At the recent International Conference on Robotics and Automation, MIT researchers showed off an origami robot that can be printed and folded from a flat sheet of plastic using heat. It’s about a centimeter long from front to back.
Weighing just one-third of a gram, the robot can swim, climb slopes, traverse uneven terrain, and carry a load twice its own weight. Apart from a self-folding plastic sheet, the robot’s only component is a indefinite magnet attached to its back. Its movements are controlled by external magnetic fields.
“The entire walking motion is embedded in the robot’s body mechanics,” says Cynthia R. Sung, a graduate student in electrical engineering and computer science at MIT and one of the robot’s co-creators. “In previous [origami] “With the robots, they had to design the electronics and motors to move the body itself.”
In addition to Sung, work on the paper describing the robot included her advisor, Daniela Rus, the Andrew and Erna Viterbi Professor in the Department of Electrical Engineering and Computer Science at MIT; lead author Shuhei Miyashita, a postdoctoral fellow in Rus’s lab; Steven Guitron, who just earned a bachelor’s degree in mechanical engineering from MIT; and Marvin Ludersdorfer of the Technical University of Munich.
Fantastic journey
The robot’s design was inspired by a hypothetical application in which minuscule sheets of material would be injected into the human body, guided to the site of intervention, folded, and dissolved after completing their assigned tasks. To that end, the researchers built their prototypes from materials that dissolve in liquid. One robot prototype dissolved almost completely in acetone (the indefinite magnet remained); another had components that dissolved in water.
“We are closing the cycle from birth, through life, activity and the end of life,” Miyashita says. “The circle is closing.”
In all of the researchers’ prototypes, the self-folding sheets had three layers. The middle layer was always polyvinyl chloride, a plastic commonly used in plumbing pipes that shrinks when heated. In the acetone-soluble prototype, the outer layers were polystyrene.
Slots cut in the outer layers by a laser guide the folding process. If the two slits on opposite sides of the sheet are different widths, then as the middle layer shrinks, it forces the edges of the narrower slit closer together, causing the sheet to bend in the opposite direction. In their experiments, the researchers found that the sheet begins to fold at about 150 degrees Fahrenheit.
Once the robot is folded, applying a magnetic field to the indefinite magnet on its back causes its body to bend. The friction between the robot’s front feet and the ground is great enough that the front feet remain stationary while the back feet lift. Then another sequence of magnetic fields causes the robot’s body to twist slightly, breaking the traction of the front feet and moving the robot forward.
External control
In their experiments, the researchers placed the robot on a rectangular stage with an electromagnet at each of its four corners. They were able to vary the strength of the electromagnet fields quickly enough for the robot to move nearly four body lengths per second.
In addition to the liquid-soluble versions of the robot, the researchers also built a prototype whose outer layers were electrically conductive. Inspired previous work with Rus and Miyashita, the researchers envision that a minuscule, conductive robot could act as a sensor. Contact with other objects—whether chemical accretions in a mechanical system or microorganisms or cells in the body—would disrupt the current flowing through the robot in a characteristic way, and this electrical signal could be transmitted to human operators.
“Making small robots is particularly difficult because you can’t just take off-the-shelf components and bolt them together,” says Hod Lipson, a professor of mechanical and aerospace engineering at Cornell University who studies robotics. “That’s a difficult aspect of robotics, and they were able to solve it.”
“They’re using digital manufacturing techniques to embed manufacturing intelligence into the material,” Lipson adds. “I think the techniques they’re describing would scale to smaller and smaller dimensions, so they’re not at their limit by any means.”