Sensor fusion for estimating ground reaction force using insole-type foot pressure and inertial sensors

Ground reaction force (GRF) analysis is critical to evaluate gait and running performances. However, installing force plates on the ground surface is costly, and their transportation is challenging owing to weight constraints and restricted measurement areas. This study proposes the method by Extended Kalman filter (EKF) to estimate the three-axis force components in the GRF, utilizing vertical force data from insole sensors, angular velocity, and acceleration data from inertial measurement units (IMUs). Shear forces were calculated using the acceleration in global coordinates, with the equivalent mass calculated by the vertical force and acceleration. The force components were then compensated for sensitivity and interference using a matrix. Moreover, the method was extended to include the center of pressure and unit position vector. The experimental protocol comprised two phases: calibration and measurement, conducted on force plates installed on the ground surface. The error compensation for force components was based on actual gait motion data and the results were compared with the force plates' outputs. The findings confirmed the effectiveness of this method. This method will be expanded to include motion measurements during long-distance walking and outdoor environments.