Development of MR brake for finite state control of othotic ankle joint

Abstract

An orthotic ankle joint for lower limb inconvenient person was developed in which external ankle joint moment is generated by MRF (Magneto Rheological Fluid) brake. The brake is a fan-shaped closed vessel filled with MRF and the bane installed in the vessel is moved in the range of 0-70 degrees. The brake moment is generated and shifted by applying magnetic field to the thin flow channel of MRF. In a past trial manufacturing, permanent magnet was moved to near of distant from the MRF flow channel. In this trial manufacturing, the electric coil was used to generate magnetic flux density to the MRF flow in the small gap of the bane, and structure of the brake became simple and compact and response was improved.

With this brake, the control strategy was established based on the finite-state-control. The three states of heel contact, toe-off, and swing-phase were detected by the sensors installed in the orthosis, constructed from foot switches at heel and ball, and potentiometer at ankle joint. With this control strategy, the plantar flexion brake is generated and foot flap is eliminated, and dorsal-flexion ankle joint position is kept during the mid swing phase by generating brake moment at the end of stance phase.

The effect on the gait motion was measured and proved by the gait analysis of the lower limb inconvenient patient wearing this orthosis