In a departure from the engineering behind typical rigid industrial robots, a team of Harvard University researchers have built what’s reportedly the first autonomous, untethered, entirely soft robot. The device, a pneumatic octopus nicknamed the octobot, is based on 3D printing and microfluidics, and potentially could pave the way for a new generation of completely soft, autonomous machines.
Describing their work in the journal Nature, the researchers said soft robotics could revolutionize how humans interact with machines. Previous efforts to build entirely compliant robots have faced roadblocks. Other soft-bodied robots housed rigid power supplies or have been tethered to external electrical or pneumatic systems.
“One long-standing vision for the field of soft robotics has been to create robots that are entirely soft, but the struggle has always been in replacing rigid components like batteries and electronic controls with analogous soft systems and then putting it all together,” said Robert Wood, a professor at Harvard John A. Paulson School of Engineering and Applied Sciences. “This research demonstrates that we can easily manufacture the key components of a simple, entirely soft robot, which lays the foundation for more complex designs.”
The device, which measures about 7 cm across and is shaped like a small octopus, is made of silicone gels of various hardness. Harvard’s octobot is “pneumatic” based, powered by gas under pressure, but not compressed air. Instead, a small amount of 50% hydrogen-peroxide solution in a fuel cell reacts with a platinum catalyst and transforms the liquid into a large amount of gas, which flows into the octobot’s arms and inflates compartments inside the eight separate limbs. Subsequently venting the gas retracts the arms to their original position.
The octobot does not rely on electronic controls. Instead, the researchers used microfluidic logic as a soft controller and a multi-material, embedded 3D printing method to fabricate pneumatic networks within a molded, elastomeric robot body. A hybrid assembly approach let the team use soft lithography, molding and 3D printing to rapidly fabricate a range of materials and functional elements required for autonomous, untethered operation of a soft robot.
A system of check valves and switch valves within the soft controller regulates fluid flow into and through the system. Flow channels only a few-hundred microns wide are patterned into the soft controller. As an electrical analogy, check valves, fuel tanks, oscillator, reaction chambers, actuators and vent orifices are akin to diodes, supply capacitors, electrical oscillator, amplifiers, capacitors and pull-down resistors, respectively.
To begin operation, 0.5 ml of fuel is infused via a syringe pump into each of two fuel reservoirs. The fuel reservoirs expand elastically to a pressure of approximately 50 kPa, forcing fuel into the oscillator. The oscillator includes a system of pinch and check valves that alternately routes fuel into the platinum-laden reaction chambers, where it rapidly decomposes. Downstream check valves prevent the resulting pressurized gas from returning to the soft controller, and it flows to the actuators. Gas pressure deflects the actuators and exhausts to atmosphere through a vent orifice. Upon venting, fuel flow into one reaction chamber stops and flow to the other begins, initiating a similar sequence in the other downstream catalytic chamber and actuator network.
The simplicity of the assembly process paves the way for more complex designs, said Ryan Truby, a graduate student and co-author of the paper. Next, the Harvard team hopes to design a pneumatic octopus that can crawl, swim and interact with its environment. Someday, soft robots might be used for surgical operations or to squeeze tools or cameras into difficult-to-access locations.