Octo-Bots in the ER


The Stiff-Flop on display at 2013 Robot Safari EU exhibition of biomimetic robots at the Science Museum in London. Image: Stiff-Flop

On first glance, the octopus may seem to be a floppy mess of arms, squishy and gelatinous; a mere rung or two above a jellyfish. But the cephalopod has a few tricks up its eight sleeves that us more rigid life forms are incapable of performing. That squishiness comes with an ability to stiffen in an instant, to make any one of its limbs an extreme nuisance to a clam that thought itself safely tucked inside a craggy hole. The octopus can slink a soft arm through a maze of coral, into an impossibly narrow crevice, then bounce from flaccid to rigid, and snatch the unsuspecting mollusk.

Such well-hidden prey remain inaccessible to us and our robots. Robots, no matter how many joints and servos you throw into them, they can’t do a lot of slithering. Even if they can get to a space that requires a twist and a turn, they’re not likely to be able to do any work there. Yet, that’s just what’s needed for any bot worth its salt in the operating room.

The robotic gripper conforms to the shape of the item it is lifting. Image: John Amend / Cornell.edu

Eight-Legged Inspiration

Allen Jiang, a consultant at Auris Surgical Robotics, turned to the octopus limb for inspiration when dreaming of a better surgical robot. To make a working octo-bot, he turned to a phenomenon called granular jamming. Stuff a balloon with coffee grounds and a bit of air, and it becomes soft and malleable. Suck out the air and it stiffens. “When the air is mixed with the particles, they can slide around and mix with each other,” says Jiang. “When you vacuum out the air, the outside pressure squeezes on the membrane of the balloon, the friction locks the grains in place, and now the whole thing acts like a solid object.” Researchers at Cornell University made a robotic gripper this way in 2010.

Inside the body, however, a jamming robot would have to do a lot more slinking, with a lot more precision, than any sack of grounds would provide. Where the gripping balloon was essentially a single-celled organism, the “Stiff-Flop” has multiple cells running the length of its arm, allowing an operator to bend and twist it wherever needed with a joystick. “If you have a bunch of them in parallel, you can stiffen some of them, and actuate others. You get different bends and curvature so it increases your dexterity,” says Jiang.

A prototype of the Core-Snake, a variable stiffness laparoscopic camera that uses granular jamming to alternate between soft and rigid states. Image: Allen Jiang

Rethinking Granular Jamming

Coffee grounds weren’t the best grains for a medical situation. So Jiang tried plastic spheres and cubes, both smooth and matte. The roughed-up cubes more than doubled the potential for stiffness, but slowed reaction time.

Jiang also tossed out the balloon. Where other granular jamming researchers ignored the material of the exterior membrane because they considered it too thin and inconsequential to even include in their equations, Jiang found it was key. Removing the elasticity of the latex used by other jammers meant retaining the same ability to go soft, but doubling the rigidity once the air was vacuumed out. “If you go to the supermarket and see vacuum-packed rice or beans, or even fish, it can be pretty stiff,” says Jiang. “The material they use is not stretchable—it turns out they know more than we know.”

The third element needed for granular jamming, the fluid, could be improved upon as well. Jiang swapped out the air for water. Now the grains could be jammed into stiffness with a mere pull on the plunger of a syringe. This meant eliminating the pump that had been needed to remove air, untethering the robot, and using much less power.

Flexible Benefits

The syringe also meant cutting down the price. At the prototype stage, the entire setup cost less than $20, including the camera at the business end.

The Stiff-Flop may have applications beyond the surgery room. Wherever there is a tough spot to get to where something needs to be done, granular jamming has a place. Welders could put it to use, as could anyone working in a complex environment such as an oil rig. There is also great potential for haptic devices. Gamers, for instance, could feel like they were actually holding a virtual object.

Perhaps we’ll offer octopi a little competition when it comes to getting at those mollusks.

Michael Abrams is an independent writer.

If you go to the supermarket and see vacuum-packed rice or beans, or even fish, it can be pretty stiff. The material they use is not stretchable—it turns out they know more than we know.

Allen Jiang,
consultant, Auris Surgical Robotics


September 2014

by Michael Abrams, ASME.org