Feasibility test of a novel power-harvesting mechanism to adjust ankle stiffness in ankle foot orthosis

Orthotic devices are used widely in orthopaedics to improve the gait of patients with conditions such as stroke, one of the most common causes of impairment, who develop drop foot. Although there are passive or power harvesting orthosis for them, their effectiveness is limited due to the fact that they usually have a unique stiffness throughout the whole gait cycle or because they focus only on modify damping. Thus, we develop and test a novel passive power-harvesting mechanism to adjust ankle stiffness in ankle foot orthosis. The mechanism is based on two matching grooves that pull a string when they are pressed, deflecting a spring that helps to generate dorsiflexion. The mechanism is optimized and tested using 3D printing technologies. Results show that it changes the stiffness through gait cycle, thus allowing dorsiflexion, although bigger torque is needed to reach average levels of ankle torque.