Inside the Autonomous Robotic Manipulation (ARM) Lab, massive KUKA robotic arms select and delicately transfer the correct beanbag from a pile of random objects. Photo: Robert Coelius

It’s one thing for a robot to sort through a pile of rigid objects like blocks, but what about softer stuff?

The beanbag test

Soft robotics has made leaps and bounds over the last decade as researchers around the world have experimented with different materials and designs to allow once rigid, jerky machines to bend and flex in ways that mimic and can interact more naturally with living organisms. However, increased flexibility and dexterity has a trade-off of reduced strength, as softer materials are generally not as strong or resilient as inflexible ones, which limits their use.Now, researchers at the&nbsp;<a href="http://seas.harvard.edu/" target="_blank">Harvard John A. Paulson School of Engineering and Applied Sciences</a> (SEAS), the <a href="http://wyss.harvard.edu/" target="_blank">Wyss Institute at Harvard University</a> and MIT&rsquo;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 will be published this week in&nbsp;<a href="http://www.pnas.org/content/early/2017/11/21/1713450114.full" target="_blank">Proceedings of the National Academy of Sciences</a> (PNAS).&ldquo;We were very surprised by how strong the actuators [aka, &ldquo;muscles&rdquo;] were. We expected they&rsquo;d have a higher maximum functional weight than ordinary soft robots, but we didn&rsquo;t expect a thousand-fold increase. It&rsquo;s like giving these robots superpowers,&rdquo; said Daniela Rus, the Andrew and Erna Viterbi Professor of Electrical Engineering and Computer Science at MIT and one of the senior authors of the paper.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1569469584573-Origami-inspired+artificial+muscles+snake+arm.jpg" style="width: 766px;" class="fr-fic fr-dib">The movement and shape of the artificial muscles is defined by the shape of their internal &ldquo;skeleton&rdquo; &ndash; in this case, made of notched blocks of foam. (Image courtesy of the Wyss Institute for Biologically Inspired Engineering)&nbsp;&ldquo;Artificial muscle-like actuators are one of the most important grand challenges in all of engineering,&rdquo; said <a href="https://www.seas.harvard.edu/directory/rjwood" target="_blank">Robert J. Wood</a>, corresponding author of the paper and&nbsp;the Charles River Professor of Engineering and Applied Sciences at the SEAS. &ldquo;Now that we have created actuators with properties similar to natural muscle, we can imagine building almost any robot for almost any task.&rdquo; Wood is also a Founding Core Faculty member of the Wyss Institute.Each artificial muscle consists of an inner skeleton&nbsp;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.&nbsp;A vacuum applied to the inside of the bag initiates the muscle&rsquo;s movement by causing the skin to collapse onto the skeleton, creating tension that drives the motion. No other power source or human input is required to direct the muscle&rsquo;s movement; it is determined entirely by the shape and composition of the skeleton.&ldquo;One of the key aspects of these muscles is that they&rsquo;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,&rdquo; said first author Shuguang Li, 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.&ldquo;When creating robots, one always has to ask, &lsquo;Where is the intelligence - is it in the body, or in the brain?&rsquo;&rdquo; said Rus. &ldquo;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.&rdquo;The team constructed dozens of muscles using materials ranging from metal springs to packing foam to sheets of plastic, and experimented with different skeleton shapes to create muscles that can contract down to 10 percent of their original size, lift a delicate flower off the ground, and twist into a coil, all simply by sucking the air out of them.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 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.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1569469620868-Origami-inspired+artificial+muscles+white+muscle.jpg" style="width: 766px;" class="fr-fic fr-dib">The zig-zag pattern of this muscle&rsquo;s interior &ldquo;skeleton&rdquo; allows the muscle to contract down to a fraction of its original width. (Image courtesy of the Wyss Institute for Biologically Inspired Engineering) These muscles can be powered by a vacuum, a feature that makes them safer than most of the other artificial muscles currently being tested. &ldquo;A lot of the applications of soft robots are human-centric, so of course it&rsquo;s important to think about safety,&rdquo; said Daniel Vogt, co-author of the paper and Research Engineer at the Wyss Institute. &ldquo;Vacuum-based muscles have a lower risk of rupture, failure, and damage, and they don&rsquo;t expand when they&rsquo;re operating, so you can integrate them into closer-fitting robots on the human body.&rdquo;&ldquo;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,&rdquo; said Wood. 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.The team was even able to construct the muscles out of the water-soluble polymer PVA, which opens the possibility of robots that can perform tasks in natural settings with minimal environmental impact, as well as ingestible robots that move to the proper place in the body and then dissolve to release a drug. &ldquo;The possibilities really are limitless. But the very next thing I would like to build with these muscles is an elephant robot with a trunk that can manipulate the world in ways that are as flexible and powerful as you see in real elephants,&rdquo; said Rus.

