Oct 15, 2015 | By Alec

Anyone who has ever used filaments such as NinjaFlex will have realized that flexible materials really open up an entirely different making dimension. That realization has also arrived in the world of robotics engineering, but few engineers have so far achieved promising results that can truly open up new research pathways. A new study by a team of Cornell University could, however, lead the way towards new robotic innovations. In a new paper, the team supervised by Rob Shepherd, reveal that they have successfully 3D printed a tentacle-like actuator that mimics the muscle properties of octopus tentacles. Key is a custom made stereolithography 3D printer that works with commercially available Elastomeric Precursor resin.

This new innovation is groundbreaking, because a proper combination of flexible and functional didn’t yet exist; degrees of freedom generally meant sacrificing functionality. But as they explain in a paper published in in the journal Bioinspiration & Biomimetics, this new 3D printing method opens up a range of new options. The study was led by PhD student Bryan Peel and supervised by assistant professor of mechanical and aerospace engineering Rob Shepherd. The study itself was funded by Air Force Office of Scientific Research, 3M and the National Science Foundation.

As professor Shepherd explained, their test suggests that 3D printing commercially available materials is definitely a viable option for robotics engineers. ‘Based on the demonstration reported here and the possibilities for improved materials, this nascent printing process for soft actuators is a promising route to sophisticated, biomimetic systems,’ he says. Unfortunately, current fabrication techniques limit the ability to create complex structures, in part because of the materials involved.

The goal, in essence, is embed the natural functions of biological organisms into robotic creations. And few animals are more capable of interacting with complex and uneven environments than octopi. ‘By mimicking the properties of biological organisms, deformable materials such as ﬂuids, gels, and elastomers change the way machines interact with their environment. Inspired by nature, previously reported soft robots imitate an octopus squeezing through tiny crevices or an earth-worm navigating uneven terrain. Furthermore, these materials platforms maintains the beneﬁts of low-cost, ease of fabrication, and biocompatibility common to many classes of polymers,’ the engineers write. ‘In theory, the ability of elastomeric materials to deform continuously permits such soft robotic systems to move and bend anywhere along their surface.’

The octopi tentacle does do this with the help of specifically arranged muscles in the three mutually perpendicular directions. 'The only likely method for achieving this level of complexity is the bottom up assembly of actuators using 3D printing; by enabling this technology to print elastomeric material, the design space for soft robots will be greatly increased,’ they say. And to recreate that, the engineers have built a stereolithography 3D printer for less than $1500, which used bottom-up Digital Mask Projection 3D printing (DMP-SL) with a digital mirror device for polymerization. This machine worked very well, and was controlled using Envision Labs’ Creation Workshop and 3D printed a commercially available Elastomeric Precursor (EP; Spot-E resin, Spot-A Materials, Inc.).

This worked very well indeed, they say. ‘We have developed the antagonistic actuator pairs that mimic the function (but not mechanism) of musculature hydrostats such as octopus tentacles. These pneumatically driven actuators are have comparable actuation times to living muscle,’ they write in their paper. The Cornell team suggests that these same principles can be applied to 3D printing complete and complex muscle structures as a single monolithic structure with a large variety of potential applications. ‘Combinations of these pairs can be used to create actuation systems of arbitrary complexity that can be 3D printed in a single process as a monolithic structure. Due the high level of design sophistication available and the material compliance comparable to some biological tissue, the DMP-SL system is uniquely suitable for developing soft machines that mimic and interact with biological systems,’ they say.

Posted in 3D Printing Applications

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