New 3D Printing Tech Could Bring Sensing to Robotics

Harvard researchers created a 3D printing ink that could bring the feeling of "touch" to soft robotics.

Soft robotics have started taking over the robotics field. These unique robots specialize in squeezing into tight spaces or having flexible structures often inspired by nature. A team of engineers from Harvard University has built upon those 'natural' soft robots by adding sensory elements to them. 

The Harvard group's additions would be one of the first ways robots could respond and sense the world around them. The researchers published their work in the journal Advanced Materials, and the paper details how the sensors accurately detect movement, pressure, touch, and temperature. 

"Our research represents a foundational advance in soft robotics," said Ryan Truby, first author of the paper and recent Ph.D. graduate at SEAS. "Our manufacturing platform enables complex sensing motifs to be easily integrated into soft robotic systems."

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While there have been plenty of advancements in soft robotics' scale and flexibility, sensors have largely remained a struggle for robotics engineers. This is largely because sensors themselves are often rigid. So, despite the flexibility and ease of motion for a soft robot, structured sensors would still inhibit the robot. 

To overcome this headache, the researchers made an organic ionic liquid-based conductive ink rather than a traditional hardware sensor. This ink could then be put into any 3D printer and printed within the soft bodies of the robots. 

"To date, most integrated sensor/actuator systems used in soft robotics have been quite rudimentary," said Michael Wehner, a former postdoctoral fellow at SEAS and co-author of the paper. "By directly printing ionic liquid sensors within these soft systems, we open new avenues to device design and fabrication that will ultimately allow true closed-loop control of soft robots."

And to test out their creations, the team turned to the bioengineering lab of professor Jennifer Lewis. Lewis serves as Professor of Biologically Inspired Engineering at SEAS and Core Faculty Member of the Wyss Institute. She said the 3D printing technique called "embedded 3D printing" could perfectly pair up the 'sensing' ink with the soft body's structures. 

"This work represents the latest example of the enabling capabilities afforded by embedded 3D printing -- a technique pioneered by our lab," said Lewis.

The team was floored with the results. They printed a robotic gripper with three actuators to test out the responsiveness of the ink. The researchers put in multiple contact sensors to give the "hand" better ideas of touch. 

"The function and design flexibility of this method are unparalleled," said Truby. "This new ink combined with our embedded 3D printing process allows us to combine both soft sensing and actuation in one integrated soft robotic system."

The researchers want to expand studying the applications for this ink and potentially apply it to other elements of 3D printed robotics. 

"Soft robotics is typically limited by conventional molding techniques that constrain geometry choices, or, in the case of commercial 3D printing, material selection that hampers design choices," said Robert Wood, the Charles River Professor of Engineering and Applied Sciences at SEAS, Core Faculty Member of the Wyss Institute, and co-author of the paper. " The techniques developed in the Lewis Lab have the opportunity to revolutionize how robots are created -- moving away from sequential processes and creating complex and monolithic robots with embedded sensors and actuators."