MIT researchers develop two-legged robot with human reflexes

MIT researchers have designed a human-machine interface that allows an exoskeleton-wearing human operator to control the movements and balance of a bipedal robot.

The technology could allow robots to be deployed to a disaster site, where the robot would explore the area, guided by a human operator from a remote location.

"We'd eventually have someone wearing a full-body suit and goggles, so he can feel and see everything the robot does, and vice versa," said PhD student Joao Ramos of Massachusetts Institute of Technology's Department of Mechanical Engineering.

"We plan to have the robot walk as a quadruped, then stand up on two feet to do difficult manipulation tasks such as open a door or clear an obstacle," Ramos said.

To give the human operator a sense of the robot's balance, the team first looked for a way to measure the robot's centre of pressure, or weight distribution, which indicates its balance and stability.

The researchers worked with HERMES, a 100-pound biped robot designed by the team, along with the interface, for disaster response. They outfitted the robot's feet with load sensors that measure the force exerted by each foot on the ground.

Depending on the forces measured, the researchers calculated the robot's centre of pressure, or where it was shifting its weight.

They then mapped out a polygonal area, the edges of which represent each of the robot's feet. They determined that if the robot's centre of pressure strayed toward the edges of this support polygon, the robot was in danger of falling.

The researchers then built the balance-feedback interface: a large polygonal platform equipped with motors, and an exoskeleton of metal bars and wires that attaches to a person's waist - essentially, the human body's centre of mass.

With computer software, the researchers translated the robot's centre of pressure to the platform's motors, which apply comparable force to the exoskeleton, pushing a person back and forth as the robot shifts its weight.

"The interface works by pushing harder on the operator as the robot's centre of pressure approaches the edge of the support polygon," PhD student Albert Wang said.

"If the robot is leaning too far forward, the interface will push the operator in the opposite direction, to convey that the robot is in danger of falling," Wang said.

In experiments to test the interface, Wang repeatedly struck the robot's torso with a hammer. Ramos, standing on the platform, was unaware of when the hammer would strike.

As Wang struck the robot, the platform exerted a similar jolt on Ramos, who reflexively shifted his weight to regain his balance, causing the robot to also catch itself.

The team also tested whether the robot kept its balance while punching through drywall. Ramos, in the exoskeleton, mimed the action, and the robot simultaneously carried it out.

The platform pushed forward on Ramos as the robot made contact with the wall. In response, Ramos rocked back on his heels, causing the robot to do the same.

-PTI