Backpacks are a mainstay of soldiers, hikers, firefighters and others who have to lug heavy loads, often over rough terrain where wheeled vehicles cannot traverse. But hauling them can be quite the chore, limiting wearers' mobility, especially over long distances.
Take heart, human pachyderms. Scientists at M.I.T. Media Lab's Biomechatronics Group have, with funding from the Defense Advanced Research Projects Agency (DARPA), developed an exoskeleton that promises to not only lessen the load of weary travelers but also to advance research that will ultimately lead to robotic limbs that improve the strength and mobility of amputees.
Researchers report in the International Journal of Humanoid Robotics that the M.I.T. exoskeleton is designed to be lighter and require less power than similar devices already under development. When a person walks, there's an exchange of energy within the body that allows for an efficient movement pattern, says Hugh Herr, Biomechatronics's principal investigator and associate professor in the Media Lab. "We attempted to build a lighter and lower power exoskeleton exploiting humanlike passive dynamics," he says, noting that it brings scientists a step closer to building prosthetic limbs that function and move more like human legs.
Here's how it works: The person wearing the M.I.T. exoskeleton places his or her feet in boots attached to a series of tubes that run up the leg to a backpack. The exoskeleton, powered by a 48-volt battery pack, uses an onboard computer, weighs 11.7 kilograms (about 26 pounds) and requires two watts of electrical power during loaded walking. The device fits parallel to the legs, transferring payload forces from the back of the wearer to the ground. The exoskeleton system includes elastic energy storage elements at the hip and ankle, and a variable-damping mechanism at the knee.
Ultimately, Herr would like to deliver a "biohybrid" prosthetic leg system in which the limb moves much like a human leg and can be controlled by the wearer's neurological system. "My dominant area of interest is the treatment of leg pathologies," says Herr, who lost both of his lower legs due to frostbite 25 years ago while climbing New Hampshire's Mount Washington.
Herr and his team in July unveiled the first prosthetic ankle that mimics the way a human ankle works and allows for a natural gait in people whose lower leg has been amputated below the knee. Powered by a rechargeable battery, the robotic ankle propels users forward using sensors and tendonlike springs, relieving the hip of having to draw the leg forward as most prostheses require. Herr's goal is to by next summer have a limited market release of the robotic ankle, whose development was funded by the U.S. Department of Veterans Affairs.
"We're seeing a move from systems that rehabilitate to systems that actually enhance," says Herr, who has himself tried out the robotic ankles. "In this century, through advances in human technology, we will largely eliminate disability through a deeper, more sophisticated interaction between humans and devices."
Exoskeleton research and development has been ongoing for the past few years. Efforts have been hindered by a number of challenges, such as developing a system design that does not interfere with the way a wearer would normally walk and can run on a small battery-powered pack rather than fuel. M.I.T.'s research is no exception. During test runs, researchers found that although the loads on their backs were lighter, walking required more exertion, causing the wearer to use 10 percent more oxygen than if he or she was not wearing the exoskeleton.
Researchers at Berkeley Bionics and the University of California, Berkeley, meantime, have developed two exoskeleton systems—the ExoHiker for walking and the ExoClimber for climbing. A third system will be introduced in January that combines the capabilities of the walking and climbing systems. The Defense Department is evaluating Berkeley Bionics's technology for possible military use.
Berkeley's ExoHiker is designed to help carry loads of up to 70 kilograms (around 150 pounds) during long military missions. The device can travel up to about 65 kilometers (42 miles) at an average speed of four kilometers per hour (2.5 mph) using a one-pound lithium polymer battery. With a pack-mounted solar panel, mission time is unlimited, the company says. The ExoHiker is designed to actually decrease the wearer's oxygen consumption by 15 percent. The company's ExoClimber is designed to assist in the rapid ascent of stairs and steep slopes while carrying loads up to 150 pounds. A one-pound battery enables a 185-meter (600-foot) ascent while carrying the same maximum payload weight.
"Our focus has been to make a practical machine that can be used for the Defense Department's forces," says Homayoon Kazerooni, chief scientist for Berkeley Bionics and a professor of mechanical engineering at U.C. Berkeley's Robotics Laboratory. Kazerooni adds that in the future Berkeley Bionics's technology may also be used to help patients learning to walk again after serious injuries.