Of all this planet’s living species, 10 percent of them—about 180,000—are of the insect order Lepidoptera, whose larvae are commonly known as caterpillars. For Takuya Umedachi, who describes Earth as “a planet of caterpillars,” their soft, simple, tubelike bodies—with no clear bone structure, controlled by a very small number of neurons yet adaptable to diverse environments—provided the ideal model for developing robotic movement using soft materials. This caterpillar robot belongs to an emerging group of “soft robots,” which use soft materials instead of hard metals and can be operated more safely in proximity of humans.
Umedachi is a leading researcher in robotics, focusing on soft-robot technology, and a project lecturer at the University of Tokyo, Graduate School of Information Science and Technology. Umedachi found inspiration in fictional works like Ghost in the Shell, which explores the relationship between a person’s body, mind, and memories. He became interested in the boundaries separating robots from humans and other organisms and began working on building robots with qualities similar to those of living things.
Most industrial robots are designed in the shape of a human arm, with bonelike links that connect at joints corresponding to a shoulder, elbow, or wrist. To realize fluid and free movement, normally six joints (axes) are used in a robotic arm. Almost all of its components are made of hard metal.
By 2010, in his ongoing research of soft-bodied robots inspired by amoebae and caterpillars, Umedachi had already built a robot modeled after slime-mold plasmodium (myxomycete), a single-celled amoeba. “It was only after I had begun my work in this field that I learned they were referred to as soft robots,” Umedachi says.
“There are many issues when creating so-called hard robots that can work in soft earth or on branches, such as weight restrictions, complex control mechanisms, and the high cost of development,” he continues. “I think the trend now is toward building robots [inspired by] the highly functional structures and shapes found in living creatures.”
Using soft materials to build flexible bodies that imitate the natural world, soft robots can be designed to change shape in multiple dimensions and make use of nonlinear mechanics. Soft robots also have the potential to go beyond structures similar to bones and joints used by hard robots, offering functionality corresponding to muscle, tendons, skin, and hair. These properties can make soft robots suitable for work near humans where safety is paramount, as well as in rapidly changing environments.
The design, manufacture, and control of such soft robots will require different approaches than hard robots. Umedachi had been using small balloons and similar structures but then encountered advanced technologies like 3D printing at the Autodesk Technology Center in San Francisco, located at Pier 9 on the Embarcadero. It left a strong impression, and soon he changed his manufacturing approach.
“Instead of having to design gears and joints, I was able to realize the functionality I wanted by setting the stiffness distribution of the body I wanted to create,” Umedachi says. “I felt these tools were the perfect match for my soft robots.”
When Umedachi built a caterpillar-inspired robot during a research stint at Tufts University in Massachusetts, he used a 3D printer to print the entire robot body instead of just individual parts. “We were finally able to use soft materials in 3D printing,” he says, “and this is the robot we made with it.”
The mechanical systems of conventional hard robots dictate that each part joined to the body has a specific function; if additional functionality is required, new parts need to be attached. In contrast, robots with soft structures can reform to take different shapes, change their elastic properties in real time responding to external forces, and maintain continuity of operation by internally transmitting motion from one portion of their body to another—all with a very small number of individual parts.
Umedachi fabricated his caterpillar-inspired robot using a 3D printer that could output soft, rubbery material and hard material simultaneously. A shape-memory alloy that contracts when electrified was wound into springs, with two embedded in the robot’s front part and one in its rear segment. By using different timings to contract these springs, the robot could advance, turn left or right, or turn around to reverse course, giving it a wide range of movement.
“The tools at our disposal now are very well developed,” Umedachi says. “It makes it easy for me to design in 3D. I think the sculpting functions in Autodesk Fusion 360 for making organic curves are perfect for my work. Going forward, I want to test how applying these organic curves to my robots will affect their physical properties.”
Umedachi is also researching autonomous decentralized controllers that adapt to changes in the environment as an organism would. Take a cat, for example: As it walks using its four legs, each leg functions independently, as well as together as a whole. The legs generate a rhythm of overall motion through interactions arising from communication (via both nerves and mechanical force) between different parts of its body. The working hypothesis of Umedachi’s research is based on these “autonomous decentralized controllers.”
To test his theories, Umedachi wanted to build a robot with a soft body that one could control freely. His design employed autonomous decentralized controllers based on the most essential of life forms: the single-celled organism. In Umedachi’s caterpillar-inspired robot, motors that perform winding operations were set to think individually and combine their rhythm of contractions to generate movement. The robot was successfully able to generate its own creeping motion.
Umedachi says one of the greatest challenges in designing such a soft robot was determining how different forces were affecting its body. Which areas should be strengthened to improve the speed of motion? Which portions propel the body along the ground? How are contractions transmitted through the soft body?
“In a soft body, any part can be a joint,” he says. “It becomes difficult to tell where forces will be applied. Robotics is a study of forces, but just like electricity, they cannot be seen, which makes working with them difficult.”
Once a robot is designed that can move well, it is a simple matter of attaching sensors to it. “These robots can be used for jobs in places humans cannot normally reach,” Umedachi says.
“For example, one project we’re working on right now with a company is a soft robot that can crawl along power lines,” he continues. “The materials for one robot cost only 2,000 to 3,000 yen [$17 to $26], so we can leave the robot on a power line to perform maintenance tasks.”
Japan holds a 56 percent share of all industrial-robot manufacturing worldwide. The country’s recent artificial-intelligence developments include creating robots that will be more useful for an ever-widening range of roles in workplaces and homes. Soft robotics is still a nascent field, and many aspects of it have yet to be reconciled with ongoing research into conventional robotics.
“We as humans are made of a combination of hard materials and soft materials,” Umedachi says. “I have a hunch that soft robots will eventually merge with hard robots into similar forms.”