“Bubble casting” tech used to create soft actuators for soft robots

Although soft-bodied robots show great promise for tasks such as squeezing through tight spaces, it’s a bit counterproductive if their soft appendages are moved by hard actuators. A new technology addresses that problem, via the use of “fancy balloons.”

First of all, some groups have already developed soft actuators (and even soft batteries), allowing for the construction of robots that are completely soft-bodied. That said, expensive machines like 3D printers or laser cutters are typically required to build them. Seeking a less expensive alternative, scientists at Princeton University have developed a technique known as “bubble casting.”

The process begins with a liquid elastomer being injected into a mold, which is shaped like the desired finished actuator. Air is then injected, displacing some of the liquid to form a bubble running the length of the inside of the mold. As that bubble rises, a thin film of the elastomer is left above it, but most of liquid ends up below.

Once the elastomer cures to a rubbery consistency, the actuator is removed from the mold. When air is subsequently pumped into the cavity formed by the bubble, the actuator naturally curls towards its base, where the elastomer is thicker and thus less stretchy.

And while the base is at the bottom of the actuator during the casting process, the device can of course be turned to any angle once it’s installed in the robot. Additionally, by tweaking variables such as the thickness of the film above the bubble, and the curing time of the elastomer, it’s possible to dictate the manner in which the actuator will move.

So far, the technology has been utilized to create a small elastomer coil that contracts like a muscle when inflated, a star-shaped grasper that can hold a blueberry without damaging it, a fishtail that flaps back and forth, and a set of finger-like appendages that curl up in sequence, one after the other. What’s more, it is believed that the system could be utilized to create actuators ranging from several meters in length down to ones that aren’t much longer than the width of a human hair.

There are some challenges that still need to be overcome, though, such as keeping the devices from popping when they get overinflated.

A paper on the research, which is being led by Asst. Prof. Pierre-Thomas Brun, was recently published in the journal Nature.

Source: Princeton University

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