Design, Control and Preliminary Test of Robotic Ankle Prosthesis

Abstract

Currently, most of commercially available ankle foot prosthesis are passive, which don't exhibit appropriate biomechanics during walking and could not adapt to dynamic property of able-bodied walking. In this paper, we present a novel robotic ankle foot prosthesis with variable transmission series elastic actuator (SEA). Slider crank mechanism is applied to transform linear motion of series elastic actuator to rotary motion of ankle foot joint. And this could contribute to variable transmission ratio while ankle angle varies. Because of variable transmission ratio, ankle joint torque is increasing while ankle angle is flexed from plantar flexion to dorsiflexion, whose feature has similar increase trend with human's ankle joint torque-angle relationship, and exhibits an appropriate characteristic for developing robotic ankle foot prosthesis. Larger torque could be obtained in powered plantar flexion, and this indicates that variable transmission mechanism would help reduce required motor torque compared with traditional mechanism. Energy stored in springs of series elastic actuator contribute a torque to powered plantar flexion. Preliminary experiments with a transtibial amputee and a transferomal amputee have been performed to test the prototype.