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New Low-voltage Artificial Muscles Are the Future of Soft Robots

21 July 2016

While soft robots are finding their way into numerous applications, they are still a bit hindered by their slow functional speeds. The artificial muscles that move soft robots, also referred to as actuators, typically depend on hydraulics or pneumatics—systems that are slow to respond.

Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have just discovered that dielectric elastomers, soft materials with good insulating properties, could offer an alternative to pneumatic actuators. Previously they were thought of as being a poor option due to their need for complex and inefficient circuitry to deliver high voltage as well as rigid components to maintain their form. However the researchers came up with a dielectric elastomer with a broad range of motion that requires relatively low voltage and no rigid components.

Artificial muscle built from a sandwich of soft, stretchable elastomers and carbon nanotubes electrodes. (Image Credit: Peter Allen/Harvard SEAS) Artificial muscle built from a sandwich of soft, stretchable elastomers and carbon nanotubes electrodes. (Image Credit: Peter Allen/Harvard SEAS)

"We think this has the potential to be the holy grail of soft robotics," said Mishu Duduta, a graduate student at SEAS and first author of the paper. "Electricity is easy to store and deliver but until now, the electric fields required to power actuators in soft robots has been too high. This research solves a lot of the challenges in soft actuation by reducing actuation voltage and increasing energy density, while eliminating rigid components."

To build the new dielectric elastomer, the team combined two materials that the researchers knew worked well individually—an elastomer based on one developed at UCLA that eliminated the need for rigid components and an electrode of carbon nanotubes developed in another UCLA lab. These two materials complemented each other and enabled the new device to outperform standard dielectric elastomer actuators.

Most dielectric elastomers have limited range of motion and need to be pre-stretched and attached to a rigid frame, but the team’s does not, which means the modified materials begin as liquids and can be cured quickly under UV light to produce paper-thin sheets that can adhere well to each other, and to the electrodes—like double-sided tape.

his soft muscle can move with low amounts of electricity. (Image Credit: Mishu Duduta/Harvard SEAS) his soft muscle can move with low amounts of electricity. (Image Credit: Mishu Duduta/Harvard SEAS)

Their method allowed each electrode to get double usage, powering the elastomer above and below.

"The voltage required to actuate dielectric elastomers is directly related to the thickness of the material, so you have to make your dielectric elastomer as thin as possible," said Duduta. "But really thin elastomers are flimsy and can't produce force. A multilayer elastomer is much more robust and can actually provide significant force."

According to David Clarke, the Extended Tarr Family Professor of Materials at Harvard, “the significance of this work is that the combination of materials and processing enables two of the current technical limitations of dielectric elastomers—the need for high voltage and pre-stretch—to be overcome.”

This type of actuator could be used in a variety of applications from wearable devices to soft grippers, laparoscopic surgical tools, ordinary soft robots or even artificial muscles in more complex robotics.

Actuation has always been one of the most difficult aspects of robots, with previous robots depending on conventional electromagnetic rotary motors. This discovery brings researchers one step closer to achieving muscle-like performance in an engineered system and makes possible many new soft robotics applications.

To contact the author of this article, email Nicolette.Emmino@ieeeglobalspec.com


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