Development of a wearable sensor system for quantitative gait analysis

This paper presents a study on development of a wearable sensor system for quantitative gait analysis using inertial sensors of gyroscopes and accelerometers. This system was designed to detect gait phases including initial contact, loading response, mid stance, terminal stance, pre swing, initial swing, mid swing and terminal swing, which is quite inexpensive compared with conventional 3D motion analysis systems based on high-speed cameras. Since conventional camera-based systems require costly devices, vast space as well as time-consuming calibration experiments, the wearable sensor-based system is much cheaper. Gyroscopes (ENC-05EB) and two-axis ADXL202 accelerometers are incorporated in this wearable sensor system. The former are attached on the surface of the foot, shank and thigh to measure the angular velocity of each segment, and the latter are used to measure inclination of the attached leg segment (shank) in every single human motion cycle for recalibration. The gyroscope is sensitive to a temperature change or small changes in the structure (mechanical wear), which leads to fluctuating offsets from sensor output in applications of human motion measurements. The orientation estimation algorithm here continuously corrects orientation estimates obtained by mathematical integration of the angular velocity measured using the gyroscopes. Correction is performed using an inclination estimation obtained using the signal of the two-axis accelerometer during the interval of mid stance in each stride. The average of root mean squared error (RMSE) was not over 5.0° (the thigh angle orientation) when the calibration was implemented. Correlation coefficient (R) approached 0.9 when the segment angles obtained from the wearable sensor system were compared with the results from a conventional optical motion analysis system.