Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Soft, energy-efficient robotic wings

01.04.2015

New discovery that can make a dielectric elastomer joint bend up and down demonstrates its potential in soft robotic applications as lightweight, energy-efficient flapping wings

Dielectric elastomers are novel materials for making actuators or motors with soft and lightweight properties that can undergo large active deformations with high-energy conversion efficiencies. This has made dielectric elastomers popular for creating devices such as robotic hands, soft robots, tunable lenses and pneumatic valves -- and possibly flapping robotic wings.


These images show: (Left) The structure of the rotary joint. (Right) The system to measure the joint rotation.

Credit: Jianwen Zhao/Harbin Institute of Technology in Weihai, University of California-Los Angeles

Reporting this week in the journal Applied Physics Letters, from AIP Publishing, researchers from the Harbin Institute of Technology in Weihai, China and the University of California, Los Angeles (UCLA), have discovered a new resonance phenomenon in a dielectric elastomer rotary joint that can make the artificial joint bend up and down, like a flapping wing.

"The dielectric elastomer is a kind of electro-active polymer that can deform if you apply a voltage on it," said Jianwen Zhao, an associate professor of the Department of Mechanical Engineering at the Harbin Institute of Technology. He said that most studies on dielectric elastomers are using a static or stable voltage to stimulate the joint motion, which makes the joint bend at a fixed angle, while they are interested in seeing how the artificial joint react to an alternating or periodically changing voltage.

"We found that alternating voltages can make the joint continuously bend at different angles. Especially, when the rotational inertia of the joint or the applied voltage is large enough, the joint can deform to negative angles, in other words, it can bend beyond 90 degrees to 180 degrees, following a principle different from the normal resonance rule."

Zhao said this new phenomenon makes the dielectric elastomer joint a good candidate for creating a soft and lightweight flapping wing for robotic birds, which would be more efficient than bird wings based on electrical motors due to the higher energy conversion efficiency (60 to 90 percent) of the dielectric elastomer.

Muscle-like Actuators

Soft robotics provides many advantages compared to traditional robotics based on rigid materials, including safer physical human-robot interactions, more efficient/stable locomotion and adaptive morphologies. Dielectric elastomers, due to their soft and lightweight inherent properties and superior electro-mechanical performances, are considered as a kind of material close to human muscles, attracting wide attention among soft-technology scientists in recent years.

Made by sandwiching a soft insulating elastomer film between two compliant electrodes, dielectric elastomers can be squeezed and expanded in a plane when a voltage is applied between electrodes. In contrast to actuators based on rigid materials such as silicon, dielectric elastomers can reach a very large extent of stretch, often exceeding 100 percent elongation while not breaking, enabling new possibilities in many fields including soft robotics, tunable optics, and cell manipulation.

The dielectric elastomer actuator Zhao used is called a "dielectric elastomer minimum-energy structure," which is composed of a thin elastic frame and pre-stretched dielectric elastomer films, Zhao said. After adhering the pre-stretched film to the thin elastic frame, the restoring force of the dielectric elastomer film bends the elastic frame, balancing at a minimum energy state.

When applying kilovolts of low-current electricity on the dielectric elastomer, the frame flattens out and the bending angle decreases. To restrict frame bending to only one axis, two stiffening frames are mounted to the primary frame as rigid non-bending edges, the whole thing then forms a rotary joint. Dynamically changing the voltage can dynamically change the joint angle, which makes dielectric elastomer minimum-energy structures a useful structure for fabricating soft devices, Zhao said.

A New Oscillation Phenomenon Found

In Zhao's experiment, the researchers stimulated the motion of the rotary joint using an alternating, square-wave voltage, i.e. a voltage with a fixed value that is periodically turned on and off, which is different from the practice of previous scientists, who "usually use static or stable voltage to study the joint motion."

"The advantage of alternating voltages is that they shift between different values, thus helping us continuously manipulate the joint's bending angles." Zhao said.

The new practice also stimulated new results. After experimenting with various parameters such as voltage values, frequencies and the joint mass in the dielectric elastomer joint system, Zhao and colleague observed a new resonance phenomenon: When the rotational inertia of the joint is large enough or the applied voltage is high enough, the joint can bend up and down like a flapping wing, reaching a bending angle over 90 degrees or what the researchers call negative angles.

"When the joint realizes negative angles, its motion will become more complicated, following a special resonance rule different than the normal one, which we call nonlinear oscillation," he said.

In normal resonance, the joint bends following the voltage frequency, and will reach the largest bending angle when the joint's inherent frequency is equal to the voltage frequency, Zhao explained. While in nonlinear oscillation, the joint reaches its largest bending angle when the provide voltage frequency is near but smaller than twice the joint's natural frequency. Meanwhile, the joint amplitude (the bending scope) is also larger than in normal resonance, indicating a larger lift force in the special resonance.

This new phenomenon and the principle, Zhao noted, may open doors for many novel soft devices, such as soft and lightweight robots for circumstances with restricted space and weight requirements or flapping wings of soft robotic birds that can generate a large lift force. Also, since dielectric elastomers feature high energy density (seventy times higher than conventional electromagnetic actuators) and high-energy conversion efficiency (60 to 90 percent), they could be good candidates for making energy-efficient devices, Zhao said.

The researchers' next step is to improve the function of the dielectric elastomer rotary joint and refine the fabrication technique to make a real flapping wing.

###

The article "Phenomena of nonlinear oscillation and special resonance of a dielectric elastomer minimum energy structure rotary joint" is authored by Jianwen Zhao, Junyang Niu, David McCoul, Zhi Ren and Qibing Pei. It will be published in the Applied Physics Letters on March 31, 2015 (DOI: 10.1063/1.4915108). After that date, it can be accessed at: http://scitation.aip.org/content/aip/journal/apl/106/13/10.1063/1.4915108

ABOUT THE JOURNAL

Applied Physics Letters, published by the American Institute of Physics, feature concise, up-to-date reports on significant new findings in applied physics. Emphasizing rapid dissemination of key data and new physical insights, Applied Physics Letters offers prompt publication of new experimental and theoretical papers bearing on applications of physics phenomena to all branches of science, engineering, and modern technology. See: http://apl.aip.org/

Media Contact

Jason Socrates Bardi
jbardi@aip.org
240-535-4954

 @AIP_Publishing

http://www.aip.org 

Jason Socrates Bardi | EurekAlert!

Further reports about: Applied Physics artificial elastomers electrodes oscillation phenomenon physics structure voltage

More articles from Physics and Astronomy:

nachricht Breakthrough with a chain of gold atoms
17.02.2017 | Universität Konstanz

nachricht New functional principle to generate the „third harmonic“
16.02.2017 | Laser Zentrum Hannover e.V.

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

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

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Switched-on DNA

20.02.2017 | Materials Sciences

Second cause of hidden hearing loss identified

20.02.2017 | Health and Medicine

Prospect for more effective treatment of nerve pain

20.02.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>