Design and Control of a Powered Knee and Ankle Prosthesis

This paper describes the design and control of a transfemoral prosthesis with pneumatically powered knee and ankle joints. The current version of the prosthesis serves as a laboratory testbed for purposes of controller development and testing, and as such is tethered for both power and control. A subsequent version will be self-contained, with on-board control and hot gas (monopropellant) actuation. This paper presents the design of the prosthesis prototype, which is in essence a two degree-of-freedom powered robot mechanically attached to a user, and describes an impedance-based control approach that coordinates the motion of the prosthesis and user for the control of level walking. The control approach is implemented on the prosthesis prototype, and experimental results are shown that indicate the effectiveness of the active prosthesis and control approach in restoring fully powered level walking to the user. Finally, an accompanying video demonstrates the functioning prosthesis in level walking.