Elastomer-based artificial muscles could allow soft robots of the future to work faster, have a broader range of motion, and work with relatively low voltages.
Soft robots today are versatile, but also slow, because the actuators that move soft robots tend to rely on hydraulics or pneumatics, which have slow response times, and are difficult to store.
Dielectric elastomers are soft materials with good insulating properties, and are a possible alternative to pneumatic actuators in robots. However, they currently require complex and inefficient circuitry to deliver high voltage.
To maintain their form, they also require rigid components. Because the point of soft robotics is to use soft and deformable materials, and compliant mechanical parts that can actively interact with the environment, and be subject to deformations, these limitations reduce the applicability of current dielectric elastomers to soft robots.
Now researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences have developed a type of dielectric elastomer that has a broad range of motion, but requires relatively low voltage, and no rigid components.
According to Mishu Duduta, a graduate student at SEAS, this new dielectric elastomer could be the holy grail of soft robotics.
"Electricity is easy to store and deliver but until now, the electric fields required to power actuators in soft robots has been too high," he explained.
"This research solves a lot of the challenges in soft actuation by reducing actuation voltage and increasing energy density, while eliminating rigid components."
The researchers based their work off two previously-developed materials: an elastomer developed at UCLA which eliminated the need for rigid components, and an electrode of carbon nanotubes developed in the Clarke Lab. By combining the learning from these two materials, the new device can outperform standard dielectric elastomer actuators. Another advantage of this new material is that it does not have to be pre-stretched.
The new elastomer begins as liquids, which are cured rapidly under UV light, creating paper-thin sheets. These sheets are sticky, and so adhere well to each other, and to the electrodes.
While conventional dielectric elastomers utilise carbon grease as their electrodes, the researchers instead used a mat of thin carbon nanotubes. This alternative electrode material does not increase the stiffness of the elastomers, not does it decrease the energy, allowing the elastomer to stretch and provide significant force.
Because the thickness of the elastomer affects the voltage required to actuate it, to achieve relatively low voltage operations, the researchers had to use thin layers of elastomer. However, thin layers are flimsy and produce little force. To create a balance between these two requirements, the researchers sandwiched the layers of electrodes between layers of elastomer in a multilayer structure.
This structure allows for greater robustness, so the actuator can provide , significant force. Additionally, each electrode gets double usage, powering the elastomer layers both above and below.
By combining materials and processing techniques, the researchers were able to overcome a number of significant technical limitations of dielectric elastomer actuators. Besides possible applications in soft robots, this type of actuator could be in wearable devices, soft grippers, laparoscopic surgical tools, or as artificial muscles in more complex robotics.