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This study introduces a lightweight (2.6 kg) and low-profile (24.5 cm) powered knee prosthesis utilizing quasi-direct drive (QDD) actuation, addressing the limitations of previous bulky prototypes. By optimizing an 18 to 1 two-stage transmission and conducting finite-element analyses, the authors achieved a peak torque of 145 Nm while ensuring low backdrive torque and precise control. Validation through benchtop tests and user trials demonstrated that the prosthesis can replicate biomimetic kinematics and peak knee extension torques comparable to able-bodied individuals, highlighting its potential for clinical application in enhancing mobility for users with transfemoral amputation.
A lightweight powered knee prosthesis achieves peak torque comparable to able-bodied performance while significantly reducing weight and bulk, paving the way for broader clinical adoption.
Fully-powered knee prostheses, unlike traditional passive knees, can perform controlled positive work, reducing the need for compensatory behaviors by users during energy-intensive activities. While quasi-direct drive (QDD) actuators provide superior torque control, backdrivability, and acoustic noise properties compared to traditional highly-geared actuators, prior QDD prototypes have been too heavy and bulky for commercial translation. In this work, we present the design and validation of a new lightweight (2.6 kg) and low-profile (24.5 cm tip-to-tip build height) QDD knee prosthesis. By optimizing an 18 to 1 two-stage transmission alongside thermal and structural finite-element analyses, we significantly reduce device mass while enabling a peak torque of 145 Nm. Through benchtop tests, we validate the device's high output torque, low backdrive torque (1 Nm), and its precision position and torque control capabilities. We also demonstrate biomimetic kinematics and peak knee extension torques (within one standard deviation of able-bodied references) during both level-ground walking and sit-stand transitions performed by three participants with transfemoral amputation and varying K-levels. By meeting or improving upon the mass, build height, peak torque, and acoustic noise of a leading commercial powered knee, this work establishes the clinical viability of emerging QDD prostheses that promise improved dynamic performance for their users.
