A low-noise low-impedance powered knee prosthesis with direct ball screw drive and torque-sensitive actuation

The standard of care for individuals with above-knee amputation is the microprocessor-controlled knee prosthesis-a lightweight and quiet device that can actively regulate joint resistance but cannot generate positive power like biological legs during ambulation. Powered prostheses aim to address this limitation with robotic actuators. However, limitations of conventional robotic actuators result in powered prostheses that are either heavy, loud, and have high joint impedance or lack sufficient torque and power to replicate key biomechanical functions of the biological leg. These limitations have limited the clinical success of powered knee prostheses. In this paper, we show that combining quasi-direct drive with a variable transmission in a novel torque-sensitive actuator can overcome the limitations of conventional actuators in robotic knee prostheses. Theoretical analysis shows that this combination of technologies substantially extends the range of torques and speeds of an electromechanical actuator without increasing its output impedance. Mechatronics implementation of the proposed design concept into a robotic knee prosthesis confirms the torque, speed, and output impedance improvements predicted by theoretical modeling. Amputee testing verifies that the proposed knee prosthesis can provide joint torques and speeds up to 145 Nm and 550 deg/s, enabling the user to ambulate on stairs and walk at 2.5 m/s. The prosthesis achieves lower impedance than the biological knee and approximates the weight (1.9 kg) and noise (45-53 dBA) of passive microprocessor-controlled knee prostheses. By enabling lightweight, quiet, and powerful prostheses, the proposed actuation concept has the potential to improve the quality of life in individuals with above-knee amputations.