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One-size-fits-all exosuits don’t work: we need exo-tailoring

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The ankle exoskeleton used in the new research reduced the energy expended by wearers by 24 percent.
Photo by Steve Collins

Exoskeletons can be incredibly useful, giving people extra strength or the ability to move freely when injured or disabled. But augmented performance comes at a cost, and users usually have to put in more effort while wearing these prosthetics. Scientists are trying to fix this: they have developed a new system that actively saves the user’s energy by adjusting the exoskeleton to their body’s natural movement.

Now, the idea that exoskeletons consume additional energy may seem a bit counterintuitive. After all, aren’t they supposed to make things easier? According to biomechanist Juanjuan Zhang, who led this latest research at Carnegie Mellon University, the problem is that exoskeletons are built on a one-size-fits-all system, and not tailored to the individual. This means users often fight against them unconsciously, or just find them uncomfortable to wear. This takes up energy.

“In theory they’re giving you an extra push, so you should be using less of your own energy. But the problem is that humans are so different from one to another, and some of us actually try to fight against the exoskeleton,” Zhang tells The Verge. “But the difficulty is not the device, it’s the fact that the human body is so complicated.”

The solution proposed by Zhang and her team in a paper published in Science today is an algorithm that automatically adjusts the exoskeleton to the wearer’s body. The researchers tested their method with an ankle exoskeleton designed to help volunteers walk more easily. The exoskeleton clips onto the shin and foot, with a motor and a pulley system lifting up the back of the heel with every step.

The amount of energy the volunteers expended was measured by monitoring their breathing, and the software automatically tweaked the exoskeleton to see what movement helped most. For example, it would try lifting the heel earlier or later during a step, or applying more or less energy, to see what suited the wearer.

This diagram shows how the exoskeleton’s mechanism was adjusted. The lines show when during a step the motor was activated, and how strong it pulled on the heel.
Image: Science / Zhang et al

This sort of personalization has been done in the past, but, according to an accompanying editorial published in Science, never so quickly or effectively. Usually changes to an exoskeleton have to be made by hand, with researchers gathering data, then tweaking, then testing again. But in just an hour, Zhang and her team were able to reduce the energy each volunteer expended while walking by an average of 24 percent. (That’s compared to walking with the exoskeleton powered off.)

The research is limited in some ways. For example, only four different factors were being adjusted in the ankle exoskeleton. For full-leg or full-body exoskeletons, there would be many more constraints to think of, and this would take more time and computing power to process.

However, says Zhang, her basic method is sound, and should scale up with the right adjustments. Then, she says, it’ll be much easier to build effective and useful exoskeletons for more people: “What we want is a personalized device for everybody.”