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Who Says Hands Need Five Fingers?

Human fingers are pretty cool: They grip, they pinch, they squeeze. They can crush bugs and hold delicate crystal. They're amazing! Because of all the wonderful things fingers can do, it makes sense that we try to replicate them on our human analogues. But recreating robotic fingers is difficult and can get rather costly. To overcome the challenges that come with creating a robotic hand, one group of scientists ditched human digits altogether and developed something far simpler but just as effective.

Creating robotic replicas of human hands is troublesome. It's difficult to get the tension right to grip an object without crushing it. Computers can be strained when controlling multiple joints with umpteen degrees of motion. Instead of trying to replicate our dexterous little fingers, scientists at the University of Chicago and Cornell University opted for another approach, creating a robotic gripper.

The team developed what they called a "universal jamming gripper" out of a latex party balloon filled with ground coffee and a vacuum pump. To operate the robotic appendage, the slack balloon is placed on an object which it surrounds with the loose coffee grinds. Then, the vacuum pump is turned on, sucking out the air inside the balloon. The fluid-like coffee grinds 'jam' into a rigid solid with a fixed grip around the object. Once the pump is turned off, the grains loosen up again and the object is released.

Several types of granular materials were tried in early grippers including sand, couscous, rice and ground up tires. Sand worked the best, but was ruled out for being too heavy. Coffee grinds which jam nearly as well as sand but weigh far less were ultimately chosen.

The gripper can pick up things that have stumped robotic hands in the past like coins and raw eggs. It does have some limitations, struggling with porous objects like cotton balls and failing to lift more than half its own weight.
Even so, the four-inch diameter gripper that was created in the lab could pick up an eight-pound jug of water and the scientists speculate that a gripper with a four-foot diameter could lift a car.

Though it doesn't much resemble a human hand, the gripper could be developed into a new type of prosthetic limb. Since it has only two modes - on and off - it would be easy for users to operate. It could also be used to clean up debris after a catastrophic event, such as the earthquake in Haiti.

To learn more about this cool little gripper, listen to the podcast from PhysicsCentral below:


  1. Very cool! The most elegant solution is often the simplest!


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