Design and control of an active ankle-foot orthosis

Abstract

Active ankle-foot orthoses are used to assist patients suffering from stroke, mul tiple sclerosis, cerebral palsy etc. through providing an external force supply to track normal gait cycles. In this study, design of an active ankle-foot orthosis prototype, and an adaptive backstepping control algorithm for it to track desired gait trajecto ries while reducing the effects of unknown disturbances are proposed. A prototype of the orthosis, which is composed of a series elastic actuator, a lever mechanism and an orthotic shoe, is developed. The prototype is mathematically modeled as a two degree-of-freedom mass-spring system and the unknown disturbances are modeled. The backstepping control law is designed for a force input supplied to the system. Addition ally, the designed algorithm is implemented in a real-time operating system to control the developed ankle-foot orthosis prototype. Simulations are performed to compare the proposed control architecture and a PID controller in trajectory tracking of the pro totype. Finally, experimental tests including user tests are conducted to evaluate the prototype in use and to compare the performances of the control algorithms. Results show that the overall system satisfies the design requirements, and proposed control architecture is about two times better than the PID controller.