Untethered pneumatic ankle foot orthosis powered by a portable piston-crank compressor

Abstract

Concurrent with the climbing rate of world life expectancy, the number of people with age related disabilities and impairments has increased placing unprecedented demands on global healthcare systems and aging-related services. Among the wide range of realms of possible disabilities, gait related impairment have been of great interest as walking is a fundamental function of one’s daily routine and a key component for the overall quality of life.

Passive ankle foot orthoses (AFOs) are generally customizable, lightweight, compact, and relatively inexpensive. As a result, passive AFOs make up the majority of the devices prescribed by clinicians to treat dysfunctions of the ankle joint. Despite the popularity, the inability to provide assistive torque during gait and inhibition of necessary ankle motion limits the functional benefit of passive AFOs. To address these limitations, current research efforts have been directed towards the development of active AFOs.

Recent advances in actuator and sensor technologies have contributed to the growth of active AFOs. Variable dampers and series elastic actuators have been developed to power AFOs and showed promising results in improving ankle functionality. The considerable masses of the systems still limit such devices in the practical perspective. To minimize counterproductive effects of the additional masses introduced by the system, remote actuation mechanisms can be utilized to distribute the masses closer to the trunk of the body.

Pneumatic powered systems carry great potential for remote actuation, especially in wearable robotic applications as pressurized air can be easily transferred through flexible tubing to remote locations. This allows flexibility in the placement of system components of the assistive device elsewhere on the body, resulting in light weight and compact sized AFOs. Moreover, the compressibility of air provides inherent compliance allowing safe and comfortable interaction between the AFO and user without additional mechanisms.

Despite the significant advantages of a pneumatic powered system, the large stationary air compressors required to supply pressurized air are large, bulky and tethered. Therefore, the objective of the work presented in this dissertation is to first design a portable air compressor that can be worn on the trunk of the body and can generate pressurized air that is sufficient to assist the dorsiflexion motion of the ankle. Along with the designed portable air compressor, a compact, lightweight, active ankle-foot orthosis was developed. Then as a proof-of concept, the developed system is tested on three drop foot patients with impaired dorsiflexor muscles. Improved ankle kinematics in the sagittal plane and pelvic tilt in the coronal plane was achieved. It is believed that this development has shown the potential that pneumatic energy sources can be miniaturized by optimizing the source with respect to the application. This can allow pneumatic systems to be fully portable, wearable and extended to other wearable applications.