An Improved Smart Ankle Foot Othosis Design Using Dual Fluid Power Cylinders

To design a smart ankle-foot orthosis (SAFO) that improves upon current ankle-foot orthoses used to treat steppage gait. Current ankle-foot orthoses are subjected to significant stresses on the ankle region of the structure, causing discomfort and the possible failure of the AFO. Although these AFOs have a constant stiffness, they do not reduce the occurrence of slap foot, where the foot slaps on the ground rather than gradually lowering it. The SAFO is an active ankle-foot orthosis that allows the user’s foot to follow a normal gait cycle. It is designed to reduce stress at the ankle by allowing for movement of the foot beyond a 90 deg angle for plantarflexion. The hinged ankle-foot orthosis is incorporated with a novel dual hydraulic-cylinder system, two tension springs, and force sensitive resistors. The force sensors are placed at the hallux, first metatarsal head, fifth metatarsal base, and heel. The foot movement actuation follows the force applied to the plantar surface of the foot during gait. The sensor outputs are fed to a signal processor and control interface to coordinate the motor actuation with the forces exerted by the user. The motor turns the screw attached to the hydraulic cylinders, which, thereby, control the orifice size by moving a plate in the cylinder, thus, changing the resistance. The cylinder filled with air will be pressurized during the lean phase, as the orifices will be closed and will provide power just as a spring would during the heel-off phase. After the heel strike, the resistance of the fluid-filled cylinder is decreased to slowly lower the foot. Once the foot is flat, the resistance of the fluid-filled cylinder is increased to keep the foot in a position to allow for toe clearance. During the heel-off event, the air-filled cylinder will assist the user with the power to push off. When toe-off occurs, the fluid-filled cylinder will decrease the resistance to allow the tension springs to bring the foot back to neutral position. To power the motor and sensors, a rechargeable battery pack is placed in a waist bag. The SAFO’s flexible design uses a novel combination of hydraulic-pneumatic cylinders to prevent foot drop, and restore the user’s sense of normalcy by providing late stance plantarflexion and a return to neutral position in early swing phase.