Pressure‐sensitive insoles for real‐time gait‐related applications

Wearable robotic devices require sensors and algorithms that can recognize the user state in real‐time, in order to provide synergistic action with the body. For devices intended for locomotion‐related applications, shoe‐embedded sensors are a common and convenient choice, potentially advantageous for performing gait assessment in real‐world environments. In this work, we present the development of a pair of pressure‐sensitive insoles based on optoelectronic sensors for the real‐time estimation of temporal gait parameters. The new design makes use of a simplified sensor configuration that preserves the time accuracy of gait event detection relative to previous prototypes. The system has been assessed relatively to a commercial force plate recording the vertical component of the ground reaction force (vGRF) and the coordinate of the center of pressure along the so‐called progression or antero‐posterior plane (CoPAP) in ten healthy participants during ground‐level walking at two speeds. The insoles showed overall median absolute errors (MAE) of 0.06 (0.02) s and 0.04 (0.02) s for heel‐strike and toe‐off recognition, respectively. Moreover, they enabled reasonably accurate estimations of the stance phase duration (2.02 (2.03) % error) and CoPAP profiles (Pearson correlation coefficient with force platform ρCoP = 0.96 (0.02)), whereas the correlation with vGRF measured by the force plate was lower than that obtained with the previous prototype (ρvGRF = 0.47 (0.20)). These results confirm the suitability of the insoles for online sensing purposes such as timely gait phase estimation and discrete event recognition