Researchers 3D-Print Robotic Hand With Working Muscles

Researchers have 3D-printed a robotic hand with working tendons and muscles, a development the team says could lead to more lifelike robots.

To create the hand, the team of researchers from ETH Zurich and MIT spinoff Inkbit developed a new 3D-printing method that creates complex structures out of multiple materials. 

Specifically, the new method uses a variety of slow-curing polymers to create structures, offering more flexible, durable and robust properties than fast-curing polymers typically can. The method also allows users to combine soft, elastic and rigid materials, printing all of these materials together to create a single structure. 

The team demonstrated its technology by printing a robotic hand with bones, ligaments and tendons all made of different polymers, in one go.

Inkbit developed the printing technology, while the ETH Zurich researchers developed several robotic applications and helped optimize the printing technology for use with slow-curing polymers. 

"We wouldn't have been able to make this hand with the fast-curing polyacrylates we've been using in 3D-printing so far," said Thomas Buchner, first author of the study. "We're now using slow-curing thiolene polymers. These have very good elastic properties and return to their original state much faster after bending than polyacrylates." 

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Elastic materials are helpful for robotic limbs as they can stand in for the ligaments that enable human’s ease of motion, creating more flexible and mobile designs. 

The team said the development could lead to significant advancements in creating complex, lifelike robots out of delicate, 3D-printed components.

"Robots made of soft materials, such as the hand we developed, have advantages over conventional robots made of metal,” said Robert Katzschmann, ETH Zurich robotics professor. “Because they're soft, there is less risk of injury when they work with humans and they are better suited to handling fragile goods.”

3D-printers typically create objects layer by layer, using fast-curing polymers that are immediately cured with a UV lamp, before a scraping device is used to smooth out any irregularities. 

The scraping device doesn’t work with slow-curing polymers as the material would jam the device. Instead, the team developed a laser scanner that identifies any irregularities and adjusts the next printed layer to compensate for any bumps in the material. 

"A feedback mechanism compensates for these irregularities when printing the next layer by calculating any necessary adjustments to the amount of material to be printed in real time and with pinpoint accuracy," said Wojciech Matusik, co-author of the study. “This means that instead of smoothing out uneven layers, the new technology simply takes the unevenness into account when printing the next layer.”

The ETH Zurich team said it will now explore other potential applications for its tech and further develop the complexity of the structures printed. Inkbit said it is planning to use the technology to offer a 3D-printing service to its customers and to sell the new printers.