistani rupees, roughly six United States dollars. The flex sensor is mounted across the knee region of the prosthetic socket and sampled at one hundred hertz on an ESP32-S3 microcontroller. A two-point calibration maps the sensor voltage to knee flexion angle, and a gait phase gate uses the calibrated angle to suppress electromyography classifier outputs inconsistent with the current gait phase. Across three sessions, the calibration showed a mean absolute error of two point one degrees, and the knee angle correlated strongly with an optical reference, with a correlation coefficient of zero point nine eight and a root mean square error of two point four degrees. During a thirty-minute walking trial, the gait phase gate reduced spurious actuator commands from forty-seven to thirteen, an overall reduction of seventy-two percent, and up to seventy-six percent under perspiration. The complete powered system costs approximately twenty-eight thousand Pakistani rupees, less than one month of minimum-wage income, against fourteen to twenty-four million rupees for imported powered ankles. A single flex sensor therefore delivers meaningful gait phase awareness at negligible cost, supporting affordable powered prosthetic technology for resource-limited settings.