Video: Coffee-stuffed balloon is an incredibly effective robot hand

This DARPA-funded robot gripper could revolutionize robotics--and it smells nice, too.

Designing robotic grippers is tough. Mimicking the human hand is a tall order for engineers. Systems based on suction or magnetics, while simpler to design, have limited uses. A DARPA-supported group of researchers from Cornell University, the University of Chicago and iRobot has a totally different idea: squishy balloons, filled with coffee grounds.

The "universal gripper," as the team is calling it, is a marvel of simplicity, and surely has scores of robotics experts slapping their foreheads. Here's how the team describes their gloriously simple new robo-hand:

[With the universal gripper] we demonstrate a completely different approach to a universal gripper. Individual fingers are replaced by a single mass of granular material that, when pressed onto a target object, flows around it and conforms to its shape. Upon application of a vacuum the granular material contracts and hardens quickly to pinch and hold the object without requiring sensory feedback.

You'll notice they've gone to a bit of effort to use improper nouns in their summary. Perhaps that's because the hand itself is built from curious components. The "hand" portion is a typical party balloon stuffed with coffee grounds, and injected with a small amount of air. This balloon is attached to a vacuum, which subtracts and adds air to the grounds depending on the desired state. When air is present, the grounds have a sandlike softness; when air is sucked out, they become rock-hard, keeping their exact shape.

This extreme behavior may sound a bit odd for such a commonplace substance. The effect is called a "jamming transition," and it's actually familiar to anyone who's bought prepackaged ground coffee, which is remarkably hard until air is introduced into the bag. Cornell Professor Hod Lipson explains:

The ground coffee grains are like lots of small gears. When they are not pressed together they can roll over each other and flow. When they are pressed together just a little bit, the teeth interlock, and they become solid.

Coffee is extremely prone to jamming transitions, and party balloons have so far sufficed for experimental purposes, but in real-world applications, both materials could be replaced by something else. (Rice, ground-up rubber and couscous proved less effective as jamming materials, and while sand was well-suited, it was a bit heavy.) In any case, it's the basic concept, not the materials involved, that could have a real effect on robotics.

Speaking of real effects, the project's leaders are optimistic. Via the Cornell Chronicle, Lipson said that the universal gripper "is one of the closest things we've ever done that could be on the market tomorrow." He sees the as a useful tool for everything from bomb-defusing robots to simple manufacturing tasks to prosthetic limbs. (Though the inherent strangeness of replacing a human hand with a squishy bag of pulverized breakfast beans might turn some off.)

Mechanics aside, perhaps the most appealing aspect of the universal gripper is its price. Unlike ultra-complicated hand-like grippers, this gripper can be built at low cost, with readily available materials.

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