Drift Removal for Improving the Accuracy of Gait Parameters Using Wearable Sensor Systems

TLDR

Signal noise causes drift in orientation angle measurements from wearable sensors. The study proposes a novel method to reduce drift and accurately measure human gait with wearable sensors. The method applies an IIR 4th‑order Butterworth filter to remove noise, subtracts static gyro offset, uses a robust double‑derivative integration to eliminate residual drift, aligns the gravitational vector from standing and sitting acceleration data to reduce attachment errors, and extracts kinematic and spatio‑temporal gait parameters from heel‑contact and toe‑off timings. The approach reduced drift, yielding average joint angle errors of 2.1°, 33.3°, and 15.6° for hip, knee, and ankle, and demonstrated the potential of wearable sensors for clinical gait evaluation.

Abstract

Accumulated signal noise will cause the integrated values to drift from the true value when measuring orientation angles of wearable sensors. This work proposes a novel method to reduce the effect of this drift to accurately measure human gait using wearable sensors. Firstly, an infinite impulse response (IIR) digital 4th order Butterworth filter was implemented to remove the noise from the raw gyro sensor data. Secondly, the mode value of the static state gyro sensor data was subtracted from the measured data to remove offset values. Thirdly, a robust double derivative and integration method was introduced to remove any remaining drift error from the data. Lastly, sensor attachment errors were minimized by establishing the gravitational acceleration vector from the acceleration data at standing upright and sitting posture. These improvements proposed allowed for removing the drift effect, and showed an average of 2.1°, 33.3°, 15.6° difference for the hip knee and ankle joint flexion/extension angle, when compared to without implementation. Kinematic and spatio-temporal gait parameters were also calculated from the heel-contact and toe-off timing of the foot. The data provided in this work showed potential of using wearable sensors in clinical evaluation of patients with gait-related diseases.