Fin Ray effect

Push the side of a fish’s fin and it does something odd. It leans into your finger rather than folding away from it. That behaviour is called the Fin Ray effect.

Copy the shape in flexible plastic and you get a robot finger that hugs whatever it touches. A team writing in the journal Micromachines 3D-printed a three-finger gripper on this principle, in one piece, weighing 68 grams. One pull on a wire bends all three fingers at once.

The pay-off is that the finger adapts to the object’s shape without anyone programming the shape in advance. It wrapped raw eggs, tomatoes, dates and longans in the researchers’ tests. The cost is force: a bending plastic wedge will never hold a heavy steel part the way a metal jaw does.