Flywheel–infinitely variable transmissions for energy recovery capabilities in artificial knee joints

In this work, we present a novel architecture of the flywheel–infinitely variable transmission (F-IVT) actuator with increased energy saving performance. The F-IVT is an actuator for artificial knee joints with energy recovery capabilities. It uses a flywheel and an IVT with the purpose of storing and releasing energy and stabilizing the motor working point. The architecture proposed herein, named “linear F-IVT”, is compared with the rotating F-IVT and with the clutchable-series elastic actuator, through a model-based approach. By simulating the operation of these actuators in walking at different speed and stairs climbing of different inclination, the linear F-IVT results to be the most effective in reducing the peak of electric power and motor torque, also achieving a reduction of the electric energy demanded. These results suggest the possibility to achieve a significant motor downsizing, possibly leading to the development of a lightweight actuator to improve the portability and the operating range of wearable robots for lower limbs. Abbreviations: BS: ball screw; C-SEA: clutchable - series elastic actuator; CVT: continuously variable transmission; F-IVT: flywheel–infinitely variable transmission; HD: harmonic drive; IVT: infinitely variable transmission