Mar 24, 2017 | By Benedict

MIT researchers are developing 3D printed “skin” for robots that changes color upon receiving physical stimuli. The technology was inspired by the golden tortoise beetle, or “goldbug,” an insect whose golden exterior turns red when prodded.

While we don’t fully know what robots of the future will look like, nor what roles they will play, many experts agree that complex systems of embedded sensors will be an important feature of such machines. Some sensor-driven tech, like the touch-sensitive surfaces on smartphones, is already ubiquitous, but more complex sensor arrays could someday be used to allow robots to fully interact with their environment. How that technology will be implemented is still very much up in the air, but a group of researchers at MIT believes that 3D printing could have a role to play.

In a research paper that has been published in Advanced Materials Technologies, these MIT researchers explain how they have developed a 3D printable, color-changing “skin” for robots that demonstrates the feasibility of flexible, printable electronics that combine sensors and processing circuitry. The research was led by Subramanian Sundaram, an MIT graduate student in electrical engineering and computer science (EECS), and shows promise for a future where 3D printing and electronics go hand in hand.

The new color-changing skin developed by the MIT engineers consists of T-shaped devices with a wide base made of rigid plastic and elongated crossbar made from an elastic plastic. Each device consists of two printed transistors and a “pixel,” which is actually a circle of semiconducting polymer whose color changes when the crossbars stretch, modifying the electrical resistance of a silver strip running the length of the crossbar. The pixel and transistors are made from the same material, though the color change is more apparent in the pixel because the transistors amplify the electrical signal from the crossbar.

Despite the technological bent of the research, the team was actually heavily inspired by nature when developing its unusual 3D printed robot skin. An organic (and currently superior) version the color-changing technology can be seen in the golden tortoise beetle, or “goldbug,” an insect whose golden exterior turns reddish orange if poked or prodded. The MIT researchers have attempted to turn this organic characteristic into a mechanical system that could be used in robots. And with 3D printing helping them out, they have found some success.

“In nature, networks of sensors and interconnects are called sensorimotor pathways,” Sundaram explains. “We were trying to see whether we could replicate sensorimotor pathways inside a 3D printed object. So we considered the simplest organism we could find.”

According to the researchers, it was important to demonstrate working transistors in the technology, since large, dense sensor arrays require at least some capacity for onboard signal processing. “You wouldn’t want to connect all the sensors to your main computer, because then you would have tons of data coming in,” Sundaram says. “You want to be able to make clever connections and to select just the relevant signals.”

The transistors in the 3D printed color-changing device are, however, quite unusual. That’s because they separate their gate and semiconductor not with a mechanical element, but with a layer of water containing potassium salt. When this gate is charged, potassium ions are driven into the semiconductor, changing its conductivity. This saltwater layer means the device can be powered by a an ordinary 1.5-volt battery, though it also makes the device less durable, with a shelf life of around two months.

(Images: MIT / Subramanian Sundaram)

The color-changing device was 3D printed using the MultiFab 3D printer, a custom-made machine built by an engineering group at MIT. That group is led by Wojciech Matusik, an associate professor of EECS and Sundaram’s advisor. Sundaram himself added a copper-and-ceramic heater to the 3D printer, which was necessary to deposit the semiconducting plastic, adding to the 3D printer’s two existing print heads, one for extruding hot materials and one for cool.

The 3D printed seminconducting plastic ends up just 200 nanometers thick after being suspended in a fluid which is sprayed onto the device surface and then evaporated.

While color-changing 3D printed skin may not seem like the most useful feature you could assign to a robot, the technology does show a great deal of promise for optoelectronic systems. “By fabricating the substrate on the fly, the approach is particularly useful for improvised manufacturing environments where dedicated substrate materials may not be available,” commented Hagen Klauk, leader of the Organic Electronic Research Group at the Max Planck Institute for Solid State Research, in Stuttgart, Germany.

 

 

Posted in 3D Printing Application

 

 

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Antoni wrote at 3/24/2017 2:24:56 PM:

I'm a regular reader of this site, having to say that technology is going faster. Thank you very much! Antoni



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