Novel 3D Printing Method Embeds Sensing Capabilities within Robotic Actuators

The development of a new conductive ionic ink brings the field of robotics one step closer to building a machine that can fully interact with its environment. Integrating the ink into the body of a soft robot using a recently developed 3D-printing technique results in the ability to sense motion, pressure, touch and temperature with a degree of accuracy comparable to human skin.

Multimedia embedded 3D printing, developed in Jennifer Lewis’s lab at the Harvard John A. Paulson School of Engineering and Applied Sciences, was used to integrate the ionic conductive ink with the body of the soft robot. (Image courtesy of SEAS.)

Embedded 3D printing allows for the insertion of multiple materials and features into the elastomer matrices of a soft robot’s body. It was used to embed the conductive ink at different depths within the robot so that, as with human tactile sensation, triggering sensors closer to the surface sent a signal that indicated a light touch, while triggering both surface and deep sensors sent feedback that the robot could classify as deep pressure. This graded response increases the types of stimuli to which a robot can respond and range of intensity it can sense.

The fine and deep contact sensors embedded in the gripping apparatus give soft robots the ability to form a graded response to tactile stimulus. (Image courtesy of Harvard SEAS.)

Up until now, the potential of soft robots to respond to their environment has been hampered by the flexible structure that makes them unique. This is partly due to the nature of most sensing equipment: rigid and difficult to integrate with a soft robot body. Imagine sticking a metal pressure gauge inside a rubber glove. As soon as the glove bends, that pressure gauge will measure the strain it’s under as the finger of the glove contorts, not the force with which the glove is gripping a ball. Fill the glove with water instead, and the water moves with the glove as its fingers bend around the ball. The new ionic conductive ink, developed by researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and Wyss Institute for Biologically Inspired Engineering, acts as a flexible network of sensors that truly permits the robot to respond to a tactile stimulus.

Gripper square holding a textured ball. (Image courtesy of Ryan L. Truby and Harvard University.)

The implications for collaborative robots are staggering. The three-pronged gripping device tested by SEAS could sense a ball that a researcher held against its prongs, then grasp it lightly and in such a way that the prongs molded themselves to the surface of the ball. Human hands are currently the best technology for picking produce from trees and bushes. The potential for a robot to grasp delicate objects with just the right amount of pressure may place the future of fruit harvesting in the gripping apparatus of machines.

For more on soft robots, check out these super-strong artificial muscles.