This paper presents a new highly accurate gait phase detection system using wearable wireless ultrasonic sensors, which can be used in gait analysis or rehabilitation applications. The gait phase detection system uses the foot displacement information during walking to extract the following gait phases: heel-strike, heel-off, toe-off, and mid-swing. The displacement of foot-mounted ultrasonic sensor is obtained from several passive anchors placed at known locations by employing local spherical positioning technique, which is further enhanced by the combination of recursive Newton–Gauss method and Kalman Filter. The algorithm performance is examined by comparing with a commercial optical motion tracking system with ten healthy subjects and two foot injured subjects. Accurate estimates of gait cycle (with an error of -0.02 +/- 0.01 s), stance phase (with an error of 0.04 +/- 0.03 s), and swing phase (with an error of -0.05 +/- 0.03 s) compared to the reference system are obtained. We have also investigated the influence of walking velocities on the performance of the proposed gait phase detection algorithm. Statistical analysis shows that there is no significant difference between both systems during different walking speeds. Moreover, we have tested and discussed the possibility of the proposed system for clinical applications by analyzing the experimental results for both healthy and injured subjects. The experiments show that the estimated gait phases have the potential to become indicators for sports and rehabilitation engineering.
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