Prototyping of an Ankle Foot Orthosis with Variable Viscosity Joint

Abstract

Ankle-foot orthosis (AFO)is an important aid for patients with gait disorder. We have investigated the relationship between hemiplegic ankle joints function and AFO joint characteristics during gait, because mechanical characteristics of AFO joint directly affect the walking function. In this article, we examined an ankle joint device using magneto-rheological fluid that rheological characteristics can be adjusted by changing intensity of magnetic field applied. The device is composed of a rotary cylinder and a short tube with restrictor connecting both cylinder ports, and its closed hydraulic circuit is filled with MR fluid. The moment and angular velocity relationship was measured for the device with a permanent magnet, and the resistant moment was evaluated under different magnet distance from the tube. This device was mounted on an experimental CFRP upright AFO accompanied with a magnet position adjustment mechanism. Gait of a hemiplegic volunteer with this AFO was improved in some time-distance parameters when viscosity was switched to low at initial stance phase and to high immediately before swing phase.