MIT robotic exoskeleton struts out of the lab, carries grad student with it


MIT grad student Conor Walsh and the leg exoskeleton he and other researchers have developed. [Photo: Samuel Au / MIT News]

MIT researchers have created a wearable robotic exoskeleton to help soldiers carry heavier loads on their backpacks. Powered legs like those could one day help elderly and disabled people gain more mobility and carry things around more easily, but since this is DARPA funded work soldiers have priority. Sorry, grandma.

The MIT exoskeleton consists of a pair of mechanical legs with a mounted backpack frame. The mechanical legs strap to the user's own legs and support much of the pack's weight by transferring it to the ground. The MIT researchers, led by Hugh Herr at Media Lab's Biomechatronics Group, report in the September issue of the International Journal of Humanoid Robotics that their prototype can take on 80 percent of an 36-kg load carried on a person's back.

And how does it work?

The MIT leg exoskeleton differs from previous systems such as Cyberdyne's HAL-5, UC Berkeley's Bleex, and Sarcos's powered legs in that it doesn't have actuators. HAL-5 uses electric motors and Bleex and the Sarcos system use hydraulic actuators to produce extra torque to the joints or actively support a backpack. These fully actuated systems require lots of power: HAL-5 needs a pack of heavy batteries and Bleex and Sarcos's system use small internal combustion engines.

The MIT robotic exoskeleton uses spring mechanisms at the hip and ankle and a damping mechanism at the knee, and it exploits the dynamics of walking and the exchanges between gravitational potential energy and kinetic energy of the person's center of mass. The spring mechanisms store elastic energy during part of the walking cycle, releasing that energy during another stage of the cycle to assist the user. The damping mechanism is a set of disks with MR fluid between them; using an electromagnet that requires low power, a magnetic field can be modulated through the disks, changing the level of damping to assist in supporting the pack's weight.

But before you can strap this exoskeleton to your legs to help you carry the groceries or the laundry bag, the MIT researchers need to make some tweaks. Tests showed that a person using the exoskeleton and carrying a 36-kg backpack, although feeling a lighter load on his or her back, actually consumes 10 percent more oxygen (thus spending more metabolic power) than if carrying the backpack without robotic help. That's because the exoskeleton interferes with the user's natural gait, and so the user needs extra effort to compensate for that.

The researchers say they are improving their design, and this being MIT it might mean their next prototype will let grandma marathon around town, leap tall buildings, and spew lightning from her feet.



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