A Fluid-Powered Ankle-Foot Orthosis to Assist Disabled Persons

Achievement date: 

Researchers affiliated with the Center for Compact and Efficient Fluid Power (CCEFP), an NSF-funded Engineering Research Center (ERC) headquartered at the University of Minnesota, developed system- and component-level models to predict the efficiency and weight of small hydraulic systems that comprise a fluid-powered ankle-foot orthosis (AFO). Researchers are also evaluating, in clinical trials on post-stroke patients, the effectiveness of a pneumatic Portable-Powered AFO (PPAFO).


Development and modeling of a fluid-powered AFO, clinical trials on a specific PPAFO, and continuing research behind similar fluid-powered devices have the obvious benefit of creating novel powered exoskeletons that can assist persons with disabilities. In addition, addressing the complex engineering issues associated with the fluid-powered AFO facilitates the development of miniature fluid-power systems by pushing the practical limits of weight, power, and duration for compact, untethered, and wearable fluid-power devices. New market opportunities for the fluid-power industry will likely result from these efforts.


The overall goal of the hydraulic AFO work is to demonstrate the capabilities and advantages of tiny hydraulics for powered, untethered, human-assist machines. The hydraulic AFO is the lightest, high-torque, untethered, and powered ankle orthosis that has ever been developed. This device holds the promise of enabling people with mobility impairments to walk with greater stability, confidence, and independence, including persons with stroke, cerebral palsy, or acute trauma.

CCEFP researchers are exploring whether the PPAFO can be used as a successful gait-assistance device for post-stroke persons (see figure). In collaboration with researchers at the Rehabilitation Institute of Chicago, testing has begun to explore the advantages, in a post-stroke subject population, of the PPAFO compared to a range of other assist devices (e.g., tibial stimulators, commercial passive AFOs). The devices are being compared in this population by asking each participant to complete a set of clinically accepted walking tasks with both the PPAFO and their personal device. During each walking task, a subject’s oxygen consumption is being measured as well as the standard outcome measures of the task.

In general, the AFO program has enabled cooperative efforts on the broader fluid-powered human-assist concept. It is anticipated that development of a next-generation AFO will push the limits of fluid-power technology. Innovative projects like this hold promise of delivering a miniature and integrated power supply, novel actuators, valves, transmission lines, and housing.