Design of a powered ankle orthosis for rehabilitation

This research describes the design, development, and testing of a powered ankle orthosis (PAO), designed to provide exoskeletal assistance with plantar flexion for a user unable to properly complete this portion of normal gait. A PAO is a powered assistive device with a large variety of potential applications, such as rehabilitation and enhancement of human performance. The PAO is an exoskeletal orthosis that is easily removable and simple to operate for any user. The PAO is worn using a simple fitted orthosis mold and no surgery is required. The PAO is strapped onto the user’s foot and shank and is generally used to provide additional force to the ball of the user’s foot during push-off.Roughly 90% of the gait cycle is spent with negligible ankle energy output. A device designed to store energy over a larger portion of the gait cycle would be able to take advantage of the ankle’s idle time to prepare for push-off. The main power source for this PAO is an electric motor which was selected because of its large power density and clean operation. In order to reduce the size of the motor needed to drive the system, a spring is compressed during gait to store the energy needed for push-off. This enables the PAO to use a small electric motor to meet the peak power demand during gait. The device is powered by transferring energy from an electric motor to compress a spring via a transmission. At push-off, the energy release mechanism quickly releases the spring’s energy. The PAO pulls the heel upward, causing the toe to be pushed down; thus creating artificial plantar flexion.After creating a conceptual design, the next phase was to fabricate and assemble the components using the College of Engineering and Technology’s subtractive prototyping lab (machine shop) for testing. Once the components were built, the PAO system was assembled and tested on a benchtop testing frame using high-speed video footage. Results from these tests include displacement, velocity, acceleration, torque, and force created during the operation of the powered ankle orthosis. Through this research, it was determined that a PAO powered by a small DC motor is able to produce enough force to be a viable option for gait rehabilitation. The analysis also provided a basic understanding of the dynamics of a PAO releasing energy from a spring. Additionally, the effect of the component properties was examined to understand how the PAO system can be configured to each individual user, as well as the effect the user’s foot size has on the performance of the PAO