An Ankle Foot Orthosis with Insertion Point Eccentricity Control

Abstract

A prototype active Ankle Foot Orthosis has been developed to control and assist plantar flexion and dorsiflexion using an innovative series elastic actuator integrated into a standard passive AFO. A motor controls the moment arm (Insertion Point Eccentricity Control or IPEC) of a pretensioned spring, and though the magnitude of the spring force remains relatively constant, the changing moment arm produces torque about the ankle. The IPEC AFO is able to provide 3.51 Nm about the ankle in dorsiflexion and 3.88 Nm in plantar flexion with a spring modulus of 3110 N/m and an initial tension of 77 N. The torque was sufficient to prevent toedrag during swing phase. This technology may benefit users with drop-foot or other ankle disorders, including those who have suffered stroke or spinal cord injury.

Mechanism and Design Analysis of Articulated Ankle Foot Orthoses for Drop-Foot

“…To restore the legged locomotion of person with spinal cord injury, Polinkovsky et al [ 9 ] developed “insertion point eccentricity controlled” (IPEC) AFO that can provide assisting torque during push-off. The IPEC AFO includes a mechanical brace in addition to functional neuromuscular stimulation (FNS).…”

“… (a) Passive AFO with four-bar mechanism [ 43 ]. (b) An AFO with insertion point eccentricity control [ 9 ]. …”

“…Through this stimulation the ankle can be flexed beyond neutral angle, which helps the ankle foot complex maintain toe-clearance during the swing phase [ 8 ]. However, activated muscle mass by FES is the fraction of available muscles resulting in less effectiveness for drop-foot prevention, which is a disadvantage of this approach [ 9 ].…”

Design of active ankle foot orthotics for gait assistance and fall prevention

“…10 Testing was performed on a single subject, and results indicated promising open-loop control results for the novel algorithm used. Polinkovsky et al, 2012, 11 describes another AFO which makes use of SEA actuation to restore legged motion in patients suffering from a spinal cord injury. The AAFO was able to reduce toe drag and foot slap of the spinal cord injury subject test users, but was mechanically unable to apply maximum torque or maximum throw in able-bodied subjects in anything faster than a slow walk.…”

Mechanical Design and Control Strategy for Hip Joint Power Assisting

“…In [ 9 , 10 ], the actuators are driven based on the walking gait information. Model-based control [ 11 – 13 ] needs to build the kinematic or dynamic model for the human-machine interaction model. Since it is difficult to obtain the inertia parameters of the human limb, some model parameters need to be estimated.…”