Variable Transmission Series Elastic Actuator for Robotic Prosthesis

Abstract

In this paper, we introduce a novel robotic prosthetic knee as shown in Fig. 1 (named as SuKnee) with variable transmission mechanism that could vary transmission ratio while knee angle varies during ambulation activities. A slider crank mechanism is utilized to transform linear motion of series elastic actuator to rotary motion of knee joint. And it contributes to variable transmission ratio with knee angle, which help obtain desired speed variation and torque output in different activities in one mechanism. This feature could uniquely give the SuKnee both: the torque necessary to assist with standing up from a chair and the speed necessary to swing the leg forward during walking. The knee has an active mode, where it operates with batteries and is capable of providing external power, and a passive mode, behaving like a passive prosthesis. Preliminary tests have been performed by a transfemoral amputee and SuKnee could provide user with power to assist walking on level ground and standing up from a chair. And a passive mode test shows it could work like passive prosthesis after battery exhaustion.