Modeling, Design and Test-Bench Validation of a Semi-Active Propulsive Ankle Prosthesis with a Clutched Series Elastic Actuator

Driven by the desire of amputees to reduce their physical shortcomings, prosthetic feet evolved from passive to propulsive bionic feet, actuated by different types of compliant actuators to provide the push-off power and with the advantage of reducing the motor power requirements. The two-latest in-house developed Ankle Mimicking Prosthetic Foot prototypes used explosive elastic actuation. They were proven to be energy efficient, but are bulky and heavy, which increases gait asymmetries and metabolic cost. In this letter, we present the modeling, design, and test-bench validation of a novel semi-active ankle prosthesis using a resettable overrunning clutch with a series elastic actuator. Unlike many designs found in literature, which are only optimized and evaluated in the mechanical domain, we modeled the drive-train dynamics to have a better understanding of the electrical energy consumption. During the performance evaluation, it is shown that the nonpathological gait cycles at different walking speeds are well replicated in both simulations and test-bench experiments. The results reveal that this clutch is a suitable device to add to a series elastic driven ankle since it offers, for an 8% relative weight increase of the prosthesis, besides the assets of natural adaptability to different gaits and terrains, also an electrical energy reduction of up to 22% for the slow walking speed.