The ankle exoskeleton algorithm adapts to speed and gait

A new control algorithm could make ankle exoskeletons automatically adapt to individual users and tasks, researchers say.

Current exoskeletons are limited because they must be tailored to an individual user performing a single task, such as walking in a straight line. Any changes require a large set of manual adjustments.

The new control algorithm shows the ability to handle different speeds, as well as changes in gait between running and walking. It could pave the way for exoskeletons that are better able to handle the uncertainties of the real world.

“This particular type of ankle exoskeleton can be used to augment people who have limited mobility,” says Leia Stirling, associate professor of industrial and functional engineering and robotics at the University of Michigan and senior author of the study at PLOS ONE.

‚ÄúThis could be an older adult who wouldn’t normally be able to walk to the park with their grandchildren. But by wearing the system, they now have extra help that allows them to do more than they could before.”

The control algorithm directly measures how fast the muscle fibers expand and contract to determine the amount of chemical energy the muscle uses while doing its job. It then compares this measurement to a biological model to determine how best to help.

Direct measurement of muscle physiology is a key departure from current methods, which use broader measures of movement. Going straight to the motion source could lead to more accurate measurements over a greater range of motion with much less computing power required.

Stirling and first author Paul Pridham, a senior research fellow in industrial and functional engineering, called attention to the ankle because it plays a key role in mobility. Assisting the muscles in the ankle could have a dramatic impact on our ability to walk further and faster.

Since the research was conducted during COVID-19 restrictions, testing with human participants was not possible. Instead, the team used data on existing ankle exoskeleton devices and muscle dynamics from previous studies to simulate, test and adjust the algorithm to be more responsive to changes in speed and gait.

Human trials are an important next step and will require real-time measurement of muscle fibers using ultrasound. While much work and refinement remains, the researchers are confident that the new avenue of research will one day help people on the ground.

“This has the potential to help almost anyone,” says Pridham. “From someone who walks a lot for work, to people in the military who are on duty for long periods of time, to people with muscular disorders who need some extra help and to the elderly who need help every day.”

The Under Secretary of Defense for Research and Engineering funded the project.

Source: University of Michigan

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