Research into soft robotics has progressed immensely over the last decade as researchers around the world have experimented with different materials and designs, with the aim of allowing once rigid machines with limited robotic range of motion to bend, flex, and move more like living organisms than industrial hardware. However, till date, increased flexibility and dexterity had a trade-off of reduced strength, as softer materials are generally not as strong or resilient as inflexible ones, which limits their use.
All this is set to change now that researchers at the Wyss Institute at Harvard University and MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) have created origami-inspired artificial muscles that add strength to soft robots, allowing them to lift objects that are up to 1,000 times their own weight using only air or water pressure. The study is published in Proceedings of the National Academy of Sciences (PNAS).
The study suggests that the muscles could be used to provide extraordinary strength to robots, yet allowing them to operate with precision and dexterity.
“We were very surprised by how strong the actuators [aka, “muscles”] were. We expected they’d lift a higher maximum functional weight than ordinary soft robots, but we didn’t expect a thousand-fold increase. It’s like giving these robots superpowers,” says Daniela Rus, Ph.D., Professor of Electrical Engineering and Computer Science at MIT and one of the senior authors of the paper.
“Artificial muscle-like actuators are one of the most important grand challenges in all of engineering,” adds Rob Wood, Ph.D., corresponding author of the paper and founding core faculty member of the Wyss Institute. “Now that we have created actuators with properties similar to natural muscle, we can imagine building almost any robot for almost any task.”
Each artificial muscle consists of an inner “skeleton” that can be made of various materials, such as a metal coil or a sheet of plastic folded into a certain pattern, surrounded by air or fluid and sealed inside a plastic or textile bag that serves as the “skin.” A vacuum applied to the inside of the bag initiates the muscle’s movement by causing the skin to collapse onto the skeleton, creating tension that drives the motion. Incredibly, no other power source or human input is required to direct the muscle’s movement; it is determined entirely by the shape and composition of the skeleton.
“One of the key aspects of these muscles is that they’re programmable, in the sense that designing how the skeleton folds defines how the whole structure moves. You essentially get that motion for free, without the need for a control system,” says first author Shuguang Li, Ph.D., a Postdoctoral Fellow at the Wyss Institute and MIT CSAIL. This approach allows the muscles to be very compact and simple, and thus more appropriate for mobile or body-mounted systems that cannot accommodate large or heavy machinery.
“When creating robots, one always has to ask, ‘Where is the intelligence – is it in the body, or in the brain?’” says Rus. “Incorporating intelligence into the body (via specific folding patterns, in the case of our actuators) has the potential to simplify the algorithms needed to direct the robot to achieve its goal. All these actuators have the same simple on/off switch, which their bodies then translate into a broad range of motions.”
Not only can the artificial muscles move in many ways, they do so with impressive resilience. They can generate about six times more force per unit area than mammalian skeletal muscle can, and are also incredibly lightweight; a 2.6-gram muscle can lift a 3-kilogram object, which is the equivalent of a mallard duck lifting a car. Additionally, a single muscle can be constructed within ten minutes using materials that cost less than $1, making them cheap and easy to test and iterate.
These muscles can be powered by a vacuum, a feature that makes them safer than most of the other artificial muscles currently being tested. “A lot of the applications of soft robots are human-centric, so of course it’s important to think about safety,” says Daniel Vogt, M.S., co-author of the paper and Research Engineer at the Wyss Institute. “Vacuum-based muscles have a lower risk of rupture, failure, and damage, and they don’t expand when they’re operating, so you can integrate them into closer-fitting robots on the human body.”
“In addition to their muscle-like properties, these soft actuators are highly scalable. We have built them at sizes ranging from a few millimeters up to a meter, and their performance holds up across the board,” Wood says. This feature means that the muscles can be used in numerous applications at multiple scales, such as miniature surgical devices, wearable robotic exoskeletons, transformable architecture, deep-sea manipulators for research or construction, and large deployable structures for space exploration.
It seems like the robots of the future are going to be much more life-like in their appearance and range of movement than even the T-800s of Terminator fame.