Design and Control of a Powered Transfemoral Prosthesis

Abstract

This thesis describes the design and control of a transfemoral prosthesis with powered knee and ankle joints. The initial prototype is a pneumatically-actuated powered-tethered device, which is intended to serve as a laboratory test bed for a subsequent self-powered version. The prototype prosthesis provides the full range of motion for both the knee and ankle joints while providing 100% of the knee torque required for fast cadence walking and stair climbing and 76% and 100%, respectively, of the ankle torque required for fast cadence walking and for stair climbing, based on the torques required by a healthy 75 kg subject. The device includes sensors to measure knee and ankle torque and position, in addition to a load cell that measures the interaction force and (sagittal and frontal planes) moments between the user and device. A gait controller is proposed based on the use of passive impedance functions that coordinates the motion of the prosthesis and user during level walking. The control approach is implemented on the prosthesis prototype, and experimental results are shown that demonstrate the effectiveness of the active prosthesis and control approach in restoring fully powered level walking to the user.