Fingerless robot 'hand' grips almost anything

A "hand" similar to a bag of coffee grounds could make it easier for robots to pick up objects ranging from fragile raw eggs to big cars.

In contrast, a new type of hand invented by researchers in the U.S. is "a dumb material that acts very smart," said Heinrich Jaeger, a University of Chicago physicist who helped develop it. An interview with Jaeger is scheduled for broadcast on CBC Radio's Quirks & Quarks on Saturday.

Without any sophisticated controls, the gripper can pick up small, soft objects such as earplugs, larger, fragile objects, such as raw eggs or light bulbs, or big, hard objects, such as shock absorbers. It can even lift and pour a glass of water or write with a pen.

Researchers from the University of Chicago, Cornell University and Defense Advanced Research Projects Agency worked on the project.

The gripping device actually looks nothing like a hand. It is "essentially an elastic bag" filled with a material such as coffee grounds or sand, Jaeger said.

The material starts off soft and shapeable but becomes hard and solid when the particles are packed more closely together. Jaeger likened it to a vacuum-packed bag of espresso coffee picked up at the store.

"You notice that often these packages are hard as a brick," he said. "Now you take that thing home, you snip off that corner and immediately, the rigidness relaxes … in fact, the coffee will just flow out."

The coffee has just undergone what's called a "jamming phase transition" from a state where the particles are so close together that they can't move to one where they flow.

Jaeger and his colleagues carefully studied how that happens and decided to make a gripper that takes advantage of it.

They published their results in the Nov. 2 issue of Proceedings of the National Academy of Sciences. Several of the authors, along with iRobot Corporation, have filed patent applications on related technology.

The "bag of coffee" presses gently against an object while it is soft, flowing around the object to form a sort of mould. Then a little bit of air is sucked out of the bag, hardening the bag around the object. There are three ways in which it gets a grip:

• Because the bag is moulded around the object, there are many contact points where friction will hold them together.
• If there is a good seal between the gripper and the object, the gripper will behave like a suction cup.
• If the object has a large opening, like the handle of a cup, the gripper will interlock with it. "It can basically pick things up the way you would … if you stuck finger straight through the handle of a cup and lifted it up," Jaeger said.

Jaeger said the researchers don't yet know what the limits of the gripper are but based on their results, they can make some estimates.

"If you could make a gripper, say, three feet [one metre] in diameter, you could pick up a car with it."