Filtering techniques using frequency analysis for inertial sensors in gait measurements

Abstract

Inertial sensors (accelerometers and gyroscopes) have recently gained attention as a promising alternative to video capture systems in studies of human movement. Secondary quantities such as velocity and displacement are calculated through integration of acceleration and angular velocities. It is now widely accepted that this technique is greatly influenced by sensor noise, non-linear and asymmetrical sensitivity/ offset signals and bias drifts. In this paper, we compare the Root Mean Square Error (RMSE) of vertical toe acceleration obtained by these sensors and derived by double differentiation from a video capture system, i.e. Optotrak Certus, NDI. Spectral analysis was performed on both accelerations using the Fast Fourier Transform to compute the correlation coefficient ρ as a function of various static band-pass filter parameters and over a range of 3 different walking speeds. RMSE and cross correlation achieved for the slowest walking speed of 2.5Km/h was 2.92m/s² and 0.668 respectively, and 4.38m/s² and 0.984 for the fastest speed of 4.5Km/h.