Robotic Ankle-Foot Orthosis with a Variable Viscosity Link Using MR Fluid

Abstract

This paper proposes a novel semiactive ankle-foot orthosis (AFO) called SmartAFO equipped with an elastic link mechanism. The design of the device is based on the understanding of gait biomechanics for gait assistance against paralysis and other gait abnormalities affecting the ankle joint function. The elastic link at the core of the developed AFO is a 1-degree-of-freedom linear-motion system, capable of regulating its viscosity via a magnetorheological fluid and an electromagnetic coil. The link is also integrated with a compression spring that allows it to store and release energy based on its coil current. This design enabled a semiactive AFO that can mitigate foot slap and toe drag without adversely affecting push-off or other gait phases. We present the development of SmartAFO and the results of experiments conducted on healthy people to verify its support functions compared to a commercial AFO. The results showed that SmartAFO can provide controllable braking torque at the heel contact, avoid ankle motion obstruction during the push-off phase, and support toe lift during the swing phase.