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Spiral Zipper Creates Robot Arm Out of a Strip of Plastic

A plastic band with zipper teeth can interlock into a cylindrical robotic arm

2 min read
robot arm

As useful as robot arms are, they tend to be heavy, bulky things that need a bunch of support and structure to get them to work properly. If you need precision and speed, this may be unavoidable, but if all you’re looking for is long reach, a high-strength to weight ratio, and very low cost (which, admittedly, are a lot of things to be looking for), another option was presented at ICRA today by researchers from the University of Pennsylvania: an arm made out of a strip of plastic that zips together with itself, creating an extendable cylinder that can be paired with winches and cables and used for manipulation.

This concept is similar in principle to some commercially available systems like the Zippermast and Spiralift, but both of those designs are heavier and significantly more complicated. The spiral zipper uses a single band that’s made of very lightweight plastic, with a relatively simple meshing mechanism that meshes the teeth on the bottom edge of one wrap with the teeth on the top of the wrap below to create a cylinder that has a very high strength to weight ratio, with exceptionally good compressive performance. And changing the length of the arm is as simple as zipping or unzipping the band: it’s completely reversible, and you can stow the arm almost entirely in a very small volume consisting of the plastic band spooled around the zipping mechanism.

The spiral zipper only creates the structure of the arm: there’s no integrated actuation, besides the extension and retraction that you get from zipping or unzipping the arm on demand. The researchers envision mounting the base of the arm on a gimbal, with a 3-DoF wrist on the end of it, to create a 6-DoF system. Since the arm isn’t particularly stiff (especially when moving), it doesn’t make sense to actuate it with motors from the base. Instead, winches mounted on the base with tethers connected to the end of the arm could be used to control its motion, which makes sure that the predominant force on the tube is compression (what the structure is good at).

In terms of applications, there’s a lot of potential for a system with such a high strength to weight ratio that can pack down into a very small size. For example, the U.S. Army is interested in mounting the arm on an octorotor being developed at the Army Research Laboratory, and the researchers are also planning on trying the arm out on indoor mobile robots as aids for the elderly. The arm could also “enable the manipulation of large objects such as furniture,” and at ICRA we saw some pictures of a prototype climbing robot that can hoist itself up by varying its arm length. It also seems like this design would lend itself to space applications, where efficiency in weight and volume are such a priority. It’s a very clever idea, and we’re looking forward to seeing what UPenn does with it.

“Design of a Spherical Robot Arm With the Spiral Zipper Prismatic Joint,” by Foster Collins and Mark Yim from the GRASP Lab at the University of Pennsylvania, was presented this week at ICRA 2016 in Stockholm, Sweden.

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The Bionic-Hand Arms Race

The prosthetics industry is too focused on high-tech limbs that are complicated, costly, and often impractical

12 min read
A photograph of a young woman with brown eyes and neck length hair dyed rose gold sits at a white table. In one hand she holds a carbon fiber robotic arm and hand. Her other arm ends near her elbow. Her short sleeve shirt has a pattern on it of illustrated hands.

The author, Britt Young, holding her Ottobock bebionic bionic arm.

Gabriela Hasbun. Makeup: Maria Nguyen for MAC cosmetics; Hair: Joan Laqui for Living Proof

In Jules Verne’s 1865 novel From the Earth to the Moon, members of the fictitious Baltimore Gun Club, all disabled Civil War veterans, restlessly search for a new enemy to conquer. They had spent the war innovating new, deadlier weaponry. By the war’s end, with “not quite one arm between four persons, and exactly two legs between six,” these self-taught amputee-weaponsmiths decide to repurpose their skills toward a new projectile: a rocket ship.

The story of the Baltimore Gun Club propelling themselves to the moon is about the extraordinary masculine power of the veteran, who doesn’t simply “overcome” his disability; he derives power and ambition from it. Their “crutches, wooden legs, artificial arms, steel hooks, caoutchouc [rubber] jaws, silver craniums [and] platinum noses” don’t play leading roles in their personalities—they are merely tools on their bodies. These piecemeal men are unlikely crusaders of invention with an even more unlikely mission. And yet who better to design the next great leap in technology than men remade by technology themselves?

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