Paper Flattens, Folds on Command

Researchers have developed simple actuators for paper that allow it to self-fold or flatten, opening the door for new designs using an old material.

Researchers have taught an old material—paper—new tricks, like how to self-fold and flatten. Specifically, the team from Carnegie Mellon University’s (CMU’s) Human-Computer Interaction Institute has developed a thin layer of conducting thermoplastic. It applies that thermoplastic to common paper with a 3D printer or by painting it on by hand.

Bend and Fold

The plastic acts as a low-cost, reversible actuator that heats and expands when an electrical current is applied. This causes the paper to bend or fold, then return to its predetermined shape when the current is removed, said Lining Yao, assistant professor in the institute and director of CMU’s Morphing Matter Lab.

Yao developed the method with her team. "We are reinventing this really old material," she said in a CMU news release. "Actuation truly turns paper into another medium, one that has both artistic and practical uses." 

The researchers found that it wasn’t very difficult to develop an actuator for the paper. The team—which also included post-doctoral researcher Guanyun Wang and former research intern Tingyu Cheng—used a basic FDM 3D printer, which lays down a continuous filament of melted thermoplastic. For the material itself, they used an off-the-shelf printing filament—a composite of graphene polyactide that can conduct electricity.

self-folding paper
Low-cost actuation technology developed in the Human-Computer Interaction Institute at Carnegie Mellon University turns paper into a medium that can bend, fold, or flatten itself. (Image source: CMU)

To marry the actuator with the paper, researchers printed it on plain copy paper in a thin layer about half a millimeter thick. They then heated the actuator in an oven or with a heat gun, after which they folded the paper into a desired shape and allowed it to cool. This shape becomes the default form for the paper, researchers said.

After the paper assumes its shape, researchers attached electrical leads to the actuator to apply an electrical current that heats it, causing the thermoplastic to expand and straighten the paper. When the current is removed, the paper automatically returns to its original shape.

"Most robots—even those made of paper—require an external motor," said Wang, a fellow at the university. "Ours do not, which creates new opportunities not just for robotics, but for interactive art, entertainment, and home applications." 

Refinement

The researchers have a website on which they published a video demonstrating their work, photographs of various paper shapes, and other information about the project. The team continues to refine their method to experiment with different folding or bending effects on the paper, expanding its range of uses.

Initially, researchers developed a number of basic actuators—some of which were based on origami and kirigami forms—to enable paper to automatically form into various structures, such as balls and cylinders. Designers also could use the actuators to construct more elaborate objects, such as a lamp shade that changes its shape and the amount of light it emits, Yao said.

The team is currently working to refine the actuation method, changing the printing speed or the width of the line of thermoplastic to achieve different folding or bending effects, she said. The researchers also developed methods for printing touch sensors, finger-sliding sensors, and bending-angle detectors that can control the paper actuators.

There remains room for improvement of the technology, Yao said. Currently, actuation is slow, which the team hopes to address by tweaking materials, she stated. The team is eying the use of papers that are more heat conductive and the development of printing filaments that are customized for use in actuators. They also are experimenting with ways that the same actuation used for paper might be used for plastics and fabrics, she noted.

The actuator is on exhibit throughout Europe this month at the Ars Electronica Festival in Linz, Austria, and at the Bozar Centre for the Fine Arts in Brussels. From October through March, it will be shown at Hyundai Motorstudio in Beijing.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco, and New York City. In her free time, she enjoys surfing, traveling, music, yoga, and cooking. She currently resides in a village on the southwest coast of Portugal.

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