Initial Results of a Variable Speed Knee Controller for Walking with a Powered Knee and Ankle Prosthesis

Powered knee and ankle prostheses can potentially improve the mobility and function of their users, but determining the best way to control the prosthesis is difficult. Controllers that vary knee swing speed have been shown to restore gait symmetry with a powered knee and ankle prosthesis. This study's goal was to combine an existing variable speed knee swing controller with an existing impedance stance controller to determine if comfortable walking with variable cadence can be achieved and if the control method transitions would be noticeable to the user. The knee swing trajectory and duration was varied based on user walking speed as a function of the previous stance phase duration. Four individuals with unilateral transfemoral amputations were fit with a powered knee and ankle prosthesis. After 30-45 minutes of practice walking with the variable knee swing controller, subjects performed a variable speed walk test, a steady state walk test, and a 10-meter walk test. A GAITRite mat was used to collect spatial and temporal walking parameters during the 10-meter walk test. Results showed that subjects could control prosthetic knee swing duration and kinematics by modifying their walking speed. Subjects were able to comfortably transition between speeds and achieve mean (SD) comfortable and fast speeds of 1.10 (0.05) and 1.51 (0.05) m/s, respectively for a 10-meter walk test. This study's contribution is to show that a variable speed knee controller can be combined with an impedance-based controller while maintaining the functionality of both controllers and to provide gait mechanics for amputee powered gait that can be used towards future studies of controller development and prosthesis design.