UIUC looks to use pneumatics to give power to your stride

The University of Illinois at Urbana-Champaign, a member of the Center for Compact and Efficient Fluid Power, is home to the CCEFP’s smallest test bed. It focuses on using fluid power to develop a more versatile, efficient and aesthetically pleasing version of an ankle-foot orthosis device. These devices are used to correct the gait of people suffering from the affects of a stroke and diseases like Parkinson’s and Multiple Sclerosis. According to the CCEFP, the goal of the test bed is to enable the miniaturization of fluid power technologies for use in human scale, un-tethered devices.

Commercially available AFO’s are typically passive devices that keep a patient’s foot locked at a 90° angle and their toes elevated to prevent them from tripping as they move their foot forward. By doing this, the patient loses the ability to push off with each step, which results in a smaller gait and slower walking speed.

The powered ankle-foot orthosis can operate for more than 40 minutes using a 20 oz canister of compressed CO2. The compressed CO2 powers a rotary actuator that  supports the foot during swing, but can also provide plantar flexor torque to help with propulsion when taking a step. Exhaust gases are then recycled to help raise the foot for the next step. The long term plan is to develop a portable power supply that can produce at least 20 W of power, run continuously for one to eight hours, weigh less than 1 kg and be designed to reduce physical interference when in use.

“Other people have all ready been looking at developing powered ankle/foot orthosis for clinical use, not portability,” Elizabeth Hsiao-Wecksler principal investigator for the human dynamics and control lab said. “They don’t really care about the aesthetics, but you couldn’t put your shoe over their designs.”

UIUC’s design uses a bidirectional rotary actuator instead of traditional linear actuators. This is done to reduce the amount of hardware on the device and allow for a greater range of motion.

Other work being conducted at the university involves developing and implementing control algorithms designed to make more efficient use of fluid power systems. These algorithms will help better determine when is the best time to produce power, the best way to distribute it and the best way to use power when split between multiple users.

“One challenge has been to develop high quality models that are accurate but simple enough to use in decision making algorithms,” Andrew Alleyne, a Ralph & Catherine Fisher professor of engineering said.

Alleyne faced this challenge when trying to come up with models for the pump dynamics and efficiencies that are useful for control design. He developed some of the first multi-input/multi-output models of power trains for high efficiency control of off-highway vehicles, work that has drawn interest from Caterpillar.

University of Illinois at Urbana-Champaign
www.engineering.illinois.edu