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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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Robot with threads near a fallen branch

RoMan, the Army Research Laboratory's robotic manipulator, considers the best way to grasp and move a tree branch at the Adelphi Laboratory Center, in Maryland.

Evan Ackerman

“I should probably not be standing this close," I think to myself, as the robot slowly approaches a large tree branch on the floor in front of me. It's not the size of the branch that makes me nervous—it's that the robot is operating autonomously, and that while I know what it's supposed to do, I'm not entirely sure what it will do. If everything works the way the roboticists at the U.S. Army Research Laboratory (ARL) in Adelphi, Md., expect, the robot will identify the branch, grasp it, and drag it out of the way. These folks know what they're doing, but I've spent enough time around robots that I take a small step backwards anyway.

This article is part of our special report on AI, “The Great AI Reckoning.”

The robot, named RoMan, for Robotic Manipulator, is about the size of a large lawn mower, with a tracked base that helps it handle most kinds of terrain. At the front, it has a squat torso equipped with cameras and depth sensors, as well as a pair of arms that were harvested from a prototype disaster-response robot originally developed at NASA's Jet Propulsion Laboratory for a DARPA robotics competition. RoMan's job today is roadway clearing, a multistep task that ARL wants the robot to complete as autonomously as possible. Instead of instructing the robot to grasp specific objects in specific ways and move them to specific places, the operators tell RoMan to "go clear a path." It's then up to the robot to make all the decisions necessary to achieve that objective.

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