Polypropylene robots utilize humidity gradient to generate signals

Autonomously reconfiguring origami units can be connected to form dynamic Boolean logic gates. For example, the state of the gate reconfiguration of an input (right) can change the shape of the output (bottom). Credit: PNAS

A team of researchers at the U.S. Air Force Research Laboratory, Wright-Patterson Air Force Base, has developed a type of soft robot that can generate signals without using electricity. In their paper published in Proceedings of the National Academy of Sciences, the researchers describe their study of origami objects and their possible use as signaling devices and possibly as logic gates.

Origami is, of course, the art of folding paper into interesting objects. In this new effort, the researchers looked to the ancient art form as a possible building block for a soft robot. Instead of using paper, the team used sheets of polypropylene—it can absorb water from atmospheric humidity without losing its main form. It does lose some of its stiffness, however, when put into a humid environment. The researchers exploited that phenomenon to use such sheets as mechanical actuators.

They found that if they bent the sheets in certain places, the sheet would flatten when exposed to humid conditions. Conversely, the sheets would rise once again when exposed to drier air. This ability to move between states, the researchers noted, allowed the sheets to serve as a trigger for actions by other types of devices or machines. It also allowed for the generation of signals using only environmental conditions—based on the way the polypropylene behaved over a humidity gradient. And under the right conditions, the sheets could exist in two states, flat or upright, suggesting their use as logic gates.

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Image courtesy of techxplore.com