“The first applications of the gecko adhesives had to do with climbing robotsclimbing people or grasping very large, very smooth objects in space. But we’ve always had it in our minds to use them for more down-to-earth applications,” said Cutkosky. “The problem is that it turns out that gecko adhesives are actually very fussy.”

The fuss is that the gecko adhesives must connect with a surface in a particular way in order to activate the Van der Waals force. This is easy enough to control when they are applied smoothly onto a flat surface, but much more difficult when a grasp relies on multiple gecko adhesive patches contacting an object at various angles, such as with farmHand.

Pinching and buckling

Below the adhesives, farmHand’s finger pads help address this challenge. They are made of a collapsible rib structure that buckles with little force. No matter the location or angle of contact, the ribs consistently buckle so as to ensure equal forces on the adhesive pads and prevent any single one from slipping prematurely.

“If you move these ribs, the buckling results in a similar force no matter where you start,” said Brouwer. “It’s a simple, physical behavior that could be deployed even in spaces outside of robotics, perhaps as shoe tread or all-terrain tires.”

The hand’s tendons are crucial as well because they enable a hyperextended pinch. While many robotic hands and clamps will pinch objects in a “C” shape, like picking something up with only the tip of your fingers, farmHand pinches with the end of its fingers pressed pad to pad. This gives the adhesives more surface area to work with.

Getting the design just right was especially hard because existing computer simulations have difficulty predicting real-world performance with soft objects – another factor in the heirloom tomato problem. But the researchers benefitted immensely from being able to 3D print and test many of the hard and soft plastic components in relatively quick cycles. They go as far as to suggest that their success may not have been possible – or at least much slower – only five years ago.

Further improvements to farmHand could come in the form of feedback features that would help users understand how it is gripping and how it could grip better while the hand is in use. The researchers are also considering commercial applications for their work.

Cutkosky is also a member of Stanford Bio-X and the Wu Tsai Neurosciences Institute. This research was funded by the Toyota Research Institute (TRI) and a Stanford Graduate Fellowship.

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