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.
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.
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.
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.
Jason Socrates Bardi | EurekAlert!
Researchers at Fraunhofer monitor re-entry of Chinese space station Tiangong-1
21.03.2018 | Fraunhofer-Institut für Hochfrequenzphysik und Radartechnik FHR
Taming chaos: Calculating probability in complex systems
21.03.2018 | American Institute of Physics
An international team of researchers has discovered a new anti-cancer protein. The protein, called LHPP, prevents the uncontrolled proliferation of cancer cells in the liver. The researchers led by Prof. Michael N. Hall from the Biozentrum, University of Basel, report in “Nature” that LHPP can also serve as a biomarker for the diagnosis and prognosis of liver cancer.
The incidence of liver cancer, also known as hepatocellular carcinoma, is steadily increasing. In the last twenty years, the number of cases has almost doubled...
In just a few weeks from now, the Chinese space station Tiangong-1 will re-enter the Earth's atmosphere where it will to a large extent burn up. It is possible that some debris will reach the Earth's surface. Tiangong-1 is orbiting the Earth uncontrolled at a speed of approx. 29,000 km/h.Currently the prognosis relating to the time of impact currently lies within a window of several days. The scientists at Fraunhofer FHR have already been monitoring Tiangong-1 for a number of weeks with their TIRA system, one of the most powerful space observation radars in the world, with a view to supporting the German Space Situational Awareness Center and the ESA with their re-entry forecasts.
Following the loss of radio contact with Tiangong-1 in 2016 and due to the low orbital height, it is now inevitable that the Chinese space station will...
Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, provider of research and development services for OLED lighting solutions, announces the founding of the “OLED Licht Forum” and presents latest OLED design and lighting solutions during light+building, from March 18th – 23rd, 2018 in Frankfurt a.M./Germany, at booth no. F91 in Hall 4.0.
They are united in their passion for OLED (organic light emitting diodes) lighting with all of its unique facets and application possibilities. Thus experts in...
A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million...
For the first time, an interdisciplinary team from the University of Basel has succeeded in integrating artificial organelles into the cells of live zebrafish embryos. This innovative approach using artificial organelles as cellular implants offers new potential in treating a range of diseases, as the authors report in an article published in Nature Communications.
In the cells of higher organisms, organelles such as the nucleus or mitochondria perform a range of complex functions necessary for life. In the networks of...
19.03.2018 | Event News
16.03.2018 | Event News
13.03.2018 | Event News
22.03.2018 | Trade Fair News
22.03.2018 | Earth Sciences
22.03.2018 | Earth Sciences