Observation of Gait Patterns and Orientation Angles for Development of an Active Ankle-Foot Prosthesis

Abstract

Recent studies on ankle-foot prostheses which are commonly used for transtibial amputees have focused on adaptation of the ankle angle of the prosthesis according to ground conditions in order to reduce the difficulties which the patients experience while walking on stairs or a ramp. For adaptation to the various ground conditions (e.g., incline, decline, step, etc.), the ankle-foot prostheses should first recognize the ground conditions as well as the current human motion pattern. For this purpose, the ground reaction forces and orientation angle of the prosthesis provide fundamental information. The measurement of the orientation angle, however, creates a challenge in practice. Although various sensors, such as accelerometers and gyroscopes, can be utilized to measure the orientation angles of the prosthesis, none of these sensors can be used as a sole sensing mechanism due to their intrinsic drawbacks. A number of sensor-fusion methods have been proposed to address this issue. In this paper, a time-varying complementary filtering (TVCF) method is proposed to incorporate the measurements from an accelerometer and a gyroscope to obtain a precise orientation angle. The cut-off frequency of TVCF is adaptively determined according to the human motion phase. The performance of the proposed method is verified by experiments.