Researchers have created a new family of grippers inspired by the gecko’s ridiculously adhesive toes. These pads could be used to improve object handling on the production line or allow robots to better interact with the world.

The gripper holding a flask of orange juice.
Image credits Sukho Song.

It’s easy to take gripping for granted, but when you really think about it (or have a robot to compare yourself with) it’s an amazing and complex skill. Our brains and bodies make it look easy — after all, even a small child knows how to handle all kinds of objects. But the number of minute processes that go on in the background, even for the simplest of gripping motions, is staggering.

Handle with care

Without even thinking about it, you know much force to apply to grip an object but not break it, how to calibrate your emotions so you’ll bring the cup to your lips — not throw it to at the ceiling. But if you want to make a robot do the same thing, you’ll have to go through a lot of programming and trial and error.

Looking for a simpler way to help our digital friends get a grip on life, researchers have done a bit of biomimicry and copied the working principles of the gecko‘s toes. The resulting pads should help address many of the problems machines today have in manipulating objects and should allow them to navigate a much wider range of shapes and materials — such as irregularly shaped walls or ceilings and slippery metal surfaces.

Gecko’s toes can stick to anything using Van der Waals forces. Long story short, because some atoms and molecules tend to be polarized (having a positive-charged side and an opposing negative-charged side) they also tend to push or pull at each other like really tiny magnets. But if there’s enough of them, the forces can stack up to an impressive effect. The gecko’s toes are covered with tiny hair-like strands which increase the surface contact between them and the surface, maximizing the Van der Waals effect and allowing the lizard to walk upside down if it so desires.

Rub my belly.
Image credits Wikimedia user Tolbunt5.

Previous research on this subject has resulted in synthetic microfiber arrays which replicate the gecko’s sticky toes, but imperfectly. The hook is that properly sticking these materials to a surface takes pressure meaning they have to be mounted on a rigid backing. Doing this, however, prevents the arrays from adhering to curved surfaces.

The FAM family

The new paper details how this issue can be solved by placing the microfibers on a thin, stretchy membrane to create a family of materials the researchers call fibrillar adhesives on a membrane (FAM), and developing a new kind of backing for the membranes.

For their gripper, the team used a FAM to cover one end of a shallow rubber funnel some 18 millimeters across. The other (narrow) end of the funnel was connected to an air pump, and after the FAM came in contact with the surface-to-be-held, all the air was sucked out of the funnel to flatten it onto any shape.

Testing revealed that a gripper with the contact area of only 2.5 square centimeters (roughly the size of a dime) could lift more than 300 grams (slightly less than your average can of soda). It could grip a coffee cup from the outside (convex shape), the inside (concave shape) or the handle (complex shape). It also has a light touch — the gripped could lift a cherry tomato without damaging it, and a plastic bag without ripping it. Inflating the gripper is all that’s needed to release the objects.

The technology could be used in manufacturing to shuttle delicate or complex-shaped components around, or in medicine to grip organs without damaging them. Alternatively, they would give robots enough grip to climb onto planes, ships, or reactors to perform maintenance and repairs.

But before we start seeing them used on a wide scale, researchers have to ensure that the grippers are durable enough to withstand hundreds of thousands of usage cycles, see how they scale up to grip heavier loads and make them economically viable in comparison to simple clamps or suction cups.

The team says that scaling the grippers up to a few tens of centimeters so they can lift heavy objects — but they’re still testing on durability.

The full paper “Controllable load sharing for soft adhesive interfaces on three-dimensional surfaces” has been published in the journal PNAS.