Assembling a future robot could be as simple as heating it up. Two new studies demonstrate how 3-D printed robots could fold into shape and assemble themselves after being exposed to heat.

To make a two-dimensional sheet of material assemble itself into a 3-D machine, the researchers used heated sheets of a type of polymer known as polyvinyl chloride, or PVC. These sheets of material were placed between two rigid polyester films that are full of slits.

When heated, the PVC shrinks and the slits eventually shut, pushing against each other and altering the shape of the PVC. This process bends the material into different shapes, based on the pattern of slits and how the heat interacts with the PVC.

As slits of different widths push against each other, the material will fold into 3-D structures, the researchers said.

"You're doing this really complicated global control that moves every edge in the system at the same time," Daniela Rus, a professor of engineering and computer science at the Massachusetts Institute of Technology in Cambridge, Massachusetts, whose group conducted the research, said in a statement. "You want to design those edges in such a way that the result of composing all these motions, which actually interfere with each other, leads to the correct geometric structure."

One of the new studies examines how to create the 2-D pattern of slits that make these foldable robots possible, while the other discusses building electrical robot components such as resistors and capacitors from "self-folding laser-cut materials."

Shuhei Miyashita, a postdoctoral researcher at MIT, specially designed an aluminum-coated polyester sensor that could be attached to the robots once they are fully assembled. The sensor looks like a small accordion, with folds of material that compress and help electrical currents pass through the system.

To enable the robot to move, a motor could be made from a foldable copper-coated polyester coil, the researchers said.

The new studies build upon previous work done by Rus and  another MIT professor, Erik Demaine, on how origami folding techniques could be used to design robots.

The findings were presented at the 2014 IEEE International Conference on Robotics and Automation, which is being held from May 31-June 5 in Hong Kong.

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