Robots Gone Soft

In Yigit Menguc’s lab at Oregon State, robots wave and slither


April 17, 2018

By Leto Sapunar

After seeing the creations in Yigit Mengüç’s robotics lab at Oregon State University, you’d be forgiven for thinking you had wandered into a sci-fi film. Tentacle arms wave, synthetic snakes wiggle and a hanging underwater machine, at first glance, resembles a living octopus. These aren’t sights most people expect when they think of robotics. However, they are typical for researchers in mLab Robotics, the Oregon State soft robotics laboratory. Here, on the cutting edge — although there isn’t a solid edge to be found on most of these creations — the group is finding revolutionary new ways to fabricate and design robots that look and feel more like flesh than concrete.

A robotic snake slithers around obstacles. (Courtesy of mLab Robotics, Oregon State University)

Often inspired by biomimicry — the design of practical systems modeled on living organisms — soft robotic researchers look for ways to make robots safer, cheaper and more versatile than ever before. Where a conventional rigid robot arm is difficult to program, complex and expensive to fabricate, a soft robotic arm has the potential to perform the same tasks with none of those limitations. This kind of design, which is particularly useful for delicate tasks like grasping coral samples on the sea floor or handing something to an elderly person, is just one of many possible applications for soft robotic technologies.

Soft robots are made from silicone, similar to the kind used in soft phone cases or ice cube trays and sometimes infused with liquid metal gallium wires. Researchers can control the motion of these soft robotic limbs by pressurizing internal pneumatic or hydraulic channels. A tentacle with four pneumatic chambers within can flex in any direction depending on which hollow chamber is inflated with air. This principle also works to make soft robotic snakes, which can locomote in a variety of different snake “gaits” depending on how its air chambers are pressurized and de-pressurized.

Researchers made this multi-armed machine with a 3D printer. (Photo: mLab Robotics, Oregon State University)

Most current robots are designed to encounter specific environments — a wheeled robot for flat surfaces or a propeller driven underwater craft. These robots can function spectacularly in the specific circumstances they were designed for, but they often lack the versatility to do much else. Soft robots, in their elastic and dexterous forms, could offer major improvements. For instance, many living snakes can swim as well as traverse flat, rocky or sandy terrain. A soft robot made to mimic that motion, like the kind Callie Branyan, a Ph.D. candidate in the lab, is working on, can already move across flat surfaces as well as through granular media like millet seeds, sand and river rocks. It can also slither through a pipe and escape from being buried under millet seeds. Branyan is tweaking the design proportions as well, in an attempt to build thinner, faster locomoting robots. “More like a garter snake than a python,” she says, “quick and small.”

Currently, the snake’s component pieces are made using a time-consuming molding process, but the lab is actively working on perfecting silicone 3D printing methods, allowing for any device configuration to be made cheaply and quickly. Osman Dogan Yirmibesoglu, another Ph.D. candidate, is using a massive 3D printer that he built to create a meter-long octopus-like soft robotic arm. “It’s actually more powerful than an octopus arm,” he corrects, explaining that an octopus arm doesn’t do well outside of water, whereas this arm will be able to support its own weight in air. Although it won’t look much like a tentacle, the arm will be able to flex in any direction and hold its position.

The material used is, as Yirmibesoglu puts it, “radiation transparent,” meaning it doesn’t interact strongly with most types of high-intensity radiation. This could make it preferable for radiological testing or emergency response robots for nuclear incidents. In such situations, high versatility is required to face intense radiation, pass over irregular terrain, investigate underwater reactor pools and operate controls. To find out how the material to responds to radiation, Yirmibesoglu printed samples of the silicone for Tyler Oshiro, an OSU nuclear engineering master’s student, who irradiated them in the university’s research reactor. Oshiro’s goal was to study how the mechanical properties of the silicone changed with high radiation exposure for his master’s thesis. He found the samples stiffened after exposure to very large amounts of radiation, but deal well with it overall. Oshiro finds soft robotics interesting because the field is, as he puts it, “The epitome” of finding “different ways to approach traditional problems.”

A soft, stretchable sensor embedded with liquid wire. (Photo: Hana Maiah)

Yirmibesoglu previously worked on hybrid soft sensors and is first author on the paper, “Hybrid soft sensor with embedded IMUs to measure motion,” published in IEEE Xplore in 2016. The publication outlines soft sensors made from silicone embedded with liquid-metal gallium wires. In the lab, Yirmibesoglu shows me one of the sensors and deforms the gray circuit board lattice in the middle by pressing it with his thumb. It stretches like a gummy worm but pops back into place as soon as it’s released.

As the material stretches, the small channels inside containing liquid metal become warped, making the wires thinner or thicker while the material is flexed in different ways. Because wires of different thicknesses have different electrical resistance, a computer hooked up to the electrodes can measure this value and determine how distorted the sensor is from its normal shape. This way a robot can tell where each of its limbs are. The technology has promise in other avenues like wearable electronics. The sensors are cheap, relatively light weight and versatile.

Building a silicone structure with internal channels of liquid metal isn’t easy. Previously, it required a difficult, multi-stage molding and gluing process with 2D printed liquid metal wires. However, the lab has recently devised a way to 3D print freestanding liquid metal and hopes to build a duel-headed printer, capable of constructing both the silicone body of a robot limb or sensor and its liquid metal veins simultaneously.

Nick Bira, another Ph.D. student, is working on figuring out the design for “soft valves” to precisely control airflow used to activate the limbs of a small octopus robot. The tricky part is building smart controls for pressure that don’t rely on conventional electrical valves. Elegant design here is key. He says the lab space reached “peak awe factor” a few months ago when, on top of the usual high-ceiling workspace filled with 3D printers, squishy limbs, and actuators, aquatic prototypes were floating in an underwater testing tank.

The group has been involved in several collaborative projects, most recently the paper, “Using an environmentally benign and degradable elastomer in soft robotics,” published in the International Journal of Intelligent Robotics and Applications. The project introduced an elastomer suitable for soft robotic construction which can biodegrade non-toxically.

In 2017, Mengüç wrote an overview piece on the field of soft robotics, published in American Scientist. In it, he describes the many avenues of a new and growing field such as electrorheological fluids — fluids which can change between liquid and solid based on an electric field — and the possibility of artificial muscles being implemented into future robots. Among already existing soft robot technologies, he mentions applications including maritime robots for inspection and welding, stealthy naval surveillance robots, safer industrial manufacturing robots, surgical tools like endoscopes and prosthetics or orthotics.

Yigit Menguc, far left, directs mLab Robotics at OSU. (Courtesy of mLab Robotics, Oregon State University)

He also puts the octopus center stage: “Many of my colleagues and I have chosen to take inspiration from one of the most alien mascots: the octopus. As soon as we take as our goal technology that is entirely soft, squishy, and stretchy, yet dynamic, agile, and intensely intelligent, we are forced to reevaluate what is possible.”

Mengüç also works with Oculus Rift, a virtual reality company in Seattle, but the assistant professor in Mechanical Engineering continues to direct the lab’s seven full-time grad students and commute to mLab Robotics meetings.

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Note: Leto Sapunar is a senior in physics at Oregon State University.

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