A Zero-Position-Difference ZUPT Method for Foot-Shank-Mounted Pedestrian Inertial Navigation Systems

Pedestrian navigation system is an important application of inertial sensor technology because it does not depend on any external facilities. However, the positioning accuracy is limited due to the cumulative error of the inertial sensor. Zero Velocity Update (ZUPT) is an effective method to compensate the cumulative error. To avoid the jitter and random noise defects of single inertial sensor, a zero-position-difference ZUPT combined with foot and shank kinematics information is proposed in this work. Firstly, the zero position difference constraint matrix with ankle joint as the connection point is established through analyzing the local motion characteristics of foot and shank. In order to get accurate attitude and position by fusing the measurement information of foot and shank, an improved extended Kalman particle filter (EKPF) based on the zero position difference is proposed. Moreover, according to the gait characteristics of foot and shank, a weight assignment strategy is designed to detect the zero velocity intervals of walking. The feasibility and effectiveness of the algorithm are verified by experiments. The results show that the error of the improved zero velocity detector is about 22% less than that of the foot-mounted zero velocity detector. The improved EKPF method reduces the positioning error by more than 35% and 45% compared with the traditional EKPF method based on shank and foot, respectively.