Origami-inspired artificial muscles are capable of lifting up to 1,000 times their own weight, simply by applying air or water pressure. (Image courtesy of the Wyss Institute for Biologically Inspired Engineering)

Origami-inspired muscles are both soft and strong, and can be made for less than $1

Artificial muscles give soft robots superpowers

Even octopuses understand the importance of elbows. When these squishy, loose-limbed cephalopods need to make a precise movement &mdash; such as guiding food into their mouth &mdash; the muscles in their tentacles contract to create a temporary revolute joint. These joints limit the wobbliness of the arm, enabling more controlled movements. &nbsp;&nbsp;<a href="http://seas.harvard.edu/" target="_blank">Now, researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences</a> (SEAS) and the&nbsp;<a href="http://wyss.harvard.edu/" target="_blank">Wyss Institute for Biologically Inspired Engineering</a> have shown how a multi-layered structure can allow robots to mimic the octopus&rsquo;s kinematics, creating and eliminating joints on command. The structure can also allow robots to rapidly change their stiffness, damping, and dynamics.The research was published in two papers in&nbsp;<a href="https://onlinelibrary.wiley.com/doi/10.1002/adfm.201707136" target="_blank">Advanced Functional Materials</a> and&nbsp;<a href="https://ieeexplore.ieee.org/document/8141952/" target="_blank">IEEE Robotics and Automation Letters.</a>&ldquo;This research helps bridge the gap between soft robotics and traditional rigid robotics,&rdquo; said Yashraj Narang, first author of both studies and graduate student at SEAS. &ldquo;We believe that this class of technology may foster a new generation of machines and structures that cannot simply be classified as soft or rigid.&rdquo;<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1569465675108-artistRendering-640x278.jpg" style="width: 766px;" class="fr-fic fr-dib"><div class="inline-image">The structure consists of multiple layers of flexible material wrapped in a plastic envelope and connected to a vacuum source. (Image courtesy of Yashraj Narang/Harvard SEAS)</div>The structure is surprisingly simple, consisting of multiple layers of flexible material wrapped in a plastic envelope and connected to a vacuum source. Without vacuum, the structure behaves exactly as you would expect, bending, twisting and flopping without holding shape. But when a vacuum is applied, it becomes stiff and can hold arbitrary shapes, and it can be molded into additional forms.This transition is the result of a phenomenon called laminar jamming, in which the application of pressure creates friction that strongly couples a group of flexible materials.&ldquo;The frictional forces generated by the pressure act like glue,&rdquo; said Narang. &ldquo;We can control the stiffness, damping, kinematics, and dynamics of the structure by changing the number of layers, tuning the pressure applied to it, and adjusting the spacing between multiple stacks of layers.&rdquo;The research team, which also included&nbsp;<a href="https://www.seas.harvard.edu/directory/howe" target="_blank">Robert Howe</a>, the Abbott and James Lawrence Professor of Engineering,&nbsp;<a href="https://www.seas.harvard.edu/directory/jvlassak" target="_blank">Joost Vlassak</a>, the Abbott and James Lawrence Professor of Materials Engineering, and Alperen Degirmenci, a graduate student in SEAS, extensively modeled the mechanical behavior of laminar jamming to better control its capabilities.Next, they built real-world devices using the structures, including a two-fingered gripper that, without vacuum, could wrap around and hold onto large objects and, with a vacuum, could pinch and hold onto small objects about the size of a marble.<iframe src="https://www.youtube.com/embed/ecTOd6O9Beg?&wmode=opaque" frameborder="0" allowfullscreen="" class="fr-draggable" style="width: 767px; height: 466px;"></iframe> The researchers also demonstrated the structure&rsquo;s capabilities as shock absorbers by attaching them to a drone as landing gear. The team tuned the stiffness and damping of the structures to absorb the impact of landing.The structure is a proof-of-concept that could have many applications in the future, from surgical robots to wearable devices and flexible speakers.&ldquo;Our work has explained the phenomenon of laminar jamming and shown how it can provide robots with highly versatile mechanical behavior,&rdquo; said Howe, senior author of the paper. &ldquo;We believe that this technology will eventually lead to robots that can change state between soft, continuous devices that can safely interact with humans, and rigid, discrete devices that can meet the demands of industrial automation.&rdquo;

This drone’s landing gear is tuned the stiffness and damping to absorb the impact of landing. (Image courtesy of Yashraj Narang/Harvard SEAS) 

grippers

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