Table of Contents
BenchmarkingListed below are the developed benchmark matrices for the actuation and microcontroller elements of the device.
Our team has developed two general concepts in order to assist the user in dorsi-flexion of the foot.The first general concept involves the users foot in place before the liftoff stage of gait and releasing the foot after the swing phase of gait. As the user steps forward with his/her normal foot, the affected foot is naturally dorsi-flexed. Prior to lifting that foot, a mechanical device can be used to constrain the person's foot from rotation while off the ground. Using the terrain sensing system, the constraint on the user's foot can be removed at the appropriate time, allowing gravity to plantar-flex the foot.
This can be accomplished using some sort of ratchet device that allows only dorsiflexion. Once the ratchet is reversed or released, plantar flexion may occur. A rotational or linear ratchet can be used.
Another method to constrain the rotation of the foot would be using a braking mechanism. A hydraulic friction brake can be used on a rod connected to the heal of the AFO. When the brake is applied, rotation of the ankle will be prevented.
The pitfall with this concept is that the locking of the foot angle will force unnatural gait upon the person using the system and will prevent push-off of the toes.
The second general concept involves using a commercial AFO with built in springs (posterior leaf spring) for dorsi-flexion and adding a method of applying torque in order to plantar-flex as needed. The most promising method of applying a torque to rotate the foot will be to use a linear actuator placed behind the heal and calf of the AFO, mimicking the motion and position of the Achilles tendon. Possible methods of toque application include use of a servomotor, solenoid actuator, power screw, and muscle wire.
A third general concept involves using a hard stop to control how far the foot will be able to move.
The following table shows the pros and cons of using each method.
The following concept selection matrix was used to rank the 3 potential concepts with respect to customer needs. According to this matrix, the "Mechanical Locking" mechanism is the best concept.
The team brainstormed various methods of "Locking" the
foot in place when on/off the ground. Ideas considered
Piston/Cylinder Arrangement (with air or a fluid)
Linear Ratchet Mechanism
The following matrix was used to rank and select our final concept.