Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Controlling the uncontrollable

18.08.2015

Researchers harness unstable responses to build new soft actuators

Instability in engineering is generally not a good thing. If you're building a skyscraper, minor instabilities could bring the whole structure crashing down in a fraction of a second. But what if a quick change in shape is exactly what you want?


These soft actuators harnessed the power of snap-through instabilities to trigger large outputs with small inputs of fluid.

Credit: Johannes Overvelde/The Bertoldi Lab

Soft machines and robots are becoming more and more functional, capable of moving, jumping, gripping an object, and even changing color. The elements responsible for their actuation motion are often soft, inflatable segments called fluidic actuators. These actuators require large amounts of air or water to change shape, making the machines slow, bulky and difficult to untether.

A team of researchers at the Harvard John A. Paulson School of Engineering and Applied Science (SEAS) has engineered a new, soft actuator that harnesses the power of instability to trigger instantaneous movement.

The research was led by Katia Bertoldi, the John L. Loeb Associate Professor of the Natural Sciences, member of the Kavli Institute for Bionano Science and Technology, and faculty associate of the Materials Research Science and Engineering Center. The work is described in a paper in the Proceedings of the National Academy of Sciences.

The actuator is inspired by a famous physics experiment in which two balloons are inflated to different sizes and connected via a tube and valve. When the valve is opened, air flows between the balloons. Instead of equalizing in size, as one might expect, the larger balloon inflates more while the smaller balloon deflates.

This unexpected behavior comes from the balloons' non-linear relationship between pressure and volume, meaning the an increase in volume doesn't necessarily increase the pressure.

"When inflating a balloon, the first few blows are the hardest but after reaching a critical pressure it becomes easier," said Johannes Overvelde, PhD student at SEAS and first author on the paper. "Similar to the balloons, in our research we connect fluidic segments in such a way that an interplay between their non-linear response results in unexpected behavior. Certain combinations of these interconnected segments can result in fast moving instabilities with negligible change in volume."

These fast-moving instabilities, called snap-through instabilities, trigger large changes in internal pressure, extension, shape, and exerted force, with only small changes in volume. If harnessed, these instabilities would allow soft robots to move quickly without needing to carry or be tethered to a fluid supply.

But first Bertoldi's team had to find a way to control something that, by definition, is uncontrollable.

The team started by building and inflating 36 individual segments with water, and measuring how they responded. Then, using a complex computer algorithm, they determined the responses of all possible combinations of the segments.

A total of 630 possible actuators could be assembled from two segments, each with a different combined response. Some of the combinations showed instabilities, others did not. The team selected the preferred response for a specific application. One combination, for example, would lead to a sudden increase in actuator length, moving it like a worm. Another combination would quickly transfer all volume from one segment to another.

These quick movements could be triggered with small amounts of volume. For example, 1 ml. of water triggered a snap-through instability that resulted in an internal volume flow of 20 ml.

"The beauty of these individual segments is that they are easy and cheap to fabricate from off-the-shelve materials. Yet, when you connect segments you get soft actuators with very complex behavior," said Overvelde. "By connecting multiple segments, you can embed a simple program in the actuator that is able to perform a complex sequence of local inflation and deflation."

The next step is to test these instabilities in soft robotics.

"Engineers have long avoided instability because it so often represents failure," said Bertoldi. "It's remarkable that instability itself has provided a way to improve and push the field of soft actuators forward."

###

This research was co-authored by Tamara Kloek and Jonas D'haen. It was supported by the Materials Research Science and Engineering Center and the National Science Foundation.

Leah Burrows | EurekAlert!

More articles from Materials Sciences:

nachricht New biomaterial could replace plastic laminates, greatly reduce pollution
21.09.2017 | Penn State

nachricht Stopping problem ice -- by cracking it
21.09.2017 | Norwegian University of Science and Technology

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: LaserTAB: More efficient and precise contacts thanks to human-robot collaboration

At the productronica trade fair in Munich this November, the Fraunhofer Institute for Laser Technology ILT will be presenting Laser-Based Tape-Automated Bonding, LaserTAB for short. The experts from Aachen will be demonstrating how new battery cells and power electronics can be micro-welded more efficiently and precisely than ever before thanks to new optics and robot support.

Fraunhofer ILT from Aachen relies on a clever combination of robotics and a laser scanner with new optics as well as process monitoring, which it has developed...

Im Focus: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Fraunhofer ISE Pushes World Record for Multicrystalline Silicon Solar Cells to 22.3 Percent

25.09.2017 | Power and Electrical Engineering

Usher syndrome: Gene therapy restores hearing and balance

25.09.2017 | Health and Medicine

An international team of physicists a coherent amplification effect in laser excited dielectrics

25.09.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>