Method for Soft Actuation Eyed for New Devices, Robots

A new method for actuation can change the shape of a flat sheet of elastomer with rapid and reversible action for new designs in robotics and other applications.

Researchers at Harvard University have designed a reconfigurable soft actuator that can mimic the complex movements found in nature for the development of next-generation robotics.

A team at Harvard’s John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed a method to change the shape of a flat sheet of elastomer using rapid and reversible actuation through an applied voltage. The method allows the elastomer to be reconfigured into different shapes, the researchers said.

An initially flat thin circular sheet of elastomer morphs into a saddle shape based on which sets of electrodes are turned on or off in a method developed by researchers at Harvard University. (Image source: Clarke Lab/Harvard John A. Paulson School of Engineering and Applied Sciences)

Expanding Motion

The new method expands actuation between the typical linear motion and rotational motion typically found in mechanical systems such as engines and motors, said Ehsan Hajiesmaili, a graduate student at SEAS who worked on the project. Linear motion is when an object moves from one point to another in a straight line, while rotational motion involves an object rotating on an axis.

Movements found in nature, however, are far more sophisticated. For example, our eyes can change focal point just by contracting soft muscles to change the shape of the cornea. This is in contrast to the synthetic movements by cameras, which focus by moving solid lenses along a line, either manually or by an autofocus.

Softly

“The traditional actuators that we use today are made of stiff components and therefore the actuation motion that they provide comes from the relative displacement of these stiff parts, which could be either linear reciprocal motion or rotational,” Hajiesmaili told Design News. “Generating a sophisticated deformation from a linear or rotational motion required prohibitively bulky and complicated mechanisms.”

While there have been other soft shape-morphing actuators prior to this work—which use other stimuli such as swelling or heat—these methods have had performance issues, resulting in slow actuation with low power density, he said. “Also, these mechanisms use mechanical inhomogeneity and therefore are not capable of reconfiguration,” Hajiesmaili said.

Multi-Layered Approach

Key to the new method the team developed is a multiple-layer approach to the reconfigurable elastomer sheet. Between each layer researchers incorporated nanotube-based electrodes of different shapes.

When voltage is applied to the electrodes, it creates an electric field inside the elastomer sheet that produces uneven changes to the geometry of the material. This is what allows the elastomer to change into a 3D shape that can be controlled, he told Design News.

“This is the first shape-morphing mechanism that uses electric field as the stimuli, leading to a fast and reversible shape-morphing with a power density that is in par with skeletal muscles,” Hajiesmaili said.

Researchers demonstrated simple actuation shapes but the method is generalizable to shapes of high complexity, he said. Moreover, the material can be coaxed into different shapes based on which set of electrodes are on and which ones are off, which can be managed independently. The team published a paper on their work in the journal Nature Communications.

Shape-Morphing

Researchers believe their work is an early step in the development of a soft, shape-shifting material for novel devices, such as a shape-morphing airfoil that can change its shape completely in order to optimize for the flight condition, or shape-morphing sculptures and optics, Hajiesmaili said.

The team plans to continue its work on the actuator by solving some current limitations with the technology as well as incorporating sensors and electronics, he told Design News. Researchers also plan to focus on “some of the exciting applications” for the actuator, as well as optimize materials and fabrication, Hajiesmaili said.

“In this work, we solved the forward problem: For a given design of the electrodes and applied voltage, what is the shape that the actuator will morph into?” he explained. “The more challenging and more interesting problem, however, is the inverse problem: To morph into a desired pre-defined actuation shape, what should be the design of the electrodes and the applied voltage? Solving this problem will be the next step.”

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco and New York City. In her free time she enjoys surfing, traveling, music, yoga and cooking. She currently resides in a village on the southwest coast of Portugal.

 

 

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