A Lightweight, Efficient Fully Powered Knee Prosthesis With Actively Variable Transmission

Amputation at the above-knee level severely impairs the ability of an individual to ambulate. As ambulation requires power generation and active control of movements, the passive nature of most available leg prostheses is a major cause of the observed deficits. Powered prostheses aim to address this limitation using battery-operated servomotors. However, due to the wide ranges of torque and speed necessary to assist ambulation, available powered prostheses are significantly heavier than passive prostheses, which limits their effectiveness and clinical viability. In this letter, we introduce the first fully powered robotic knee prosthesis that matches the weight of state-of-the-art passive prostheses while providing suitable torque and speed to power ambulation on level ground and stairs. Dynamic simulations are shown together with an extended experimental assessment supporting the design of a new actively variable transmission. A preliminary validation is provided by an above-knee amputee subject ambulating on level-ground and stairs.